Adding a DRO and want to integrate with linuxcnc, recommended hardware?

Hello,

I've been a longtime LinuxCNC user, I can't quite recall but definitely since the EMC days.  Always had a lot of fun and a great experience.  Right now I've got a great setup with a desktop manual+CNC machine that can run in either mode.  Everything is working well.

I want to add a DRO, something like this Little Machine Shop DRO package that uses read heads and linear bars to measure positions.  If I got that, it wouldn't integrate with LinuxCNC at all, so obviously that's no good.

I read about the encoder setups folks are using, but I'd rather something that was post-backlash and also I like the idea of never having to home (with an absolute measurement).

Does anyone have a similar setup working well?  What hardware would you recommend?  I'm happy to spend money for the right solution.

The best I've come up with so far (with ChatGPT's help) is:

• Encoders: Heidenhain LC 483 Absolute Linear Encoders on all axes
• Interface Card: Mesa 7i93 FPGA Card with 7i74 RS-422 Breakout Board
• Power Supply: Dedicated 24V DC linear power supply
• Mounting Hardware: Custom brackets and protective enclosures

Thanks!

Andy

Do you plan to use this for CNC closed-loop positioning or just want a DRO for a manual mill?

Both -- my setup has steppers that have handles on the ends. Right now it works great for both CNC and manual mode, albeit without a DRO if you're in manual mode (motors off).

My dream is to be able to boot up linuxcnc and use that as a display for a DRO and also have it be able to enable CNC mode at any time.

Here's a photo:
 

Do you already have it set up for LinuxCNC? What hardware are you using now?

Starting from scratch I think I'd get a 7i93 plus a 7i47S. (I think that might be the most inexpensive Mesa option with full functionality.)

Mesa 7i95T should do the job. As for the encoders, you need regular TTL linear glass scales. No need to shell out money for Heidenhain stuff. Chinese ones will work just fine for this application.

It currently runs LinuxCNC with a Stepperworld FET-3 board (see attachment) that I got for Christmas of 2006.  Amazingly the entire setup still works perfectly with a PCIe parallel port card.

I'm happy to get a Mesa board, they look very nice.  I'm also happy to upgrade the stepper driver board, I've definitely gotten good value out of mine.  Do you have any recommendations for drivers that are easy to use with the Mesa boards?  If I'm buying new hardware I definitely want to go with whatever will work well with LinuxCNC and a Mesa board.  Perhaps the 7I32, but that is only 2 motors?

My understanding of TTL glass scales is that they are all incremental encoders.  Is there a version which is absolute?  Or am I overly worried about this and I should just accept that I should home it and basically leave it on all the time?

I think you will find that absolute encoders are considerably more expensive

If you don't go with expensive absolute encoders make sure you get glass or magnetic encoders with index signals for accurate homing. It doesn't look like a quick homing operation at power up would be a problem with your machine.

Also pay a lot of attention to how you will install and adjust. You need to install/adjust colinear with the axis movement. On my lathe, I found machined surface for X that works great with magnetic.

I use mesa boards with glass and magnetic encoders with index signals. I enable the quadrature error detection. I needed to update mesa firmware and add a connection or two to get the Stepgens to reset on the encoder index. That was quite a while ago, not sure if config index default is automatically correct.

Got it, thanks.  I'm OK with expense, if I do go with absolute encoders, is there a recommended path for a board + integration with LinuxCNC?