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

MERLIncMan

Registered
Registered
Joined
Oct 15, 2020
Messages
208
Fellows,

The PM-727V arrives soon (sabre rattling in the straits of Taiwan notwithstanding....). I got the model with the DRO because - mandatory!

Anyways, yesterday the BS-0 dividing head arrived. It is so little! I laugh because it seems bigger in This Old Tony's gearing videos, I guess he's got smaller hands than me :)
It's actually a pleasant "failure" on the part of China (or India) that the BS-0 is supposed to have a BS-7 taper in the headstock, but actually has MT2. I have three tapers: R8, ER32, and MT2 (not counting the MT4 in the PM-1030, for which I've got an adapter) - I am super happy about that, I am loath to have too many adapters, what for cumulative errors and all...

So! Having searched for a universal dividing head, I was stymied to find a ~5" (125mm) size, and they're all really expensive, and none come with MT2 - and would interfere with the power-feed on the mill in any case. So, I cried and bought the BS-0, thinking the helix was forever beyond me. Not so!

The mill DRO scales are 2 channel 90 degree 5v ~50mA square-wave TTL. Arduino knows what to do with that!

The plan:
1. Tap into the X-axis scale for the A and B (solder and shrink-tube a pigtail breakout).
2. There is a chip - 7474 I think - or a shield that can count the waves and send friendlier data to the Arduino (my weakest area - where I need the most help).
3. Arduino running the program... 16 key membrane keypad and a 2 or 3 line LCD
4. Stepper driver for a NEMA 23 (17 might work, but a bit weak)
5. ~1:2 timing belt-drive from the stepper to the dividing head input.

Program logic is such that I can divide or jog by degree (I found someone's sketch) for simple indexing, but here is where it gets crazy!

I intend to add code such that the TTL gives the Arduino side A of a triangle, and it uses User Input as side B (rotations / unit of linear travel) and by magic of the Tangent, I get a dividing head slaved to the X axis!

Tan = A/B, where A = X axis travel and B = arc of rotation
ARCTAN(A/B) is my helix angle (b), so A*TAN(b) = B
Arduino does steps/rev (with drive pulleys and dividing head worm ratio figured)
Thusly, while in Helix Mode of the program, turning the leadscrew of the X-Axis causes proportional rotation of the dividing head, according to the helix-angle that I select - yes?

The program is to allow for standard divisions (by integer divisor, or by degrees arc; a DivisionMaster clone) and jogs, but have the added menu for Helix:
1. We'll call the dividing head Axis A
2. Enter helix angle OR
3. X : A ratio

This is the plan.
I will need to purchase a NEMA 23, a driver for it, some timing pulleys and belt, and whatever TTL-interpreter chip is best for single axis DRO decoding. I already have the arduino, keypad, and LCD.
Then I will need to adapt the arduino-rotab-driver sketch that I found.

I will 3D print an ABS enclosure for the brains, and machine a mount for the stepper to mount to the T-slots on the mill, between the dividing head and the power-feed bracket - with a key to the dividing head to make it line up easily when mounted on the mill. I will use a nice connector for the X-axis-scale-breakout so that the whole works can easily be removed, and since I'm at it, I'll figure out how to get this thing to also run my 4" tilting rotab as well. Might even put a breakout on the Y-axis-scale as well, but probably not necessary.

The whole project should not cost more than $100 ~ $150 as I already have the BS-0, and some of the electrics. Not bad for an MT2 universal dividing head - the cheapest universal head is B&S-10 taper, 8", and ~$950.00 delivered...

SO!
Seeing as this is intended for my PM-727V, and unless I am mistaken most PM mills have the same DRO scales, this seemed to be the place to put this post - I apologize if that is incorrect.

I hope this to be a community-type project (my coding is terrible - except in Qbasic and DOS!!!) and it'll all be available to you PM-bench-mill owners.

Suggestions? Comments? Criticisms? Angry at me because I put this in the wrong forum group?

Wanna play with the magic-pixies with me?? I need help - especially with the TTL-to-arduino side...

Thanks guys, I hope you like the plan!
 
First, Welcome to the group!

Don't worry, no one here will get too uptight about this being in the wrong place.

I hope you like the plan!

I'd need another read (or two) to understand it better.
All I really got from the first time thru is that you've got an idea and you're excited and determined to implement.

I will be following along!

-brino
 
:D

Revised Standard Abridged Version:
Semi-Universal Dividing Head + Arduino = Helical Milling!
 
An interesting concept. I had seen some strictly mechanical versions for similar machining tasks. Topologically, it is the same as threading on the lathe. The spindle is the driving element and the lead screw advances in sync with the spindle to cut the helix. The Clough ELS substitutes electronics for the gears to accomplish the same task.

In one way, your task is less complicated as every position on a linear scale is unique.

I look forward to reading about your progress.
 
If I live my life well, I'll never have to mill a helix. But this seems like a fun and interesting project. Best wishes!

And you offer an interesting perspective change...when I got my BS-0 I thought it was bigger than expected.
 
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
 
This looks dang exciting.

Oh, Welcome to the best machining group on the web!!! :welcome::party:
 
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.
 
Back
Top