MT3 Collet Chuck In lathe - runout

[Huub Buis]

The shaft of an end mill is good enough to get an indication of the run out. Once you are looking below the 0.01 mm run out, the shaft should be ground and the indicator free of backlash. Using 2 different indicators when you question the results, is a good practice.
When you measure the run out at the gauge pin, you measure the sum of the run out of the spindle, collet and gauge pin. You should repeat this measurement a few times while repositioning the collet and the gauge pin to get a mean value. Depending on the position, these run out errors can add up but also reduce eachother.
Your setup for measuring (indication) the run out is pretty decent. I always use some oil to reduce friction (false reading) and wear. Any backlash in the indicator will give slightly optimistic values.
I prefer the dial indicator for outer measurements when the indicator can be setup easy at a 90° angle. The poupi indicator is my choice when it is hard to position the dial indicator.
My (5 second) setup for aligning CNC drilling tools using a 3D printed holder and a dial indicator

 

[Ben17484]

Once again, thank you for everyone that’s commented so far. It’s been a big help.

I’m now on my third day running of testing the runout and I’m now fairly convinced that there’s a problem with the spindle.

Inside and outside I can get a repeated 0.08mm runout. This leads me to believe that it can’t be burrs etc internally as the external runout wouldn’t be effected by that.

I did test the deflection (???) by using an MT3 alignment rod in the spindle:

(I tested the same thing with the dial directly on the spindle and get very similar results)

I fixed this by tightening the bearings and also the bolts that hold the spindle in:

So now the deflection is pretty much zero.

I’m going to assume that the issue with the spindle runout is beyond bearings? Could bearings cause that much consistent runout? What should I check next? Thanks all In advance.

Also, what direct effect will this runout have on making parts?


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[Huub Buis]

You should check the spindle play horizontal and vertical. You don't want to measure the deflection of the base,bed, etc so putting the indicator stand on the head stock is the way to go.
Warn or damaged bearings can lead to run out in the spindle. To inspect the state of the bearing, you need to take the shaft out of the lathe so you can rotate that bearing by hand. You can feel if it is worn or damaged. You can also use an indicator and check the runout on the bearing. If it has no runout, you spindle is the cause.

How much the run out will affect the turning depends on what you want to make. If you have to swap the part to turn the side that was in the collet, it can be a problem.
This problem also happens if you have a chuck that has run out. For precise parts that have to be machined on both sides, I use a 4 jaw chuck. For lower precision parts, I use a collet. For all other task a 3 jaw chuck.
My 3 jaw chuck on my (old) mini lathe has 0.06 mm run out. That has never been a problem for me.

I assume this lathe has a ball bearing at the chuck side!

 

[Ben17484]

I maybe got ahead of myself here, but the spindle is out:

How do I check the spindle whilst it’s out?


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[Ben17484]

You should check the spindle play horizontal and vertical. You don't want to measure the deflection of the base,bed, etc so putting the indicator stand on the head stock is the way to go.
Warn or damaged bearings can lead to run out in the spindle. To inspect the state of the bearing, you need to take the shaft out of the lathe so you can rotate that bearing by hand. You can feel if it is worn or damaged. You can also use an indicator and check the runout on the bearing. If it has no runout, you spindle is the cause.

How much the run out will affect the turning depends on what you want to make. If you have to swap the part to turn the side that was in the collet, it can be a problem.
This problem also happens if you have a chuck that has run out. For precise parts that have to be machined on both sides, I use a 4 jaw chuck. For lower precision parts, I use a collet. For all other task a 3 jaw chuck.
My 3 jaw chuck on my (old) mini lathe has 0.06 mm run out. That has never been a problem for me.

I assume this lathe has a ball bearing at the chuck side!

Thanks HuubBuis. I’m not sure how to check the runout on the bearing itself? Or the spindle (as I don’t have anything reliable to spin it in)

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[Huub Buis]

The bearing on the picture is a trust bearing to absorb the axial forces. I assume you lathe has a bronze bearing, no ball bearing!

You can place the spindle on 2 V-blocks. Place the V-block at the bearing position. Put an indicator on top and turn the spindle by hand. There should be no run out.
If you don't have a v-block, measure the thickness of the shaft on multiple circular positions. It should be equal on all position.

To measure if the spindle is bent, you need 2 v-blocks. Place the spindle on the (fixated) v-blocks and rotate the spindle. Place the indicator on a ground surfce between the v-blocks. A run out indicates a bend spindle. The angle of the V-block is not important and you could make one your self from wood or aluminum.
If you have made the v-blocks, you can measure the inside run out again. If it is 0.08 mm, than the spindle is the cause.

You can put the spindle in the lathe and measure the runout at the chuck and far away from the chuck. The difference in the 2 values is an indication for the bent of the spindle.

Huub

 

[Ben17484]

The bearing on the picture is a trust bearing to absorb the axial forces. I assume you lathe has a bronze bearing, no ball bearing!

You can place the spindle on 2 V-blocks. Place the V-block at the bearing position. Put an indicator on top and turn the spindle by hand. There should be no run out.
If you don't have a v-block, measure the thickness of the shaft on multiple circular positions. It should be equal on all position.

To measure if the spindle is bent, you need 2 v-blocks. Place the spindle on the (fixated) v-blocks and rotate the spindle. Place the indicator on a ground surfce between the v-blocks. A run out indicates a bend spindle. The angle of the V-block is not important and you could make one your self from wood or aluminum.
If you have made the v-blocks, you can measure the inside run out again. If it is 0.08 mm, than the spindle is the cause.

You can put the spindle in the lathe and measure the runout at the chuck and far away from the chuck. The difference in the 2 values is an indication for the bent of the spindle.

Huub

Thanks again Huub. I'll follow your instructions and try and get some measurements tomorrow. I'm going to move tracking this problem in to the main lath "restoration" thread I started a while ago as this problem is now definitely about the lathe and not what this thread was originally about (MT3 ER32 collet runout).

(oh, and I just realised that in my post about spindle play I posted the same photo twice - I did measure the play vertically and horizontally, I just messed up posting):

The main lathe restoration thread where I'll track the rest of the investigation: https://www.hobby-machinist.com/thr...lly-my-new-smart-and-brown-sab.100937/page-11