[spaceflightmeow]

Say I have two 0.016" sheets and a 3/32" springback dimple die pair. I can dimple each sheet individually, or overlay them and dimple together with the same die. Can dimpling the sheets together achieve a more closer-fitting set of dimples?

 

[Jesse]

If those two holes are getting the same rivet, then it may work, but if just saving time and they don't go together, then you will get different dimples in the two parts. I've never tried that, but separately dimpled parts seem to fit very well. It ain't broke, so I personally wouldn't try to fix it.

 

[wirejock]

dimple two sheets

Welcome Dmitry
If your sig is current, it appears your working on a practice kit. Great.

I've done it when I messed up and missed a dimple but the result is two sheets with a less than desirable dimple. The result was just not as crisp. I would avoid it if possible.

 

[spaceflightmeow]

I tested this out today. Here's a picture of a test coupon with two holes: the one on the left (SD) had each sheet individually dimpled. On the right (DD), both sheets were dimpled simultaneously.

After dimpling:

Here's the result after squeezing:

Section of double dimpled rivet:

On the bottom side of the bottom skin on the "double dimpled" hole ('DD' in photo), there is more of a radius (less crisp appearance from bottom), but I'm not sure if that matters. My intent with doing the double dimpling was so that the bottom skin uses the top skin as the dimple die, effectively making the bottom dimple slightly larger, as you might do if you used a substructure or tank die.

On another note, I'm looking at Cleaveland's tank dies and substructure dies and trying to understand the difference between the two. Cleaveland even says it's ok to use the tank dies as substructure dies. Also, I've read this entire epic thread (http://www.vansairforce.com/community/showthread.php?t=87568&page=5) but am still confused.

 

[N427EF]

I wouldn't

It is clear from your pictures that the double dimpled holes, at least the one
on the bottom sheet is a degraded and poorly formed dimple.
Imagine an exaggeration of what you are trying to do by dimpling say 5 sheets together. The bottom one would most likely not even get a dent in it.
Can't blame you for asking and I too have done it a few times when a rivet had to be drilled out or holes did not mach up precisely. All in all maybe a half dozen times over 2 airplanes.
If saving time is on your mind you are not going to find a lot of opportunity to dimple 2 sheets stacked on top of each other. Most rivets will either attach an aluminum sheet to a bulkhead where the sheet can be dimpled in a bench dimpler/riveter and the bulkhead is dimpled with a squeezer because of its shape. When joining 2 sheet of aluminum attached to one another along an edge you cannot stack the sheet unless you have a 20 foot table to hold and align the rivet lines and move them both along at the same time. Now you need 3 people helping you, a job that can easily be done by yourself in a conventional fashion, one piece at the time.

When using tank dimple dies stick to tanks and follow Van's instruction for the rest of the airplane. Don't over think the dimpling, it is really quite simple and easily mastered after just a few skins on the empenage kit.
Congratulations on getting started.

 

[wirejock]

dies

Tons of RVs have been built with standard dies.
That said, now Cleveland has options.
If I understand correctly...
For a typical part, you would use the standard die for the skin and the tank dies for the substructure.
For the tank, you would use the tank dies for the skin and the substructure dies for the substructure.
I just ordered a set of substructure dies to run samples for my tanks so take this for what it's worth because I haven't actually tried it. I'm hoping the rivets sit better in the tank dimple.
I did try a sample using the tank dimple dies for both. The dimple would not nest completely so I expect it will with the substructure dies.

 

[spaceflightmeow]

It is clear from your pictures that the double dimpled holes, at least the one
on the bottom sheet is a degraded and poorly formed dimple.
Imagine an exaggeration of what you are trying to do by dimpling say 5 sheets together. The bottom one would most likely not even get a dent in it.

Is it necessarily bad that the bottom one barely gets a dimple? My theory of dimpling the sheets together was that they would mesh together better (because they were dimpled together). Funny you should mention the example of five sheets. The book "Aircraft Structural Technician" by Dale Hurst demonstrates how to dimple holes of multiple sheets, using different angle dies:

The first skin is dimpled at 100 degrees, the 2nd at 112 degrees, the 3rd at 124, and so on. Continuing on, the 4th skin would be dimpled at 136 degrees and the 5th would be dimpled at 148 degrees. There would indeed be a very slight dimple on the 5th skin, and the angle on the bottom side of that skin would be 160 degrees.

