[JWB_Machining]

Hey,
I've got some Fins from some projectile here and i have to make tensile specimen as always. The Fins have a taper though and I need to make them uniform thickness, Is it safe to face these with a 2" shell mill or should I block them in with washers on my magnetic chuck and grind them?

[Geof]

I am a little confused; you mention Al, magnetic chuck and grind. The first is not compatible with the other two.

[extanker59]

I'm also a little confused but for me its a constant state of affairs.
Do you mean .09 thick? .9 thick seems pretty thick to me. Or is this a big sheet and it may chatter?

[JWB_Machining]

Sorry Guys I went to talked to some of the people at the big shop here and they helped me out. Imagine a 0.9" thick rocket fin, not the best for clamping in a vise. It's not entirely prismatic so I need to face it to make it the same thickness throughout. I was thinking about grinding it by blocking it in on my magnetic chuck with pieces of steel. The shop here told me to just face it in the mill n to wear a face shield haha.

[Geof]

Here is a hint for clamping tapered parts in a vise.

Get a piece of cold rolled steel the same height and width as the vise jaws but about 50% thicker; if you have Kurt vise this will be about 6" x 1-3/4" x 1" to 1-1/4".

Mill a .5" radius grove about 3/8" deep across the 1-3/4" width in the middle of the 6" length; when this piece is oriented the same as the vise jaws this groove will be vertical.

Get a 1-3/4" long piece of 1" dia round bar and machine a flat along it; take off about 0.2 which will result in a flat about 3/4" wide.

Place the grooved piece in the vise near the moving jaw and slide the 1" round piece down into the groove with the flat against the jaw; now you have a rocker jaw that can accommodate a tapered piece in the vise.

Provided the taper is not too large, say 20 degrees included angle, friction will prevent it squeezing out, but if you want to be sure bolt a stop on the table against the wide end.

[One of Many]

Seems like more info would have came with that test specimen request. As in grain direction, surface finish and specific dimensions of the piece to fit the tensile tester.

I had cut quite a few out of forged aluminum prop blades with a bandsaw, then finished them on the mill as any piece of roughed out stock.

DC