My machine is a tease. It has a cutting area of 24"x24"x3.5". I’m using the Makita RT0701C. I have tried cutting a large sign out of 1/2" Birch plywood. My first attempt was going really well. I used the downcut bit from V1. I was cutting at 30mm/s at 6mm DOC. I hadn’t intended on cutting that fast, but I forgot to change the tool It still managed to cut fairly well. About 80% the way, I lost the bit. Not sure if it snagged something in the plywood, grabbed something on the spol board, or it just wasn’t tight enough.
Since the first attempt was working well up until then, so I figured I would just give the same GCODE a go. Only now it cut like absolutely garbage. Checked all of the belts, grub screws, and they seemed tight. I thought maybe it was the bit so I bought some replacements on Amazon. I tried a bunch of test cuts on the messed up boards and things seemed good. So I bought another section of birch. This time I slowed it down to 15mm/s and 3mm DOC. It started out fine, but then I started getting some bad cuts. I let it go, but dialed the speed to 50% so it started cutting much slower. It didn’t seem to make much difference. The bigger cuts seemed to go well, but the smaller stuff is where the bad cutting is noticeable.
I’m not smart enough for this machine. Every time I have some success, it doesn’t seem to last. Here’s some photos and a video. Looking for some help. Let me know what other information that is needed, but I appreciate any help.
That kind of wobble is sometimes caused by loose grub screws on the toothed pulley on the steppers. Have you check those lately? did you use LockTite on them when you installed them?
Any chance some piece cracked when you lost the first bit? I’d expect that to have been a pretty violent event. Can you find any sources of mechanical wobble in the machine? I’d test this with the motors engaged but the spindle disabled/unplugged.
Just out of curiosity, what is your spindle RPM? As @ttraband has pointed out, that wobble could be from something loose (your mount or something has cracked), or it could be from chatter because the RPM on the router is set a little high. I want to say I would get the same issue on my other CNC machine when I had the RPMs too high and not allowing the bit to actually cut properly and basically “bounce” along the wood. I could be wrong, but something else to check out.
I have the RPMs set as high as it goes. I could never find a balance between RPMs and speed. It seems to chatter if I slow it down too much. And the downcut bit is 2 flute, so I thought you had to have higher RPMs. I’ve always created dust and never chips.
Interesting. I have always heard that the lower the RPM is better. There are equations out there to help figure out Feed rate and RPM setting to get the proper chip load, but there is also the “that just sounds right” ear test. With the machine I have (non-MPCNC), I had a router that had a fixed 25,000 RPM, and using both an upcut and downcut 2 flute bit, I was making dust like you. Had a lot of burn marks on my edges, as well as that wobble as the bits were bouncing along the cut. I really couldn’t get the feed rate fast enough to compensate for that high of an RPM. I now have a different router and for most cuts, I run 10000-13000 RPM (lowest couple of settings) and my feed rate is usually in the 600mm/min (23.6 in/min) range and the sound and cuts are so much better. I have also moved to using single flute bits and even black walnut is cutting like butter! I know that I am referencing a different machine, but as I have researched getting the MPCNC, I think the speeds of the 2 are comparable, so the “theory” of the feed rate vs RPM should be similar as well. If someone else here smarter on the MPCNC can correct me, please do so as I don’t want to put out bad info. Just looking at your images and what I have seen in my stuff, just thought it might be relevant. Just a thought! As always, YMMV with all of this information.
More flutes = higher feed rate to avoid smaller ‘bites’ that lead to rubbing.
The rpms are generally governed by tool material, coating, and diameter vs stock material, but often enough we just run what we can.
I went back over the machine. One of the core clamps was a bit loose. I’m not sure if that was enough to cause what I was seeing. I did run the test cut on a piece of high density foam. That cut exactly what it was told, but it made it clear that there is also issues with the SVG I’m using.
I need to fix the SVG, which is a whole other issue.
If I do get the SVG fixed, I have one more section of birch to try it out on. Or am I better off trying the cut on something cheaper like OSB or something?
Finally success! There were plenty of hurdles along the way and a lot of wasted birch. It’s the price of experience. It’s a boost in confidence. Time to see what else I can get done before Christmas.
Thanks for the advice. Hopefully there will be more makes in the near future.
