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

[plastikdreams]

Could damn well be the culprit. Sometimes it's the little things that make a big deal. Hope it solves the issue!

 

[MiniMillMachinist]

Could damn well be the culprit. Sometimes it's the little things that make a big deal. Hope it solves the issue!

Thanks, I hope so too! It makes sense... everything else checks out good. Literally can't find anything wrong with the spindle or the machine geometry, slop etc. Obviously people have mentioned more advanced testing methodologies, but with the tools Haas and myself have used so far it checks out good.

 

[Houdini16]

Should have mentioned this earlier, HAHA, Yeah with the taper length difference, and the pull stud length difference, It more than likely did some damage.

 

[MiniMillMachinist]

Should have mentioned this earlier, HAHA, Yeah with the taper length difference, and the pull stud length difference, It more than likely did some damage.

Didn't realise there was a difference in taper length too! Ok so a good starting point for trouble shooting then!

 

[Houdini16]

Didn't realise there was a difference in taper length too! Ok so a good starting point for trouble shooting then!

If I remember correct CAT40 has a longer taper and a shorter pull stud. No bueno.

 

[MiniMillMachinist]

Should have mentioned this earlier, HAHA, Yeah with the taper length difference, and the pull stud length difference, It more than likely did some damage.

It honestly never came to mind, but you are absolutely right!

 

[MiniMillMachinist]

Ok guys, so Haas UK have had a discussion with Haas US and wish to try changing the belt, checking the pre-load on the spindle bearings, and trying some shims or washers (I've totally forgotten whether they said shims or washers). Does anyone know what the purpose of the shims/washers would be? The only shims I can think of are the ones between the casting and the spindle itself, but the spindle is very well trammed - I think I measured around 5 microns or so deviation over a 150MM radius. In terms of washers - would they be referring to a crush washer which I know some spindles are fitted with to protect a spindle in the event of a crash?

 

[Milland]

I don't know for sure, but it may be they want to try shimming the drawbar to preload the Belleville washers a little more for higher tool retention force. I don't think it would be for spindle bearings, any change (by shim removal or thickness variation) in stack clamping distance meant to further preload the bearings is likely too gross a change and would damage the bearings.

I don't think Haas spindles include any crash protection outside of the spindle itself being a replacement consumable...

 

[MiniMillMachinist]

I don't know for sure, but it may be they want to try shimming the drawbar to preload the Belleville washers a little more for higher tool retention force. I don't think it would be for spindle bearings, any change (by shim removal or thickness variation) in stack clamping distance meant to further preload the bearings is likely too gross a change and would damage the bearings.

I don't think Haas spindles include any crash protection outside of the spindle itself being a replacement consumable...

Since they had their eyes on the drawbar at first, that would make sense. I'll be away next week but I will keep this thread posted on progress with this.

 

[MiniMillMachinist]

One thing I have noticed is that my effective tool length will grow by 10-20 microns or so between cold and hot. I never noticed this sort of thing with my router - is this just to be expected with a mill?

 

[Milland]

That's in the range I'd expect - Haas doesn't do thermal design very well.

 

[MiniMillMachinist]

That's in the range I'd expect - Haas doesn't do thermal design very well.

Good to know! There are some compensation settings IIRC but I haven't experimented yet. I'll have a look at that after this issue is resolved.

 

[MiniMillMachinist]

Haas have told me the shims may need to be placed in the spindle end cap, this does sound more like a bearing thing... does anyone know?

 

[Milland]

Haas have told me the shims may need to be placed in the spindle end cap, this does sound more like a bearing thing... does anyone know?

With a new machine/spindle? I'd be telling them to replace the entire spindle cartridge, not try to "fix" it in your shop. If they take the current spindle apart, load the bearings more, then it fails out of warranty, will they cover it? If not, insist on a good, new assembly.

 

[Houdini16]

Did you get this figured out?

 

[JasHarvey]

Do you get the same vibration/chatter on a straight cut? If not, the problem could be in your G code.

 

[MiniMillMachinist]

Sorry guys, was away on holiday. Haas were here yesterday and the day before and did bearing preload tests, a drawbar test again, and fitted a new belt, along with running some test cuts.

The preload tests showed 17 tenths where the limit is 25, so in spec. The drawbar test showed the drawbar in the middle of the spec.

The new belt has made the issue about 50% better I would say. There is still come scalloping in the cut but it is considerably reduced. I had an apps guy here and he thought there was still some oddness to the cut, but I'm not sure if this is normal for a mini mill now. The cuts aren't perfect but as I say they are better. Does anyone have a mini mill they could reproduce a similarly light finish pass with a low chip load on for comparison?

For some reason the techs were sent a test for floor finish which showed no issues - I haven't had any issues with floor finishes and this came out great - better than the super mini mill they had a comparison of, but this super mini mill seemed to have an issue with coining so it wasn't a fair comparison really.

Interestingly the spindle power consumption has been reduced with the spindle running in free air. I noticed it went from 2KW to 1.6KW at 10,000RPM with the new belt. It's also a lot quieter!

The fact the belt made such a difference has made me think it was imparting artifacts through the spindle bearings, which in my mind shouldn't really be possible?!

Anyway, I welcome everyone's thoughts on this!

 

[MiniMillMachinist]

Did you get this figured out?

Hi Houdini, see above — getting closer

 

[MiniMillMachinist]

Do you get the same vibration/chatter on a straight cut? If not, the problem could be in your G code.

Unfortunately these issues are all present on straight cuts — all of the photos I’ve attached are of straight cuts

 

[Orange Vise]

The fact the belt made such a difference has made me think it was imparting artifacts through the spindle bearings, which in my mind shouldn't really be possible?!

It just sounds like vibration.

Can you get a good finish at 6-8K RPM with the new belt?