Manual Operation After Cnc Conversion

[JimDawson]

I take it that [decouple] is electrical rather than mechanical?

It's more magnetic, the motor tries to keep stepping, but can't. It just sits there and growls. Under some conditions, like trying to run faster than the motor wants to go, a stepper will do that even with nothing attached to the shaft.

 

[JimDawson]

Read up on the drives - it's one of the things you set when you are configuring the drives.


Actually, 3 or 4 times full load torque, plus the impulse from the load back driving the screw
Then have a good "safety factor" so the controls guy doesn't break anything when he does it all over again..

Jim, I see you have been there and done that! A controls guy wouldn't do that

 

[Jim_Hbar]

A controls guy wouldn't do that

I strongly suspect that we know a few of the same people...

 

[hmwhitehead]

Here is what I did for my conversion. I am using NEMA 23's with 430 in oz torque with at 4.5:1 belt drive reduction. By using a belt drive I am able to keep the handles on the lead screws. (I have just upgraded to ball screws). Maximum speed is around 15 in/min. on the X and Y axis at 24 volts. I am currently working on changing that to 36 volts so should get a few more inches/minute once that is done.
In order to eliminate the voltage feedback when operating the mill manually, I have installed DPDT relays between the amplifiers and the motors which breaks the circuit when the CNC is not being used. Otherwise, if you do not do this, you will blow the driver transistor in the amplifier (learned that the hard way) when using the mill manually.
Hope that helps, HarryView attachment 123256 View attachment 123256

 

[wjstape]

When converting to CNC, can I use dual shaft steppers with a hand wheel on the outside shaft to use the mill manually by simply unplugging the motor before manual operation?

I like the idea of being able to do a quick manual job.

Hi,I've converted several manual lathes to CNC and all case I wanted to retain a manual capability. Here are some things to consider:
- If you put handles on the stepper motor rear shafts the handles will spin when you are running in CNC mode, so be careful of the flying handles - you could get hurt.
- All my machines had a lead-screw setup that moved .0005 per revolution so when you wish to hand crank the machine you will do a lot of cranking - not fun.
- most CNC control software proved you with MDI and MPG control modes so you can run your machine in a semi-manual manner. I use MACH 3 and a Shuttle Pro MPG which works really well. No need for hand cranking.

 

[Billh50]

I am thinking of converting my mini-lathe to CNC. I am thinking that if I use dual shafts and put a piece of round stock set screwed onto the shaft with cross slots. I could make a wheel that fits over the piece with dowels in it to fit slots for manual operation and remove it for CNC. Does this sound very feasible?

 

[JimDawson]

I am thinking of converting my mini-lathe to CNC. I am thinking that if I use dual shafts and put a piece of round stock set screwed onto the shaft with cross slots. I could make a wheel that fits over the piece with dowels in it to fit slots for manual operation and remove it for CNC. Does this sound very feasible?

Completely feasible. Should work great

 

[cozmogeek]

I thought I'd want to have handles still after converting my mill but I've found that I can just use the USB pendant controller or the computer keyboard to move things around. It's a lot easier to hold down an arrow key than to crank and crank that stupid handle

 

[Firebrick43]

View attachment 123255 View attachment 123255 View attachment 123258 Here is what I did for my conversion. I am using NEMA 23's with 430 in oz torque with at 4.5:1 belt drive reduction. By using a belt drive I am able to keep the handles on the lead screws. (I have just upgraded to ball screws). Maximum speed is around 15 in/min. on the X and Y axis at 24 volts. I am currently working on changing that to 36 volts so should get a few more inches/minute once that is done.
In order to eliminate the voltage feedback when operating the mill manually, I have installed DPDT relays between the amplifiers and the motors which breaks the circuit when the CNC is not being used. Otherwise, if you do not do this, you will blow the driver transistor in the amplifier (learned that the hard way) when using the mill manually.
Hope that helps, HarryView attachment 123255View attachment 123256 View attachment 123256

With ball screws how do you keep the cutting loads from back driving the axis???? I work on large cnc machines and without the servo/brake it's very easy to back drive the axis, a single finger on some of the linear way machines, a palm on standard box ways once stiction is broken. Acme screws have enough friction for the most part. Vibrating/pulsing loads can sometimes cause an acme to slowly back drive occasionally

 

[JimDawson]

With ball screws how do you keep the cutting loads from back driving the axis???? I work on large cnc machines and without the servo/brake it's very easy to back drive the axis, a single finger on some of the linear way machines, a palm on standard box ways once stiction is broken. Acme screws have enough friction for the most part. Vibrating/pulsing loads can sometimes cause an acme to slowly back drive occasionally

You are correct the ball screws present so little friction that it can be an issue even when taking light cuts. Since I have no table locks on my machine, when operating manual, I have one hand on each wheel to prevent movement.