I have a G0704 clone (Weiss VM25L) with a CNC ballscrew/Clearpath Servo conversion on it. It has an 1100w motor that I have Hoss' timing belt drive conversion and it currently hits just a hair under 5000rpm. When I bored the pulleys my gibs were too tight so the radial concentricity isn't great, which I believe creates vibrations. (Just another reason to buy a lathe, right?) I'm redoing this as soon as soon as the new pulleys arrive since the XY is much more accurate now. I'll probably end up upgrading to a more powerful motor and changing to a 1:1 pulley ratio in the future so I can have the spindle automated also.
I have mostly cut aluminum so far and have had pretty good luck using NYC CNC's speeds and feeds video (youtu.be/uw8uL2jjEBs) for that. I still have some adjusting/upgrading to do because using 100% tool diameter DOC and 20% WOC I can hear the motor working a little too hard. Kind of surprising for an 1100w motor, I thought it'd handle it a big better.
For steel, I don't plan on cutting it as often as aluminum, but I'd like to have an idea of speeds and feeds for that as well. I have a piece of 1215 steel 1"x1"x12" to test feeds and speeds on. I tried following along to this NYC CNC video: (
), but haven't really had any luck. I know that's for a Tormach 770, but I would think the baseline numbers should be working for me.
My justification for that is John cutting 4140 at much more aggressive F/S setup on a 440 in this video (
). The cut in that video sounds great. I believe these G0704's should be pretty dang close to 440's as far as rigidity goes, mostly lacking in the spindle. The problem I have is that even with conservative feedrates, I'm having chatter problems. I'll add some pictures and a video below to show how I have this part setup. On the back and side of the cut is where I'm getting chatter. The front sounds good and like it could be pushed further. I moved the part all the way into the vise and it helped slightly, but if you listen carefully in the video (over the air) you can hear the kind of squealing sound going on. On the finished cut I can also just tell by the surface finish it's chattering. I'll post the different cut recipes I used at the bottom also.
I'm not sure why this is. Could it be the way I have the gibs adjusted? I adjusted the XY gibs to be as tight as I could get them before I started noticing lost motion, then backed them off slightly. There doesn't seem to be any visible play in the table. The Z gib I adjusted from a starting point where I believed it was too tight. I noticed drills wouldn't really follow the spot drill and I read that other people had this problem because the gib was too tight. So I loosened it until the drill didn't visibly walk. I also checked the lost motion on this and it seemed to be really good also. I also have the mill trammed pretty well too. My only other thought is that the spindle pulley vibration is causing the issue, but I would think that it would chatter on all sides, so I'm not sure.
Any suggestions would be great, recipes, pictures, and video below. Thanks! (Sorry for the vertical video, and the poor formatting, I couldn't get it just right for some reason.)
I have a PM25 I cnc converted. I machine mostly 1018 steel. My experience is that the column twist and flex. The best way to minimize chatter for me is to use a small cutter, and go up on the RPM as much as possible. This is the fastest way to remove metal and not have chatter. To that end, I pulled the stock spindle and put a 3KW, 24,000 RPM spindle on it. It cuts a lot faster now, but the column flex is still a thing. Anything over 1/4" cutter in steel, it doesn't like it.
Column flex is not what I would have guessed, they seem pretty decent. What kind of feeds and speeds do you run with? I have a 2.2kw spindle for my router but I'd rather not take it off there and I also hated dealing with the VFD and water cooling and everything. If you could go below 6000rpm and still have torque I'd do it.
My tests were also done with just a 1/4" endmill aswell, hadn't tried anything else yet. Just wanted to get a baseline idea and since I was following NYC CNC's video I just used the same cutter size.
Today I was machining 1018 steel with a 1/8" end mill.
.125" DOC
.025" WOC
6115 RPM
17.12 IPM
.0007 IPT
This has not chatter at all.
For a 1/4" end mill, I don't have numbers in front of me but usually something like 250SFM, 1x diameter DOC, 5-10% radial engagement, and set IPM to do about .001" per tooth.
If I try to run a 1/2" end mill, it will chatter if I get aggressive. About a 0.1 MMR is about all I can do before chatter begins. Around 0.15 MMR and it's got some chatter and I don't push it any more.
The 3.0KW setup with a 2.2KW VFD, it has fairly decent torque. More than the PM25 did in high gear, almost as much as the PM 25 did in low gear. If it had an encoder it would be amazing. Once you're up to 3000, the torque is pretty good. Below 2,000 not great. At 1000, torque is terrible.
Your spindle sounds like it's much better than the typical chinese ones then. Does that have just like an ER collet taper in it, or can you get different holders? I do love using TTS holders. The one I have isn't even supposed to run at less than 6000rpm because apparently it will screw it up. Besides the fact I always had to custom edit the gcode to start it at a high RPM, then dwell, then lower it if I wanted it lower since it had some voltage barrier or something it needed to cross in order to not error out.
Those cut parameters seem very similar to what I was using with a 1/4 end mill, looks like I need to mess around some more with them. Maybe I need to give it more RPM. I know that's often the thing people do to sort out chatter but I've just been trying to play sort of proper, by the books. On my router with aluminum (and the steel test cuts I did) it was basically max out the RPM and gradually increase the DOC/WOC until the chatter sounded utterly ridiculous.
How did you figure out it was the column flexing? Is it something that's easily measurable? I also wonder if how rigidly these mills are mounted could affect that too. I've been wanting to build an actual steel tubing stand with a steel plate on top to bolt it too but I don't have a welder nor the power output for a decent one in my garage so I've been putting it off. The stand it's on now is nice because it can be moved around and it's easy to mount to, has a shelf, but it's not very rigid at all. I bought this used (although I don't think it ever made chips) so that's what it came on.
I'm running a chineese spindle, but a WJ200 VFD. I think the VFD really helps the torque, and it's a 220V setup too. Also the 3.0KW spindle is a lot bigger than what most run on these small mills, and that does help the torque. If I put an encoder on this thing, it would output twice the torque of a PM25 in low if not more.
On my mill, it's bolted to a huge heavy enclosure. Enclosure weighs more than the mill by a good amount. I used my phone to measure vibration levels, the head stock was twisting about. You can feel it with your hand when it's chattering bad. I also put a damaged cutter in and torqued it against a piece of metal, you can actually watch the column twist when doing so. The column looks beefy, but it's not on my setup. If I had the time/money, I'd make a new column as that's the weak link on my setup by a lot.