Broken gear wheel

[fred]

The above image shows a broken gear wheel.Am I likely tp obtain a replacement off the shelf ? If so how do I define what I need and where would I look ?

Many thanks for all help offered

[Brian Reay]

It depends what it is off/for.

A replacement motor / gear for the item may well be available.

If you want a gear that simply fits, possibly. Measure bore, dia, teeth, and look on the net. Even Ebay.

As for exact details, you will find drawings showing the gear profile you can compare (the basics I suggested should get you started, they worked for me) once you locate people selling gears.

There are other options, depending on the application.

I've made new teeth by hand and brazed or even epoxied them in place. It takes time and is only practical if there isn't much load / stress on the gear. I've replaced two teeth, you seem to have lost more but the photo isn't clear. One isn't too bad, two is quite hard. Three, I'd have to be serious....

A local model engineer or small workshop may 'cut' one for you.

[Harry Bloomfield]

on 29/08/2018, fred supposed :

I would try to araldite the missing part back in place, if it is no under much stress. It appears to be plastic and the unit it mounts onto, appears also to be plastic and is broken too.

I doubt you would get one off the shelf. Other options would be to find a model engineer, with the equipment to make a replacement, or someone with a 3d printer, who could print a plastic gear. Some on here have 3d printers.

[fred]

Its off an electrically motorised garage roller door. Yes the mount is brok en but I think I can fix that. The broken cog (its about 30mm in diameter) rides on a ring inside the rolled up door. It controls, via micro switches, the open and closed positions of the door. The door is about 25 years old so no spares are available. I don't fancy replacing the whole door as it is a double garage so is quite wide.

I'll follow up on Brians suggestions to start

[Brian Reay]

If, as Harry suggests, it is plastic (I didn't spot that from the photo), and given the application, you could try making one.

Use a bit of thick cutting board (the nylon stuff). Use the chunk you have as 'stamp' to make a template from paper. Use that to make out the board, rotating it to fill the gap.

Cut out a circle and file in the teeth.

It won't be perfect but it doesn't sound a critical application.

[John Rumm]

Another approach would be to laminate up some ply to the right thickness, and then cut the gear from that with a band saw or scroll saw.

You could also print a template for it with Matthias Wandel's gear designing program / site:

[Brian Reay]

Very interesting site!

Amazing how these things 'creep' out of the woodwork on here (no pun intended), on of the things that makes this (and some other groups) useful.

A bit of Tufnol, if you can get a bit, would be ideal but do be careful of the dust- it is nasty stuff.

I've seen some clocks made with hand cut wooden gears in museums and exhibitions etc- both very old and modern ones. The workmanship is outstanding- far beyond that I managed when replacing the odd tooth in various things over the years. My dexterity isn't what it was (side effects of a stroke) and find fine work difficult, at best, these days.

[John Rumm]

I have some plans here waiting for the right shape of tuit to build a wooden clock....

A good starting place is:

[The Natural Philosopher]

Best source of gears in UK are model robot suppliers.

e.g.

[Martin Brown]

Your best bet is find a local model engineering club and someone with a lathe. You need to know diameter of wheel, number of teeth and how the cog is attached to the shaft. Looks to be other things wrong with the mechanism if the background fractured plastic is anything to go by.

If you take them the bit they should be able to make one for a price (or a few beers).

A nylon gear ought to be good enough. I doubt if PLA would last long.

[FMurtz]

Another approach would be to get a replacement from the garage door maker ?? or am I missing something?

[fred]

e Tried the manufacturer (in Australia would you believe, and the door was cu stom made. But at 25 + years old they don't have spares

[Rob Morley]

If you have the missing pieces you could stick it back together, take an impression of the whole thing and cast a replacement in fibre-filled resin.