Under-dimpling Epidemic DRDT-2

Hi,
Just read an article in the April 07 EAA105 newsletter, www.eaa105.org/Newsletter/nl-200704.pdf page 18 by Randy Lervold. In it he compares dimples done with the DRDT-2 both with and without preload to the dimples made with the Avery c-frame. He says all the pieces done with the DRDT-2 were underdimpled just less so with those that were preloaded. His reason for testing was that he is seeing an epidemic of under-dimpling in some recent projects he has looked at.

What are your thoughts and experiece? I have just started welding together a DRDT-2 frame for my RV-10 project and am now wondering if I made the right choice in a dimpling tool.

Bill Greenley
ordering an RV-10 tail kit

i would bet on that

i would bet a 6 pack he is correct. when the pressure is applied that slow it would seem unlikely to get the crisp dimple you would with a c- frame. you dont get crisp dimples with a squeezer either but they'll do. the squeezer yoke spreads and creates pressure concentrations on the throat side of the dies if not carefully adjusted. just like a pop rivit dimpler,the dies come
into full contact, yet the skin is not level leading up to the dimple. take the same piece and put it in the c-frame and one light whack and the skin is flat until the apex of the dimple. very hard to even see where they are on a well done wing skin. when my wings were in spected with there mediocre workmanship i was asked if i was building a show plane. not hardly but the c-frame produces better results.
as usual, ymmv, my .02, and IMHO

it should be noted ive never used a drdt and my hypothesis is purely from observation. i would however put the c-frame up against one at any time. people call the c-frame crude and prehistoric. maybe, but when something is this simple and effective it needs no improvement.

Nonsense. The DRDT II consistenly makes the best dimples I've seen...period. Call Van's and ask them...they use one.

It definitely helps to adjust the DRDT-2 dies with a preload- I use a preload because it gives a little better consistency with thicker materials. But, I have to wonder if the differences between the C-frame and DRDT part of the test might be better explained by differences in the dies themselves? I ask that because I have never seen a halo around a DRDT dimple when the dimples are all the correct depth.

I think the real advantage of the DRDT is the consistency of dimples, much easier use, quiet operation, and faster hole alignment without the chance of punching unwanted holes if something moves. I'd further think a "halo" might be a source of potential stress cracking- I don't find it particularly attractive either- is it really needed??? FWIW, Ive also been recently shown that a light deburring, after dimpling, makes a big difference in achieving a smooth surface over dimples.

If someone is worried about under dimpling with the DRDT-2 with a light pressure adjustment, why not use a set of fuel tank dimpling dies?

jcoloccia said:

Nonsense. The DRDT II consistenly makes the best dimples I've seen...period.

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I agree, my DRDT does a great job. However, before I figured out how to properly adjust the thing, I was under-dimpling my first parts. (I later went back and re-dimpled after I got a clue) So, I agree that with a DRDT it is possible to make a whole bunch of consistently under-set dimples if you don't set it up right, but that's the fault of the operator, not the tool. My dimples are all very nice and I wouldn't trade my DRDT for anything.

mcb

I asked Paul to comment on Randy's article. The following was his response:


I didn't see the article before. Thanks for bringing it to my attention.

Randy seems to be fair in his assessment but I don't necessarily agree with his conclusion.

Impact dimpling (or it is really stamping) will replicate the dies the best. Think of the coins we us as currency. Very sharp reproductions from the masters. However impacting the skins isn't necessarily the safest approach to dimpling. Impact dimpling isn't performed in commercial or military aircraft production.

As you know from experience that setting up the tool properly gives you the best result. So everyone who uses the tool and sets it up properly should yield very good results. I didn't see a picture of results #2 compared to results #3 in his article, just a few opinions.

I didn't notice a mention of how the set rivets looked once shot in either of the test pieces, just the dimples.

From what I have seen comparing the differences between the DRDT-2 dimples and impact c-frame dimples is very little. The impact dimples might be a little crisper but not significantly. Once painted I do not think you will ever tell the difference.

I am going to send a note to Randy.

Thanks for the heads up.

Sincerely,

Paul Merems
ExperimentalAero

This needs some clarification....

My dimples with the DRDT-2 look much better that the c-frame. Just because you don't leave crisp die marks does not mean that they are not good. My skins have improved apearance greatly since switching to the DRDT-2.

I set mine up by checking the dimple with a rivet, adding preload until the rivet is perfectly flush. No probelm!

My holes with the c-frame sometimes would get oblong and sometimes would be under dimpled if I was not paying 100% attention to each hole.

With the DRDT-2, the first is the same as the last. Not to mention, I am not sweating profusely and the neighbors are not calling the police to report the noise.

