New Machine Build- Stall Issue at Start

[mlk1950]

Just got my new 3' x 5' 3- axis leadscrew machine all hooked up with Mach3. I was jogging the different axis and noticed a couple of things. (#1)It seems to be running nice and smooth, so I think all components are adjusted fairly close. The A-axis is slaved with X, and noticed sometimes when I first hit the jog button on the X-axis, the steppers seem to stall at first, no matter where the gantry is on the X screws. Then when I hit the button again it takes off and runs smooth. It only does it after it sits for a minute or so. After I get it going it seems fine, even if I reverse direction. As long as I keep it going it's fine, but when I leave it sit for a short period, it will stall at first.
(#2) Also, I am new to CNC and not real sure what the steppers should sound like. I noticed that the Y-axis stepper seems to have a higher pitched sound than the others. Is that normal. It seems to be running very smooth though. The machine has 1/2 x 10 Acme (single start) on the X and 3/8 x 10 on the Y and Z. It's running 305 steppers. I tried slowing down accel and velocity and didn't help. I know it's something real simple, maybe just a fine adjustment somewhere. I'm hoping the CNC vets will share their wisdom with me.

Thank's Mike

[ger21]

What drives are you using? Could be resonance.

Try increasing the pulse width to around 5 in motor tuning.

[tkubic]

What it sounds like to me is your drivers have a built in idle current detection, which means it either turns the motors off or reduces the current running to them by some amount (50%ish). Problem with idle current is people experience problems exactly as you have described.

Without idle current your motors might overheat, try increasing the acceleration. Too bad Mach3 doesn't have a feature for a complex acceleration curve.

[tkubic]

Just as a point of curiosity what how does increasing pulse width change resonance?

[mlk1950]

I tried the pulse width and no change. I unhooked the leadnuts from the screws with just the screws turning. Doesn't do it with no load, with the gantry unhooked. Do you think it's a small bind on the X screws. It only does it on the X axis. Y and Z are fine.

[mlk1950]

Originally Posted by tkubic What it sounds like to me is your drivers have a built in idle current detection, which means it either turns the motors off or reduces the current running to them by some amount (50%ish). Problem with idle current is people experience problems exactly as you have described. Without idle current your motors might overheat, try increasing the acceleration. Too bad Mach3 doesn't have a feature for a complex acceleration curve.

I think you may have hit the nail on the head. Here is the board I'm running. Do you have a suggestion on how to work around this? Thank's Mike
HobbyCNC PRO Chopper Driver Board Kit | HobbyCNC

[tkubic]

I'm using a hobbycnc board as well, you can disable the idle current reduction by placing a jumper pin on jumper 4(?) this may overheat your motors though since the full current will flow through the motors when they aren't moving.

The motors are inductors, immediately after energy is applied to an inductor resistance is infinite, this reduces as time progresses. With idle current the motors aren't as powerful nor able to react as quickly to the quick stepping.

Only two options I can think of are eliminating idle current reduction or increasing the acceleration in motor tuning on Mach3.

I'm still learning and all my knowledge has been learned within the last 6 months.

[mlk1950]

So basically we either have to use it with the 10 second delay or none? Did you ever solve the problem or just learn to live with it? Thank you for the input, I'll just keep playing with it.

[ger21]

Originally Posted by tkubic Just as a point of curiosity what how does increasing pulse width change resonance?

It doesn't. I should have mentioned that the pulse width can fix other issues.

[tkubic]

My first cnc is super small (rebuilding larger), so it doesn't matter for it. Probably does in your case with a larger machine. (mine turned a 1/4-20 all thread on a 12"x12" machine).

There is a resistor that you can increase in value if you would like a longer delay, It's in the build manual, or just e-mail hobbycnc to find out which one.

[mlk1950]

Originally Posted by tkubic My first cnc is super small (rebuilding larger), so it doesn't matter for it. Probably does in your case with a larger machine. (mine turned a 1/4-20 all thread on a 12"x12" machine). There is a resistor that you can increase in value if you would like a longer delay, It's in the build manual, or just e-mail hobbycnc to find out which one.

Yep, I've been reading about that. You can replace the 10K resistors on R2,R4,R6 and R8 with 4.7K resistors, which will take it from 50% reduction to 30%. I think that would help alot in my case. Any opinions on whether that would be a risky thing to do, as for as stepper heat or would that be fine?

Thanks Mike

[mlk1950]

Well, I took the 10K's out and installed the 4.7K's. I'll hook it up tomorrow and post back on the results.