Cutting this intricate shape

[JasonBModerator @jasonb]

I suppose as there is very little material at the tops of the frames they need more width than the usual deeper ones found on the average Loco not that I'm a train man.

[Chris HammondParticipant @chrishammond37041]

John – a 7/8 forum acquaintance in the US scaled the plans to 7/8 scale. I have just measured the gauge on the drawings, it's 42mm, which is 1.65". Does that sound right?

[John HaineParticipant @johnhaine32865]

That sounds even more puzzling, assuming that the gauge is the distance between the rails. If the frames are 8mm thick, total 16 mm, that sounds quite out of proportion to the gauge! For example, what thickness would be used for the frames of a 3.5" gauge loco? Looking around I found a reference here to 3mm frames on 5 inch gauge…

[Chris HammondParticipant @chrishammond37041]

I'll try and post a couple of images from the drawings before I throw the plans out of the window!

[Chris HammondParticipant @chrishammond37041]

Ok, here goes, finger's x'd!

[Chris HammondParticipant @chrishammond37041]

Ok, so the images are from the plans enlarged slightly by my acquaintance, to 7/8 scale.

The first shows the info on the plans, which I assume refers to the full size loco (I have no idea how large the pdfs I inherited were, but I am assured they are now correct for 7/8 scale). You can see in the second image, the frames marked in brown. These measure, physically on the printed out drawing, 8mm.

The gauge, also on the printed drawing, measures 43mm or 1.65".

Help!

If any of you gentlemen would like the scaled up drawing jpegs mailed to you so you can help further, please let me know your email address.

Edited By Chris Hammond on 19/01/2017 15:15:17

[JasonBModerator @jasonb]

So if I'm thinking right these are the frames for the front 3 axles on your "Lucky" 2-4-4

You have Dan's drawings for 7/8" to the foot which should give a gauge of 1.75" as the full size is 2' 0" narrow gauge

But what gauge are you building to? have you doubled up his 1.75" drawings to fit 3.5" gauge track?

Blowing that picture up until the "brown" bits are 8mm gives a gauge of 45mm, are you sure that is the frame and not the axle box as it sems really thick for  aG1 loco and would need to be a lot more if you ar emaking a 3.5" g loco.

J

Edited By JasonB on 19/01/2017 16:00:22

[Chris HammondParticipant @chrishammond37041]

Jason – no this is a different loco to Dan's, it's not a Shay. This is a Baldwin.

I am hoping(!) to build it to 7/8 scale, as per the drawing. Which is, I am told, an accurate enlargement and accurate print (bought from a copy shop I know have calibrated machines).

So, there is obviously some discrepancy somewhere as the gauge, when measured with a good old fashioned ruler, is definitely measuring 43mm which is 1.69291".

Hmmm,,, that's a good point re whether it's the frame or axle box…. I could have read it wrong (I am very new at this as you can all tell!)….

OK, so the instructions on the plan say that that main frames should be cold finished steel or similar, 3.56 x .5 (7.62 x 1.0) nominal section.

Does this help?

 

Edited By Chris Hammond on 19/01/2017 16:08:25

[JasonBModerator @jasonb]

See my PM

So if you are looking at the Lucky drawings then that is for 3.5g track and is 2ft gauge in full size that equates to 1.75 :ft and drawings say frame is 0.5" thick (bracketed figures are for the larger 7.25g lucky)

You say you want to make it smaller at 7/8" :ft which is half the 3.5g drawings so frame would be 1/4" or nearest metric would be 6mm thick.

I thought you wanted a large model are you sure you want to build for 43mm gauge?

Y

Edited By JasonB on 19/01/2017 16:18:37

[Chris HammondParticipant @chrishammond37041]

Jason – I believe you are 100% correct, so thank you. It does look like I have made a mistake – what I assumed (one should never assume) was the frame, doesn't look like it was. 

I found another view of the frame, drawn looking from the top, on another page of the pdf, and it measures 6mm wide when enlarged by the same percentage as the other drawings. See pic, the pink rectangle measures exactly 6mm wide.

However, this doesn't solve the gauge issue does it. What would you recommend I do? Enlarge the drawings slightly to fit the 1.75" gauge?

Edited By Chris Hammond on 19/01/2017 16:23:08

Edited By Chris Hammond on 19/01/2017 16:25:17

[Neil WyattModerator @neilwyatt]

According to an ancient encylopaedia of railway things bar frames may be three to seven inches thick, so in 5" gauge that's roughly 6mm to 15mm thick, and up to 11mm think in 3 1/2" gauge, so 8mm seems pretty reasonable.

Neil

<edit> Ah 1.75" gauge 8mm is a tad thick, 4-6mm might be closer to scale, if they are bar frames.

Edited By Neil Wyatt on 19/01/2017 16:27:52

[JasonBModerator @jasonb]

Neil 7/8 scale is only G1

[Chris HammondParticipant @chrishammond37041]

All this enlarging of plans n stuff, brings me to another question. Do you enlarge the fasteners and such like too by the same proportions?

