Another Rupnow 1 by 1
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Hi Bob,
With the "spring" of the boring bar, you may expect it to be constant for the length of the bore... But a few quirky things happen. As the tool engages with the start of the cut, it cuts "full" until it starts to get into the metal, then when the tool is fully engaged it springs back a touch more. On the first cut, this may only be for 0.010" ~0.020" - ish, depending on how wide the cut actually is, when fully engaged. This tiny taper, then exacebates the next cut "start taper", and again, and again, so you get a bell-mouth or initial taper from the outer-edge narrowing further down the bore. Also, as the cylinder heats up when the cut is traversing down the bore, the last bit of bore is thermally expanded a tiny amount larger than the first bit of the cut. Again, with 20 cuts, this is exacerbated 20 times... so the bottom of the bore - after cooling (normalising) temperature - then returns to a slightly smaller diameter than the top of the bore. Complicated, but it is the reason that modern production machining floods the parts and cutters with coolant to keep the temperature the same from end-to-end of any cut. - Hence, without any mis-alignment of the lathe, there may be a detectable taper of larger at the top than the bottom of the bore, from these 2 factors...
If you have a larger bottom than top diameter, then that is the natural misalignment of the lathe, and not the dynamics of cutting metal...
Or that's what I remember from 30 ~ 50 odd years ago...
I think a taper of 0.0015" over a 1~2" length is a lot! When I was boiring car blocks in the 1960s (on WW2 machines - well worn) we had less than 0.001" variation of bore top to bottom. In fact I can't rememebr any difference, measured with a clock to 0.001". But when I was honing the bores afterwards, I had to stay withing 0.003" max variation top to middle to bottom... As the hone reached ends only momentarily, but passed the middle on the up and down strokes, we had to double the cut at the bore ends to keep the bore from barrelling: I.E. bigger in the middle.
If I made a mistake ( as an apprentice) the boss would take chaarge and "re-parallel" the bore, as he had 40 years practice more than I had! But it didn't happen after I "got the knack". Incidentally, the Hone was not for sizing the bore, but to remove around half of the peaks of the cut-surface from the boring tool, so instead of the piston and ring surfaces sliding on a saw-toothed set of "peaks" from machining, they rode on a series of flats, with tiny valleys retaining the oil. This honing is seen as the cross-hatching of bores, familiar to most engine mechanics.
The rings have to do a lot of work to retain a seal while adjusting to the bore size with 0.0015" variation, and the piston skirt will flap a bit more at the larger diameter, compared to the smaller... The skirt changes loading at TDC and BDC, or thereabouts, and causes piston slap when you have an extra thou at one end...
Do you have a miller or precision bench mill? If you do, you can set the boring bar to rotate, and the cylinder static, aligned to the axis of the quill. (A dummy bar or Go-NoGo gauge can be used for alignment). Then when you pass the boring bar - for finishing cuts - down the bore, the tool will describe a circle, and the quill traversing will make a true cylinder, compared to the tapered bore you have from the lathe. What you have at the moment, is a part rotating, and the tool is traversing an axis that is mis aligned to the axia of the rotating part, so you are naturally machining a tapered bore, not a cylinder.
When you have a true cylindrical bore, you can set a mandel in the lathe - to a tailstock centre for stability, with the cylinder fitted on the mandrel, and then cut the bottom flange face perpendicular to the bore.
It will all make a better engine.
Have fun!
If any other experts want to teach me better methods, then I am willing to learn more! (I'm not perfect - yet!). Just because I think I am right does not make it true... (That only applies to top politicians!).