You can make bad dimples with with the c-frame, a squeezer, or the DRDT-2. Bad setup or operation does not make the tool at fault.

I will never go back!

You can easily UNDER DIMPLE with ANY dimpling tool. Like most things in this hobby, operator error 100%.

dan said:

You can easily UNDER DIMPLE with ANY dimpling tool. Like most things in this hobby, operator error 100%.

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Well put Dan!

rleffler said:

I asked Paul to comment on Randy's article. The following was his response:

Randy seems to be fair in his assessment but I don't necessarily agree with his conclusion.



Impact dimpling (or it is really stamping) will replicate the dies the best. Think of the coins we us as currency. Very sharp reproductions from the masters. However impacting the skins isn't necessarily the safest approach to dimpling. Impact dimpling isn't performed in commercial or military aircraft production.

As you know from experience that setting up the tool properly gives you the best result. So everyone who uses the tool and sets it up properly should yield very good results. I didn't see a picture of results #2 compared to results #3 in his article, just a few opinions.

I didn't notice a mention of how the set rivets looked once shot in either of the test pieces, just the dimples.

From what I have seen comparing the differences between the DRDT-2 dimples and impact c-frame dimples is very little. The impact dimples might be a little crisper but not significantly. Once painted I do not think you will ever tell the difference.

I am going to send a note to Randy.

Thanks for the heads up.

Sincerely,

Paul Merems
ExperimentalAero


​

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Paul,


Thanks for your comments, and I think your description of the process is very apt. The last thing I want to do is disparage anyone's product (DRDT-2), yet I did feel compelled to comment on what I've been observing and the results of our little test. I would agree with your statement on the difference between a CORRECTLY adjusted DRDT-2 dimple and a c-frame dimple... "The impact dimples might be a little crisper but not significantly." IMHO both are within the window of good results, but the difference is visible nonetheless, even to a new builder. To be clear, dimples made with the DRDT-2 without some preload are not within that window just as dimples under-struck with a c-frame or under-squeezed with a squeezer are not.

As the maker of the DRDT-2 thanks for your objectivity. The lesson/message to all the builders out there is to dimple correctly (don't under-dimple) whether this means adjusting your DRDT-2 properly, striking your c-frame correctly, or using your squeezer properly. On this I think we can all agree.

Best,

I tend to agree on the operator setup/error theory. A bad swat of the hammer on a C-Frame, and a poor setup on a squeezer or pneumatic squeezer can also yield poor dimples. One crisp swat with my Avery plastic mallet always did the trick on my C frame. On my pneumatic squeezer, I always ran the dies up til they touched when fully extended. I used an adjustable set holder. I'm sure the DRDT-2 is a great tool, but can also be missused. Bottom line is, if your rivets aren't setting in correctly, something needs attention before you rivet.

Roberta

I don't have much to add except to say that I built a DRDT and love it. I did have to set the preload to get the right result, but that can be determined with one dimple and a quick adjustment. That takes less than a minute. From then on, it's consistent results.

Even in our little backyard factories, there's no substitute for a good die trial and first piece inspection.

My two cents....

randylervold said:

Paul,

Thanks for your comments, and I think your description of the process is very apt. The last thing I want to do is disparage anyone's product (DRDT-2), yet I did feel compelled to comment on what I've been observing and the results of our little test.

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I think the key here is that someone noticed a consistent problem and took the time to track it down. Thank you, Randy!

As I see it, the problem IS in the setup. The DRDT-2 is an excellent tool, IF setup/used properly. When I set mine up the first time, I spent about a half an hour with test pieces and rivets until I got just the right dimple. If you just assemble the tool and expect perfect dimples, you will be disappointed. Like any other new tool, some trial and error is in order for the best results. If it's setup incorrectly, you'll get consistently incorrect dimples, and vice-versa.

ExperimentalAero's comments

Thank you all for posting your views on the dimpling comments in the article.

To Randy, thank you for your follow-on response.

The Internet and the forums are great tools for information. Good news travels fast, negative news travels faster. I am concerned that the information in Randy's article unintentionally painted a negative picture of the DRDT-2 performance with respect to under dimpling and final quality of the finished dimples.

I want to make sure everyone who reads this understands that the DRDT-2 produces high quality dimples when setup and used properly. The manual explains how to set up the tool, which also includes alignment and preload directions (http://www.experimentalaero.com/DRDT-2 Manual & Drawings.pdf). I extensively tested the tools about a year before it was introduced to the homebuilders. These tests included intentional misalignment and various preload adjustments on various thicknesses of materials. Time after time I found that is was very hard to set the tool up incorrectly and setting the preload was easy.

