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ACF
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?

Chris

beckley23
12-27-2005, 08:07 PM
IIRC the original is steel.
Harry

CCWKen
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.

JCHannum
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.

wierdscience
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.

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

ACF
12-27-2005, 09:00 PM
JCH,
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.

CCW,
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,
Chris

wierdscience
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-

http://www.matweb.com/index.asp?ckck=1
http://bbs.homeshopmachinist.net//tongue.gif

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

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

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

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

Chris

sauer38h
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.

ACF
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.

Chris

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. :-)
...lew...