Clamp Ring Tolerances

[diesel0621]

Hello,

I have a sheet metal part that is rolled in to a cylinder, roughly 10.5" inner diameter (+/- .010"), with two flanges at TDC, used to mechanically fasten to a lifting plate. We have had some poor workmanship in these parts from our vendors and I believe it may be the lack of GD&T, or dimensional control of the part.

Please find a sketch of the part with most of the dimensions as it currently is manufactured. Looking for your recommendations to locate datums, as well as type of control to specify. Orientation of the flanges near TDC is critical as they are supposed to fit up to flat plate (.25"thk).

Any information would be greatly appreciated.

 

[jassco]

Hi, Diesel0621:

I can answer your questions as I used to design and manufacture this kind of clamps.

Depending on how you use it, it can be called a strap clamp, or mounting clamp, or strap/mounting clamp. It appears that you want to use it as a strap/mounting clamp. This means that you want your clamp to tie a cylindrical object and simultaneously be fastened to a plate.

I would not call "some poor workmanship" in your parts. It is a nature of roll-formed straps. Asking for +/-.010" is not reasonable. This strap is not round to your specification. Strap manufacturers do not measure roundness at free state. They generally measure gap at the flanges ("ears") under certain torque specification.

You can control roundness or diameter of the strap at free state, but it will be a big number (very big). What you need to learn is process capability from your vendor.

If you want to use GD&T, you can use ID as datum A, vertical plane (perpendicular to your computer screen) as datum B, and center plane through width as datum C. You need to control the holes with a true position. The holes need to be through all, rather than through.

Please keep in mind that it is not easy to tie a cylindrical object and fasten it to a lifting plate as there is redundancy in the system.

Good luck!

Alex

 

[diesel0621]

Jassco,

What tolerances are achievable on a 10/11" diameter based on your experience?