Lathe 0.02"ish part to part variance?? What am I missing?

Machine is a 2005 tl-1 with a c series multiflex quick change tool post.

Boring a 0.8625-0.8635" hole 0.75" deep with a 0.5" diameter bar with a c series cutter. Bar has 1.25" pullout. (Has to be out this far due to part/carriage clearance)

Part starts as a 6061 blank 10" dia with a 0.47" hole in. Centre, and gets 10 min of facing cuts to profile the front of part. (Ya ya, the tl has no balls) then a quick boring cycle. 1400 rpm 0.018"per rev 0.05" depth, a 0.01" at 0.004/rev finishing pass followed by a spring pass.

I've had great luck and made lots of these parts in the past with consistant boring. Now I am chasing an offset that keeps moving around by 0.02", totally random seeming.
Tool post and holder is very clean every time. I've put a dial on the tool tip mounting the mag base to the frame of the machine. Pushed pulled, repeatedly placed and locked tool. Repeats within tenths and no loose Components.

What gives? Tips tricks, am I blindly missing something??

Machine had a pretty bad crash a while back. But the run after on some small 4140 pins repeated within 0.0003" non problem.

Thanks for reading my novel and any input you have

We have a TL2 in our shop that I also encountered a random .020" move with. Parts were holding well then a 20 thou jump, check insert and its fine so I comp it. parts hold good for a few more then 20 thou back. I never sorted out the gremlin. I speculate it was skipping an encoder count or something. It only happened on the one job and, knock on wood< has not been back.

Good luck, ill watch to see what others chime in with.

I would think it is set up issue. Maybe insert or bar not tightened down correctly. We have a 2008 TL-1 and run production almost daily and have never seen anything like this. If you're sure about the set up I would call my local Haas Factory Outlet they are always very helpful.

I'd look for a loose Thrust Bearing and/or Ball Screw while your there.

If its the first piece on startup, I'd look at the Proximity Switch for homing machine.

If you have Thermal comp...could be set wrong...Although =/-.o2 is a bit much, I used to show slow growth then flicker between a couple tho til we got it sorted.


Then comes the, could part be shifting, boring bar or insert shifting?

Last, material being alum...have you tried another batch? Sometimes a gummy sticky batch can leave a hunk of material welded to the tip of cutting edge deflecting bar.

Aside from that...is there a way you can use an indicator to verify bar is where it needs to be on the last cut. Verify stocks not shifting...

Of course a bad encoder...but going back and forth. I usually get a following error with a bad encoder. That is beyond me and a call to HFO time.

Sorry I am all over the place...but its things that can go wrong and we have little to go on.

are you using tool comp that is .020 ??

DMF_TomB said:

are you using tool comp that is .020 ??

Click to expand...

No.
It will be .005 small let's say.
I'll run another spring pass. No real change.
I'll adjust 0.0046 to be on the safe side. Boom. .02 over.
Or I'll be 0.01 over on a part adjust it by 0.01, next part 0.02 under.....

Stirling said:

No.
It will be .005 small let's say.
I'll run another spring pass. No real change.
I'll adjust 0.0046 to be on the safe side. Boom. .02 over.
Or I'll be 0.01 over on a part adjust it by 0.01, next part 0.02 under.....

Click to expand...

.
.
some tools and parts if you adjust .001" it will rub and not bite in and cut then you adjust another .001 and it bites and cuts .002"
.
you in inch or mm ?? in mm then .02 mm is not much and often it will rub and not bite in and cut
.
some cutters there is a minimum cut you can reliably take. for example finish cuts at .025mm to .075mm, below and above you start having problems
.
i would plan on leaving
.125mm and measure
.050mm and measure
then final cut
.
if talking .020" i am not sure what the problem is

your cnc use stepper or servos. open or closed loop ??
.
stepper motors with no feedback on position if slide too tight screw dont turn or you miss a step or more.
.
with servo and closed loop feedback it reads position and keeps moving til it reads it actually moved to where wanted
.
some cnc will read x,y, z and hold position if cutting forces move it out of position it moves back to position. other cnc once to position if something moves it out of position it stays out of position hard to describe
.
on a prototrak in position drill mode if you grab handle and force move in X it will move but when you let go it goes back to position. many cnc do not do that

DMF_TomB said:

.
.
some tools and parts if you adjust .001" it will rub and not bite in and cut then you adjust another .001 and it bites and cuts .002"
.
you in inch or mm ?? in mm then .02 mm is not much and often it will rub and not bite in and cut
.
some cutters there is a minimum cut you can reliably take. for example finish cuts at .025mm to .075mm, below and above you start having problems
.
i would plan on leaving
.125mm and measure
.050mm and measure
then final cut
.
if talking .020" i am not sure what the problem is

Click to expand...

Ya it's 0.02" out :/
And it's a servo machine

I know you said you checked, but if the tool is the kind that has a shim/seat, check again. Make sure that the insert is not only tight, but that it is actually sitting down on the shim ( or in the seat ) and not sitting "up", or on a chip. I have had both - that ( unrecognized loose insert ), and a chip under the insert cause what you describe.

Found the problem.
The boring bar is held in a 1" key stock with a .375" slot and 4 set screws. Then placed in a qc tool block.
I had put a dial on the tool and tried to push it around all over hard at multiple angles. Nothing. So I took that as secure.
The set screws where very tight, the qc lugs tight at setup.
When I backed off the qc lugs the boring bar was loose in the adaptor block.
The block was orientated where the qc lugs pushed down squeezing the "c" adding force to the already tight set screws. I assumed this would help. It looks like it stretched the set screw threads and it worked loose. I could not push it around, but the machining forces could overcome it.

Thank you all for your advice. It is appriciates.
Glad it's not the machine. Feeling stupid though. Shame is ive used that little bar setup for 15 years without trouble.

Stirling said:

Found the problem.

Feeling stupid though. Shame is ive used that little bar setup for 15 years without trouble.

Click to expand...

Why feel stupid? You found the problem, corrected and moved on.

That is what this site is about isn't it.

Sometimes the obvious is overlooked as it is...well obvious.
That's what makes fresh eyes great