RivetBangers.com

[CalKid]

Started to use the #30 dimple die on a the rear hzstab and noticed that the resulting hole looked bigger to my eye. I measured it and sure enough was .011 bigger in dia after dimpling. Wierd. Wondering if the cause was that I had perhaps turned the dies down too tight rather than just too touch if that makes sense.

[cjensen]

Nope. The resulting hole is always going to grow a slight amount because you are moving the edges away from each other in the circle. It's normal.

The dimple dies will only go so far, meaning you can't over-dimple a #30 hole with a #30 dimple die. You can under-dimple if it doesn't seat all the way, but once the dies come together, that's as far as they'll go.

No worries!

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Chad Jensen
N755CB|RV-7|Airworthy 7/6/2010
RV-7 Build Log

[CalKid]

Thanks Chad. That makes perfect sense.

[TomNativeNewYorker]

[Wicked Stick]

I adjust the dimple dies so that when the pneumatic squeezer is full travel, the dies are just touching each other. Any more than that is overkill. I watched a video from one of the tool manufacturers when I first started building and the technique was to have them touch, but you could still spin the die a bit. If you couldn't spin the die by hand when it was full travel, you had them too tight.
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Dave "WS" Rogers
RV-8 N173DR

[cjensen]

I use the same technique WS...but, it doesn't really matter all that much. If they are a little tight, all that's gonna happen is the yoke will flex a little. You still can't "over dimple" the hole if they are too tight.

Just shoot for 'em touching, still able to spin, and you're good!


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Chad Jensen
N755CB|RV-7|Airworthy 7/6/2010
RV-7 Build Log

[JohnR]

The above is correct, the hole is a little larger.

My tech counselor told me the biggest mistake people make is not dimpling enough. He then showed me the procedure as WS and Chad have talked about. We looked at an under dimpled hole and one that was dimpled to the point of a little "coining" (you can see where the dies were) and sure enough the ones dimpled more were much better and provided a smoother flatter surface when the rivets were set.

I also found I seemed to get better dimples with my Cleaveland Tool spring back dies than the cheap ones I had so I bought a complete set and always use them.


My $.02 worth, and probably about what it is worth.
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JohnR
RV-7A - Fuselage - SOLD, just not supposed to be
Numbers 6:24 - The LORD bless thee, and keep thee

[captain_john]

[JohnR]

Heh!


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JohnR
RV-7A - Fuselage - SOLD, just not supposed to be
Numbers 6:24 - The LORD bless thee, and keep thee

[dons]

Not to start anything, but I too believed you couldn't over dimple, so I did some testing and did find you could easily compress the dimple area beyond the point where only metal under the dies was being affected. I really set out to find out what the ideal dimple should look like using a DRDT-2 and in the process found I could over do it. Here is a link to something I wrote about it.

Link
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Don Sinclair
CYKF
RV-7A (Fuselage)

[cjensen]

I kinda figured it was only a matter of time before somebody presented something about over dimpling.

I almost changed my post to reflect the fact that you can distort the metal by using too much pressure, but the dimple itself can only fit the shape of the tool moving the metal.

Using the common sense all of us have, adjusting the dies to contact each other when the air valve is fully open, will result in the desired dimple. If it's adjusted beyond that, of course the metal will distort.

It's not over-dimpling the hole, it's distorting the metal around the dimple because of too much pressure...
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Chad Jensen
N755CB|RV-7|Airworthy 7/6/2010
RV-7 Build Log

[dons]

Chad is right, it is a splitting hairs kinda thing, put too much pressure on the dies and you can push a very very small amount of material out of the dimple area into the surrounding metal and thus cause some (and very little at that ) distortion. The only way I could 'measure' it was with light reflection, which can be a very sensitive and powerful tool in the right situation.

From my experimentation, it is far better to error on the side of more pressure making the dimples than too little.

You can make quite a mess with a 5 pound sledgehammer and a c-frame with dimple dies, but that was done on purpose knowing it was way over kill just to what would happen. My testing for the 'over dimpling' was more for the curiosity (substitute another word if you like) of knowing, and since I calibrated my DRDT-2, it was easy to pick a close to ideal pressure repeatably anyway. Yes, I over analyze and engineer a lot of things I do, that's why I could never design my own plane, I would never get it done!
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Don Sinclair
CYKF
RV-7A (Fuselage)

[Mike Balzer]

I have used spring back tank dies in all my ribs and under structure and regular spring back dies on all skins. I have used a hand made DRDT and have had great Flush results.
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It is better to be on the ground wishing you were in the air, then being in the air and wishing you were on the ground. N78MB

[dons]

to rivetbangers Mike. I have been using tank dies for under structure and regular ones for skins as well, works great. If there are three layers, I only use the tank dies on the bottom layer and use a counter sink tool to slightly hit the middle layer.
_________________
Don Sinclair
CYKF
RV-7A (Fuselage)

[Mike Balzer]

I do the same when I have three layers. I welded up my own DRDT with 2x4 steel 3/16 thick and cut gusets to reinforce the DRDT from bending. I under cut the DRDT so I could use it to dimple all the way to the trailing edge of the elevator and rudder.

I am new to the site and would like to know what the class code means under the name of the members.
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It is better to be on the ground wishing you were in the air, then being in the air and wishing you were on the ground. N78MB

[Brantel]

[jakec]

Don,

Great write-up on the DRDT-2. One question for you. You mentioned in your article that there was a different turn setting for each thickness of sheet. Do you re-calibrate it with the scale each time you change thicknesses or is it simply a matter of remembering how many turns gives you good results for each thickness and setting it accordingly?

I'm not looking to build a show winner but I would really like my skins to be as smooth as possible. Thanks.

Can't wait to get started.
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Jake Crause
Baghdad, Iraq
www.homebuiltairplanes.com

[dons]

Thanks Jake. Each time the thickness of the material changes I follow this very quick procedure:

1- loosen the lock nut
2- turn the adjustment screw a couple of turns so the dies will not touch when the handle is fully pulled down
3- pull the handle all the way down
4- turn the adjustment screw by hand until the dimple dies touch
5- read the scale on the adjustment screw
6- lift the handle
7- turn the adjustment screw for the optimal pre-load for the new thickness
8- tighten the lock nut

It looks like a lot of steps, but it only takes 15 or 20 seconds. The amount of pre-load required will vary depending on the stiffness of your frame, in my case with the factory built version, about 1 turn works for 0.025" material as an example.
_________________
Don Sinclair
CYKF
RV-7A (Fuselage)

[jakec]

Thanks Don. Appreciate it!
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Jake Crause
Baghdad, Iraq
www.homebuiltairplanes.com