1/3 Scale Ford 289 Hi-Po
- Thread starter mayhugh1
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Well, it turns out that I've lost 90% of the vision in my right eye after the surgery. I thought cataract surgery was pretty much routine, but evidently it isn't always. The doctor agrees something is wrong but she isn't yet sure what went wrong. The autorefractor that tested the lens in my eye seems to likes it even less than I do, but it just gives up testing with no hint about why. I go back next week for a consultation but without knowing what the problem is, I'm not sure what the next step will be.Hi Terry, So sorry you are struggling after your eye surgery. I wish you a speedy recovery. Many thanks for your reply.
I've restarted work on the block to get my mind off all this. I found that if I cover up my right eye, I can see enough through my left to work for short periods without the nausea. - Terry
Hope your next report is a positive one
You do amazing work
You do amazing work
nj111
Member
Wishing you all the very best for a positive outcome. Thank you again so much for sharing your amazing craftmanship, I have learnt so much from your builds. Nick
Yes, I think I can speak for most everyone here in that we all look forward to seeing an engine progress report from Terry. Always top notch!
Hang in there and get well rested! Very much praying you eyesight improves soon.
Hang in there and get well rested! Very much praying you eyesight improves soon.
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So far, my eye doctor hasn't been specific about what went wrong with my cataract surgery. It's a good thing that protocol is to do only one eye at a time, but I was expecting a lot more for the extra $3K spent for a 'premium' lens. An appointment was scheduled for earlier this week, but she's out for a week with her own personal emergency and hopefully OK. I hoped resuming work on the engine might help with my current depression, but this is a tough hobby for someone with bum eyesight.
I eventually recalled why I'd planned to drill that pair of 1/4" coolant distribution holes through the cylinder banks even though the water jackets around each liner would be interconnected. They were intended to feed coolant from the jackets to the heads through vertically drilled transfer holes located safely away from the edges of the head gasket. The cooling scheme inside the head isn't fully worked out yet, and with so little space for effective coolant flow, replacing metal around the combustion chambers with passages that might entrap air or stagnant coolant might not be a smart move. In any event, the 1/4" thru-passages were drilled, but the transfer holes will be drilled later.
The cylinder bores were machined next. With the block mounted to its fixture plate and setup on the 45 degree angle table, the bores were started with 5/8" pilot holes. The bores themselves were interpolated on my Tormach using a long reach 1/2" diameter end mill. Although the x and y axis backlashes on my machine have been .0005" and .00075" respectively for the last dozen years, the worst circularity error measured just over two tenths. Before machining the bores, the cutting parameters were tuned during a few practice runs on the first block's carcass.
The integral water jackets were designed to hold just under a cubic inch of coolant around each liner, and they were machined using a key seat cutter. To obtain this volume, a 1-1/4" diameter cutter that barely cleared the bore's entrance had to be used. Its 3/16" thickness, though, proved to be 2x too much for chatter control.
My CAM software refuses to create tool paths when a portion of the part overhangs the cutting zone. Tricking it into working by lying about the part required care and manual g-code changes to the cutter's lead-in and lead-out to avoid what would have been a spectacular crash. The code was designed around a single cylinder and tuned using practice runs on the scrapped block before being run eight times on the real thing.
The large diameter 3/16" thick cutter was a bell waiting to ring. It screamed during the entire full thickness passes at the top of each bore regardless of parameter tuning. Flooding those top level passes with WD-40 took some of the edge off the incredibly loud noise, but the first three minutes of each operation were pretty scary and had not only my full attention but also my hand on the emergency stop. Once the full thickness passes at the top of a bore completed, the half-thickness passes below it were much better behaved and the surface finishes surprisingly nice.
The tappet bores were drilled/reamed next. As mentioned earlier, their axes are tilted slightly toward the centerline of the engine to present the correct pushrod geometry to the rocker arms. The two degrees that I used may not sound like much, but it will make a significant difference at the tips of the pushrods.
