Need ideas for a fixture with expanding diameter
Need ideas for a fixture with expanding diameter
(OP)
Hello,
I'm designing an inspection fixture that must fit into two pilots. Each pilot is about 8" dia x 0.75 thick with a diameter tolerance of +/- .0015". I need to easily mount a bearing into each pilot while maintaining center to the pilot +/- .0001.
I don't have room for an expanding chuck (too large and heavy) and expanding collets too.
The best idea I have is a ring that is just a few thou under size of the pilot, with single split running from the center to the OD. Then a tapered pipe plug or taper pin centered on the split to make it expand. Then mount the bearing in the center with reliefs around it so the expansion is distributed over the diameter. Only thing is I'm not sure how well this concept will hold center.
I'm interested in any comments about the direction I'm started on, or other suggestions.
Thanks,
David
I'm designing an inspection fixture that must fit into two pilots. Each pilot is about 8" dia x 0.75 thick with a diameter tolerance of +/- .0015". I need to easily mount a bearing into each pilot while maintaining center to the pilot +/- .0001.
I don't have room for an expanding chuck (too large and heavy) and expanding collets too.
The best idea I have is a ring that is just a few thou under size of the pilot, with single split running from the center to the OD. Then a tapered pipe plug or taper pin centered on the split to make it expand. Then mount the bearing in the center with reliefs around it so the expansion is distributed over the diameter. Only thing is I'm not sure how well this concept will hold center.
I'm interested in any comments about the direction I'm started on, or other suggestions.
Thanks,
David





RE: Need ideas for a fixture with expanding diameter
http://www.fennerdrives.com/trantorque/
RE: Need ideas for a fixture with expanding diameter
Consider aluminum or Delrin for the spacer material.
A pipe plug is not a bad idea, but be gentle; it gives you a lot of mechanical advantage.
Mike Halloran
Pembroke Pines, FL, USA
RE: Need ideas for a fixture with expanding diameter
For the split spacer you're right aluminum or delrin could work, but I was considering a 1/2" steel plate. It now occurs to me that I can test the effectiveness before I invest in the whole fixture by buying just the spacer plate first, then CMM it with the pin/plug fitted and confirm concentricity. I figured on a wire EDM to make the spacer plate so that perfect concentricity is assured.
Thanks,
David
RE: Need ideas for a fixture with expanding diameter
RE: Need ideas for a fixture with expanding diameter
David
RE: Need ideas for a fixture with expanding diameter
A steel spacer with a EDM surface may scratch the bearing races.
Steel is also going to be stiff, so you may need extra sawcuts, depending on how much adjustment range you need.
Mike Halloran
Pembroke Pines, FL, USA
RE: Need ideas for a fixture with expanding diameter
Bill
RE: Need ideas for a fixture with expanding diameter
Has anyone tried this kind of thing? Did it work for you?
Thanks,
David
RE: Need ideas for a fixture with expanding diameter
You _can_ use an o-ring as a sort of leakproof hydraulic fluid, by trapping it in a cavity with no free space and then moving one of the cavity boundaries; they don't compress easily.
Have you got a machinist in your shop?
Ask him to show you how to make a 'pot chuck'.
Mike Halloran
Pembroke Pines, FL, USA
RE: Need ideas for a fixture with expanding diameter
RE: Need ideas for a fixture with expanding diameter
The intuitive approach is to replicate the machine, and build a fixture that rotates within two of the cylinders. For the reasons discussed above, it's hard. I spent a lot of time thinking within this paradigm.
I'm not going toward an approach where the fixture is stationary and the part will rotate. The two cylinders that form the datum centerline can be expanding, and if you set the clearance to allow a tiny slip fit, we think the part should rotate consistently around that axis to allow inspection of the 3rd cylinder. The inherent issues with this method - namely - wear on the part, wear on the fixture, friction due to part weight can all be managed. I'm still debating whether it's necessary for the fitted diameters to expand - if the user keeps the component pushed firmly toward the indicator, the clearance has little effect.