Ford 300 Inline Six

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mayhugh1

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Terry,
Your work on this engine is awesome. I'm really interested in trying your epoxy method of holding parts while machining the part. What do you use for an oven? Can I use a convection toaster oven?

Jerry
Jerry,
I use my small heat treat oven, but a little toaster oven should be fine. There is a bit of odor and so my wife wouldn't allow it in our kitchen oven. I used to use a heat gun, but I think they changed the formulation of their epoxy a few years ago and an oven seems to work best now. You need to wear gloves and remove the part while still hot or the epoxy will tend to re-seize as it cools. - Terry
 

awake

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Jerry,
I use my small heat treat oven, but a little toaster oven should be fine. There is a bit of odor and so my wife wouldn't allow it in our kitchen oven. I used to use a heat gun, but I think they changed the formulation of their epoxy a few years ago and an oven seems to work best now. You need to wear gloves and remove the part while still hot or the epoxy will tend to re-seize as it cools. - Terry
So what you're saying is ... no half-baked approach will work.

:)
 

mayhugh1

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I've been getting up to speed on helical gear machining since my last post, and so I don't have much show & tell. I've finally gotten serious about the helical gear set needed to drive the mid-engine'd distributor from the camshaft. These .303" diameter gears aren't commercially available, and with 14 teeth @ 72 DP and a 45 degree helix, they're on the edge of what's practical to machine in a home shop. George recognized their difficulty early on and made sure he could make them before completing the design of the engine.

Most of my recent 'shop time' was spent studying related gear posts which began showing up some seven years ago when Chuck Fellows published his design for a fixture he used to machine helical gears on his lathe. Chuck and I were members of a local metalworking club, and I got to watch his progress first hand. Although we had lots of discussion about tooth profiles, I never tried to machine any of my own.

Rather than duplicate Chuck's fixture which George used in a mill setup, I'm planning to machine mine using a 4-axis setup on my Tormach. I've been in contact with George about these gears, and his generous advice has been invaluable.

In order to set my rotary table 45 degrees nose up under the Tormach's spindle, clearance limitations forced me to align it with the mill's x-axis. I had hoped to use the y-axis instead which would have allowed me to avoid the machining needed to adapt my tilting angle table. Hoisting that 60 lb rotary onto the mill's table isn't something to be taken lightly, and the final setup require planning, some trial and error, and a couple Ibuprofens.

During study breaks I was able to tie up a few loose ends. A three-bolt exhaust pipe flange was made to match the output of the exhaust manifold. It was machined from a piece of 303 stainless flat bar that was temporarily epoxied to a piece of MDF. The flange was brazed to a simple exhaust pipe bent from 3/8" diameter 304 stainless tubing. Two flanges were made so I'd later have the option of an alternate exhaust.

The exhaust manifold was airbrushed with POR-15 high temperature (1200F) paint. By greatly thinning the paint down using the manufacturer's special thinner, I was able to spray a very light coat that changed the manifold's color without leveling its glass-beaded textured surface. This paint requires a 24 hour room temperature drying time followed by a 300F bake and cool down cycle in order to complete its cure.

The intake manifold was similarly airbrushed with light gray Gun Kote. This gasoline resistant coating requires a similar cure but offers much less heat resistance. - Terry

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gbritnell

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Terry,
The colors on your engine sure do enhance the look of it!
 

mayhugh1

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Terry,
The colors on your engine sure do enhance the look of it!
George,
Thanks. I've long wondered about adding color to an engine but so far have only experimented with the display stands. This one seemed like a good candidate for full paint since I still clearly remember Ford's full-size engine. I'm not yet sure how I feel about painting, though. Their shiny machined surfaces always seemed to say 'hey, this was made with care by a machinist," Painted, they seem to say "this is a Toyan RC model from China." - Terry
 
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L98fiero

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George,
Thanks. I've long wondered about adding color to an engine but so far have only experimented with the display stands. This one seemed like a good candidate for full paint since I still clearly remember Ford's full-size engine. I'm not yet sure how I feel about painting, though. Their shiny machined surfaces always seemed to say 'hey, this was made with care by a machinist," Painted, they seem to say "this is a Toyan RC model from China." - Terry
I'm pretty sure no one will ever mistake your engine for a Chinese 'production' model.
 

mayhugh1

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Specialized equipment and manufacturing processes are used to commercially manufacture precision helical gears. Reasonable facsimiles, though, can be made using equipment in a typical machine shop. Two things are required. The first is a method to coordinate the moves of the cutter along and around the axis of the gear blank, and the second is a suitable cutter.

