CNC machining parts

[5upercrab]

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.

quote.PNG


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.

Hmmm

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

5C

[Ocracoke]

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!

[James Williams]

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. https://drizzlebots.co.uk/

[5upercrab]

Cheers folks

Quote was from protolabs

So it does seem like they are a bit pricey. Have reached out to a few more CNC centres. I didn't know about drizzlebots. Looks a nifty website that, will have to get in touch.

[Ocracoke]

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.

[5upercrab]

So an update on this. Got a quote for two of them for less than that original quote... Machining4u in the end. Quick lashup on a drill to test the balance and they are sweet as a nut. Just a few countersinks to put into them and some delicate hacking of some screws and they are good to go bashing with!

Fun fact, Turnigy provide motors with countersunk prop mounting screws that foul the motor shaft!

Spinners.jpg

Build thread coming soon

[TechAUmNu]

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?

[firefly1]

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

[5upercrab]

Yeah I did contemplate water cutting, with a different assembly method. £96 for the two in the end. Ummed and ahhed over cheaper ways but figured the hours of labour that would go into them would be significantly more than doing a shift of overtime in work, and the quality would not be as good!

At some point I may invest in the tooling to do these things myself, but it is a major investment so I will see how far I take the whole robot thing first .

Quick lashup of the spinner and it runs very smoothly, no vibration and high RPM. Need a laser tachometre to measure it!

[TechAUmNu]

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