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Inconsistent Tool Lengths

Hoppy

Cast Iron
Joined
Feb 21, 2005
Location
Millington, NJ
The tool lengths in my Haas Super Mini Mill are not repeatable. Here's what I mean. Let's say a load a tool into pocket #1 and use the table probe to set it's length. I switch to another tool. If I then come back to tool #1 and probe it, the length will be anywhere from a few tenths to 0.008" different. At first I thought the problem may be the probe, but I've confirmed the findings with an indicator. The problem is not confined to just one tool - all ten tools in the carousel behave the same way. What could cause this?
 
How old is the mill? How many tool changes on the drawbar? What condition are the pullstuds? And the toolholder and spindle taper surfaces? Any chips floating around inside the spindle?

Measure the gap between spindle face and toolholder flange with gage blocks over numerous changes - if you mark which side of the spindle you're measuring, that should be the most reliable way of getting good numbers on stickout scatter.
 
The mill is from 2008 and I am the original owner. I replaced the spindle earlier this year, so its surface is pristine. The toolholders and pull studs look fine; in fact, some of the pull studs are new.

This problem seems to have come out of the blue. The machine runs every day and, until yesterday, all was well.

I'll measure the gap and let you know what I find.
 
Have you checked to make sure your stylus is not loose?

I would recalibrate everything and continue testing.

Sent from my SM-G955U using Tapatalk
 
OK - I took the same tool and loaded/unloaded it five times, measuring the spindle face to toolholder flange gap each time. I got four different values with a range of 0.005". I tried the same procedure with a different tool and got similar results. This seems to point to a problem with the way the tools are retained. Drawbar pressure?
 
OK - I took the same tool and loaded/unloaded it five times, measuring the spindle face to toolholder flange gap each time. I got four different values with a range of 0.005". I tried the same procedure with a different tool and got similar results. This seems to point to a problem with the way the tools are retained. Drawbar pressure?

now before you do that do this.

grab and indicator put it on the solid flat bottom part of the spindle. hit tool ejected button, check it.
if you do it right you can get a indicator right between the flange of the tool holder and the spindle surface and not have to move anything. just hit the button.
my guess is your preload in your spindle bearings could be bad.

The other thing is I assume you made sure your tool probe was flat in all directions and you didnt use anything bigger than a 3/8 endmill for your test.
 
now before you do that do this.

grab and indicator put it on the solid flat bottom part of the spindle. hit tool ejected button, check it.
if you do it right you can get a indicator right between the flange of the tool holder and the spindle surface and not have to move anything. just hit the button.
my guess is your preload in your spindle bearings could be bad.

The other thing is I assume you made sure your tool probe was flat in all directions and you didnt use anything bigger than a 3/8 endmill for your test.

All worth doing, but the errors he's getting between the spindle face and the toolholder is indicative of something messing up inside the spindle - bearing preload or tool probe stuff won't matter here.

It's time to really check out the spindle taper for loose materials, or worn retaining balls in the drawbar, or bad bellevilles, etc. I suspect ultimately you'll be pulling the spindle unless you find an easy fix (debris in the taper).

If that's the original spindle and you've gotten 12 years from it, you did pretty well in my book...
 
Said he replaced the spindle earlier this year.

Sent from my SM-G955U using Tapatalk

doesnt make any difference they replaced 2 factory ones in mine in less than 30 days. and tahts when it was new less than a week on the floor
 
Said he replaced the spindle earlier this year.

Sent from my SM-G955U using Tapatalk

Oops - didn't notice that (little sleep over the last week). Welp, still some sort of issue inside the spindle, the variable gap from toolholder to spindle face is pretty convincing evidence.

OP, when the toolholder gap is at its greatest, are you able to shake the holder within the spindle? That much axial displacement must lead to slop between tapers, unless it's chips or something filling the gap. And it sounds unlikely to be chips...
 
All worth doing, but the errors he's getting between the spindle face and the toolholder is indicative of something messing up inside the spindle - bearing preload or tool probe stuff won't matter here.

It's time to really check out the spindle taper for loose materials, or worn retaining balls in the drawbar, or bad bellevilles, etc. I suspect ultimately you'll be pulling the spindle unless you find an easy fix (debris in the taper).

If that's the original spindle and you've gotten 12 years from it, you did pretty well in my book...

actually it will, if the spindle nose when it goes back into clamp mode is .0008 difference its going to show up on the tool probe and even the cut.

sorry not between spindle face and tool holder, you need to measure the spindle face when clamped and not clamp and a few times in between. sorry I think I worded that wrong in my 1st reply..

for example. with no tool in spindle face repeats with in a .0001 put tool in spindle face is out .0008 take tool out goes back to .0001.
I had this very problem which effected my parts and including tool offsets, however mine was .002 exactly. cold spindle warm spindle didnt make a bit of difference.also the spindle started running warmer than normal and had a different pitch. Luckly we had a ss job that ran for 2 months at a slow rpm spindle didnt get warm over 8k I also ran a coolant line up against the spindle case. when i went back to alum I ran to 10k max hoping to get some more time out of the spindle before it was shot. almost 10 months later I am running max spindle speed and no excessive heat nor weird sounds and Z it repeats with in a few tenths.
how and why I have no clue that it went back to normal. with my luck I will start it up in the am and it will blow. ;)
 
heres a picture i found on the net.
put your indicator on this face, press clamp and unclamp a few times notice the difference if any, then put a tool in the spindle and do the same. There is enough room to place the indicator between the tool and the spindle face so you wont move or damage the indicator. your measuring the face of spindle only nothing else
hope that now makes better sense

P3260008a.jpg
 
Stop!

Repeated tool clamping with 'cold' spindle and tool holder not repeating the gap between the flange and spindle face better than 0.001" - IS A SERIOUS MALFUNCTION!

The tool cannot possibly be seated properly. Drawbar needs inspection/servicing, spring stack, release piston the whole of it.
Check stupid stuff first - like a loose pull stud, chips and smutz on taper and up into drawbar.
 
I generally agree, but if it's not making noise I don't think it's the release piston. That should lead to squealing if the piston's rubbing on the drawbar, so I'd think undiscovered chips or damaged spring washers, or some strange wear on the retaining balls.

I think he's go to pull the spindle, then the drawbar, and do a thorough checking of all the bits.
 








 
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