Electronic Dividing Head using the Arduino

[John S]

Chuck,
Are you sure it can hold against cutting forces ?
I built one some years ago, similar design but far bigger and heavier but on splines you could see it cogging and producing helical splines.
Scrapped it and went to worm and wheel.

John S.

 

[cfellows]

Chuck,
Are you sure it can hold against cutting forces ?
I built one some years ago, similar design but far bigger and heavier but on splines you could see it cogging and producing helical splines.
Scrapped it and went to worm and wheel.

John S.

I'm never entirely sure about these things until I actually try it. Other than radial drilling, I hadn't planned on using it to do any kind of milling operation other than maybe gears. Since that doesn't put any rotary torque on the spindle I can't see that there would be a problem with that. In the end I went with this design because 1) I had all the parts needed, and 2) turning the spindle through a worm gear takes a lot of steps. If it turns out not to work, it will be easy enought to convert it to a worm gear.

One thing I've discovered on these bipolar motors is that you can get the motor wiring wrong and it will still work, but with far less torque. Once I got the wiring right, I couldn't turn the spindle by hand, even grasping the large timing pulley.

Chuck

 

[fcheslop]

Hi Chuck, I have been watching with a lot of interest as its a future job.Would it be possible to fit a locking pin to the shaft as per the Harold Hall indexing head that was built on here recently?
Thanks for posting its giving me some idea
kind regards Frazer

 

[Blogwitch]

Frazer,

As already mentioned in another post on here about the same sort of project.

Once you put a manual lock into the system, it can cause major problems.

If you forget to remove the stop when going to the next point, the stepper will stall, but will still count on the electronics as the next numbered step, with all the consequences of what that means, usually, starting from the beginning all over again with a new blank.

John

 

[fcheslop]

Thanks John,thats me back to the drawing board
best wishes frazer

 

[n4zou]

How about a brake that's operated via another stepper motor?

 

[johnmcc69]

Maybe use a solenoid with a detent?
Could be programmed to lock?

 

[Blogwitch]

John,

Maybe use a solenoid with a detent?

Major problem if you are stepping to all different settings.

How do you have a detent for 27 positions, then one for say 39 and another at 76, you would have to have thousands of holes for your detent to drop into to cover every situation.

It is for this reason you use the stepper and it's associated drive system to automatically hold for you as you carry out the machining.

That was why John S came in about Chucks belt drive.
Even though rigid to the feel, when you get cutting forces on there, not maybe for drilling holes, but say for gear cutting, the belt WILL flex backwards and forwards, causing all sorts of weird cutting effects, and if you tighten the belt up to get rid of it, the stepper won't have enough torque to move and will stall. A catch 22 situation.


John

 

[John S]

How about just using a worm drive box that's been used for years and not reinventing the wheel with a puncture ?

 

[Ken I]

Speaking from ignorance here - but why not add one of those small DC motor brakes - the software will ensure its turned on (brake off) before attempting to move the stepper.

This only for static machining not for NC interpolation of helixes or rotary machining.

2c

Ken

 

[johnmcc69]

Bog, you're absolutely correct, that would be VERY ugly.
Even if you "stacked" multiple rings with alternated (staggered
Holes & additional solenoids.)

I'm looking forward to seeing how Chuck handles this...
He never ceases to amaze...

John

 

[ddmckee54]

If I got a vote, and Chuck I realize I don't, I would vote for a mechanical brake on the indexing spindle with a feedback signal to the Arduino for Go or No Go. You already have the indexing code written, a Go/No Go signal would be a simple modification to that code. That way you could lock the indexer and if you forgot to unlock it the Arduino would not try to move until you unlocked the indexing spindle.

Just my 2 cents,
Don

 

[cfellows]

If I got a vote, and Chuck I realize I don't, I would vote for a mechanical brake on the indexing spindle with a feedback signal to the Arduino for Go or No Go. You already have the indexing code written, a Go/No Go signal would be a simple modification to that code. That way you could lock the indexer and if you forgot to unlock it the Arduino would not try to move until you unlocked the indexing spindle.

Just my 2 cents,
Don

I like your idea, Don. I had already decided that if I needed more braking power for some reason, and I'm not yet convinced I do, that a mechanical brake would be easy to add. I don't like the extra step of tightening and loosening a brake between steps but it is an option. Adding a go/nogo switch would be an easy addition. First I want to try some drilling and maybe hobbing a gear and seeing if the motor will hold. Unfortunately, more home improvement tasks have been set before me so it'll be a few days before I can get back to this.

Chuck

 

[cfellows]

This has me thinking about my electronic dividing head on a whole new level...

[ame=http://www.youtube.com/watch?v=ZhICrb0Tbn4]http://www.youtube.com/watch?v=ZhICrb0Tbn4[/ame]

Chuck

 

[Rayanth]

what an amazing amount of control and precision, to get a gear blank to come out that nicely in such a fashion. Impressive for a home-brew.

- Ryan

 

[cfellows]

Did a live test on my dividing head today. I ran two tests, milling evenly spaced flats across a piece of 1/2" aluminum round. On the first test, I cut 9 evenly spaced flats and it worked flawlessly, even holding the piece rock steady during the cutting pass. However, on the second test which I was doing for a video, the stepper started "letting go" during the stop / hold phase. I'm pretty sure the driver was overheating causing it to shut down current to the stepper for short durations. Uploading a video will have to wait for awhile until we get our house put back together (putting down wood flooring).

Chuck

 

[cfellows]

Here's a video of my dividing head in operation. I took the slack out of the belt and put a makeshift heatsink on the stepper driver chip so now it works consistently and reliably. The holding power of the stepper is enough for me to satisfactorily tighten the collet chuck with a crescent wrench. I can get it to slip with the wrench but not easily.

[ame=http://www.youtube.com/watch?v=ODf9sJzXHzA&list=UUZB8pRNp9Plbd0-T9RmyR9g&index=1&feature=plcp]http://www.youtube.com/watch?v=ODf9sJzXHzA&list=UUZB8pRNp9Plbd0-T9RmyR9g&index=1&feature=plcp[/ame]

I've got an Arduino Nano on order that I plan to use in a finished version of this dividing head. I'll also use a separate LCD display and input keys to put the whole thing into an attractive and more robust case. I believe this is going to be a really nice little addition to my shop. Next I might tackle my rotary table.

Chuck

 

[Don1966]

Very nice Chuck, are we going to see any plans in the download section upon completion?
I like the idea of just keying in the divisions.

Don

 

[Blogwitch]

Chuck,

I am truly surprised at how this has turned out, I honestly thought that the belt would flex too much, but you have proved me wrong.

Have you tried doing a bit of machining on the run?


John

 

[cfellows]

Very nice Chuck, are we going to see any plans in the download section upon completion?
I like the idea of just keying in the divisions.

Don

Yep, I can probably throw something together. I assume any kind of plans would have to include wiring diagrams and part numbers for the absolute newbie.