Mastodawn

Let Friction Ring.

Dear Lazyweb, I have this pulley wheel, 50mm inside diameter, 4mm groove. I need a rubber traction ring to go inside it. I cannot find anyone who will sell this to me. The ring must be flat or concave, not round like a typical...
https://jwz.org/b/yk33

Update: after only a week, Plasti-Dip has proven to be even more bullshit than Sugru.

Nonya Bidniss 2d ago

@jwz Ah, that sucks. I've always wondered.

iridescent_justien 2d ago

@jwz interesting problem. I would try mixing a friction substance, such as fine sand, polyester or nylon fibres, or similar, with metal glue, then brushing on a thick layer into the seating groove, and letting it completely dry.

@jwz Quick, non-destructive thing to try: Scotch self-fusing silicone rubber tape.

Chancerubbage 2d ago

@jwz it’s mostly meant for putting insulation on plier handles isn’t it?

@Chancerubbage What is your point, because I'm sure it's *incredibly* helpful

Chancerubbage 2d ago

Incredibly unable to figure out the problem you are meaning to solve. No ill will intended.

@Chancerubbage There is an invention called a hyperlink that one can click

Chancerubbage 2d ago

Assuming I saw your initial post of 24 days ago. So sorry to bother you. Good luck.

@Chancerubbage Don't reply without looking at the thread that is *right there*, jackass! *plonk*

@jwz do you have a workshop that repairs/maintains sailing ships/yachts in your city? Try there. These people do not do online. From my experience only plain old rubber will do. Everything else is most probably useless.

Thomas Sibley 2d ago

@jwz maybe silicone tape? https://esigrips.com/collections/rct-wrap/products/self-bonding-silicone-tape

Self-Bonding Silicone Tape

@trs Based on an earlier suggestion, I ordered some of this stuff https://sundialwire.com/products/tape-12-yard-roll-1-4-self-fusing-silicone-tape?variant=30050321039424 (apparently their last roll, since it's now sold out) and while it hasn't come off yet in one or two tests, it also doesn't seem to be providing the necessary level of friction.

TAPE: 12-yard roll 1/4" Self-Fusing Silicone Tape

Thomas Sibley 2d ago

@jwz Eh, drat. What about skateboard grip tape?

@trs Yeah that shit's really stretchy and peels right off.

Whom It May Concern

@jwz Try using RTV silicone gasket maker. It wouldn't be hard to use something with a similar radius to the rope to shape the bead so that it has the right shape. It is pretty durable.

Attila Kinali Feb 27

@jwz If nothing works, you can always try getting a small, thin line of silicone on the inside. That should provide enough friction for such an application.

@attilakinali Silicone is not much hardier than sugru, so I doubt that will last.

Attila Kinali Feb 27

@jwz Hmm... I don't know sugru, so I can't say. But I do know that silicone is used in such applications (often injection molded) friction layer inside transmission wheels. Maybe that's a specialized variant. Maybe it's low performance systems only. Maybe it's just because it's thin enough and thus doesn't need much sheer strength...I don't know....

Greg Whitehead Feb 27

@jwz Maybe you've already looked here, but if McMaster Carr doesn't have what you want, it probably doesn't exist
https://www.mcmaster.com/products/pulleys/

Can you replace the rope with a rubber belt? https://www.mcmaster.com/products/pulleys/round-belts-1~/

Pulleys | McMaster-Carr

Choose from our selection of V-belt pulleys, timing belts and pulleys, and more. Same and Next Day Delivery.

@grwster No, replacing the rope is not an option. The problem with McMaster is that I demonstrably don't know what the thing I am looking for is called, so can't search for it.

Matthew Dockrey Feb 27

@jwz Hrm, I don't know of anything like that. Couple thoughts:

Is the pulley intended for round belts? If it's just a random hardware store v-belt pulley, there might be some extra friction to be had with a round belt one.

I wonder if the ridges on a timing belt pulley would give enough friction (without shredding the rope). I don't see any near that diameter, but we could cut ridges into a larger plain one.

I see what you mean about using an o-ring, but what about two, sized to fit side by side inside a v-belt pulley? That would leave a little groove between them that the rope could ride in.

@attoparsec No, I'm not re-engineering the entire thing to have a second wheel, come on.

How the fuck am I supposed to know what the pulley was "intended" for?

Matthew Dockrey Feb 27

@jwz What second wheel? I only meant modifying this one, or else a replacement like you indicated openness to in the post. (And was volunteering to help with the mods if needed.)

