September 4, 2017 at 1:12 pm #43243
I can speak for the dull bits. I actually just cut something with one. I am able to get decent tolerances with it, but you can tell the machine is NOT happy. I may make a video on it, you can actually see the dewalt start to change angles as it cuts since it is rubbing more than cutting. When it cuts trochoidal, you can see my whole z axis start to wiggle a bit. The bit does not move as much as the steppers are, indicating some serious flex!!
I agree not to test cf anymore. It will eat your bits so fast as well as your wallet on wasted material.
I built my machine almost as rigid as you can make the mpcnc. Minus my lack of SS, my machine is on the smaller size and is extremely short and I still get some flex. It is just the way it is. I have learned to design with this in mind. My main point is don’t fight it, just design and adapt to it, otherwise your machine won’t in any way be worth using.
If your pockets are undersized, put your finish tool on estlcam as a lower diameter than it actually is, so it forces the bit inwards to compensate for the flex.
Milling is weird sometimes. I sometimes get better results actually cutting faster than slowing things down, the opposite you would think especially with our not-so-aerospace grade setups.September 4, 2017 at 1:20 pm #43244
Bits are brand new and made for CF, the cuts aren’t coming out right on the very first cut of the bit. I actually managed to cut a part and on the OD finish pass it broke lol. It seems that the bigger bits work better though. I would like to be using a 2mm bit, but that doesn’t work. I tried a 2.5mm bit and while it is better, it’s still not what it should be. I have a hole size set for 3.5mm in my part to fit an M3 screw but it doesn’t fit when the screw itself is ~ 2.9mm.
I can try faster, I just fear it will cause even more flex. I’ve tried both climb and conventional milling, adaptive and trochoidal aren’t really an option for some of the holes and slot sizes for my drone frame. I actually had another 3″ prop frame in mind where I’d be using that to pocket out some thicker CF but haven’t even bothered designing it yet until I can get cutting what I already have down pat.September 4, 2017 at 1:29 pm #43246
Now you’re making me feel something is loose. Are you able to wiggle around your legs? I can barely move mine. About that play in the gantry, how would you describe it? Do you have any bearings that feel like they’re not making much contact on the conduit? I remember once I had this racking motion in my gantry because I didn’t have enough pipe tension and because my pipes were wearing a flat spot. I fixed it by tightening some tension bolts and rotating the conduit to fresh zinc.
Make sure your belts are tight. The belts actually play a rigidity roll in a way. If they are loose at all everything gets sloppy. Also, put a zip tie over the main zip tie loop so it can’t stretchSeptember 4, 2017 at 1:40 pm #43247
Hmm yeah it seems like a few bearings aren’t making full contact as they spin a little more freely than most. I may need to take my Z axis out and reassemble that. I’d have a hard time believing the conduit was already that far worn down, the machine really hasn’t had a whole lot of run time.
But legs are definitely good and belts are tight also.September 6, 2017 at 8:11 pm #43378
Yeah I might need to take a break from CF. Took apart the middle assembly and tightened up some bearings so they make full contact. I couldn’t hear or really feel any more of the play that I was describing, but after cutting it was still cutting it poorly. Slow, fast, you name it. The only other idea I’ve got at this point is taking a slightly more shallow cut at a medium speed and MAYBE messing with the RPM slightly (I have one of the router speed controllers that apparently applies voltage under load to keep constant RPM but who knows if that works).
I know wood cuts alright so I guess maybe I should get my vice set back up and try some aluminum flat bar again 😛September 6, 2017 at 8:21 pm #43379
How about wood and plastic? You really need to get those mastered before you dive into things like aluminum. Make sure your dimensions are correct in softer materials first. Then you will know hows fast and deep you can push it and you will have a better understanding of all the settings. Aluminum is a “soft” metal but it is still a metal. With wood you don’t have to worry about bit coatings, chips, air blast, coolant, nothing. Aluminum isn’t the best to experiment on. Plastic adds a bit of chips and cooling, metal is everything all at once.September 6, 2017 at 8:41 pm #43380
Wood I’ve done a couple times, but mostly just to test things out. It’s worked out to come within less of half a MM to my nominal numbers and that was before I fixed the little bit of play (if that even bothers to make any difference. I’ve also done a couple thinner acrylic pieces that worked out pretty well after I messed with it a little bit. Very similar situation to the carbon fiber as far as my cutting method goes (but it came out correctly lol).
