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Roland MDX-40A weird X-axis problem.

Posted: Wed Feb 06, 2019 8:32 am
by ilmastodontti
Hi everyone.

I work at a goldsmiths atelier with emphasis on 3d manufacture. We're still keeping our old MDX-40A war horse working. We use it to mill our ring wax models for casting. The machine has some 20k hours in it so it's been lovingly used. Now we've run into a problem that we just can't fathom.

When we do indexed cutting, the resulting piece is too small in x-axis direction. In other axes the dimensions are fine, but in x-axis direction there's always less. As an example, If we're milling a wax that's supposed to be 20mm in diameter, the resulting wax is 19.5mm in x-axis and 20mm in in y-axis. Recalibration didn't help. The correction doesn't help, as you can't set the distance correction to over 100%.

Has anyone had anything like this?

Re: Roland MDX-40A weird X-axis problem.

Posted: Thu Feb 28, 2019 7:40 am
by Plowndes
I have the same issue. X and y dimensions fall around 0.6 mm short. I have changed the belts and tried altering the belt tension but to no avail.
I put this down to the inevitable backlash/flex in the machine. Unfortunately there is no backlash adjustment facility in the software. At least it is consistent so when exact dimensions are important I adjust the file to add an extra amount.

Re: Roland MDX-40A weird X-axis problem.

Posted: Mon Mar 04, 2019 11:15 am
by Plowndes
I measured the backlash and found it is negligible, c. 0.02mm, under no load.
However using just finger pressure a flex of +/- 0.3mm can be achieved in both the x and y axis, measured against the spindle. On top of this the z axis will flex +/- 0.2mm in the y axis. With a long tool bit that flex could be greater when the machine is under load.
In the real world a deviation of 0.5mm seems within reasonable expectations.

Re: Roland MDX-40A weird X-axis problem.

Posted: Mon Mar 04, 2019 1:52 pm
by Patrick Thorn
A bit of info to add. The slides for XYZ are on bushes on the shafts. Any debris etc will cause more drag and therefore make the slides not position as well. On older machines, I have seen improvement if the slides and slide-way bushes are cleaned. It is not documented or approved, however, a bit of common sense and loving care will alway help maintain your machine.
1. Remove cutters and position X and Z central of their travel and power off.
2. Vac all debris from the X and Z slide rods, maybe a clean with a .
2. Use something like WD40 or very thin oil and apply some to the slides, protecting the other areas of machine.
Maybe a bit of news paper on the table and held behind the slides etc
3. Power the machine on and it will home.
4. Using VPanel move the axis back and forth to get the dirt out of the slides, wipe this with a cloth. Maybe repeating several times.
5. Finally apply a little thin oil on each slide, move around and then wipe clean with a lint free cloth.
You do not want oil on the slides as it will attract swarf.
6. With help of a colleague you can lift the front of the machine about 200mm off the bench and put something under each front foot, like a pile of books to support it securely in place.
7. Looking underneath you can now get to the Y axis and give it the same treatment, it should be much cleaner.

Hopefully the axis will now all run a lot smoother and help improve positioning.

If you need more help, then contacting your local Roland DG office should be the next port of call.
In the UK you can log a support call here.

Re: Roland MDX-40A weird X-axis problem.

Posted: Mon Mar 04, 2019 9:36 pm
by Plowndes
Thanks for the tip.
After cleaning and lubricating I now have 9.65 diameter bushes in 8mm delrin cut with a 2mm bit coming out at 9.55 by 9.52mm which I think is pretty good.