Coordinated cutter moves are what CNC is all about, and so I used my Tormach to handle the first requirement. Since I don't have a right angle spindle drive and want to use a circular cutter, the rotary had to be mounted nose-up under the spindle at an angle to the table equal to the helix angle.

Several years ago on this forum, Chuck Fellows published his design of a fixture that enables helical gears to be machined on a lathe or mill without the need for CNC or even a rotary. George Britnell later published a Youtube video demonstrating the machining of the gears for this engine using his version of Chuck's fixture.

Chuck used commercial spur cutters to make his helical gears, and this spawned discussions about tooth profiles. A spur gear cutter is designed to cut an accurate (although not necessarily perfect) profile for teeth that are square to the face of the cutter, but this isn't how helical teeth mate. The mismatch increases with the angle of the helix as well as the cutter-to-blank diameter ratio. It soon came to light that it's common shop practice to cut one-off helical gears using conventional involute cutters designed for a somewhat higher tooth count than specified for the helical gear. (For the same DP, the pitch diameter of a helical gear is greater than the pitch diameter of a spur gear by a factor equal to 1/cos(A) where A is the helix angle.) A common multiplier for the tooth count is 1/[cos(A)]^3. For example, to cut a 14 tooth 72DP 45 degree helical gear, a 72DP spur gear cutter intended for 40 teeth would be used.

One way to visualize a helical gear is to imagine many identical spur gears cut from thin sheets of metal and bonded together so each successive layer rotates slightly beyond the one behind it. Solidworks has a modeling feature capable of handling this, and the first photo contains 3-d models and specifications for the gears to be machined. A pair of these gears is needed to connect the engine's camshaft to the distributor.

Even though these particular gears are lightly loaded, and neither wear nor noise are concerns, they aren't necessarily good choices for a first machining attempt. There are lots of potential errors in setup and machining that can quickly add up on a .303" o.d. gear with .030" teeth.

The block's angled boss for the distributor was designed assuming the distributor's driveshaft will pass by the camshaft with the gears' theoretically correct angle and spacing. Even though the angled (and blind) distributor bore hasn't yet been done on the otherwise finished block, a small error in the theoretical .275" gear-to-gear spacing should also be tolerable.

Neither 72 DP cutters (nor the gears they cut) seem to be commercially available, and so the cutter had to be shop made. The drawing package for the engine doesn't currently include how-to information on the machining of these gears, and so I decided to try my hand at making a cosine cutter. Using data intended for 14-1/2 degree PA button cutters, I came up with the cutter profile shown in the second drawing. The tables in Ivan Law's bible are incomplete for some reason, and so I've included a table I lifted from the online Nov. 2015 issue of the Home Metal Shop Newsletter. This profile was manually machined on the end of a piece of 3/8" drill rod using a Nicole profiling insert. After gashing it to obtain four teeth with a bit of back relief, the cutter was hardened and tempered at 300F.

I've included a rendering of the cutter's profile projected onto the cutting plane of the helical gear model. The fit is reasonable, but the gear's involute contact line that will shared with its mate is questionable. This profile was then used to create CAD models of the gears I might expect to see using this cutter. The accuracy of these results are limited by the fact that I assumed a zero thickness 2-d cutter to create them. I was never able to figure out how to take into account the finite diameter of an actual circular cutter.

I've also included photos of the actual cutter that eventually machined over a dozen brass and steel gears. Due to a rookie mistake that resulted in my worksheet having the profiler's in-feed moves called out as radii while my lathe's DRO was set in diameter mode, my first cutter was devilishly misshaped. Since helical gear machining was a brand new experience for me, I spent days looking in the wrong places for what was wrong. My correspondences with George were very helpful and, in fact, he offered to let me borrow his fixture and cutter, but by this time I was obsessed with doing it myself. Most of my modeling efforts were done while troubleshooting this cutter problem.

My next post will include information about the actual gear machining process and its final results. - Terry

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gbritnell

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Hi Terry,
I'm glad to see things are sorting themselves out regarding the helical gear making. I took your suggestion and included a drawing of the required cutter in the drawing set. This will help anyone wanting to build one of these. LOL. I doubt there's not many who would want to tackle a project like this.
gbritnell
 

a41capt

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Excellent explanation of the math employed in designing your cutter Terry. Way beyond my capability for sure, but wonderfully illustrated, thanks for the education

So looking forward to hearing it run!

