Haas Mini Mill spindle/tool holder/tool balance issue?

[MiniMillMachinist]

Hello guys, I have contacted Haas about my problem, but in the meantime I wondered if I could gather thoughts on the problem I am facing.

When running a low chip load pass (I'm adjusting for chip thinning here) of 0.04MM/T or smaller, with my spindle running at 10K RPM in my Mini Mill, I'm getting weird surface artifacts that after my analysis appear to be the result of spindle, tool holder, or tool vibration. I have come to this conclusion because when I run the same chip load, but a spindle speed of 2K RPM, the result is much cleaner. If I run the spindle at 10K RPM, but with a 0.08MM chip per tooth, the result is again much cleaner, and the artifacts are gone, however now tool marks are evident (as you'd expect!), so I'd like to be able to run a low chip load at a high RPM with good results.

The passes are 0.2MM radial, 12MM axial, and I get the same result with any of my 3 flute or 2 flute cutters, and with all of my tool holders. For this reason I am doubting the tool holder being at fault, and in any case, this particular run was done with my YG1 hydraulic holder balanced to G2.5 at 25000RPM - I'd be really surprised if this was out of balance.

My tools all have less than 4 microns of runout at the tip, I believe this particular one was around 2-3.

Am I expecting too much out of this machine? I have paid a lot of money for it, and frankly the results I get from my much cheaper router spindle at 24000RPM with a similar chip load are much cleaner.

Any thoughts on this? I am aware the Haas spindles can be rebalanced with grub screws, so I'm hoping we can make progress this way.

 

[mhajicek]

How old is the machine? Are you the original owner?

In what condition are the spindle bearings? If you put an indicator on the table touching a toolholder, and push and pull on the holder, how much motion do you see? Now if the indicator is on the spindle nose (the part that spins)?

How good is the taper? Do you see any evidence of fretting?

Does your machine have a spindle vibration G meter like mine? If so, what does it read at 2k vs 10k?

 

[MiniMillMachinist]

How old is the machine? Are you the original owner?

In what condition are the spindle bearings? If you put an indicator on the table touching a toolholder, and push and pull on the holder, how much motion do you see? Now if the indicator is on the spindle nose (the part that spins)?

How good is the taper? Do you see any evidence of fretting?

Does your machine have a spindle vibration G meter like mine? If so, what does it read at 2k vs 10k?

Thanks for your reply. It's a brand new machine, about a month old. I've barely used it as I've been trying to figure this issue out. There's about 2 microns of runout on the taper itself. My machine has a vibration meter but I'm not sure it's measuring the spindle vibration?

When I put an indicator against a tool holder there's basically no play in the system, only the deflection from the force I'm applying which is 2-5 microns or so in either direction with maybe 10KG of force. The needle returns to centre within 1 micron. Hard to say how much force I'm applying for sure though. It would appear to be perfectly normal to me though.

 

[mhajicek]

It sounds like your machine is fine; it could just be that you hit a harmonic of that tool at that stickout in that holder. Happens to me once in a while. I just fiddle with the overrides until the cut quiets down, then record the new numbers to update the program for next time. As you found, increasing the chipload can sometimes damp out some vibrations.

 

[MiniMillMachinist]

It sounds like your machine is fine; it could just be that you hit a harmonic of that tool at that stickout in that holder. Happens to me once in a while. I just fiddle with the overrides until the cut quiets down, then record the new numbers to update the program for next time. As you found, increasing the chipload can sometimes damp out some vibrations.

That's what I originally thought, but the artifacts definitely increase with increasing RPM - I've tried 2000 (great), 3000, 4000, 5000, 6000 and so on and it is noticeably worse with each increment in RPM. I obviously can't be running my finishing passes at 2000RPM as they'd take forever and one of the reasons I bought a 10K spindle is so I can get work done at a decent rate (alongside the fact I use small tooling which requires the faster spindle speed). Increasing the chipload certainly does improve the artifacting, but it also gives me a less smooth appearance to the cut because the cut lines are spread further apart.

