Rudder stiffners are bending when dimpled.

[Roy25101]

The rudder stiffners, particularly the longer ones are bending slightly when dimpled. I experimented with dimple depth and pressure and I am using what is required for a nice nest with the skin. Should I try and straighten them prior to back riveting or will it just work itself out? Thanks...

[N427EF]

The stiffeners are of pretty thin material and will easily expand a bit as a result of the dimple squeeze.
I would use the fluting pliers to straighten them out before riveting.
That stiffener will have a memory and always keep the curve in it if you don't straighten them out.
As a rule, I never join material that does not fit without forcing it in place.

[MarkW]

Hey Roy,
I see you are local. There are a few of us RV'ers and builders in Sanford. Check your dimple dies carefully. Sometimes if you use a large die it will hit the inside curve of the vertical and cause that problem. Use the small female die on those. They should not be changing the shape of the stiffener.

[Roy25101]

I'm using a sub structure die. Perhaps that's the issue.

[Ralph Inkster]

Try using less force or pressure while dimpling. The force required will vary with the different thickness material you are working on. Practice on some scrap till you get the right 'feel' before tackling actual airplane parts.
Also remove plastic before dimpling.

[Ralph Inkster]

What is a sub structure die?

[Roy25101]

Cleveland sells sub-structure dies. The back side of a dimple in skin will be a different size than the front. Therefore the dimple in the ribs for example are a different size. So far they have worked well.

[MarkW]

I have also not heard of a Structure die but Cleveland shows them as the standard die. They also show a small die. It is included in their kit.

http://www.cleavelandtool.com/Dimple.../#.WLnTdFXyvcs

You defiantly have to use the small die on the stiffeners.

[Roy25101]

Yep. Y'all are correct. Do not use sub-structure dies on thin pieces.

[wirejock]

Originally Posted by MarkW

Hey Roy,
I see you are local. There are a few of us RV'ers and builders in Sanford. Check your dimple dies carefully. Sometimes if you use a large die it will hit the inside curve of the vertical and cause that problem. Use the small female die on those. They should not be changing the shape of the stiffener.

Some builders grind a flat side on the female die so it clears the flange. All of mine are flat sided. At first it was tough to grind up a brand new die but after scrapping a few parts, oh well. Just don't grind flat into the part touching the mating die.