Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: mlk1950 on January 08, 2011, 06:31:18 PM

Title: First test on new machine build question
Post by: mlk1950 on January 08, 2011, 06:31:18 PM
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. 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.
  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. ;D

Thank's Mike
Title: Re: First test on new machine build question
Post by: DaOne on January 08, 2011, 06:50:45 PM
Sounds like sticktion to me. I have helped a friend with a large lathe that ended up going with servos to get rid of the issue. Sounds like its take more force than your stepper can deliver to start the motion once its settled... its seated.
Title: Re: First test on new machine build question
Post by: mlk1950 on January 08, 2011, 11:11:52 PM
I posted over at CNC Zone and someone suggested that it could be "Idle Current Protection". Sure enough my board comes with it set at 50%. This is the board I'm using: http://www.hobbycnc.com/products/hobbycnc-pro-chopper-driver-board-kits/
Title: Re: First test on new machine build question
Post by: Tweakie.CNC on January 09, 2011, 06:48:32 AM
The idle current reduction is just to reduce the heat in the motors (save wasted energy) because steppers require less holding current (torque) than they require driving current (torque).
Stiction occurs mainly with heavy machinery incorporating cast iron way and gibs etc but there are lubricants available these days that can reduce that effect to a bare minimum if you have sliding bearing surfaces rather than ball or roller types.

What voltage are you running the steppers at 24V ? and have you increased the drive current ?

Tweakie.
Title: Re: First test on new machine build question
Post by: mlk1950 on January 09, 2011, 09:28:40 AM
Just a shade over 24V. I haven't changed the current and don't know how. I had someone from CNCzone suggest possibly turning up the acceleration.
Title: Re: First test on new machine build question
Post by: mlk1950 on January 09, 2011, 10:37:07 AM
I'm running Dumpster leadnuts(Delrin) and will be cutting wood. What would be the best lube to use on the screws?
Title: Re: First test on new machine build question
Post by: Tweakie.CNC on January 09, 2011, 10:54:18 AM
May be an idea to contact Dave at Hobby CNC to get the instructions on how it is measured (location of test point) and setting up the stepper drive current. I am guessing that if you can increase the motor torque it should solve your problem.

In my book you do not need lube on the screws with delrin nuts (the wood dust sticks to the lube and it just makes things worse).

Tweakie.
Title: Re: First test on new machine build question
Post by: mlk1950 on January 09, 2011, 03:05:38 PM
Thank's for the help Tweakie. I did that and he said to slow down the acelleration to give the board time to wake up. Seems like it helped. One thing I noticed that forgot  to do was set motor tuning for the A which is slaved to the X.
Title: Re: First test on new machine build question
Post by: DaOne on January 09, 2011, 03:11:45 PM
I had some dumpster nuts on a machine and ever once in a while it would squeak like mad. Some dry lube spay for guns was the ticket. Keep grease away or the dust that gets into it will form an abrasive compound. I will actually wear the screw more than the nut.
Title: Re: First test on new machine build question
Post by: ger21 on January 09, 2011, 03:35:56 PM
I use pneumatic tool oil with my dumpster nuts. It's very thin, and doesn't build up at all.
Title: Re: First test on new machine build question
Post by: Hood on January 09, 2011, 04:16:11 PM
Silicone spray may be a good option, dont work with wood but it doesnt collect dust so I would imagine it to be ok for wood dust.

Hood
Title: Re: First test on new machine build question
Post by: mlk1950 on January 09, 2011, 07:41:20 PM
May be an idea to contact Dave at Hobby CNC to get the instructions on how it is measured (location of test point) and setting up the stepper drive current. I am guessing that if you can increase the motor torque it should solve your problem.

In my book you do not need lube on the screws with delrin nuts (the wood dust sticks to the lube and it just makes things worse).

Tweakie.

I know how to adjust the current on the board. It's at the Potentiometers. The label on the steppers says 3A, which is 3 amps. Should I have the board adjusted for 3 amps then ? The pots is  where you adjust the board current. By increasing the voltage to .42VDC at the pots, the instructions say will give you 3 amps.   
Title: Re: First test on new machine build question
Post by: mlk1950 on January 09, 2011, 08:51:10 PM
I forgot to mention that Dave says in the instructions to try running the settings at the pots @ 70%, which would be about 2 1/4 amps or .30 VDC. He says the steppers will run much cooler at that setting. Thats what I think they are set at now. Do you think I should increase that?

Thanks Mike
Title: Re: First test on new machine build question
Post by: Tweakie.CNC on January 10, 2011, 03:01:32 AM
Mike,

Stick with what Dave has said, he is the expert here, but check the settings anyway - they may be set lower than 2.25 Amps.

Tweakie.
Title: Re: First test on new machine build question
Post by: mlk1950 on January 10, 2011, 07:55:36 AM
Will do, Thanks for the input ;)