First cut in progress!
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So I did my first cut, and (surprise!) it wasn’t deep enough, as I used the wrong offset in Fusion 360 2D contour. But since I have homing on my machine which (kind of) works (with lower motor power, stealth mode enabled and lots of prayers), I thought there is no need to worry. I fixed my gcode, homed the machine again, moved to the same coordinates and started a new cut on top of the previous one. And (another surprise!) the new cut was off by around 1mm on the Y axis. Not pretty!
This made me wonder how accurate those cheap mechanical endstops are. Is 1mm difference from the previous cut normal? Would optical endstops be more accurate?
Absolutely not. They should be more than accurate enough for our uses.
Kind of? Why stealth mode?
Because reducing motor power and stealth mode (probably reduces power even more) help with the endstop issues I’m having. Apparently when it does home, it still doesn’t do it very accurately.
Probably the best thing to do while I’m waiting for the new board is either not use homing or restore motor settings to defaults after homing.
I highly suggest you stick with ALL the firmware settings as we have them while doing any testing. Changing firmware introduces thousands of variables that make it too difficult to help.
Try just physically separating your end stop wires from all the rest by more distance to see how much that helps.
So … a few weeks later I received yet another SKR Pro board…
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Problem solved! I homed it 20-30 times without issues with the machine cold and warm and with increased and decreased motor power etc… no issues at all ! (so far). Will do more testing tomorrow.
Regarding motors getting hot at 900ma… mine were completely cold. I think I noticed a few skipped steps during some cuts, so I increased the current using small increments and left it at 1200ma. Anything higher than that makes the stepper heatsinks hottish while the motors are only slightly warm.
Next tasks: make the table more rigid, connect the vacuum and finally do the first foam cuts! I am slighly worried that the super light foam chips might clog the vacuum quickly, but we will see.
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Fuck my life, the problem is still not solved 
It still seems to depend on the temperature, worked fine yesterday when I tested the board in a box without the lid. Today I put the lid on, after some 10 minutes everything went back to weird mode.
I will be replacing the endstop cables and go through the list of suggestions from @SupraGuy . One thing I noticed about the endstop cables is… not sure how to say it in English… basically the cables are thick, but there are many wires inside that are super thin and when I solder them they have a tendency to burn and get damaged. I think the contacts might be weak.
TMC drivers will reduce their current if they get too warm. You may be setting the max current to 900 or 1200mA, and it is dropping it to the point the motors are cool to the touch.
The fact that it works without a lid is a good sign that the drivers need some cooling. Instead of a lid, install a fan.
The serial log can give you a hint about this. IIRC, there is a print anytime the current setting changes due to heat. M122 also has a lot of info, including OT prewarn (which is over temp pre warning).
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Inspired by the example from @vanillasky9 , I soldered a few resistors on the back side of the SKR Pro:
In the end this seems like a very simple solution which doesn’t need any cable rewiring etc. So far homing seems to work, will see how it goes in the next few days after I do some cuts.
Overall the 2nd board worked better than the first one. I did have homing issues but not nearly as often as before. Also, the first board usually failed at homing Z axis, and the 2nd board usually failed at X… Hopefully this solution takes care of both problems.
Today I tried to cut foam for the first time. The machine is going through the foam as if it doesn’t exist! Well, almost 
I will want to increase speed and also increase stepdown to make things faster.
Since the foam is going to be everywhere anyway, I thought I would get away without using the vacuum system and then just clean up after finishing the job, but unfortunately it doesn’t seem to work that way. The foam dust sticks to the X beam tubes so much that it restricts the bearings from moving freely. I will try loosening the adjustment nuts a bit, but I have a feeling I will have to use the vacuum anyway.
You will 100% need a vacuum, and be sure to run a ground wire down the hose. Foam is full of static and increases significantly in volume.
Don’t loosen anything up.
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I think I might have had them just a bit too tight. Loosening half a turn seems to have fixed the X jamming problem and the LR core still seems to be sitting very stiff on the beam.
No matter if I use vacuum or not, the bearings get covered in foam dust in 2 seconds when milling large amounts of foam at higher speed. My last setting was 20mm stepdown @ 8m/min. Eventually I will buy a larger milling bit so there will be even more dust than there is now
Do you need to have the cutter hang down so far? If you do you need to make the dust shoe longer with bristles or soft plastic. Vacuum only works in close proximity to cutting.
Is that a burr on your spindle?! No wonder you have so much dust, you’re grinding the foam…
“Chips? We doan’ need no steenkin’ chips!”
Yes, I know foam doesn’t exactly produce “chips”, but you could go for cold drip rather than espresso grind…
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Agreed an endmill would surely do better with less dust and more larger particles.
Yes that is a burr! All of the industrial cnc’s I’ve seen use these for cutting surfboards. It cuts the foam super easy and smooth.
I’ve tried a traditional endmill as well. It produced bigger chips but the chips were flying further away from the machine so in the end I liked the burr better, as the dust settles more around the area of cutting instead of flying everywhere.
I need to cut 10 cm deep around the edges. So I either need the endmill to hang down 10 cm below the core or I need to cut all the foam around the edges to prevent the gantry from hitting the stock.
When the endmill is so far down, the dust collection is much less effective.
Below is a scaled down version of a board. I expect to mill full size next week.
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Love that! As i drink my espresso!!
Hold-over from a mis-spent youth, before “coffee house and pastry clerk” turned into “barista”, and the green goddess escaped from Seattle… I could probably still use one of those big, copper and brass Italian monstrosities with the slot-machine press…
Okay you have my full attention. I can’t wait to see what comes of this.
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Today I had some free time and checked the speed limits of my machine with the current 12V PSU.
Got first skipped steps at:
- X axis: 20m/min
- Y axis: 22m/min
- Z axis: 4.2m/min
Those were the tests without any load. The torque seems to be pretty solid at 75% of top speed. Unfortunately I don’t have any tools to measure it, so I just put some resistance with my hands and checked how strong the machine is pushing before the steppers start failing.
In general those numbers are higher than I expected.
I want to do more tests with a 24V PSU and also check what the max speed is in a real world scenario such as 20mm stepdown foam cut.
Another thing I noticed is that in order to drive the machine at higher speeds I also need to increase the acceleration, other wise it doesn’t have enough room on the table to reach 20m/min.
No homing issues so far after soldering the pullup resistors.
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