RAMPS/Polulo/Stepper Strengthening ?

Mostly Printed CNC - MPCNC Troubleshooting
#1

Hey folks,

Been cutting 3/4" plywood lately at high speeds with 1mm passes with pretty good success. As a test, I’ve been cutting small rectangles approx. 2"x3" out of 24"x48"x3/4" piece of plywood. I’ve cut like 60 of them with varying success trying to tune the cutting speeds for this bit/material combination. In most cases, when you go too far, the steppers skip pretty much at the beginning of the job. No brainer, that’s too much for the stepper so you back off from there.

But last night the last 6 or 7 attempts saw the steppers skip maybe half way through the job almost in the same place it would seem. I backed off the feedrates quite a bit and it still occurred. I called it quits at that point so I haven’t had time to investigate so I have a few questions regarding this new behaviour.

Could it be that the steppers or polulos warm up after some time and essentially have less power over time during the job ?
I bought the RAMPS and steppers from you guys and they seem pretty solid, but should I go through the whole polulo current tuning process ?
Is there a way, other than the above tuning, to beef up the strength of the drivers/steppers or add/replace some components ?
Could we use one driver per stepper rather than running 2 steppers on 1 polulo each for the X and Y ? Would this cause additional issues of synchronization ? Z is fine of course.
If the steppers are being worked too hard, will they warm up ? Mine are cool to the touch even after the failed jobs.

Phil

#2

https://www.v1engineering.com/software-updates/

Have you read this,? Make sure you are using updated estlcam or fusion post processor.

How fast are you trying to move? actual numbers will help here or screen shots.

#3

Thanks for that. I’m using Fusion 360 not sure which post processor but downloaded it a couple days ago. I’ll check tonight at home. I probably do need to update the RAMPS firmware so I’ll look at that tonight too. For the screen shot, yep, tonight too. But I’ve been running (20,000 RPM * 2 flutes * .005 * .423333) = 85 mm/s at 1mm depth consistently until the last 6 or 7 attempts. Will check all this tonight and report back. Again, thanks for that.

#4

Firmware is: RC7_MPCNC_LCD_9916
Fusion Post Processor: MPCNC_Fusion360_V10_SDcard.cps
Feed rate: 85mm/s @ 1mm depth @ 1/4" Double Upflute in 3/4" plywood.

Should the drivers/steppers be ok with this ?

#5

Maybe, but that is not how I do things.

If you watch any of my videos you will get a sense of my feeds and speeds. I do my rapids at 35mm/s I cut at about 10-14mm/s. You are going to have a hard time with those speeds and that size bit (i’m a little surprised you haven’t broken anything). I’m not even sure mid-range production wood specific machines cut that fast at 20 times the cost.

#6

You should really take a look at the link I shared with you earlier. Above 30-35mm/s you lose power in the steppers very fast. I would think you are loosing a ton of steps.

#7

I hear what you’re saying. I’ll try and see how well my current setup can handle those slower speeds by checking the bit temperature after cuts. The problem I have is that I can’t currently reduce the RPMs below 20,000 which would be great to run slower feedrates without overheating the bits. I’ll report back. You said 30mm/s is peak power. I’ll try that out and maybe push more material and see what happens. Nothing has broken yet ! Phil.

Here’s a great PDF from Onsrud. Interesting info. Check out the chart on page 19. In my setup at .002, (20,000RPM x 2 flutes x .002) = 80 IPM x .423333 = 34 mm/s or 2031 mm/min. Pretty close to your 30mm/s eh!

http://www.onsrud.com/files/pdf/LMT-Onsrud-CNC-Prod-Routing-Guide.pdf

#8

So I had a chance to investigate further last night. Around 30mm/s seems to be the low end for my setup. Slower than that and the bit warms up.

I did try the passes from .5 to .25 and was able to do those fairly well. But the missed steps reappeared nonetheless. And it didn’t appear to be running into any additional bit resistance.

It looks as though the tips of the bits are now dull/dulling. Plunging seems to be harder for it now. Cleaned the bits somewhat but need to clean them completely and see if it’s just buildup or in fact dullness. That and get some more bits.

There were several times when you could hear the steppers do the usual shudder when they skip and then the bit would be cutting outside the tool path once it got to a corner. Always around the same depth approximately 3/4 of the way through the material. It also seemed to be suddenly taking far more material than in previous passes. Must investigate more. I have to verify whether each pass is in fact what I’ve programmed in the CAM setup to see if there is an issue with the Z movement.

Could it be something in the movement of the gantry causing skipping ? Dust buildup on the rails/bearings ?

There were two times when the movement actually stopped almost as if it were hung then resumed. That’s new. Will need to see if it reoccurs then switch over to SD card cutting to eliminate the MacBook as a cause.

Could this be a lack of power issue ? MacBook delays ?
Any ideas folks of what might be causing this behaviour ?

#9

Not sure about the missed steps, but I found easy off oven cleaner will clean the bits off wonderfully. Not sure what it will do to the plastic stops on some bits though. I also tried acetone, goof off, simple green, and windex. None worked as well as the oven cleaner. Just let it sit in the stuff overnight and the plywood glue buildup just wipes off. Heavy buildup might need a second dunking. I just sprayed some into a plastic test tube until there was enough real liquid to submerge about a half inch of bit.

#10

They are currently soaking in the Freud stuff (smells like oranges and is orange in color…), but if that doesn’t work, I’ll give easy off a shot. That and a brass brush. Thanks.