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Thread: CNC machining parts

  1. #1
    Hello chums

    Since botfest the other week I have decided to get myself into gear and upgrade wee gremlin. Gremlin has dome a decent job for the last couple of events, and generally works exactly as designed, but I think I need something more advanced if I am ever going to challenge the big guns at these events.

    So I am working on something new, which for now is TOP SECRET/ NOT FINISHED, one of those two. But I am currently mooching around trying to get this part CNC machined, which is, err..., a wheel of some description.

    disk plan.PNGdisk oblique.PNG

    I went ahead and got a quote for it from protolabs in stainless steel, but the numbers coming back were a little scary! stainless was not actually much dearer than aluminium, but it is significantly denser and tougher, which provides more moment of inertia for a given size and more durability.


    This is not a cheap hobby - Ocracoke 2018

    Yeah it really isn't - 5upercrab 2019

    So I am casting this one out to the forum. Are protolabs pricey and will there be some magical cheaper CNC place I can use? Or is it all more or less the same? This is probably the cheapest and fastest way to get this thing built, as if I buy the tools it will cost a fortune and will likely be significantly poorer quality. Might have to bite the bullet.

    Water cutting is another interesting option but I am not sure this part would be possible as a single piece of metal, meaning I would need to assemble it somehow and probably lose precision.

    Having said that, I am not actually sure what kinds of tolerances are required on err, wheels, like this one. I have taken care to balance the C of G in the CAD design by offsetting the hole, but how likely am I to get significant vibration if the C of G is a few hundred microns off axis?

    A final option might be to go to a bar shaped... wheel... which could be milled somewhat more easily with a drill press or similar. No need for CNC, but it would mean quite a radical redesign and I would be struggling to fit certain bits in.


    Open to advice anyway. Good to see lots of you the other week and hope your projects are continuing apace!


  2. #2
    Ocracoke's Avatar
    Team Kaizen

    That is some insane pricing, it is probably worth asking around on that, who quoted that?

    You typically balance a single tooth like this with a counterweight on the opposite side of the tooth equal to the mass of the tooth from what I have seen of single tooth discs.

    Good to see you too at the event!
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  3. #3
    Have you tried Drizzlebots? ICYMI Tom Brewster has a shop specifically for antweight "wheels" & offers a custom "wheel" commission service. Having only bought the standard "wheels" he has on offer I don't know how much or how long it will be but it might be worth a shot.
    Team Phyte

  4. #4

  5. #5
    Ocracoke's Avatar
    Team Kaizen

    Quote was from protolabs
    Ah, you did say in your initial post. Speed reading and all that :P

    Kevin had one of those blades on his spinner at BotFest, the "Shredder" variant. Looks nice really but I'd go for the double tooth bar for the extra bite. Still, I think the mini drum wheel you've got going is certainly more original.
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  6. #6

  7. #7
    If you wanted to waterjet/laser that you would need to split the flat part with the bolt holes and then bolt it onto the other part. You won't get the same precision that you get with machining them though and unless you use somewhere with an adaptive head it will have a ~2 degree taper. To waterjet/laser that would probably be <£7 per spinner plus postage.

    Out of curiosity roughly how much did they end up costing?

  8. #8
    Where do you go to waterjet/lasercut? I doubt k-kut would hand me those prices Euan

  9. #9

  10. #10
    Sounds great! I get all my profiles done at kcut.

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