TIR

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Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: TIR

Post by Mr Ron »

Thank you for your input. I learn something new every day; and thank you for putting up with my dumb questions.
Mr.Ron from South Mississippi
spro
Posts: 8016
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: TIR

Post by spro »

I cannot let this stand. These are not dumb questions because the answers aren't dumb. I do agree that by the questions, we learn something every day.
johnfreese
Posts: 219
Joined: Thu Jan 21, 2016 2:10 am

Re: TIR

Post by johnfreese »

I don't see any way the axis of rotation could describe a cone. It is constrained by the spindle bearings. It is likely that the axis of the WORK held in the chuck describes a cone. The axis of the turned surface would still be concentric with the axis of rotation. If the axis of rotation is not parallel with the bed the turned surface will be conical if your misalignment is front to back. If the axis of rotation is tilted vertically with respect to the bed you can get an hourglass shape or a non-cylindrical tapered surface. If you indicate on the a turned surface you should see zero runout. If the work is wobbling in the chuck due to worn jaws or other reasons there is no predicting what result to expect.

Try this test: Chuck up a piece of cold rolled. Measure the runout at the outboard end. Take a light cut off the diameter at the end of the bar. Make sure it cleans up all the way around the bar. Take a spring pass. The turned area only needs to be long enough to indicate on. Indicate the turned surface. It should have zero runout.
Magicniner
Posts: 532
Joined: Thu May 30, 2013 4:40 am

Re: TIR

Post by Magicniner »

johnfreese wrote:I don't see any way the axis of rotation could describe a cone. .
That's not what I said, read again, inwardly absorb and understand!
What I said intimates that if the front bearing was off then the axis of the spindle may not be on the axis of rotation, the same would result from a poorly machined spindle in good bearings, the SPINDLE AXIS then describes a cone when it rotates.
In that case any work you wish to set true in any chuck (unless mounted on a machined-in-situ mounting plate) would need to be shimmed or hammered into alignment as the jaws would be on the axis of the chuck and thus spindle and that axis would not be the axis of rotation.
I'd say it's not rocket science but then perhaps it is?
Magicniner
Posts: 532
Joined: Thu May 30, 2013 4:40 am

Re: TIR

Post by Magicniner »

Mr Ron wrote:Thank you for your input. I learn something new every day; and thank you for putting up with my dumb questions.
There are no dumb asked questions, only unasked questions and some answers are dumb,
Regards,
Nick
John Hasler
Posts: 1852
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: TIR

Post by John Hasler »

Magicniner wrote:
johnfreese wrote:I don't see any way the axis of rotation could describe a cone. .
What I said intimates that if the front bearing was off then the axis of the spindle may not be on the axis of rotation, the same would result from a poorly machined spindle in good bearings, the SPINDLE AXIS then describes a cone when it rotates.
I think that the confusion here is that to johnfreese and I "spindle axis" means "axis of rotation". We would call what you are calling the spindle axis the spindle centerline.
hanermo
Posts: 60
Joined: Tue Oct 01, 2013 5:47 am

Re: TIR

Post by hanermo »

All spindles have some runout in TIR.
Say 0.1 microns for a Moore Nanotech, or airbearings for diamond turning optics (or semiconductors etc).
1 Micron for best smallish common 12" lathes (Hardinge HLVH, Monarch 10EE, Star (Hardinge copy), Wheeler, etc.)
2-4 microns any good workshop lathes, including better chinese ones.
5-8 microns typical cheapest far east hobby lathes.

Chucks do not really enter into that at all.

The industrial wisdom is;
a spindle in a lathe will deliver a bit better runout in TIR for the workpiece, if work is well done, than the HS outboard bearing TIR.
This is what Timken, SKF etc. state in their very high end machine tool bearing booklets available online.

A typical 12" (or more) etc chuck has a huge amount of momentum when it rotates at 100 rpm+.
It simply cannot drop or rise once/rotation, by the full spindle bearing error when measured at 0 rpm for TIR.
Likewise, the bearing grease spreads the error around in use, averaging it around the n balls in the bearing vs a bump or drop in the bearing shell.

Likewise, when You cut a workpiece, any error in drop (valleys in the bearing system) will not cut the workpiece, as it moves away from the tooltip.
Any bump towards the tool will cut off a bit more from the piece.
This cut error is then averaged out over the workpiece, tool, all bends/yields/momentum etc.

I have no data as such, but think/feel the achieved results are or may be about twice as good as spindle tir, commonly.
My "feel" is also that heavier chucks, lathes, workpieces do better, and worse bearings like in the cheap chinese hobbylathes improve more proportionally in TIR delivered as the momentum benefit aids them to avoid most of the proportionally-larger error.

My results were:
a tiny 7x hobbylathe had under 0.01 mm TIR == 0.008 mm TIR.
Results were better than that on work with finish passes and polishing.

A very good 450 kg short heavy 12x chinese "light-industrial" lathe had 2-4 microns TIR new.
Has 2-4 microns TIR now, after 2-3000 hours use, often heavy, all steel cutting, often heavy interrupted cuts for hours.
A polished small workpiece will often clock at 0 or 1 microns TIR, if some fiddly finish work is done with abrasives and *rigid* metal backing, gaging and experience.

A workpiece finished with abrasives is usually barrel shaped, and edge or corner rounding is typical and must be avoided or taken into account.

Common results:
Endless hobby people make engines and polish insides of bores to fits in the 1-3 micron range with a huge variety of often weakish lathes.
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: TIR

Post by Mr Ron »

Now that I understand TIR better, would it be cost effective to replace the HS bearings with ABEC 7 taper roller bearings on a Sheldon 11" lathe that is in excellent condition other than the TIR.
Mr.Ron from South Mississippi
John Hasler
Posts: 1852
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: TIR

Post by John Hasler »

Mr Ron wrote:Now that I understand TIR better, would it be cost effective to replace the HS bearings with ABEC 7 taper roller bearings on a Sheldon 11" lathe that is in excellent condition other than the TIR.
Where are you measuring the TIR? Do the existing bearings have any play in them?
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: TIR

Post by Mr Ron »

John Hasler wrote:
Mr Ron wrote:Now that I understand TIR better, would it be cost effective to replace the HS bearings with ABEC 7 taper roller bearings on a Sheldon 11" lathe that is in excellent condition other than the TIR.
Where are you measuring the TIR? Do the existing bearings have any play in them?
When I checked it, it was out .002, but that was taking the reading with a DTI on the OUTSIDE of the spindle. I now know that I should take the reading from the bore ID. I haven't tried Harold's test of trying to lift the spindle with a 2x4 while reading a DTI.
Mr.Ron from South Mississippi
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