According to pogo :
I got some 1/2" OD 1/4" ID steel light duty reducer bushings from
McMaster-Carr to use as
adapter from a motor shaft to a lawn mower wheel for my new robotics
project. I drilled a small hole perpendicular into it for a "set screw" --
but
am using some 3/4" long "regular" screws from Home Depot
First mistake -- these are typically very soft mild steel. It
is chosen to make the screws easier to make, not better.
Go back to McMaster-Carr and get a box of the same size, but
black finished Allen head capscrews, which will be much harder. (And
probably a box of 100 will cost less than four or five from Home Depot. :-)
since I want it go
through the lawn mower wheel shaft, too. When I tighten it down all it takes
is a small amount of extra force to strip the screw. I am thinking the hole
I drilled before I tapped it is too big, and/or the screw is too soft. (
I'll try another hole tomorrow )
What is the screw thread? It looks something like 10-32.
What drill did you use to make the hole? IIRC, the tap drill
for a 10-32 is a #21 "wire size" drill. No fractional size is close
enough to do the job right.
If you examine the screw after this happens, are the screw's
threads stripped? If not, you can probably start with the size of the
hole which you tapped. (You *did* use a tap to make the threads in the
hole, did you not? You don't want to use any kind of self-tapping screw
for this kind of thing, you really want to have a proper tap to cut the
threads without the screw being involved.
What would I need to ask for in a screw to make sure it is hard enough to
keep it's threads ?
It is more a matter of *where* you get it. The ones which I
described above should do quite well -- either from your McMaster Carr,
or from MSC. I prefer MSC, simply because it is not like pulling teeth
to get a catalog from them, and the catalog has pages of choices of
screws. The black oxide finished ones tend to be rather painfully hard.
The following URL shows a photo with inset of the bushing and screw for
reference:
http://www.waycoolgear.com/ebay/wheel.jpg
But no photo of either the hole or the stripped thread, both of
which would have been more useful in diagnosing the problem
I apologize if I've gotten too basic in what I sad, but your
wording of your question, and what you did not say suggested that you
needed this level of detail.
BTW If you don't yet have the tap, try to avoid getting taps from Home
Depot as well. Those tend to be high carbon steel, and you will
be better off with HSS (High Speed Steel) taps -- they are
tougher and a bit more difficult to break. Your McMaster Carr
should also have excellent quality taps, and for this style of
project (not a blind hole) I would suggest that you get a "gun
tap" (spiral pointed, and it chases the chips ahead of it, so
you don't have to back up the tap ever half turn or less to
avoid clogging it with chips and breaking it.
Also -- if you don't have one, get a good tap wrench of
appropriate size from your vendor (*not* Home Depot) at the same
time.
Good Luck,
DoN.
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