Denford Software & Machines

Hi
I was turning a part last night, which has a rised donut type ring feature on the face and found when the X axis had finish its feed move up the face and about to rapid to position for another pass, it seem to lose 20mm ish in the X travel, as if some thing was slipping belt, leadscrew etc.. Im not quite sure haven't had one of these machines apart yet.

I would re-reference the machine axis out.
Which seemed to work fine for the next few components, then it would happen again.

Any info on this subject would be great before I start taking it apart.

Cheers

Adee

Adee wrote:Hi
I was turning a part last night, which has a rised donut type ring feature on the face and found when the X axis had finish its feed move up the face and about to rapid to position for another pass, it seem to lose 20mm ish in the X travel, as if some thing was slipping belt, leadscrew etc.. Im not quite sure haven't had one of these machines apart yet.

I would re-reference the machine axis out.
Which seemed to work fine for the next few components, then it would happen again.

Any info on this subject would be great before I start taking it apart.

Cheers

Adee

It is possibly due to the curve you are trying to machine, if it`s a tight radius then could be an issue of the steppers working one against the other and it sounds like the X axis motor is being "overridden" by the Z and the force causes it to in effect "jump" it`s position, a bit like a ratchet slipping.

I had the same problem a few years ago with a Denford Easimill 3 on very tight rads.

For now that`s my best guess!!!

Regards
Rob

Cheers Rob for your input.
But it seems to jump, when the tool is just about to rapid to the start of the next facing pass from a safe clearance postion from the last pass. would what you suggested still effect this movement?

Adee

Adee wrote:Cheers Rob for your input.
But it seems to jump, when the tool is just about to rapid to the start of the next facing pass from a safe clearance postion from the last pass. would what you suggested still effect this movement?

Adee

What does your code look like??

Have you tried running at the cutting feed rate to a different "safe" point before it rapids, may be a faulty stepper that has a problem stopping at that point, a simple change in the code might do it??

Regards
Rob

I haven’t got the actual code to hand, but it would go a bit like this

N1~~~
N2~~~
N30G0X5.00Z3.00L
N31G1X5.00Z-1.00FX75.0L
N32G1X20.00Z-1.00L
N33G1X22.00Z1.00L
N34G0X5.00Z3.00L

The error doesn’t seem to happen on the same bit of code all the time, it can be on any move which switches to G0 from G1 when transverse down the Xaxis and the error when it happens is only in the Xaxis.

I must add, I ran the machine last night for a short while and didn’t get any position errors at all.

Adee

Does it do the same thing if you run the program without cutting anything?

Does it still do it if you set an offset in the X & Z axes (such that it's using a different bit of the lead screws)?

Does it do it if you use a G01 instead of G00 with a slower feed rate?

I'm guessing it's just loosing steps for some reason. It could be a tight patch on the bed/cross slide. Possibly wear in the lead screws.

If the G00 to G01 fixes it - I'd look at the stepper driver just not delivering enough current to keep the motor in step, or it can't cope with the speed of the pulse train or the motor being tired?

Si

The error happens with or without cutting the part and on different areas on the leadscrew, but only every now and then.
I did think about changing all the G0 to G1, but it was getting late the other night and theirs 200 lines to sort through, but will try that out later.
Apparently the machine hadn’t been used for 4 years until now, so maybe a bit gunged up.

BTW
Si, hows the retro fit going on your easiturn?

Adee wrote:The error happens with or without cutting the part and on different areas on the leadscrew, but only every now and then.
I did think about changing all the G0 to G1, but it was getting late the other night and theirs 200 lines to sort through, but will try that out later.
Apparently the machine hadn’t been used for 4 years until now, so maybe a bit gunged up.

BTW
Si, hows the retro fit going on your easiturn?

I think Simon may well have it right that there are tight areas in the machine travel particularly in the X axis, could even be some rust if the machine has been sitting idle for 4 years!!

It would be having the same effect as the motors working against each other, in other words extra load especially when changing speed, the acceleration/deceleration could be causing it to lose steps particularly if any of the electrical components on the X axis drive card are a bit "tired", electrical components especially capacitors can deteriorate quite badly over time, and if the machine was stored in a cold possibly damp environment then that makes it worse!!

