"Wild_Bill" wrote in message
...
I don't recall the details about the earlier discussion wrt
metal-over-substrate, but it wasn't about wood-epoxy filler products, not
that I recall.

A while ago you were asking about adding a skin over foam or MDF or maybe
some other substrate(s).

Good memory!!
Apropos of that excellent discussion, I came up with an elegant solution:
No glue at all!!
I just had delivered 1/32" sheet alum, and 1/2" ply, and I'm just going to
let the alum "float" or slide on the ply substrate, as it will be very well
constrained along all 4 edges, by 3/4 x 1.5 x 1.5 (1/8") channel.

Eventually I WILL use glues of sorts, as I think that altho mechanical
engineering insights in that thread were valid, that I'll still be able to
generate add'l stiffness without the aluminum shearing the top layer of ply
off the wood. It will be an ongoing experiment.

But, as it is, the ply itself is stiff enough, just more would be better.



Then there was an even earlier topic of screws with deep/aggressive
threads, such as those used for plastics.. but you were contemplating
using them in metal (mounting a device to metal door frames, IIRC).

You have a scary memory!! LOL
Indeed, and I found that the coarse drywall screw was actually pretty well
suited for this, esp. with being so hard -- but indeed a bit brittle..
I found some other type screws as well, but I'll have to dig those up --
sumpn with "mixed pitch threads", or sumpn.


I assume that you're aware that countersinking thin materials/sheetmetal
can be a little troublesome since common cutting tools will tend to lift
the material, making consistent countersink dimensions problematic.

Using a multi-flute countersink cutter which doesn't have any, or little
cutting edge relief angle (like dressing a drill points' relief angles for
drilling brass) so the cutting forces are more like that of a reamer -
scraping away the metal.. should eliminate lifting of the thin materials.

Sheetmetal screw threads are very reliable in wood, although depending
upon which particular wood and the screw size (diameter), predrilling may
be a good idea.
Driving sheetmetal screws into dry hardwoods will likely cause a lot of
pressure, and possibly splitting when not predrilled (definite maybe).

Predrilling doesn't necessarily mean a HSS twist drill, when doing
carpentry-type stuff.. a nail with the head removed, mounted in a drill
(or flutedYankee drill) will generally suffice.

The cutting points of decking screws (at a more premium price, but
probably a better quality fastener) can eliminate the need for drilling in
most S-P-F woods, but maybe not in dry hardwoods YMMV.

Yes, those SS deck screws I have seem very high quality, and "built to
drill".

The FH screw Q was not for sheetmetal, tho, but for that apparatus in a
doorway, with sufficient alum "meat" to c-sink.
I myself would not even contemplate c-sinking sheetmetal -- there's nuthin
to c-sink!!

Same problem exists for FH machine screws in material that's too thin, eg,
1/4-20 FH in 1/8 alum. You wind up enlarging the hole itself.

I solved my problem with the MSC 82 deg spot drill for any #10 FH screw, and
drywall screws, altho not 82 deg, nevertheless "fit". I most likely won't
stick with drywall screws, I'll do sumpn with deck screws, or trad'l
sheetmetal screws, or sleuth down some type of custom/specialty screw, of
which there are an absolutely dizzying array.

--
EA




--
WB
.........


"Existential Angst" wrote in message
...

Attaching metal apparatus to wood.
From a c-sink pov, I should proly go to sheetmetal, but from a
drilling/grabbing pov, I really like coarse drywall screws, whose threads
are deeper, sharper.



Oh, the wood filler/epoxy thread.... Why are drywall screws bad for
that, besides rusting like crazy?
What is a good choice?