yesterday I milled some particle / press board (Dunno what it’s called in english?) and experienced some difficulties. It was a board I had laying around and I wanted to run a test on it just to check the dimensions.
I noticed that the pressed wood chips started coming off on its own while being milled, but didn’t care that much about it.
30 min program, after about 20 minutes in its last cutting procedure, the X-axis started stuttering, resulting in step loss… I also experienced Step Loss on the Z-axis at the beginning. I searched for starting values considering vref back then, getting “0,7v for X/Y and 0.48v for Z”. After experiencing step loss in Z, I changed the vref to 0.7, which works fine now. But after yesterday I was wondering what I can do about that. My steppers are 2A steppers and one post from Heath (searched the forum for “max vref”, getting this link) he stated the following:
So if your steppers are 1 Amp:
VREF = 1A * 8 * 0.068 *0.9
VREF = 0.4896VDC
If your steppers are 1.5 Amp:
VREF = 1.5A * 8 * 0.068 *0.9
VREF = 0.7344VDC
The DVR8825 stepper drivers have a much more simple vref formula:
VREF = Current(A)/2
So I was thinking: I should be able to set X/Y to 1V on Vref. I actively cool them with 2 25mm fans directly onto them while a 40mm blower sucks the warm air out of the case where the RAMPS is placed.
Maybe some more infos on top of that:
12mm mill (6mm one broke :( )
2mm doc
480mm/min X/Y movement
about 20k RPM
45% Stepover
As I'm new to CNC milling, these are the starting values I started with. Any hints where to change something here are appreciated :)
As for voltage, Best I could ever get reliably is 1.1V after that I would get random overheats. Yes you can get a tiny bit more power but it is diminishing returns in my opinion. Focus on your CAM, proper CAM is extremely low load.
Yeah, as the 6mm one broke I only had that one left. On top of that, there are not many cheap endmills for 6 or 8mm routers. I finally ordered a 3.175mm adapter thanks to a link I found in the forum. As soon as that gets here, I’ll be able to test smaller mills.
Again, as I’m new to milling, I don’t want to waste 10-20€ per mill on my testruns. As soon as I get good and reliable results with cheap mills and get familiar with all the settings, I’ll have everything at hand to invest in good mills.
After two of my drivers burnt out on 0.7V (these were pretty old DRVs) I got a new package of 5 and started changing in pairs - So now I got 2 old DRV on X, 2 new on Y and 1 new on Z. The steploss occurred on X. I’ll get back to testing as soon as the new adapter is here.
It’s good to know that the DRVs can take up to 1V in vref, this way if I run into further issues I can turn it up in 0.05v steps.
For safety, you typically want your absolute max current to be 80% or less of your motor rated current. So for a 2A motor and DRV8825s, a Vref of 0.8V is probably ideal. More and you’re generating unnecessary heat and decreasing motor and driver lifespan.
Yes, I realized this is a necropost after replying but maybe someone else has the same question.
