Odd runout on mini lathe

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THMguy123
Posts: 7
Joined: Mon Mar 11, 2019 10:38 am

Odd runout on mini lathe

Post by THMguy123 » Mon Mar 11, 2019 11:29 am

HF special here, from what I can tell it is the C3 version. Prior to me doing any work, I indicated the front inner spindle with 0.0015 of run out. I did not indicate the rear end of the spindle.

Fast forward and I've installed roller taper bearings. The front inner spindle is reading 0.0005 of run out and the finish on my turnings have been a huge improvement. However the rear end of the spindle is terrible. I'm seeing 0.012-0.015 of run out at the rear, and you can see and feel the vibrations. Link below for a video of the run out.

Not sure what to check or adjust next...

https://i.imgur.com/z2w3gfz.mp4

pete
Posts: 1630
Joined: Tue Feb 10, 2009 6:04 am

Re: Odd runout on mini lathe

Post by pete » Mon Mar 11, 2019 1:21 pm

It's best to learn that indicators need to have the plunger shaft square and 90 degrees in both directions to the surface that's being indicated for accurate results. Starrett and possibly others make an attachment that allows a reading 90 degrees from the vertical indicator shaft. The 670A, 670B,or 671 universal attachment would be an example of what your needing or you could also use what's known as a dial test indicator. A dti type indicator or those Starrett attachments would allow reaching further into the Morse Taper bore which is also an important check.

That rear runout is pretty bad but it's most likely the spindle was only drilled and done poorly at that in the factory. If it were me? I'd want to pull the head stock's sheet metal and indicate both the front and rear spindle bearing journals that the spindle bearings locate the spindle on. They should be fine, but it's a check I would have done once the new bearings were installed and adjusted.

If that run out really is causing poor results in your turned surfaces you've got about two choices. Find someone who really knows what there doing to set up and single point bore that section of the spindle in there lathe. Or Little Machine Shop in California sell all the replacement parts for your lathe. You could buy a second spindle for not much money and if that one needs it rebore it in your working lathe then switch the spindles. Doing this accurately isn't the easiest job. I'd want the spindles chuck end zeroed in a 4 jaw independent and I'd probably want to have the rear bearing installed and hold the bearing O.D. in the fixed steady so the parts being rotated in it's own bearing.

johnfreese
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Re: Odd runout on mini lathe

Post by johnfreese » Mon Mar 11, 2019 1:43 pm

I have owned several lathes over the years. None of the lathes had what I consider a highly finished bore on the back end of the spindle. I would not trust the bore to be true to the OD. Your runout issue may be merely the result of the bore not being ground after machining.

spro
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Re: Odd runout on mini lathe

Post by spro » Mon Mar 11, 2019 5:44 pm

While I agree about rear spindle internal finish, this is worse. You can actually see the spindle OD and attached gear running eccentric. I'd call that a Bad/ damaged spindle. Like bent.

THMguy123
Posts: 7
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Re: Odd runout on mini lathe

Post by THMguy123 » Mon Mar 11, 2019 7:27 pm

Thanks for the replys, ill run some more check in the next couple days.

I've turned a few things and they are hitting the 0.001 runout mark when finished. So its a bit odd when im only getting runout on one end...

spro
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Re: Odd runout on mini lathe

Post by spro » Mon Mar 11, 2019 7:41 pm

Look, I'm only seeing your video. I didn't hear audio but expect it matches. Try with your fine feed, going thru those gears and see if the surface is continuous.

John Hasler
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Re: Odd runout on mini lathe

Post by John Hasler » Mon Mar 11, 2019 7:57 pm

The bore at the back of the spindle is just a clearance hole for feeding stuff through. It needn't be precisely concentric and often isn't.

Put a piece of straight ground shaft in a good collet in the spindle taper and check the runout close to the collet and again a few inches out. Turn the spindle by hand. This will tell you if your spindle is bent.

I agree with spro as to the visible gear runout, but that may be a seperate problem. It may also be the cause of the noise and vibration and possibly be causing some of the runout that you are seeing in the taper.

You aren't going to see runout on a surface you just turned. Think about it. You may get taper, though. Have you checked for that?

pete
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Joined: Tue Feb 10, 2009 6:04 am

Re: Odd runout on mini lathe

Post by pete » Mon Mar 11, 2019 8:46 pm

I had to go back and watch that again since I missed the gear run out Spro. I still can't be 100% sure just how much is there, but I've seen a few threads mentioning some gears on these mini lathes not being concentric to there bores. That or your bent/warped spindle idea are two possible reasons of vibration affecting the surface finished. At low rpms a bent spindle or non concentric gear should make a noticeable change in sound during every revolution. Does that happen THM?