The final operation was to be the bore for the distributor. It's currently a deep and angled multi-diameter interrupted cut that I over-designed without enough thought about how it will be machined. I need some time to reconsider its design and to make a few practice runs before risking the nearly finished block.- Terry
I eventually recalled why I'd planned to drill that pair of 1/4" coolant distribution holes through the cylinder banks even though the water jackets around each liner would be interconnected. They were intended to feed coolant from the jackets to the heads through vertically drilled transfer holes located safely away from the edges of the head gasket. The cooling scheme inside the head isn't fully worked out yet, and with so little space for effective coolant flow, replacing metal around the combustion chambers with passages that might entrap air or stagnant coolant might not be a smart move. In any event, the 1/4" thru-passages were drilled, but the transfer holes will be drilled later.
The cylinder bores were machined next. With the block mounted to its fixture plate and setup on the 45 degree angle table, the bores were started with 5/8" pilot holes. The bores themselves were interpolated on my Tormach using a long reach 1/2" diameter end mill. Although the x and y axis backlashes on my machine have been .0005" and .00075" respectively for the last dozen years, the worst circularity error measured just over two tenths. Before machining the bores, the cutting parameters were tuned during a few practice runs on the first block's carcass.
The integral water jackets were designed to hold just under a cubic inch of coolant around each liner, and they were machined using a key seat cutter. To obtain this volume, a 1-1/4" diameter cutter that barely cleared the bore's entrance had to be used. Its 3/16" thickness, though, proved to be 2x too much for chatter control.
My CAM software refuses to create tool paths when a portion of the part overhangs the cutting zone. Tricking it into working by lying about the part required care and manual g-code changes to the cutter's lead-in and lead-out to avoid what would have been a spectacular crash. The code was designed around a single cylinder and tuned using practice runs on the scrapped block before being run eight times on the real thing.
The large diameter 3/16" thick cutter was a bell waiting to ring. It screamed during the entire full thickness passes at the top of each bore regardless of parameter tuning. Flooding those top level passes with WD-40 took some of the edge off the incredibly loud noise, but the first three minutes of each operation were pretty scary and had not only my full attention but also my hand on the emergency stop. Once the full thickness passes at the top of a bore completed, the half-thickness passes below it were much better behaved and the surface finishes surprisingly nice.
The tappet bores were drilled/reamed next. As mentioned earlier, their axes are tilted slightly toward the centerline of the engine to present the correct pushrod geometry to the rocker arms. The two degrees that I used may not sound like much, but it will make a significant difference at the tips of the pushrods.
The final operation was to be the bore for the distributor. It's currently a deep and angled multi-diameter interrupted cut that I over-designed without enough thought about how it will be machined. I need some time to reconsider its design and to make a few practice runs before risking the nearly finished block.- Terry
Although I don't remember the distributor in my old Mustang's 289 not sitting vertical, a ten degree tilt was needed to move its axis away from the crankshaft so it can drive an oil pump. The distributor itself will be driven by the camshaft through a custom 1:1 helical gear set. In order to fit within the available space, a shop-made fractional DP cutter will be needed to machine these gears. Since I had to do something similar for the inline six in my last build, I should be a little ahead of the learning curve.
The bore for the distributor is complicated by its multi-diameter requirements and the deep interrupted cuts created by the features around the camshaft bore. A SolidWorks rendering shows the bore's cross section. The distributor shaft is supported by a pair of ball bearings inside the distributor, but when modeling I added a third bearing just below the helical gear. Its purpose was to help stabilize the distributor and to ease insertion of the oil pump driveshaft into the pump.
All this looked good on paper but seemed like something that should be mocked up before adding it to the nearly finished block. For practice I machined a duplicate set of block front end features around the camshaft bore on the scrapped block (in fact, they were added to both ends). The bottom line result of my testing was that the third bearing was probably a good idea.
The pair of bores that locate the top and bottom ends of the distributor body to the block were roughed in with plunged end mills and finished using boring heads. Since I had two boring heads, I left their practice settings untouched for use on the block and was very surprised when the block's bore diameters ended up some .005" undersize. The discrepancies turned out to be due to rpm differences created by a last minute decision to bore the block using the mill's back gear. The rpm had become important due to tool deflections in the interrupted cuts. Returning to the original practice rpms eliminated the differences.
