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aostling
08-28-2007, 01:59 AM
I need about ten pulleys for 0.008" music wire. The wire can bend over a 2" diameter without exceeding its elastic limit, so I'd use this as the pulley OD. with a 0.25" ID to fit on a drill rod axle. I'd cut 2" diameter blanks from 1/8" aluminum sheet with a hole saw, put the blanks on a mandrel, and turn the grooves with a 60˚ tool bit.

Acknowledging that some of you could have finished this project in the time I've taken to describe it, I am not averse to buying the pulleys if they are a stock item, in some catalog I've never heard of. Seen anything like that?

P.S. Better make that 3" pulleys. The music wire will be in considerable axial tension, adding to the bending stress of going over the pulley.

darryl
08-28-2007, 04:31 AM
Just off the top of my head, I don't think you'll find pulleys like that. I could be wrong.

Interesting that you consider the larger diameter pulley because of the reduced stress on the wire. For .008 wire, a 3 inch pulley seems awfully large. It doesn't seem like that would be needed, but again I could be wrong. With the sizes you've stated, I'd be more worried about the pulley going sideways on the drill rod, unless there's a hub of some sort added to it. If it's just a hole in the 1/8 thick pulley that rides the drill rod pin, that could happen fairly easily.

Evan
08-28-2007, 04:57 AM
Somebody makes them, I know that much since I have some. Note that even though obviously intended for a very low load these still have a small hub as Darryl suggested.

http://vts.bc.ca/pics2/pulleys1.jpg

dalesvp
08-28-2007, 11:06 AM
Here are some pulleys, plastic, but maybe these people know the source:

https://www2.carolina.com/webapp/wcs/stores/servlet/ProductDisplay?jdeAddressId=&catalogId=10101&storeId=10151&productId=44717&langId=-1&parent_category_rn=1287|94|2071

https://www2.carolina.com/webapp/wcs/stores/servlet/CarolinaBio/images/medium/954820_kss.jpg

aostling
08-28-2007, 12:56 PM
Interesting that you consider the larger diameter pulley because of the reduced stress on the wire. For .008 wire, a 3 inch pulley seems awfully large. It doesn't seem like that would be needed, but again I could be wrong.

Darryl,

You are not wrong. I had done a calculation, using the formula for maximum bending stress (σ) in a circular rod (or wire) having a cross-section radius r bent in a circle of radius R.


σ = (r/R)*E where

E=modulus of elasticity = 30,000,000 psi for steel

I chose a value of σ=120,000 psi, thinking this was merely a little conservative, for music wire. Since r=0.004" for my music wire, this formula gives a value of R=1", or a 2" diameter pulley.

But your comment prompted me to look in my Metals Handbook, Vol. 1 "Properties and Selection of Materials." It has this plot of strength for spring steels. My 0.008" music wire has a tensile strength of about 400,000 psi. For anybody used to thinking in terms of structural steel, this is an astoundingly high strength.

Evidently I can use 1" diameter pulleys, and not worry about exceeding the tensile strength of music wire.

Thanks! This makes my design a lot easier.


http://i168.photobucket.com/albums/u183/aostling/springsteel.jpg

aostling
08-28-2007, 01:25 PM
[QUOTE=dalesvp]Here are some pulleys, plastic, but maybe these people know the source:

These pulleys are stated to be for kids in "Grades 3-6." I'm hoping I have not regressed quite that far, yet.

Frank Ford
08-28-2007, 04:36 PM
.008" ?

That's pretty skinny wire.

I can't imagine why you'd need a huge pulley.

Electric guitars run that kind of wire nearly at the breaking point, around tuning posts of 1/4" diameter or less, and it's common for the string to break somewhere other than on the bend around the post.

I think the tnesion needed to break .008" music wire is around 20#, which works out to something like the 400,000 PSI you mentioned.

Cheers,

Frank Ford
FRETS.COM (http://www.frets.com)
Gryphon Stringed Instruments (http://www.gryphonstrings.com)
My Home Shop Pages (http://www.frets.com/FRETSPages/Machining/index.html)

cybeknight
08-28-2007, 05:58 PM
Hello,
I am a new guy here and saw your post. I work in a wire mill and we use ceramic pulleys on the fine stuff. We also use a ceramic coated aluminium pulley also. They hold up very well with steel wire from .026-.091 and not much drag on the wire. Here is a link to the company who makes them:
http://www.heany.com/pulleys.pdf
Also there regular home site:
http://www.heany.com/
I have used there pulleys from 2" dia - 8"dia , bores for the bearings are selectable from them on order.
Glenn

aostling
08-28-2007, 06:00 PM
Electric guitars run that kind of wire nearly at the breaking point, around tuning posts of 1/4" diameter or less, and it's common for the string to break somewhere other than on the bend around the post.
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Frank,

I was thinking the pulley should be sized subject to the constraint that the 0.008" wire not take on a permanent set when bent around it. So now (belatedly) I tried bending the wire around drill rod of different diameters -- 1/4" is too small, but bent around a 1/2" drill shank the wire springs back to straight.

The wire will be under considerable tension, so avoiding a permanent set is probably unnecessary, as long as the wire doesn't break. So I appreciate your comment that the rupture (when it occurs) is usually not at the wrap.

Twenty pounds breaking strength, you say. I can hardly even see this wire. I'm tempted to suspend some hefty art object from the ceiling, simulating levitation.

Your Old Dog
08-28-2007, 06:08 PM
Not knowing exactly what you are doing and how much service these pulleys are going to see... I think I'd be making them myself out of 1/4" aluminum sheet, or if heavier service, steel sheet. (or, think of a stacked array such as with washers of two different sizes only much larger of course)

cybeknight, when I read post like yours it is a reminder that we got folks from all walks of life in here. Who would have thought a board member would be fully knowledgeable with a topic as narrow as this? :D

cybeknight
08-28-2007, 06:30 PM
Hi Your Old dog
I have been working in the wire mill for 30+ years now and built all the machines except the BIG wire drawing machines, only install and fix those. We draw the wire down to the size we need then We put a nylon coating on the wire for spirial binding and custom orders for other jobs.
Getting back to the pulleys. The ones we use are very light weight and with the hard coating, wear (grooving) is at a minium. Drag on a wire line is a killer but they hold up well and keep spinning. .008 is some fine wire but I believe these pulleys would work. We did some .006 brass and stainless (experimental) and they worked pretty good.
Glenn

aostling
08-28-2007, 06:31 PM
a stacked array such as with washers of two different sizes only much larger of course)


I'd thought of this. A stacked array of washers might be the simplest way to fashion a multiple-sheave pulley block for 0.008" wire. Each sheave (consisting of a small washer sandwiched between two large washers) could be separated by a teflon washer, allowing independent rotation.

I doubt that stamped hardware-store washers would be flat enough. What do you think?

Your Old Dog
08-28-2007, 09:59 PM
I think you have a lathe, I'd try turning some thick washers if you have them large enough otherwise I'd use some thin steel plate with a mandrel type jig to hold them in. It shouldn't take long to come up with something.

If you don't have a lathe then you may be skating up hill.

aostling
08-29-2007, 12:06 AM
I think you have a lathe, I'd try turning some thick washers if you have them large enough


Yes, a Sherline, and a 6" Atlas. I have not succeeded in eliminating some rocking-slack in the Atlas compound. But the Sherline is perfect for this job, so I must quit my stalling. No more on this until I have some pulleys to post.

ERBenoit
08-29-2007, 01:21 PM
If you are looking for an off the shelf item, Stock Drive Products may have something:

http://www.sdp-si.com/