Does anyone know if there’s an existing bolt on expanding mandrel chuck that fits the micro arc4 or is the only option an adaptor plate or drilling the mandrel mounting plate?
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I make small ones out of material drops to use on lathe and 4th axis. The ones shown below are blind and lock from back. I have others that lock from the front. Great for mill ops on tubing and or making gears. They mount in collet blocks or 3 and 4 jaw chucks. Can be quickly sized to fit material .
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I’m planing on making watch case bezels so I need enough precision to suit an interference fit with a circular sapphire crystal. So do you have good concentricity on yours?
I turn these to size required on a 8l lathe so concentricity is not much of a issue. Then slots are cut on mill with a arbor saw to complete the tool.
“concentricity” or run out when mounted in a 4th axis 3 jaw chuck might be a little problematic.
Almost no way to avoid that. Even if you change 3 jaw chuck with a 5c collet chuck you can still end up with run out that you need to fiddle with.
Only true way to zero out run out in material in a lathe or 4th axis is a 4+ jaw chuck.
I’m not clear what the setup is on a micro arc to create the interference fit you want.
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I wonder if the typical expanding mandrel idea like what @Lane_Burkhart has, could be made with a tapered back slightly larger than the through bore of the micro arc. If the clamping screw is then made long enough to extend past the rear of the microarc, and another tapered plug is inserted in the back end, the two tapers might work to hold everything concentric to that through bore. Of course, that assumes the bore is perfectly concentric to the axis of rotation. It also wouldn’t be terribly rigid under higher cutting loads
A better approach is probably a zero-point style interface that bolts to the output of the microarc, and provides mounting provisions for the arbors. Dial in the interface/adapter plate once on install, and the arbors are made to be concentric to that plate. Some lathe work involved to make that happen but probably not a terribly difficult design to produce.
So when making these I assume you use tool steel for these. Do you harden them expanded or just loose? Do you finish with a grind to final tolerance?
How do you design the outer jaws to stay parallel when the jaw expands? Or do you turn the O.D. after the center expansion bolt is tightened. Also guessing the clamping range is less than 1/32 or 1mm similar too a normal collet?
My train of thought is drill a round bar then cut the taper with a MT-1 taper cutter, then cut the jaws with a slitting saw? I’m just afraid the jaws are going to start wiggling after the first couple saw cuts. I am making it as short as possible 11mm 3/8” so it might be ok.
The ones shown are made from 1", 3/4", 1/2" alum. bar drops. Just like soft jaws!
They work great for holding tubing, large gear blanks and round stock for lathe operations. Brass is expensive, bore the brass drop and blind mount it in arbor. Run lathe ops and you end up with almost no waste.
Anyway you can make what you need from tool steel, brass, aluminum or whatever.
Just a solution to a work holding or fixture holding problem. I like the blind arbor style enough I applied it to a number of other tools I use like cnc router and table saw to hold custom fixtures in locations.
Custom Face plate with a flange to mount an expanding arbor in would also be a decent solution.
Install face plate and zero the run out on the arbor mount.
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