Wrong gear in Backwoods kit

Hubert Hirst · June 13, 2020, 20:57

I have not used the forum for many years so please forgive me if I make any silly mistakes.
Some years ago I bought the Backwoods kit of the Darjeeling & Himalayan Class B 0-4-0. I started to build it but got waylaid and it ended up at the back of a drawer. During the present crisis, after the garden was tidied I pulled it out and continued where I left off. The valve gear was challenging but is now successfully completed. I then started on the gearbox and to my horror realised that one of the gears was incorrect, despite having, I thought, checked all the parts when I first got the kit some years ago. Pete McParlin has ceased trading and I am seeking a source for the correct gear. A long trawl of eBay has not produced any results.
The gear I am after is a double spur gear with 20 teeth and 10 teeth, 8.9mm diameter over the 20 teeth and 4.55mm diameter over the 10 teeth for a 2mm shaft. Can anybody supply one or put me in touch with someone who can supply one? It is the bottom of the three gears in the box and meshes with the gear on the axle.
It seems such a waste to ditch £80 of kit and many hours of work already done. I obviously did not check the parts properly when I bought the kit.

Alec Hudson · June 13, 2020, 22:05

Hi.

I can highly recommend these gears. I think M0.4 are what you require. Both sizes you require are available with a 2 mm bore, push fit. If you calculate the widths you should be able to position the first gear centrally under the worm. You may want to replace the remaining gear as well so they are all the same.
I have used the M0.3 gears in a Backwoods Fairlie.

https://shop.kkpmo.com/product_info.php?info=p614_gearwheel-pinion-m0-4---20teeth.html

Graeme Dunbar · June 14, 2020, 08:56

I've found a couple of gear calculators that I've found handy for identifying gears. They warn they are not 100% reliable as there may be some error in measurement, manufacture and due to "adjustment" for small tooth number, but they seem reasonable.

The first is from Ultrascale and in this case it requires "working backwards" and guessing at the MOD first: https://www.ultrascale.uk/node/15

The second from Technobots calculated the MOD from diameter an number of teeth. https://www.technobotsonline.com/gear-size-calculator.html

Hubert Hirst · June 14, 2020, 11:09

Thanks Alec and Graeme. Your replies have certainly eased my concerns. Graeme's reply has allowed me to confirm what I had worked out--I am looking for Modulus 0.4 teeth. Alec's suggested website confirms that I can obtain the appropriate gears. However, as I stated in my original post, it is a double gear that I need. That is one component with two sets of teeth on it. I could buy two separate gears and fasten them together if necessary, but I would prefer the single piece option. I'll hang on a bit longer to see if anyone else comes up with the perfect answer.
Thanks to you both. At least I am now pointing in the right direction!

Alec Hudson · June 14, 2020, 12:41

Hi
You buy the 2 separate gears and push them together on the axle. They are a tight fit, no glue required and don't slip. The Backwoods Fairlie comes with 2 separate gears but the small one is to big and you are supposed to glue it on and I did not like that idea. That is why I changed all the gears.
I now wish I had done this to Linda as well.

Scottish Modeller · June 14, 2020, 21:01

Quote from: Hubert Hirst on June 13, 2020, 20:57
I have not used the forum for many years so please forgive me if I make any silly mistakes.
Some years ago I bought the Backwoods kit of the Darjeeling & Himalayan Class B 0-4-0. I started to build it but got waylaid and it ended up at the back of a drawer. During the present crisis, after the garden was tidied I pulled it out and continued where I left off. The valve gear was challenging but is now successfully completed. I then started on the gearbox and to my horror realised that one of the gears was incorrect, despite having, I thought, checked all the parts when I first got the kit some years ago. Pete McParlin has ceased trading and I am seeking a source for the correct gear. A long trawl of eBay has not produced any results.
The gear I am after is a double spur gear with 20 teeth and 10 teeth, 8.9mm diameter over the 20 teeth and 4.55mm diameter over the 10 teeth for a 2mm shaft. Can anybody supply one or put me in touch with someone who can supply one? It is the bottom of the three gears in the box and meshes with the gear on the axle.
It seems such a waste to ditch £80 of kit and many hours of work already done. I obviously did not check the parts properly when I bought the kit.

Hi there,

Have you tried contacting the maker using the link on the website?

http://www.backwoodsminiatures.com/index.htm

I had a similar problem with my DHR Class B and used the site contact details to let them know what was missing and then got the correct gear.

In my case I had 2 gears the same instead of different.

Phil H

Hubert Hirst · June 14, 2020, 22:39

That was my first move, but as it says on the home page, Pete has ceased trading. I have not received a reply to my email to him.

JulienW · June 15, 2020, 09:46

If I recall correctly Pete's later kits used gears from High Level. That link will take you to their Gearboxes page, and whilst the site doesn't list individual gears there is a contacts page and assuming my memory is correct they may be able to help, either with supplying a replacement themselves or with the technical details (either a DP -diametrical pitch or MOD - moudule - number) to source a replacement gear from elsewhere.

The other suggestion would be to replace the whole gearbox, but I have a feeling that those in Pete's kits were bespoke for each kit and getting something 'off the shelf' to fit both in the space available and in the small space between the wheel backs (about 7mm) may be tricky. I recall that Golden Arrow did an etch for an 009 gearbox but I can't remember whose gears they were designed to use (possibly Graham Farish? - available from BR Lines).

