LBSC Green Arrow
As usual with raw castings it's a case of deciding which face to make a start on, For the steam chest castings I picked the bottom face as that was the flattest. With a bit of filing and rubbing on emery paper I got the castings so that they would sit on the surface plate without rocking.
Someone had been a little over enthusiastic when fettling one of the castings and I could only get one side to sit on the corners. That was enough though.
The castings were set up in the mill vice with the prepared face against the fixed jaw and the bottom edge against a small parallel. A skim was the taken off the top edge to clean it up.
The casting was square enough as cast for this to work ok and the edge machined fairly evenly all the way across. The casting was then rotated 180° and the other side cleaned up.
Next, the casting was mounted in the vice with the bottom face sitting on parallels and the top face cleaned up.
It was then turned over and the remaining face cleaned up.
I did have a bit of trouble getting the castings to sit down on both parallels securely which meant the previously machined edges weren't quite true to the bottom. I expected this as the bottom had only been trued up with a file etc. as previously mentioned. I managed to get them to seat properly with a bit of fiddling and a few 'tappy tap taps' (where have I heard that before!) with my 'knocker' (a lump of cast lead).
Because of this I repeated stage one with the now machined bottom against the fixed jaw and took a couple of thou off the edges to make sure they were truly at 90°. I now had two casting with the top, bottom and both edges perfectly square to each other but still oversize.
The plan of action is to now machine the ends and the bosses to size and then go back to the mill to finish machining the top, bottom and edges.
I wanted to turn the bosses and face the ends in the ML7 lathe but how to hold the castings? I looked at using the angle plate again as it would be easy to get the casting properly lined up with the lathe spindle but the clamping arrangement wasn't really suitable. I thought about using a four jaw chuck instead but wasn't happy with that idea as the chuck jaws would have been too short to hold the castings securely. I could have used the larger Denham lathe I suppose but I've still only got one four jaw chuck useable for that and the jaws are pretty stiff which makes setting it up a pain (note to self - must get the backplates machined for all the other chucks that I have for it!)
So it was back to the angle plate with a modified clamp to hold the castings. This just involved drilling and tapping each face of the vee for a 6mm bolt and drilling a hole in a piece of scrap steel for the clamp. It worked well.
Before carrying out any machining I tapped the angle plate about with the bolts just nipped up until the boss ran reasonably true. It didn't need to be exact as the final machining on the castings will be done relative to the machined bosses and there is plenty of spare material on the castings to be machined off later.
At this point I've just cleaned up the boss and the end of the casting to get an idea of how much metal needs to come off. There is about 0.02" more to come off the diameter of the boss and quite a bit to come off the end face so plenty of metal to play with.
To machine the other boss and face I can just turn the casting around but I need to drill and ream the 5/32" hole for the valve rod before I can do that. The hole needs to go through both bosses and be perfectly in line and I'm not sure that an ordinary drill will run true enough to guarantee this. It will also need to start a true hole on the inside face of the stem chest when the drill has gone through the first boss. I could do with either a very long centre drill or a long spot drill, neither of which I have. Time for a search on Ebay!
I had a look on Ebay but couldn't see any suitable long centre drills or spot drills. I then had a look through my collection of 'miscellaneous' drills and found two brand new Dormer split point 3.7mm drills. One of those micht do the trick. As the drill is a split point it should start a true hole on a flat face without needing a centre to guide them. However, the inside face of the steam chest was still rough cast so I put it in the mill and cleaned up the face just enough to give a flat surface where the drill needed to start.
After that, the casting was returned to the lathe and the hole drilled using the 3.7mm drill with no trouble at all. I did have to stick the drill out of the tailstock chuck as far as I dare though to get it to reach all the way through!
The hole was drilled through the first boss with the drill all the way in the chuck as usual and only extended out to finish drilling the second boss all the way through. It seems to have come out nice and true.
Whilst working on this end of the casting I turned the boss down to the finished diameter and faced the end to the required length. To see how much needed to come off the end I took the casting out and measured the overall length, subtracted the required length and then divided that by two. I was careful to make sure that the cavity in the casting would come out central to the ends. It didn't need to be exact as I will probably clean up the inside edges of the casting anyway as at the moment it is undersized. If you don't do this you will often find that you can't get the full travel of the valve due to it hitting the ends of the cavity.
The above was repeated for the second steam chest casting and then I decided to go ahead and ream the first boss to 5/32" which is the diameter of the valve rods. The 3.7mm hole was a bit small for the reamer but I managed to find a decent 3.9mm drill so used that first. I drilled all the way through both bosses again but the reamer was only long enough to go through the first. The second boss will have to be done when the casting is turned around.
