I disagree on the topic of using grease on the lathe bed. The problem is that even a thin film of grease will attract dirt and swarf that grind down the ways. Ideally you should use way oil, it contains 'tackifiers' that help it stick to the slides and not get washed off. Failing that, for my Atlas milling machine the manufacturer specified SAE 30 motor oil... Which will no doubt have the purists up in arms, but you can't satisfy everyone.
A big help for bed lubrication is a set of felt way wipers, they'll prevent the swarf from getting under the saddle and also act as oil wicks to keep re-oiling the ways as the saddle moves.
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.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
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.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
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.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
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
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.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.
Blondiehacks also has a demonstration of alignment by cutting a test bar, which you could follow.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.
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