Charles Vincent wrote in
:

Fortunat1 wrote:


Oh dear, which means I've just wrecked a whole lot of parts. I'll
have a looksee with a magnifying glass. I did try to cut them out to
7.9 mm, but I was afraid it might be too deep a cut and that the
triangular hole cut by the drill might leave it's remains around the
edges.

Don't make any assumptions based on my comments. I am unfamiliar with
the plane you are building, I do not know the metal variety you are
working with and have not seen the parts. Finally, I do not have
experience building enough airplanes to rely on experience when
answering you. Metalworking I do know about, so I could make a
pretty good guess as to what your problem was and the probable
ramifications. I suggest you talk to the designer of your airplane or
another builder of it.


Well, both the guys who had a hand designing this thing are dead, so
that's going to be a bit difficult! (Neither in a Hatz, BTW)
The material is 4130 steel which is a relativley high carbon steel if
you're not familiar with it.
Seems to me you've hit the problem on the head first time out. Your
experience is obvious!

I had a look with a not too powerful magnifying glass and couldn't see
any obvious cracks. There's the occasional scratch in the holes in the
direction of the cut, presumably from a bit of swarf getting caught in
the reamer. The ridge around the edges mostly stand up about .002 or so,
and maybe a little less than that in thickness. They're more regular in
appearance and much thicker than you'd see from drilling, for instance,
but they're still not so perfect around their edge you could tell a
crack from just an irregularity.At least I couldn't.
I do have someone who can look at them here, though, so that's what I'll
have to do to be sure.
Thanks for the heads up on that! They say you make two airplanes when
you make your first one, the one you fly and the one you throw away..
;(