Hi all, trying to get my newly built MPCNC working right and having trouble getting expected results. When I cut a shape (circle, rectangle, pattern of holes) the shape is off. Hoping you can help!
Details:
It's built using parts from the site, 1" stainless tube, plus a cheap-ish 500W chinese spindle. Using RAMBO board, Windows 10, ESTLCAM and Repetier
This problem has existed since I built it a couple of weeks ago. Originally, it was built exactly to plan. I noticed that I was having some trouble keeping things square and plumb. So, a couple of days ago, I switched from the stock legs to a bracketed and squared MDF box, inspired by this: https://www.thingiverse.com/thing:2754792. It's now much more square, but still having the issue
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Here’s what I find: (see attached images) when cutting a gear, I see about 1-2mm different dimensions for the diameter. Also, the pattern of holes drilled in the middle of the gear aren’t arranged in a circle as expected. [attachment file=53950]
I switched to simple 50mmx20mm rectangle and found that it ended up being 50.3x18.5, with the 18.5mm on the y-axis. This happens whether the cut is completely through the piece or just .2mm deep.
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One odd thing is that when I cut a larger rectangle (80mm x 200mm), there’s much LESS of a problem. I ended up with 79.7mm x ~200.5mm. I don’t completely trust the 200.5 measurement because I couldn’t use my calipers for that long a measurement.
So, at this point, I don't know if this is mechanical, electrical, or something related to the controller. Any suggestions on what to test?
Seeing that the center holes all seem to be misaligned by the same amount in the different cuts makes me want to say it is a CAM problem. Have you tried drawing the shape with a pen instead of cutting? If so, does it do the same thing?
Before you start your cut, make sure your gantry is square. you can do this by making sure the steppers on each axis are the same distance from a corner. If the machine is built squarely you can still pull the gantry out of square. So a quick check before each cut should fix it.
That would not explain the weird center holes though…Mike has a good idea, we should check you gcode.
I discovered that the right side stepper wasn’t working right. I couldn’t really see it with the belt attached, but when I removed the belt and moved the gantry with repetier, I noticed that the stepper on the left moved normally, but the one on the right would just sort of twitch. cut off the wiring connector and reterminated it, and now it seems to work better.
I’m trying some kinetic sculpture making. I’m working right now from plans from here:
I built one of these a couple of years ago, but the hard way, which involved a lot of trying to cut to patterns by hand. I’m guessing once I get the CNC working right it’ll be a little easier this way!
My plan is to build from my own custom-made ply, made from resawing walnut into 1/8 or 1/16 plys and laminating.
BTW, totally off topic, but it’s been quite a shock coming to the CNC world from 3d printing in terms of software. The options for CNC seem way more complicated and painful than the integrated slicers. I can go from idea to sketchup to print much faster than I can with CNC, even for simple 2d. I’d kill for a CNC version of simplify3d and thingiverse…
Just had a similar problems with previously working circles going oval - being smaller than they were previously in the Y direction.
After lots of tightening and head scratching finally came across this thread - and my problem ended up being similar - the right hand motor was not pulling as well as the left hand one.
Once I had released both belts I realised that the thumb screws had worked loose on the belt pully - tightening them up and re attaching the belts seems to have sorted the problem.