If a shaft is supported in a chuck and the other end with a dead center in the tail stock when a longitudinal test cut is made the only possible run out would then be from a really poorly machined and a slightly egg shaped bearing bore affecting the bearing run out (maybe doubtful?) or really poorly made spindle bearings if they were installed correctly. That cutting test also allows checks to be made if your lathes cutting a taper. However the tailstock offset could be out as well. Without further tests for the lathes alignment there's still too many unknowns to properly diagnose what could be one or a whole combination of problems. If it were me I'd also do a check for the axial run out on the face of the spindle the chuck mounts to and that stub it locates on. I've seen some issues with a lot more expensive Chinese lathes than the mini ones, and it makes one wonder how the factory's part alignment fixtures ever got that far out to allow some of these problems in the first place. Without checking everything then there's zero that can be taken as being correct with any confidence that they are.

spro
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Location: mid atlantic

Re: Odd runout on mini lathe

Post by spro » Mon Mar 11, 2019 11:03 pm

All of this is good info. In particular, mentioning that much larger ~ lathes have had the bore eccentric to the teeth. This is particularly bad as it presents a "gear forming" torque at the teeth instead of perfect pitch diameter. We know this stuff and how it wears all gears in the chain of them. So yes, the spindle may be okay at OD and have bad gears. Multiple possibilities. I'd remove the gear/s from that and measure the spindle's OD runout.

Harold_V
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Re: Odd runout on mini lathe

Post by Harold_V » Tue Mar 12, 2019 3:30 pm

John Hasler wrote:
Mon Mar 11, 2019 7:57 pm
Put a piece of straight ground shaft in a good collet in the spindle taper and check the runout close to the collet and again a few inches out. Turn the spindle by hand. This will tell you if your spindle is bent.
It may, or may not. It may display run-out, but won't necessarily determine why it's there. The piece may not be gripped parallel to the spindle, even using a collet.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Harold_V
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Re: Odd runout on mini lathe

Post by Harold_V » Tue Mar 12, 2019 3:36 pm

pete wrote:
Mon Mar 11, 2019 8:46 pm
If a shaft is supported in a chuck and the other end with a dead center in the tail stock when a longitudinal test cut is made the only possible run out would then be from a really poorly machined and a slightly egg shaped bearing bore affecting the bearing run out (maybe doubtful?) or really poorly made spindle bearings if they were installed correctly.
Plain and simple. That isn't a wise way to determine much of anything. It can determine if the tailstock is in alignment with the spindle, but if the tailstock barrel has any play at all, the resulting turn will not be concentric with the center drilled hole, as the material in the chuck will have to deflect to run true. That transfers some of the motion to oscillation of the tailstock ram (or quill), resulting in eccentricity of the turn in relation to the center hole.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

pete
Posts: 1630
Joined: Tue Feb 10, 2009 6:04 am

Re: Odd runout on mini lathe

Post by pete » Tue Mar 12, 2019 5:09 pm

I'm only aware of people mentioning eccentric bored gearing with these mini lathes Spro. While both my larger lathes have had different issues than what the OP is seeing the change gears at least have been ok. Likely He isn't yet aware of the old trick of using a piece of common printer paper between each change gear to set the gear lash as there tightened in position. It's one I always use even with known to be good gearing since it's eliminates setting the lash too tight and with the gearing always set to the same depth it slows the wear. If some of those gears of his do have eccentric bores then setting them that way would at least prevent the teeth from bottoming out until he can get replacements.

And that's exactly why I mentioned further test's for the lathe's alignment Harold. Ideally the OP would be starting with a correctly leveled and neutral lathe bed condition, then center the tail stock stock to the head stocks C/L. Very doubtful he's got that at this point. A longitudinal turning test is still helpful at any condition the lathe is currently in because it will point out there is or isn't further issues. So yes it's always worth doing one. No it certainly won't pin point the exact problem areas, but it will show what the lathe is capable of doing. It's still a process of doing those turning tests and figuring out what might be causing the results your seeing. It's no different than test driving a car having mechanical issues. Brand new high end machines installed by factory trained techs still get turning tests done and possibly some minor adjustments or even major part replacement if something serious got missed at the factory before the machine's released for service. If the tail stocks quill does have any play during part rotation an indicator will show that as well. Since the condition and accuracy of his live center is still unknown that's why I suggested using the dead center since it eliminates what ever run out that live one has. It's still only a mini lathe, and from the various issues with them I've seen mentioned in the past a great deal of work is usually required to get even some of there built in problems sorted out. But your correct and I should have mentioned doing the work between centers instead of holding the one end in a chuck since that would be the better method.

One thing in his favor is there's dozens if not hundreds of threads of people who have already been down the same route he's on with the exact same lathe so there should be ample information about what they had to do. There's a few threads where there was barely an untouched part on the almost rebuilt machine before the owner was satisfied.

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