On Mon, 1 Apr 2013 09:15:51 -0700 (PDT),
wrote:
Hi guys. I have a unique garage business selling hardware to builders and repairers of upright basses. Check bass capos dot com for details. One thing they need is a small but strong pulley wheel with a 1/8" dia. round belt race. The ones I supply are brass with a sealed bearing and are a bit overbuilt and expensive for the application. I want to arrange for a run of a few hundred which would be more fit for purpose, and hopefully a bit cheaper.
The plan is for a 7/8" dia. x 1/4" wide brass pulley with a 1/4" brass axle and without the sealed bearing. There is a constant force of about 120 lbs. on the shaft, but almost no rotation. Maybe +/- 1-2° a few times a day for tuning, and no adjustments at all sometimes for weeks or months, and it must be usable for decades. I think that simple brass on brass should work if both parts are well machined/polished/lubricated, but there have been anecdotal failures. So, I need to do something more if only for marketing, but also I stupidly offer a ten year warranty. So, I must be very careful about how I design and produce my wares!
Anyway, what are some options?
1. A polished SS shaft instead of brass? Good, but the customer needs to cut the shaft to length and polish the ends. Not practical for most violinmakers /repairers. They can always special order the needed length, so not out of the question, but extra pain.
Not sure what's in a typical violin makers shop, but a 1/4" SS (303 or
304) round is easy to cut with a decent hacksaw.
2. A bearing-grade bronze shaft with brass pulley? Seems like the most cheap and practical, but how durable?
I doubt a bearing bronze will be much better than what you've got.
Though not ideal, you might get away with an aluminum bronze or other
hard alloy, but you may find they're not much easier to cut than SS,
and you may have trouble finding the shape and tolerances you need.
Ampco would be the place to look.
http://www.ampcometal.com/en/index.php?page=home
2. A greased bronze or SS sleeve between the brass shaft and the pulley? Sounds good except that afaik it would have to be machined from solid round, upping costs. Anyone know of bushing sleeve available in small diameters like this?
My gut is you could get SS bushings made for $1 or less in the
quantity you mentioned. There are thin steel bushings with various
anti-friction linings available, but they're generally not
inexpensive. A drill jig bushing would work, but also not cheap.
3. Delrin bushing sleeve? This seems available in the size I need, but some customers really don't want any plastic on their bass. I know. It's just something you have to deal with in my world.
Not Delrin, something from Igus. Probably less than $.25 in quantity.
http://www.igus.com/default.asp?PAGE=IGLIDE
4. SS or bronze Pulley? sounds expensive.
Anyway, I hope there is someone out there with interest and understanding of the specific issue I discuss, and who has the time to give advice.
Please do not post if you wish to warn me of:
A - the risks to life and limb of using metalworking machinery, or anything else which uses electricity or has sharp cutting edges.
B - the liability risk of altering something without UL approval, or using it for a purpose not described by the manufacturer.
--
Ned Simmons