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fencepost
05-11-2006, 09:07 AM
I need help (okay, that is pretty obvious), I am looking for some metric taper pins (5X35 so the parts list says). The rub is the pins need to be brass as they are used as a shear pin. I've looked high and low, nadda. The manufacturer of the machine is no longer around (imagine that). I have one left and need some more as back-up. We have a large quantity parts run on tap and I need to be sure we have a back-up plan (you know if you only have one you will need two - never fails).

I'm not too leen on re-reaming the hole, I would like to stick with what is there.

Any ideas??

Danke,

Axel

Rich Carlstedt
05-11-2006, 09:29 AM
Mc Master carr has metric taper pins
see
www.mcmaster.com

But you may have to ask about brass?

fencepost
05-11-2006, 09:34 AM
Rich,

I looked in the catalog but didn't see brass, good idea on calling them. I also tried MSC, ENCO, and some of the other tool books - nothing in brass. A google search has turned up dry too. Gotta be someone out there with 'em, just have to find them.

Still lookin',

Axel

JCHannum
05-11-2006, 10:27 AM
Since the shear strength of mild steel is about twice that of brass, reducing the diameter of a steel pin by about 1/2 in the area of shear will cause the steel pin to fail at the same point a brass pin would.

Shear pins are like fuses, and often steel shear pins are undercut in the area of stress to control their shear point. A benefit of this is that the shear will be clean, and the broken pin will be easier to remove.

Forrest Addy
05-11-2006, 11:51 AM
I like JCHannum's suggestion. Determiae the shear diaameter of the brass pin, Re-ream the taper pin hole for good honest US standard steel taper pins (US taper 1/24; wierd-a$$ metric taper 1/25). Using a pointy threading tool, groove the steel pins to 1/2 the shear area of the brass pins making a dozen or so.

Evan
05-11-2006, 12:00 PM
Reducing the diameter by 1/2 will reduce the shear strength to about 1/4 of the full diameter strength. Reduce diameter by .707 times instead to reduce strength by 1/2.

JCHannum
05-11-2006, 12:45 PM
There is a not enough information to worry about third place decimals here.

Not knowing the composition of either taper pin, the actual alloy is not known. The shear strengths can vary by a factor of two or three or more, and the method of reducing the diameter will have an effect on the shear point. Most shear pins made with reduced diameter use a radiused cut to reduce stress risers, a V groove or a filed notch will behave differently.

Not knowing the application or cost of failure, it is best to err on the low side, and cautiously work up if failures seem to be premature.

Evan
05-11-2006, 12:51 PM
There is a not enough information to worry about third place decimals here.

That wasn't the point of giving the third place. It was a hint that the correct ratio is 1/2 times the square root of two to produce a circle of half the area and therefore half the strength.

Erring on the low side is advisable but making it only 1/4 the strength isn't.

Mike Burdick
05-11-2006, 01:49 PM
Sorry, but I've got to ask...Why can't you just make some replacements? For stock, one can use some brass brazing rod.

fencepost
05-12-2006, 01:41 PM
Update: I found 'em. One of the board members contacted me off line and said Jet uses them on some of their lathes - hhhmm. Anyway, I looked on line and found them for $1.10/ea - but $19.95 shipping. I want 10 of them, that pushes the price each to $3. A call to their customer service got them on their way for a spot under $20 tax and shipping included (okay, a few are on backorder, but I can live with that).

So, on with more important things, someone on the floor indicated the blue gill are biting - I'm on my way.

Danke,

Axel