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C Frame vs DRDT-2 Dimple Shapes

rockitdoc

Well Known Member
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So, I have both. But, I cannot seem to prevent the C Frame from creating 'craters' around the dimple. The DRDT-2 does not do this at all.

Yes, I am hitting the C Frame with significant vigor...twice with a 24 oz dead blow hammer. Works great, except I don't like the 'crater/dent' created around the dimple by the C Frame. I even changed the elevation of the table around the C Frame to make sure the male die and surrounding table were at the same elevation, thinking that if the table were slightly higher, it might tend to bend the skin around the die. Doesn't matter.

I hope you can see the difference in the pic if I can figure out how to put the photo here:

dateposted-public


Guess not.

I know it's prolly just cosmetic, but still, the DRDT-2 creates a really nice clean divot with no dent/crater.

What am I doing wrong. Or, is this a characteristic of the C Frame?

Thanks, in advance, as usual.

S
 
I've built two RVs with a C-frame and don't care for the DRDT at all, having tried one and returned it early in my second project. The C-frame, in addition to its other attributes, is a far more versatile tool.

The pic doesn't show, but you're definitely over-hitting with a 24 oz. dead-blow. I use a relatively lightweight, wooden dimpling mallet. Two strikes per dimple does the trick.
 
I've built two RVs with a C-frame and don't care for the DRDT at all, having tried one and returned it early in my second project. The C-frame, in addition to its other attributes, is a far more versatile tool.

The pic doesn't show, but you're definitely over-hitting with a 24 oz. dead-blow. I use a relatively lightweight, wooden dimpling mallet. Two strikes per dimple does the trick.

It was my understanding that one couldn’t hit it too hard, but not hitting hit hard enuf causes underdimpling.
 
It was my understanding that one couldn’t hit it too hard, but not hitting hit hard enuf causes underdimpling.

You definitely have to hit it hard enough, but hitting it harder than that won't help and might hurt. It's a calibrated strike sort of thing which just takes a little experience.
 
I second that

You're most likely over-driving the dimples. As suggested above from a well respected builder, use a lighter mallet/lighter hits. When the dimple is fully formed, the tap and the related sound should change (sounds "crisper" for lack of a better term).

I assume the crater you reference is uniformly around the new dimple, i.e. you don't have an alignment issue. As a double check, I'd verify the part numbers of the related punch and die are for your intended use.

If your parts aren't staying (****-near perfectly) straight after dimpling, that would be more evidence of overstriking. Best of luck
 
C-frame

I also use a two pound dead blow and hit every hole twice really hard. No craters.
My money is on one of these issues.
1. Under dimpled. I've tried to over dimple. I hit a test piece as hard as I could swing my sledge hammer with one hand. Looked the same. I'm not saying it's impossible to over dimple. Just saying.
2. Platform misalignment. I've messed up one top skin by not shimming the platform so the skin was perfectly aligned to the dies. It had crater at every dimple.
3. Dies. Never seen a bad set but it's possible.
 
Take a look. Too much force?

That's either too much force, a bad/misaligned set of dimple dies, or both. Remember: all you're trying to achieve is to bring the two dies together to form the dimple - more force isn't necessary and should, as a matter of orderly building practices, be avoided.
 
Test samples

I think it's an alignment problem. Either something is shifting or the skin isn't staying perfectly in line with the mating line of the two dies. Is it possible the C-frame is sitting on something that gives? Try a small piece of scrap on the concrete floor.
Just for grins, grab a small piece of scrap and hit that thing as hard as you can.
 
I think it's an alignment problem.

I agree. The aluminium sheet needs to be properly and extensively supported across the work table at exactly the height of the dimple die interface. Not higher, not lower, not on an angle.

I dimpled my whole RV7 with a C frame and never had any dimples like in your photo. And you don’t need to smash the cr*p out of it with a heavy steel hammer. I used 2 blows with a computhane hammer.

