# Knee mill/drill spindle play



## Chuck B (Jan 31, 2021)

I have a ZX-7025 Knee mill/drill that has a chatter noise when milling. It is especially loud with an interrupted cut. I found a Radial runout of 0.018" and an axial of 0.0015". Is there any way to tighten this up? Or am I looking at a new set of spindle bearings, spindle shaft  and spindle taper sleeve? The mill is identical to a Jet JMD-15.


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## Ken226 (Jan 31, 2021)

That's pretty bad!

It depends on what is wrong.   It could be anything from bearing preload out of adjustment to a bent spindle.  I'd check the bearing preload first, as it's free to fix and easy to check.

Get an indicator on it and check the spindle endplay, and for radial movement. Not runout, but actual movement inside the quill.  Your mill probably has tapered rollers, and loose adjusters will result an a spindle that can wiggle around inside the quill.

 You could get lucky and just have a loose bearing spanner nut.  To check and tighten this, you'll have to pull the quill and remove the spindle from the quill.

If it's tight, and still runs out that much, bad bearings would likely give an overt audible clue.   At that point, it would be time to start disassembling things, while hoping for the best and expecting the worst.


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## Ken226 (Jan 31, 2021)

Your machine looks similar to the Wrong-Fu type mill/drills.    This guy gets into the bearings on his, I bet yours it pretty similar.   He gets to the bearings @ about 10 minutes.


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## mikey (Jan 31, 2021)

Chuck, welcome to HM. If this is your mill then you have a standard mill/drill, not a knee mill.




There are two sets of bearings that impact spindle run out, a pair of spindle bearings and a pair of drive sleeve bearings. If either of these sets of bearings are worn, run out increases. The spindle bearings will be tapered roller bearings and the drive sleeve bearings will be shielded radial ball bearings. I suspect that the total cost to the manufacturer for all these bearings was probably under $10.00, meaning they are cheap junk.

The proper way to evaluate these bearings is to check the concentricity of the spindle with a DTI. I am not sure what you mean by "Radial run out" or "axial" but a properly preloaded spindle with good bearings will have almost no axial play and will have a spindle run out hopefully in the 0.0002" or less range. Assuming you checked run out properly then yeah, you've got excessive run out.

If the spindle bearing preload is loose then this will definitely affect the spindle run out. There is no prescribed method for adjusting these; you adjust them and check run out to see if is acceptable while also ensuring the temperature of the bearings while running does not exceed about 120 deg C. You can try tightening down on the preload nut and see if run out improves. If it gets down below 0.0002" TIR then you'll be okay as long as the bearings don't run too hot.

The drive sleeve, or the spindle taper sleeve, rarely needs replacement but the bearings that support the sleeve can definitely affect run out. If you are tearing down to either maintain or replace the spindle bearings then just change the drive sleeve bearings while you're in there. A pair of Nachi sealed deep groove bearings will cost less than $25.00 and eliminate the concern.

By the way, I watched the video (just a little bit) and that guy is greasing his spindle bearings wrong. If you pack a tapered roller bearing full of grease as he did, it will overheat and damage them. Spindle bearings require greasing only about 25-30% of the bearing, then running them in to spread that grease out. His bearings will be running very hot and will not last long. Rather than using tapered roller bearings that require annual cleaning and re-greasing, a better option is to use maintenance-free angular contact bearings. If you go for precision class bearings then you can expect run out in the low tenths. This will not only make you feel better but will also impact on tool life, accuracy and finishes.


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## Ken226 (Jan 31, 2021)

Abec7 rated angular contact bearings aren't overly expensive,  and the next thing down, abec5s can be had cheap.  I used NSK Abec7s when I rebuilt the spindle in my 8000rpm 2hp CNC spindle 5 years ago.   It was my first spindle rebuild, and I packed way too much grease in the bearings.  Luckily, it's still running like a champ as of today.

I just replaced the spindle bearings in my lathe 2 weeks ago with Timken P5 tapered rollers.   @ 250$, shipped from France, it wasn't a bad price at all.






I posted the video above to give you an idea about how to get things apart. Not as advice on how to grease bearings or which ones to buy.   It's the only video I could find showing the innards of that style chinese mill/drill.

Use due diligence, and come back here to ask questions once you figure out what needs repaired or replaced.


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## mikey (Jan 31, 2021)

Ken226 said:


> I posted the video above to give you an idea about how to get things apart. Not as advice on how to grease bearings or which ones to buy.   It's the only video I could find showing the innards of that style chinese mill/drill.



My comments about the grease was not intended as a reflection on your advice, Ken. Sorry if I came across that way. I just wanted to make sure that Chuck was aware of the need to be careful about this.