A final issue arose when machining the 3/8" pocket for the bottom bearing. A press-fit in this hard to reach location would have created bearing servicing problems. Even though the floor of the pocket had been designed with a tiny breakout for a shop-made removal tool, I made a last minute decision to change to a close slip fit. All my 3/8" end mills cut 373"- .374" diameters even when extended as far as possible in a collet, and the deflection of a tiny long reach boring tool would have added too much uncertainty. My final solution was to chuck a 3/8" end mill in one of my dollar store drill chucks and take advantage of its runout. By adjusting the stick-out I was able to dial in the pocket diameter for a near perfect fit. One of the photos shows the dummy distributor parts used to mock up the distributor assembly in the finished block. Measurements showed the center-to-center gear spacing to be within a couple thousandths of my target.
I wouldn't normally machine the distributor hold down bracket this early in the build, but its tiny size and ten degree mounting base made it one of those pita parts that I just wanted to be done with. It was machined from an odd piece of aluminum temporarily epoxied to a block of MDF and wasn't as problematic as I had expected. Working from its bottom surface, the entire part was machined in a single setup. Its sloped mounting surface was machined using a ball cutter and tiny waterline steps.
This essentially completed the block's machining except for a pressurized oiling system that will be revisited later. - Terry
The bore for the distributor is complicated by its multi-diameter requirements and the deep interrupted cuts created by the features around the camshaft bore. A SolidWorks rendering shows the bore's cross section. The distributor shaft is supported by a pair of ball bearings inside the distributor, but when modeling I added a third bearing just below the helical gear. Its purpose was to help stabilize the distributor and to ease insertion of the oil pump driveshaft into the pump.
All this looked good on paper but seemed like something that should be mocked up before adding it to the nearly finished block. For practice I machined a duplicate set of block front end features around the camshaft bore on the scrapped block (in fact, they were added to both ends). The bottom line result of my testing was that the third bearing was probably a good idea.
The pair of bores that locate the top and bottom ends of the distributor body to the block were roughed in with plunged end mills and finished using boring heads. Since I had two boring heads, I left their practice settings untouched for use on the block and was very surprised when the block's bore diameters ended up some .005" undersize. The discrepancies turned out to be due to rpm differences created by a last minute decision to bore the block using the mill's back gear. The rpm had become important due to tool deflections in the interrupted cuts. Returning to the original practice rpms eliminated the differences.
A final issue arose when machining the 3/8" pocket for the bottom bearing. A press-fit in this hard to reach location would have created bearing servicing problems. Even though the floor of the pocket had been designed with a tiny breakout for a shop-made removal tool, I made a last minute decision to change to a close slip fit. All my 3/8" end mills cut 373"- .374" diameters even when extended as far as possible in a collet, and the deflection of a tiny long reach boring tool would have added too much uncertainty. My final solution was to chuck a 3/8" end mill in one of my dollar store drill chucks and take advantage of its runout. By adjusting the stick-out I was able to dial in the pocket diameter for a near perfect fit. One of the photos shows the dummy distributor parts used to mock up the distributor assembly in the finished block. Measurements showed the center-to-center gear spacing to be within a couple thousandths of my target.
I wouldn't normally machine the distributor hold down bracket this early in the build, but its tiny size and ten degree mounting base made it one of those pita parts that I just wanted to be done with. It was machined from an odd piece of aluminum temporarily epoxied to a block of MDF and wasn't as problematic as I had expected. Working from its bottom surface, the entire part was machined in a single setup. Its sloped mounting surface was machined using a ball cutter and tiny waterline steps.
This essentially completed the block's machining except for a pressurized oiling system that will be revisited later. - Terry
With the model for the timing cover seemingly in good shape, it was machined next. Its rear face will bolt up to the front of the block through a Teflon gasket, and the water pump which hasn't been designed yet will bolt to it's front face through a second gasket. The timing chain and distributor gears will lie behind the cover, and the crankshaft will spin in a fluoroelastomer seal. The full-size cover has an integral mount for the fuel pump on the driver's side, but the scaled mount will be a bolt-on for a cosmetic pump. On the passenger side is the tube for a functional dipstick.
Clearances for the timing components on the rear face of the cover were machined first. Its more interesting front face retains most of the features on the full-size cover and was machined next. Machining the two faces left the semi-finished cover still attached to its workpiece through a partial framework of excess stock. Quickset epoxy was used to safely secure the finished part to the top half of the workpiece while it was machined free from the bottom half. An hour at 300F cleanly released the part from the remnants of its workpiece.
Due to its small features I wasn't able to come up with a realistic looking cover that could be finish machined with a 1/4" ball cutter as I did with the block. Its shallow features, however, allowed the use of practical length 1/8" and 1/16" cutters although at the expense of machining time. The cover's twelve hour machining time was spread over several days.