Thinking a bit more about this, and re-reading your initial post that suggests that you already have a final drive gear fixed to the axle, and fitting a new gearbox may need that to be removed and I'm not sure getting it off and a new final gear onto the axle will be possible without basically taking the whole chassis apart and starting again. On that basis I suggest that contacting High Level first might be the better course of action.

Another thought would be to drop Neville Kent at N-Drive productions a line. Not that he can supply a replacement gear but as he had taken on a lot of the Backwoods range, and that this may or may not have included the DHR B class kit, he may have some ideas as to where a replacemnet could be sourced.

Hope that helps,
Julien

Hubert Hirst · June 16, 2020, 17:03

Thanks for that Julien. As you suggest, I think each model had its own gearbox. I also have a gear on the axle and would probably scrap the lot rather than attempt to change the gear. The thought of doing the valve gear a second time turns me off completely!
However, I have followed one of the suggestions above and have ordered the appropriate gears from KK produkjca in Poland. It will mean changing from loose gears on a fixed shaft to fixed gears (two separate ones) on a rotating shaft. The gears are to the same spec (modulus 0.4) so they should match up OK. The only problem I can foresee is wear by the shaft on the gearbox casing which, as I don't have a layout, is not likely to be a problem for some time. As I am now 80 I don't think I'll worry too much about it!
Thanks to you all for the most helpful suggestions--typical 009 Society. I'll do a final post when I have the gearbox complete and working.

JulienW · June 17, 2020, 10:04

Quote from: Hubert Hirst on June 16, 2020, 17:03
Thanks for that Julien. As you suggest, I think each model had its own gearbox. I also have a gear on the axle and would probably scrap the lot rather than attempt to change the gear. The thought of doing the valve gear a second time turns me off completely!
However, I have followed one of the suggestions above and have ordered the appropriate gears from KK produkjca in Poland. It will mean changing from loose gears on a fixed shaft to fixed gears (two separate ones) on a rotating shaft. The gears are to the same spec (modulus 0.4) so they should match up OK. The only problem I can foresee is wear by the shaft on the gearbox casing which, as I don't have a layout, is not likely to be a problem for some time. As I am now 80 I don't think I'll worry too much about it!
Thanks to you all for the most helpful suggestions--typical 009 Society. I'll do a final post when I have the gearbox complete and working.

Happy to help. :)

Just a thought - and I'm not sure if this is possible as I've not studied the kit - but if going from a "fixed shaft & rotating gears" to a "rotating shaft & fixed gears" you may need to open the holes in the gearbox sides out slightly to allow the shaft to spin. If this is the case, or even if it isn't, might it be worth opening the holes out a little more to take some brass bearings? Probably best to use what I would call 'straw hat' bearings (not as long as the top hat type) and a little filing may be needed to keep the width of the gearbox the same overall (I'd try mounting the bearings with the flanges on the inside and file off any bearing protruding on the outside) and open the holes in the etched gearbox sides with a broaching tool rather than a drill - even a rat-tailed file will do the job at a push.

Even if you decide not to fit the bearings it's probably worth a quick go at the holes in the etch with something to remove the etching cusp from inside the hole as leaving it there will not help matters!

Hubert Hirst · June 18, 2020, 23:06

I have reflected on the suggestions and have ordered replacement gears. As they are separate, I have to use them interference fit on the shaft to transmit the motion. This means that the shaft must rotate in the gearbox frame. Having thought about this for a day or two I have made the conscious decision to mount the shaft directly in the nickel-silver frame and will slightly open the holes with a five-sided broach as I did when I removed the etch cusp as recommended in Pete McParlin's instructions. This is a considered decision versus the suggested fitting of brass bushes. I feel that the nickel-silver, being harder than brass, will not wear much faster than thicker brass and it is not worth the hassle of obtaining and fitting brass bushes.
Thanks once again for all the helpful suggestions.

JulienW · June 19, 2020, 10:55

The other suggestion (& the thought just came to me) is if you have some (brass?) tube* that is a running fit over the shaft in the gearbox you could open out the gears to a press-fit on the tube (not too tight - you don't want to split the gears), thereby making the 2 gears into one 'compound' gear and maintaining the 'fixed shaft & rotating gears' set up that Pete designed with a nice big bearing surface (the inside of the tube) into the bargain...

(* equally a long 'top hat' bush / bearing might do the job.)

Hubert Hirst · June 19, 2020, 20:30

Unfortunately the small gear is only 10 teeth which as mod 0.4 does not leave enough 'hub' to allow any enlargement over the original 2mm diameter shaft size. It is only 5mm diameter with teeth that are about 1mm deep and a 2mm shaft which only leaves leaves just 0.5mm between the bottom of the teeth and the central hole! Great care and very careful use of Loctite will be needed.
Thanks for the thought, though. Wish me luck!

Hubert Hirst · July 05, 2020, 11:31

This is just an update to say that I now have a working gearbox on my D&H B Class! Thanks to Julien for his several potentially useful suggestions and particularly to Alec for his suggestion for sourcing the necessary gears. I cannot fault the company in Poland that he suggested (see earlier post). They despatched the correct gears in three days, which then took nine days in the post to arrive. A tiny bit of reaming and judicious use of primer and superglue means I now have a shaft and gears which are as near perfect as possible. Thanks guys.

JulienW · July 05, 2020, 12:14

That is good news Hubert - well done!

Please keep us posted on the rest of the build.