Cutting Speeds

[kmacht]

So what is everyone getting for cutting and rapid move speeds on their machine? I set my machine up with 250 oz/in motors and 1/2-10 acme leadscrews and can't get more than 40 rapid and about 30 cutting with it. I was hoping for better but can probably live with this for a while. I am going to try and pull some of the friction out by putting in dumpstercnc backlash nuts instead of the homemade ones. I am also thinking that a higher voltage power supply would help. I am only at 24volts right now but have a computer power supply I can try tying it to increase it to 36 volts. Any other thoughts?

Keith

[Jason Marsha]

What is your electronic setup i.e motor drivers and motor specs?

[kmacht]

I am running Pac-Sci PowerMax II stepper motors in bi-polar mode. They should be rated at 253 oz/in. I am using the probotix bipolar drivers, breakout board, and 24 volt powersupply. I think that my limiting factor right now is the voltage on the power supply. The motors are rated at 2.3 amps per phase. My drivers are good up to 2.5 amps per phase. The power supply I have is good to 6 amps which should be plenty. Why I think that the voltage is the limiting factor is because using the inductance formula I think that these motors should be driven around 80 volts. I don't have the money to get an 80 volt driver and powersupply setup right now. The probotix drivers are also limited to 40 volts. I was thinking of isolating the ground on an old pc power supply and hooking it up in series to the 24 volt power supply I have running right now. That would put me at 36 volts and 2.3 amps per phase which is about the best I could do out of the current drivers. The motors seem to have plenty of torque for my application, the torque curve just drops off too fast to get good rapid speeds. I am hoping that more voltage will take care of it.

Keith

[Mogal]

Just guessing here, but if you installed some Harmonic dampeners, you might/should be able to get about 80-90ipm.
When I first built mine, I could only achieve 60ipm reliably. Once I installed the dampeners, I now run reliably at 160ipm.

My setup is with 460oz motors, 36V PSU and a 1/2-10 double start acme...

Here's a great thread, read through this. There are designs for the dampeners there.

Cheers!
Chris

[msholden]

The bi-polar stepper driver from Probotix has current limiting adjustments on the by-polor stepper bord which can be set to acheive the propor current for a 260 zo motor. The power supply is designeg to put out 6 amps at 12vdc. The single motor has a max current draw of 2.5 amps or so. You need to limit the current not to excede the motor current raitings. As I do not know the original starting point of this thread. It seams that I have jumped in the middel of a conversation. The best way that I know is to measure the current going to the motor. This will tell you how much work it is doing while taking in consideration a lot of factors you do not need to concern your self with.

if the power supply supply is able to deliver ti's raited power of 6 amps and the by-polor steper driver board is set to 2.5amps on the motor you should receive the designed power to the motor.

I hope this may help.

[kmacht]

I read the thread on harmonic balancing. Seems like an easy thing to try. Parts should be easy to make for it now that the machine is running. I set the amperage for the motors on the probotix boards already. The settings they show are to set vref at 3.2volts for 2.0 amps and 4.0 volts for 2.5 amps. The spec sheet for my motor rates it at 2.3 amps. I set v-ref at 3.75 volts to get the 2.3amps. Is there a reason I should set it at something differently? The motors have plenty of torque at low speed. I could cut 1/4" wide grooves at 3/4" deep as long as I slow the machine down to around to 15ipm. It is when I go to rapid that I can't get much above 30 or 40 without stalling the motors. I guess my plan is to try the harmonic balancers to see if it is mid range harmonics that is causing the problem. If that isn't the issue then I have some dumpstercnc backlash nuts that I can try instead of the homemade ones. Hopefully I can dump alot of friction in the system that way. The third and final option is to up the voltage to the drivers. That is, unless anyone has other suggestions.

Keith

[ger21]

I use the exact same motors, with a Xylotex, 24V, and dampers. But, I use 1/2-8 2 start acme and dumpster nuts. On my 40" Y axis, I get 190ipm. On my longer X axis, I'm limited by screws whipping to 155ipm.

You really need to change the screws.

My Z axis, with 1/2-10 and no damper, is only good for 55ipm, with the same motor. The Z motor doesn't have a dual shaft, so I can't put a damper on it to see how fast the 1/2-10 will go.

[kmacht]

For those with the same type of issues MAKE SOME DAMPERS!!! I switched the backlash nuts out to the dumpster cnc type nuts. It helped a little bit giving me another 5 or so ipm. Not a big gain but it seemed to make things a little smoother. I then decided to play around with a damper. I took a piece of 3" x 3/4" round puck of mdf I had laying around and drilled a hole slightly smaller than 1/4" in it. I then pushed it onto the end of the other side of my motor (they are duel shaft). When I went back and tried to play with increasing the speed I am now easily getting 75ipm. I went from 35 to 75ipm by doing nothing but putting a chunk of mdf on the end of my stepper motor. I think I can go faster. They are still hitting a resonance frequency above 75ipm. I am going to make some of the rattler style dampers and see how it does tomorrow. I'll post an update once I have them on and working.

Keith

[msholden]

When you get to the point that the motor stales. Which motor stalls, is it the spindle motor or the motors for X or Y-axis?

You need to know what current the motor drawing when it stalls. If 15 ipm feed is ok but 20 ipm or above is not. What is limiting the performance of the motor? If you try to feed a material faster than the spindle and the particular bit can cut you will overload the spindle, which would slow it down or stop it. If the axis motors are trying to run in this condition they could over load. The current limiter on the side stepper board will hold the current to it's setting.

To further pinpoint the problem place a DC amp probe in series with the motor and observe the current as you change the feed rate. Remember that the X and Y-axis drivers have current limiter features and they should never exceed the settings on the driver board. If they do there is a problem with the board a d it should be replaced.

Do the same examination on the spindle using what ever instruments required.

I did notice at certain steep speeds there seams to be an internal noise generated in that particular driver board. In some applications I have done has caused me a lot of trouble. I called Probotix and a tech responded with sever ideas, which did not solve the problem. I sent O-Scope information to show the problem, which did not solved at this point.

If I can help further please let me know.

[ger21]

Steppers don't draw more current when they stall.

[msholden]

If a stepper motor did draw more current that planned it would tell you if the current limiting function in the motor driver board is working correctly.

[jvangelder]

our jgro is slowly being converted to rack and pinion

we have 460oz motors running 36v on a home brew rack and pinion w/o gear reduction

15inches of travel in the x and it max's out around 700imp in feed moves, takes about 6" to reach the 700ipm then it starts slowing down

Y axis isnt done yet however we are hoping for aprox 1000ipm feed moves

-Jacob
our Y axis has 96" total length, hoping to get