Only after finishing its machining did I notice the lower half of the raised mounting boss for the water pump lacked a similar number of mounting screws to its upper half. An online search for photos of the original Ford timing covers showed they were similar. Although I wouldn't give a second thought to using sealer on a full-size engine, I try to avoid its use on models. So, I drilled and tapped two additional holes along the lower portion of the mounting boss. Although these particular screws will lie outside the gasket, they should help it seal.
The mount for the faux fuel pump was machined from a separate block of aluminum and bolted to the side of the cover with a hidden pair of 2-56 screws. The dipstick tube is a length of 5/32" stainless tubing whose exact length and shape will be determined later after the location of its upper mounting bracket on the head is determined. A 2-56 grub screw in the rear of the cover secures the tube's bottom end. Finally, the timing cover gasket was cut from .010" Teflon sheet using a vinyl cutter on my Tormach.
The cover was bead blasted in preparation for later painting, and the block will eventually receive the same treatment. In order to save some block machining time, I used some rather coarse waterline steps on a couple of its features that I now regret. They'll need to be filed/polished out before bead blasting, but my vision is now so poor that I can barely see them. And, the doctor who did my cataract surgery doesn't know why. She's hoping the problem will go away on its own in the next several weeks, but I'm not so optimistic.
The model for the heads needs a little more work, but I think the heads will likely be the next parts I'll try to work on. - Terry
Clearances for the timing components on the rear face of the cover were machined first. Its more interesting front face retains most of the features on the full-size cover and was machined next. Machining the two faces left the semi-finished cover still attached to its workpiece through a partial framework of excess stock. Quickset epoxy was used to safely secure the finished part to the top half of the workpiece while it was machined free from the bottom half. An hour at 300F cleanly released the part from the remnants of its workpiece.
Due to its small features I wasn't able to come up with a realistic looking cover that could be finish machined with a 1/4" ball cutter as I did with the block. Its shallow features, however, allowed the use of practical length 1/8" and 1/16" cutters although at the expense of machining time. The cover's twelve hour machining time was spread over several days.
Only after finishing its machining did I notice the lower half of the raised mounting boss for the water pump lacked a similar number of mounting screws to its upper half. An online search for photos of the original Ford timing covers showed they were similar. Although I wouldn't give a second thought to using sealer on a full-size engine, I try to avoid its use on models. So, I drilled and tapped two additional holes along the lower portion of the mounting boss. Although these particular screws will lie outside the gasket, they should help it seal.
The mount for the faux fuel pump was machined from a separate block of aluminum and bolted to the side of the cover with a hidden pair of 2-56 screws. The dipstick tube is a length of 5/32" stainless tubing whose exact length and shape will be determined later after the location of its upper mounting bracket on the head is determined. A 2-56 grub screw in the rear of the cover secures the tube's bottom end. Finally, the timing cover gasket was cut from .010" Teflon sheet using a vinyl cutter on my Tormach.
The cover was bead blasted in preparation for later painting, and the block will eventually receive the same treatment. In order to save some block machining time, I used some rather coarse waterline steps on a couple of its features that I now regret. They'll need to be filed/polished out before bead blasting, but my vision is now so poor that I can barely see them. And, the doctor who did my cataract surgery doesn't know why. She's hoping the problem will go away on its own in the next several weeks, but I'm not so optimistic.
The model for the heads needs a little more work, but I think the heads will likely be the next parts I'll try to work on. - Terry
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Amazing work Terry. I'm glad you are able to soldier on. We all appreciate it and are in awe of your work.
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Hi Terry!
Amasing work!
One more wonderful project.
Did you recover from you eye problem?
Tks,
Edi
Amasing work!
One more wonderful project.
Did you recover from you eye problem?
Tks,
Edi
Even though the cylinder banks are staggered, the left and right heads are identical. Some but not all of the asymmetry in the assembled engine will be visually absorbed by the block and intake manifold.
Since the vision in my right eye still hasn't returned after cataract surgery, I've not spent much time in the shop lately and instead made another pass at the head modeling. In particular, I wanted to reduce the insane number machining setups I'd allowed to creep into its design.
