St40n turret alignment

ModulusAndy · Oct 31, 2014

We have an old ST40 2 axis lathe. We just bought it cheap for roughing but the machine turns out to be in pretty good condition. There's jus one problem.
We can't get the centre height for the turret set right.
The Turret has 5 holes in the turret face for mounting U-Drills, boring bars etc. Then tooling blocks (Turning and boring) that mount on the periphery of the turret.
The problem is if we set the height for the boring bar holders in the face of the turret then the turning tools are not on centre.
I have no idea how this can be. I am guessing maybe the turret itself is too low. I can see there are shims between the carriage and the turret itself. How it could end up with the wrong shims beats me. there does not appear to be any appreciable wear on the slideways and the machine cuts reasonably parallel. The error between the face holders and the turing tools is almost 2.5mm!
I was beginning to wonder if there were two curvik couplings, one for the inner set of holes and one for the outer.
If anyone has any ideas on this I'd be grateful to hear.

Cheers Andy

wippin' boy · Oct 31, 2014

i have never seen a st40n but i was able to google a couple of pictures
i can't imagine how the holders are that far off turret holes
but
that is a super slant you got going there
i have seen some pretty weird sht related to head taper on those heavily slanted beds
especialy when the head is flat (which i have no clue about how yours is built) and the x rails on that big slant
when ever i check turret height issues i first set the head taper straight
another thought is
on those old mazaks with bolt on odd ball holders there is sometimes and adjustment on the holder it self, maybe someone before you got the holders screwed up. a simple 1 or 2 degree rotation on that pin setup would change stuff a lot

i would be surprised to see 2 curviks

IronReb · Oct 31, 2014

Since you got it cheap and it seems to be a good machine, go ahead and call a tech if you have one in your area, it could be a days worth of labor to realign the turret if your lucky.

If no tech then fill up a memory card with pictures of the turret and headstock after the outside sheet medal has been removed and I am sure there are people who can walk
you through the alignment process.

The comment wippinboy made about the tool holders them selves having locator pins could very well be all that's wrong.
Post some pics of your turret and tool holders.

The dial pin on our turret that centers the tool holder is on a cam.
You can rotate that pin and change center height by about .012'' if I remember correctly.

ModulusAndy · Oct 31, 2014

No adjustment on the toolholders unfortunately.
One thing I just noticed on further inspection is that the headstock, though mounted at an angle, does not seem to be mounted at the same angle as the X axis slide. So maybe the headstock is not positioned correctly. It does cut parallel though. Maybe it is just too far forward or too far back. If they are at different angles to each other that would affect the centre height.

wippin' boy · Oct 31, 2014

Post some pics of your turret and tool holders.

absolutely MORE PICs !!

we ALL need to know more about just what the hell a ST40N is all about

ModulusAndy · Oct 31, 2014

OK, How do I post pics on here?

ModulusAndy · Oct 31, 2014

St40n

Some photos

wippin' boy · Oct 31, 2014

if you take the tool out and sweep the bottom of the turn tool pocket in -X- what does it show?

Philabuster · Oct 31, 2014

The sheetmetal on that machine is in pristine shape---especially for an old machine. Usually the sheetmetal behind the chuck looks like hammered dog shit due to parts being ripped out from the chuck.

ModulusAndy · Oct 31, 2014

wippin' boy said:
if you take the tool out and sweep the bottom of the turn tool pocket in -X- what does it show?

If I adjust the turret for turning tools then the bottom face clocks true. But then the face holders are incorrect

nupress · Oct 31, 2014

check the headstock alignment. With the configuration of the turret as it is if the machine has had a hit this will cause the symptoms you have
A simple check is to mount a dial indicator on a piece of 1" stock say 2 foot long. Push most of the stock up inside the spindle and dial a boring bar holder close to the chuck. Now wind the Z axis towards tge tailstock and pull your dial out on the barstock reclamp and dial again.

ModulusAndy · Nov 1, 2014

nupress said:
check the headstock alignment. With the configuration of the turret as it is if the machine has had a hit this will cause the symptoms you have
A simple check is to mount a dial indicator on a piece of 1" stock say 2 foot long. Push most of the stock up inside the spindle and dial a boring bar holder close to the chuck. Now wind the Z axis towards tge tailstock and pull your dial out on the barstock reclamp and dial again.