 

[rzbill]

Too much effort being spent on this. It is not that useful.

From a practical standpoint, there are very few places during the build where it would be easier to dimple both parts as an assembly. Take the wing for example. One would have to hold a loose rib and a skin in position on the dimpling device. Total PITA. The skins are done on a c-frame/DRDT2 and the rib flanges are commonly done with a handheld dimpler.

Yes, you can dimple two thin sheets together. I had to do it a few places. I think it was when I was installing the wing root fairings but my memory is not clear.

 

[Veetail88]

Seems to me that we're dimpling the sheets to keep the flush rivet flush and not for the sake of making dimples.

Theoretically, dimpling sheets all together should make the sheets nest perfectly, but I think elasticity of the material and quality of the tooling would have an effect on the actual quality of said assembly.

In the end though, I would agree with Bill. Probably not worth worrying about a lot for the number of times you could actually put this method to use. I do it when I need to and don't give it a thought. Course, I did ignore an edge distance problem on one of my floor sheets once! so consider the source!

 

[BillL]

I tested this out today. Here's a picture of a test coupon with two holes: the one on the left (SD) had each sheet individually dimpled. On the right (DD), both sheets were dimpled simultaneously.

After dimpling:

Here's the result after squeezing:

Section of double dimpled rivet:

On the bottom side of the bottom skin on the "double dimpled" hole ('DD' in photo), there is more of a radius (less crisp appearance from bottom), but I'm not sure if that matters. My intent with doing the double dimpling was so that the bottom skin uses the top skin as the dimple die, effectively making the bottom dimple slightly larger, as you might do if you used a substructure or tank die.

On another note, I'm looking at Cleaveland's tank dies and substructure dies and trying to understand the difference between the two. Cleaveland even says it's ok to use the tank dies as substructure dies. Also, I've read this entire epic thread (http://www.vansairforce.com/community/showthread.php?t=87568&page=5) but am still confused.

Nice test and evaluation procedure, it will serve you well as you proceed. Like others, I had to redimple two (or more) sheets at times, but always dimpled individually first. Good to know, from your cutaway, that the double thin sheet method makes a good tight joint should you ever need it!

Knowing that the second sheet dimple needs to be slightly different than the top geometry was something I never thought about but discovered and usually just took a deburring tool with a couple of rounds to make them nest perfectly. Tight nesting will yield a better looking surface in general, or that is what I found.

Happy building and welcome to the best hobby in the world! (just my opinion)

 

[comfortcat]

Spaceflightmeow - Wow!

I'd like to make an observation. Not about dimpling, but about the new member of the list.

Welcome Dmitry!

One of the big dangers of any public Internet Listserve is that you can get tangled up in OWT (Old Wives Tales) and get bad advice that sounds like good advice.

It is often said that building an RV does not take rocket science, but it looks like Spaceflightmeow IS in fact a Rocket Scientist! AND he is willing to contribute to the list with time, effort, pictures and real live examples and tests.

*sigh* I only wish you were a few years farther along, and past the point where I am working.

Your public profile says SoCal, so I assume you make washing machines up in the desert.

CC

 

[spaceflightmeow]

Although saving time was not the main point, it might save time compared to dimpling the top skin with a regular die and the bottom skin/rib with a substructure die. Either way, I want to know if double-dimpling produces better meshing parts and if there is any downside. My own experiment seems to suggest it's a good idea but that's sample size of 1. I did repeat try this a few more times on another plate but haven't cut it up yet to look at the results.

Part of the reason this came up is that a coworker mine dove right in to his RV tail kit and told me he is dimpling both multiple sheets together. Also, the illustration in Hurst's book brings up the different angle dies.

Also, I appreciate the warm welcome.

 

[rzbill]

Part of the reason this came up is that a coworker mine dove right in to his RV tail kit and told me he is dimpling both multiple sheets together.

Curious. Would that coworked be assembling with clecos, match drilling and disassembling for deburring prior to the additional steps of reassembling to "match dimple" before disassembling to prime (if you lean that way)?

Match drilling = burrs between sheets. Obviously not good to crush into the dimple.