Ken
With the "spring" of the boring bar, you may expect it to be constant for the length of the bore... But a few quirky things happen. As the tool engages with the start of the cut, it cuts "full" until it starts to get into the metal, then when the tool is fully engaged it springs back a touch more. On the first cut, this may only be for 0.010" ~0.020" - ish, depending on how wide the cut actually is, when fully engaged. This tiny taper, then exacebates the next cut "start taper", and again, and again, so you get a bell-mouth or initial taper from the outer-edge narrowing further down the bore. Also, as the cylinder heats up when the cut is traversing down the bore, the last bit of bore is thermally expanded a tiny amount larger than the first bit of the cut. Again, with 20 cuts, this is exacerbated 20 times... so the bottom of the bore - after cooling (normalising) temperature - then returns to a slightly smaller diameter than the top of the bore. Complicated, but it is the reason that modern production machining floods the parts and cutters with coolant to keep the temperature the same from end-to-end of any cut. - Hence, without any mis-alignment of the lathe, there may be a detectable taper of larger at the top than the bottom of the bore, from these 2 factors...
If you have a larger bottom than top diameter, then that is the natural misalignment of the lathe, and not the dynamics of cutting metal...
Or that's what I remember from 30 ~ 50 odd years ago...
I think a taper of 0.0015" over a 1~2" length is a lot! When I was boiring car blocks in the 1960s (on WW2 machines - well worn) we had less than 0.001" variation of bore top to bottom. In fact I can't rememebr any difference, measured with a clock to 0.001". But when I was honing the bores afterwards, I had to stay withing 0.003" max variation top to middle to bottom... As the hone reached ends only momentarily, but passed the middle on the up and down strokes, we had to double the cut at the bore ends to keep the bore from barrelling: I.E. bigger in the middle.
If I made a mistake ( as an apprentice) the boss would take chaarge and "re-parallel" the bore, as he had 40 years practice more than I had! But it didn't happen after I "got the knack". Incidentally, the Hone was not for sizing the bore, but to remove around half of the peaks of the cut-surface from the boring tool, so instead of the piston and ring surfaces sliding on a saw-toothed set of "peaks" from machining, they rode on a series of flats, with tiny valleys retaining the oil. This honing is seen as the cross-hatching of bores, familiar to most engine mechanics.
The rings have to do a lot of work to retain a seal while adjusting to the bore size with 0.0015" variation, and the piston skirt will flap a bit more at the larger diameter, compared to the smaller... The skirt changes loading at TDC and BDC, or thereabouts, and causes piston slap when you have an extra thou at one end...
Do you have a miller or precision bench mill? If you do, you can set the boring bar to rotate, and the cylinder static, aligned to the axis of the quill. (A dummy bar or Go-NoGo gauge can be used for alignment). Then when you pass the boring bar - for finishing cuts - down the bore, the tool will describe a circle, and the quill traversing will make a true cylinder, compared to the tapered bore you have from the lathe. What you have at the moment, is a part rotating, and the tool is traversing an axis that is mis aligned to the axia of the rotating part, so you are naturally machining a tapered bore, not a cylinder.
When you have a true cylindrical bore, you can set a mandel in the lathe - to a tailstock centre for stability, with the cylinder fitted on the mandrel, and then cut the bottom flange face perpendicular to the bore.
It will all make a better engine.
Have fun!
If any other experts want to teach me better methods, then I am willing to learn more! (I'm not perfect - yet!). Just because I think I am right does not make it true... (That only applies to top politicians!).
Ken
Last edited:
Bentwings
Well-Known Member
I agree, no grease way oil is fine cleans up easily does the job grease on the lead screws made a mess on our lathe cleaned up. Trying gear lube seems ok gears like it but it’s stinky and can be a mess if there is too much
Byron
Keep in mind that boring on the mill will only make a true circle if the spindle is trammed to be perfectly parallel to the direction of feed. Tram errors will cause it to cut an elliptical bore.
The lathe will always make a circular bore but as you have noted it may be tapered by various factors, wear in the ways or insufficient levelling of the bed being common culprits alongside tool deflection.
