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!