Mike, Don't drill #40 then dimple with 1/8" die. If you look at the
finished dimple under high power magnification (ie; jewelers loupe), you
will find the metal has cracked around the edges of the hole due to
distortion. Not good. Definitely drill #30 for your 1/8" dimple. Also,
dimpling the hole definitely makes it bigger. Try putting the undrilled end
of a number drill in the hole before and after dimpling. You will find the
hole grows by a drill size or two. The Cleveland tank dies I used stretched
the hole about .0045 larger and I had trouble making 3/32" rivets hold
properly. Look at the geometry of the die on a cross section and picture
what the hole will do if you push the cone deeper into the hole. For my two
cents, I'll stick with standard or springback dimple dies from now on. As to
your problem, my guess is either your drill bit could be dulled or you're
not staying straight with the hole when drilling. Also, be careful how much
deburring you do on a hole after drilling. Too many turns and the hole gets
bigger. YMMV. Good luck and keep driving those rivets. Bill Korff

"Bruce E Butts" wrote in message
...

Mike,
Veeduber recommends that one drill with a #40, deburr and then dimple with
the 1/8" dimple dies. I have done some like that and some using the #30
drill first. Sometimes I have to 'open up' the hole a bit with a reamer
when trying to put in the rivet when I use the #40 bit first. Veeduber's
advise was in reference to using blind rivets iirc.

The springback dimple dies are meant for dimpling fuel tank skins so that
smearing sealant will not make the rivet stand proud of the dimple so I
think they may be a few thousandths oversize.

Hope this helps and remember all advice is worth what you paid for it!
Bruce