The Hi-Po engines used roller rockers mounted on individual studs. The valve train components aren't yet designed, and so rough equivalents were used to verify the top-end geometry. The stud mount locations were finalized with a 1.6 rocker arm ratio and clearances between the valve train components and the valve covers. The current design includes bronze valve cages which will allow pretesting the valve seats independently of the finished heads.
During our recent arctic freeze the shop was warmed up for some low-risk chip making while creating workpieces for the heads. Even though the head design was still evolving, its envelope was locked in some time ago by the finished block. The workpieces were sawed from the same piece of 7075 from which the block was taken. Using a rather sketchy setup, the cross-cuts for the heads were also sawed length-wise to make blanks for the valve covers. The head workpieces were then squared up identically and with .015" excess stock on each face.
The purpose of the excess stock was to allow the workpieces to be re-squared around the 3/16" coolant through-holes that were going to be drilled on the lathe. Instead, they were drilled half depth from either end on the mill using a 134 degree Guhring drill. The ends of the coolant passages were tapped so they could be blocked off with screw-in 'freeze plugs'.
There are lots of advantages to having identical heads, but I found myself confusing the workpiece orientations until they received some unambiguous machined features. The transfer passages connecting the coolant through-holes to the mounting faces of the block and intake manifold became these features and were drilled next. The coolant return paths through the intake manifold still have to be worked out. - Terry
Since the vision in my right eye still hasn't returned after cataract surgery, I've not spent much time in the shop lately and instead made another pass at the head modeling. In particular, I wanted to reduce the insane number machining setups I'd allowed to creep into its design.
The Hi-Po engines used roller rockers mounted on individual studs. The valve train components aren't yet designed, and so rough equivalents were used to verify the top-end geometry. The stud mount locations were finalized with a 1.6 rocker arm ratio and clearances between the valve train components and the valve covers. The current design includes bronze valve cages which will allow pretesting the valve seats independently of the finished heads.
During our recent arctic freeze the shop was warmed up for some low-risk chip making while creating workpieces for the heads. Even though the head design was still evolving, its envelope was locked in some time ago by the finished block. The workpieces were sawed from the same piece of 7075 from which the block was taken. Using a rather sketchy setup, the cross-cuts for the heads were also sawed length-wise to make blanks for the valve covers. The head workpieces were then squared up identically and with .015" excess stock on each face.
The purpose of the excess stock was to allow the workpieces to be re-squared around the 3/16" coolant through-holes that were going to be drilled on the lathe. Instead, they were drilled half depth from either end on the mill using a 134 degree Guhring drill. The ends of the coolant passages were tapped so they could be blocked off with screw-in 'freeze plugs'.
There are lots of advantages to having identical heads, but I found myself confusing the workpiece orientations until they received some unambiguous machined features. The transfer passages connecting the coolant through-holes to the mounting faces of the block and intake manifold became these features and were drilled next. The coolant return paths through the intake manifold still have to be worked out. - Terry
You always make everything perfect !
peterl95124
Well-Known Member
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very much enjoy watching your impeccable work.
my own experience with the type of drill you used for your coolant passages
is that they are too flexible (the chip grooves are ground too deep), so I use
extra long drills with normally ground grooves and lots of pecking to clear the
chips. Also I shimmed the part in the vise so that a dial-indicator in the quill
showed that the part was perfectly parallel to the quill before starting (which
went spotting drill, stub length drill, jobber length drill, extra long drill, then
flip the part over and do it all over again from the other end, also I always fill the
hole with tapping fluid while drilling, just in case !, especially if doing the drilling
after having already invested a lot of time machining the part ).
my own experience with the type of drill you used for your coolant passages
is that they are too flexible (the chip grooves are ground too deep), so I use
extra long drills with normally ground grooves and lots of pecking to clear the
chips. Also I shimmed the part in the vise so that a dial-indicator in the quill
showed that the part was perfectly parallel to the quill before starting (which
went spotting drill, stub length drill, jobber length drill, extra long drill, then
flip the part over and do it all over again from the other end, also I always fill the
hole with tapping fluid while drilling, just in case !, especially if doing the drilling
after having already invested a lot of time machining the part ).
