Has anyone used cheap Chinese spur gears?

[Steve VenessParticipant @steveveness43038]

Hi there,

title says it all really. I need to construct a small spur gear differential for an off-road wheelchair project. Something like the picture below. Gear speeds will be generally very low, since when the wheelchair is going straight the whole differential unit turns and the gears stay stationary relative to one another.

I need at least 6 spur gears and I am trying to keep the costs down, so I was thinking of trying some of these from eBay:

Link Removed see CofC

No doubt they will not be very precise or hard wearing but as the relative movement will be slow and limited (and as this is a prototype) I thought I might do better spending £20 or so on these than £70-80 on some UK sourced gears (which are probably made in China anyway.

Any thoughts / suggestions?

Thanks

 

A spur gear differential:

Edited By Steve Veness on 17/09/2020 10:07:26

Edited By JasonB on 17/09/2020 10:34:22

[Steve VenessParticipant @steveveness43038]

[JasonBModerator @jasonb]

Yes I've used them in the past and also ones via UK suppliers such as Belting on Line good enough for your use I should think.

[SillyOldDufferModerator @sillyoldduffer]

Is buying gears off ebay an opportunity or a disaster waiting to happen? Both – it's a risk.

In this example the gears are unbranded and cheap. In the absence of a specification they could be fine or unsuitable. It depends on the application. If the gearbox will be much used and heavily loaded using unknown gears is high risk. Same gears could be entirely suitable for a lightly loaded infrequent work. Cheap gears are also likely to be noisy, if that's a concern.

A problem with ebay and similar non-specialist sellers is items like gears are multi-sourced without much technical control. What's on sale could be anything between high-quality surplus and manufacturing rejects. Or wholesaled from different makers working to different specifications. There's no guarantee the same seller will send the same gears each time, or even in the same order. Risk, risk, risk.

I suggest unknown gears (no specification) are suitable for prototypes, lightly loaded applications, and when the owner doesn't mind taking a punt. If the application is important – high reliability and hard work – the design has to meet a Requirement, which either means coughing up for expensive gears and bearings, or confirming by test and inspection that cheap gears will do the job. High-end gears are not necessarily expensive because they're better made, but because their qualities are documented.

I use ebay a fair amount and am mostly happy with what I get. But I always accept it's a risk. Every so often I come unstuck, but hey that's life. Not as dangerous as buying a Rolex for £200 off a stranger in a pub car-park, where the chance of the watch being genuine is zero.

Dave

[BazyleParticipant @bazyle]

I think the only difference that would be significant, regardless of country of origin, is between gears cut from steel and gears forged or specially cut and treated for maximum strength. It might be better to try and find a diff from a mini tractor or go cart type application.

[old martParticipant @oldmart]

As the application is not high speed, and the gears don't even move when the chair is going in a straight line, it would be a waste of money buying high quality gears. More importance should be addressed to keeping the gearbox sealed against ingress of dirt which will shorten the life severly.

[Steve VenessParticipant @steveveness43038]

Thanks for the replies. I have ordered the gears from China – delivery in 4 to 6 weeks.

I ordered 10 x Mod 1 20T in carbon steel for £19.70 inc delivery – can't really see how they do them for that.

@Old Mart – The differential case will be fully sealed apart from shafts running in bronze bushes to drive the two axles.

I'll post some updates when they arrive.

[Pete WhiteParticipant @petewhite15172]

Good luck with the project, keep us posted. As said its low risk and low cost punt, should be fine. Most things in life are a risk especially these days.

Pete

P. S. The chair not be used first try out on an alone sahara crossing is it ? lol

Edited By Pete White on 18/09/2020 16:57:52

[Author]

Posts