Hi,
Is this similar to checking for taper? Or is it checking something else.
If I turn a 80 dia bar over 200mm I get about .025mm taper. On a machine of this age I'm happy with that.
I'm going to have to go back and double check that when the turning pocket is parallel to the X axis slideway that it really is cutting on centre.
I just can't get my head around how there can be such a huge discrepancy.
I'm actually modelling the whole machine in solidworks now to try and figure out what could be wrong.

ModulusAndy · Nov 3, 2014

Well, I made a model of the machine to see how I could reproduce the errors I am finding.
It seems the only way I can get this strange behaviour is if the headstock is too far forward on it's 45 degree mounting.
The error at the bottom face of the turning tool holders at the moment, with the face holders clocking true to the spindle, is 0.6 degrees.
If I could move the headstock by around 3 mm that would give zero error.
However, I thought that the only adjustment on the headstock was rotational about a pivot pin. Anyone have any knowledge about the mounting arrangements on these machines? I just cant figure it out from the machine drawings that I have in the manual.
I'll try and call Mazak today see if they have anyone who has had the headstock off one of these machines.

nupress · Nov 3, 2014

Well done reproducing the error in a simulation. That has saved hours of pulling stuff apart that didn't need to be pulled apart. Keep us posted with the progress.

wippin' boy · Nov 3, 2014

restating the "I have never seen one of these fellows" disclaimer
IMHO the tool pocket being flat when the turret is aligned to the turning tools says that is where the turret is supposed to be, has to be, or installing a common turn tool becomes a layout exercise.

However, I thought that the only adjustment on the headstock was rotational about a pivot pin

all the mazaks I have seen are as you describe
I do have a hardinge that is not on a pin and the headstock can move straight in and out. which is one of the adjustments to achieve proper turret height.
if that Mazak of yours was not on a pin it would have adjustments on both ends of head stock not just one so the book could answer that one.

two other swags to throw out
twisted bed allowing the 3mm error
factory eccentric holders on boring pockets

this one has me scratching my head

ModulusAndy · Nov 3, 2014

wippin' boy said:
restating the "I have never seen one of these fellows" disclaimer
IMHO the tool pocket being flat when the turret is aligned to the turning tools says that is where the turret is supposed to be, has to be, or installing a common turn tool becomes a layout exercise.

I know what you mean. If the pocket clocks true then that implies the centre height is correct. As it stands it also implies the face holders are on a different centre height to the turning tool holders!

This has me completely baffled. It's as if the geometry of the machine is just plain wrong. Maybe it's two machines welded together.

Philabuster · Nov 3, 2014

ModulusAndy said:
If I adjust the turret for turning tools then the bottom face clocks true. But then the face holders are incorrect

Sounds like the turning and facing tools are mismatched or made incorrectly for this machine. The turning holders bolt on the machine. Mazak did make both inch and metric holders. What size stick tools are you using in Sheffield--metric or inch stuff?

My opinion, clock the turret so the integral boring bar pockets in the face of the turret are on center using a Co-Ax indicator. Beware regular test indicator internal mechanisms are affected by gravity.

Rework the stick holders by milling all the stick holder pockets the same height and use an 1/8" thick spacer under the tool holders. Again, only mill the holders after you have aligned the turret.

wippin' boy · Nov 3, 2014

Sounds like the turning and facing tools are mismatched or made incorrectly for this machine. The turning holders bolt on the machine. Mazak did make both inch and metric holders. What size stick tools are you using in Sheffield--metric or inch stuff?

My opinion, clock the turret so the integral boring bar pockets in the face of the turret are on center using a Co-Ax indicator. Beware regular test indicator internal mechanisms are affected by gravity.

Rework the stick holders by milling all the stick holder pockets the same height and use an 1/8" thick spacer under the tool holders. Again, only mill the holders after you have aligned the turret.

I do see that as a possible avenue to pursue,

but

I would also talk to more than a couple Mazak factory people before such changes are made

ModulusAndy · Nov 3, 2014

Ok, Just had a long chat with the service engineer at Mazak.
Apparently there are some jacking screws on the headstock for moving it forwards and backwards.
Another thing is there are some shims between the carriage and the turret assembly. according to the engineer these should not be there. (they also look suspiciously home made).
Maybe we are dealing with a bodge after a crash, then multiple bodges thereafter trying to correct errors caused by the first bodge.
Maybe it is fixable. but moving the headstock looks like a pain in the proverbial.
Could do with starting this job from scratch.

wippin' boy · Nov 3, 2014

a pain in the proverbial.

I've found those headstocks a whole bunch easier if you pull that front sheetmetal which is usually easier than you would think
especially the 2nd time after I leave half the bolts out :skep:

St40n turret alignment

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