I am pretty far through my MPCNC build but now I am facing a lot of stuttering on my X-Axis. Here are some specs of my machine:
Length: about 1,5m
Width: about 1,3m
Height: about 0,25 m
Electronics: Ramps 1.4 (I guess) with CNC Shield powered with 24V
Drivers: DRV8825 @1,2V Vref
I don’t have any kind of spindle attached right now, so my motors are stuttering already while there is no cutting in process.
What I already did:
Raising the Vref Voltage of the Drivers
Fiddling with the Screws on the rollers
Tightening the belts
So far, nothing helped. From my intention, I still think my rollers are too tight, it is quite hard to move the axis by hand when the motors are off. How much force is normal for moving the motors and which screws do I have to tighten/untighten to change the tightness? I tried all of them and for me it didn’t look like it changed something.
The axes should move with the pressure of a single finger, certainly not “quite hard”.
Did you have any trouble inserting the tubing into the bearing clusters (three bearing set)? If so, did you print the correct parts for your tubing size?
After tightening I loosened them to check for this. Same behaviour. Also, how can I my motors move without belts :D?
I think my mpcnc is pretty high, I will measure again though. I planed to stiffen the corners with extra brackets and also print some pillars that can support the tubes while keeping the rollers still able to move.
Maybe have a look on the video I added. There you might can see the height.
EDIT: Okay, measured again. Its 25cm which is about 10 inches. 40cm is my Z axis tubing.
I see the video now. That Z is huge (not your current problem). The trouble isn’t the feet/legs, it is the Z axis sticking out that far to reach your spoil board. The rigidity drops exponentially in that critical dimension. If you are going to print with it, no big deal. If you are hoping to mill with it, I think you will be in for a rough time. You can minimize that by raising the work all the way up to the gantry, but it will be silly when it is lifted 20cm.
But on to your original issue.
It looks like it is skipping steps. What reference voltage are the drivers? Could it be bad wiring?
I suggested removing the belts to see if it would roll smoothly with no belts. Those tubes look very smooth so I would expect it to roll really smoothly. If it isn’t, then thats where I would start.
So, I found time to check the mpcnc. I removed all bolts from the sleighs and removed all the bearings from the sleighs besides the ones sitting on top of the steel tubes. To make it short, that means there can not be any disruptive friction coming from the sleighs as the x/y-cross (gantry?) is more or less just sitting on the outer frame.
Still, it is very hard to move the axises. Therefore I think my issue is the middle part. Any suggestions how to continue? I tied loosening and fastening the bolts of the middle part but it did not change the amount of friction. I alsy measured some parts of the middle. In my 3d tool I checked that some parts had to be 13.1 mm thick and measured them on my mpcnc. Most of them were 13.1mm but one was 13mm and one was 13.4mm. I don’t trust my measurements though, as it was hard to measure with all the bolts still attached.
Anyway does anyone have suggestions how I can reduce friction in the middle part?
One problem I had was an imperfectly printed part, and it’s not easy to explain, but check all your bearings spin freely.
I found that one part I had printed had a slight ridge which meant the PLA which was meant to sit against the stationary centre of the bearing was restricting the movement of the outer mobile part of the bearing. It wasn’t easy to see, but it was obvious when I tried to move the bearing.
Finally after all that stuff happening right now I had some time to look again on my MPCNC. I have the following new information:
I tried to measure the Force I need to move either the X or the Y Axis. Its about 50N. I have nothing to compare to but I think it is too much. I could probably do some math with the torque of the nema motors, but my physics class was long ago :D.
I have a closer image of the middle part here. The problematic direction of movement is the red arrow ( and of course the other axis which is 90° to that.
I got a new 3d printer in the meantime so maybe I try to print the parts again to hope that it was just some inaccuracy of my old printer (which is really worn out). If there are other suggestions. e.g. any ideas on how to make the green circled ball bearings have less grip on the steel rod, feel free to suggest.
The bolt we see with the nut on top should be loose. The nut and bolt head should just touch the printed part without actually putting any force on it. If it was tight, and after loosening the bolt it’s still tight, keep using it for a bit. The plastic should relax with the tension off.
I did loosen the bolt you told me for both axis and also the long middle bolt as he seems to have the same purpose for the bearings on the other side. It did get a bit more loose but not enough I guess. So you said I should move it back and forth? Should I do it manually like 100 times or did you meant it some other way?
It’s still not moving correctly? The nuts are there to keep the bolts from falling out for the most part. Most of mine I can wiggle with my fingers. I don’t think it’s a scaling issue, otherwise the bolts wouldn’t go in. Have you verified the tubes are 25mm outside diameter?
I have dual endstops. Sometimes one of my motors comes loose from the Rambo board and I get a studdering motion. I press my connection down and boomtastic
So, I re-printed the two parts which held the X and Y axis tubes for the middle assembly and with proper “non”-tightening of the bolts garry mentioned it is running fine now. Thanks guys
TL:DR; Problem was slightly off or slightly deformed prints and bolts to tight. Solution: Reprint and loosen bolts.
How often does this happen on your RAMBO board. I just built mine and have cut foam and one board but seems like every little movement for Y1 cable causes a studder. I have re-crimped that cable but i notice that the connector rocks back and forth a tiny bit.
