Series 1 CNC Motor upgrade

[austin.mn]

I have a Series 1 Boss 3 machine

I have upgraded the motor drives to some compumotor microstepping drives, but the stepper motors that are on the machine just don't microstep. They will pretty much only do full stepping.

What has everyone else replaced the large beehive steppers with? has anyone used the Nema 42 motors from keling? I had thought that would be the easiest solution, I don't have the $3500 to get it switched to brushless servos, although I think that would probably be the best solution. I just want some better resolution for 3D contouring on parts. At the moment you can see a step notch on parts that I would really like to be rid of.

[fredhh47]

The best that the Boss 3, 4, and 5 machines could do was .001 steps, after the pulley/belt reduction. The boss 6 finally progressed to .0005 steps, but that wouldn't be good enough for what you seem to want. Still, are you sure it's the stepper and not your software? I make complicated 3d contours on my servo driven CNC and frequently use .010 steps to save program size, and still get a fairly smooth surface with a 3/16" ball endmill. Maybe your software is creating larger steps than you think. There may be a default setting that you overlooked. As for steppers I would think a robust type 42 would be fine. I think that the Boss 5 steppers were rated at something like 1700 oz/in (I may be wrong), and they were reduced about 5:1 or so (again, not sure of exact numbers). Food for thought.

[titchener]

You might be better off with a size 34 motor, the latest generation of these motors have a lot of power for their size, and you can probably find one that has at least as much power as your current older motors.

I'm using the 34 size 1800 oz-in motor from here on the knee of my BP clone machine:

http://www.homeshopcnc.com/RSstepperMotors2.html

Its handling the knee pretty well, and seems to have as much power as the vintage 2000 round size 42 steppers I have on x and y.

Picking the correct stepper is tricky as the bigger you go the lower RPM range the motor has, so depending on your gearing contraints (ie how much you can gear down) you sometimes are better off with a smaller motor because it will make more torque at the RPM's you need with your gear ratio.

Paul T.

[austin.mn]

Here is a picture of one the parts that I make. they are custom corvette emblems. they sand out just fine. But I know that I can save myself a bunch of work if I could keep the step notchyness to a minimum. I would really like to hear from someone who has used the square framed Nema 42 motors that are available. I would imagine that they would be much better than the oldschool motors I currently have, and would bolt up with a minimal amount of work. Where as the Nema 34 motors would require that I find new pulleys, and probably new belts as well as make adapter plates.

I might just order one and put it onto the quill and test it out. Speed isn't really an issue here, with the small bits that I use top speed is usually only 30ipm.

[titchener]

My BP clone mill has round size 42 steppers that were made around 2000, much better than the old BP ones, but not as good as the later square type. They're rated for 6 amps per phase, are at 1 to 1 drive and the machine has tons of power, but not tons of speed, max jog is 60 ipm x and y, 90 ipm Z, with the accell set to around 2.

I imagine the newer square type are even better, so I would expect you'll get good power and accuracy but not super speed with that big of a stepper motor. Microstepping works pretty well on my motors, I get pretty smooth transitions on a 0.0001" diag gauge, and holding power is good at any microstep position. Its probably even better on the square ones.

Those new 42's probably pull a ton of amps, make sure your drive can handle them, you might have to run them at reduced voltage in series rather than parallel. I'm actually doing that now with my motors and still have tons of power.

Paul T.

[austin.mn]

Here are the motors that I have been speaking of:

http://www.kelinginc.net/NEMA42Motor.html

I was actually surprised to see you can wire them for 3 amps. Of course I doubt that they would have much performance even at 100rpm wired like that. My motor drives are compumotor S6 and will microstep all the way to 50000 steps/revolution. With the motors that I have now, on the 2000 steps setting you can watch the motor do nothing, nothing, nothing, nothing nothing ... then step. They just do not microstep at all. I haven't tried to half step them, but I would imagine they won't do it.

It's nice to hear that your clones motors will microstep. Knowing that I will probably just go ahead and order the motors up. I will have to turn the shafts down a bit, from 3/4 to 5/8 so they will fit the pulley hubs that I have, but that shouldn't be a big deal.