Peter,
I agree with your comments about small diameter Guhring drill flexibility and more importantly about the need for a plumb set up. I once had an 1/8" diameter 6" deep Guhring hole go off course even though it had been started with a stubby drill. In this case, 3/16" seemed to work well on its own with lots of WD-40 and 1/4" pecks. You can tell early on by the sound the drill on its way back into the hole during pecking if you're in trouble. - Terry
As it turned out, I wasn't able to significantly reduce the number of setups needed to machine the heads. Each one requires 62 drilled holes, and nearly all of them at odd angles to the faces of the workpiece. Their precise angles and entry/exit points through the heads' surfaces are critical for proper mating to the block and manifolds not to mention the need to navigate through the coolant passages. Many of these holes were inherited from the block and manifold models via a SolidWorks assembly (think of them as having been virtually transfer drilled), and so they didn't come with their own standalone dimensions.
In addition, the setups needed to drill most of the heads' holes aren't going to be the same as those used to machine its surfaces. So, I decided to pre-drill them all while the workpiece was still square and easy to work-hold.
The first step was to drill (undersize) the through-holes for the head bolts and temporarily tap them for attaching to a dowelled fixture plate. The dimensions of the rest of the holes were then derived with respect to the faces of the workpiece and the drilling accomplished with the help of an angle table. Since the corners of the workpieces had been carefully finished so they could be unambiguously indicated with a spindle microscope, tooling balls weren't needed. One of the photos shows a typical setup on my crappy imported angle table. That isn't a parallax error in the bottom t-slot. The rest have been re-milled parallel, but the bottom one was left as it was received and custom t-slot stops slid along it to fine tune workpiece alignments.
Since work-holding wouldn't be affected, the combustion chambers were machined before going on with the rest of the drilling. They're a lot of work for a typical model engine, but I was impatient to see them. Except for their equal-sized intake and exhaust valves, the model's wedged chambers are very similar to those used in the full-size engine. Their very prominent un-shrouded spark plugs should perform well in a model.
The pushrod guide/clearance holes required an angle of 88 degrees, the valve cage bores and rocker stud mounting holes an angle of 70 degrees, and the intake manifold mounting holes and counterbores an angle of 45 degrees. The exhaust ports and flange mounting holes required a 60 degree setup and so a pair of 90 degree 3" angle plates were prepared to support the dowelled fixture plate on the angle table. The intake ports required a 15 degree setup on a across-wise mounted angle table.
The drilling was completed except for the spark plug holes which in my infinite wisdom currently require a compound angled setup. These holes require drilling, threading, and counterboring for a seat all of which must be done in the same setup. There's little margin inside the combustion chambers to handle mis-drilling, and so some more more thought is going to be needed.
I'm scheduled for surgery in two weeks to repair the damage done to my right eye during my cataract surgery. Hopefully, my vision will improve shortly after that. For the past seven weeks, it's been measure once, measure twice, measure three times, measure four times, drop the highest and lowest, average out what's left, cross fingers, and then drill. - Terry
In addition, the setups needed to drill most of the heads' holes aren't going to be the same as those used to machine its surfaces. So, I decided to pre-drill them all while the workpiece was still square and easy to work-hold.
The first step was to drill (undersize) the through-holes for the head bolts and temporarily tap them for attaching to a dowelled fixture plate. The dimensions of the rest of the holes were then derived with respect to the faces of the workpiece and the drilling accomplished with the help of an angle table. Since the corners of the workpieces had been carefully finished so they could be unambiguously indicated with a spindle microscope, tooling balls weren't needed. One of the photos shows a typical setup on my crappy imported angle table. That isn't a parallax error in the bottom t-slot. The rest have been re-milled parallel, but the bottom one was left as it was received and custom t-slot stops slid along it to fine tune workpiece alignments.
Since work-holding wouldn't be affected, the combustion chambers were machined before going on with the rest of the drilling. They're a lot of work for a typical model engine, but I was impatient to see them. Except for their equal-sized intake and exhaust valves, the model's wedged chambers are very similar to those used in the full-size engine. Their very prominent un-shrouded spark plugs should perform well in a model.
The pushrod guide/clearance holes required an angle of 88 degrees, the valve cage bores and rocker stud mounting holes an angle of 70 degrees, and the intake manifold mounting holes and counterbores an angle of 45 degrees. The exhaust ports and flange mounting holes required a 60 degree setup and so a pair of 90 degree 3" angle plates were prepared to support the dowelled fixture plate on the angle table. The intake ports required a 15 degree setup on a across-wise mounted angle table.
