Friday, May 31, 2019

Sheet Metal Screws

I have been trying to move away from using acetal for the part that holds the caster.  Aluminum is half the price, and I get $0.28/pound for aluminum scrap.  Acetal scrap goes into a landfill.  Unfortunately, aluminum is much more labor.  With acetal, a .140" hole into the acetal means that I can screw an 8-32 screw through the aluminum sleeve into the acetal, without tapping the acetal.  Just power screwdriver the screw in.

Tapping the hole in aluminum is slower.  I have to mark the hole in the aluminum insert through the hole through the hole in the sleeve, then drill to depth and tap.  This is slow.  (I have also found that tap charts recommend a drill size that consistently breaks the tap.  Going up to 5/32" drill size stops the breaking, but creates a less than perfect hold.)  Sheet metal screws are for thin metal, and are not going to tap holes in a drilled hole.

Any suggestions, other than staying with the expensive acetal?

Thanks, all. I found some #10 self-tapping screws in my enormous collection of odd screws that I will never use; drilled an appropriate sized hole in some 1/4" aluminum; and turned it into the hole.  I will buy some #8s the next time I am in the valley (the holes in the sleeves are .172", so slightly too big for #10).  Also, what I have are screwdriver heads.  I will get some hex heads.  I prefer socket head or hex head fasteners because the heads don't strip so easily and I can turn them in very tightly and quickly with a power screwdriver.  You can that with slot and Phillips heads also, but it is harder to keep the bit in the head, and they seem to strip more easily.


  1. Self tapping screws?

  2. Self-tapping machine screws won't work? I use 10/32 self tappers at work in punched holes in 1/8 steel, and the few times I've used them in aluminum they seem to hold tight.

  3. Ford used a tapping screw for some applications. It did not come to a point, but it did have a taper near the tip. It also had a single slash with gap in the side of the tip that gives it a thread cutting ability. I've seen it in several screw sizes, and I think some of them had an integral washer. The gap gives space for material to collect as it cuts. I don't recall the actual uses.