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Old 07-15-2017, 07:30 PM   #1
abby
 
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Most of my model engineering output is in the form of lost wax castings which I supply to clients wanting the very best that their money can buy.
For the most part these castings are destined to become part of the model that the client is building.
This work usually requires me to produce a 3D drawing of the part , so that a pattern can be printed .
From this pattern a flexible rubber mould is taken , allowing the wax replicas to be made which ultimately become the castings.

However when I am on my own time my interest is in gauge one steam locomotives , and in particular the Merchant Navy Class engines which ran on the southern region of the British railway network.
It is not my intention to bore you with details of these engines , if you want further information there is plenty to be found on the net.

No , I rather thought that I would describe how I go about producing parts for the small batch of engines that I am slowly building , nothing will be new to the old hands but perhaps some newcomer to the hobby may find a useful tip or two.

As I started out saying I mostly make castings , mainly in copper based alloys , brass ,bronze , gun-metal and nickel silver.
I always try to design the parts that I require as castings because there is always room in a mould of customers work for a few bits of my own .
You might say that my stuff comes almost free , quite cheap anyway.

Right at the front of all engines are the buffers , these absorb the shock loads during pushing operations.
Some components are common to a wide range of engines and I make a very nice gauge one ( 10 mm to the foot scale) buffer stock.





I also make a buffer beam casting for the Merchant Navy class



Unfortunately , to save money on the laser cutting , I changed the frame steel thickness from 2.0 mm to 1.5 mm so the cast beams no longer fit , I decided that rather than modifying the castings it would be easier to fabricate new beams.
Which I did from 5/32 sheet brass , with silver soldered joins.





the short length of sprue left on the back of the buffer stock helps locate its position on the beam and keeps it secure whilst being soft soldered.



The beam is attached to the frames with countersunk head socket screws , with the restricted access these are easier to fit than anything else as they can be firmly held on a long series allen key.
The screw holes need to be very accurate , and repeatable between sets of frames so I use a jig made from a spare piece of frame.



The jig is positioned and clamped to the beam with a small tool-makers clamp and the first hole drilled.



after drilling the hole a second clamp is added alongside the first.



with the second clamp firmly home the first clamp can be removed and the second hole drilled



By using this method the beams and frames are interchangeable , hopefully if I can maintain this method throughout the subsequent builds should be like assembling kits.

to be continued


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Old 07-15-2017, 07:31 PM   #2
abby
 
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For the buffers themselves I used some scruffy old bolts from my scrap tin , I selected bolts at least 0.512” AF and turned the heads down to 1/2” , I made a note of the dial readings so that the size could be repeated to within a couple of thou.
After turning all the heads the shanks were turned down to 0.200”



With the shanks to size the heads could be thinned down to 1/8” or so.



With the top-slide of my Pultra instrument lathe set over as far as it would go



I put a shallow chamfer on the back of each buffer.



then parted off the surplus shank



The buffers now need to be drilled and tapped 7BA ( I use this size quite a lot as it threads 3/32” dia perfectly , and I have loads of 7BA nuts and bolts )

I have made an ER20 collet chuck for my little lathe and this will hold 1/2” , so with the shank held in a collet in the tailstock the buffer can be offered up to the ER20 collet



Now the tailstock collet is changed for the Jacobs drill chuck and what a beauty , this is the rare No.0 sized chuck 0-5/32” made in the USA and probably 50 years old .



So centre drill , drill tapping size hole and thread 7 BA



The Pultra tailstock is lever operated and has no depth stop , I want the threaded holes no deeper than 1/4” or they could break right through so here is the method I use.
I push the lever forward to fully extend the tailstock spindle and clamp the spindle.
I now push the tailstock forward until the drill contacts the workpiece and clamp the tailstock.
I now unclamp the spindle and insert a piece of 1/4” brass spacer between the drill point and the workpiece.



re-clamp the spindle , unclamp the tailstock , remove spacer , push tailstock until drill point re-connects workpiece , clamp tailstock and unclamp spindle !
phew sounds tedious but actually it is quite quick and you can now safely drill to the limit of tail-stock travel.

The front face of the buffer can now be finished using a chamfering tool followed by a smooth file and a bit of a polish with emery cloth.



The buffers now need to be fixed to the stocks and for this we need a small bush.



the bush pushes into the stock and acts as a guide for drilling the 7 BA clearance hole through the stock and beam.



Assembled with a suitable spring in the buffer stocks the beam is complete , painted in acid etch primer it is ready to be fixed between the frames.
Actually it still needs a towing hook and chains plus a vacuum pipe but you get the picture.



And a small production run doesn’t take much longer than making one off , even if you need one or two jigs.



Hope that wasn’t to painful , I will add more as the build progresses if members want to see it , but the development is fairly well covered on my forum here
http://www.unionsteammodels.co.uk

Dan.


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Old 07-15-2017, 08:33 PM   #3
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Innovative brain, nice workmanship
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Old 07-15-2017, 11:56 PM   #4
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Great build. Thanks for sharing.
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