A builder of an all-aluminum kit dimples thousands of holes before the airplane is skinned. Where the skin is too thin to countersink for a flush rivet, the hole is pressed into a cone between a male and a female die, so the countersunk head sits flush and the skin is formed rather than cut away. The kit maker's construction manual says which holes are dimpled and which are machine countersunk. The tool that does the pressing, and how it is set up, decides whether the dimples come out uniform.
Cleaveland Aircraft Tool publishes a one-page instruction sheet for each of its dimpling tools. Here is what they say.
The C-frame
The C-frame is a steel frame with a 22-inch throat that sits under a table. A male die goes in a set holder at the bottom, the female die in a ram on top, and the ram is struck with a hammer. Cleaveland's sheet says it makes dimples for 3/32 and 1/8 inch flat-head rivets and for #4, #6, #8 and #10 screws. The bottom socket takes any rivet gun set with a .401-inch shank, so the same frame back-rivets with a flush set.
Cleaveland treats the table as part of the tool and includes plans for one (a 36 by 48 inch plywood top over a pine frame, carpeted, on adjustable feet) because the table holds the skin square to the dies. The carpet keeps the skin from being scuffed by chips, which fall into it instead of rolling under the sheet; the sheet says to vacuum it now and then.
Setting it up, by the sheet:
- Put the male die in the bottom, the female in the ram. The dies are all the same thickness, so the setup holds whatever die is in.
- Lay a razor blade or other thin, flat piece on the flat face of the male die, not on its pilot, and let the ram come down on it. Adjust the table's feet until the blade hovers 1/16 inch above the carpet.
- Check with a small square that the ram is square to the carpet, front to back and side to side, and adjust again until it is.
- Put the blade back and check the die still stands about 1/16 inch proud of the table. A die recessed below the table leaves a dent beside every dimple.
- Lock the feet with their nuts and set the O-ring so there is about 3/4 inch between the ram and the set holder at rest.
To dimple, the pilot of the male die goes up through the hole, the female die is set over it and held down by hand, and the ram is struck. The sheet names the most common mistake as striking the ram too hard: it leaves rings around the top of the dimple and deforms the sheet. Two or three light blows are better than one hard one. Cleaveland's comparison page adds to listen for the change in tone that marks a complete dimple, and its sheet says to practice on scrap aluminum and try different hammer weights before starting on a real skin.
For holes too close to a flange for the female die, Cleaveland's tight-fit fixture (DIE4263DF) screws to the bench overhanging its edge by about 5/8 inch; the rib slips over it, and a standard 3/32 male die in the C-frame ram is tapped in. Its sheet warns against side loads, which can snap the male die's pilot.
The DRDT-2
The DRDT-2 is a welded steel frame worked by a lever instead of a hammer. Cleaveland lists a 22-inch throat, so it reaches the middle of a 44-inch-wide sheet, aluminum up to 0.040 inch thick, and the industry-standard dies with 3/16-inch shanks. It is close to silent, and since no hammer is held, both hands are free to move the sheet. A light return spring keeps the head from dropping onto the skin if the handle is let go, and a relief under the lower frame clears spars, ribs and leading-edge skins.
The trade-offs are in Cleaveland's own comparison: the DRDT-2 only dimples, where the C-frame also back-rivets; it weighs about 55 pounds against the C-frame's 11; and it has to be clamped or bolted to a sturdy table. It ships separately from its supplier rather than from Cleaveland.
A rivet squeezer
Dimple dies also go in a hand or pneumatic squeezer's yoke and ram, which reaches holes near an edge without carrying the sheet to the bench. Cleaveland's sheet for its Main Squeeze hand squeezer gives the setup: put the dies in the yoke and ram, then thread the ram out until the dies touch, with nothing between them and no pressure on the handles, when there is about an inch of space between the handles. The same sheet sets limits that apply whenever the ram is adjusted: with the handles closed, the ram is never to stick out more than 1 inch from the base of the yoke (1-1/8 inch from the squeezer body with an unusually tall yoke); where more travel is needed, a longer set is used instead, because over-extending the ram breaks the tool.
Close-quarter dies
Some holes are out of reach of every frame and yoke. Cleaveland's close-quarter dies are pulled together by a mandrel in an ordinary pop rivet tool, and the sheet is plain about their limits: they are for places conventional dies will not fit, and do not make as good a dimple. They work best in 0.016-inch skin, as on control surfaces.
The 3/32 set comes with 10 soft copper mandrels that fit the #40 hole closely, and 2 steel ones. In 0.016 skin the copper mandrel alone sets the dimple: the female die goes over the mandrel and through the hole from inside the skin, the male die slips on from outside, and the pop rivet tool, with its closest-fitting tip, is squeezed slowly until the pressure changes, which is where the metal stops forming and the mandrel starts to stretch. The grip is eased and that pressure reached once more. In thicker skin the copper pull is done first to align the dies, then a steel mandrel finishes the dimple the same way. With the 1/8-inch dies the hole starts at #40 and is drilled to #30 after the dimple is formed.
The angle matters too. The standard U.S. flush rivet, the MS20426, has a 100-degree head, as AC 43.13-1B notes; Cleaveland sells separate 120-degree dies (DIECS4-4) for 1/8-inch pop rivets.
Before the first skin
Cleaveland's C-frame sheet and its Tool School page say the same thing: practice on scrap aluminum before the kit. The faults its sheets describe, rings around the top of a dimple from striking too hard and a dent beside each one from a recessed die, show up on scrap as well as on a skin, and are far cheaper to find there.
Sources
- Cleaveland Aircraft Tool, Comparing squeezers and dimplers, read October 28, 2026.
- Cleaveland Aircraft Tool, instruction sheets on its Documents, Instructions and Tool Guide page: C-Frame Dimpling Tool and table plans (CF80, December 2024); Close Quarter Die, 3/32 (DIE4263CQ, August 2025); Dimpling Fixture for tight-fit 3/32 rivets (DIE4263DF, October 2025); Main Squeeze hand rivet squeezer (SCH22, January 2025). Read October 28, 2026.
- Cleaveland Aircraft Tool, product pages for the C-Frame (CF80), the DRDT-2 and its dimpling tools and dies, read October 28, 2026.
- Cleaveland Aircraft Tool, Practice projects and test gauges, Tool School, read October 28, 2026.
- FAA, AC 43.13-1B with Change 1, paragraph 4-57 (the MS20426 100-degree countersunk rivet).
- Picture: Vans RV-7 -G-TRVR-.jpg), Alan Wilson, May 7, 2017, CC BY-SA 2.0, via Wikimedia Commons.