Oval holes

This topic contains 7 replies, has 3 voices, and was last updated by Profile photo of Barry Barry 4 months, 1 week ago.

Viewing 8 posts - 1 through 8 (of 8 total)
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  • #17612
    Profile photo of Andersen
    Andersen
    Participant

    Hi

    My MPCNC seems to be working, but it is not as accurate as I had hoped. I am currently using a Dewalt D26200. I started with a Dremel, but that was too weak.

    The attached image is of a Dice that I am trying to make. When I measure the pieces, then they are between 0.2mm to 0.5mm too big.

    I have tried with a 1mm endmill, and a 3.175mm endmill. With about the same result. I am running fairly slow, both are cut with 50mm/min, at a depth of 4mm in plywood.

    My main concern is the holes are not round. Is it reasonable to expect a better result, or is this normal?

    Thanks,
    Andersen

    #17619
    Profile photo of vicious1
    vicious1
    Keymaster

    Nope That isn’t normal. Did you buy your parts from me?

    Do test cuts in foam then pine, foam adds almost zero cutting drag so if you have issues you know it isn’t the material causing them, pine will give better accruacy, plywood sucks to cut for a bunch of reasons.

    Lets see a few pictures of the whole machine.

    From what your shown, I could say maybe belts are loose, or maybe that vac hose is pulling on your gantry. Attaching a vacuum can add a ton of drag and it looks like you have the rigid part of it still on there, it works just like a wrench extension. pulling even harder on your tool. On top of that you are using a very large tool. What kind of bit are you using, an actual end mill or a router bit? 1 flute or 2, up or down cut or flat, what approx RPM?

    You speed is really far off did you type it correct? Watch some of my vids 50mm/min is about .8mm/s I cut at about 5mm deep 10k rpm, 15mm/s for ply.

    #17626
    Profile photo of Andersen
    Andersen
    Participant

    Thanks for the quick replay. It is good to know that it is not normal. 🙂

    I sourced the parts my self. I live in Denmark. If there were an European reseller, and maybe a metric version, I would defiantly have considered buying a set. I am using a Smoothieboard to control the machine. I have some experience building 3d printes, but I have very little CNC experience. I have added a few more images of my machine.

    From what your shown, I could say maybe belts are loose.

    That was the first thing I checked. The belts are quite tight, not like on a Guitar, but almost.

    or maybe that vac hose is pulling on your gantry. Attaching a vacuum can add a ton of drag and it looks like you have the rigid part of it still on there, it works just like a wrench extension. pulling even harder on your tool.

    Yes. I will try again without the vacuum hose. I think I have done that, but I will try again to be sure.

    On top of that you are using a very large tool. What kind of bit are you using, an actual end mill or a router bit? 1 flute or 2, up or down cut or flat, what approx RPM?

    Yes. The Dewalt D26200 is quite large (I think it the EU version of the 661), I initially tried with a Dremel, but that seemed too weak. I could hear it loosing speed. I am running the Dewalt D26200 on max, that is 27000 rpm. It can go down to 16000 rpm. Should I do that?

    What kind of bit are you using, an actual end mill or a router bit? 1 flute or 2, up or down cut or flat, what approx RPM?

    The bit that seems to work the best for me is this: ebay 1mm. What type of bit is the best to start out with?

    You speed is really far off did you type it correct? Watch some of my vids 50mm/min is about .8mm/s I cut at about 5mm deep 10k rpm, 15mm/s for ply.

    Yes. I did cut with 50mm/min. It is very slow. I wanted to try out slow, to eliminate speed issues. (The speed was an issue when I used the Dremel). I have tried with 200mm/min (3mm/s) with the Dewalt, and it is the same result. As I said I am quite new to CNC, and do not really know what is reasonable.

    Do test cuts in foam then pine, foam adds almost zero cutting drag so if you have issues you know it isn’t the material causing them, pine will give better accruacy, plywood sucks to cut for a bunch of reasons.

    I do not have any foam, and I am not exactly sure what it is. For now I only have plywood and acrylic glass (Plexiglas). I will try to get something else and try that.

    Again, thanks.

    #17634
    Profile photo of vicious1
    vicious1
    Keymaster

    Can’t help you with smoothie board settings, you have a ton of setting to set speed, acceleration, jerk….Usually no where near 3D printer settings so you can’t really go by that. Make sure you are not using arcs in your gcode for now, that seems to screw up most holes.

    You need to do some research on feeds and speeds. You can’t just go slower, chip load is a factor. I am assuming you are just burning your way through the material and not actually cutting it at that speed. 1mm bit is too small, its requirements are very precise.

    You are new to cnc and you have the two worst materials to learn on, ply and acrylic. If you can’t find the high density foam at your hardware store get the softest wood you can buy, usually pine.

    Have a look at my videos and try to get your setting close too mine, start there.

    If you can move your spindle up. Mount it so the bottom of the collet is as close to the bottom of the z tubes as possible, and move your material up even higher.

    #17647
    Profile photo of Barry
    Barry
    Participant

    Gotta say, that yellow looks good!

    #17674
    Profile photo of Andersen
    Andersen
    Participant

    I made a few changes:

        I tried without the arc G-codes (G2 and G3), it took some time to figure out how to get fusion 360 to “linearize” the output.
        I removed the vacuum holder
        I also tried with 400mm/min (6mm/s). It burns the wood much less.
        I used a 3.125mm one flute end mill ebay link. I do not know if it is any good?

    The result is not too good. See attached.

    I still need to try something softer then plywood.

    I do suspect that maybe the x-axis to be too long, and maybe the aluminum tubes I have used are too flexible…

    Again, thanks for the suggestions.

    #17676
    Profile photo of vicious1
    vicious1
    Keymaster

    Try estlcam, with arcs turned off. Fusion is a pretty advanced program you could easily be overlooking something.

    You are still going very slow, and those bits are not the right ones I have no idea what those are actually for. Look in the shop page for the recommended bits and get them from anywhere you want. Did you raise up the material, that will minimize the problems from too long of rails, if that is even a problem.

    #17685
    Profile photo of Barry
    Barry
    Participant

    Usually use single flute for plastics. These almost look like roughing end mills, but aren’t.

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