Dimples

tshort · Post by **tshort** » Thu Feb 17, 2005 11:26 pm

Anyone have any shots of dimpled HS/VS skins (preferably closeups)? My dimples aren't as crisp as I think they should be and I was looking for others for comparison.
Thanks in advance.

Thomas

captain_john · Post by **captain_john** » Fri Feb 18, 2005 6:58 am

Your dimples can't be that far off.

What is the problem... rivets not sitting flush?

I would say quickly touching the rivet seat with a 100 degree deburring tool. Not so much as to remove a TON of metal, just enough to seat the rivet.

I will post a pic later if you really need one or if no one else does. It is just that my camera sux on closeups. Only 2 mega pix.

CJ

tshort · Post by **tshort** » Fri Feb 18, 2005 9:21 am

Nah, the rivets sit fine.
It just seems that there is a little more disturbance of the metal around the dimple than I would expect. Probably just me being too particular about these things...

Thomas

Post by **Spike** » Fri Feb 18, 2005 9:27 am

Ive seen that to Thomas. Ill see if I can get a better picture of my skins tonight as Im also waiting for the weather to break before I prime. I wouldnt sweat it.

tshort · Post by **tshort** » Fri Feb 18, 2005 9:30 pm

I answered my own question today before work...
I was not setting the dimples nearly hard enough, either with the pneumatic squeezer or the C-arm.
With the squeezer, I have to go a little past where the dies spin easily; with the c arm, I really have to bang the crap out of it. This is .032, which I believe differs from that on the -9 and definitely on the -10.

You can tell the top row has been done over; the row in the middle needs to be struck again. There is a definite difference, hitting harder pushes the dies together and brings the skin around the dimple up where it should be rather than leaving a shallow spot leading up to the dimple.

I feel a lot better after getting this figured out!

Thomas[/img]

Post by **Spike** » Fri Feb 18, 2005 9:34 pm

Oh, yeah buddy, that first row looks much better than the second

I two have had to redo a few rows of holes with the C-frame do to understriking. Good Job.

Which part of the tail is that? Your moving along. Didnt you just get that kit?

tshort · Post by **tshort** » Fri Feb 18, 2005 10:07 pm

That's the right HS skin. It definitely looks better!!! I was frustrated till I figured that out.

I got the kit on 2/6 I think. So far the all parts of the HS and VS are drilled, deburred, dimpled (except for the few I'm going to do over!) and ready for priming. I got out the rudder parts yesterday. Gotta wait for warm weather to prime, so I'm going to do all the fabrication stuff and then have one massive day of priming.

Thomas

captain_john · Post by **captain_john** » Fri Feb 18, 2005 10:30 pm

Glad you got it sorted out. Looks like you are getting the hang of it.

The hardest thing about building is, you don't know what you don't know.

You know what I mean?

CJ

bmurrish · Post by **bmurrish** » Sat Feb 19, 2005 12:05 am

Stupid question. Since the second row looks like it has been dimpled too much, is there any way to put something on the bottom side like a 2x4 and un-dimple?

mustang · Post by **mustang** » Sat Feb 19, 2005 2:16 am

I dunno, something doesn't look right here on the row running down the center spar line. Are you sure you have used the correct matching dimple dies??? It looks like there was no female bottom die??

You should be using the male die on top with the female on the bottom. Ensure the dies are a matched set. Ensure the die set is the correct one for the AN426 D3 rivets. To be sure, drop the required rivet into the female dimple die. It should fit perfectly. Ensure the female die has not filled up with debris from multiple dimple operations. The male die should fit down flush on the female die when engaged. Support the skin around the C-Frame/female die with carpet covered 2 X 4's to provide a totally flat skin that just skims the suface of the female dimple die. The C-Frame needs to be on the edge of a table with lots of overhang. This will allow the bottom of the folded skin to slide under the overhang and allow you to work unrestriced on the top skin surface. You can even overhang the female die on the C-Frame over the end of the table a couple of inches when you get holes close to the leading edge of the skin.