One thing I have found that plays a more important role in the quality of the dimples are the dimple dies. Not all dimple dies produce the same results. There are at least 5 manufactures of dimple dies out there and all are cut slightly differently. Through in to the mix spring-back vs standard dimple dies and there are even more variables. One area that was unclear in the article was whether the same dimple dies were used with the DRDT-2 and the impact c-frame dimpler. I have used my set of dimple dies in both the DRDT-2 and c-frame dimplers and there is very little difference in the results. Once painted or polished the difference is imperceptible. The DRDT-2 produces the same quality dimples as a good hand or pneumatic hand squeezer (properly setup).

I do believe impact c-frame dimpling can achieve a crisper or sharper dimple. Think of the coins we use as currency. These are produced by stamping which replicates the master with fine detail. Impact dimpling should be called "stamp" dimpling because that is what it truly is. The harder you hit the better the replication. However the harder you hit the more work hardening to the dimpled area and the possibility of damage to the skin. In additional the quality/consistency of the impact dimple varies with the each hammer blow.

The DRDT-2 is in the hands of builders, training centers, aircraft repair facilities and aircraft factories all over the world. The DRDT-2 must be working well for these customers or I would hear about it (I get emails regularly from customers thanking me for a wonderful product). I have new homebuilders as well as several repeat builders (2nd or 3rd RV's). These repeat builders have a lot of experience with the impact c-frame dimpler but have chosen to switch to the DRDT-2 on their new project. The training centers have been helping new builders build literally hundreds of empennage kits with the DRDT-2 and have a tremendous amount of experience with both the DRDT-2 and the impact c-frame dimplers.

If you have any doubts just post your questions on the forum. If you want to get some real world high use feedback on the tool contact the Alexander Tech Center (RV training center www.buildtofly.com), they have been using the tool extensively and have produced several empennage kits with the tool (don?t know the exact number but I believe it is 100+).

The DRDT-2 is for the builder who wants a better way to dimple that is consistent, easy, safe, less fatiguing and noise free then the impact c-frame dimpler. If you have any questions or comments please email me [email protected]. Feedback is always welcome.

Build on...............................................

I'm responding here only because I hope NO builder will come away from this thread thinking there is anything even remotely wrong with the DRDT2. I assembled the tool two years ago and started dimpling away. I think it is pretty hard to set up or use the tool incorrectly if you make even a cursory reading of the directions Paul provides. I suppose it could be possible that my dimples are "underdimpled," but if so I certainly don't care since my rivets sit perfectly fllush! Hands down, this tool was the best "luxury" tool I purchased and definitely believe that builders will make fewer mistakes with this tool than they will with a c-frame (and I have both). Thanks Paul for a great product!

I can't imagine a dimpling tool that is easier to use, makes better dimples, and has less risk of adding aditional holes in my skins than my DRDT-2. I performs flawlessly and properly every time. I've used it on the major portion of the substructure and all of the skins.

~10,000 DRDT-2 dimples in place. None are under-dimpled. All were formed quietly and precisely.

I am in no way associated with the company.

Guy Prevost

The best tool, IF setup correctly...

I too read the article and would like to ask a question/ pose a thought. While I agree that a C-frame gives a great dimple, so does the DRDT2 when properly set up and used. When I first purchased mine, I left it temporarily on the bench top and was able to dimple by using a temporary table set up around it to create a flat work surface. I too noticed what you are saying about the lack of the halo/fish eye, and a slight depression around the dimple. What I found out was that however slightly the DRDT2 was rising of the table top causing an angle. Since I found this out, I now bolt down the DRDT2 when dimpling, and have the same preload you mention in your article. Now when it is bolted down I can get the same consistent dimples as with the C-frame, I can apply the same force to the set as with a hammer. What was lacking was keeping the DRDT2 in the same place consistently on the table top. The directions for the tool does not stress enough it needs to be mounted in this way, and allot of the local builders here have taken the liberty of putting it on a movable top rather than fixing it to a rigid structure.

I would suggest we rerun the test with the tool rigid mounted and see the difference it can make and how much quieter, and stress free dimpling can be when the tool is setup correctly.
"You could not pry this tool out of my cold dead fingers, Yes I like it that much!"
and I am not affiliated with the company in any way other than a totally satisfied customer.

Dan Lloyd
N289DT RV10E

Good input-Tip

When I use/tested the DRDT-2 I always had it clamped or bolted to the bench.

When I demonstrate the tool at shows I usually stick a 2x2" piece of wood through the lower beam and clamp the wood to the bench. You only have to secure the rear of the tool to prevent it from lifting during dimpling.

