I dug the wheels out again today and finished turning them. Most of the turning had already been done and fortunately the bores had been bored true and all to the same size so it was just a case of mounting them on the usual jig held in the four jaw. I had done a bit of work on them some time ago which was mainly cleaning up the balance weights which had only been part machined and the ends of some of the spokes which were jutting up. Unfortunately the previous builder had made the common mistake of not machining enough off the back of the wheel before tackling the front and he/she had machined a bit off the front of the ends of the spokes at the rim. However, this wasn't too serious and a bit of filing on the spoke ends will render it less obvious!
The wheel turning jig
The treads are coned at 2 degrees and the final cut was made on all the wheels with the lathe tool at the same setting. This ensures all the wheels are the same diameter which definitely helps!
The chamfer on the front edge of the rim was done with the topslide set over to 45 degrees and the edge of the flange roughly machined using the sides of a pointed tool and then finally rounded off with a file and carborundum paper.
Machining the chamfer on the edge of the tread
Rough shaping the edge of the flange
If you look closely at the two pictures above you can see where the ends of the spokes have been machined off!
Next job is to drill and ream the bosses for the crankpins which I think I will probably do in the milling machine.
The Simplex crankpins (like most others) are actually turned with a reduced diameter to fit into the wheel bosses but my original intention was to leave the diameter of the pins full size and drill/ream the bosses to 7/16 inch diameter to suit. There is no real need to reduce the bit that goes into the boss and there is always the possibility that the turned section may come out eccentric to the main diameter if the bar is not set up accurately. Similarly with axles, there is no need to turn a step on the end of the axles to fit into the wheel bosses. It does make it easier to get the wheels the right distance apart but there is always the chance of eccentricity again.
As it happens, I decided against leaving the pins full diameter as a full size hole would have left the walls of the boss a bit on the thin side. Instead I made the reduced part 3/8 inch diameter instead of 5/16 inch which will make the pins a bit stronger.
I utilised the wheel turning jig still mounted in the four jaw to hold the wheels for drilling and reaming the crankpins. The four jaw is one that screws directly onto the spindle nose of the lathe without a separate backplate so the back of the jaw is flat. This made it easy to clamp the chuck onto the table of the milling machine. I then made up a drilling jig with a spigot to fit the axle hole in the wheel and a 3/8" reamed hole in the position of the crankpin. I actually only used this jig for the final reaming of the crankpin hole just in case the drilled holes had wandered slightly. I didn't bother hardening it as it only had to serve for six holes.
Wheel turning jig and chuck clamped to milling table with reaming guide
A wheel was fitted onto the jig along with the reaming guide and the milling table adjusted until a short length of silver steel held in the drill chuck lined up with the crankpin hole in the reaming jig. The table was then locked to prevent any movement so that the holes drilled in the wheels would all be exactly the same distance from the axle hole. I removed the wheel again and drilled a clearance hole in the backplate to allow the drills and the reamer to pass right through.
Using a pin in the chuck, the wheel was rotated until the pin was on the centreline of the crankpin boss and the wheel clamped to the backplate with a couple of clamps to prevent it moving. I've seen quite a few wheels where the crankpins are off centre and it looks awful!
Using a pin in the chuck to centre the hole in the middle of the boss
The boss was then centre drilled and drilled through with a small pilot drill.
Next the reaming jig was repositioned using the bit of silver steel in the chuck and the hole drilled out and finally reamed. I think I could have got away with not using the reaming jig actually as all the holes seemed to come out bang on and the reamer went through without touching the jig at all.
Drilling the hole before finally reaming to size
The axles are straightforward turning jobs from 3/4 inch silver steel but it is necessary to make sure they are running true in the lathe before turning the wheel seats. The ML7 spindle bore is too small for the axles to pass through so one end was held in the chuck and the outer end supported by the fixed steady. The axle was set up to run true before positioning the steady and fortunately my chuck held true to better than 1 thou (0.001") for the axle diameter. It does vary though with the diameter held and which chuck key hole you use to tighten the chuck. Once the axle was true the steady was positioned and adjusted to the diameter.
