Would like to increase IPM cutting speed

[Joe Weldor]

When I’m doing small engraving projects my machine is set up at 5 IPM cutting speed, which is fine for the engraving. Started to do some photo carving and would like to go about 20 IPM. But when I try to go that fast the motors just won’t maintain the accuracy they have @ 5 IPM and they make a little more noise but no increase in temp. I was thinking about changing the PS to 24V to 36V 8A to 10A and swap out the power resistors. Am I on the right trail here or should I make this a software question and go to that forum?
Basic info, I’m using a Stepper world FET3 controller, 12V from a switching power supply to run the motors and I have 1.5ohm power resistors on the board running the steppers in high torque mode. The motors are 4.5v 1.4A with 2 deg. /step. Everything comes together with Kcam software.

thanks

[UUU]

It might be instructive to try a more modest increase in speed, using your existing set up, to see how far you can get.

[ozzb]

May not be either at that rate of speed the bit may not handle the chip load and is flexing. Check that out first. It could be your problem.

[Joe Weldor]

Thanks guys, I have tried the ramp up in small amounts and the motors start to get goofy around 10 IPM that’s not really much of an improvement on a file that might take as much as 8 hours to cut. As far as drag on the tool not sure, using a 60deg included angle half round bit with .020" or .025” cutting dia. cutting .035” depth at the most on wood, should not create any flexing. Thanks for the thought, just thinking there might be someone else out there with a FET3 using Kcam getting 20 or so IMP on wood.

[ger21]

For good performance, you'd want to be closer to 10-15x the motors rated voltage. But 36V should get you roughly 3 times faster. The downside with the FET3 is that you'll need bigger resistors, which give off a lot of heat. A more modern drive will give you much better performance, but 36V would still be recommended. 24V minimum.

[Joe Weldor]

I’m somewhat curious about a more modern drive of which you speak. I would like to do some research on that. What drive do you recommend?

[ger21]

Gecko G540, which can handle up to 50V.

[James Newton]

Gecko's would be great... even perhaps a bit of overkill for 1.4 amp motors. If you are handy with a soldering iron and want to save rather a lot of money, you might check out the Linistepper 3 axis full kit for $115; less than half the price of the G540 and with those motors, you won't see much, if any, difference in performance.
www.piclist.com/techref/io/stepper/linistep/index.htm#kits

[Joe Weldor]

Looked @ the info on the Gecko's and the Linistepper both look pertty good. Gecko's are a little pricey for my low budget. Linistepper seems to get pertty good reviews' thing is it looks like I would need a bigger PS to start with and also would need to buy resistors as well in order to optimize it. That puts me back on square one with the FET3 I'm using now. FET3 will handle up to 50Volts and I would have to come up with different resistors anyhow. Came across a nice big transformer in my shop with the right rectifier, add the capacitors, got a bunch of them lying around and I've got the PS for which ever board I end up with. I'm going to build the 48V PS, put the right resistors on the FET3 board, well next to the board on a heat sink, throw all this in the magic hat tap it with the magic stick and see if I can pull out a quicker rabbit than I all ready have. If that don't work I'll be off to the pet store for a new rabbit.
Thank you all for your input.

[James Newton]

The resistors for the Linistepper cost $2 and can be ordered at the same time. The Linistepper and Gecko drives actively regulate the current supplied to the motor so that the resistors are just sensing the coil voltage, not dropping it. The FET3 driver doesn't regulate current the way the Linsitepper does so you are never going to get the performance you want out of it. I'm not sure how much that 48 volt supply is going to cost you, or the power resistors, but if it's more than $38 I'd recommend you try a Linistepper first.

A 24 volt supply with a 1.5 amp motor is pumping 36 watts and should easily drive a reasonably sized axis at more than 20 IPM. The formula Maris gave us is:
watts = ( IPM * lbs ) / 531
A little algebra gives us
lbs = ( 531 * watts ) / IPM
at 20 IPM with 36 watts, you should be able to move several hundred pounds... given a current regulating driver.

The more accurate way of figuring this out is by measuring the actual torque required to turn the leadscrew, as that takes friction and so on into account. See the calculator at:
techref.massmind.org/techref/io/steppers.htm#Estimating

[johnmac]

I used a Stepperworld FET3 on my first router table. It would not run faster than 8 IPM. For me, the solution would be either lead screws with fewer TPI, or replace the FET3 with something else.

I chose to build a bigger machine.

John

[Joe Weldor]

Hello James,
In response to my last post you stated.
“The resistors for the Linistepper cost $2 and can be ordered at the same time. The Linistepper and Gecko drives actively regulate the current supplied to the motor so that the resistors are just sensing the coil voltage, not dropping it. The FET3 driver doesn't regulate current the way the Linsitepper does so you are never going to get the performance you want out of it. I'm not sure how much that 48 volt supply is going to cost you, or the power resistors, but if it's more than $38 I'd recommend you try a Linistepper first.”
Where can I pick up one of these Linistepper 3 axis controllers for $38 or did you mean to $138?
Thanks again for all the good info.
joeweldor