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## Ken226 (Jan 31, 2021)

I didn't take it that way sir.  It's very good advice, and he would be wise to listen.  Once those bearings are greased and installed, is the worse time to realize they are over packed or too tightly preloaded.  It's all gotta come back out to adjust.

I only meant to point out that there are a few other things in that video he shouldn't use as guide, aside from the grease. Like the 10$ truck bearings for the spindle.  Though, even those would likely be better than what's in there now.

    But, for a guy figuring out how to get to those bearing nuts for the first time,  the video is acceptable.


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## Chuck B (Jan 31, 2021)

Thanks for al your advice and information. Once I get it torn down I will let everyone know the results.


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## Ken226 (Jan 31, 2021)

According to jets manual:


			https://www.google.com/url?sa=t&source=web&rct=j&url=https://content.jettools.com/assets/manuals/350020_man_EN.pdf&ved=2ahUKEwij_-_7lMfuAhUyJzQIHQ2cBewQFjAAegQIAxAC&usg=AOvVaw2NyUL5P4vD2_oVbJChsmIn
		


It uses 6007zz carrier bearings.  The lower spindle bearing is a 30206 tapered roller, and the upper spindle bearing is a 30205 tapered roller.

I found all of them on Amazon, prices range from 10$ for chinese skateboard level accuracy to 300$ for NSK P5 bearings.   

I cross referenced the tapered roller sized to find the pn# angular contacts, and they 7206, to replace the 30206 (1.25mm thinner, will require a spacer)
And 7205, to replace the 30205 (also 1.25mm thinner).


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## mikey (Jan 31, 2021)

Chuck, in case you are interested, I explored the cause of excessive run out on my RF31 and wrote it up here. I went on to detail how I changed the spindle bearings and the drive sleeve bearings. This might save you some time and confusion on how these things are done. Your mill may have different bearings but the process will be the same. Good luck!


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## cbellanca (Jan 31, 2021)

I might not have been completely clear in my description of radial runout. I mounted a dial indicator in the chuck pointed horizontal and butted against a plate held in the vice.  I rotated the chuck by hand without moving the drive pulley. Resulting in a 0.018 radial play or back lash. Side play about 0.0015. Vertical play next to zero.


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## cbellanca (Jan 31, 2021)

I may have not been clear on my description of radial run out. I mounted a dial indicator in the chuck and butted it against a plate held in the vice. I rotated the chuck by hand without moving the drive pulley. This resulted in 0.018" play or backlash. Side play of 0.0015" No vertical play could be noted.


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## Ken226 (Jan 31, 2021)

I'm having a tough time understanding how that works.  Rotating the chuck without rotating the drive pulley? Allowing the drill rod to rotate in the indicator mount?

I think your method is a little suspect, and may be affecting your measurements.

Drill chucks suck for concentricity.  Put a peice of drill rod in a collet.   Your spindle R8 or mt3?   Mount the indicator to your vice or table, or to the head with a magnetic base, with the probe against the drill rod. Then rotate the spindle.

A magnetic indicator base attached to the milling head, rather than  the vise or table will allow you to measure the spindles runout and/or movement without the error induced by a flexing column.   Even my 2000lb knee mill flexes a few ten thou just from a few lbs of hand pressure.

Measure at the top, near the collet,  then again several inches below the collet.

Just a sec, I'll post a video.


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## Ken226 (Jan 31, 2021)

I went out and took a quick video to explain.  It's slow uploading, so it may take a bit.    I'll edit this post with a link when it's uploaded.

This copy/paste  explains the definitions of radial and axial runout:

*Radial runout* is when the axis of rotation is off-center from the main axis, but still parallel. ... *Axial runout* is when the axis of rotation is tilted to some degree from the main axis, meaning the axis of rotation is no longer parallel to the main axis.

I suspect that you drill chuck may be part of the issue.

I doubt your spindle is bent.  If it were, I'm certain you would remember the event that bent it.

If your bearings were bad enough to cause .013" of runout,  it would probably sound like a dryer full of gravel.


First video of 3,  measuring with a Grizzly R8 collet.






Shop Fox drill chuck:





Directly off spindle bore:





As you can see, reading directly off of the spindle bore eliminates all of the other variables.

Edited to add:

If you take your measurement from reading directly off the spindle bore, and subtract it from the measurement off the toolholder,  it gives you a basic idea of how accurate the toolholder is.

For example,  I got a bit under .0002" off my spindle bore, and about .0002" off the end mill/grizzly collet.  Telling me the collet is pretty good.

I got a little under .0002" from the spindle bore, and about .013" off of the end mill/shop Fox drill chuck.  So, my shop Fox drill chuck has about .011" of runout.   I can expect any holes drilled with that chuck to be a bit oversized.

