Axis sticking

[jolyonjenkins]

I have a Denford Micromill. I have replaced all the Denford electronics with new generic stepper drivers
like this

https://www.ebay.co.uk/itm/352981992806

and it now runs on Linuxcnc

It all used to work fine with the old Denford electronics until I fried them.

BUT now the Y axis is sticking. Sometimes it makes a grinding noise and won't move past certain points in either direction. These points vary. Other times, it moves fine. Sometimes I need to give it a helping hand (i.e. I give it a shove and then it moves). It has the feel of a mechanical problem but I cannot see anything that could be blocking the motion, and it is all lubricated. The wiring seems OK (I have swapped round the drivers and the same thing happens). I messed around with the dip switches to change the microsteps and I also gradually increased the max current. But when I went from 2.5A to 2.7A the driver blew so now I am waiting for a new one.

So in the meantime, any bright ideas?

[Clive S]

I have a Denford Micromill. I have replaced all the Denford electronics with new generic stepper drivers
like this

https://www.ebay.co.uk/itm/352981992806

and it now runs on Linuxcnc

It all used to work fine with the old Denford electronics until I fried them.

BUT now the Y axis is sticking. Sometimes it makes a grinding noise and won't move past certain points in either direction. These points vary. Other times, it moves fine. Sometimes I need to give it a helping hand (i.e. I give it a shove and then it moves). It has the feel of a mechanical problem but I cannot see anything that could be blocking the motion, and it is all lubricated. The wiring seems OK (I have swapped round the drivers and the same thing happens). I messed around with the dip switches to change the microsteps and I also gradually increased the max current. But when I went from 2.5A to 2.7A the driver blew so now I am waiting for a new one.

So in the meantime, any bright ideas?

Are you saying it worked with the drives you have now or with the original drives ?

Is the Y axis stiff to move or is it binding .

What micro stepping and speeds are you using ?

Can you post your hal and ini files ?

[jolyonjenkins]

I think it may have been a lubrication issue, since the axis is now moving freely.

However, I still have a problem. Both the X and Y axes will occasionally miss steps. I can run it overnight and find it still in the right place next morning, or I can leave it for a few hours and find it has shifted 1 or 2 cm. Which is no good.

All the cables to the steppers and from the BOB to the drivers are shielded

The hal and ini files are attached. I didn't change them much from when I was using the Denford drivers (when everything worked fine).

I have tried various microstepping settings since to be honest I don't really understand the issue. The ones that have worked best are 400 pulse/sec, described as 2A and 2B on the drivers.

[Clive S]

I think it may have been a lubrication issue, since the axis is now moving freely.

However, I still have a problem. Both the X and Y axes will occasionally miss steps. I can run it overnight and find it still in the right place next morning, or I can leave it for a few hours and find it has shifted 1 or 2 cm. Which is no good.

All the cables to the steppers and from the BOB to the drivers are shielded

The hal and ini files are attached. I didn't change them much from when I was using the Denford drivers (when everything worked fine).

I have tried various microstepping settings since to be honest I don't really understand the issue. The ones that have worked best are 400 pulse/sec, described as 2A and 2B on the drivers.

I don't see much wrong but I would try changing

setp stepgen.0.dirhold 150000 to 35000
setp stepgen.0.dirsetup 150000 to 50000

for all axis.

Also on another note why do you have the Z home at -40

It should be -ve going down and +ve going up .

If you have it like that its fine but it means that when you home the Z it will move down 40mm and if there is something on the bed it could crash.

What voltage are you supplying the drives with and what current setting do you have

[jolyonjenkins]

Thanks. I will try those settings
The Z axis is like that just because I never use the whole Z height and it's convenient to have it come down a little after homing
I have 36V going to the drivers and the current is set to 2A (2.2A peak). When I set the current to higher, it seems to cause the drivers to switch off (I thought I'd blown one but it just seemed to have shut off)

[Clive S]

36v is a bit high for those drives your right on the limit.

[jolyonjenkins]

Yes it's higher than I expected. I just took the 28V AC from the existing transformer and put a bridge rectifier and huge capacitor in place, and forgot that the DC voltage would be higher.
Would this cause it to be inaccurate do you think?

(The hal file edits you suggested doesn't seem to have improved it; I've slowed down the maximum speed to see if that makes any difference)

[dazp1976]

You buy drives worth £8 or less.........
You get performance worth £8 or less.

[Clive S]

Yes it's higher than I expected. I just took the 28V AC from the existing transformer and put a bridge rectifier and huge capacitor in place, and forgot that the DC voltage would be higher.
Would this cause it to be inaccurate do you think?

(The hal file edits you suggested doesn't seem to have improved it; I've slowed down the maximum speed to see if that makes any difference)

28V AC rectified will be about 39.6V the drive max say 40V

[jolyonjenkins]

28V AC rectified will be about 39.6V the drive max say 40V

Yes but I guess there is a voltage drop from the rectifiers too. I will add a voltage regulator and bring it down a bit. It seems to be working ok at a lower speed so hopefully a cleaner and lower supply will let me take it back up again.

[JAZZCNC]

You buy drives worth £8 or less.........
You get performance worth £8 or less.

Daz you took the words from my mind.

To the OP with 28V voltage, you are playing Russian roulette and you will blow those drives if you try to run at high feeds and deaccelerate quickly as the steppers turn into dynamos and dump 40v + back into the drives.! . . . . . . Careful with the regulator as well because if it shuts down with the back EMF you'll get hassles.

My advice is to buy decent drives and throw those toys away and run the higher voltage, it will transform the machine.