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 Mechanism Design - An ongoing experiment
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Author Topic Next Topic: Highliners Wire Grills  

adrian_batey
Fireman

Posted - 08/27/2020 :  10:15:07 PM  Show Profile  Visit adrian_batey's Homepage  Reply with Quote
I though i would start a discussion and draw on the experience of the machinists of the group and the tinkerers.

I have recently been working on my local prototype in Tasmania. Tasmanian railways used 3'6" gauge. There is a small group of modelers who build in Sn3 to get the correct gauge while others build in OO 4mm and HO scale with 16.5mm gauge track.

A very small few build in what could be called OOn14. Some may have seen the works of Simon Handby in narrow Gauge Down Under.
Simon recently offered me some a 4 wheel wagon kit to try out that has led to what can only be described as jumping into a rabbit hole of new modelling.

Now for the focus of the thread. There were only a few Diesel locomotives used in the era I like to model. Mainly the TGR X and Y Class. More info on these can be found here https://www.railtasmania.com/loco/

Simon has made castings of these and adapted chassis over the years to suit but im now on the task of making my own chassis for these models with 14mm gauge.

I hope that in the following posts the machinist of the group will be able to jump in and comment on thoughts and musings of possible problems i may encounter.
Owen Pass Lumber Company
HO Logging Layout in a Shed.
https://owenpass.blogspot.com/

Country: Australia | Posts: 1303

adrian_batey
Fireman

Posted - 08/27/2020 :  10:39:54 PM  Show Profile  Visit adrian_batey's Homepage  Reply with Quote
With the demise of Hollywood Foundry the availability of quality mechanisms for custom gauges is some what limited.

I would hope that i am able to produce something that can be adapted to my fleet of up to 10 locos and possibly consider both bobo and coco wheel arrangements.

My first thought was to start looking at old KTM mechs and there issue. I have an old S1 that i swapped the mech out for an Atlas one.

From my limited experience these were poor runners due to cracking in the truck frame and poorly cut gears on the gear tower. Anyone care to comment further do jump in?

I am contemplating a folded etch to mimic the truck frame that commonly cracked and use a worm and wheel gear drive. Sounds simple enough to develop an etch that allows top hat gear bearings on all surfaces ect.

Now the sticking point is the transfer gearbox up to the motor. Hollywood used a belt drive system of various types. Centre mounted under deck for trolley motors and also truck mounted.

Im curious on experience of those who have uses the belt drive system vs a gear tower and also thoughts on a centre transfer i guess similar to the old MDC shay vs the more tradition above the chassis board.

As for some parts, im looking at ultrascle in the UK for worm and gear sets. https://www.ultrascale.uk/eshop/products/CAT015

PPD in the UK for photo etching - They also offer laser cutting of nickle silver

I am also considering small batch machine shops in china for the brass pulleys for belt drives or a minilathe for my home shop with the steep learning curve associated.


Owen Pass Lumber Company
HO Logging Layout in a Shed.
https://owenpass.blogspot.com/

Country: Australia | Posts: 1303 Go to Top of Page

Tyson Rayles
Moderator

Premium Member


Posted - 08/28/2020 :  08:53:14 AM  Show Profile  Reply with Quote
Interesting project.


Country: USA | Posts: 13222 Go to Top of Page

Bernd
Fireman



Posted - 08/28/2020 :  12:08:00 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
Well now, this is right up my alley so to speak. I'm willing to bet that you would hope I would jump down the rabbit hole with you.
How can I resist such an offer as putting my 2 in on such a subject.

I'm going to make this short since I won't be near an internet connection until Sunday night again. After reading your two posts and seeing what you want to do I suggest that you invest at least in a lathe. Remember a lathe can also be used with proper equipment to mimic a mill. The learning curve is not that bad with a bit of practice. A new lathe need not be purchased. Look around for a used lathe, but make sure it's in good condition. Of course I'm biased toward Sherline. You won't need anything larger than that for the scale you want to get into.

A drive mechanism. I've been looking into what is known as a tank drive. Something similar to what the Hobbytown drive trains are. One thing I don't like about the drives is the gear tower and the multitude of universal joints needed to get the power to the wheels. If not properly aligned much vibration can occur.

You also mention a belt drive. I've experimented with two belt drives so far. One in a build challenge here on the forum and one I modified a Tyco engine drive.

Belt drive on an "N" scale DD-40 truck for an HOn30 boxcab.





These were the end result.



My other belt conversion was for a Tyco Plymouth CR-4.



