Mazak QT20 Ball Screw

TheScorpio · Aug 24, 2017

Hello guys, i am new here.
I bought an used Qt20 lathe from 1997 and everything was working fine but the other day, when cutting off some part, it got stuck between the chuck and the tool. From then on, the X axis got noisy when moving and vibrates afecting the surface finish.
I supose that something went wrong with the ball screw, does anyone know if these machine ball screws are only sold by mazak resselers or are they Standard? Is it hard to disassembly? Can it be anything rather than the ball screw?
Thank you all very much in advance.

hanermo · Aug 24, 2017

Anything is available, if you pay enough.

It might be the mounts.. as well as the screws.
Or the coupler.

Screws (end machining) (OR PROVIDER) and mounts can be re-done or made by anyone here.
Mazak is a high-rigidity/accuracy machine.
It needs high-accuracy screws.
These are very expensive.

Ballscrew rebuilders exist.

carbonbl · Aug 24, 2017

I cannot say whether your problem is due to a bad ballscrew, but I am going through an X-axis ballscrew replacement on my 1989 QT8, as part of rebuilding this previously neglected machine.

Ballscrews are available direct from Mazak. In the USA I registered with Mazak USA and they will quote whatever I need over email. Not sure if it will be different in Portugal, but at least here there is no reason to deal with resellers for parts. They had the ballscrew in stock for immediate shipment (for a 1989 machine, I was impressed!).

To save some money as I was not worried about downtime on that machine, I ended up getting a replacement screw fabricated by a ballscrew specialist. This was based on a recommendation from my independent Mazak tech. Cost wise, the new ballscrew from the specialist was approx. 1/2 the cost of a new part from Mazak, but about a 2 month lead time. They would have rebuilt/reground the old screw for approx 1/3 the cost of the new Mazak ballscrew. That rebuild cost was dependent on condition and mine needed full regrind/rechrome, new seals, tubes, balls etc.

I have the new screw and it "looks" excellent but I still have yet to install it. So the final outcome is still unknown.

TheScorpio · Aug 24, 2017

I know Mazak resellers will deliver any part shortly, the main reason of this question is because they are closed for vacation now here at Portugal... One thing I forgot to mention, the axis load meter reaches 70% load on the positions where it makes that noise...

wippin' boy · Aug 29, 2017

might just be the thrust bearing locknut came lose in the wreck.
might just need thrust bearings rebuilt.
or not
but a set of bearings are a whole bunch cheaper and might just get you buy
seems like that may be a belt driven axis too might of just shredded that

carbonbl · Sep 19, 2017

carbonbl said:
I cannot say whether your problem is due to a bad ballscrew, but I am going through an X-axis ballscrew replacement on my 1989 QT8, as part of rebuilding this previously neglected machine.

Ballscrews are available direct from Mazak. In the USA I registered with Mazak USA and they will quote whatever I need over email. Not sure if it will be different in Portugal, but at least here there is no reason to deal with resellers for parts. They had the ballscrew in stock for immediate shipment (for a 1989 machine, I was impressed!).

To save some money as I was not worried about downtime on that machine, I ended up getting a replacement screw fabricated by a ballscrew specialist. This was based on a recommendation from my independent Mazak tech. Cost wise, the new ballscrew from the specialist was approx. 1/2 the cost of a new part from Mazak, but about a 2 month lead time. They would have rebuilt/reground the old screw for approx 1/3 the cost of the new Mazak ballscrew. That rebuild cost was dependent on condition and mine needed full regrind/rechrome, new seals, tubes, balls etc.

I have the new screw and it "looks" excellent but I still have yet to install it. So the final outcome is still unknown.

Following up on this for anyone who reads this thread and is interested...long story short, it's been a big hassle and I wish I just bought new from Mazak. Cost of wasting my and my Mazak guy's time is about equal to what extra I would have paid for a new screw from Mazak. Couple critical dimensions were wrong on the new screw- threads for one of the retaining nuts not fully formed causing seizing of the nut during installation, also the section of the shaft where the servo coupling attaches is approx 0.002 oversize, messing up the coupling fit. I shipped it back to the ballscrew mfg to fix the threads which they did at no charge (after complaining "I didn't know you were reusing the old nut" :confused:

), THEN I discovered the oversize shaft section after we continue the install :angry:

Trying to rework the coupling in house now- boring out the coupling then shimming and/or Loctite 680 for a good fit is the current plan.

I'd maybe still try a rebuild but this experience does not give me confidence in getting a new ballscrew made by a non-OEM.

TheScorpio · Sep 27, 2017

Well... In my case it seems not to be the ballscrew after all, now it got worst and it gives the alarm "21 drive unit power malfunction" and on the drive it generates the "a3" error wich is "overcurrent". If I invert the axis on the drive all this problem migrates to Z axis, any idea about what could it be?

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