Turning the wheel seats using the fixed steady
The seats were rough turned with a carbide tool and then carefully finished to size with a sharp HSS tool. HSS tools seem better at shaving a few thou off than carbide tools which like a good cut to perform properly.As the wheels will be Loctited on to the axles, I used the 'cotton reel' method for producing the seats. The seat is turned to a good push fit in the wheel and then the centre of the seat reduced in diameter by a couple of thou leaving about 1/8" at each end of the seat to make sure the wheel runs true. The reduced middle section gives room for the Loctite which likes a slight gap to bond properly. In the past I've turned the whole seat to a couple of thou smaller than the bore but if you are not careful the wheel can go on wobbly!
I turned the seats to slightly longer than necessary and then trimmed them to the right length by fitting the wheel and facing off the end of the axle until it was just proud of the wheel boss. It was nice to see that all the wheels ran perfectly true with no wobble or eccentricity while I was doing this!
Facing the axles off to length
When one end of the axle was done, I turned the axle around and machined the second seat. I had deliberately rough cut the length of the axle so that I had a bit of excess to play with. When the second seat was machined, I carefully checked that the distance between the seats, and hence the back to back distance of the wheels, was the correct 4-11/16 inches. This did mean taking the axle out of the chuck to measure the distance and then replacing it but I was careful to use the same chuck key hole to tighten the chuck so that the axle still ran true. I found it easier to get the back to back distance correct and then reduce the seats to the right length rather than making the axle the 'right' length and then measuring the length of the seat from the axle ends.
Finally, the ends of the axles were centred and drilled down for an oilway to the needle roller bearing. A small cross hole was then drilled to feed the oil to the bearing race. The axle was then tapped for a 6BA grub screw to seal the axle hole off and keep out dirt etc. When the bearings need oiling (probably yearly?) the grub screw can be removed, a bit of oil squirted in, and the grub screw replaced.
Drilling the oilway down the axle
The small cross hole to fed oil to the bearing race
Drilling the hole down the axle was actually the worst part of the job! Silver steel is not nice stuff to drill and these holes had to be 1-1/4" deep. I took each one very slowly and used plenty of cutting oil, withdrawing the drill at regular intervals to clear the swarf from the drill flutes. Fortunately all the holes went well with no drill breakages!
Time to tackle the pony truck wheels. These are front bogie truck wheels for Don Young's Black Five which will machine to the diameter I want. The rims are actually not the same shape as the Simplex ( V shaped as opposed to flat) but they will do for the time being. If I find any others with the same rim shape I may change them but I'm not too bothered!
The castings were machined in the usual way. Firstly, the wheels were chucked in the four jaw by the edge of the flange and set so that the inside of the rim ran as true as possible. A skim was then taken over the tread just to clean it up.
Bogie wheel set up in 4 Jaw to true up the tread
The casting was then held by the tread in the three jaw and the back cleaned up and the flange turned to the correct diameter. The boss was then drilled and reamed for the axle.
Wheel in 3 jaw to machine the back and bore the axle hole
The wheel was then mounted on a wheel turning jig to finish off the tread etc. as described for the driving wheels. Fortunately, a jig I had used to true up some Rob Roy wheels proved to be suitable as the bore for the axle was exactly the same (7/16") and the wheels are a similar diameter.
Finish machining the tread on the jig used for some Rob Roy wheels
The axle for the trailing wheels was machined as for the main wheels but this time the axle would fit through the lathe mandrel so I didn't have to use the fixed steady.
Today I took the chassis with wheels temporarily fitted down to the club to try it around the curves on the track. We have a ground level track with very sharp curves and the chassis pushed around those with no clearance problems. The only problem I did find was that the spring pins on the trailing axle boxes are slightly too long and catch on the 3½ inch rails on the raised track! They just need shortening by 1/8" to solve that.
Rolling chassis on the club steaming bays
I've turned up the crankpins from silver steel and the nuts for the rear pins but have spent the rest of the time stripping the chassis ready for final assembly. I've put the chassis on our club stand at the Midlands Model Engineering exhibition this weekend so it has been a bit of a rush to get it back together again in time!
