How to machine motorcycle swing arm?

mcarroll_nz

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Hi, my first post here. I'm a machining newbie but having a lot of fun learning along the way.

I have an aluminum box section motorcycle swing arm that I want to open the axle channel by 5mm to accept a larger diameter axle. I'm not sure how to go about suitably holding the piece for machining due to the awkward shape. The only way it will fit in my mill is by clamping one end to the table or securing in the vice but my big concern is chatter ruining the finish.

Any guidance, suggestions, alternatives greatly appreciated. Thanks.

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If your mill head can not swing left or right where you could let the arm clamp to the table and have the other side under the table..... you could get a bit of steel and build a triangle clamp that too the upper and secure it to your table with standard hold downs.
 
Thanks for the response.

Yes, the head does swing thru 90 degrees (it's a PM-932M mill). I had thought about this and coming at it from the side for machining. I could well be wrong but I had read that these machines can be a pain to get aligned vertically again?

I would love to be able to clamp the arm that's being machined with the other side under the table. Unless I'm missing a trick, I can't see how to position it this way as the stand is solid and the piece needs to be centered for milling.
 
You will have to build a fixture to hold them, this may cost more then the machine however.

If it is a hobby job and time and materials are not an issue then have at it.
 
I would remove the vise then put the swing arm like you have in picture except put some wood between the swing arm as support. Cut wood exact fit if not a touch heavy. Then use some strap clamps with some looong threaded rod to hold it all to the table. Align slot and cut. Two setups obviously.
 
Just a thought. Could you move the mill onto a temporary stand that would allow the other side of the trailing arm to go below the mill? A heavy table would work. This will save you a lot of hassle.
Robert
 
Doing it on a lathe would be easier, or on a horizontal mill. But lacking those, Cadillac's approach in post #5 is probably the best
mark
Tilting the head is a possibility, but you still need to mount the swingarm a considerable distance above the table.
Re-tramming the head is a minor concern
 
I think I would build a fixture and try to mount it on the cross slide of the lathe. It would be finicky to set up but would likely be more rigid.
 
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