Joining flat toothed belting

Has anyone successfully joined flat toothed belting? My 5" gauge freelance electric tram loco (poorly designed by me in terms of maintainability) has broken its intermediate drive belt. It has had a good long life and I've now bought a new belt but installing it requires virtually a complete strip down because of my poor design.

If a successful way of cutting and joining the ends of the new one is available it would save a vast amount of work.

I wonder if a long diagonal splice might work? It means the split section might actually be split over a length which partially wraps around the toothed pulley, and you will have more area to apply the rubber adhesive. You could then apply a patch over the back of the belt covering the whole thing.

To be honest I'm not over confident but you don't have much to lose by trying it.

Might be worth experimenting with the old belt first. Superglue plus diagonal slice as mentioned above might work at least for a while.

Doug

Wasn't there an ad for super glue way back that featured a car fan belt cut in half and joined back together with super glue?

Maybe I imagined it?

I was a bit suprised to find that a commercial "joinable" timing belt is available - see here

Cutting & splicing has at least two problems - the strength of the belt comes from the continuous cord embedded in it & the teeth over the join need to maintain the correct pitch. While a diagonal splice & something glued over the back as reinforcement may work, it would only be as strong as the glue line as the cords have been cut.

The makers of the "joinable" belt above don't recommend it for "most drive belt applications" - aimed primarily at conveying. I didn't see any indication of pricing, but unlikely to be "bargain basement".

Nigel B

My own experience, and I have also seen it mentioned online, is that superglue dries 'hard', so any flexing around a pulley will eventually cause a superglued joint to fail. Also, as mgnbuk says, the main source of strength in these belts is the continuous cord - which will not exist in a cut belt.

As for the superglued car fan belt - how long did that last?

If you want reliability, I guess you will have to strip it down and fit a new belt.

Just been having a read out of interest, as I'd never seen it before.
Minimum splice length of 700mm might be a problem too

Bill

Not all CA adhesives are rigid. Permabond make a range suitable fos flexible polyurethene.
https://www.antala.uk/permabond-flex-ca-cyanoacrylate-range/

A long tapered joint might work. You can keep the teeth aligned with a spare bit of belt. You could at an extreme put two cut belts "back to back" with the joins off-set. This would keep constant stiffness and spread the loading over a maximum bond area.

Robert G8RPI.

Could you sew the ends together, with flexible glue as well?. Fine synthetic thread is very strong, and you will likely need a spike to make holes. Add a woven backing to the non toothed side.

it might be possible to scarf the belt across its width then insert pins through the teeth. HD do this with their emergency drive belts

This may sound very drastic, but could you cut the axle in half with a small angle grinder, then join them back together with a slip coupling. Being split, you could pass the belt between the split half and then join with the coupling.

Bob

I have glued several poly-vee belts with superglue and a long splice and none have parted so far.

Buy the glue from a double glazing shop. You can get a big pot of it for about 6 quid and it's slow setting stuuf, very strong compared to the thin quick-setting ones.

Just a thought...if you do strip it down, why not put an extra belt loose out of the way ready for future breaks? If there is room of course!

I have glued one of my lathe flat belts from an overhead countershaft using Gorilla glue, one side has the glue spread thinly and the other end is wetted.

It has to be compressed for 2 hours and then it's incredibly strong

One last suggestion from me, if you have the width you could use two belts half the width of the original, then place the spliced joints 180 degrees from each other. When the glued part is under the most tension it would be next to a section of unjoined belt.

Thanks to everyone for the various and innovative suggestions. As the practice is not commonplace I assumed it had an element of risk but the dismantling to do the job properly is such a large job it's worth a try. I'm going to do a diagonal cut about 6 teeth long on a new belt and will use an offcut from the old belt on the toothed side as a temporary template to align the ends while I glue. I'm going to use Permabond 743 as a flexible superglue to fix another piece of the old belt over the spliced joint smooth sides to smooth sides. I'll post an update to this thread if it fails. I don't know how long it would have to last for me to say it's a success!

Thanks again - this forum is guaranteed to feed the old grey matter.

Read and understand mgnbuk's post about where the strength of this type of belt comes from.

I have read and understood this post. My experiment will determine if a modern adhesive is any sort of substitute for the continuous cords. As I said I am prepared for failure but it is worth a try.

If you Google "belt skiving" you will find lots of information on traditional and current methods of joining flat belts and conveyor belts etc, by peeling back layers of the belting and overlapping the embedded fabric or cords then gluing. I have used epoxy glue in the past for skiving and joining flat belts on the old Drummond lathe. Seems like the same principles should work on a toothed belt, which is basically a flat belt with the teeth added on.

I wonder about using a suitable flexible glue, and wrapping the finished belt with stranded, or fabric, Kevlar might be a possibility.
That way, you will still have continuous cords, just on the outside of the belt, rather than within it.

You could see if there are any local manufacturers of flame resistant overalls, for motorsport, or industrial use.
Some of those will be Kevlar, rather than just a flame retardant Proban treatment on a cotton fabric.
They may well let you have some offcuts.

Bill

Edited By peak4 on 21/08/2022 23:29:41