Bar runout

edtcadcam · May 30, 2021

Hello everybody,
I need to make a lot of parts from 4' long bars, O.D. is 1.750" we don't touch it, inside boring to 3.150" depth, eccentric tolerance is .005 ". I use a bar puller and put 3 plastic sealing rings inside the machine tube. There is almost no runout near the collet, but at the end of the bar it is about .01 ", but not always, sometimes runout is OK - .002", I cannot fix this problem. What to do? Can the Spindle Liner help?

13engines · May 30, 2021

Never mind... I read it wrong. Deleted previous stuff. (Insert head slap)

Milland · May 30, 2021

edtcadcam said:
Hello everybody,
I need to make a lot of parts from 4' long bars, O.D. is 1.750" we don't touch it, inside boring to 3.150" depth, eccentric tolerance is .005 ". I use a bar puller and put 3 plastic sealing rings inside the machine tube. There is almost no runout near the collet, but at the end of the bar it is about .01 ", but not always, sometimes runout is OK - .002", I cannot fix this problem. What to do? Can the Spindle Liner help?

Are you starting with centerless ground material?

mhajicek · May 30, 2021

Solution: runout to the bar.

plastikdreams · May 30, 2021

You are using barstock that doesn't have the od turned...and you are wondering why there is deviation...are you high?

Scruffy887 · May 30, 2021

From information provided. Do something at other end, maybe something different in the middle. First few parts OK? Good, make first few parts and get another bar. Or maybe OK, make more parts. Or day off and go to bar.
Most times a problem must be very well defined before any solution can be offered. Most times defining the problem accurately will give you the solution as you define the problem.

If the wind does not get to you, the wife will. Maybe wrong Province. Police tape all over the lobby went we went to breakfast. Seems somebody decided to rob the hotel night clerk. She beat the crap out of him and he ran off.

Trueturning · May 31, 2021

Spindle liner can help the less gap the getter. Less gap is better you maybe can make a thin cap to fill in any gap. Slide it over the end of shaft into sleeve. Tape it in to stay.

When it turns it can run out more the more gap you have. Bar feeder may be hurting you. OD of material can be bumpy so you can run a file gently over the od even pull it through 7 inches turn it slow and gently file the od safely any raised spots can be seen and filed off gently here and there . This gives your precision collet a better surface to clamp on it is more accurate.

Best end first to clamp on with the collet. There are ways to check the runout using precision V blocks or down and dirty the gap on the bed of a manual mill. Look the od of the material over any bump will freak you out as you might think your shaft is running out. Two precise V blocks and rotating it by hand with the V blocks clamped or say in clamped two vises. Shaft is spun by hand and use a indicator on I’d and wherever you think it makes you conceive how it actually is. I think it will be good.

I hope this helps you in some way. I think some precautions will help. What you see as .01 over four feet likely can be lessened with some thinking and attention. Oft times I will clamp turn 120 degrees and check and again check and again check each time for runout to see if how it clamps effects the runout better or worse. Work with something patiently and persistently things will come to mind.

Red James · May 31, 2021

Saw your parts to near finish length ... gives you collet a chance to hold true without orbiting and ruining your collet head. Likely won't loose any more material than you are wasting with a cutoff tool.

edtcadcam · May 31, 2021

This is cold rolled 1018.

DDoug · May 31, 2021

edtcadcam said:
This is cold rolled 1018.

So it's NOT ground material.

enginuity · May 31, 2021

edtcadcam said:
This is cold rolled 1018.

It's cold drawn. Many times at the end of cold drawn bars you will find that it is bent from the shearing process.

You can try by cutting 4-6" off each end first to see if that helps the problem.

As already stated, I would highly recommend getting centerless ground bars for process reliability.

plastikdreams · May 31, 2021

Or get 1.875 or 1.8125 and hit the od real quick.

DDoug · May 31, 2021

more discussion going on here:
Bar runout

the OP "cross posted it"..... :nutter:

dennis8803@gmail · May 31, 2021

What do you call a lot of parts . Best case cut off and face and bore using pie jaws. May take more time but you will get good parts.

Dennis

litlerob1 · May 31, 2021

Eeesh, Solutions above and below. Because what you're doing isn't ever going to work with CR bar stock.

A. Pull bar, insert M0, indicate bar close enough, Bore, cut off.
B. Cut parts to length, Bore inside the closer.
C. Get TGP.
D. Bore inside closer, push out, cut off.
E. Something else.....

R

edtcadcam · May 31, 2021

dennis8803@gmail said:
What do you call a lot of parts . Best case cut off and face and bore using pie jaws. May take more time but you will get good parts.

Dennis

This is about 12,000 parts, everything should work from a bar, quickly and without problems.

edtcadcam · May 31, 2021

Too much time and cost. This is a production of 12,000 parts. Besides, the material was purchased by the customer.

edtcadcam · May 31, 2021

1018 cold rolled is a pretty precision material with a tolerance of .002 "

plastikdreams · May 31, 2021

edtcadcam said:
1018 cold rolled is a pretty precision material with a tolerance of .002 "

Regular off the shelf cold rolled bar is not straight, nor concentric. If you believe that than you are more the fool than originally led on. Centerless ground bar will be straight and concentric.

If only a few are out of spec, throw em out and continue on.

litlerob1 · May 31, 2021

edtcadcam said:
Too much time and cost. This is a production of 12,000 parts. Besides, the material was purchased by the customer.

I gave you solutions that require very little time, just a change in operations. Cold roll isn't round, it isn't straight. Also you don't know the vendor, if it's customer supplied. Could be Chicom shit. 12,000 pieces isn't that much, your guys will get very fast at using a deadblow.

R

Bar runout

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