Tuesday, January 8, 2008

Tender Body

The original drawings showed what I think is the Hawksworth tender - I've previously made one in 5 in gauge, and thought the Collett tender would make an interesting change. It has a couple of major challenges - the top of the sides are flared, and also the rear corners of the tand are very rounded, so a tricky compound curve is created where they meet.

I took the basic dimentions from the drawings, and scaled the Collet specifics from a couple of photographs. The fact that the major lines of the tender matched up with the profile of the cab gave me some useful reference points.
Then there's a raised extension which fits on top. I left a tab which I curved to match the lower part of the tender, and riveted and soldered the two together.

The other tricky bit was the rivets -there are several hunders of them, and they're very prominent.

My solution was to make the tender tank out of thinner brass than usual -about 22 gauge. (Another reason for this was that I had a couple of sheets of this size availible!)
It made it easier to form the flared tops - I'd intended to form them around a 1 in dia steel bar, but eventually realised that the front edge of my workbench (originally intended as a kitchen work surface) was about the right radius. So I gently tapped tthe sheet to shape using a rubber mallet. I cut away the flared top in the region of the rear corners, and bent them to shape around a steel bar.

I took a lenght of 1 in dia copper tube and flared it (just like making the petticoat pipe.) It needed frequent annealing to get it to shape. I cut two 90 degree sectors out of this, and soft soldered them into the gaps in flares at the corners. A bit of excess solder and a file blended the curves together and it looked ok.

I worked out the rivet patterns from the photographs. To 'create" them, I made up a jig, to allow me to punch through from the inside. On the anvil of the jig, I formed recesses for the heads, using a ball nosed end mill. The upper leg of the jig had matching holes for the punch, and the two were kept in alignment by two pins in reamed holes. Finally, the punch had a step to fix the depth of the depressions.After a few trials on scraps of the same brass, I was surprised by how well this worked, creating convincing and even rivet lines, and very quickly.

A few real rivets held 1/4 x 1/4 / 1/16 brass angle to the bottom edges and to fix the coal plate. Once this was complete, it formed a very rigid structure, which was attached by 6 BA screws to the soleplate.

I made up the water filters from very fine mesh stainless woven cloth. The drawing showed these to be 1/4 in diameter; I chose to make them a good inch diameter to greatly increase the surface area and reduce the chance of them getting choked or reducing the flow rate. I soft soldered these together! I know stainless doesn't take solder, but it penetrated the mesh easily, and held the filters together, although they probably wern't soldered in the true sense of the word.

I painted the wheels, frames and body before final assembly.


Babs Banter/QUILTECH said...

Fabulous - knew a chap in north wales who was very much involved with scaled locos - sold parts.

Brother is making engine and carriages to run on tracks around his rather large garden - for grandchildren to have rides - with David as engine driver of course.

Must be wonderful to have creative hubby/wife team. Filled with envy. DH and me were teachers in previous life - art/drama.

Babs Banter/QUILTECH said...

Have passed on your blog to my brother David Brown who is also an engineer - retired- think he will find it very interesting.
Have 2 grandsons studying engineering at Uni and my father and grandfather were engineers - hence my interest in your blog., Wish I'd taken up engineering instead of drama!!

Babs McInnis