qt15n has started to turn inconsistent diamters???

M K · Oct 16, 2020

My Hyundai QT15N which is a mazak license copy has the T32B control, Its an old machine i know, think it is 1999 but its been ok since ive owned it, no issues or problems, no flat battery or memory loss etc but this last 2 weeks it has started to produce inconsistent diameters?

Normally il turn a part and then adjust the tool ofset until the dia is correct but now it seems to have different size errors on different diametrs all on the same feature using the same tool?

Say for example i turn a part with a 10mm od a 20mm od and a 30mm od the first may be under 0.4mm the second will be good and the third will be oversize by 0.7mm

The machine has not been crashed or bumped to cause this sudden inconsistency so i am stumped and have no idea how to try and fix it? yes i can lie about the part dimensions to dial it in but thats not what i want to do everytime i make a part, i don't use it everyday just as and when i need it so dont have the money to buy anything newer to replace it

Any ideas?

Thanks
Marc

wippin' boy · Oct 16, 2020

thrust bearings on -x- or tool height way out would be my first thought
inconsistent turret clamp would be one also
mount an indicator on the turret
position feeler against a bar hung in the chuck
load up the indicator in the positive direction .001 pulse wheel
stop. go back the other direction
if it takes more than 3 or 4 clicks (thous)to start the indicator moving in the other direction you got loose shit in the axis.
thrust bearings are first and easiest to address
on a little used seldomly looked at old girl you may be able to just smack down the lock nut a time or two and tighten stuff back up.

M K · Oct 16, 2020

Thanks, are they easy to get at do you know? i will have a look first chance i get,

im guessing they are accessible from the rear of the x axis?

Thanks
Marc

M K · Oct 16, 2020

Had a quick look behind the rear panel at the x axis motor and leadscrew

Is there any guides online or manuals as what to tighten etc?

Here’s a pic

gmc1724 · Oct 16, 2020

Say for example i turn a part with a 10mm od a 20mm od and a 30mm od the first may be under 0.4mm the second will be good and the third will be oversize by 0.7mm.

Is the above consistent?
The thrust bearing you want to look at is under the x-axis way covers at the front of the machine but before you have a go at tightening it have a look at the encoder coupling on the x-axis ballscrew. There's a small grubscrew (maybe 2) that nips the spring coupling to the encoder shaft, if it's loose you'll get inconsistent diameters.

M K · Oct 16, 2020

My picture above is of the couple screw I think as that is the servo end of the ballscrew? Not a lot of access to it to tighten up though and I’m not sure what but I should try and tighten if these parts, unfortunately I’m not sure how to make the picture bigger.

So if I pull the front X axis way covers then that’s where I should find the thrust washers you say?

I’d searched old post and I see the thrust washers causing this sort of problem is common

I also read about the backlash parameters but this old T32-B doesn’t seem to have that

Thanks
Marc

gmc1724 · Oct 17, 2020

M K said:
My picture above is of the couple screw I think as that is the servo end of the ballscrew? Not a lot of access to it to tighten up though and I’m not sure what but I should try and tighten if these parts, unfortunately I’m not sure how to make the picture bigger.

So if I pull the front X axis way covers then that’s where I should find the thrust washers you say?

I’d searched old post and I see the thrust washers causing this sort of problem is common

I also read about the backlash parameters but this old T32-B doesn’t seem to have that

Thanks
Marc

I'd forget backlash parameters for now, the thrust bearing nut lives under the front way covers and if you're getting that much inconsistency it will be obvious if it's that. I'm thinking more of a loose encoder coupling though, take a look at ebay no 252753410874 to get an idea what it looks like, your machine may not have one though.

M K · Oct 17, 2020

Ok so I removed the covers

Removed the nut cover to reveal the thrust bearing nut,

The 3 small grub screws were barely tight and I could move the but fairly easily with a C spanner

So I tightened by hand as much as I could and then gave it half a dozen blows with a blunt chisel and and hammer to tighten it

I marked it first with a pen and after tightening it has rotated roughly 5mm further than it was

This is the best photo I could manage but you can see how the black lines are out from each other now to show how much further it done up

I will try that first as see if it makes a difference

Thanks
Marc

M K · Oct 17, 2020

Ok so it made no difference at all!

