Unusual bearing design question

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.

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!

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.

and practical, but how durable?

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?

customers really don't want any plastic on their bass. I know. It's just something you have to deal with in my world.

the specific issue I discuss, and who has the time to give advice.

else which uses electricity or has sharp cutting edges.

for a purpose not described by the manufacturer.

If you have a premium product, why not stick with the bearings and brag about them?

is your product just functional or something you and the buyer will be proud of owning?

How polished do the ends need to be? You can cut a 1/4" piece of music wire to length with a cutoff wheel in a Dremel tool and a bit of patience

-- is this not an expected tool in your customer's shops?

I would think that a hard alloy steel shaft would be way better than stainless -- stainless isn't known for being low friction, and I'm not sure if the grease would stay in place over months.

Does the pulley have to be free to turn no matter how small the rotation demanded of it, after a month of sitting still? What kind of torques are involved? You may have some stick-slip issues to contend with.

It may be that the bee's knees for this is a hardened steel shaft that's been hard chromed and polished, with a bronze bearing surface on the pulley -- but that may be even more overkill than you have now.

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.

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!

What's wrong with an oil+PTFE-impregnated bronze bushing bearing on the 1/4" shaft? You'll need something like a 3/8" hole in the pulley. It's a standard part costing less than $1.

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.

and practical, but how durable?

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?

customers really don't want any plastic on their bass. I know. It's just something you have to deal with in my world.

the specific issue I discuss, and who has the time to give advice.

else which uses electricity or has sharp cutting edges.

for a purpose not described by the manufacturer.

Watch out for paper cuts when you type out the P.O.

[snip]

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!

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. [snip]

Dowel pins might work. Click Dowel Pins, 1/4" diam, alloy steel, etc at

A package of 25 each 1/4" diam by 3/4" long alloy steel dowel pins appears to cost $5.24; other lengths that are multiples of 1/8" also are inexpensive, eg $3.62 for 25 ea. 1/2" long. Odd multiples of

1/16" are available but several times as expensive; eg $14 for 10 ea 11/16" long. You could include one each of the 5/8", 3/4", and 7/8" pins in your kit for a cost to you of about 60 cents. The user can grind off 1/16" or whatever, if the needed length is between two of the cheap sizes.

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.

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!

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.

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.

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.

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.

the specific issue I discuss, and who has the time to give advice.

else which uses electricity or has sharp cutting edges.

for a purpose not described by the manufacturer.

repairers of upright basses. Check bass capos dot com for details. One thi ng 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 over built and expensive for the application. I want to arrange for a run of a f ew hundred which would be more fit for purpose, and hopefully a bit cheaper .

le and without the sealed bearing. There is a constant force of about 120 l bs. on the shaft, but almost no rotation. Maybe +/- 1-2° a few times a da y 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 wo rk 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!

cut the shaft to length and polish the ends. Not practical for most violinm akers /repairers. They can always special order the needed length, so not o ut of the question, but extra pain.

eap and practical, but how durable?

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?

me customers really don't want any plastic on their bass. I know. It's just something you have to deal with in my world.

of the specific issue I discuss, and who has the time to give advice.

ng else which uses electricity or has sharp cutting edges.

g it for a purpose not described by the manufacturer.

A ball-bearing isn't needed in this application, it's not in constant rotation, a waste of money. You need a non-deforming shaft/sleeve combination, hardened steel and cast iron would work, a bronze sleeve might deform with constant load, depending on how large the shaft is. Make your pulley of cast iron, use a hardened dowel pin and you're set. Figure out your unit load pressure, I think you'll be surprised since it's pretty much going to be a line contact.

Stan

Thanks everyone for the info so far. I find some of it very useful and I'm glad to see that the forum still has some real content. Robobass

Excellent! I'll study this.

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.

1. A bearing-grade bronze shaft with brass pulley? Seems like the most cheap and practical, but how durable?

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?

1. 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.

2. 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.

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I think if I were doing this, I would press-fit the shaft into the wheel and have the bushings at the ends of the shaft. That would prevent the wheel from wobbling due to any clearance in the bushing. Perhaps the shaft could have just a short section of the larger diameter in the middle to make press-fitting during assembly easier. For the bushing, if you can not find the right stainless sleeve, you could drill out an unthreaded stainless steel spacer to the right size (or size the shaft to match). You could also use some stainless tubing and drill it out to the right size (often then have a weld seam that protrudes on the inside). Although one problem with this whole concept is you would need a step in the shaft at each end to keep the shaft from moving laterally, so that would require specific lengths that you were trying to avoid.

Here's another idea: The brass wheel rotates on a short S.S. shaft made from an internally threaded spacer. The ends of the shaft are made from hollow brass spacers held to the center portion with screws from both ends (perhaps brass for aesthetics?). The OD of the brass spacers could be larger than the center portion of the shaft to provide strength and some lateral support against wobbling.

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.

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!

