Fehlmann Picomax 50 CNC conversion/refurb

[Robin Hewitt]

repeating position over 200mm for the x and 150mm for the y better than 0.01mm (in fact pretty consistently within 0.003mm)

3 microns is an interesting number BUT what about the backlash?

[Agathon]

3 microns is an interesting number BUT what about the backlash?

What backlash? This thing is Swiss! I would think that the 3 microns is simply down to vibration in the mechanical loop between the digital dti and the mount. If you're not careful you might provoke another mind numbing video!

[EddyCurrent]

Try the attached spreadsheet (I use LibreOffice if you don't have excel)

Just enter the desired spindle speed in cell A4 and it will calculate the inverter frequency and contactor to energise.

That logic needs put into a Brain using Mach3 DRO 169-Cmd SpindleRPM as the desired frequency.

It uses an inverter frequency up to 100 hz and assumes the manual adjuster is set to 1.5 * motor speed, so for the 1400 speed it's set to 2100 RPM then the inverter will take it to 4200 RPM

[Agathon]

Try the attached spreadsheet (I use LibreOffice if you don't have excel)

Just enter the desired spindle speed in cell A4 and it will calculate the inverter frequency and contactor to energise.

That logic needs put into a Brain using Mach3 DRO 169-Cmd SpindleRPM as the desired frequency.

It uses an inverter frequency up to 100 hz and assumes the manual adjuster is set to 1.5 * motor speed, so for the 1400 speed it's set to 2100 RPM then the inverter will take it to 4200 RPM

Thanks, that's really kind of you. I do have Excel so I'll take a look.

Can anyone tell me what G0 code will make the x axis move +100 back to zero and then +100 repeatedly - say 10 times? I'm looking around for a simple answer but can't seem to find one.

[Agathon]

Ignore that last request I worked out how to do it - probably in a very labourious way but none-the-less it worked.

[Neale]

3 microns is an interesting number BUT what about the backlash?

when I was testing the touchplate setup on my router, I was getting repeatability to within +-0.003mm. Quick back-of-envelope sums showed that this was equivalent to one microstep. Might this be why this magic number is there? Mind you, my backlash is a bit more than that..

[Agathon]

As it happens Neal I've just run some more tests. Prepare to fall asleep! Contrary what the fool in the vid says, the Y does seven cycles!

Despite all the grunting (not mine) the steppers don't appear to be losing steps at 2500mm/min.



Actually, I don't know what the backlash is yet. I would think it was small but I need to set-up a proper test.

[Agathon]

Just measured the back-lash at 0.03mm on each axis. I'm a little surprised by this since I can't push/pull either axis by more than 0.01mm. The motors are coupled to the screws with flexible star-type couplings (see pic) - which are original and in good condition, but I have to say I've always been suspicious of. Now they are robbing me of precious microns!

Seriously though I can live with 0.03mm.

[Robin Hewitt]

Seriously though I can live with 0.03mm.

I used to tell myself that I could live with a slight backlash but deep in my heart of hearts I knew it wasn't true.

I move 5um per step. Could I watch it step 6 times without moving the table then sleep at night?

Difficult question...

[Agathon]

I used to tell myself that I could live with a slight backlash but deep in my heart of hearts I knew it wasn't true.

I move 5um per step. Could I watch it step 6 times without moving the table then sleep at night?

Difficult question...

I'm not sure I can either! After I posted I took another look and the back-lash is at the feedscrew. I think I slackened the pre-load on the X too much and need to tighten up the Y. Watch this space....