I may see if I can get my hands on some UHMW or PVC or something to try out, that might be fun.
Oh and I’ve also done a little bit of facing on HDPE to square up the slab I bought to replace my MDF table. That stuff is meesssyy. Cut nicely though. Ended up being ~5.5mm DoC at 1500mm/m with a .25″ endmill on the highest side of the unevenness. That started to sound like the machine’s limit at 30k RPM.September 6, 2017 at 8:55 pm #43381
There are a ton of subtleties you really should make some more cuts in wood and plastic, cut the same exact parts and learn the differences. That way metal will make more sense. This is the same for wood I tell the guys have wood issues to start in foam…you skipped a whole step. I know it sucks to put in all the extra time but it can be really complicated with a huge amount of variables but as soon as people start digging for hardware issues I lean real hard into CAM issues instead. Unless you have a giant machine reasonable tolerances are easily obtainable with the MPCNC hardware. So usually it is a case of unreasonable tolerances or CAM that has not been properly optimized. I screw up all the time so it isn’t like you are screwing up something easy, I screw up in wood, metal is a whole new level.
As for the carbon fiber thing, I stay out of it because I have zero experience with it. I finally bought a piece and it is sitting right here so When I start cutting it up I will have more of an opinion about how to best approach it. Sorry.September 6, 2017 at 9:07 pm #43382
Nah no worries man I hate to be posting on here and taking up time out of anybody’s day (especially yours I’m sure you are a real busy guy lol). My machine’s work area is no more than 500×500 so I think I’ve got that down. Let me know if you try out your carbon fiber sheet, I’m interested to get somebody else’s approach on it. I’m not so much picky about tolerances as long as I can get my M3 screws through the hole and things line up sort of straight lol.
I’ll have to switch to Fusion for some CAM work, I’ve just been using Estlcam since it seems so simple and right up my alley for doing any flat 2D part cuts. I’ll pick up some thicker UHMW and see if I can’t use Fusion to do a nice and easy 3D part with it.
Now let me see where I can find some wood sheets and plastic to order…September 6, 2017 at 10:05 pm #43383
Hey hey hey I may try some cf soon. Though I am a little occupied with my production right now. Gah I wish I could just fly over to your house and have a look. After as many cuts I have done I would like to think I have an eye for what might be the issue, cause what you’re describing is not normal. Seems like you can do wood okay. Come to think of it, I never never tried wood…..uhh. I jumped straight to aluminum which was in a way a bad idea but I have no regrets, it’s just so fun to watch being cut.
Just ditch the carbon fiber, sadly nobody here has any experience with it, none I have seen. I would save it for later until then. If you really are having trouble with aluminum you can PM me or something. I have plenty of time to waste. If you haven’t seen my thread for aluminum you may want to check it out. I have it dialed down to where I basically just sit and eat pizza and watch it run. I get kind of bored in there so I have time to burn on these here forums.September 7, 2017 at 2:05 pm #43400
Haha I mostly started going straight to aluminum too. I have too privileged of a background in metalworking coming into something like this. Waterjets, manual mills, laser, Haas mills, etc lol. I’ve been looking at your thread as it’s been updated (I should probably subscribe to that lol), very cool that you have a part that people want to get ahold of. I’m not very creative myself so almost every time I wanted to try aluminum again I was always stuck on what to cut lol.September 7, 2017 at 2:39 pm #43402
You might want to try Carbide bits for your CF. And they’ll only be good for a part or two. If your bits are low quality they will dull the instant it touches the carbon. Carbon is nasty stuff and can be a really pain to work with.
Carbide is what we use to drill carbon parts on airplanes. I can do about 20-25 holes with a double flute bit. Granted, I’m not CNCing any of this, but I’d still go with carbide if it where me.September 7, 2017 at 4:07 pm #43412
He did use carbide. Infact, he took it a step further to use one of those coated cutters suited for abrasive CFRP.September 7, 2017 at 4:36 pm #43414
Yeah I don’t even bother with HSS endmills for anything and had purchased PCD coated ones made especially for CF.
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