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 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 would I need to ask for in a screw to make sure it is hard enough to
keep it's threads ?

The following URL shows a photo with inset of the bushing and screw for
reference:
http://www.waycoolgear.com/ebay/wheel.jpg

Can't you just drill, pin and loctite? or is this a use that requires
the removal of the shaft?
not sure what you want to do but just setscrewing that onto the shaft
sounds like a fairly bad idea... (using the setscrew to transfer
torque, that is.). In our application in robotics, it tends to dig a
groove in the powered shaft until it is no longer transmitting torque,
or snaps off..

Also, do you mean "strip the screw" as in the threads outside or the
screw head or the screw threads? because I suspect its the outside
threads that are stripping.. the stuff outside looks like soft plastic
(which will strip..) and the inside metal could be overdrilled.. not
sure what you're doing but standard zinc ones should hold (at least
just by hand-tighetening)

Tatsu

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.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Also, do you mean "strip the screw" as in the threads outside or the
screw head or the screw threads? because I suspect its the outside
threads that are stripping.. the stuff outside looks like soft plastic
(which will strip..) and the inside metal could be overdrilled.. not
sure what you're doing but standard zinc ones should hold (at least
just by hand-tighetening)

It's the threads of the screw that stripped off (worn down)

First mistake -- these are typically very soft mild steel. It
is chosen to make the screws easier to make, not better.
........
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.

I want to respond to your post in detail & with a different photo but since
I need to get to bed right now I will do so tomorrow night. Thanks for all
of the detail! It's what I need at this stage in my education !

I will answer this more completely sometime tomorrow night ( EST time. )

Thanks again -
JCD

"Brian Lawson" wrote: (clip) why not just drill right through and then use
a nut and bolt. (clip)
^^^^^^^^^^^^^^^^
Or drill right through and use a roll pin. Or drill and ream and use a
taper pin.

In fact, any screw of this type as shown will
be damaged as soon as it gets tightened, and will become
difficult/impossible to remove/loosen. A proper dog-point set screw
would help a lot.

Thanks! I am considering that, too.

What does "dog point" mean ?

Thanks to everyone kind enough to help me with this!
Here is a (hopefully)better photo of the screw and also a somewhat blurry
one showing the penetration of the screw into the bushing where it stops at
the motor shaft flat. I hand tightened it on the motor shaft and slid it off
to show this.

Here's the latest link: http://www.waycoolgear.com/ebay/screw_in_bushing.jpg

When I screw it in more (with the motor shaft removed), it seems to bite in
and hold just fine without stripping at all.

I'll try to get even better photos if you guys think it will help more. Just
let me know exactly what you need to be of assistance.

Thanks !

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.
:-)

Good idea. But to make sure I am not getting the same kind of metal, what
could I look or ask for ?

What is the screw thread? It looks something like 10-32.

8-32. That is based strictly on the tap I used. I don't have a screw thread
gauge ( what do you call it ? ) right now, so I just place the screw against
the tap until I get one that lines up with the threads perfectly, then I
make a test run on something and see how the screw works. I do have a
plastic "catch-all" gauge from Home Depot and the screw fits in the #8 hole.

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.

The only markings I can see on the drill bit are
25
ST
HS
one under another just like I typed it above.

(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.

Yep - I used a tap. I'm new but now that new! Pretty close, though!
I think it is the size of the hole and also that the end of the screw is
tapered too
much (before I even use i) for the depth of the hole that has the threads I
cut in it.

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.

I'll give a thorough look over the next couple of days and
post back here to see if I am on the right track.

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 just posted a new photo in this thread, although I'm not sure how much it
will help.
I *had* some perfect ones and accidentally deleted them from the
camera. It took me forever to get just the one I posted today so I went with
it.

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.

You got it all perfect as far as I am concerned! Thanks!

I have a cheapo tap from Sears, and a few from a friend of
mine that used to do this stuff in his younger days.

Thanks again for all of the help! Hope what I have written here helps you to
help me !

Thanks!
JCD

Can't you just drill, pin and loctite? or is this a use that requires
the removal of the shaft?

I want to be able to remove the wheel now and then to get to the motor and
mounting hardware.
Thanks !

The very tops of the screw threads are knocked off cleanly. Either the
screw is undersized near the tip, the screw is REALLY soft, or your hole
was drilled oversized.

I'd try a REAL setscrew. These are black phospate covered, use an allen
wrench to tighten, and have a suitable point to dig in. The point is
sometimes called a "dog point", come in serveral flavors: you may find a
sharp point, a cup, or a star shaped arrangment that looks like the
character *

Any big box home store should have a display with small parts. Ask for a
'set screw'. Terrribly expensive if you need lots, easy to buy just one
for $.39 Buy a longer one so it has some meat sticking out.

My guess is that the set screw will hold in the bushing even though the
screw did not. But use the proper siced drill for your next experiment.

pogo wrote:

Thanks to everyone kind enough to help me with this!
Here is a (hopefully)better photo of the screw and also a somewhat blurry
one showing the penetration of the screw into the bushing where it stops at
the motor shaft flat. I hand tightened it on the motor shaft and slid it off
to show this.

Here's the latest link: http://www.waycoolgear.com/ebay/screw_in_bushing.jpg

When I screw it in more (with the motor shaft removed), it seems to bite in
and hold just fine without stripping at all.

