View Full Version : Leadscrew Taper Pin

12-27-2005, 07:43 PM
There's a taper pin that connects the leadscrew to the gearbox on my sheldon lathe. There is some slop between the taper pin and the piece that comes from the gearbox. The pin is some type of brass looking metal. I needed to get some stuff from Mcmaster and decided to get a new pin, however, the pins they have are 12L14 steel. Is that brass pin used as a shear pin to protect the lathe in case of a crash? If that's the case would the 12L14 pin be too strong and not act as a shear pin? What you all think?


12-27-2005, 08:07 PM
IIRC the original is steel.

12-27-2005, 08:10 PM
How did you verify the "brass looking metal"? Is it brass or cad plated steel?

If it is brass, it's about 1/6 as strong as 12L14.

12-27-2005, 08:38 PM
Mine is steel. There is a micarta gear in the gear train that will self destruct in the event of a bad jam to protect the rest of the system.

I know this.

12-27-2005, 08:45 PM
Every lathe I have ever seen with that type coupling the pin has been steel.

Me I would use the 12l14 and not think twice about it.

I would also order a matching taper pin reamer to freshen up the hole before installing a new pin in case the old holes are burred or dinged up,just a thought.

shear modulus for 360 brass 5,370
shear modulus for 12l14 steel 11,600

So it's about twice what brass would be.

12-27-2005, 08:52 PM
Oh, thanks D. I should quit trying to use my memory. http://bbs.homeshopmachinist.net//eek.gif

12-27-2005, 09:00 PM
I believe your lathe is very similar to mine, but, there are no micarta gears on mine. My lathe was made in 1970, maybe things were changed by sheldon as the years went by. Mine is a EM-56P model. Maybe when they replaced the micarta gear, they changed the pin to brass to make it the weak link.

I didn't verify the composition of the pin, all I can tell you is it visually looks like brass. I'd wonder why they would use a cadmiun plated piece here as there would be no need for any corrosion resistance.

If I was to make a pin from brass, what alloy would be suitable?

Thanks all for the input,

12-27-2005, 09:01 PM
<font face="Verdana, Arial" size="2">Originally posted by CCWKen:
Oh, thanks D. I should quit trying to use my memory. http://bbs.homeshopmachinist.net//eek.gif</font>

Here's how I remember-


Coarse heah in Missasippy we'ud just stuck a nail in na't sucker and runit http://bbs.homeshopmachinist.net//biggrin.gif Getterdun!

12-27-2005, 09:14 PM
Is it magnetic?

12-27-2005, 09:47 PM
If I get a chance tomorrow, I'll take it out and get a better idea of what's there.

Thanks for the shear info.
I gots lots of nails.


12-27-2005, 09:49 PM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
shear modulus for 360 brass 5,370
shear modulus for 12l14 steel 11,600</font>

If that's the elastic shear modulus, it should be in the millions of psi, not the thousands. 6-7 million for copper/bronze/nickel, 11-12 million for steel, about 10% less for stainless.

But then, that's an elastic property, and has nothing to do with the yield strength or ultimate strength.

01-02-2006, 06:59 PM
I finally got around to taking the pin out and it was brass, not magnetic. Made a new one out of some brass I had on stock and away we go.


Lew Hartswick
01-02-2006, 09:14 PM
The 8 Clausing Metosas in the school shop all
have brass taper pins in that location. I know
very well, have had to manufacture and install
several. :-)