6" Burrell Gold Medal Tractor

My first batch of castings loaded into the car

24 January 2009: I Visited Edward to collect castings and material for the front and rear wheels.  After a civilized adjournment to drink a few cups of tea it was time to collect the castings.  While I had only intended to collect wheel castings on seeing the smokebox and front axle parts I became inspired as I could see how I could machine most of them with my limited facilities.  The upshot was that I came away with a few more casting than I intended.

Judging by their look, the casting are of high quality, as can be seen in this detailed photo.  At this early stage of development Edward has not yet have a full set of drawings so I will have to be careful I do not make anything incompatible with the eventual design.  I decided that the smokebox and front axle was a fairly safe place to start as it has few interfaces with the rest of the engine.  I selected the chimney saddle as my first task as I though it would be straight forward.

Taking the first cut with the saddle mounted on an old fence post


Machining the top flange of the chimney saddle

The attraction was I thought it would be easy to hold for machining as it has a nice flat flange but I first had to machine this flange true.  This was a setback until I visited my club and one of the wise members pointed out that I could scale up locomotive practice and mount saddle on a wooden mandrel.

28 January 2009: On returning from the club I went into the garage a cut off the end of an old 4" fence post and mounted it between my four jaw chuck and a revolving centre.   Pretending it was metal I set about turning the post down to slightly above the inside diameter of the saddle.  I then fine tunned this so that the saddle could be slide on and jam (ie a slight taper).  I removed the improvised mandrel (fence post!) from the lathe and whacked the saddle on and fortunately it jammed at about the right place.  I then return it to the lathe and used a dial gauge to adjust the 4 jaw chuck jaws so that the mandrel ran true.  The casting proved again to be of good quality as the top ring and outside surface ran remarkably true.   I then proceeded to machine the top flange with only one minor problem.  I could not get my vernier onto the flange to measure it's outside diameter as there was a lump of wood in the way!  I was saved by the upmarket DRO I have recently fitted to the lathe as I had previously calibrated the tool and "knew where it was".  I was pleased to find that when I removed the saddle the top flange was spot on at 5.000"

Boring out the chimney

1 February 2009: I initially planned to mount the saddle by its top flange on on faceplate but when I tried this I found it difficult.  My problem was that there was not enough room between the outside diameter of the flange and the edge of the face plate to use a simple clamping arrangement.  My thoughts then tunned to my 3 jaw chuck but it was too small.  I then realised I would be able to hold it in my 4 jaw chuck.  Now that I am am accustomed to it, I find setting a job to run true with a dial gauge takes no time at all.

Hitherto I have found that my 1/2 shank boring tool to be substantial enough for all the boring jobs I have undertaken.   On this occasion I had to have it extended so that it overhang by about 5".  The lack of rigidity was immediately apparent and I was only able to take fine cuts.  I also found that because the bar was flexing several passes were needed to take the spring out of the tool. 

Rigidity of the cutter was a problem whilst flycutting the saddle base

2 February 2009: I was keen to see if I could finish machining the saddle using only my existing machine tools.  The 6 3/16" radius of the saddle is really beyond the capacity of my milling machine.  Not only is the radius too big the table traverse is only 5" and the saddle is just wider than this.

I decided to make a bar in which I could hold a lathe tool in my milling machine whilst it is configured in its horizontal mode.  I had hoped to use the arbor end support to provide addition support near the cutter but when I came to fit it I discovered that it only worked on the tip of the arbor.  On some horizontal machines the end support bearing may be slid down the arbor and in that case I would have been able to position in just inside the cutter.  I decided to have a go despite the lack of rigidity.  I got on OK but was only able to take 5 thou cuts whilst using a fine feed.  I then had to reposition the cutter to make up for the limited table traverse.

Despite the limitations of my equipment I had completed all the major machining operations on the saddle and was very pleased with my efforts.