Is the groove semicircular, such that a round belt would fit snuggly in it with full contact all the way around, or does it have tapering straight sides and a flat bottom?

@attoparsec Oh, I thought you were suggesting sandwiching the cord between two wheels. Sorry.

The groove inside the wheel is flat on the bottom. Basically it's a 50mm x 4mm disc with a pair of 54mm x 1mm disc walls on the outside.

Matthew Dockrey Feb 27

@jwz Well, I was going to say that trying a round belt pulley would be the easiest place to start, but now I can't find one with a hub and set screw, even imperials ones I'd need to bore out. So I guess I'd fall back to the timing belt pulley idea. The diameter would be a bit less, but I think the ridges would make up for that.

Daniel Carosone Feb 28

@jwz @attoparsec so maybe two very thin o-rings, such that they sit in the corners on either side and help grip the rounded cord?

Otherwise: a few windings of teflon tape, perhaps, and that will similary squash to fill the sides. Does it reverse direction or only spin one way?

@uep @attoparsec It reverses. Why do you think Teflon would help?

Daniel Carosone Feb 28

@jwz @attoparsec the tape is soft and deforms easily into crevices (threads, usually), and stringy as it wraps around. Reversing direction may mean it unwinds though. Worth a try perhaps.

@uep Teflon is explicitly used in cases where you want to minimize friction. Here, we want to maximize it.

Daniel Carosone Feb 28

@glace I think you're conflating this with non-stick pans, which is a different case entirely.

look up teflon lock nuts sometime.

@uep No, I’m aware of how it’s used in both pans and in industrial bearings.

https://www.mcmaster.com/products/bearings/dry-running-metal-reinforced-plastic-thrust-bearings~~/

https://www.mcmaster.com/product/6153K69

PTFE is teflon.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 700,000 products. 98% of products ordered ship from stock and deliver same or next day.

@uep @glace I was curious so I took the time to look up Teflon locknuts.

I did find a link that referred to them as anti-slip, saying they were less prone to come loose under vibration. However, besides its chemical inertness, by far the most common use case for Teflon in engineering is reducing friction, and even the description of those locknuts listed this as a benefit, making them apparently both low-friction and anti-slip.

I'm not inclined to doubt that there's science behind the design that means that they both can be true, but I would suggest that understanding that science is crucial to knowing in what circumstances a famously low friction material could contribute to increasing friction.

@attoparsec The thing that confuses me is that, here is a wheel that is intended to move a band through friction. So let's make the surface as slick as possible! No there is not an option for a non-slick surface, why do you ask.

Hart of the Wud Feb 27

@jwz Could you take a strip of 4mm toothed-belt / timing belt and glue it in there with the teeth facing out of the groove? It should provide enough friction and hold up well but it might also wear down your rope.

@praxeology I tried that and it was impossible to stretch the belt enough to get it over the lip.

anarchy_punk_nonbinary

@jwz @praxeology if thinking of gluing, maybe just cut the belt, measure in place for the exactly right length and glue it down there with contact cement ?

@Primavera @praxeology There is not a hope in hell of that standing up over time.

Thomas Sibley Feb 27

@jwz Have you tried an ordinary rubber band inside the groove?

Or something ever so slightly more specialized, like one of these? https://www.amazon.com/dp/B0GGB2MDHT

(sorry for the Amazon link)

Amazon.com: 50 Pcs Cassette Belts Recorder Rubber Belts Recorder Repair Maintenance Tape Machine Rubber Belt 40-135 mm Mix Size 4mm Width Flat Cassette Belt for DVD CD LD VCR Repeater Drives : Electronics

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@trs Yes, like you, "is there a rubber band in the house somewhere" was literally the first thing I thought of.

Twotired Feb 27

@jwz Misumi sells configurable pulleys intended for round belts, with vee grooves for non-slip, e.g. P/N SL-MBRDA45-2-P8. It’s pricey (US$22). Search on Misumi Components (they’re worldwide).

Gnome Tsunami Feb 27

@jwz on a conveyer belt system it would be called "pully lagging". But I've never seen anything like it on a machine like yours. Not sure if that keyword helps you?

spectrophagus Feb 27

@jwz do you or a neighbor have access to a 3D printer and a spool of TPU?

@spectrophagus No

a high doom Feb 27

@jwz cut a strip of adhesive backed skateboard grip tape?