P.S. an SAE 841 sleeve bearing with a Pmax of 2,000 will have a maximum load (zero RPM) of 125 lbs on a 0.25" shaft if it is 0.25" long. A 3/8 long 1/4" bearing would be rated proportionally more.

They recommend shaft hardness >Rb 85 for the shaft material.

Best regards, Spehro Pefhany

There is some food for thought! I just found some small oil impregnated bronze sleeve bearings which cost only 34 cents and could hold up to 250 lbs. This would allow me to stick with a 1/4" brass shaft, so I think I'll go with that. Thanks everyone!

A bronze bushing on brass shaft is somehting that I have never seen and it is certainly not how the bronze bushing was meant to be used. It is quite possible there would be too much chemical affinity and they would start to stick and gall.

Absolutely. Do not use such similar materials for shaft and bushing unless they are extremely hard and have low cohesion coefficients. No way do you want to use two copper alloys together.

Music wire or other hard, high-carbon steel is the logical choice for the shaft. If rust is an issue, then 440-grade stainless steel.

The ideal wheel would be a high-strength (over 100,000 psi compression strength) bronze, but it probably isn't necessary. Even yellow brass (~ 40,000 psi compression) probably is adequate. And impregnated material will help with stick-slip.

A milder steel shaft probably would be Ok, too. If you go too soft on the shaft, you'll eventually run into a stick-slip problem. But I don't think it's likely to show up here, even with a mild-steel shaft.

repairers of upright basses. Check bass capos dot com for details. One thi ng 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 over built and expensive for the application. I want to arrange for a run of a f ew hundred which would be more fit for purpose, and hopefully a bit cheaper .

le and without the sealed bearing. There is a constant force of about 120 l bs. on the shaft, but almost no rotation. Maybe +/- 1-2° a few times a da y 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 wo rk 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!

cut the shaft to length and polish the ends. Not practical for most violinm akers /repairers. They can always special order the needed length, so not o ut of the question, but extra pain.

eap and practical, but how durable?

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?

me customers really don't want any plastic on their bass. I know. It's just something you have to deal with in my world.

of the specific issue I discuss, and who has the time to give advice.

ng else which uses electricity or has sharp cutting edges.

g it for a purpose not described by the manufacturer.

Don't gamble with your quality. If the ball bearing you use has gone up in price, then switch to a drawn cup needle roller bearing, full complement, on a steel shaft. Easy to press into your brass wheel. You've a high static load and want no compromises. Needle bearings should be inexpensive enough for this application, and may even be a marketing advantage. Add brass screw-on end finals to the design, with your logo engraved on the ends perhaps. They can support through the wood and screw onto the steel shaft to allow for scroll width adjustment by the end user.

Good luck

In that what you are selling has a marketing component as well as engineering requirements, lignum vitae:

Kevin Gallimore

Thanks. I think that LV or needle bearings would not work on this small size. I appreciate the advice against using brass and bronze together. I think I'll go with a delrin sleeve and brass shaft.

appreciate the advice against using brass and bronze together. I think I'll go with a delrin sleeve and brass shaft.

Don't do that. Delrin is not strong enough (Pmax = 1000), IMHO. (disclaimer: IANAME)

I would suggest trying a steel or SS shaft and oil/PTFE impregnated bronze. Follow the bronze bearing recommendations on the hardness of the shaft Rb 85+ or whatever it is. Test it at higher than expected loads. SAE863 (oilite+) is stronger than 841 (Pmax 4,000 vs 2,000)

Best regards, Spehro Pefhany

ize. I appreciate the advice against using brass and bronze together. I thi nk I'll go with a delrin sleeve and brass shaft.

Lostfr,

Hate to be a pest but...

Needle bearings are compact enough to easily increase your shaft size to 5/

16" in a 1" brass pulley. They come as small as 3/16" IIRC. Look at Timken 's references.

Use drill rod for a 5/16 threaded shaft. 3/8" dia. brass screw-on end-caps for finals/width adjustment spacers. Saves customer's cutting & polishing work installing. A 3/8 hole is almost same as 9.5mm. Works worldwide, no ne ed to send a 1/4" drill with the kit! That saves you cost.

Delrin on brass may creep over time under high static load. Keeping C-strin g in-tune may be harder. Hate to see your nice C-extensions compromised wit h a poor bearing choice.

How come this is such a cost-sensitive problem for you? A C-extension is m any hundreds of dollars to install, no? You need lower-cost CNC machined p arts? If so I may be able to help. I like interesting side work. Small run s are no problem on my gang-tool lathes.

Good luck.

I appreciate the advice against using brass and bronze together. I think I'll go with a delrin sleeve and brass shaft.

Which is why I mentioned Igus products in an earlier post. They offer standard bearings and materials with Pmax from 7500 to 21000 psi. Prices for a 1/4 x 1/4 x 5/16 bearing run from $.57 to $2.00 at qty

100, depending on material.