Spinner back plate question

[Charles in SC]

I fitted and riveted my back plate and stiffner together and noticed that it was not flat across it's diameter. Thinking I must have warped it I ordered another set and it was not flat across it's diameter either. My question is, has anyone else had this problem and if so did you flatten it and if so how? If not, did you just install it and trust the prop hub to pull it flat? Mine is a constant speed Hartzell. Thanks in advance!

[Rupester]

Never checked mine. GIven how it gets sandwiched - and torqued- with the prop, squash plate, etc; I can't imagine a little non-flatness makes a difference.

[bret]

I used the trick from doing the emp parts way back when, when I was drilling the holes for the back plate and doubler, I drilled right into my flat work bench top and clicko into the table as I went, this made all the holes line up flat on the work bench table. I also installed a few more rivets than the plans call for.

[fixnflyguy]

Mine was warped as well...as a metal guy, the part is formed in the annealed condition, and when heat treated it will warp a bit. As others have mentioned, cleco to the bench or back up with a plywood circle. once the spinner gets drilled up to it, all will be fine.