It's also worth noting that ALL of my end mills produce this finish in any of my tool holders with a high RPM and low chipload.

 

[memphisjed]

I am going with harmonics and screw bearings. Not bad bearings, just a smidgen light on preload.
Not a machinist disclaimer, but I had this exact issue earlier this week.

 

[MiniMillMachinist]

I am going with harmonics and screw bearings. Not bad bearings, just a smidgen light on preload.
Not a machinist disclaimer, but I had this exact issue earlier this week.

Spindle bearings? Anything that can be done? I literally can’t run a finish pass with a chipload under 0.04mm per tooth and get a nice finish with the spindle above 3k. Would light preload not cause the issue at 2-3k too? If you mean the linear rail bearings, wouldn’t the issue present at 2-3k too since cutting forces are the same?

 

[memphisjed]

Spindle bearings? Anything that can be done? I literally can’t run a finish pass with a chipload under 0.04mm per tooth and get a nice finish with the spindle above 3k. Would light preload not cause the issue at 2-3k too? If you mean the linear rail bearings, wouldn’t the issue present at 2-3k too since cutting forces are the same?

Mine was ball screw bearings. Harmonics amplify everything and are powerful. I had enough friction in bearing housing to stop the slop at slow rpm and bigger bits.
I would go with mjacks suggestions first and pay with overrides to find sweet spot and more important bad spots.

 

[MiniMillMachinist]

Mine was ball screw bearings. Harmonics amplify everything and are powerful. I had enough friction in bearing housing to stop the slop at slow rpm and bigger bits.
I would go with mjacks suggestions first and pay with overrides to find sweet spot and more important bad spots.

Honestly, I’ve tried from 2000-10000 at 1000 intervals, it just gets progressively worse as I increase the rpm — is it possible that it’s a division of 1000 that might improve it? Just based on this I’m really feeling like it’s the balance of the spindle or tool, but I agree that it could be that too.

 

[Milland]

Find a convenient threaded hole on the bottom of the head near the spindle snout. Bolt a flat plate to it such that you now have a shelf jutting out from the head.

Take a plastic cup of water and fill it part way, then place it on the shelf. Start the spindle and after a warmup, ramp through RPM and observe vibration patterns and "drop spatter" within the cup (a video camera or phone on a mount might be helpful to record if you can focus in closely). You can try this with different toolholder combos.

If you get noticible changes in the vibration patterns, there's likely an imballance or mechanical issue with the spindle or motor. If you don't see much activity there may be poor axis control on X or Y at faster movement rates due to slop in thrust bearings or ballscrews, or even servo control issues.

 

[plastikdreams]

What material are you cutting?

 

[MiniMillMachinist]

Find a convenient threaded hole on the bottom of the head near the spindle snout. Bolt a flat plate to it such that you now have a shelf jutting out from the head.

Take a plastic cup of water and fill it part way, then place it on the shelf. Start the spindle and after a warmup, ramp through RPM and observe vibration patterns and "drop spatter" within the cup (a video camera or phone on a mount might be helpful to record if you can focus in closely). You can try this with different toolholder combos.

If you get noticible changes in the vibration patterns, there's likely an imballance or mechanical issue with the spindle or motor. If you don't see much activity there may be poor axis control on X or Y at faster movement rates due to slop in thrust bearings or ballscrews, or even servo control issues.

Thanks for the info, I’ll give this a go! I will say the machine was ball bar tested on installation and had very little backlash, I believe under 1 micron on x and y — does this rule out bearings?

 

[MiniMillMachinist]

What material are you cutting?

This is 6082 aluminium, but it happens with CZ121 (360) brass too

 

[Milland]

Thanks for the info, I’ll give this a go! I will say the machine was ball bar tested on installation and had very little backlash, I believe under 1 micron on x and y — does this rule out bearings?

