How to dimple for #8 screw without cracks?

Brantel · #1 10-19-2007, 10:45 AM

So you do a nice job drilling a clean hole for a # 8 screw using a #19 bit, you do a good job deburing both sides of the hole, then you take your #8 dimple dies and dimple the hole only to find that you have small cracks around the ID of the hole.

How do you prevent this?

gpiney · #2 10-19-2007, 11:13 AM

Was the piece too thin to machine CS? Is it a structural piece or something like an inspection cover? The only ones I have done were machine CS'ed.

w1curtis · #3 10-19-2007, 01:33 PM

Guess I've been lucky but I use the CP-214 pneumatic squeezer and I haven't had any cracking on #6, #8 or other size holes. I use the standard dies from Avery.

Jamie · #4 10-19-2007, 01:36 PM

Well, for better or for worse I use a slightly larger bit if the skin starts cracking (#18, sometimes a #17). I haven't fallen out of the sky yet.

Brantel · #5 10-19-2007, 02:37 PM

Quote:

Originally Posted by gpiney

Was the piece too thin to machine CS? Is it a structural piece or something like an inspection cover? The only ones I have done were machine CS'ed.

Yes the side skin of the rear fuse is too thin to machine CS and the tank skins as well for a #8 screw.

Brantel · #6 10-19-2007, 02:39 PM

Quote:

Originally Posted by w1curtis

Guess I've been lucky but I use the CP-214 pneumatic squeezer and I haven't had any cracking on #6, #8 or other size holes. I use the standard dies from Avery.

I use the same dies and same squeezer as well as a hand squeezer and a DRDT2, all produce micro fine cracks on #8 dimples with a #19 predrill. They are very short small cracks from the ID of the hole to about halfway down to the flat part of the dimple. So small that you must look carefully to see them but they are there.

Brantel · #7 10-19-2007, 02:40 PM

Quote:

Originally Posted by Jamie

Well, for better or for worse I use a slightly larger bit if the skin starts cracking (#18, sometimes a #17). I haven't fallen out of the sky yet.

I will have to try a larger pre drill to see what happens. The #8 dies tend to really open up the ID of the hole anyway so why not give it less metal to move in order to prevent a crack? The only problem I see with this is that it is then harder to keep the die centered in the hole till the dimple is formed.

alpinelakespilot2000 · #8 10-19-2007, 06:45 PM

Quote:

Originally Posted by Brantel

I will have to try a larger pre drill to see what happens. The #8 dies tend to really open up the ID of the hole anyway so why not give it less metal to move in order to prevent a crack? The only problem I see with this is that it is then harder to keep the die centered in the hole till the dimple is formed.

Brian-Are you using quality dimple dies? I've heard great things about Cleaveland's dies (that's what started their business I was told), pretty good things about Avery's, and not so good things about everyone else's.

Brantel · #9 10-19-2007, 07:14 PM

I have Avery's dies for #6, 8# and 3/32" and Cleveland 3/32" and 1/8".

Can't tell much difference in the results from using both of the smaller dies.

I tried using a #16 predrilled hole with the #8 and it worked out great! No cracks and I measured the ID of the hole afterwards and it was no larger than one that was predrilled with a #19 so from now on #16 will be my drill of choice for predrilling for #8 dimples!

704CH · #10 12-17-2009, 11:17 AM

Just saw this thread after someone asked me why my tank dimples aren't cracked. The only thing I can think is that if you debur to much, the skin around the outside of the hole gets thin and can lead to cracks. Maybe lighter on the deburring here would sovle the problem.

I used a #19 with a 2 by 4 backer, then deburred lightly, (2 light turns with the debur tool). Squeezed with pneumatic squeezer set really tight, and no issues with cracks.

Just a thought.