Set Screws

[Philjoe5]

Ok fellas, I know we're not building full size locomotives (are we anyone? :big but I have to ask this question about set screw length. The answer seems intuitive, therefore, I must ask since my intuition has failed me in the past. I have just tapped two holes in an eccentric that are 1" long. I have 10-32 set screws in lengths up to 1/2". Should I use the longest set screw possible for maximum holding power?

Cheers,
Phil

 

[rake60]

You just tapped two holes 1" long 10-32 ? :bow:

I'm no engineer but I do know the rules of thumb.
2 X the Dia of a set screw gives you all the thread contact
you need for a secure lock.

1" deep for a 10-32 I would have drilled it through with a #21
bit (.159") Then I would have drilled it 5/8" deep with a #9
bit (.196") The 10-32 has a major diameter of .190"
Now you only need to tap through 3/8" the rest is clearance.

I won't say it's right, just how I would approach it.

Rick

 

[steamer]

I dislike setscrews....they always loosen up or turn on the shaft gauling the shaft which makes the locked part near impossible to come off without tearing up the hole

If you must use a set screw, turn the end down to the tap drill size x two tap drill diameters long and spot drill the shaft 1 tap drill dia x 1 tap drill dia deep as well.

When you set the screw home, it will pin the shaft, not just hold it by friction. Coming apart will be ever so much easier.

Dave

 

[Mcgyver]

like Rick said. it'll make life easier on you next time

 

[Philjoe5]

Thanks Rick. That rule of thumb is what I was looking for....a set screw length of 0.190 x 2 = 0.380" will be the maximum needed. Then, of course, the thread length only needs to be that dimension.

Thanks Dave, you're absolutely right about set screws putting a burr on the shaft. I like your idea about using the screw to pin the shaft.

Cheers,
Phil

 

[Mcgyver]

right about set screws putting a burr on the shaft

always file a flat on the shaft for the set screw or that burr will make getting the shaft off difficult and will score the bore

 

[rake60]

Another issue with a locking set screw is the potential flaring of the end.

Set screws are generally soft (Grade 5) steel.
If they are over tightened the contact point will flare distorting the threads
making removal a "Charactor Building" experience.

A quick lap around the contact end on a grinder removes the first thread.
Manufacturers call that a "Dog Point" and figure it to be worth twice the cost
of a standard set screw.

Maybe they just have it figured out better then we ever could.. :

Rick

 

[steamer]

I would much rather use a taper collet. Like a "Transtorque".

I have home brew taper collet one on the flywheel of my launch engine. One quarter turn with a pin spanner and its on, one quarter turn and a knock with a mallet and it's off. Always concentric too and never damages the shaft.
ETW had it right when he used them EVERYWHERE!

Dave