waxy plastic gear repair

Cut a groove around the perimeter, deep enough to get past the gear teeth. Wrap a steel wire around the gear in the groove, and twist the ends to make it tight. If cyanoacrylate will stick to the plastic, use that to get the pieces assembled before you add the wire.

Isaac

My guess(tm) would be Molybdenum disulfide lubricated nylon gears. Search google for "self lubricating plastic gears".

However, glue is not going to help. No glue will stick to a plastic gear that is impregnated with some manner of wax or grease. Your best bet is to temporarily stick the gear together with some manner of cyanoacrylate adhesive (super glue), and make a lost wax plaster mold in order to clone the gear.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Skype: JeffLiebermann     AE6KS    831-336-2558

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Are you saying cut a slot through the middle of the teeth into the bulk under the teeth? I suspect a .4mm saw in a Dremmel would end up as a melted mess and not a slot, perhaps a heated scalpel blade in a jig

Or perhaps use some nicrome wire with some silone sleeve at the overlap, apply a weight and some adjustable current. Hope the wire melts into the bulk of the plastic and perhaps ypu can ignore twisting off of the wire. May need to recess 3 pins into the disc part , then swathe in hotmelt or something, if the 3 sections have failed with smooth edges, before doing the wire job

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on second thoughts as its 2.2 inch there is probably quite a thickness of bulk material. Wire and twist around the teeth to act as an alignment jig , then 3 pins and generally hotmelt "soldering" along all the joins, cut away the wire. Precede with a test that the plastic and hotmelt are compatible in the first place.

The Lady from Philadelphia advises you to purchase a new pencil-sharpening instrument.

You've just posted that 'reply' to a thread with repair in the title on a board with repair in the title

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I've come across them but don't remember where, glossy looking as though covered in oil , hard white material but not PTFE , and slippery to the touch but no oil film. IIRC quite coarse teeth and pitch as though not very structural plastic.

what is a waxy plastic gear? I can't picture any gears being made of wax or material soft like wax?

Jamie

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But common sense has a place even in a repair group.

You're rather missing the point.

The reference is to a character in Lucretia Peabody Hale's short stories "The Peterkin Papers". Said lady was a fountain of common sense, giving simple solutions to what appeared -- to the Peterkins -- to be complicated problems.

Yup. Exactly.

Just use a coping saw.

Something to hold it together long enough to get the groove cut would make it easier. Even clamping the pieces between a couple of washers might do it.

Isaac

Thanks to all the replies!!

The unit is at least 20 years old.

The gear is brown Bakelite in color. I say waxy because it has a soapy feel and I can scrape the material with my thumbnail and get some to come off. Like very hard wax. Odd for a drive gear material so I suppose it changed in nature over time. The exterior seems most changed so perhaps there is some material strength remaining.

The teeth are about twice as wide as the body and none have broken off. A clean

3 way break. The body is too thin for making a groove around the perimeter.

Adhesive would be required in and around the breaks for adequate strength.

I cannot think of an adhesive for this material so I posted here hoping for anyone familiar with it to chime in.

As an alternate to a lost wax reproduction, I thought of reassembling the gear and wiring it to stay put, some holes could be drilled through the disc (several on each segment) and a 2 operation repair then be undertaken. On one side a layer of JB Weld between hub and teeth, then a repeat on the other side. Would give a metal sandwich with the holes ensuring the teeth remain in roper position and are driven. Will look over the unit to see if any special clearance need be observed. Likely the best option in hand.

Just discovered someone who has cloned the gear and is selling them $12 or so.

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They call it micarta

Jamie

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In that case, known as Tufnol in the UK . But as those are cloth reinforced I would not have expected the material to split , has it got fibrous mat reinforcement?

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I suspect its this material , upper left cog but I don't know what its called

from structurally poor but decouples vibration from a gear train

Micarta is the trade name for the company that created the process. I guess you can use a wide range of material to make it, you need to be specific in its use, which dictates the composites better suited for the jobs.

People that make knife handles could use micarta composite and what they mostly do is use layers to clothe soaked in a resin and compressed in a bundle until hardened...

I've seen them use all sorts of different materials over the years, including hemp.

Jamie

Knackered, I'd say ...

Arfa

Color looks about right. Will get a scan of it tomorrow and post it. I saw a number of posts on web sites referring to odometer repair while looking for info on this gear. Also found a site where there are dozens of people with this same problem asking for some reason: My post "Boston Model 18 Lg Gear Needed"

There is no binder or substrate to it. Heft in the teeth and hub, body half as thick.

I see that the center hole of the hub which is keyed to the drive shaft may have worn a bit allowing the shaft some slack and instead of all force delivered to driving the gear, some was directed against small points on the hub surface. The drive has a 15 degree or so pitch and this slack would allow the gear motion off axis which would also work to crack it.

A little slop may be what killed it.

If I go with a JB Weld repair I will grease the shaft and use JB weld on the hub also.

Thanks to all for the conversation.

The original micarta was developed by George Westinghouse. As a laminate, Westinghouse sold it well into the 1960s. GE had a similar product, textolite, which was used for countertops, gears, etc. Both are similar to Formica.