If it only ever seems to happen on the X axis then you could try swapping the X and Z axis drive cards (They just plug in) and if the fault stays on the X axis then it is either mechanical issue on the X axis or the X axis stepper motor, if it moves to the Z axis with the card then it would seem to be a card problem!!

Regards
Rob

Adee wrote: BTW
Si, hows the retro fit going on your easiturn?

Just about gathered together all the bits I need. CNC4PC card arrived this week. Taken original controller apart - decided to keep most of it intact and just replace CPU keyboard & interface boards with breakout board - and keep the rest.

Sockets from Rapid turned up today which will let me plug the original leads into the breakout.

Probably see if it works next week some time!

Si

Great news Si, I may follow you down the retro fit road.
The PNC3 is very limited, now I have had a good play with it.

Right! X Position error problem!

It hasn't happen for a few days now, which is good.
But have noticed when I initially power up the machine, but not powering up the drives and press the 'zero' button I get a error message "drive fault in X"
If I just reset and power up drives and zero machine out it seems ok?

Any ideas??


Adee

"drive fault in X"

Whitout the drives enabled there is no power to the stepper drive cards. Therfore the control does not recieve the correct fault signal from the drives.

From what I remember that is exactly how they allways operate.

As Martin says - that's exactly how it should behave!

Si

Hi, did you ever get this sorted out as i'm experiencing exactly the same problem.
Kind Regards,
David

Hi David
I think it came down to taking out the small rapid moves and changing them to fast feedrate moves.

Not sure if all of these machines do the same thing, but this worked for me.
I couldnt find any fault with the x axis, all seem fine.

Adee

Thanks Adee. I'm managing to machine stuff the way you managed by removing the G0's. But i'm really looking for a solution which will let me use them again. Since my last post i've stripped my crosslide and checked the screw/ballnuts, the slide for rust/tightness and the motor belt for wear. Everything is as it should be.
However, when i had the cover off i tried turning the belt by hand with steady finger pressure and noticed that every now and again it would 'jump'. Not jump as in the belt slipping on the pulleys, but almost as if the steps of the motor were not there if you understand. It almost had the feeling of turning a dc motor rather than a stepper motor. Now i've checked that both pulleys are tight so i'm wondering if just maybe my motor is a bit iffy. Does anybody know what an iffy stepper motor is like?
Many Thanks,
David

Does anybody know what an iffy stepper motor is like?

well, a normal one can be rotated by hand and you should feel a slight resistance along with a smooth pulsing/notching through the shaft.

If this is one of those big green round steppers mounted on posts, then I reckon I've seen the same thing on a Starturn8 recently, the slide runs smoothly but the X stalls intermittently and the pulley>motor feels too stiff to me.
Maybe its to do with corrosion or the bearings have worn out, but for the cost of a new motor I'd just replace it.

It could be bearings or corrosion, but that would tend to lead to stiff spots as you rotate the shaft. What you describe sounds like free spots. It could be that there is a load of resistance except in a couple of places where it is easier to turn - which I suppose could give the same effect.

It would be worth stripping the motor and making sure the bearings are free and clean any corrosion off the stator & rotor. The original motors are pretty good as they go so are worth half an hour and a couple of bearings to put them right!

Si

Simons right of course... changing the stepper motors for a newer, smaller one is not that straight-forward.
For me, making new bits fit and work is the best part of it (when you have access to the right equipment that is )

Many thanks for the replies guys. I've considered just replacing the motor, however, all the nema34 ones i've seen would need to be sealed somehow and the nema 23 ones would need an adaptor flange. I have the facilities to be able to make something up for either motor but would rather be able to overhaul the old one. I read on cnczone once that if you take a stepper apart that it loses some of it's magnetism. I don't suppose one of you guys has a 'known good' spare motor kicking around for sale?

Regards,
David

Ok, so an update. Tonight i completely removed the motor from the machine and stripped it down. It is an MAE HY-200-3437-400-A8. The bearings are as good as new and there was no corrosion about it either. After rebuilding it I then turned my attention to the crosslide. Light finger pressure is all that is needed to turn the top pulley and it completed it's travel back and forward several times with no tight spots evident. Any other ideas? I'm tempted to just buy a nema34 from Motion Control!

Regards,
David