aluminium machining

[drumsticksplinter]

It sounds like something I could make, but I can't be sure or give a price without first seeing a drawing

Thanks Jonathon, its basically the bearing side of the revolving ballnut design. I'm working on a drawing, but I'm not very good with the 3d stuff at the moment... Its really just an aluminium block approx 110 x 110 x 60 with an 80mm bore either side to take 2 angular contact bearings. Oh, and I need 2 of them please...

[drumsticksplinter]

I've just put some dimensions on some drawings I started, Hope you can understand them ok:

[Shinobiwan]

Not surprised your getting high quotes. It looks like a simple part on face value but start to think of how to machine it and your looking at working on up to 3 different orientations, 2 of which would require a a double sided jig to ensure the bearing recesses are aligned to a high tolerance.

My advice would be to redesign the part otherwise you'll either pay a lot or I can't imagine anyone on here taking it on for peanuts.

[m_c]

For two off, CNC isn't really worth it.
A lathe with four jaw chuck would get the boring done. Bore center bore and one bearing recess, flip, dial in, bore other recess.
Mill would soon sort out the flanges (either horizontal with a slab mill, or vertical with flycutter or large facemill). Then holes can be drilled in a pillar drill.

If they're getting made from sawn stock, you'd have to mill at least 4 faces flat first (you could face the other two in the lathe), and to save set-up time you could machine the flanges at the same time before doing the boring.

A couple notes about the drawings-
1) what tolerance do you need on the bearing bores (i.e. interference, sliding)?
2) if you're putting a 8mm bolt through the flange holes, you need them drilled larger than 8mm for clearance

I could do them, but I just don't have the time.

[Jonathan]

Nothing difficult about that - there are various ways to get the bearing bores concentric and machine the bottom face parallel to their axis. It looks like you've chosen 7208 bearings, which are bigger than you need for a 25mm ballscrew - I'd use 7207 instead to reduce the moment of inertia and cost. Have you drawn the rest of it?

Edit: On the rotating ballnut mounts I have made I've tended to make the bearings a light interference fit, but I expect either would be fine. They need to be a sliding fit on the shaft to allow pre-loading.

[drumsticksplinter]

Thanks for the replies and advice guys!

I wasn't really sure the best way to machine this piece, I do actually have a lathe, but I wouldn't really know where to start with getting the piece center....

It looks like you've chosen 7208 bearings, which are bigger than you need for a 25mm ballscrew - I'd use 7207 instead to reduce the moment of inertia and cost. Have you drawn the rest of it?

Thanks for that advice Jonathan, I was just allowing a little more clearance for the screw, but I think the 7207 would be better like you say.

[Jonathan]

I wasn't really sure the best way to machine this piece, I do actually have a lathe, but I wouldn't really know where to start with getting the piece center...

Presumably your lathe is big enough and you've got a 4-jaw chuck and dial indicator? If so then you can just do what m_c said, as that's how I'd do it (or I might line bore it). If you buy the bearings first then you can use them to help with the machining - when it's close take very small cuts and keep trying the bearing to see if it fits. If you set the compound slide to an acute angle you can use it to advance the tool in small increments more accuratel than using the cross slide.

Edit: This thread has more information: http://www.mycncuk.com/forums/steppe...-steppers.html