The drilling was completed except for the spark plug holes which in my infinite wisdom currently require a compound angled setup. These holes require drilling, threading, and counterboring for a seat all of which must be done in the same setup. There's little margin inside the combustion chambers to handle mis-drilling, and so some more more thought is going to be needed.
I'm scheduled for surgery in two weeks to repair the damage done to my right eye during my cataract surgery. Hopefully, my vision will improve shortly after that. For the past seven weeks, it's been measure once, measure twice, measure three times, measure four times, drop the highest and lowest, average out what's left, cross fingers, and then drill. - Terry
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AllenS
Member
You might check Tamiya. The used to build an RC motorcycle that used something like 1/8" pitch for the final drive. Was very small and i have seen that there are several rd motorcycles still being builtI found plenty of #25 ( 1/4" pitch ) But nothing smaller
Scott
The spark plugs in the full-size engine are angled down and away from the head to avoid interference with the stock exhaust manifold. Since the same head is used on both sides of the engine, the plugs on each side will face in opposite directions. Even though I'll likely fabricate a set of headers, the model's plugs were set to slope 30 degrees down and 10.3 degrees front to back.
A crosswise mounted angle table supplied the 10.3 degrees, and a 60 degree shop-made angle plate provided the 30 degrees. That poorly thought-out plate was a drawn-out effort typical of what happens when I'm machining without a drawing.
The long side of the workpiece was easily indicated along the mill's x-axis, but the angle plate prevented alignment of its short side with the y-axis making it difficult to indicate. The spark plug seat depths are important because they set the plug depths inside the combustion chambers where there is little excess stock around the plug noses. In order to insure accuracy in such a complex setup, the drilling was done with the aid of tooling balls.
Normally one would incorporate the tooling ball into the machining fixture, and although the dowelled fixture plate had the needed accuracy it didn't have the real estate. Instead, the stem holes for the balls were drilled in the excess workpiece stock that will be milled away later. With the workpiece mounted flat in a vise, a hole was drilled/reamed adjacent to each spark plug location. A single tooling ball can be sufficient in some setups, and its location usually arbitrary. My thinking was that one ball per spark plug might reduce error build-up in my fairly complex setup. The same x,y,z incremental coordinates could then also be used to locate each hole which would reduce my chances of making a careless mistake.
But, what the heck is a tooling ball?
A tooling ball is simply a precision metal ball attached to a stemmed pedestal. Commercial tooling balls can be purchased in various sizes, or they can be shop-made. Their big advantage is that once they become a part of the workpiece or machining fixture, the ball's center can be indicated and used to locate features on the part regardless of the part's orientation. The ball becomes an integral part of the design, and difficult features can be dimensioned to it. The ball's height above its installed surface is fixed by its design. The use of a tooling ball in drilling the spark plug holes and seats is illustrated in the sequence of photos.
The first photo shows the particular tooling ball that was used. This one was from McMaster-Carr and is designed for a close slip fit in a .250" reamed hole.
The second photo is a CAD rendering of the workpiece showing where the holes for the tooling ball stems were drilled into the workpiece while it was clamped flat in a vise. The actual locations were arbitrary, but the trivial drilling setup allowed them to be precisely placed. Only one ball was actually used, and it was moved from hole to hole.
The third photo is a CAD rendering of the workpiece fixture'd in virtual space. The spark plug seat surfaces are parallel to the milling table and ready for drilling. The pre-calculated angles of the table and plate were verified in this model.
The next photo is the actual part set up in the mill and ready for drilling. Before proceeding, a number of sanity checks were made using a spindle microscope to verify the setup. The NW and SE corners of the workpiece were picked up, and all four tooling ball locations were indicated.
The fifth photo is a worksheet showing measurements recorded during the sanity checks. The worst case error in the x direction is .005" and in the y direction it is only .002". Not bad considering all the potential error sources in such a setup.
The next CAD drawing shows the x-y incremental moves to be made from each tooling ball to locate each drilling point.
The seventh drawing shows the seat depth referenced to the top of the tooling ball which includes a piece of .001" shim stock to protect the tooling ball from the end mill during touch-off.
The next photo shows a typical hole machining operation in progress. The seat was plunged with an end mill before spotting, drilling, reaming, and threading a .165" hole for a 10-40 VR-1 spark plug.
