Today I wanted to cut 3mm dibond (aluminum composite) and it was a disaster…
I used a 1 tooth flute at very low speeds (I tested between 150mm/min and 700mm/min)
I also tested in a single pass of 3mm depth and in several passes of 0.5mm
The MPCNC cuts well but the dimensions are not good at all…
For a 100mm wide part I get 96mm which is very imprecise
What do you think?
Have you done a e-step calibration yet? (Do a 100 mm move on the X axis, measure actual distance, repeat for Y axis).
Size of bit set properly in CAM? (Specifying a 1/8” bit and using a 1/4” bit might produce this result).
Yes I have already calibrated the e steps
In fact I built the machine several years ago so I forgot a little but:
before the dibond I cut 3mm medium to test and get used to it again and I only had a shift of 1mm on 50cm so it remains acceptable
I have defined a 3.175mm bit
I have the impression that the machine is straining and skipping steps
Yet dibond looks so easy to cut in videos on the internet
Are there speeds to respect or something else?
If you look at the bottom of the page, there are several links with the same issue and with good troubleshooting tips. Top of the list (after e-steps and grub screws, which you have already addressed) are loose cores, cracked cores, and possibly skipped steps.
This sounds pretty much like tool deflection, so to check this, try measuring some air cuts, do some climb and conventional test cuts, do some test cuts of different sizes to see if the difference is proportional or fixed, etc.
My first guess, however, would be a loose core. See if there is any movement or play, and adjust the lower bearings if needed.
I think I don’t have the same subjects at the bottom of the pages because I see very different subjects
But thanks to your help I will be able to search on Google more easily
When I cut softwood (MDF) the dimensions were correct
But with composite aluminum I have the impression that it was forcing
I will recheck all the belts and bearings and overall all the mechanical parts to see
I disagree with this advice. The motors have exactly 200 steps per rotation. The pulleys have exactly 16 teeth. The drivers count 16 microsteps per step. All of that is more precise than I can measure.
The GT belts have 2mm per tooth, and that can flex a little. But the fiberglass inside is pretty hard to over stretch.
So 100 microsteps per mm is closer than most initial measurements. So I usually advise to leave them at 100 until you have done plenty of other adjustments first.
For starters, post some pictures of the cuts and the machine. Sometimes we catch things like steel belts or something built backward.
If you are doing something with precision (like matching parts), you either need to cut super conservative or use a finishing pass. If the rough pass gets everything but 0.1mm, the finishing pass has nearly zero load and will just cut to the final dimension.
Also check your grub screws (set screws) on the motor pulleys.
Skipping steps sounds like grinding gears. It is the motor jumping from one magnet to the next magnet of the same pole. If that is happening, then there could be a few causes. Some are electrical (like a loose wire) some are gcode related (like sending it a travel move through material). Sometimes rhe but isn’t cutting effectively and the load is enormous.
ACM should be harder to cut than wood, but definitely possible.
I agree that this is what is supposed to be, but I have also read (several times) in these forums where someone is using 20 teeth pulleys, so hence the suggestion to check the e steps. Perhaps calibration is not the right ter.
Double check your CAM program, could be the center of your bit cutting on the outline of the part.
I won’t be able to check the machine until tomorrow in the meantime I have uploaded the videos I made if that helps you
I use repetier and estlcam
But when she cut the wood the dimensions were good, it’s only when I cut composite aluminum that it’s strong (we see it in the video)
I will check the pulleys etc.
wood:
Aluminum composite:
Maybe try my all-time favourite trochoidal milling. 
Okay so today I went to look at the mpcnc I checked all the pulleys and bearings and everything looked good…
But by looking I understood the problem I think…
I built the machine quite high and above all the center of the machine is very high and therefore when the machine cut the wood without force the dimensions were good but when I tried to cut the aluminum composite it had to be forced and with the The leverage effect created my wrong dimensions (96mm instead of 100mm)
I think the best thing is to reprint the machine in its new version by making it lower especially in the middle
In addition the new version looks more rigid on base
It’s only a problem if the feet are very high. The Z-axis does not mind being long as long as it does not go down too much beneath the core.
Yes you are right, what maximum height in z would you advise me?
And do you think I should build the new version that came out afterwards?
Is it much more rigid?
Because otherwise I can only cut the feet
I’d start with cutting the feet, no need to build a new one.
I really thank you for your advice!
I will definitely do that
The Primo version is a lot more rigid. If shortening the feet doesn’t work, I would switch to the Primo version. I had the previous version and really like the Primo better.
It obviously is, but as long as the other one is working, there is no need. I didn’t have the Burly and was really happy with the Primo and I would upgrade the LowRider in a heartbeat if there was a new one, but not because I need it but want to.
It’s true that I built this version many years ago but the primo one looks much more solid, it’s cool to confirm that to me
I already have the bars, the bearings, the motors, the electronics etc…
In the end I would just have to reprint parts in 3d (good thing I finished building a voron ^^)
I haven’t studied the primo too much but only the belts seem different