Magnetic scales on new gantry mill

Hi all,

I am designing a new machine and would like to use Ditron magnetic scales on X & Y. 

• The Y axis has dual motors, should I use a scale on each side or just one?
• Any recommendations of mesa boards to use here? 7i95T + 7i84U or 7i96 + 7i85
• Whats the process for setting this up in LCNC?
• I don’t believe these scales are differential signal, should I look for that?
  
  Many thanks for your help!

jackdavies wrote:

The Y axis has dual motors, should I use a scale on each side or just one?
Any recommendations of mesa boards to use here? 7i95T + 7i84U or 7i96 + 7i85
Whats the process for setting this up in LCNC?
I don’t believe these scales are differential signal, should I look for that?

1. You should, the expense does not justify having missed steps on one side and ending up with a miss aligned gantry
2. For step/dir drives, 7i95T should be enough if you do not need a lot of IO. So a 7i84 would be required on both combos if you do need more IO.
3. a bit of editing will be needed either way, plenty of info and help here once you get to that point
4. differential are better for noise immunity, but Mesa works with both differential and single ended. They should be incremental TTL, as far as i know. Absolute type would require other boards/config/ depending on type of comms.

I use Ditron magnetic scales all the time. Installed my first ones in 2019 on my 5 axis machine. Since the I have used installed about 20 of them. Not a single failure yet.

Be sure to specify that you want 1um resolution. Reader head model DMR2000. And also specify that you want the index pulse version (z signal) otherwise you get only A and B.

Yes. They are differential output

Henk

What's the difference to linear scales with glass scales?

Thanks Henk,

super useful!

Is the index Z pulse that you mention the R/-R signal on this table?

www.ditron-dro.com/product/ditron-high-p...g-machine-dro-tools/

Megnetic are cheaper but more dust tolerant, just like rotary encoders.
Pros are price and dust/ contamimation tolerance, unless you get them full of steel shavings they will work.
Optical, glass scales will fail sooner than magnetic if you install them within fine dust presence area.
Big con is magnetic field sensitivity. Use of magnetic holders for coolant/air nozzles may shift your readings.
My(£100 motor and driver) magnetic encoder servo motors suffer so bad(plastic encoder covers) can make them rotate 3°(0.1mm axis move witn 10mm pitch screws) by putting magnetic indicator base next to them. Running spindle makes z motor 120mm away move the axis up/down 0.02-0.05mm and with right spindle speed it would start oscillating into oercurrent error. swapped the motor to optical encoder(£40 extra) and it all went away...