Adding An Encoder To A Dividing Head?

[Susquatch]

I just can't resist.......

You enjoyed that didn't you?

As soon as you said 200 steps per rev, I was done thinking about it. Why the 10:1 belt drive (I assume cogged timing belt)?

Out by one whole second.

Do we care?

Nope. Unless it accumulates in constant turning applications.

My only concern with automating the positioning is the impact of forgetting to lock or unlock the spindle as each tooth is cut.

 

[jcdammeyer]

You enjoyed that didn't you?

Yup!

As soon as you said 200 steps per rev, I was done thinking about it. Why the 10:1 belt drive (I assume cogged timing belt)?

I mentioned the belt drive and reduction for two reasons. It's usually easier to mount a motor to something and not worry about alignment. Although my little motor on the small rotary table is direct drive. But then I didn't want to the nearest 1 second accuracy. Not even sure the table worm and gear has that level of accuracy.

Even at 400 and 10:1 it was 0.0025 degree positioning. Let's say I want to make metric change gears for my lathe. 100 and 127 tooth. The 127 tooth is a tooth every 2.834645669291339 degrees. With the 0.0025 positioning that means 1133.858267716535 steps (or encoder edges if just counting an encoder on the hand wheel at 10:1.

Counting lines on the hand wheel and turning it enough to move the table 2.834645669291339 degrees is virtually impossible but lining up the pin into a hole on a disk that is one of 127 holes is very accurate.

Or in my case I'd set my ELS to jog the correct distance (within the math resolution inside) and then on each press of the jog button it would turn the hand wheel as close as physically possible to 2.834645669291339 degrees.

Nope. Unless it accumulates in constant turning applications.

Ah yes. Good call. Which is why you set the Z home position for the first tooth. Then after the 127th tooth you don't start again but return to the home position.

My only concern with automating the positioning is the impact of forgetting to lock or unlock the spindle as each tooth is cut.

Too true. If I was adding a custom rotary table feature I'd want to also add a solenoid or even the X axis motor to operate the locking lever. Motor drivers are so cheap nowadays (along with BoBs) I'd just make a dedicated power unit for it and then unplug plug the lathe DB-25 cable and plug in the Rotary Table cable.

I've see youtube videos of people driving the table directly via toothed belt. They make the assumption that the belt and motor are stiff enough to hold the table. Of that I'm not sure. I'd still want to lock it manually.

OTOH, my Harmonic Drive 4th axis (project #42) is supposed to be stiff enough when held in position to not need a manual lock. Don't know yet. Seems like it is.

 

[Susquatch]

Not even sure the table worm and gear has that level of accuracy.

Not even close...... LOL!

Very Cool John. I love it all. I admire your dedication to the task.

Me? I'll just keep cranking handles - close enough for a gear that will never know the difference.

 

[jcdammeyer]

A bit of internet searching brings up this calculator and since I have a set of M0.5 gear cutters seems the ideal set of values to use. I think the cutters are 20 degree pressure angle.

Gear Dimensions Calculator | Evolvent Design

Calculator to make the right dimensions for a gear or gear blank: calculate gear pitch, outer diameter (OD), root diameter, and clearance.

evolventdesign.com

Inputs
Number of Teeth: 127
Module: 0.5
Pressure Angle: 20 degrees
Gear Type: External

Outputs
OD Reference: 64.5000 mm 2.5394 in
Pitch Diameter: 63.5000 mm 2.5000 in
Root Diameter: 62.2500 mm 2.4508 in

Addendum: 0.5000 mm 0.0197 in
Dedendum: 0.6250 mm 0.0246 in
Working Depth: 1.0000 mm 0.0394 in
Whole Depth: 1.1250 mm 0.0443 in
Circular Pitch: 1.5708 mm 0.0618 in
Tooth Thickness: 0.7854 mm 0.0309 in
Base Circle: 59.6705 mm 2.3492 in
Undercut: No

If I understand the values then I make a disk which is 65.5mm diameter and after touching off the spinning cutter do a depth of 1.125mm.
So then it's just a matter of turning the blank to create 127 positions. If I have a chance I'll take a stab at this. Never cut a gear before.

 

[Susquatch]

So then it's just a matter of turning the blank to create 127 positions. If I have a chance I'll take a stab at this. Never cut a gear before.

I enjoy cutting gears and even changing them. My lathe is one of those semi gear boxes that have 16 gear changes built in and then the rest done by changing gears.

They say happiness is a choice. I choose to be happy changing gears. Lots of ways to find happiness. Maybe, despite being the father of ELS, you will find happiness changing gears too.

 

[jcdammeyer]

I enjoy cutting gears and even changing them. My lathe is one of those semi gear boxes that have 16 gear changes built in and then the rest done by changing gears.

They say happiness is a choice. I choose to be happy changing gears. Lots of ways to find happiness. Maybe, despite being the father of ELS, you will find happiness changing gears too.

Actually the reason for the ELS was that to do threading on the Gingery Lathe I'd have to build the mill, shaper and dividing head to be able to cut gears for the lathe to be able to thread. Instead the ELS with the DB-25 parallel port connection so it could run the lathe or the lathe could be run by what was then MACH2. Still have the PC that has MACH2 on it. Like my son, I have trouble disposing of things that work. Unlike my son I do dispose of things that don't.

But I still want to try redoing this project with metal gears. It was to be for the Robot Arm tool changer idea but since then of course I got into the AR3/4 Robot arm kit and that's now project 42 (also unfinished). Plus I can't really do any of this the way I'd like until I finish my harmonic drive 4th axis and cast the case and face plate (both projects #42).