@jwz Auto parts stores often have specialized materials for use in harsh environments. Chemical resistant, high temperature applications, etc. It may be worth wandering through one to see what's there, and asking the clerks if they can think of something which would work.

@jwz Hoo boy. The phrase "Dear Lazyweb" is like seeing flashing lights and a lane closure up ahead on the highway. You know you're about to drive past a car crash.

Normally it's software, so it's amusing to watch people who know a bit of python try to explain software to jwz.

This one is mechanical hardware, so it's people suggesting to jwz that he use a rubber band. But, I hadn't anticipated "I'm a qualified pulley engineer, and you're holding it wrong."

@merc Truly the lazyweb is a land of contrasts.

@jwz So, I had some questions, but the linked blog post and "previously" post answered a lot. For those on mastodon who haven't read them, do, they're not long. That said: it's to drive a homebrew curtain open/close mechanism. I'm interested to see how the project goes as I have a couple of curtains I've thought about doing this with myself.

Also for those on mastodon, you may have missed the "update: If you're going to say "why don't you just" or "have you searched for" without a purchase link to a product of the correct size, please know that you are not helping. "

@GerardThornley The reason I did not use the word "curtain" is because I was trying to dodge the inevitable flood of responses of the form, "You know what you OUGHTA do is replace the whole curtain track with this $8,000 Internet-of-Shit Clown-based thing that has a worm gear. It says it works on curtain tracks 1/3 as long as yours so I'm sure it will be fine!"

@jwz I don't think I can help you, but your post makes me curious: how comes the rope slides off the track instead of just slipping? It doesn't seem to be tensioned with a twist, but perhaps I'm seeing this wrong. (I'm also curious about the rationale of using this kind of rope as a belt to drive a high torque application.)

@karl It doesn't slide off the track, it just slips. With a round O-ring type friction element, it would slide off which is why that's a no go.

@karl @jwz if you follow the links, you'll find it's driving a curtain rail, I assume the cord is dictated by the rail.

@jwz I've been wondering if tension can be adjusted, but I see the pulley's only supported on one side and the motor bearings probably aren't designed to take the forces. In any case, I'm sure if you can adjust it, you'll have tried it and it mustn't have worked.

In the absence of increased tension, I think the advice to use an extra wrap or two around the pulley is your best answer, but you'd need a different pulley.

I think the right way to go would be:

• Put a new, wider pulley on a separate spindle, and use two or three wraps of the cord.
• Use a couple of gear wheels to transfer the drive from the motor to the pulley spindle.
• The pulley spindle would need a suitable bearing at each end.

Benefits:
• You're no longer limited to pulleys that fit your motor.
• No more lateral forces on the motor spindle.
• If they wear, only the bearings would need replacing, not the whole motor.
• It'd cope with more tension than you need - I'm certain the limit would be the curtain rail.
• If needed, you could choose a gear ratio to better suit your motor & aesthetic effect. Otherwise 1:1 will do.

Downsides:
• More work.
• You'd still need a gear to fit the motor, but I think that will be easier.
• Probably a little noisier.
• Would need a facility to access one side of the pulley to wrap the cord round it.

@GerardThornley
Q: I would like to buy this wheel, but with a rubber edge.

A: You know what you oughta do, is completely re-engineer the entire thing from scratch with custom metalwork and a multi-gear system.

@jwz I know. I'd be irritated, too.

randomwizard Mar 1

@jwz Maybe a polyurethane resin would last longer.

https://www.belzona.com/en/products/2000/2311.aspx

https://silpak.com/products/polyurethane/rubber/

Belzona 2311 (SR Elastomer) - Emergency Repair Elastomer

A cold applied abrasion and chemical resistant elastomer for emergency repair, rebuilding and protection with very minimal downtime.

www.belzona.com

CounterPillow Mar 1

@jwz buy the 90mm one, cut 4mm slice off, shrink to fit with heat gun or hair dryer or, god forbid, a lighter. https://aliexpress.com/item/1005005326536181.html

1 METER 22/25/30/35/40/45/50/60/70/80/90/100/120/150 mm Schrumpfschlauch, Wickelset, Isolierschlauch, thermobeständiger Schlauch - AliExpress 13

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randomwizard Mar 6

@jwz Does the wheel spin fast? I had this cheapo idea that maybe you could just put a draw string bag over it.

https://www.greencotton.com.my/product/canvas-drawstring-bag-can203/

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