[titchener]

Originally Posted by austin.mn Here are the motors that I have been speaking of: http://www.kelinginc.net/NEMA42Motor.html I will have to turn the shafts down a bit, from 3/4 to 5/8 so they will fit the pulley hubs that I have, but that shouldn't be a big deal.

Turning down the motor shafts accurately (ie no runout) is not going to be easy, you can't disassemble these motors because I believe you lose alot of magnetic flux if you so so.

Can you bore your current pulley hubs out to 3/4 or buy new ones with 3/4" hubs?

To be honest, those motors are also pretty overkill in output torque, I know some people have used size 34 motors as low as 1200 oz-in on a BP with ok results. Personally I'd probably go with 1800 oz-in size 34 motors if I was starting from scratch, they match up well to the full current voltage and current capability of the Gecko drives (7 amps, 80 volts).

If you can't bore or get 3/4" hub pulleys I think it would be easier to make adapters for size 34 motors, and they would be cheaper and might actually give you better performance because of the higher RPM capability.

Paul T.

[austin.mn]

Ok, Here is what I am going to do....

I already have a few Nema 34 square framed motors that I bought for a project that was never even started... I got them just before I picked up the Bridget and that ended up consuming my time and resources. They have a .5 inch shaft and a little looking around, I found that 1/2 copper pipe is about .5 inner and .625 outer diameters. So the plan will be to take a cut off wheel and cut them similar to a nice er style collet, 4 cuts around the diameter from one side and four from the other. Then cut a motor mounting plate and just try one on the Z axis. I know that bushing adapter isn't going to give me optimum results, but it should be good enough for me to see how a 1200 oz 34 will work for me. I would imagine that it will work just fine, I think the torque curve on the original motors drops off quite rapidly.

[titchener]

Sounds like a plan, please report back how it works out for you.

Paul T.

[pcp2005]

I am looking at buying a series one bridgeport cnc mill.
I was wondering if anyone could get me started in the direction to retrofit it to run off a computer, I don't think it has a rs232 plug just the tape reader. Also what would be a good price for this machine, it was built in 1978 and only has machined alum. it has not bn run in the last 10 years, but it looks to be in excelent shape.
Thank You,Keith.

[austin.mn]

I picked mine up from an old boss quite reasonably. however I have seen them on craigslist for between $1500 and $5000

In any case, whatever you pay for it, it will be cheaper than buying a used bridgeport manual machine and making it into a cnc machine.


I made the motor mounting plates to put the 34's on, but, the shafts on them were just too short, I only had a little less than 3/8" to mount the pulleys to. So I will have to make thicker mounting plates, and make an extension shaft to go from the .5" to .625"

However, I just got a line on some older robot servos that sound like they may be close to fitting the boss right off the bat. I will report back with my findings about them. Of course even if they do fit with minimal effort, I will still have to come up with suitable servo drives before I can use them.... But I think that servos is what I would ideally want, I just didn't want to part with the $3500 for motors and drives that are already to go for the machine.

[austin.mn]

I got the Servos, very reasonably... Picked up four of them so I have a spare.

Here is what I know of them.

1. They were pulled off of an Automatix Robot, AID800

2. Have differential quadrature encoders (a, a not, b, b not, z, z not) they are also equipt with a tach.

3. with a voltage constant of .0139/rpm I am assuming that max voltage is 41.7V, chime in if that is incorrect.

4. I have no idea of what current these should run, or how I could get that info. If anyone has a simple test I would appreciate it.

Just for fun I hooked up one of the Servos to a variable power supply. They are very smooth. I held onto the shaft with a rag wrapped around it, and started to increase the voltage. At 5volts the motor was pulling 6 amps and I was unable to keep a grasp on it. I think that they will move the table on the Boss quite nice.

So now I am looking into motor drives and was interested in the ARGON1 servo drives, because of the differential encoder input. But, after a quick search I was unable to find anyone with any experience with them. Has anyone used those drives?