Building my own rotary and need some assistance

[keith]

Hello Everyone,
It’s been a while since I’ve posted, but I am tackling a project and could use some advice. I have an older (2005 era) PRT 96. My project is to build a rotary axis. (But before you say ‘you can buy one!’….I know that. ) I am doing this as a project for a local SolidWorks user group. The project will help develop presentation material, so in the end I’ll be able to present the project (and have a rotary axis J
My question is specifically about the motor. I emailed back and forth with Ryan at ShopBot who was very helpful. I plan on buying the tail stock and making a 4 jaw chuck. The challenge (for me) is the motor. I was recommended to buy an Oriental Motor, with an amp level below 3. With some of the math that Ryan provided, here is what I understand:

• A basic stepper will rotate 1.8 degrees per step, so 200 steps per full rotation.
• My board (ShopBot Controls V3.54) I believe has ¼ stepping., or 800 steps per full rotation
• Sooo….am I to understand that this results in 0.45 degrees per step? (360 degrees/800 steps = 0.45 degrees / step)

If my math is correct, I’d like some recommendations from anyone that has tinkered with this sort of thing as to how I should proceed. My feeling is I’ll need to do a few things:

• Design a motor bracket (most likely will be done on a mill out of aluminum.)
• Add some gearing to increase the resolution.
• Modify the control software and my post.

Am I missing something?
Also, does anyone have experience with buying an Oriental Motor? Do these connect directly to the older V3.54 control boards, or will I have to do some splicing and wiring?
And finally, is it at all practical to buy an identical motor to what comes standard on my X and Y axis? Or are we comparing apples to oranges?
Thanks for the help…any advice would be appreciated.
-Keith
PS: If Ryan is reading this...thanks again!

[Burkhardt]

A direct drive rotary with a stepper motor will leave you with too little resolution and too little torque rigidity. Usually the reduction is 1:5 for very small diameters up to 1:100 for larger diameters.
On my machine I use a 1:50 harmonic drive gearbox with a smallish stepper, sourced as a combo through eBay for about $400. it can do 7500 degrees/minute which is ample. I built the tailstock myself but used a Oneway Talon 4-jaw chuck. I can dig out some pictures if that helps.

[keith]

Yes, pictures would help greatly. For reduction, is it reasonable to find a solution (homemade, bought on ebay, etc) and then just configure the values in the post and control? Thanks.

[JimmyD]

Keith,

I built my own rotary a few months ago and had indispensable help from Gary Campbell, screen name IslaWW. He set up the gear reduction and the motor/driver for me. I highly recommend his assistance and expertise. My indexer is shown in the following thread. http://www.talkshopbot.com/forum/sho...-indexer-lathe

If I can be of any assistance just ask.

Jim

[Burkhardt]

I found the pictures...here it is. Back then (2013) when I built it, the seller of that 1:50 gearbox (forgot the name) had it only with a 3-jaw chuck and I adapted the Talon chuck myself which was a pain in the behind. I believe nowadays you can buy such gearboxes on eBay with 4-jaw chucks already installed from various Chinese companies. I am happy with mine. It is backlash free and rigid enough for the size of parts that fit my machine (up to 6" diameter and 34" length).

I made the tailstock myself. Not sure if that was a great idea since you can buy them for little money as well. The advantage of my design is the precision adjustability of the live center in Y and Z direction. That helps if absolute cylindrical symmetry is required (see last pic as example).