# TAPERING SPRING WIRE (Warning: No Political Content)

• posted on January 6, 2013, 10:52 pm
I have an application where I need to make some small stainless steel core pins for a mold. I have some .090 spring wire that would probably work fairly well after I straighten it. Straightness does not have to be perfect, so I'll probably just do that part by hand. Then I run into my issue. I need to taper it from .090" down to about .070" over a reach of about 1.25 inches.
The only thing I could think of is to to a shallow v block and clamp that it the tool holder on the mini lathe. Then lay a file against one end of the V block and slowly bring it back until its just scuffing the wire at the 1.25 inch mark. The grove is to hold the wire from bending against the cutting force of the file. My concern is if I will be able to continue to cut the wire with the file as it work hardens from the action of the file. My other concerns are that I have my hands so close to the spinning lathe, and that this seems to be a very hand skilled approach to the problem.
No the pre tapered pins for sale from McMaster absolutely WILL NOT work for this application. Besides. I already have several hundred feet of .090" 316 spring wire left over from a past project.
I guess its time to go play with a file and see....
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• posted on January 6, 2013, 10:53 pm
My apologies. Accidentally posted to the wrong group.

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• posted on January 7, 2013, 12:46 pm
On Sun, 6 Jan 2013 15:53:54 -0700, Bob La Londe wrote:

No problem, here is a formula to calculate the internal volume of your tapered pin.
Volume = pi (r1^2 + r2^2) L/2
r1 = small end radius r2 = large end radius L is lenght
This formula is also used to calculate the internal volume of wood power poles, which are manufactured and sold by volume, "Cubes" in that business.
Making this somewhat on topic. :)
basilisk
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• posted on January 7, 2013, 8:25 pm

While the formulas are useful, I have gotten lazy in my old age. I draw a 3D representation in ViaCad and then ask it what the volume is.
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• posted on January 7, 2013, 1:20 am
Bob La Londe wrote:

Silicon carbide wet or dry? Seems like after experimenting, that would come up with a reliable system that worked to the tolerances you require, unless of course, you require conical-perfection.
Bill

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• posted on January 7, 2013, 8:30 pm

A polished conically perfect core actually seems to be harder to release from the casting than one that is just a tiny bit rough I have found. The initial moment of inertia requires greater force. I'll use a parting powder (sprayed on dry graphite) so it should be a nonissue, but there is often a small amount of discrepancy between theory and practice. LOL.
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• posted on January 12, 2013, 4:33 pm
On 1/7/2013 12:30 PM, Bob La Londe wrote:

That makes sense to me, as that's how the Morse taper (or any other taper, for that matter) works. That's why you have to make sure your taper is clean before you mate the parts, otherwise you don't get the tight fit.
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• posted on January 12, 2013, 7:44 pm
On Sunday, January 6, 2013 2:52:50 PM UTC-8, Bob La Londe wrote:

I'd think of etching the wire (reverse electroplating). A bit of dilute nitric acid, a few milliamps of current, and the metal vanishes. Maybe it'd help the surface finish to tune it up afterward with a bit of 400 grit sandpaper.
Pull the wire slowly from the solution to make the taper (for quick and dirty operation, a slow-drip drain from the plating solution tank will accomplish this).