I discovered after getting it all together that the pulley ratio had to be reversed due to the gear reduction of the motor. First picture shows a smaller pulley on the motor and a larger on the driven shaft. Talk about crawling speed. The second picture shows a larger pulley on the motor and smaller on the driven shaft. Much better top speed.





I did find one other belt drive I design and that was going to be for a TT scale boxcab using an HO scale Roundhouse Shay truck.



I won't recommend a belt drive for larger scale engines. One thing about these belt drives is that they are hard to source. I sourced mine from Nigel Lawton in Great Britain. This is the only place I have found these tiny .090" square belts.

I've got more to contribute on drives. I'll check back into the forum Sunday night, my time. Until then I've got something to contemplate over the weekend. Start looking for a lathe. You'll never regret getting one.

Bernd


WWG1WGA

Country: USA | Posts: 3629 Go to Top of Page

acousticco
Fireman



Posted - 08/28/2020 :  8:27:53 PM  Show Profile  Visit acousticco's Homepage  Reply with Quote
I'm not sure if this is useful information but while dabbling in O14 (7mm scale, 14mm gauge), I figured out it's pretty easy to narrow a power truck from the old Bachmann GE 44 ton diesels to 14mm gauge. I don't exactly remember how I did it but do remember it not being terribly difficult.

I'll see if I can find it and let you know any clues I can discern.

Good luck with the project, I'll be following along!

-Cody



Country: Canada | Posts: 1715 Go to Top of Page

jbvb
Fireman

Premium Member


Posted - 08/28/2020 :  10:15:16 PM  Show Profile  Visit jbvb's Homepage  Reply with Quote
The 1970s Hobbytown drives used quality parts, but the 5-pole open frame motors of the day were prone to 'cogging' as the iron armature rotated slowly. Their nylon universals were durable but were molded with some clearance so had a little slop. This amplified the cogging. It's been on my list for a while to remotor one with a coreless motor to see how it performs. Hobbytown bearings were bronze initially, but later were changed to nylon. Because the parts are all assembled by pressing, they're fairly easy to take apart and reconfigure. One nice feature is the helical gears on the longitudinal shafts in the trucks driving helical gears on the axles: because power can be transferred both ways, they don't buck on grades like a worm can. One tiresome feature is the long universal shaft between the trucks; getting the trucks pointing in different directions could pull one end out of the socket. They could be reinserted without disassembly but it took some fiddling.

Boston Gear Works was Hobbytown's supplier in the old days. They still offer a broad range of parts, but I didn't find gears quite as small as Hobbytown used the last time I examined their catalog. And being a US company, you might find shipping more of an issue than from China.



Country: USA | Posts: 6518 Go to Top of Page

adrian_batey
Fireman

Posted - 08/29/2020 :  8:11:54 PM  Show Profile  Visit adrian_batey's Homepage  Reply with Quote
Bernd, I may have intentionally posted here to get a response from you.

Your comments on the belt drive are valued and will certainly take them on board. I think the lather will be worth it just with a few tools i wish to make. A fellow modeller has made a press to allow wheel sets with 25.7mm axle length to be re gauged to 14mm. That in in itself is worth some money. as well as track laying tools it could produce.

I have been reading and looking into the cheap mini lathe as an option. I know not the best but from the reports I have read that being realistic in its ability and you get what your after. Certainly more research to be had in this space. Its not a lot more then one of my brass shays or some rolling stock sold off and at 33 yrs old it would be a long term investment for me and lets face it a skill i have always waned to learn.

The options for used here are limited. Market is pretty small due to the big ditch between us and the mainland. Ones that do come up get snapped up through word of mouth pretty quick.

Bernd are you cutting your own wheels from brass?

Back to the mechanism thoughts. I did re gauge 2 GE 70 ton bachman mechs to hon3 years ago with the NWSL wheel conversion. Some of the Alco RS locos have similar wheel dia and spacing as the Tasmanian X and Y. I would need to look at the 1.25mm i need to trim off either side of the frame to get the gauge down to 14mm. Im sure there are other possible candidates.

As to the hobby town mechs. if everyone sent me all there parts from the junk yard i would be set :-) IN all honesty though the gears from one of them will likely be my starting point for some trials.

Not a lot of bench time right now as i have a 13wk old and a 2.5 yr old. will be some imagineering going on. More discussion later on when i have a spare minute.




Owen Pass Lumber Company
HO Logging Layout in a Shed.
https://owenpass.blogspot.com/

Country: Australia | Posts: 1303 Go to Top of Page

Bernd
Fireman



Posted - 08/30/2020 :  8:33:59 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
Back from the summer home for the week. Had some time going over some thoughts on the drive for engines. Will post some more thoughts on the subject tomorrow (8-31). Glad you're looking into getting a lathe.