Hi Nerd, As this relies on long shafts in the quill, precision machined by the manufacturer to be concentric for bearing locations, and the quill sliding surfaces, these quill axis versus rotational axis mis-alignments are very small compared to all the things that will develop a tapered bore from the lathe. It is why industry uses boring machines for engines that are equivalent to a mill or drill with a rotating Quill passing along an axis that becomes the axis of the bore. (I used boring machines in the 1960s, using 1940s machines. Modern factories - e.g. the ones I saw in 1989 in Japan, etc. - use CNC boring bars of basically the same strategy. - The "CNC bit" checks and measures as it cuts, and resets/replaces tooling automatically - which is what I did manually in the 1960s - after every cut.).
I use an old and worn miller-driller to bore my cylinders, as it is simply better (a more true cylinder) than the lathe. With 0.0001" DTIs (bore gauges) in the 1960s we never managed to see any ovality in the bores, yet with honing (as I was learning the skills of manually traversing the hone in the bore developing cross-hatching) we could develop tapered- , barrel- , and hour-glass- bores of a few 10ths of a thou. The target was as true a cylinder as we could get axially, as the circularity was not a problem.
However, if you have managed to make elliptical bores doing it that way I am surprised? (Amazed!).
K2
I use an old and worn miller-driller to bore my cylinders, as it is simply better (a more true cylinder) than the lathe. With 0.0001" DTIs (bore gauges) in the 1960s we never managed to see any ovality in the bores, yet with honing (as I was learning the skills of manually traversing the hone in the bore developing cross-hatching) we could develop tapered- , barrel- , and hour-glass- bores of a few 10ths of a thou. The target was as true a cylinder as we could get axially, as the circularity was not a problem.
However, if you have managed to make elliptical bores doing it that way I am surprised? (Amazed!).
K2
My mill hasn't got enough Z travel to bore cylinders (it's an Atlas MFA horizontal mill, there is maybe 4" of Z available depending on setup which leaves very little space for a boring head), so I have no choice but to use the lathe.
I made that remark because a lot of hobby machinists use inexpensive Chinese mills, and some of those machines are notorious for head tramming issues including the head moving after being trammed due to poor manufacturing of the mating surfaces or dubious clamping mechanisms. With such equipment it's probably a good idea to check the tram of the head every time the head is moved. Of course it would take an egregious amount of tram error to make a noticeably oval cylinder, but it's just another thing to watch out for.
Hi Nerd, Thanks for that - Fair comment! - I do not have that experience of the mills, nor of horizontal mills.
Incidentally, My Dad didn't have a Mill, nor suitable bench drill, so he set the cylinders on the tool post location - with home developed fixturing - and traversed the cylinders along the axis of the lathe with boring bar set between chuck and tail-stock centre. It is quite easy to make the boring bar - a 1/8" or 1/4" hole drilled in the middle of a long bar, with locking screw, to hold a tool-bit from round HSS. The bar between chuck and tailstock needs to allow for the length of cylinder each side of the tool, so the tool can pass fully through.
Similarly, Your 4" Z-travel would allow a bit less than 2" long bore for a cylinder that was around the bar. (4" subtracting the tool bit thickness and maybe another 1/4" for end clearances...). I am sure you could make a small bar for your miller, if you had a cylinder less than 1 3/4" long? Do you need a sketch? - or can you envisage my idea?
K2
Incidentally, My Dad didn't have a Mill, nor suitable bench drill, so he set the cylinders on the tool post location - with home developed fixturing - and traversed the cylinders along the axis of the lathe with boring bar set between chuck and tail-stock centre. It is quite easy to make the boring bar - a 1/8" or 1/4" hole drilled in the middle of a long bar, with locking screw, to hold a tool-bit from round HSS. The bar between chuck and tailstock needs to allow for the length of cylinder each side of the tool, so the tool can pass fully through.
Similarly, Your 4" Z-travel would allow a bit less than 2" long bore for a cylinder that was around the bar. (4" subtracting the tool bit thickness and maybe another 1/4" for end clearances...). I am sure you could make a small bar for your miller, if you had a cylinder less than 1 3/4" long? Do you need a sketch? - or can you envisage my idea?