I decided it would be better to etch prime the stretchers and the inside of the frames before they were put back together so everything was thoroughly degreased with POR Marine Clean and then sprayed with Upol Acid 8 primer. I didn't paint the outside of the frames just yet. I will do that when all the dings and screw holes have been filled and sanded down. Also, I have decided to fit some brake gear to the chassis to act as a parking brake when the loco is stationary on the steaming bays etc. This will mean drilling a few more holes. There are still a few holes surplus to requirements that need filling as well.
When I reassembled the frames I used thread lock on all the bolts and screws to stop any working loose in service. Can't have bits falling off when we are hurtling around the track!
I'll be having a break for the next week as I won't get the chassis back until next Thursday. Still, I've got some tidying up to do and I also want to do a bit more on the Kingette.
I've spent the last three days struggling to load up a new PC after my old one went bang at the weekend! The motherboard decided to pack up and I couldn't easily get a new one to support my original processor. It turned out cheaper to buy a complete s/h PC rather than upgrade the old one! I've now got a much higher spec machine but have had to load all my programs etc. again.
I had a bit of a break after the Midlands Exhibition but am back on track again now. I've machined up the buffer stocks from 1 inch square mild steel but haven't got enough round bar for the heads so they will have to wait for a bit. The original Simplex stocks are actually 1-3/16" square but that's not a standard size and I had the 1 inch square to hand so used that instead. The original design also calls for a threaded stub on the back of the stock for holding them onto the buffer beams but I did away with that and they will be fastened with studs and nuts. While I was in 'square turning' mode I made up the rear coupling as well.
Buffer stocks and rear coupling
When I assembled the chassis for the exhibition I fitted the buffer beams using threadlock on the bolts which turned out to be a waste of time as it was easier to take them off again to drill the mounting holes for the stocks!
I decided it was time to 'glue' the crankpins into the wheels and the wheels permanently onto the axles so I made up a simple quartering jig in the lathe as usual. I know some people make up fancy free standing jigs for doing this job but I don't really see the point if you've got a lathe!
I turned up a centre from 7/16" diameter steel bar (the same diameter as the crankpins) and held that in a drill chuck in the headstock spindle. I then clamped a small engineers square to the cross-slide with the edge against the side of the centre. This gave me the location for the crankpin on one of the wheels.
Headstock end of the 'jig'
I already had another similar centre and this was held in another chuck in the tailstock. I then turned up a length of bar to act as a height gauge for the crankpin of the second wheel. The height of this was equal to the centre height of the lathe less half the thickness of the crankpin. Therefore, when the axle was mounted between the two centres and one crankpin was against the edge of the square at the headstock end and the other resting on the height gauge, the crankpins would be at 90 degrees (or near enough!) The actual angle is not critical but must be the same for all the wheel sets.
Tailstock end with height gauge
The wheel bores, crankpins,and axles were then thoroughly cleaned with thinners to remove all grease etc. The crankpins were glued in and one wheel on each axle glued on with Loctite 603 and the axle boxes etc. fitted on the axles (don't forget to put them on before gluing the second wheel!). (Actually, before fitting any of the wheels I put a 1/8" pin half in the driving crankpins and half in the wheel to make sure these crankpins would not move under the load from the return crank driving the valve gear. I didn't pin the leading and trailing crankpins as there is very little rotational load on them).
The axles were then mounted between the centres and the second wheel glued and the position of the wheel adjusted so that the crank pins just touched the edge of the square and the top of the height gauge. The tailstock centre was deliberately left long so the second wheel could be moved clear of the end of the axle allowing the Loctite to be apllied to the axle after putting it between centres. Having the axle already mounted before applying the Loctite gives a bit more time to get the crankpins aligned before the Loctite goes off!
Axle mounted between centres but Loctite not applied yet
Loctite applied and second wheel being fitted
The quartering on all three axles went without incident so the next job is to get some steel for making the coupling rods. Not one of my favourite jobs!
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