Maybe - if little backlash is due to comp settings and not mechanical integrity it could still be an issue. If comp settings themselves are low or zero it's a good sign.

When you try the vibration test be sure not to execute an automatic tool change if the shelf can foul the toolchange process. Sounds obvious, but I sometimes forget such things...

 

[MiniMillMachinist]

Maybe - if little backlash is due to comp settings and not mechanical integrity it could still be an issue. If comp settings themselves are low or zero it's a good sign.

When you try the vibration test be sure not to execute an automatic tool change if the shelf can foul the toolchange process. Sounds obvious, but I sometimes forget such things...

Great, thanks for the info. I don’t believe there was any backlash comp, but I will say the servo settings were way out on delivery and had to be recalibrated. And thanks for the tip too — I’m definitely also guilty of forgetting silly things! I’ll also report back on what haas say. They have been good to me previously with the ball bar test I requested, so hoping they check this out for me with a vibration meter.

 

[Milland]

Great, thanks for the info. I don’t believe there was any backlash comp, but I will say the servo settings were way out on delivery and had to be recalibrated. And thanks for the tip too! I’ll also report back on what haas say. They have been good to me previously with the ball bar test I requested, so hoping they check this out for me with a vibration meter.

Well, that's a clue right there - I'd have Haas dig deeper into this, perhaps by putting an X-Y accelerometer on the table and getting vibration readings during operation at different feed rates. It's the "big boy" approach that is mimicked by the cup of water, done when you have to move, not just get some feedback on vibration amplitude alone.

 

[MiniMillMachinist]

Well, that's a clue right there - I'd have Haas dig deeper into this, perhaps by putting an X-Y accelerometer on the table and getting vibration readings during operation at different feed rates. It's the "big boy" approach that is mimicked by the cup of water, done when you have to move, not just get some feedback on vibration amplitude alone.

Yeah… interesting… is there any way I could test this myself?

After adjustment the accuracy of the machine seemed great, I think all the parameters for motion were in spec, but not sure if this would measure smoothness? I believe the test was performed at 1500mm/m, which is faster than what I performed my cuts at I think. They used a Renishaw QC20 I believe?

 

[Milland]

Yeah… interesting… is there any way I could test this myself?

Do you have a X-Y accelerometer?

Haas has got a bad rep for delivering incomplete/unfinished machines, and that your settings were off at the beginning is almost certainly tied to the bad finish. But you need to know your beans if you start playing with servo settings on your own, I wouldn't on a new machine. But you'll likely have to lean on your support contact to get this done right, they'll try to half-ass it with less competent personnel otherwise.

 

[MiniMillMachinist]

Do you have a X-Y accelerometer?

Haas has got a bad rep for delivering incomplete/unfinished machines, and that your settings were off at the beginning is almost certainly tied to the bad finish. But you need to know your beans if you start playing with servo settings on your own, I wouldn't on a new machine. But you'll likely have to lean on your support contact to get this done right, they'll try to half-ass it with less competent personnel otherwise.

Interesting. I don’t have one but I can see my local hardware store carries some — they aren’t cheap though!

Also I am locked out of any servo settings apparently — I was told I’d have to buy a key to access settings like this. Like you say, on a new machine I don’t want to touch that stuff anyway!

I have to say, I’m dealing with Haas UK and they’ve been just fine so far, so I do hope they will sort it out. I’ll report back on what the result I get in any case.

 

[MiniMillMachinist]

Hi guys, just wanted to add the original ballbar test result along with the one after the engineer adjusted some of the settings. It's got me thinking... was the ballbar tester out of calibration?

I also put my hand on the spindle at 10K, there is a very slight vibration but it's not that dissimilar from what my Jianken spindle produces in terms of vibration, at least to the touch. I tried the water in a cup trick and the water didn't move at all.

Cheers,
Mike