Also, take care in aligning the leadscrew end supports and the backlash nut. You want everything in a straight line and if your backlash nut is pulling the screw out of alignment any, this can also feel like a bent screw. Loosen the 2 backlash nut mounting bolts, run the x axis carriage back and forth (manually turn the leadscrew) then re-tighten the backlash nut mounting bolts. This will allow the nut to self align. Report back if this helps.
One other thing that really helps those 8mm leadscrews (if possible) is to tension the leadscrew from the outside of the end plates as opposed to having the leadscrew lock collars on the inside of the plates. Check out my Sphinx build for examples. I used 3/8 leadscrews but the concept is the same.
Thanks Rob & Michael! I'll try to get the screw tensioned and look at the backlash nut for alignment. In the meantime, I've finally managed to fabricate the mounting plates for the steppers and the spindle, so I had a try at assembling the whole thing. Good news is, spindle weight doesn't seem to be a problem (it's not going down on it's own weight and it doesn't seem to need a lot of power to pull up - at least as far as I can tell hand turning the leadscrew). However, I noticed there's some diagonal play on the Z axis so I think one of the wheel eccentrics on that gantry aren't properly adjusted. I'll have another whack at it in the following days if my 9-to-something leaves me enough energy. Cheers, Catalin
Success! At least in part. I finally managed to put it all together this weekend and I thought about giving it a go at a test cut in. It finally came out nice and clean, even if I did notice a bit of vibrations at the beginning (maybe a bit of deflection, maybe just a bit of oscillation... don't couldn't tell). I need to figure out the best feed, as the speed will be topped at 12000rpm for aluminium. I'm still concerned about some play on the Z axis. It looks as it's compound from multiple locations: - the long V-slot profiles are flexing a bit - I'll fix this by getting a real C-beam instead of using something that's build _like_ one from 20mm profiles - there's some movement in the mini gantry and I'm starting to think this is not meant to support such weights at 90º - I might use it to build a new Y rail for the table and get a universal gantry for the Z axis. Would appreciate you guys' opinions. I tried to make a short video to show the play on the Z axis... kinda hard to see, but it's there: https://photos.app.goo.gl/1nc39XMKiwS4foFk8
You could get away with some simple 2060s for the columns if you had some nice beefy plates to mount them to the sides of the base. You could skip buying a C-Beam profile by, again, making some plates. If the profiles are rigidly screwed together along their lengths, you'll get 90% of the rigidity increase. Just some simple 40x40 squares with 5mm holes drilled in a 20mm square in the middle, about 1/3 of the way in from each end, or something along those lines. It might be a cheaper and faster option if you already have some 1/8" sheet.
That's my problem now. The long X axis profiles are not coupled along their lengths and they flex... however you did give me a good idea with those plates. I'll give that a thought this week. What's your take on the mini gantry issue?
Wasn't really sure what the mini gantry thing was about. I was referring to the gantry (x-axis) in terms of the plates to make the quasi-C-Beam.
Yeah, I got what you were saying about the X axis. The mini gantry plate is in the Z axis. I feel there's some play in there as well and it's leaning forward due to the weight of the spindle. I was certain the eccentrics were properly set up, but maybe the wheels are just too small.
Oh, the plate? You hadn't said plate. Yeah, you may just need more wheels/surface area. Could you add a second Mini Gantry Plate on the back of the gantry, and then bind them together? Maybe an additional SBR rail on the top of the gantry to keep the whole thing pulled back a bit?
I made some plates for the X axis and it did improve the situation a bit, but not totally. However, considering the first cut was quite ok, I may be over-strengthening the machine for my use case. Still, I'm going to get the XL Gantry C-beam gantry plate, as it's the only way I can beef up the Z axis now and reduce play to a minimum.
I got the XL Gantry plate this week and I wanted to install it this weekend, but had the unpleasant surprise to notice that the mounting holes for the spindle aren't compatible with the Mini Gantry plate, so I need a new spindle adapter plate. I put the machine back together and re-adjusted the eccentrics, tightened the wheel nuts and Z axis play was no more (just the flex from the frame remains). I still want to use the XL Gantry plate for the Z axis and relegate the mini to a new Y axis for the table, but until then, I decided to do some test cuts again to figure out my feeds and speeds. I remembered to adjust my X and Z axis resolution as the old lead screws required 800 steps/mm and the new one needs 400. The first cut I tried two weeks ago worked decent with a 75mm/min ramp (with 2º) and a 150mm/min cut feed. Considering that was with the wrong steps and I cut twice as fast on X, I figured I could actually go higher and turned it up to 125 (ramp) and 250 (cut), and tried to cut some circular holes (10mm diameter) - a complete disaster. I got a lot of deflection / chatter, so I decided to turn things down and I finally got a good result at 50 (ramp at 1º) and 100 (cut), but even this had some issues. I do think however that some of this is caused by backlash on the Y axis (I can slightly move the Y axis with my fingers a bit, without turning the leadscrew - something I can't do on X and Z now that I've upgraded them). This would explain why I managed to cut the previous slot much faster, as it was orientated with the long side on the X axis and I only did a short cut on Y. Now, the circular holes had a lot more action on Y. Also, I'm thinking that maybe the aluminum stock I'm using is not quite right. It always felt a bit strange when cutting it on my table saw, as it didn't seem to have a uniform consistency - I didn't feel it having the same resistance when pushing it against the blade, as sometimes it required much less effort and sometimes it felt like trying to cut steel (in the same cut). This kinda resembles what the CNC is encountering in the video below https://photos.app.goo.gl/3WtsPnMoBBRu3xUXA
