29/06/09

After spending a long time working on other peoples locos I thought it was about time I did a bit on my own!

I've finally christened the new mill and machined the horns to take the axle boxes. This was a doddle with the larger mill but took a fair time to machine all 3 pairs of horns. The frames were clamped vertically on the table using angle plates and various G clamps.I used a long series 16mm endmill in the collet chuck. It was a bit too long really and there was a bit of vibration while cutting but it was the only one I had that would cut the full depth of the horn slot. I found the best method of milling the slots was to machine each side to the full width in one pass and then machine the slot to the full depth taking 1.25mm downward cuts (the mill is metric!). I've never had much success milling these slots using the full length of the cutter and feeding sideways. I always seem to get a very poor finish doing it that way.

Milling the horn slots

I sharpened the cutting edges of the endmill after each slot was cut as they were getting a bit blunt after cutting both sides. This entailed making a new collet for the cutter grinder as my biggest one was only 1/2"!

Whilst I was in 'milling mode' I made all the new frame stretchers by sawing them from 3/8" steel flat and then milling the ends square and to the right length. I did keep the large front stretcher from the originals as this is the same size in the new design.

Next job was the buffer beams. I had to replace the rear beam as the angles that bolt it to the frames are closer together in my design so the rivet holes were in the wrong place. While I was at it I decided to replace the front beam as well as the holes for the buffer stocks were a bit out. Also both original beams had been drilled for 1/8" rivets instead of 3/32". The new beams were made the same way as the stretchers i.e. sawn from steel flat and then milled to length and to square up the ends.

Trimming the buffer beams to length

You'll notice in the above photo that I've treated myself to a clamping set which is proving to be very useful!

The beams then needed to be drilled for the rivets etc. and I used my favourite method of marking these out - a paper template printed with CAD and then stuck on with double sided tape! The holes were then spotted with a fine dot punch and then with a centre punch before drilling in the mill. I drilled all the holes with a small pilot drill before enlarging them to the correct size.

01/07/09

I had a senior moment yesterday when drilling the buffer beams for the spigot on the buffer stocks (I blame it on the heat wave!). On the front beam which I did first I picked the wrong pilot holes to enlarge and consequently the holes were in the wrong place! Fortunately, I drilled the holes with a ¼" drill before the final 3/8" and realised my error before drilling to final size. At least I've only got two ¼" holes to fill in! Also, the square flange of the buffer stocks will cover most of the mistake.

Next job was to bolt the frames to the stretchers, starting with the large horizontal one at the front. When fixing frame stretchers I drill and tap for one or two bolts on one side only and then bolt the stretcher to the one frame. One or two of the mounting holes in the other end of the stretcher are spotted through once the frames are clamped together and I am happy that everything lines up properly. Finally, the rest of the mounting holes in that stretcher are drilled and tapped and the bolts fitted.

To make sure the two frames were exactly in line the assembly was clamped to the milling machine table (which made a good surface plate) and a length of aluminium bar a good fit in the horn slots was fitted to the front horns. I also checked everything with a square to make sure the frames were vertical and not leaning to one side!

I had a slight problem with the front stretcher (the original) as one bolting face was not exactly at right angles to the top and when bolted up the stretcher 'leaned' slightly. I couldn't afford to take much off otherwise the stretcher would have been too narrow but I managed to mill off a couple of thou which was enough to square it up.

Frames clamped for fitting the large front stretcher

When the front stretcher was in place, the ones above and behind the centre axle were fitted. The aluminium bar was fitted to the centre horns to keep those aligned and a straight edge held against the sides of the frames to make sure they didn't finish up banana shaped!

Middle stretchers now fitted

(Most of the hex bolts will be replaced with countersink head screws)

Now I need the rear frame extensions. The rear frame stretcher can then be fitted and the buffer beams. Time to start thinking about the radial horns for the trailing axle!

05/07/09

The frame extensions were roughly cut out as a pair from 4" wide mild steel using a paper template again. They were then milled and filed to finished size and the holes drilled for the radial horns.

Frame extensions roughly cut out

The extensions were next clamped to the rear of the main frame so that the mounting holes could be spotted through and drilled.

I also needed two spacers to go between the main frames and the extensions to set them in and give enough clearance for the trailing wheels to move sideways. The spacers were cut from offcuts of the 1/8" mild steel and again clamped to the frames so that the mounting holes could be spotted through. I am not really sure how much clearance the trailing wheels will actually need so I've erred on the generous side. I did draw the frames and trailing wheels in CAD with the wheels on a 60 feet radius curve which suggest that just bolting the extensions inside the main frames would not give enough clearance, hence the extra spacers. When the frames have progressed to a rolling chassis I'll take it down to the club and push it around the track to see what happens!

The extensions and spacers were next clamped to the frames with the rear stretcher in position and the holes in the stretcher for the fixing bolts drilled and tapped. During this operation the frames were clamped to the milling table again to make sure everything remained straight and true.

