7mm Richard's 9f workbench

richard carr

richard carr

Western Thunderer


Having got to the point where all 3 chassis' are fitted together with the tabs, I thought it was worthwhile to get one of them running before I soldered them together, If it didn't run, taking it apart again would be relatively easy .

I need not have worried, the chassis ran perfectly under finger power at the first attempt, as you can see in the attached video. The chassis is only held together by the tabs.

The other 2 chassis' have therefore been soldered together, the tabs removed and the overlays added.

20210602_153504.jpg

The kit supplies 1.5mm rivets to secure the coupling rod joints, these are just not appropriate and are far too long, I have used some 12BA nuts and bolts for now but I will need to make up something a bit more accurate later.
If you are using the MOK wheels crankpin "nuts" are supplied for the leading 3 axles, but the rear 2 axles are tapped 12 BA.


20210602_153509.jpg


20210602_153528.jpg
 
Iain Gould

Iain Gould

Member
Maybe it would be nice to see somone do a Crosti 9 build albeit the final version as they were an ugly ducking but had something about them.

KR

Iain Gould
 
mickoo

mickoo

Western Thunderer
I suspect it's the Severn Models one in which case that's a real silk purse from a sows ear Tony :eek::thumbs:

7mm - The Derby Line - DJH/Piercy B1

I had one once, the sheer complexity of the etches to form the steam pipe covers beside the smoke box convinced me that they were never going to fit, so it was sold untouched. These days they'd be a perfect 3D print replacement part.
 
Dave Holt

Dave Holt

Western Thunderer
Wow! Four, or even five, weeks to build a model loco? Four months would be rushing, for me, and four years not unusual. Good job I don't make models commercially.
Dave.
 
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richard carr

richard carr

Western Thunderer
I haven't had a chance to do much on the 9fs recently, but yesterday I finally found the rest of my 9f drawings !
So now I'm ready to draw up some new coupling rods.
Here's an small excerpt from one of the drawings that show how the coupling rods line up and how tight the clearance is behind the cross head.

20210626_122001.jpg
 
richard carr

richard carr

Western Thunderer
I have spent a bit of time drawing up the first of the coupling rods. This will be a six layer lamination using 0.38mm nickel silver. This will come out a tiny bit too thick but thinning it down to he correct size is relatively easy, and using 5 laminations would have been too thin.

I have been trying to upload a PDF of the drawing but it doesn't seem to work, does anyone know how to do this ?

Thanks

coupling rod1.pdf
coup rod 3.pdf
 

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  • coup rod 3.pdf
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Dog Star

Dog Star

Western Thunderer
Richard,

How do the thicker rods impact on the crankpins supplied with MOK wheels?

How do the thicker rods impact on clearances in the area of the slidebars / crossheads?

thank you, Graham
 
Steph Dale

Steph Dale

Western Thunderer
Similar to Graham's question, but looking in the other significant chassis dimension - how are you ensuring the rod crank pin centres align with the wheel centres? They don't need to be more than a few thou out and running will be severely compromised.

Steph
 
mickoo

mickoo

Western Thunderer
richard carr said:
I have spent a bit of time drawing up the first of the coupling rods. This will be a six layer lamination using 0.38mm nickel silver. This will come out a tiny bit too thick but thinning it down to he correct size is relatively easy, and using 5 laminations would have been too thin.

I have been trying to upload a PDF of the drawing but it doesn't seem to work, does anyone know how to do this ?

Thanks

coupling rod1.pdf
coup rod 3.pdf
Click to expand...
I can see them just fine, you simply have to download them and then view them locally on your PC.

You may or may not know, but the 0.375 mm material is hard to find now, PPD stopped it last year, you can only get 0.3 or 0.4, that may have an impact on your design and thicknesses.

This is a right pain as I've been centering more and more on 0.35 mm as my ideal mid ground material thickness and could just cope with 0.375.
 
richard carr

richard carr

Western Thunderer
Graham

I don't think it will make much difference to the crankpins on the supplied wheels.
If the rods do come out slightly too thick , it will be easy to file them back to scale thickness, and when I say too thick on the one I've drawn so far it is 0.129 mm on the bosses. On the real thing there is also a bearing behind the boss that is 1/2 an inch thick (0.2917mm to scale) which I'm not planning on using on mine.

I haven't drawn the front rod yet, but it is considerably thinner on the real thing, almost an inch thinner at the very front boss. again it has that half inch thick bearing so I'm not anticipating any significant issues.

Steph

All MOK kits rely on the slot and tab construction method to place the horn blocks in the right place, in the Q1 and LMS 4mt this worked just fine and the test above in post 122 was to make sure that it would work too on a 10 coupled engine, before building all 3 of them, I need not of worried it does work just fine. I have no worries that mine will work too they are correctly drawn at 5 foot 5inch centres.
This is an idea you should borrow for your kits.


Richard
 
Steph Dale

Steph Dale

Western Thunderer
Richard,

We're ahead of you on the hornblock alignment stuff! :D

My concern is that you've drawn your rods to scale, and assumed Dave Sharp has. Production methods do apply a variance so you're still trying to hit a moved target. Over the length of the 9f wheelbase, those variances could be enough to cause a problem.

Admittedly, I don't think you'll be far wrong, but in general I'd not advocate replacing rods unless building the chassis using some form of jig to ensure the alignment of the crank pins and axles - that's an advantage of not having hornblocks 'hard' aligned in the chassis.

Steph
 
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