K2
Yes I've considered that. It should even be possible to support the other end of the bar with the overarm, which would of course be ideal for reducing tool deflection issues, similar to your dad's line boring on the lathe. I would need to make a custom Morse taper holder to support the spindle end of the bar without taking up too much space, as a typical collet chuck occupies a fair bit of my limited real estate.
Cheers Nerd, (Do you have a more "Human" handle?).
You are the expert of your machine. The fun is resolving the tooling issues! Add a picture when you work out a solution! Good for us all to learn!
Cheers!
K2
You are the expert of your machine. The fun is resolving the tooling issues! Add a picture when you work out a solution! Good for us all to learn!
Cheers!
K2
Is boring an engine done on a mill (or similar machine) due to greater accuracy ... or rather due to the great difficulty of spinning an engine block on a lathe?
I'm thinking the lathe is generally going to be more accurate, but it just isn't suited for some types of boring.
Bentwings
Well-Known Member
You already have a good handle in tool dynamics . I’d almost think we came from the same apprentice program. Midterm in my engineering caree I was introduced to a gentleman that assisted me with tool dynamics using one of my structural analysis programs so I was able to simulate some of thes issues on screen. With the advent of carbon fiber I think it only a matter of time before someone comes up with ultra stiff tools with bonded carbide or other super hard cut tinging edges weight is not the issue. CF HAS AS MUCH AS 10 times the tensil of steel so tools could be much stiffer. It would then go to how ridged is the machine or holder then we will se Star Trek tritanium and even more exotic materials. The ultimat being unobtanium. LOL BY THEN WE WILL HAVE REPLICATORS SO MACHINE TOOLS WILL BE OBSOLETE . My mind is drifting sorry I missed caps lock was on.
Byron
Simply:
A rotating tool describes a circle. As it progresses along the axis of the quill it makes a "perfect" cylinder.
A static tool and rotating part makes a circle, but the axis of the lathe, is never perfectly true to the bed so the lathe makes a tapered bore, not the desired cylindrical bore. This is because the tool does not run true to the axis of rotation.
K2
A rotating tool describes a circle. As it progresses along the axis of the quill it makes a "perfect" cylinder.
A static tool and rotating part makes a circle, but the axis of the lathe, is never perfectly true to the bed so the lathe makes a tapered bore, not the desired cylindrical bore. This is because the tool does not run true to the axis of rotation.
K2
Don't know if this has been said. I have a LeBlond Duel lathe made in 1947. When I moved to Indiana, I just put it on my garage floor. I am no where near any of your talent. No matter what I tried with my lathe, I was always getting that taper of a thou or more over 7 to 8 inches. My mentor asked me, "Did you level the ways when you got to Indiana"? UUHH, no. So I grabbed my Dad's machinists' level and yes, I was out of plumb. Plumbed it and a very small adjustment to my tail stock and things are a million times better.
Grasshopper
Grasshopper
My lathe is mounted on a pair of accessory cabinets that were intended for it.
I've noticed that at certain RPMs, it will rattle more, as if the cabinets are going through some sort of resonance. Above or below that speed range, no rattle or perceptible movement. I have a shop crane and could conceivably lift the lathe and the cabinets. Perhaps while getting pushed into place, it went out of level. Or never was.
I don't have anything like the precision Starrett level that Blondihacks used in her video of aligning the lathe.
I've noticed that at certain RPMs, it will rattle more, as if the cabinets are going through some sort of resonance. Above or below that speed range, no rattle or perceptible movement. I have a shop crane and could conceivably lift the lathe and the cabinets. Perhaps while getting pushed into place, it went out of level. Or never was.
I don't have anything like the precision Starrett level that Blondihacks used in her video of aligning the lathe.
Blondiehacks also has a demonstration of alignment by cutting a test bar, which you could follow.
Alternatively it is actually possible to level your lathe using a plumb bob. There are some videos on YouTube that cover the topic, E.g.
