Gouges while dimpling

jlfernan · #1 01-05-2007, 04:43 PM

I've had this happen a couple of times a now I'd just thought I'd ask. Sometimes while dimpling a hole near a bend in a part such as where the F-787 stiffner web attaches to the F-706 bulkhead, which worked on today, I made tiny gouges into the metal. Maybe 1/16" long but not very deep. The edge of the female dimple die contacted the material. On side of the die is ground flat to give me extra room, but it must have turned just before I squeezed the dimple. A few passes withe Scotch-Brite pad and some primer and they are all but invisible. My question is, is this a problem or am I just paranoid? I know that on the rudder spar you are warned about this, but I assume it's because of the twisting loads the spar may experience. Any comments?

cytoxin · #2 01-05-2007, 08:02 PM

pics would make this alot easier... but 10 % of sheet thickness IIRC..thats after dressing it out.

jlfernan · #3 01-05-2007, 10:35 PM

Picture added.

G-force · #4 01-05-2007, 11:06 PM

Are you using a small diameter ( I think 3/8") female die? My Avery kit came with two different diameter female dimple dies for 3/32 and it got used often.

jlfernan · #5 01-05-2007, 11:20 PM

These are 1/8" rivets. One side of the female die is ground flat. But I guess in a moment of inattention it had turned to the other side.

G-force · #6 01-05-2007, 11:47 PM

Gotcha. The Avery kit came with a 3/8" dia 1/8 female dimple die as well that would prevent your problem. Reguardless, I would just build on, those dont look bad.

cytoxin · #7 01-06-2007, 06:11 AM

one or two I would let slide but a whole row i would probally replace the part. really doesnt look bad but then it is in a bend and the metall is already thinned here. its a coin toss and a call to vans but i no what they'll say. and im sure it would be correct. on a side note, when the dies are ground to close to the dimple will also do this in flat sheet stock.

Rick6a · #8 01-06-2007, 06:56 AM

Radius defects can be especially suseptible to crack propagation. In all likelyhood the nicks will never grow. Van might say to just ignore it. Still, based upon my experience on the shop floor, good practice would inevitably dictate blending and polishing out the better part of the nicks. Engineers like to call it "breaking the sharp edges" and "radiusing to a smooth transition." In this case, it can be easily done without removing a lot of material by using a fine ball stone followed up by a polishing wheel fitted to a pneumatic pencil grinder or Dremel tool. Alodine to finish. This is common standard procedure in the production environment.