Good afternoon or morning or evening depending on where you are and when you read this :)

I'm thick into making my form blocks for my 750 STOL.  Trying to decide the order of operations and when making the final shape.

I've rough cut the shape of the forms from 3/4" plywood.

Should I router the 1/8" roundoff edges first, then sand the edges for "spingback" angles?

Or, should I sand the springback angle edges then router the 1/8" roundoff edges?

I'm thinking the first option makes the most sense as long as my form block dimesions aren't compromised.

The other option would be to add a routed 1/8" aluminum backing plate on each face, but that's a ton of work and expense I'm not sure I absolutely need.

Thanks in advance for all the wisdom you care to share :)


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So far I have only made forms for two rudder ribs. I used 3/4" MDF and rounded the edges first with a router and then relieved the "spring back" angles with a sander. Worked well that way for me.

Not sure about the plywood but with MDF you can apply super glue to the tighter bend areas of the forms that will harden it up enough to resist deforming under more rigorous hammering.


I would do the roundover before you sand the angle then sand the angle to meet the bottom of the roundover. if you sand the angle first the router bearing will ride farther in because of the angle causing your form block to be undersized. you will then also have to further blend the roundover to meet your springback angle making it more undersized. Dan.

Router then sand the angle.  Dan's right regarding the shaping problem if you do it in the other order.

Don't ask me why I know.

Thanks gentlemen for your input.

Time to dust of the router bit box :)


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