Bernd


WWG1WGA

Country: USA | Posts: 3629 Go to Top of Page

Bernd
Fireman



Posted - 08/31/2020 :  09:43:57 AM  Show Profile  Visit Bernd's Homepage  Reply with Quote
The Hollywood Connection.
quote:
With the demise of Hollywood Foundry the availability of quality mechanisms for custom gauges is some what limited. Now the sticking point is the transfer gearbox up to the motor. Hollywood used a belt drive system of various types. Centre mounted under deck for trolley motors and also truck mounted


It was sad news when he decided to shut down the business. I surfed his site many a times with great interest in the design and building of his drives. One thing I'm always interested in is the sourcing of parts. I don't think he produced many of his own parts. I did like several of his, I'll call them tank drives since that's where the gearing and motor are located, and saved the pictures. I was looking at building something similar but using miniature ball bearing for less friction. Here are two pictures of those drives.

Here he uses gearing.



This one is belt a belt drive.



This last drive is a familiar design. I first saw this sold by Walthers for their Doodlebug kit way back. I have one of those kits. Here are two pics of those drives.





This last one is from LaBella Woodworking Company. It's the drive used in their D&RGW Gasoline Rail Motor Car.





I collected lots of pictures of different ways to power models because I had a high interest in creating my own for some ideas I've had for critter designs.

quote:
Bernd are you cutting your own wheels from brass?


I'm assuming you mean the pulleys. I haven't tried to do wheels yet. If I did I would be using 303 stainless steel. And "yes" I use brass pretty much for all builds for drives.

I've run out of time. I have much more on ideas for drive designs. You have asked some good questions, some of which I still need to answer. I'll do that when I get a bit more time.

Bernd


WWG1WGA

Country: USA | Posts: 3629 Go to Top of Page

MarcusF
Section Hand

Posted - 08/31/2020 :  10:16:26 AM  Show Profile  Reply with Quote
Not to distract too far from the topic of the thread, but what's the rationale for using a novel gauge? I get that there's a challenge in modelling colonial gauge regardless of the scale, but I would think that from a functional point of view, it seems Sisyphean to pick a gauge for which you have to fabricobble almost everything (track, running gear, drivelines) which are arguably make up the majority of the modeled pieces.
Why not save some pain and at least work around readily available track/running gear/mechanisms and use HO (16.5mm) as your gauge? Since you're modelling a very specific and unique prototype, you're going to wind up scratchbuilding almost everything anyway. If I were looking at it strictly from an efficiency point of view, doing that you'd have more time to devote to the other aspects of modelling.
On the other hand, I can also appreciate the appeal of doing things "the hard way", just for the challenge.
I'm not criticizing, and I think it's a neat project, but I am genuinely curious as to why you'd choose this route to modelling this prototype.



Country: Canada | Posts: 99 Go to Top of Page

Philip
Fireman



Posted - 08/31/2020 :  11:35:41 AM  Show Profile  Visit Philip's Homepage  Reply with Quote
Great stuff!

If only a short low center gravity unit would be nice for vehicles?

Philip



Country: USA | Posts: 3232 Go to Top of Page

BurleyJim
Fireman

Premium Member


Posted - 08/31/2020 :  11:48:13 AM  Show Profile  Reply with Quote
quote:
Originally posted by MarcusF

Not to distract too far from the topic of the thread, but what's the rationale for using a novel gauge? I get that there's a challenge in modelling colonial gauge regardless of the scale, but I would think that from a functional point of view, it seems Sisyphean to pick a gauge for which you have to fabricobble almost everything (track, running gear, drivelines) which are arguably make up the majority of the modeled pieces.
Why not save some pain and at least work around readily available track/running gear/mechanisms and use HO (16.5mm) as your gauge? Since you're modelling a very specific and unique prototype, you're going to wind up scratchbuilding almost everything anyway. If I were looking at it strictly from an efficiency point of view, doing that you'd have more time to devote to the other aspects of modelling.
On the other hand, I can also appreciate the appeal of doing things "the hard way", just for the challenge.
I'm not criticizing, and I think it's a neat project, but I am genuinely curious as to why you'd choose this route to modelling this prototype.



Marcus, not to be a naysayer, but take a longer look at some of the threads of builds amongst this forum's folks, that are ready, willing, and very much accepting challenges, even Sisyphean ones.

Jim


Take the red pill

Edited by - BurleyJim on 08/31/2020 2:04:32 PM

Country: USA | Posts: 5583 Go to Top of Page
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