SCREWED

[BMITCH]

Ok, so back to the old question of SS screws. Seems to be difficult to find 8-40 flat head screws that I like. So my question is...if you run a 8-32 tap through say a Tib frame for the 114H( which is a 8-40 thread) do you risk screwing up the frame? Do you get a good fit? Aren't the screw dia. The same on an 8-40 and a 8-32.? Your just changing the pitch, right? Or do I need to tap to the next largest size?
Bob

[Bunnlevel Sharker]

I think as long as the walls arent to thin and the screw is lightly greased and fits well you will be fine

[Irish Jigger]

Be very careful.
First establish exactly what thread is in the Tib frame.
Are you sure it is not 8-36 UNF as 8-40 is a non standard size?

[LTM]

Also, the diameter is the same HOWEVER your going from 32 tpi to 40tpi which is a FINER thread and your screw may very well not hold and skip a thread ore two. Wait till you get more POSITIVE feed back. Keta/Lee is one our resident machinist whom I consult with on details such as this.

Leo

[Keta]

It should be ok.

8-32 major diameter .1631"  minor diameter .1248"
8-36 major diameter .1632"  minor diameter .1291"

major .1632-.1631=.0001 loss
minor .1291-.1248=.0043 gain

8-32 thread contact  .0383"
8-36 thread contact  .0341"
The re-taped thread contact will be .0332"

http://www.engineersedge.com/screw_threads_chart.htm

[LTM]

SEE WHAT I MEAN? Thanx Lee for the link!!

Leo

[BMITCH]

So Lee & Leo, I should be alright if I tap out a existing 8-40 thread with a 8-32. The Penn 114H side plate screws are a 8-40 correct? If I tap them out to an 8-32 I believe there are many more options of SS screws that can be used?

[Irish Jigger]

The Penn 114H side plate screws are a 8-40 correct?

Yes 8-40,which is a non standard size and hard to source other than from Penn.

[BMITCH]

The Penn 114H side plate screws are a 8-40 correct?

Yes 8-40,which is a non standard size and hard to source other than from Penn.

Tom, my point exactly! So if I tap out the 8-40 to 8-32 do you think there is enough "meat" to be able to bear down on the side plate screws??

[BMITCH]

Or maybe go up a size to a 10-32 and make the holes through the side plate and rings larger? I really don't like the penn screws. Not a cost issue more an aesthetics issue.
Bob

[LTM]

Bob Im not your guy for this question, just the referral to Keta/Lee

Leo

[Irish Jigger]

Bob,I would not cross thread the holes by tapping them 8-32 and would stick with the original 8-40 chromed brass screws.

You could try tapping a 114H post 8-32 and see how well the screw holds.

[Alto Mare]

Bob, I would stick with the original 8-40 chromed brass screws.

Same here.

[Irish Jigger]

Bob, run an 8-32 die/die nut down an 8-40 screw and see what the threads look like before contemplating tapping the Tib frame.

[Keta]

Bob, run an 8-32 die/die nut down an 8-40 screw and see what the threads look like before contemplating tapping the Tib frame.

X2.  I've successfully ran a course tap in a fine thread hole in steel but they were much larger.