making a copy of a stripped gear?

[havoc]

When treasure hunting I found an old cine camera the has belonged to my father (1950's, fully mechanical). I tried it: completely blocked. As it is spring driven I suspected a broken spring. So I started taking it apart to see if it is repairable.

After some time poking around in the thing I saw this:



In the whole gear train there is a single phenolitic gear. This is screwed to a brass holder. I think it is there to save the rest when needed.

Obviously this gear needs replacing. But how? Buying a new one is problematic as the manufacturer is already long gone. I have no manual that can tell me more about it. I fear this predates the standard modulo gears. All I do know is that the camera is french...

My course would be:
- measure outside and inside diameters
- determine number of teeth
- find closest module
- make such a gear in delrin or so
- hope that it beds in after some use

Any better way to tackle this?

[lancelot]

Hello Havoc,
would it just be possible to tidy up the gear where the stripped teeth are, then using the gear to produce a (TWO PART SPLIT) pattern mould with whats left of the gear...I/E pourable mould latex... the new gear could be made using Carbon Fibre Epoxy Resin Potting Compound... this is a Resin base filled with chopped carbon fibre paste...the part could be Air cured or Oven baked to cure... I think this should work. (you might have to shop around for the material a bit) I did something similar in the workplace...
All the best for now,
John.

[havoc]

Might work. Never done any mould work either. I'll have to look around for the materials.

[abby]

Silicone rubber would be a better bet for your mould , mould more than half of the gear , when the rubber has cured remove the gear and rotate it, then pour the remainder of the mould . The two halves will bond together as one , you could try a white metal gear cast directly into the rubber , or a castable ureathane of sufficient hardness. Some of the 2 part plastics require very accurate measuring of the components and are expensive in small quantities.
PS. the silicone rubber can easily be cut with a scalpel and goes back together precisely. If you do use white metal mount the broken gear on a shaft and include this in the mould to provide a sprue for pouring the metal , you will have to machine this away after casting.

[albertsell]

Hello Havoc,
Have a word with the following about your gear:- HPC Gears,Unit 14,Foxwood Industrial Estate,Foxwood Road,Chesterfield,Derbyshire. S41 9RN.Tel:- [phone].
www.hpcgears.com [e-mail]
A catalogue I have is 840 pages it contains gears of all types and materials.I think they can help you.
Bye Albert

[Noddy]

Tiranti sell the silicone rubbers. It looks like you have less than 1/2 stripped, so the silicone route sounds a good possibility

Keith

[havoc]

I'll try to contact hpcgears but I'll first try to cast a working copy. That way if they ask to send it then I have at least something in case it gets lost.

I really want to cast it in something about as strong as the stuff originally used. To me it is no coincidence that in the whole drive train there is only a single gear not in metal. Not only that, but it is at a critical place (just before the shutter mechanics) and can be reached and replaced without taking everything apart. It is the only gear mounted in such way.

Time to visit some hobby fair, there always are stands selling those casting materials.

[chris vine]

Hi Havoc,

Please dont take this the wrong way, but these cameras are not worth much in monetary terms as they have been overtaken by video and mobile phones.

However you obviously cherish this one and wish to see it working again. I notice that there are quite a few on ebay going for a few buttons. Maybe not the type you are looking for, but if you keep your eyes open you might find the same one.

I think you could probably get it for a few quid (euros) and just use it for the spare part you require.

Regards and luck
Chris.

[havoc]

I know it isn't worth anything that's why I want to repair it myself and not send it out. As this type doesn't seem to be popular (I found 1 pic on the net) I fear a spare one will not be that easy to find. And since the broken part is clearly sacrificial the chances to find a good one look slim.

[havoc]

actually, I would bother. Gears is something I really avoid at all cost if possible.

[spurley]

Havoc

I think Chris might have been suggesting looking on ebay for a similar camera and cannibalising it for the gear you want? Just a thought. However, I also wonder if you might feel that, for a small amount of effort, repairing the camera might be just the thing rather than throwing it out?

The gear material looks like 'Tufnol' in your picture, could you make a new one from a suitable offcut from a printed circuit board?

Cheers

Brian

[chris vine]

Hi Havoc,

Brian has just set a thought going.
You can often find tufnol in large bits of redundant electrical kit, switch gears etc. Also the Myford super 7 tumber gears are made of tufnol and plenty have been stripped over the years. I should imagine that a damaged one of these would give you plenty of material to machine one out of.
There is a cheap and dirty way of machining gears using a tap in the 3 jaw chuck and mounting the gear blank on a spindle. When pushed into the tap it will spin and cut the teeth.- if you have the right pitch tap etc!!
To help get the process started you could just file some notches, reasonably accurately spaced around the blank.

Have fun,
Chris.

PS Can you still get the film for it or is that just an academic questions?!
C

[havoc]

I have a vague impression I'm repeating myself...

- yes, buying a spare one would be possible, but this is THE piece meant to break first so the chance to find an intact one is slim. I looked but not much to be found about it.
- yes, I'm not repairing this to get rich it is pure sentiment and the joy of tinkering (don't you guys like to tinker?) My father made only 2 films with it. One is me waking up in my cot. (no, I'm not going to post it)
- yes, I could make another one if I knew how. Material isn't a problem, determining what form of gear it was is the problem. I'm not deep enough into the history of gears to know what kind of geartooth were used in France in 1950.

Might be tufnol. It is kind of cloth (jute?) in phenolitic resin. The kind used in pcb's isn't reinforced like that, I tought they use some paper.

[steam4ian]

G'day Havoc

The fibre/resin material predates nylon and modern more stable plastics. I have come across similar gears in ratio reducers for radio tuning (often with an anti backlash feature). The most interesting use of gears like that that I have seen was on a positioning system on a steel rolling mill! I think it was first developed as a naval gun aiming "computer" and passed into rolling mill technology.
Fibre gears were selected for quietness, I know of one popular make of auto engine that used one as a timing gear (Ozzies will know the Holden motor).
Luckily you have most of the circumference so can work out a pitch and diameter; there is even enough to make a mold as has also been suggested.
Since we are all craftsmen ("crafts persons" for the PC squad) in the making why not file a new gear? Your base material could be built up from fibre glass printed circuit board (with/without copper).

regards,
Ian

[havoc]

why not file a new gear?

You really want an answer to that? ;D

Never found them in radios. Those that I found there were most brass and alu. Once a brass/alu anti-backlash combination. Put rope/pulley was more common.

[JohnP]

I think it's Tufnol. There are several different flavours, all with some kind of marine theme. "Whale" and "Walrus" brands come to mind, though I think they were all made by the same people.

Before fibre glass, PCBs were usually SRBP (Synthetic resin bonded paper), whereas Tufnol is SRBF (Synthetic resin bonded fabric).

JohnP

[spurley]

I have a vague impression I'm repeating myself...

I have a vague impression I'm repeating myself...

Hey Havoc

Why don't you try and make a replacement? ;D ;D

Best of luck, whatever solution you find. And yes I too like to tinker, as you woud know as I posted recently about a spring for my old clock!

Cheers

Brian

[circlip]

Best thing to do would be to throw it away as the methods of re manufacture are the same ones locked in the annals of time by the old masters.

[alanstepney]

Fortunately, model engineers are, in many ways, the custodians of the "old methods".


Havoc, is the camera a Pathe? If so, which model. I have several of them.

[havoc]

It is a "Levéque L.D8". But I have no clue as to what model exactly as they had more than a few only distinguished by something that came after it.