Fixing a crack in Pioneer PL-L800 TA lift gearbox

[kotofei]

Hello,

I'm working on a Pioneer PL-L800 linear tracker. Got it off eBay local seller in mostly working conditions, just needing a deep clean and a new cartridge.

The tonearm lift works but it's kind of sluggish so I decided to remove old grease from lift gearbox as was suggested here. Found a crack in a plastic piece of gear that drives the eccentric (see picture). The crack goes through all of the part that holds the piece on the axis; however, the part with teeth has no cracks.

Despite the crack, the whole little piece appears sturdy and capable of fulfilling its job.

The question is- how to fix it the best way? First I thought about applying some epoxy glue on the crack then got an idea of wrapping a thin piece of wire around the cracked part, twist it and epoxy glue.

Any other suggestions or positive experience with fixing broken plastic gearboxes?

 

[pfcs49]

find a closed coil spring with a smaller ID than the cracked hub.
If the hub is a compression fit to the shaft it's on, you might want tolerance it a little but not a lot. (#drill or tiny rat-tail file)
Work the spring onto the hub, cut off any overhanging excess, then push back onto shaft.
We used to repair broken European odometer gears this way. Was very effective.
Seemed that the interference fit on the shaft finally would crack the gear which would stop working when the cracked gap reached the driving gear. We would close the crack with the spring and selectively fit it until the gear pushed over the shaft with a reasonable effort. IE: not too hard but strong enough to do the work of spinning the odometer which was not much.

 

[Mr Boochie]

Small zip tie?

 

[kotofei]

Could be a good idea. However, the distance between the cracked hub and the adjacent gear is very small so a zip like this should have a very low-profile "head". Don't know if these are available.

Small zip tie?

View attachment 2005049

 

[Mr Boochie]

Copper wire wrapped around the shaft. Then, epoxied or soldered?

https://www.amazon.com/BENECREAT-20...ds=20+gauge+copper+wire&qid=1602564184&sr=8-4

 

[Looneytoons]

I would consider taking the broken gear off its shaft. Possible to have a metal gear replacement fabbed? They can do wonders with a laser scan and 3d print also. IDK about cost though.
Otherwise thin strong wire wrap with epoxy should get the job done nicely.

 

[anchorman]

I recently fixed something like this with a piece of brass tubing that I enlarged to fit around the cracked plastic. It’s a light press fit. Easy to do if you can get the gear off. I’ve also used fishing line wrapped around and reinforced with super glue. You’ve got to get clever with your knot tying in order to get it all to work. The slight Stretchiness of Fishing line helps to get it good and tight. I suppose the copper wire idea above would work too, if done thoughtfully.

 

[anchorman]

Soldering wire around the plastic won’t work, as it will get too hot and melt the plastic. Usually when nylon starts to crack it’s not long before it fails other places too. Consider getting a new part 3D printed if you can make a model of this successfully. Not sure if the gear teeth will be accurate enough for this part if 3D printed, but the technology is getting better all the time.

 

[kotofei]

Thank you everyone for helpful suggestions.

Unfortunately, I can't take the gearbox apart so using bronze tubings or closed coil springs wasn't possible

What I decided to do is to glue across the crack a plastic tubing cut diagonally in the way as shown at the first picture. An epoxy glue was carefully applied to the cracked hub and the tubing was put on it in such away that the crack, also filled with epoxy, was completely covered by a tubing. I also applied a glue between tubing and the geared wheel and in between tubing's cut edges.

So the crack now is filled with epoxy and covered by a tubing which is (hopefully) firmly glued to the hub.

Don't' know yet how it all will work and keep my fingers crossed.