As you can tell, my drill chuck isn't reading much better than the runout you were reporting.  Drill chucks suck.  Cheap ones suck even more.


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## mikey (Jan 31, 2021)

Chuck, I'm not sure what you're measuring but it isn't the run out of the spindle, which is what I think you're interested in. Your set up gives you almost no useful information. 

Rather than point out all the potential errors in your set up, let me give you an idea of what you should be doing to at least have a reasonable chance at estimating the accuracy of your spindle. This will require you to have some basic equipment; if you do not have these tools then put this off until you do have them.

You will require a dial test indicator, ideally one that reads to 0.0001".
You will require a test indicator holder, ideally a two-arm holder that can be set up rigidly. Here is one that works very well for this purpose.
Then go here and read this post so I don't have to re-type all of it. In your case, you have to set up the indicator so that the tip touches the spindle taper. Mark the quill (this mark doesn't move) and the spindle (this mark does move) with a Sharpie so you can turn the spindle and line those marks again. Follow the steps in that other thread and determine what you spindle run out actually is. When measuring deviations, there will usually be a maximum and minimum reading on a given pass; your TIR is the max minus the min. Be sure to measure at least three different places in the spindle taper to be sure the TIR you're seeing is consistent. If it is then that is your spindle's TIR.
Most of us accept run out/TIR in the 0.0002" or less to be acceptable for a milling machine spindle. If yours is greater and cannot be improved by adjusting preload then you're looking at bearing changes.


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## cbellanca (Jan 31, 2021)

Ken226 said:


> According to jets manual:
> 
> 
> https://www.google.com/url?sa=t&source=web&rct=j&url=https://content.jettools.com/assets/manuals/350020_man_EN.pdf&ved=2ahUKEwij_-_7lMfuAhUyJzQIHQ2cBewQFjAAegQIAxAC&usg=AOvVaw2NyUL5P4vD2_oVbJChsmIn
> ...


Ken, I removed the chuck and inserted a collet and drill rod with a 12" scale attached. I could rotate the spindle 3 degrees by hand without moving the dive pulley. The 0. 018 movement may have been exaggerated by the lever arm were the DI was installed.


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## Ken226 (Jan 31, 2021)

cbellanca said:


> Ken, I removed the chuck and inserted a collet and drill rod with a 12" scale attached. I could rotate the spindle 3 degrees by hand without moving the dive pulley. The 0. 018 movement may have been exaggerated by the lever arm were the DI was installed.


That is likely just the clearance between the carrier/drive sleeve and spindle splines.  3° may be excessive, but I'm not sure. I dont have a machine with that type system.   

I doubt it has anything to do with runout. When the motors running, the load on the end mill vs motor torque takes up all that slack.   Without having one to measure, and not knowing with certainty, I'd guess it's probably normal for that type machine.

@mikey would be more qualified to advise on that. He's more familiar with these.


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## Ken226 (Jan 31, 2021)

cbellanca said:


> Ken, I removed the chuck and inserted a collet and drill rod with a 12" scale attached. I could rotate the spindle 3 degrees by hand without moving the dive pulley. The 0. 018 movement may have been exaggerated by the lever arm were the DI was installed.



I think I may understand what your talking about now.  I've converted some small bed mills to CNC, and they have a similar carrier/spindle arrangement,  as do knee mills like my PM935 knee mill.

In order for the quill to be able to move up/down in the head, for drilling without the pulley moving up/down with it, the must be seperate parts.     The pulley is attached to carrier, with a female splined hole in it's center.    It rides in a set of radial bearings and other that rotating, doesn't move.

The upper part of the spindle has male splines on its outside diameter,  which match the female splines in the carrier.  This allows the spindle/quill to move up and down inside inside the fixed carrier, while the carrier still transfers rotary power to the spindle.

Being a low cost chinese machine, the best way to make sure that alot of mass produced parts with large allowable tolerance can still fit together, is with very, very generous running fit tolerances.   It's not uncommon at all to see a 14mm shaft in a 16mm hole.   That slop your noticing is a side effect of keeping costs way down.   I doubt it's will be anything more than an annoyance, and likely won't effect anything.

The G0704 CNC conversion crowd can attest to their hatred for that sloppy running fit between the carrier and spindle splines.   I've seen everything Frome custom EDMd carriers, to attaching pulleys directly to the spindle and locking the quill in place.     I have a G0704 CNC, and I locked the quill permanently and put a synchronous pulley directly on the spindle shaft.


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## cbellanca (Feb 2, 2021)

Ken, Again, thank you for your informative replies. As you suggested, I checked the run out with the drill rod installed in the collet. The TIR was 0.001".  Other than the noise this is fine for the kind of work I do. I kind of thought the play was in the spline, but didn't know if there was an adjustment for it.


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