Move the skin around to get to the next #40 drilled/deburred hole and engage the top male die into the hole. Now, holding the male die firmly with some downward pressure to keep it engaged through the skin and into the entrance to the female die, grab your rubber mallet and strike the sliding shaft with a sharp rap. This will give you a crisp, clean, dimple, slightly deeper than required for a flush rivet. The biggest danger is not holding enough downward pressure to keep the job in alignment while grabbing the mallet. If the die slides out of the hole slightly and you lose engagement, you get a double hole or an elongated hole and an off center dimple. This is not good! A couple of solutions for this one; (a) Just use the next size up rivet and drill to #30, and redimple using the correct die set. (b) Use a cheater rivet if the hole is elongated with a larger shank but same head if it is possible. Redrill to #30 and carry on.

Cheers, Pete

tshort · Post by **tshort** » Sat Feb 19, 2005 3:12 am

The only problem with the dimples over the front spar (the center row in the picture) is that they are not dimpled enough.
Going over them with the c frame and giving them a solid hit corrects the problem. If the dies are not hit hard enough (especially on the thicker .032 skins) then they do not completely approximate, which leaves a depression leading up to the dimple.
To answer your question, Bill, they actually haven't been dimpled too much (I think I tried to describe this in my original post but wasn't too clear)

And, all of what Pete (mustang) said, except with the addition of making sure you're hitting hard enough.

Thomas

rick6a · Post by **rick6a** » Sat Feb 19, 2005 12:36 pm

I would say quickly touching the rivet seat with a 100 degree deburring tool. Not so much as to remove a TON of metal, just enough to seat the rivet.

George Orndorf demonstrates that very technique in his RV6 series of construction videos. It really does allow the rivet to seat just a tad better. Slightly extra work to be sure, but then the bar is raised extremely high if one's desire is to produce the best possible result. If "good enough" is good enough, fine. Don't worry, be happy. But if one's goal is to produce an award winning homebuilt aircraft, attention to subtle detail such as this does not go unnoticed by the judges.

Dan A · Post by **Dan A** » Sat Feb 19, 2005 10:52 pm

When I was at this stage I too had the same problem but I found that striking the C-tool twice set the dimple correctly. Have fun!!
Dan

Wicked Stick · Post by **Wicked Stick** » Mon Feb 21, 2005 12:14 pm

Dan A wrote:When I was at this stage I too had the same problem but I found that striking the C-tool twice set the dimple correctly. Have fun!!
Dan

I just wanted to throw out a few tips on this from my experience and the experience of others.

Don't strike the thing while it's still away from the surfaces, rather, hold it down and then strike it.

I use a plastic dead blow hammer (it's filled with lead shot) and by holding the shaft down when striking it, it allows me to feel and hear it being dimpled properly. I usually hit twice to confirm a good dimple.

Placing the male dimple die on the bottom allows you to keep the skin in place while bringing the female die and shaft down onto it before striking it. This way it doesn't move on you and avoids an extra Unwanted hole. Just remember to lift up away from the protruding male dimple die when moving the skin to the next hole so you don't scratch the surface of the skin.

Making a c-frame table is well worth it. It really helps to keep the skin flat while dimpling, and makes working with a large skin a piece of cake for 1 person.

tshort · Post by **tshort** » Mon Feb 21, 2005 2:09 pm

I agree. I ended up hitting most twice, some three times. The deadblow mallet is definitely the best hammer.

I, however, prefer the male die on top (keep snickering to minimum...

) - just make sure it fully engages and hold the rod down before hitting. I think it is easier to not have to worry about the other side of the folded skin - this obviously doesn't apply to flat sheets, which I have yet to dimple.

I didn't actually make a c-frame table, but used some plywood sheets covered with cardboard on top of 2x4s laid sideways - this was the perfect height, and allowed me to easily move the c frame forward and back to get the dimples close to the leading edge...

Thomas

Guest · Post by **Guest** » Sat Feb 26, 2005 9:41 am

Experimental aero DRDT-2 dimpler. check it out online. This great tool will remove most all of your troubles! Well worth the extra cost, hell you've got quite a few to do!

www.experimentalaero.com