John W
 

mayhugh1

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Although just two .250" long gears are needed, several .4" long brass and 12L14 steel blanks were prepared. The longer blanks nearly doubled the machining time, but the longer spares might be more useful in some future project.

In order to set up the work offsets, I made the alignment tool George came up with for use with Chuck's helical fixture. It looks deceptively simple, but it took a couple tries to get one indicating true on a surface plate. The tool was installed on the rotary's mandrel and after indicating the two arms parallel to the mill's table, the rotary's DRO was zero'd. An edge finder was then used to indicate the spindle to the center of one of the arms so the X DRO could be zero'd. The edge finder was then replaced with the cutter which was visually aligned with the pointed end of one of the arms so the Z DRO could be zero'd. Finally, the alignment tool was replaced with a gear blank. After positioning the cutter at X=0, Z=0, it was touched off to the blank's outside surface, and the Y DRO zero'd.

An end point for the cutting passes was then chosen. With the work offsets completed and the rotary pointing up at 45 degrees, equal moves along the X and Z axes keep the cutter properly aligned to the blank. With cutting taking place on the front side of the blank, the cutter will travel upward at a 45 degree trajectory while the rotary turns CCW. In my particular setup, a suitable end point where the cutter just clears the blank turned out to be X=.250, Z=.250. For convenience, the cutter was moved to this location and the X and Z DRO's zero'd for the last time. A suitable starting point for the cutting operation turned out to be X=-.450, Z=-.450.

Between my particular start and stop points, the cutter will travel a total distance of .450" x 1.414 = .6363" along the .400" long blank. One last parameter needed for coding is the gear's lead which is the length over which one full rotation of the gear's helix will occur. Lead is a function of the circumference of the gear's pitch circle and helix angle. It's calculated as L = [pi * N]/[DP * sin(A)] where N is the number of teeth and A is the angle of the helix. For this particular gear, L = .8639". Therefore, in my setup, the cutter's .6363" travel will require a simultaneous rotary movement of 360 x (.6363/.8639) = 265.196 degrees.

A full listing of the g-code is included. Since I was a newbie with the helical gear making process and still troubleshooting my cutter debacle, I didn't attempt a universal program with parameters. I did include plenty of comments. With the machine in incremental mode (G91) and a starting point at (X-.450, Z-.450, Y-.015, A0), the single line of code that does the actual cutting is simply:

G1 X.450 Z.450 A-265.196

During testing, I found it best to machine the .030" teeth in two .015" passes. For reasons I still don't understand, there was a lot more noise and vibration while cutting the brass gears compared with the steel gears which machined dead quiet.

Due to burrs raised by the cutter, the resulting o.d.'s of both gear types consistently came out .007" greater than the starting diameters of their blanks. They were finished on a lathe by re-facing their ends and skimming their diameters back to their blanks' original values. This, of course, left yet another tiny burr on the inside edge of each tooth. These were manually cleaned off using a cobbled-up de-burring tool fashioned from a Nicole .040" diameter profiling insert. Drawing this tool just once through the space between each pair of teeth removed these tiny burrs without significantly affecting the tooth profiles.

The tooth profiles on the finished gears are different from that predicted by my cosine gear model. The difference is probably at least partially related to the non-zero diameter of the actual cutter. The final parts certainly look like helical gears and they do mesh smoothly, but I don't expect a true involute contact line.

One last sanity check is the measurement of the axial spacing between a pair of freely turning 90 degree meshed gears adjusted for minimum backlash. The theoretical number is .275" which is the pitch diameter. The measured spacing of the four gears in my first batch ranged between .276" and .277". After some thought, I decided it would be smart to have a few more options to choose from in case the still-to-be-done drilling operation for the distributor driveshaft bore veers off its course. The diameters of two more batches of blanks were tweaked plus and minus .0015", and I wound up with two more batches of gears with spacings ranging between .271" and .273" and between .280" and .281".

The little shop-made cutter held up much better than I expected - so much better in fact that I don't believe I'll be buying any more expensive commercial cutters. - Terry

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Thommo

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I have to say Mayhugh1, every time I look at one of your posts, I immediately realise just how inadequate my machining skills are in comparison to yours lol. A fantastic job you are doing. Can’t wait to hear it running.
 
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