Tip:

For dimpling large pieces place cardboard boxes (with carpet remnants or towels over the tops) outboard of the DRDT-2 to act as outriggers to support the work. If the parts are very large, use more boxes. When the boxes aren't needed fold them up and store them. Simple, cheap and takes up very little space.

using the DRDT correctly?

Hi Paul (and group). I am a novice builder / dimpler and I don't own a C-Frame cause I didn't like the way it worked at the SportAir workshop. I've been using the DRDT-2 from day 1 and am thrilled with the tool.

I did not understand when I started that a "pre-load" was necessary. The dimples looked "good enough" to me with my non-experienced eye. I have since learned (about 1/2 way through the HS) that it seems to need some pre-load, but it doesn't seem to matter how much.

What I have found is that, as long as the last 1" or so of handle throw is gently compressing the dies together (actually slightly bending the frame apart, with nothing between the dies) it seems to work just fine. I don't seem to have to try more or less amount of pre-load. As long as I have some it seems pretty non-critical. If I have none (the dies just touch when the handle is down) then I don't get the great dimples. Is this what others see? If so, maybe Paul could add a line about pre-load to the manual.

Thanks for making such a great tool!

got DRDT?

anybody in benalillo NM got one ? id like to see it used next week

Thanks for the feedback

Thanks for all the great responses, some groups you wait weeks for one answer, while here you get lots of serious responses and no flames.

My summary of the responses is that the DRDT-2 is a great tool, but as with any tool it can be misused, and that three items are important to using it for dimpleing.

1. Have a small amount of preload.

2. Make sure you have good dies.

3. Make sure the tool is secured well.

4. Make some test dimples and put a rivet in and check before doing the real thing.

Ah, 4, I guess I need to learn to count.

Thanks again for all the great feedback. I can't wait for the shop to be ready so I can start on the RV-10 empennage.
Bill Greenley

cytoxin said:

anybody in benalillo NM got one ? id like to see it used next week

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I've got one in Albuquerque, 15 miles North of Bernalillo. I'm sure a demonstration can be arranged.

G

Preload?

Call me dense, but I don't understand the preloading requirement. I have been using my DRDT2 successfully for a year and a half and it produces great results. I can't help but wonder though if I have set it up incorrectly. I have it set so that my dimple dies are tightly together when the handle is lowered. You can't spin the dies at all. Should I be setting it so that there is more lever travel possible even after the dies meet? This approach would seem to just be stressing the mechanism.

Preload

Antony,

If you are setting your ram adjustment so that the dies are in contact with each other and they are forced together and "can not spin" you definitely will get a preload when you dimple a part. You only need enough preload to produce an acceptable dimple. I typically look for the "witness mark" produced by the die on ALCAD surface. This mark is the ring mark that is the outer diameter of the dimple die minus the 2 times the edge radius of the die. Any additional preload WILL NOT DAMAGE the aluminum at all but just will require a little more pressure on the handle.

You set the DRDT-2 preload just as you would set you hand or pneumatic squeezer. Adjust the rams until you achieve the desired dimple.

It sounds like you have things under control.

If you have any question please email me at [email protected]

Thanks

Thanks for the confirmation Paul. My technique has been producing great results, but I was curious if I should be doing something differently.

The dimpling process takes hardly any effort. I can do it with two fingers on the handle. As you depress the handle you feel the metal give, then as you release pressure the handle "springs back" ever so slightly and you know the motion is complete.

Dimple Die Observation...

I've followed this thread with great interest when it was hot since I own a DRDT-2 and LOVE it. (You can have it when I'm dead) It prompted me to do a comparison and I thought I'd share it with everyone.

My original die, and the one I used for my HStab, VStab, Rudder Skins and stiffener holes in the elevators came with the ATS tool kit that I ordered. When this thread, and the article that prompted it, first posted I ordered a set of spring back dies from avery. Here's a photo of the difference between the two side by side. Although the photo isn't great (darn cheap camera), there is a noticable difference between the two.



I've always set the "loading" of my DRDT-2 as per the instructions, so these two dimples, using different dies, were loaded the same. You can see that the spring back die creates a crisper dimple. When a rivet is placed in the dimpled holes they both look good. I haven't riveted any of the holes that have used the new die, but my gut feeling is that I'll be happier with the quality, especially on skin surfaces that aren't flat.

If there is an under dimpling epidemic, set correctly, it's not the dimpler...

I use the DRDT-2, and absolutely love it. I had the hole thing made up for me. I don't use a special bench set up for it, I pull it out and set it on the bench and go for it. Now I don't know if this is the proper way to set it up, but it works for me and I use this way on all dies. I put the bottom one in place, then put the top one in place, loosen the lock nut, put the arm all the way down, take the top shank with die in place and turn it down until it touches the bottom one, lock the lock nut and dimple away. I've always liked the result.