machineing radius edges

[charlieuk]

cool wasn't aware you could get something like that for metal, I was searching for round over bits but only found wood type ones. I may be able to put that in my x2 mini mill just. I can get away with not having the step for the prototype . I guess the best way to get that would be on a 4 axis machine, if anyone thinks they can cnc this if its not going to cost a fortune just drop me a pm

many thanks

[Neale]

Are the radiused edges purely cosmetic, or is sizing critical? You could start with a round bar chosen to give about the right radius on the corners and then machine flats to form the faces? Not sure how you would then handle the stepped-down section; personally I would probably stick the bar in a 4-jaw chuck and turn the corner off on a lathe. CNC isn't the only answer! Be interested to hear how you solve it in the end.

[charlieuk]

its not 100% critical I'm making another part that this will slide into, I was wondering about getting a 4 jaw chuck for my lathe and doing exactly that but I drew it up and it just didn't look nice at all so left that idea. I had also considered trying to find some 8 sided hex. bar but that doesn't seam to be easily available. I really must get on the case of building a better cnc to do this sort of work although it looks like that will now have to include a 4th axis!

[charlieuk]

so I purchased the bit but didn't realize er20 collet doesn't go up to 16mm so I had a try on my X2 mini mill however it was a bit of a struggle for it and it didn't turn out perfect, just wondering if anyone in the Sussex area had any sort of machine that would take the bit and could do any of the machining for some beer tokens?

[phill05]

Removing the bulk of material could be done with a TCT wood cutting router bit shaft sizes go up to 12mm, could the transition be finished on a lathe.

Phill

[charlieuk]

I had a go at machineing the keyway yesterday with my less than perfect cnc designed for cutting polystyrene and although I had to go very slow and I only took 1mm cuts it did get the job done quite well, it would have been even better if I had a long enuff bit too.

Now I just need to find some one with a machine that can do the radius a bit better.

[magicniner]

could the transition be finished on a lathe.

Only if the design is such that the corner radius is >= half the part width.

-Nick

[spluppit]

Only if the design is such that the corner radius is >= half the part width.

-Nick

Which makes it a piece of round bar if its square or not doable if it isnt.

[charlieuk]

Update: I took the part to a proper machinist and its taken 4 weeks for the guy to put the radius on the corners, I get it back today and my attempt on my x2 mini mill was better! I think 1 out of the 4 sides is ok the rest he has not got the full radius on and one of them is a mile out its hardly touched it! so frustrated I wasted so much time waiting for the guy to do it let alone the £20 I still got charged.
so back to square one! looks like im going to have to try and do it on my cnc but just use a very small step down and then Finnish it by hand.

so the question is whats the best way to machine it like this? running down the length or short vertical passes?

[magicniner]

The answer depends on your machining strategy, are you using a corner rounding cutter?
If using an End Mill then I'd go with linear cuts with a square endmill to rough it out to fine steps quickest then vertical passes with a ball end mill to best smooth the corners.

At the size transition step can you get away with a groove around the part? Thus allowing it to fit flush to the step edge but eliminating the machined transition from the rounded corners at the step size transition?

- Nick