I got LongMill mk2 while ago but didn’t use it much until recently, so if somebody with a bit longer experience could give a few pointers I’ll appreciate it.
Squareness - what is realistic to expect assuming that everything is setup properly as per instructions? - I tried to cut dog holes for MFT style workbench top that I’m building, and it failed quite bad - about 3mm over 1m length, and while that might not sound much, it affect fit if you are trying to make cabinets or any other type of box where sides need to match exactly. I can cut perfect 90 with track saw with attached square add-on, but can’t do it on CNC, which is a bit annoying.
Bit sizes - as someone previously posted, 1/4" bit is not really 1/4, which would not be a big deal if all 1/4" bits out there were the same, doesn’t matter on which side of 1/4 error is. But since all seem to be different, what do you do to account for it? - cut grove with each bit, measure it and label them so that you know for next time?
what would be best way to achieve repeatability, so that you can cut e.g. square (never mind that it’s not exactly square) and then to cut that exact same square 2 weeks later - again, doesn’t matter that is not exactly square, as long as it matches exactly previously cut peace
gSender has a calibration tool that you can use to determine how far to move a Y rail to be square. The problem is “How do you move your mill by 1.42mm?”. The best answer that I’ve seen is to mount the LongMill’s Y rails on strips of MDF that have a some slots in them. Then using the slots and some bolt holes you fasten the the strips to the table. I just remounted my LongMill about a week or two ago and did it that way. According to gSender my original mounting was about 1mm off. Now it’s as close as I can measure. I posted about the remount with some pics.
I’ve started to use dial calipers to measure the diameter of my bits and then enter that into the CAD/CAM tool database. You’ll still need to do some trial and error if your trying to make parts fit together. Due to the resistance to cutting, machine flex etc, holes tend to come out small and profiles a bit big and the difference can change with whatever material your using. I was just doing some tests to try dog holes in my spoil board with 3D printed dogs. I decided to use 20mm diameter holes. I needed to cut the holes at 20.25mm and print the dogs at 19.7mm in order to get something that didn’t wiggle to much but was still removable.
If your trying to cut the same square in the same location on your mill I think homing with sensors/switches is the way to go. If it doesn’t need to happen in the same place then using a probe block and mounting the mill and work square should do if you save the files used.
Suggestion to mount rails on moveable platform looks promising, too bad I didn’t thought of that before I mounted it all
Regarding holes, I found it as well that they are too small by 0.3-0.4mm regardless of bit used, so in another words, it looks for anything that require high precision you need to fiddle with test cuts in same material, adjust numbers and then cut real thing
