more centering work questions

[timeone]

Im remaking my bracket as in another thread and had nearly finished when the work slipped one of the clamp nuts had come loose so im out of centre.
so how do i centre it again ive got a 52 mm hole so no centre mark or anything.

appreciate some helps guys

jason

[BillTodd]

Can you mount a 3 jaw small chuck on your rotary table and hold it by the centre hole?

Or

Machine a 52mm disc and use that to re-centre the part

Bill

[DMIOM]

Jason,

Have you got a dial indicators with a finger? if so, you can get, or make, a clamp to hold it in the spindle and then sweep it round by hand and when (as you tweek X/Y) there is no oscillation on the indicator, then you're centred (this is also how a Blake or co-axial centring indicator works).

Another approach (which really needs DROs or negligible backlash) - take a contact edge-finder type probe and creep up in, say X at approximately the widest point; when you make contact, note the X reading; then wind X until you make contact on the other side, note that reading (or the number of turns etc. it took to get there) and halve it - that will be your central X value; then repeat for Y.

Dave

[timeone]

Bill thats a good idea and maybe the one to go for.

Ive got dro but havent finished fitting it yet so my fault i cant use it. kind of putting it off as got to make a few brackets to fit the linears

ive only got normal dials gauges maybe i could set it up in some way to dial it in ill play tomorrow and see.

better get my ass in gear and get it sorted out

jason

[andyf]

Jason, from the pic you linked to in your other thread http://www.allproducts.com/metal/daizan/02-l.jpg , precise concentricity between the outside and inside diameters doesn't seem to be absolutely essential; the things will clamp up even if one side ends up a millimetre thicker than the other. Either of the two suggestions already made: using the X and Y dials, or making up a 52mm plug, should get you close enough. If you turn the plug, which could be wooden, on your lathe, you could use a centre in the tailstock to impress a centre mark into the wood, and then use that mark as a guide on the mill. A slight taper on the plug could be helpful when it comes to fitting it into the work.

Andy

[mgj]

You can do the halving system with ordinary dials A DRO makes it very easy, but mandraulics work fine.