Apologies for the naive questions all, but one has to start somewhere!

[Anonymous]

As I read it the drawing is for a gauge of 3½" or 7½", so I don't see why they've been enlarged if you're talking about a smaller gauge. The two trapizoids at the bottom of the drawing probably represent the track, the inside dimension will be 3½" or 7½".

The numbers you quote for the frames will be the cross section (in inches) for 3½" and 7½" respectively. On that basis for a gauge of 1.75" that gives a frame thickness of ¼". It's bad form, and inaccurate, to scale off a drawing.

Personally I'd make the frames from hot rolled steel; cold drawn will end up like a banana.

Andrew

[Chris HammondParticipant @chrishammond37041]

Neil, yes you are right… 6mm seems to be indicated on the drawings. As I mentioned in my post, I was looking at the wrong part!

[JasonBModerator @jasonb]

Posted by Chris Hammond on 19/01/2017 16:22:13:

However, this doesn't solve the gauge issue does it. What would you recommend I do? Enlarge the drawings slightly to fit the 1.75" gauge?

I suppose it really depends on what you want out of the loco. Is it just something you want to build and sit on a shelf, maybe run on a raised track.

Or is it something you want to sit behind and go round in circles

Not really being a loco type I don't know if anything smaller that 3.5g would be able to pull you around, even if a smaller gauge would it may be hard to find a track that you could ride on.

[JasonBModerator @jasonb]

The fasteners shown on the plans are for a larger (3.5g or 1.75" :ft) loco so they should be made smaller for your 7/8:ft scale.

Best way is to work out what the actual reduction is in the form of a decimal and then multiply all WRITTEN dimensions by that then adjust to nearest stock size or avalable fixing.

[Chris HammondParticipant @chrishammond37041]

Andrew, the pdf was kindly given to me by a friend. I have no idea how big the scans are on the pdf. They don't appear to have any relevance to the measurements stated in the drawing scale boxes.

Therefore, a 7/8 forum colleague in the US enlarged the drawings we have by measurement.

The great news is, at least now something tallies up, because you state a frame thickness of 1/4" and I just measured another drawing and got 6mm which is of course 1/4" (or there abouts). Phew.

Yes I plan to use hot rolled steel for the reasons you state.

I can't thank you fellows enough for all your help. It is wonderful to have such a wealth of knowledge and expertise around.

Please can I ask, if its bad form to scale off a drawing, how else should I do it?

[Chris HammondParticipant @chrishammond37041]

Jason, how would you work out what the actual reduction is please? Could you give me an example please?

[JasonBModerator @jasonb]

Posted by Chris Hammond on 19/01/2017 16:22:13:

However, this doesn't solve the gauge issue does it. What would you recommend I do? Enlarge the drawings slightly to fit the 1.75" gauge?

Chris I wonder if you are mixing up a scale of 1.75" to the foot with the gauge of the track 3.5" in this case

your 7/8" to ft scale gives a 1.75" gauge

[JasonBModerator @jasonb]

Chris send me the pdfs, I have messaged you my e-mail.

J

[Chris HammondParticipant @chrishammond37041]

Jason, email sent

Cheers

I could be mixing up everything, at this point I don't know whether on my head or elbow!

[Neil WyattModerator @neilwyatt]

Posted by JasonB on 19/01/2017 16:25:47:

Neil 7/8 scale is only G1

Caught by the open a page and don't read it for several hours gotcha…

[JasonBModerator @jasonb]

OK

Swapped a couple of e-mails with Chris and he is looking for a "garden railway" size engine I have suggested G1 with 45mm between tracks. This is the same size trak as the American 7/8 guys run their 2ft narrow gauge engines on too. Being the original is a narrow gauge loco it will still give a good size model about 30" or 750mm long.

He has a set of 3.5g drawings so suggested everything is halved and as he likes to work in metric have said to multiply all dimensions in inches by 12.7.

J

[Perko7Participant @perko7]

I don't think you should 'scale up' a drawing in a known and accepted scale in order to match a track gauge. The scale determines the overall size and proportions, and the track gauge for the model is a consequence of the scale. If the track gauge from the chosen scale does not exactly align with an accepted track gauge, then modify only those parts of the design which would allow the different track gauge to be used. Take a lesson from the model railway fraternity, with the OO/HO and N-scale arrangements having different scale bodies running on the same gauge of track.

I am happily building a 3ft 6in gauge prototype loco at a scale of 1/8 full size (that's 1-1/2ins to the foot) to run on a 5in gauge track. If i was using the correct scale gauge it would be 1/8 of 3ft 6ins (1/8 of 42ins) which would be 5-1/4in gauge. I just make the wheels a bit closer together on the axles and all is well.

Metric or imperial does not matter.

[Author]

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