I did the same with read but that was tight and didn’t move at all!

I put my dial indicator on the big turret housing casing and set the indicator up on the tailstock ways,

In Z axis it had 0.050mm run out over a 9.5”” length which is poor I know so that’s so thing I want to sort

When I measured the backlash in X axis it was inconsistent as per the diameters have been!

When I set the clock to zero it was ok about 85% of the time when I moved it with the pulse jog wheel but every now and then I would turn the jog wheel 1 click at either x 1 or x100 and it wouldn’t move at all like the machine didn’t register it? Then next click it would move as it should, sometimes this would have 3 or 4 clicks in a row so it explains the issue the machine is having if it is missing a signal or something?

Anyone have any ideas on where to go next?

Thanks
Marc

gmc1724 · Oct 17, 2020

M K said:
Ok so it made no difference at all!

I did the same with read but that was tight and didn’t move at all!

I put my dial indicator on the big turret housing casing and set the indicator up on the tailstock ways,

In Z axis it had 0.050mm run out over a 9.5”” length which is poor I know so that’s so thing I want to sort

When I measured the backlash in X axis it was inconsistent as per the diameters have been!

When I set the clock to zero it was ok about 85% of the time when I moved it with the pulse jog wheel but every now and then I would turn the jog wheel 1 click at either x 1 or x100 and it wouldn’t move at all like the machine didn’t register it? Then next click it would move as it should, sometimes this would have 3 or 4 clicks in a row so it explains the issue the machine is having if it is missing a signal or something?

Anyone have any ideas on where to go next?

Thanks
Marc

Have you checked the encoder coupling yet? Take a picture or two of the rear of the x-axis assy'.

M K · Oct 17, 2020

This is all that is visible

Thanks
Marc

cnctoolcat · Oct 17, 2020

Try tightening up the big spanner nut on the servo motor end as well. Of course you have to loosen the set screws to get it to move...and a few good whacks will set the torque.

Also make sure your flexible coupling bolts between the servo and ballscrew are all tight...and like said, verify encoder coupling set screws are tight. (Sometimes they will have a lock set screw over top of the actual set screw!)

Good luck,

ToolCat

M K · Oct 17, 2020

The only ones I’m able to tighten are the 2 C spanner nuts and they are as tight as I can get them,

I can’t access anything else with it built up in the machine like it is?

Also I can not see an Encoder coupling like the one pictured in the eBay link?

Thanks
Marc

M K · Oct 19, 2020

Another thing I noticed is that my X axis spindle load monitor fluctuates continuously from 0- 13% load when sitting still but this could just be the servo motor trying to hold the position as the X axis is on a slight slope

Gobo · Oct 19, 2020

M K said:
Another thing I noticed is that my X axis spindle load monitor fluctuates continuously from 0- 13% load when sitting still but this could just be the servo motor trying to hold the position as the X axis is on a slight slope

That is normal.

Gobo · Oct 19, 2020

We had a cracked encoder coupler on the B axis and it was behaving the same way.

M K · Oct 20, 2020

Thanks for everyone’s help and input,

Especially gmc1724 for helping me out via phone

I tightened up the thrust bearings as best I could and it did make a difference but there was still mechanical slop, I’d been looking at it as an electrical/servo issue and overlooked the basics

Well it seems the cause was mainly down to the actual ballscrew nut being loose!

The nut is bolted to the underside of the turret housing by 6 socket cap head screws, 2 towards the rear and 4 towards the front.

4 of the these were not as tight as the ought to be so I done them up and then adjusted the backlash parameters as best I could and it’s seems to of done the trick,

It’s still and old worn machine so I don’t expect too much but I ran off 50 parts today and everyone was within .01mm straight off the bat,

There’s a few other things I’d like to sort with the machine but I’m well happy it’s back on track.

If anybody has the machine S and SP parameters for this machine that they could email me that would be great as I have all the main ones but my book doesn’t contain those ones

Thanks
Marc

wippin' boy · Oct 23, 2020

awesome
loose shit is the most common shit
its just that there is so much shit that could be the shit

congratulations
you're now what we all strive to be
a shit fixer
and since its a mazak
you're a high class shit fixer

qt15n has started to turn inconsistent diamters???

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