When you get it right you can hear from the sound of the second thud that the dimple is fully formed. You can hear it bottoming out.

And finally, it’s bad form to be trying new construction techniques on the actual aircraft. Best practice on scrap...otherwise your aircraft becomes the scrap. ;)
 
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use your free hand to push down on the shaft of the c-frame so the dies are in contact with the sheet, then hit it with the hammer. Don't hit is with the shaft fully sprung back, it will bind in the bushing and you lose all the energy.
 
The great existential debates of our time....

1, Prime or do not prime?
2, Is there a God?
3, Tricycle gear or tailwheel?
4, Is being told to wear a mask an infringement of my freedoms?
5, C Frame or DRDT-2?
 
I helped a buddy of mine set up his DRDT-2 correctly; his initial dimples were under-formed as evidenced by the oil/beer can deformation visible around the dimple in low-angle lighting. There should be a slight++ over center action with the material between the die.

I just ran a sample coupon of .016" 2024-T3 so you can see the effects of each machine. Note, the "under set" C-Frame was created with a single blow from a nylon mallet. The "slightly over set" C-Frame example was created with two hits from a 24Oz dead blow hammer. I think it is possible to deform the metal surrounding the dimple if you're too exuberant, as seen in the example.

Good luck!
 

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IMO you should see the halo around the dimples, as it tells you that every part of the die is pressing the aluminum into shape.

Also, as was mentioned earlier, both tools should be set up over a part of the work table that has a vertical support going all the way to the floor, otherwise some of the energy/effort will dissipate in the bending of the table surface.
 
A "halo" should be just a scuff on the surface around the dimple, not a dent. When I set up the DRDT-2 to do my -3 tail, I'd get the halo, and also lay a straightedge up on edge across the surface of the dimple to check for dishing. I wanted it as flat as possible around the rivet. I found that if I followed the directions included with the DR and used a good die set, I could make a pretty darn nice dimple. (Taught my ex-husband how to set the dang thing up right. ;))
 
DRDT2.... Set up correctly.

I also have used both the c-frame and DRDT2. Love the DRDT2! Once it's set up correctly, per the instructions, it is a set it and forget it machine for dimples. It's much quieter and (IMHO) easier to use than the c-frame, because the c-frame requires hitting the "sweet spot" of force with your hammer. Not saying it's not perfectly doable with a c-frame, but the DRDT2 is the superior tool.
 
If you are using “spring back dies”, over striking is not desirable as the dies slightly over bend the AL as it will relax back. Easily tested with a rivet to see if the head sits proud. Marty
 
Hmmm,
just noticed the OP's picture & where the piece is sitting in the DRDT-2, the male dimple set must be leaving some nasty scratches on the skin's outside surface.
 
The video posted by Ed Fleming in Post #15 is a must view for the OP and for everyone else who wants to see a truly objective review by Cleaveland Aircraft Tools of the real differences between the DRDT and the C-Frame. I’ll reproduce it here.

https://www.youtube.com/watch?v=_mpbsQF1eu0&app=desktop

Note that Cleaveland points out that the C-Frame can be used for actual riveting (as opposed to just dimpling) in some areas where access is very limited. I find that much of the discussion about builder preference between the DRDT and the C-Frame tends to boil down to defence of personal choice without too much actual knowledge of the pros and cons of the two devices. In my opinion this video review sums it all up very well.
 
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Comparing dimple dies

Related to this thread:

What is the difference between the 3/32" dimple dies from different sources? Aircraft Spruce has them for about $20 and Cleaveland sells them for $42. I think Cleaveland makes their own dies. Are they better?
 
Related to this thread:

What is the difference between the 3/32" dimple dies from different sources? Aircraft Spruce has them for about $20 and Cleaveland sells them for $42. I think Cleaveland makes their own dies. Are they better?

I have the Brown tool version, and it works great. And it is under $20. You can get a 4 piece kit for under $50. Have not tried the others.
 
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