Our little company bought cnc mill http://www.cnc-router-store.com/prod...pezium-screws/ 4 years ago and recently we started to suspect that it needs some parts replaced or maybe just fixed, but we want to try it on our own. The main problem is that x and y axis are wobbly, if you apply force to it, you can measure that it moves back and forth 0.1mm on x axis and 0.5mm on the y axis. we can't do any precision work with the mill anymore. So can we just order from somewhere new bearings and replace them ourselves or any other suggestions? There are some other issues as well and I would appreciate if anyone could comment on them! First, while measuring the range of free movement on axis, I discovered, that by applying a bit more force, I can actually make threaded rod to move(spin) as well, is it normal? second, sometimes during operation, motors from axis produce weird sound and mill stops moving on an x and y axis, when the sound stops and operation continues, x y zero point coordinates have been changed like it would have been moving all the time without that stoping.
There will be other people that know about building CNC machines that will chime in in a bit, i am only posting as i am an owner of a similar model the S1400 by Heiz, so i have a very good idea of your setup.
Luckily the S1400 has Hiwin 15mm to backup the round rail on the X axis on my machine so it is rock solid on the X, however on the Y axis Direction i have a similar issue as yourself, i have not measured the movement but i would guess at 0.25 + by feel when enough force is placed at the bit, i am lucky that as i cut neary 100% HDPE that this doesnt come into play as such as it is like cutting butter and i doubt much force is ever presented.
Notice that i said in the Y axis direction rather than it actually being on the Y axis, i would suggest you double check as i initially thought it was the Y axis bearings but it is actually sideways play on the 2 Z axis bearing blocks on my machine. If you get your fingernail on the edge of the bearing you might be able to feel the movement, it is very small but this is obviously magnified at the bit.
As far as replacements, i am not sure whether Heiz would be particularly helpfull from what i have heard and how easy it would be to replace them i do not know, i certainly dont think it is an easy job on this machine, from what i have heard elsewhere.
If i was going to sort mine out i think i would build a whole new gantry with Hiwin rails on the Y and Z to match the X, however as you have all 3 axis to do, you may be bettter selling it and upgrading to a better machine if you need good accuracy, i mosty cut basic panel shapes and edges are hand finished so it is not so important to me.
I have read about this being a problem with a few Heiz machines on this and other forums that after a few years some play is introduced
As far as the weird sound and the mill stopping moving that may well be the acme screws binding against your anti backlash nut and causing the steppers to stall, the reality is you just cannot have these too tightly adjusted, obviously you want to get as much mechanical backlash out as you can by adjusting the nut, but try and squeeze it down too much and you will get binding, also whats good for one part of the Acme Screw might be too tight further down.
I know that is the case on mine as obviously the threaded Screw is not perfectly accurate.
You will have to knock off the rest of the backlash with the anti backlash in mach, you just arent going to get the mechanical backlash that low on the S model which doesnt have ballscrews.
Regarding being able to spin the screws, it depends what you mean, if you mean that mm of slack either way with the steppers powered down, then thats just your backlash, if the Steppers are off you can move the whole gantry up and down with a little force, with the steppers powered up i cannot move mine at all.
Last edited by howser37; 17-11-2015 at 01:31 AM.
Also it just occurred to me that you should also check the squareness of your Y axis to the X axis, as if they are not square this can also lead to stalling steppers, and as you said you have been moving the screws by hand then this is a good possibility to check.
An easy way to do this is to very slowly jog your Gantry to its end stops on the X and they should both touch at the same time on either side, if one side has touched and there is a gap on the other side then turn your steppers off and square it up by turning the screw manually, obviously this will only be accurate to a certain degree but worth a check to start.
the strange noise is due to the fact that your stepper motors are stalling.
The stalling can occur if your powersupply or drivers are not supplying enough current to the motors or if you have set your accelerations and rapid speed too high. Not sure what software you are using so best look through your settings yourself.
Trapezoidal screws can be backdriven, as howser says, if their pitch is long enough. Under operation, the stepper motors are energised which applies a holding torque. That is what stops the axes moving when you are cutting. So yes it is normal.
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