I'll try to get even better photos if you guys think it will help more. Just
let me know exactly what you need to be of assistance.

Thanks !

The very tops of the screw threads are knocked off cleanly. Either the
screw is undersized near the tip, the screw is REALLY soft, or your hole
was drilled oversized.

It was the hole size! I drilled a smaller hole with a bit marked 27 and even
using the stripped screw I couldn't budge it once I torqued it down to the
motor shaft.

Thanks again !
JCD

According to pogo :
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.
:-)

Good idea. But to make sure I am not getting the same kind of metal, what
could I look or ask for ?

Well ... assuming that your screw was a 1" long one, and looking
in the MSC catalog for the 8-32 size which you say you are using (and I
would suggest 10-32 anyway for that), the prices for a box of 100 range
from $5.64 for the "import" (which is still pretty good from MSC) up to
$16.87 for the ones made by "Unbrako" (which are really tough steel).

I see that they have the same screws in 25 screw packages ("Made
in USA", but with no brand) for only $4.13

The 10-32 screws in the same length range from $7.15 (for the
import screws) to $17.17 for the Unbrako. (And with a similar 50-screw
pack of unbranded "Made in USA" screws at $10.57.)

Any of these would be much better than the ones which you picked
up from the local Home Depot. *Some* local hardware stores will stock
good screws, but it is hard to predict which will and which won't. I
would not trust anything from Home Depot if you need strength.

I don't have anything resembling a recent McMaster Carr catalog,
so I can't get the prices for you from there.

Anyway -- the description in the MSC catalog is "Alloy Allen
head cap screws".

What is the screw thread? It looks something like 10-32.

8-32. That is based strictly on the tap I used. I don't have a screw thread
gauge ( what do you call it ? ) right now, so I just place the screw against
the tap until I get one that lines up with the threads perfectly, then I
make a test run on something and see how the screw works. I do have a
plastic "catch-all" gauge from Home Depot and the screw fits in the #8 hole.

There are thread pitch gauges (many folding blades with a
sawtooth edge to match the thread pitch for checking), and there are
plates into which the screws can be fitted for checking the size and
pitch. The latter is sold under the name "Screw Checkr" (or perhaps
"Screw Checker"), and I got mine from MSC -- they show up frequently in
their sales flyers once you get on their mailing list. I have and use
both.

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.

The only markings I can see on the drill bit are
25
ST
HS
one under another just like I typed it above.

O.K. It is a #25, and the "HS" means "high speed steel". The
"ST" might be a maker's mark.

Anyway, looking up the recommended tap drill for an 8-32, the
size should be a #29. (Except that for some reason, the table in
Machinery's Handbook gives the same size for 8-32 and for 8-36, but
another table gives differing sizes, both of which are close to the #29
drill bit.

And the table does say that I correctly remembered a #21 for
tapping a 10-32 thread. (Note that the larger the number, the smaller
the drill bit in the wire (number) sizes.

So -- you used too large a drill bit for drilling the hole for
tapping. You now have little choice other than going up to the next
screw size (10-32). And you'll need a set of Allen wrenches (also
called "hex keys" for driving the screws which I suggested.

Normally, I don't bother with the handbook, because the HUOT
drill indexes in which my drill bits are stored have the sizes for
common threads on the hinged metal base which holds the first row of
drill bits.

(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.

Yep - I used a tap. I'm new but now that new! Pretty close, though!
I think it is the size of the hole and also that the end of the screw is
tapered too
much (before I even use i) for the depth of the hole that has the threads I
cut in it.

It has a tapered point? That almost sounds like a supposed
"self-tapping" screw, which is designed for use in mild sheet metal, not
in tapped holes.

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.

I'll give a thorough look over the next couple of days and
post back here to see if I am on the right track.

Try the MSC catalog on their web site. You have above the
description to look for, and their URL is (IIRC)

http://www.mscdirect.com/

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 just posted a new photo in this thread, although I'm not sure how much it
will help.
I *had* some perfect ones and accidentally deleted them from the
camera. It took me forever to get just the one I posted today so I went with
it.

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.

You got it all perfect as far as I am concerned! Thanks!

Glad to help.

I have a cheapo tap from Sears, and a few from a friend of
mine that used to do this stuff in his younger days.

The ones from your friend may be better quality taps --
depending. I would not expect a good one from Sears, either.

Thanks again for all of the help! Hope what I have written here helps you to
help me !

I think so. What I have not found is your newly-posted photo
(though the URL might be in some other branch of this thread). I could
not find it by working uphill from the previous URL, as indexing of the
directories is turned off.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Well ... assuming that your screw was a 1" long one, and looking
in the MSC catalog for the 8-32 size which you say you are using (and I
would suggest 10-32 anyway for that), the prices for a box of 100 range
from $5.64 for the "import" (which is still pretty good from MSC) up to
$16.87 for the ones made by "Unbrako" (which are really tough steel).
....
I think so. What I have not found is your newly-posted photo
(though the URL might be in some other branch of this thread). I could
not find it by working uphill from the previous URL, as indexing of the
directories is turned off.

Man - thanks for the absolute WEALTH of information !

Here's the URL: http://www.waycoolgear.com/ebay/screw_in_bushing.jpg

Anyway, I am copying your post to my notes and will be referring to it
frequently, I am sure!
Thanks!
JCD