To truly align the tailstock with the rotating head shaft, the best bet is to machine a test bar, supported between centers, driven with a lathe dog. Test bar should be at least 10" long. Machine a section about 1/2" long at one end, taking note of your cross-feed setting. Move to the other end and machine about 1/2" at exactly the same crossfeed setting. Use a micrometer, not a Vernier caliper to measure the two diameters. If they are both the same, you have perfect alignment. If they are not, then your tailstock is out of alignment.
The "out-of-level" sydrome twists the bed and misaligns the saddle as it moves away from the headstock, as well as misaligning the tailstock - that is all the centre drilling, boring and long OD machining "knackered", and because the saddle is at any unknown position away from the headstock, the cross-feed - so all facing is knackered as well! -
In other words, the whole lathe becomes a lot less accurate (and ALL your work with it!) than the manufacturer made it.
So aligning the lathe MOUNTING correctly is SUPER IMPORTANT!
Pressed steel cabinets are not as stiff as triangulated steel frames. The more solid the mount, the better you will maintain the lathe in whatever alignment it has. Brian's check above is used in the factory to check the lathe before shipping, and the makers use strong pallets to minimise any changes during shipping, but you need to set the support frame mounting points true before mounting the lathe. Usually, a car jack, or levers, can lift one end at a time to permit insertion of appropriate shims - after you have determined any misalignment in the lathe bed mounting.
K2
In other words, the whole lathe becomes a lot less accurate (and ALL your work with it!) than the manufacturer made it.
So aligning the lathe MOUNTING correctly is SUPER IMPORTANT!
Pressed steel cabinets are not as stiff as triangulated steel frames. The more solid the mount, the better you will maintain the lathe in whatever alignment it has. Brian's check above is used in the factory to check the lathe before shipping, and the makers use strong pallets to minimise any changes during shipping, but you need to set the support frame mounting points true before mounting the lathe. Usually, a car jack, or levers, can lift one end at a time to permit insertion of appropriate shims - after you have determined any misalignment in the lathe bed mounting.
K2
A fair explanation here:
K2
K2
I have used a fine tapered burr (comes to a point) that I use for setting a centre when drilling gas jets down to 0.25mm (~0.010"). With the test bar, set at the headstock, faced and a centre marked, I then extend it to the longest length from the chuck and see where the point in the tailstock lies against the tiny mark in the centre of the test bar. Very quickly you can see the misalignment between head and tail of the lathe caused by twist.
Check yours, then follow corrective procedures as per the videos...
Or if you have a really good test bar (stiff enough it doesn't deflect under its own weight? - And without any bend!) you can pop a DTI in the tool post and watch the pointer change as you traverse along the test bar, on the side, and on the top.
Then reset the lathe as per the videos, and recheck with the DTI on the test bar....
K2
Check yours, then follow corrective procedures as per the videos...
Or if you have a really good test bar (stiff enough it doesn't deflect under its own weight? - And without any bend!) you can pop a DTI in the tool post and watch the pointer change as you traverse along the test bar, on the side, and on the top.
Then reset the lathe as per the videos, and recheck with the DTI on the test bar....
K2
I think my problem is more fundamental. I can't measure worth a flip.
I just took 20 measurements of the inside diameter of both ends of the bore. There's some sort of taper there, wider at the bottom of the cylinder (lathe chuck end) than the other end, but my measurements are all over. The outer measurements run from .9491 to .9510. The bottom end runs from .9514 to .9550. I did five sets of a few measurements and the variation is mostly between the sets.
I'm using a micrometer and a telescoping ID gauge.
Anybody have any favorite videos for this? Websites?
I just took 20 measurements of the inside diameter of both ends of the bore. There's some sort of taper there, wider at the bottom of the cylinder (lathe chuck end) than the other end, but my measurements are all over. The outer measurements run from .9491 to .9510. The bottom end runs from .9514 to .9550. I did five sets of a few measurements and the variation is mostly between the sets.
I'm using a micrometer and a telescoping ID gauge.
Anybody have any favorite videos for this? Websites?
