Hammerforming

[DanH]

Once upon a time, an RV was built from raw sheet by forming over hammerforms. Obviously we don't do much of that anymore, although there are some remaining plans-builders who do.

Anyway, this is a rescue project, a fuselage former for a Yak 50, the station being about a foot aft of the firewall. The airplane did a bit of belly crawling following a gear problem, happily on smooth grass, and the original former wasn't salvagable. Apparently the parts are no longer available from the Mother Country, so the repair required the fabrication of a new former.

I was able to pull measurements from another 50, and combined with the remains of the broken former, I got the shape nailed down in AutoCad. Took the .dwg file to a waterjet shop and had them cut the basic hammerform profile from a chunk of 3/4" 6061T6 plate pulled from my scrap bin. The rest is hand work, notably edge radius, lightening hole locations, and a die to press the lightening hole flanges.

First I tried a practice part in 2024-T3, just to see if I could avoid a trip to the heat treat shop. As expected, it wasn't possible to shrink T3 enough at the wide outer flange. Probably could have done it with flutes, but the original Russian part had none, and the goal was a exact copy. So, out came the 2024-0 soft stuff. One quick practice part to tune the tools, then this part. I'll probably send it to the rib shop that builds your RV ribs for Vans, and ask them to tuck it in with a batch for heat treating to the T3 level.

Hammerform on top, new Russian-American fuselage former on bottom. And yes, if your local Yak flyer happens to develop a bad belly rib, tell him you know where to get a duplicate

[grubbat]

Dan,
Wouldn't that be T-4 rather than T-3 on the heat treating?
cj

[wirejock]

Nice work. That takes an artists touch.

[g zero]

Looks good Dan, pretty satisfying making something from nothing .Lucky for most Vans came along otherwise there would be about 487 Thorpes finshed by now .

[sblack]

Be prepared to receive a pretzel from the heat treater

[g zero]

Originally Posted by sblack

Be prepared to receive a pretzel from the heat treater

How could this problem be solved before heat treating ?

[David Paule]

It looks as if there's no allowance for spring-back after forming. I've never worked with 2024-T0 before. Will it need any?

Dave

[fixnflyguy]

At my day job we heat treat every day, often some very interesting parts. If you were in Greensboro NC, Id have it done for you tomorrow. 2024-0, treated to 2024-T4 or T42 (T3 is only achieved by the mfg. of the alloy)is a simple process, and some warping will likely occur. Often, the part can be wired with safety wire to a rigid steel item which will prevent most of the warping. We use baskets made from perforated steel mesh, but have also used angle iron ect. If the quench process is done quickly and correctly, its is minimal. Most RV ribs require fluting to remove such twist/bowing, as we all know. Any straightening will be easiest just after the quench and prior to the age hardening, but I wouldn't worry too much about that. I make many parts for vintage birds at my home shop, and its always very rewarding..keep up the good work!

[DanH]

Originally Posted by David Paule

It looks as if there's no allowance for spring-back after forming. I've never worked with 2024-T0 before. Will it need any?

Not much. Actually, I did sand a springback allowance for the outside flange, as it is the widest, faces the skin, and the one requiring shrinking. None on the inside, as the flange is only 3/8" wide, and doesn't need to be perfectly 90 degrees to the web.

[sblack]

Originally Posted by g zero

How could this problem be solved before heat treating ?

I don't know if it can. It is long and skinny so I would expect it to curl up somewhat - just because of its basic shape - nothing to o do with how it was formed. The maddening thing is that right out of heat treat it will still be soft enough to correct for some period of time. But if your heat treater is on the other side of the country it's difficult.