Slaved Motors Pros & Cons

[destro]

Hi everyone,

Some friends and I are are making a CNC plasma cutter for a final project. We are tying to decide if we should use slaved motors for the long axis with rack and pinion. I have read alot of posts here (it has become a valuable resource ) and people are either for or against it. I was hoping people could post their opinions about this, especially those who have used it (successes and failures) and how they used it (how its slaved, driven, ect.).
I am hoping to post our initial design drawings here by the end of the week.

Thanks
Steve

[freak_brain]

It has it's good sides and bad I guess. What I believe one should be most concerned with when slaving motors is to make sure your motors are big enough to do what you want them to do. If one motor misses a step because of the lack of power...or for any reason.... it can get ugly. It works really nice with MACH3 and is mainly set up in the software. Mechanically driving both sides with one motor has it's good and bad sides too. The good is, that if your motor misses a step it is missed on both sides since it is driven with one motor. The bad is that you have to get the drive over to the other side. I hope this helps you make your decision. I'm not really sure there is a right or wrong here. It's a personal preference thing!

Allen

[jcc3inc]

Sir,

It depends on the size of the machine which you plan to make and whether you want to do routing or plasma cutrting. If you can give us more requirements, it is easier to answer you.

Regards,
Jack C.

[destro]

It will be a 4x8 cutting area and it would be for plasma cutting only. The other features we are planing on using are:
- Stepper motors
- Gecko drives
- Mach 3
- MP1000-THC
- Rack & Pinion for X & Y, Ball screw for the Z
The other features are design related and I will be posting drawings soon.

Thanks freak brain & jcc3inc for the responses I hope this is enough info.

Steve

[Torchhead]

I have been running a slaved design now for almost 4 years. No major problems. My gantry was pretty heavy since I originally built a combo router/plaz cutter. It's 100% plaz now. I had pretty wimpy servos so using one with a jackshaft all the way across the table did not seem like a good idea....besides I had twin ballscrews so the transmittion would have been a real Rube Machine. I like the fact that I can square my gantry with the table simple by moving one of the home switches. A lot of the commercial machines use the single big motor and jackshaft approach but they have the tooling to properly turn and align the shaft and mount the bearings properly.

Are you going to direct drive the rack pinions off the stepper or use a belt reduction? Most tables I see with steppers use about a 3:1 belt reduction so you are operating in the best part of the torque/speed curve. You need torque for rapid acceleration (good for making detailed cuts and sharp corners) and speed for the longer cuts and rapids.

Tom C
CandCNC

[destro]

Thanks Tom;

We were definitely planning on using a belt reduction but haven't got as far as the ratio so I will keep the 3:1 in mind.
How are your motors slaved, in the hardware or software?

Also, we were thinking of making the bed slightly bigger than 4x8 so a full sheet has a 3" border around it. Do you think this is nessesary?

Steve