Split gears BUT?????

[Dr Al]

I'm more inclined to go with aging of plastic than too tight a fit at manufacture as the white gears don't split - same mould, same axles, same fit but the fit does have an effect.

I think all are an effect. The initial build was definitely an issue though - I bought a couple of brand new locos around 1997/1998 when I started in N, and they had split after a year, with little running, stored in temperate room! Also, out of interest when I started changing gears out I tried fitting a gear from the same bogie to an axle that had split, (so same gear, made at the same time) and the fit is generally hugely tight, putting a lot of stress on the gear. If this is the way they were fitted in the factory, it's no wonder there's problems!!

There's been a huge list of possible reasons for splits over the years and I think it's fair to say there's been no 100% conclusive answer. But the situation has definitely improved somewhat, although there are still some cases in newer models. The ones I've changed out have all still used the 16 tooth standard gear on their axles, but there may be oddities about.

The white gears seemed to be a less brittle plastic (though there seems variation in the black plastic too - some of it seems very brittle, some less so). Seen a couple of split white gears too so they aren't immune, and the white drive couplings used in the armature blocks of 1984-1993ish Poole Farish regularly split too.

The replacement of Dapol 73 wheels with Bachmann ones is an excellent fix - though if you get any more let me know - I have a few spare 73 wheels here!

In terms of supplies, currently all gears for Poole Farish apart from the 16 tooth type 2 (101/Railcar armature end gears) seem to be readily available. The type2s are out of stock at BR Lines, but Lytchett Manor models are apparently doing a new run of their own tooling of the gears. Hopefully this will replenish supplies of all the different types for a while to come.

Cheers,
Alan

[Dr Al]

If you like that then the farish 16 tooth gear also fits the top gear in the Dapol 9F that meshes with the worm (the one that gets chewed to bits).

Interesting you've seen this too - I've had one 9F with a chewed gear. Supplies of actual Dapol gears can be obtained via DCC supplies these days, though they are currently out of stock (perhaps that tells a story  )

Also - the Dapol B1 has a bit of a major design flaw in the gear meshing - the worm only just meshes with the top gear meaning it can easily wear the corners of the gear teeth away and lose drive completely. Seen at least 3 with this problem...

Cheers,
Alan

[H]

I'm more inclined to go with aging of plastic than too tight a fit at manufacture as the white gears don't split - same mould, same axles, same fit but the fit does have an effect. Temperature changes seem to make it worse - nothing makes it better.

I'm inclined to agree that age and environment is definitely a contributory factor - I stored Farish locos in the loft for several years and all the ones with plastic gears split.

H.

[EtchedPixels]

The problem is too tight an interference fit at manufacture. The same Farish gears do not split if correctly fitted to the axles.

I talked to people in the plastics trade when wondering about what would be involved in making better replacement gears. It's not just the tightness of fitting. I was told its two things

- poor choice of gear pitch (the pitch and arrangement of teeth govern the stress on the material)

- using the wrong plastics. You make gears out of materials like nylons. Actually what was said about their choice of plastics isn't repeatable here but did cast doubt upon both the species and the parentage of the decision maker

H: Storage definitely seems to have an effect. If they get very cold or they get heat cycled a lot they appear to break more often.

The 2mmSA replacement finescale axles/gears don't split - but they don't run on N gauge track either

Alan

[PostModN66]

Could some enterprising modeller make replacement gears from nylon, I wonder?

Jon   

[Dr Al]

Could some enterprising modeller make replacement gears from nylon, I wonder?

Jon   

Lytchett Manor models have their own tooling to make replacement Farish gears, so clearly yes. I'm not sure whether they use nylon or a different material for their replacement gears though. Maybe worth asking them?

Fitting the existing gears so there is a much less stressed fit is the easiest way round all this IMHO though.... 

Cheers,
Alan

[PostModN66]

Hi Al - I guess this means a bit of reaming - could you suggest a tool/method?

Cheers

Jon   

[RussellH]

Hi Guys

Copy of what I posted elsewhere for fav tool for "reaming" gears..

DIAMOND REAMER & COUNTERSINK SET - FLDR18...to be found here (any many other places!) page 94 of squires.

http://www.squirestools.com/11-06a.pdf

Dont use a broach - thats designed for metal, dont use a drill as thats got the potential to cut the hole eccentrically.

Regards
Russ

[Mr Sprue]

Hi Mr Sprue

Yep - it works. Just need to widen the inside of the tower to accept the raised area of the axle (one of those ball shaped burrs works), and the axle slot needs to be slightly larger without being sloppy. Make sure you get them dead centre as the rims are very close to the frame.

If you like that then the farish 16 tooth gear also fits the top gear in the Dapol 9F that meshes with the worm (the one that gets chewed to bits).

eNjoy

Russ

Thanks once again Russ, another valuable tip noted!

Regards
David

[Mr Sprue]

Hi Guys

Copy of what I posted elsewhere for fav tool for "reaming" gears..

DIAMOND REAMER & COUNTERSINK SET - FLDR18...to be found here (any many other places!) page 94 of squires.

http://www.squirestools.com/11-06a.pdf

Dont use a broach - thats designed for metal, dont use a drill as thats got the potential to cut the hole eccentrically.

Regards
Russ

Sorry Russ for once I have to disagree about using a broach as they are designed to open holes gradually, hence why they are only slightly tapered and have five cutting sides. Ok agreed they were originally designed for working with metal but I find them equally as good with other materials including plastic.

I have to add over the years they have been a great asset to my modelling.

[RussellH]

Hi Mr Sprue

The broaches I tried had only 4 edges for cutting (smooth square profile) and with the flexibility of the 12 tooth gears seemed to have little effect - maybe if I had gone on long enough I might have got somewhere. The diamond reamers are quick and can even be marked up so you know how far to work them in for a good fit. Can you send me a link to what your broaches look like etc?

Regards
Russ

[Mr Sprue]

Hi Mr Sprue

The broaches I tried had only 4 edges for cutting (smooth square profile) and with the flexibility of the 12 tooth gears seemed to have little effect - maybe if I had gone on long enough I might have got somewhere. The diamond reamers are quick and can even be marked up so you know how far to work them in for a good fit. Can you send me a link to what your broaches look like etc?

Regards
Russ

Hi Russ adding to the collection I already have, I bought a nice set at the Ally Pally last year. I'll have a root about later to see who sold them to me and get back to you.