Jimbojones
Active Member
TS has some give to it; I'll oil the heck out of it and apply very little lateral pressure as I just want to clean it up. Was disappointed with the alignment bar taper but I'd rather adjust/toss a $35 tool than $6k lathe.
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Anyone with a close-tolerance lathe want to experiment with a alignment bars I bought?
- Thread starter Jimbojones
- Start date
Tell me more about how you arrived at 0.003". I'm 100% confident Dabbler knows his stuff but will throw out some food for thought just in case.
If you put the test bar between HS & TS dead centers & then measured the MT taper, that presumes that the TS axis is 100% aligned to the HS axis. But if your TS was say 0.002" in/out or up/down it would yield a false MT reading. Picture this scenario if it was a parallel bar like the Edge tool, a DTI measurement difference has nothing to do with taper, its TS position related. But if you first ran the DTI down the straight section of the test bar & that was 100% parallel, it gives confidence to TS position & is the right step-1
When you measured the taper, I assume you held a DTI in toolpost, ball exactly on bar center, contact a point on thick end, zero DTI, move carriage over 3.000", contact ball on thin end to DTI zero, obtain cross feed delta & compare that against MT taper spec... something like that? I think I get 0.0753" on a 3.0 X displacement. But its highly dependant on the inputs like same backlash direction & dial accuracy. Do you have DRO on these 2 axis or reading off the dials? The other big thing on tapers is if the ball is not precisely on center, then as you jog over, the ball will ride up or down the taper & exaggerate skew the reading big time. This could happen if for example your TS was high. Lots of them are apparently high 'to allow for wear' which I've never understood.
Anyway, if you guys checked this stuff off, that's the extent of my experience & I guess maybe you have a dud bar in terms of taper angle.
If you put the test bar between HS & TS dead centers & then measured the MT taper, that presumes that the TS axis is 100% aligned to the HS axis. But if your TS was say 0.002" in/out or up/down it would yield a false MT reading. Picture this scenario if it was a parallel bar like the Edge tool, a DTI measurement difference has nothing to do with taper, its TS position related. But if you first ran the DTI down the straight section of the test bar & that was 100% parallel, it gives confidence to TS position & is the right step-1
When you measured the taper, I assume you held a DTI in toolpost, ball exactly on bar center, contact a point on thick end, zero DTI, move carriage over 3.000", contact ball on thin end to DTI zero, obtain cross feed delta & compare that against MT taper spec... something like that? I think I get 0.0753" on a 3.0 X displacement. But its highly dependant on the inputs like same backlash direction & dial accuracy. Do you have DRO on these 2 axis or reading off the dials? The other big thing on tapers is if the ball is not precisely on center, then as you jog over, the ball will ride up or down the taper & exaggerate skew the reading big time. This could happen if for example your TS was high. Lots of them are apparently high 'to allow for wear' which I've never understood.
Anyway, if you guys checked this stuff off, that's the extent of my experience & I guess maybe you have a dud bar in terms of taper angle.
Dabbler
ersatz engineer
We were not using centres to do the measurements. We were not using the toolpost. I was using radial runout to prove the bar. The .003 estimate is based on a caluclation and measurement of the lack of fit in the MT3. It is achieved by measuring both sides of the offset when the male MT3 is tapped into the female, and it still noticably wiggles. ( BTW Jim had already tested the diameter of the bar at several places).
This technique I was using was shown to me by a toolmaker - it is a short cut to get to proving a test bar without introducing errors from the carriage and nonparalellism of the vee ways.
FWIW the bar measures withing spec on the parallel section. The taper just isn't a perfect MT3, that's all.
-- If I get a chance I'll upload a video to youtube on how we tested the bar. (we still have a MT2 test bar to test after all)
This technique I was using was shown to me by a toolmaker - it is a short cut to get to proving a test bar without introducing errors from the carriage and nonparalellism of the vee ways.
FWIW the bar measures withing spec on the parallel section. The taper just isn't a perfect MT3, that's all.
-- If I get a chance I'll upload a video to youtube on how we tested the bar. (we still have a MT2 test bar to test after all)