Frame extensions bolted to main frames and rear stretcher

I decided to next tackle the front buffer beam and it's fixing angles which was a bit of a fiddly and tedious job. The beams are held to the frames with four lengths of angle, two each side of the frame, which are rivetted to the beams and bolted to the frames. The angles that came with the original package proved to have curved faces which would have needed milling flat so I cut some new ones from some angle I had in stock. Unfortunately, this proved to be about 93 degrees angle instead of 90 degrees so I still finished up having to mill one face square! Still, better than having to do both faces.

The fixing holes had already been drilled in the frames so I had to make sure that the holes in the angles would line up with these. To do this I clamped the inside angles to the frames in the right position and then spotted through the frames into the angles and drilled the angles with a 4BA tapping drill. I am not sure if Martin Evans meant the angles to be fastened with a nut and bolt but I decided to just use bolts fitted from the outside and threaded into the inside angles.

The inside angles were then clamped to the outside angles and the outside angles drilled with the tapping drill. The holes in the outside angles were then drilled out to 4BA clearance and the inside angles tapped 4BA.

With all the angles bolted to the frames, the buffer beam was clamped in position making sure it was central and the frames were the correct distance apart at the ends. Two rivet holes were then drilled in each angle using the beam as a jig. The angles were removed from the frames and rivetted to the beams with just the two rivets in each. The beam and angles were then refitted to the frames to check that nothing had moved and everything still lined up ok. Everything did so the beams were taken off and all the remaining holes drilled and the rivets fitted. I also fitted the two pieces of brass angle to the top edge of the beams for securing the running boards.

Front buffer beam angles fitted (you can just see where I've filled in the wrongly drilled holes for the buffer stocks!)

There's still a bit of work to do on the front beam before finally fitting it. There's two little bits of brass angle to fit to support the bottom end of the running board valance (which aren't on the original design), the holes for the buffer stocks need to be drilled through the outer angles, and the square hole for the front coupling hook needs to be cut. I've now got to repeat the whole process for the rear buffer beam!

12/07/09

Both buffer beams are now complete and fitted. I've filed down all the rivet heads flush and given the beams a quick coat of primer to show all the little bits that will need a spot of filler before final painting. I'll do all that when the frames are complete as there are still spare holes to fill and probably a few more to drill.

Buffer beams completed and fitted

24/07/09

I've spent the last week fabricating the 'casting' for the radial truck horns. This is a one piece affair that fits between the frames and acts as a stretcher as well as providing the curved guides for the radial axle boxes. It's a fairly simple job from 3/16" mild steel for the top and end plates with the two curved guides made from 1/8" brass. I chose brass here as I thought it would be easier to roll the curve using my little bending rolls. It was still a bit of a struggle and the brass required annealing several times before the required radius was obtained. 1/8" brass is really at the limit of these rolls but they managed it eventually! I kept checking the radius against a printed out drawing as I went along as I wanted to get it as close as possible to reduce any final machining necessary to a minimum.

Component parts of the radial horns

The parts were held together with screws and then all silver soldered together in one go.

Various views of the horns before silver soldering

All soldered together!

The 'casting' now needs machining to final size. I deliberately made the width oversize as I thought there may be a fair bit of distortion caused by the soldering which would need truing up. Also the lugs of the horns need to be machined to fit the slots in the frames. I'm not sure yet how to finish machine the curved faces of the guides but hopefully the amount of metal to remove will be minimal. I could use the rotary table with an extension to get the required radius or maybe fly cut them in the mill? Incidentally, the radius of the centre of the slot is just under 6 inches (calculated using Baldry's rule)

25/07/09

Today I machined the ends of the horns to fit the frame. This was done in the mill with the horns clamped vertically to an angle plate using a square against the edges of the horn plates and making sure everything was dead square. I had visions of the lugs that fit the frame slots not being exactly in line and the slots having to be 'adjusted' to fit but everything came out spot on and the horns fitted like a glove. I think someone must have been looking over my shoulder as I was doing it!

Setup to machine the ends of the horn 'casting'

Trial fit in the frames. Spot on!

I decided to go with the rotary table for final machining of the curved slot in the horn and this meant bolting an extension piece onto the table to get the required radius. A length of 4" x 3/8" steel flat was bolted onto the top of the rotary table and the horn clamped onto the end of this. To make sure the horn assembly was aligned properly with the axis of the mill/rotary table, I printed out a paper template with the inside edges of the slot and the centreline and taped this to the top of the horn. The position of the horn on the extension bar was then adjusted until a needle point held in the mill chuck followed the centreline of the slot when the rotary table was turned. To help this adjustment, two screws each side were used in previously tapped holes in the horn flanges to position the horn relative to the extension bar. When all was lined up correctly, the horn was clamped rigidly to the bar using G clamps and the adjustment screws tightened to prevent any movement during the milling process.

Aligning the horns prior to milling the slot

Finish milling the slot

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