Plastic gear repair (is JB Weld strong enough)

[Techie1961]

I have a Pioneer head unit that is a slide out type. The gear that drives the screen outwards before it rotates to vertical broke a few teeth off. It is the last plastic gear before mating with a metal gear so it sees the most torque in the plastic gear group. I have been waiting about a week for a reply from Pioneer on the part and it looks like it might be a bit pricey ($45ish) and has to come from Japan. I am thinking that I can fix it though.

Two ideas on fixing it:

Make a small mold to form some new teeth out of JB Weld (or other ideas please). I was going to remove some material to give the epoxy some geometry to bind to. Next, make a mold from the good teeth with some other epoxy and a release agent and then form the new teeth. Question - will JB weld be strong enough or is there a better material to use. I have no idea what the gear is made from but likely Delrin or similar acetal maybe. I don't think it is Nylon.

The other idea for fixing it is the metal gear beside it. The DP of the gear is a bit off but it should be okay. The outside diameters are the same but the original has 14 teeth and the other has 16. I was thinking of making a thin gear from the metal one and then possibly riveting it along with some cyanoacrylate glue to the other one. I'll have to do a test glue to see if it will stick.

Thoughts???

 

[southalabama]

I got a buddy who built part of a gear from jb weld for a fertilizer spreader on a tractor. I wouldn't have believed it but it worked.

 

[raddksn]

I will be watching this one!

 

[ChevyEFI]

3d printer job?

 

[James_B]

What's the thickness of the gear? A replacement may be able to be cut from sheet acrylic or plexi with a LASER cutter. It really depends on how small the gear is. I know I could probably cut it on my system. I have a copy of Matthias Wandel's gear design software, but getting the parameters right would be the biggest problem.

 

[MagnumForce]

Laser cutter or 3d printing all sound like more than 45 dollar solutions to me.

 

[shawhite]

A lot of those electronic parts can be ordered from vendors other than the manufacturer. I would get the part number and search the web for a replacement just so I would not have to keep taking my dash apart if the jb weld does not hold

 

[Katodog]

Take the gear to your local hobby shop (a real hobby shop, not Hobby Lobby), chances are they can match it or get really close. I had some gears to replace on glo-bowl lights, co-worker went to the local hobby shop and came back with an exact match to the plastic gears. Cheap and easy.

 

[James_B]

Laser cutter or 3d printing all sound like more than 45 dollar solutions to me.

You are probably right. A bespoke item is usually going to be a lot more expensive than a mass produced genuine replacement part. The 3D printed or LASER cut parts are only going to be a practical option when Pioneer eventually tells Techie1961 that while the part is listed on their books as a spare, there are none available unless somebody can find a NOS item tucked away at a repair centre or warehouse somewhere.

It took one company 2 years to eventually tell a client that the critical part that had been on order for all that time, was never going to be supplied.

I've created new gears and other parts for obsolete equipment for which there are no spares available, so I know it can be done. However, the costs involved usually mean that it's got to be either a very high dollar piece of equipment and/or irreplaceable and/or critical to make it worthwhile.

 

[Hpozzuoli]

I bet JB weld will work and last for the foreseeable future. I have JB'd a sector gear in a steering column to get a vehicle home. Bought a new gear, but haven't needed to put it in for the guy. This was a few years ago. Typically since that gear controls the start function I would change it ASAP, but the owner wants to see how long it will last. I think it's a good experiment, but I wish it was another gear and not that one. When it breaks he's not starting the car again.

 

[Techie1961]

So I decided to try JB Weld and tomorrow I will see what it looks like once the "mold" comes off. I found a supplier in the US that I can get for about $40 pluse shipping so it will cost me about $70 once I get it. I don't know that the unit is worth that much to repair.

I don't have a lot of experience with JB but have heard that it is pretty damn strong. I'll post a photo of the finished piece tomorrow night. For the "mold" I used Loctite Metal Magic putty. It is a thick putty so not suitable to flow into the teeth of the mold. I sanded most of the cured Loctite away and then separated it from the gear. Since the tooth count is not even on the small and large gears, I had to cut away the teeth on the larger gear and just use its outer diameter to locate it. I then put some small holes in the gear to give it some geometry to hold onto.

 

[Techie1961]

Once the gear and mold were ready, I oiled up the mold and then put a blob of JB on it and using a small rod, pushed it into the holes and around the back of the gear. When I pushed the mold on, the JB pushed its way out and I used a small rod to make sure the teeth were filled.

Fingers crossed.

 

[MagnumForce]

Brilliant, if it works that repair will last forever.

 

[Craptain]

My only concern is what plastic the gear is made of. If it is nylon or nylon based the JB weld will not form a good bond.

 

[scrumpy]

I am guessing you thought of this but before you try to put that in service you may want to cast a full mold of the repaired part. Then you have future options if it does not work.
-scrump.

 

[Techie1961]

My only concern is what plastic the gear is made of. If it is nylon or nylon based the JB weld will not form a good bond.

It's definitely not Nylon. I did a lot of R&D work with it and know all too well how difficult it is to bond to. The company that I worked for had a contract with Dupont and was the only one that was able to do a full bond that was nearly equal to virgin. It was pretty cool work. We were trying to make car radiators fully out of Nylon. Never fully got there but did come up with some other rads that were all Nylon.

 

[Techie1961]

Not really successful but not a total failure either. I didn't put enough undercut into the gear to hold the last tooth on the right and it came off. I put in some small holes and I am trying to build it up with dabs of JB Weld and trimming the teeth with an Exacto knife. There was one tooth that came out nearly perfect and the others had some difficulty with the release from the mold.

I have to admit to getting a bit of a kick out of trying. Success or not, it's been fun. Hopefully tomorrow I will have a good gear to try out.

 

[Vegaman_Dan]

Take your 'repaired' gear and make a new mold of it, then pour a new casting of that all in epoxy. Then you'll have a solid gear of one material to work from.

 

[mike7]

This is a really good idea. I'll have to remember this for future uses.

 

[JonBoehman]

You may give Plastex a shot. http://www.plastex.net/Home_Page.php

 

[southalabama]

Dental mold. Thinks it's latex.

 

[Krokodil]

This is really interesting.

 

[Techie1961]

I finished it up! After the JB Weld cured, I refaced the end with 400 paper and then hand shaped the gear teeth. I am quite pleased with it and it works. I was able to keep the same tooth profile on the gears that were damaged and did my best on making a new tooth for the first one on the right in the photo. In the photo, the tips of the teeth don't look very good but they are actually better than they look. The teeth ended up a little too thin (I was a little overzealous when I was facing it on 400 paper) so I had to build them up. The tips are a little shy on the planar face at the tip, not the tooth face. The gear that it is mating with is metal.

Things that I learned from this are that you really need to have the undercut geometry to hold onto the teeth and provide solid roots. I also tried to remove the mold a bit too early. My thinking was that I didn't want it to have enough time to really bond with the mold. I don't know what I could have done differently for a mold release but it worked out overall.

I don't know if it will last but I did cycle it quite a few times. Video at

 

[southalabama]

Cool deal.

As I said earlier it worked in a buddies fertilizer gear box on a tractor. He got another year out of it. It's som Italian deal with no USA parts available.

Glad it worked for you. You certainly have patience.