Spoof the DRO scales to drive a Dividing Head for Helical Milling

[Lo-Fi]

Welcome!

Helical milling is fun, I've been working on my geared setup. Look at TouchDRO and the Clough electronic leadscrew projects for inspiration, they both deal in encoders and linear travel. Looking forward to seeing the project as it progresses.

 

[MERLIncMan]

I think I'll stick with my geared version ----

Well, you're just one of those lucky guys who found him a fully universal DH then aren't you

I'd love a BS-2, but it's super expensive, and the headstock taper is B&S-10 rather than the stealth MT2 (that is supposed to be a B&S-7, but is not) of my BS-0 HD.

Also, the change gears would interfere with the power-feed (or vice versa) as, for some reason, all table accessories bolt on the left....

Anywho - I'm a bit jealous of your change gears, but I'll have infinite divisions! - well, up to the max of the microstep I suppose

 

[MERLIncMan]

The scale output is TTL (0-5 volt) already so I would think you could feed it straight to the Arduino. No?
A 7474 is a flip-flop, would trigger a data edge by a clock or give a divide by 2
-Mark

Arduino will accept the TTL easily (AFAIK), but arduino has issues with converting the pulses or something... the 7474 was suggested by somebody on some forum somewhere for making an arduino-based DRO, the idea being that it does "the heavy lifting" (whatever that means) and gives more arduino-friendly digital signals.

I honestly haven't figured it out yet... When I began this adventure, I figured the arduino would have no issue with TTL, but apparently the clock speeds or something... yeah... I recall reading 40mHz somewhere... can't remember the context

Still putting together the details on that part.

You sound like you know what's up? Wanna do weird tinkery stuff with a mag-scale?

 

[MERLIncMan]

Well, I made a Clough ELS, so I guess I could make this too, if I had a dividing head. My brain keeps threatening to duct tape a stepper to my little rotary table. I could probably adapt the setup to that. I don't know when I'd use it, never been quite sure why one couldn't do the same thing on the lathe with the right TPI or similar and the proper cutter.

YOU!!

YOU!!!!!

(!!)

Yes.... let us plot together!

The dividing head is merely adjunct, peripheral, end-user... the ability to slave a stepper to a TTL scale, with suitable options for the ratio of that slavery; this is the meat-n-taters of the idea

The applications are ENDLESS!!!

Yes... let us scheme?

(Pardon the enthusiasm...)

 

[MERLIncMan]

Thank you sir!

This looks dang exciting.

Oh, Welcome to the best machining group on the web!!!

 

[ttabbal]

YOU!!

YOU!!!!!

(!!)

Yes.... let us plot together!

The dividing head is merely adjunct, peripheral, end-user... the ability to slave a stepper to a TTL scale, with suitable options for the ratio of that slavery; this is the meat-n-taters of the idea

The applications are ENDLESS!!!

Yes... let us scheme?

(Pardon the enthusiasm...)

Indeed enthusiasm is there.

Well, first thing is reading the scale. I only have glass scales here. I understand they use quadrature encoding. It sounds like you want to use a magnetic scale? Do you have any idea what the waveforms look like? The touchDRO project documents some different types of scales. They might have some useful code to start with.

 

[markba633csi]

Use your bookmarking feature often for those little tech tips you see on other forums- sometimes saves hours of work not having to blaze a trail that someone else has already blazed, I've found.
(Speaking of the Arduino interfacing stuff, that is)
Nothing more frustrating that coming across something useful on the net then needing it a couple days later and forgetting where you saw it.
-Mark

 

[MERLIncMan]

Indeed enthusiasm is there.

Well, first thing is reading the scale. I only have glass scales here. I understand they use quadrature encoding. It sounds like you want to use a magnetic scale? Do you have any idea what the waveforms look like? The touchDRO project documents some different types of scales. They might have some useful code to start with.

I do believe that the PM DRO is magnetic rather than glass - the docs say 90 degree square waves 0-5v. I'll go for a search on TouchDRO and see what I can purloin. Stealing the A and B leads from the scale ought to be rather straightforward, and I think one CAN put that directly into Arduino digital I/O pins, but I recall that it tends to lose a pulse here and there doing it this way - necessitating some conditioning of the TTL. I would need to identify the proper shield/module (I believe it is 7474 based) and then find the libraries for that connection.

Will read up a bit more and report back.

 

[MERLIncMan]

Use your bookmarking feature often for those little tech tips you see on other forums- sometimes saves hours of work not having to blaze a trail that someone else has already blazed, I've found.
(Speaking of the Arduino interfacing stuff, that is)
Nothing more frustrating that coming across something useful on the net then needing it a couple days later and forgetting where you saw it.
-Mark

You are correct, of course. Is why my bookmark bar is.... a bit overloaded

I found it while reading on the Arduino-DRO using Igaging scales. I do not believe that Igaging scales will match the PM DRO scales, but there are many generic TTL scales, and I should be able to find a shield/module/schematic on that logic.

Besides, in Google's haste to command and control everyone on the planet, they've accidentally made it possible for me to retrace my own steps - if I put the right search-string back into their searcher, the first links to come up are the ones that I've already visited, with dates even.

But yes, I should use my bookmarks more - and organize them somehow :/

 

[ttabbal]

I do believe that the PM DRO is magnetic rather than glass - the docs say 90 degree square waves 0-5v. I'll go for a search on TouchDRO and see what I can purloin. Stealing the A and B leads from the scale ought to be rather straightforward, and I think one CAN put that directly into Arduino digital I/O pins, but I recall that it tends to lose a pulse here and there doing it this way - necessitating some conditioning of the TTL. I would need to identify the proper shield/module (I believe it is 7474 based) and then find the libraries for that connection.

Will read up a bit more and report back.

I don't have PMs DRO, so I can't be sure. If you post a pic of the scale, we can find out though.

If the signal from the scale is too fast for arduino, it might be better to use a different microcontroller. There are some with hardware built in to deal with fast signals. If it's quadrature, which you can boil down to TTL square waves, then the one Clough42 used on the ELS is a good choice. It has a hardware quadrature decoder built in that simplifies it significantly and helps prevent missed signals.