The last two photos show the final results. All eight holes ended up where intended and as can be seen there was little margin for error. The next steps are to mill away the workpiece material and finally reveal the heads. - Terry
A crosswise mounted angle table supplied the 10.3 degrees, and a 60 degree shop-made angle plate provided the 30 degrees. That poorly thought-out plate was a drawn-out effort typical of what happens when I'm machining without a drawing.
The long side of the workpiece was easily indicated along the mill's x-axis, but the angle plate prevented alignment of its short side with the y-axis making it difficult to indicate. The spark plug seat depths are important because they set the plug depths inside the combustion chambers where there is little excess stock around the plug noses. In order to insure accuracy in such a complex setup, the drilling was done with the aid of tooling balls.
Normally one would incorporate the tooling ball into the machining fixture, and although the dowelled fixture plate had the needed accuracy it didn't have the real estate. Instead, the stem holes for the balls were drilled in the excess workpiece stock that will be milled away later. With the workpiece mounted flat in a vise, a hole was drilled/reamed adjacent to each spark plug location. A single tooling ball can be sufficient in some setups, and its location usually arbitrary. My thinking was that one ball per spark plug might reduce error build-up in my fairly complex setup. The same x,y,z incremental coordinates could then also be used to locate each hole which would reduce my chances of making a careless mistake.
But, what the heck is a tooling ball?
A tooling ball is simply a precision metal ball attached to a stemmed pedestal. Commercial tooling balls can be purchased in various sizes, or they can be shop-made. Their big advantage is that once they become a part of the workpiece or machining fixture, the ball's center can be indicated and used to locate features on the part regardless of the part's orientation. The ball becomes an integral part of the design, and difficult features can be dimensioned to it. The ball's height above its installed surface is fixed by its design. The use of a tooling ball in drilling the spark plug holes and seats is illustrated in the sequence of photos.
The first photo shows the particular tooling ball that was used. This one was from McMaster-Carr and is designed for a close slip fit in a .250" reamed hole.
The second photo is a CAD rendering of the workpiece showing where the holes for the tooling ball stems were drilled into the workpiece while it was clamped flat in a vise. The actual locations were arbitrary, but the trivial drilling setup allowed them to be precisely placed. Only one ball was actually used, and it was moved from hole to hole.
The third photo is a CAD rendering of the workpiece fixture'd in virtual space. The spark plug seat surfaces are parallel to the milling table and ready for drilling. The pre-calculated angles of the table and plate were verified in this model.
The next photo is the actual part set up in the mill and ready for drilling. Before proceeding, a number of sanity checks were made using a spindle microscope to verify the setup. The NW and SE corners of the workpiece were picked up, and all four tooling ball locations were indicated.
The fifth photo is a worksheet showing measurements recorded during the sanity checks. The worst case error in the x direction is .005" and in the y direction it is only .002". Not bad considering all the potential error sources in such a setup.
The next CAD drawing shows the x-y incremental moves to be made from each tooling ball to locate each drilling point.
The seventh drawing shows the seat depth referenced to the top of the tooling ball which includes a piece of .001" shim stock to protect the tooling ball from the end mill during touch-off.
The next photo shows a typical hole machining operation in progress. The seat was plunged with an end mill before spotting, drilling, reaming, and threading a .165" hole for a 10-40 VR-1 spark plug.
The last two photos show the final results. All eight holes ended up where intended and as can be seen there was little margin for error. The next steps are to mill away the workpiece material and finally reveal the heads. - Terry
ninefinger
Well-Known Member
Thank you for the explanation of the tooling ball use. I've heard of them before and generally thought I understood their use but a practical application / example always helps to bring me clarity. Much appreciated and great work. Wishing you a successful repair visit to the eye surgeon.
Mike
Mike
Thanks Terry ! really nice write up and a masterful execution. It is really amazing how much time and effort goes into where that drill is going to go. 
Several days of planning and fixturing for a couple hours of drilling and tapping.
But your results speak for themself. Nicely done.
As always thank you so much for taking the time to document and share your work. It is really appreciated and enjoyed.
Scott
Several days of planning and fixturing for a couple hours of drilling and tapping.But your results speak for themself. Nicely done.
As always thank you so much for taking the time to document and share your work. It is really appreciated and enjoyed.
Scott
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