I think the reamer I used is getting a little tired as it took some pushing through. I never thought to look for a better one even though I've got loads of small imperial reamers in a drawer!
The next job is to turn the castings around and machine the second boss and face the casting to overall length. I used the same set up but because the second set up was not an exact mirror image of the first I had to adjust the position of the faceplate slightly to get the drilled hole in the boss running true. That was easy enough to do by putting the 3.9mm drill in the hole and clocking the shank with a DTI.
The reason for it not running true is because the drilled hole is not necessarily the same distance from the top and bottom face of the casting and now the casting is sitting on the other face. Remember, at the moment the castings still need finish machining on the top, bottom and sides.
I finish machined the second boss to diameter and took the required amount of the end of the casting to bring it to the final length. I then tried it on top of the cylinder casting and it was exactly the same length - I must be getting better at this!
On to the second casting but I noticed that when I measured the length to check how much needed to come off the second end, the calipers rocked. The jaws weren't parallel to the ends of the casting. After a bit of fiddling about it seems that the end that I had first machined wasn't square to the sides of the casting. Either there was a bit of swarf between the casting and the angle plate when I mounted it or I had pushed the casting too far back towards the faceplate. The rear boss, which at that time was unmachined, was too big to enter the spindle bore and would have pushed the casting off to one side if it went in too far. So, I'm going to have to put it back in the lathe and give it a slight skim to true it up. Oh well, I'll do that tomorrow.
At this point in time I have not decided whether to use the threaded type glands again for the valve rods so have not faced any of the bosses to the length shown on the drawings or drilled and tapped the holes for them. I really don't like threaded glands and much prefer to use a fixed gland with an O ring seal or a PTFE seal. Threaded glands really need to be screw cut in the lathe to make sure that the threads are true to the bore so that the rods don't bind up when they are tightened, unless you make the bore of the gland a sloppy fit on the rod and then the rod is only supported by the packing.
Another thing that I found tonight was that the original valve rods and piston rods have been made from mild steel instead of stainless so they are going to have to be replaced. Looking through my stock I have plenty of 3/16" stainless for the piston rods but no 5/32" for the valve rods. Looking online it looks like you can't get 5/32" anymore, only 4mm which is only about 0.030mm (0.0012") larger in diameter. So that's not really a problem but I will have to re-ream the bosses to 4mm and order some 4mm rod.
I set up the casting with the out of square end again and took a slight skim off the face to true it up. This time it came out ok so I carried on and machined the other end to length and machined the boss.
I made the decision to go with O ring seals for the valve rods so all the bosses now needed facing to final length and a counterbore machining for the O ring. Facing the bosses was straightforward and I used a 7mm four flute endmill to cut the counterbore for the O ring as that was near enough the correct diameter to suit the O rings I had and would give a flat bottom hole which they needed.
To get the recess the correct depth I used a lathe tool in the toolpost to act as a stop against the front of the drill chuck.
To set the 'stop' I put the milling cutter in the tailstock chuck and slid it up to the boss so that it touched the face and clamped the tailstock. Next, I engaged the leadscrew and moved the toolpost back towards the drill chuck until it was nearly touching and the dial on the leadscrew handle read zero. I then moved the tool back until it touched the end of chuck using the topslide feed screw. This is easier than just winding it back all the way with the leadscrew handle as the dial is fixed and not 'zeroable' and saves having to remember the number on the dial and working from that.
It was then just a case of winding the tool towards the chuck the required depth using the leadscrew dial and locking the saddle. To drill the hole I just moved the tailstock barrel until the chuck touched the tool again.
I saw this method on Youtube I think. I've never used it before but it works quite well. The tailstock barrel does have graduations on it but only every 0.125" so you have to 'guestimate' anything inbetween so it's not particularly accurate or repeatable. One day I will probably adapt a digital caliper to fit the tailstock and give accurate depth readings as many people have already done.
The finished boss with counterbore:
The glands will be a simple round plate with a spigot that fits into the counterbore to align it and leaves the correct amount of gap for the O ring to fit in as shown below.
I used this design on Helen Longish and have never had any problems with it. What you must ensure is that the gap formed for the O ring to sit in is wide enough to allow the ring to expand sideways as it is compressed by the bore and the rod. It should not be a close fit and as a rule of thumb the width of the gap should be 1.5 times the width of the O ring. This also allows the ring to roll slightly which spreads the wear over a larger part of the surface.
The next job on the castings is to machine the sides to the right dimensions making sure that the valve spindle finishes up in the right position and then machining the top and bottom. The thickness of the finished steam chest is smaller than the diameter of the bosses so the bosses overlap the cylinder block and the steam chest cover which makes it more difficult to machine. It's actually easier to make the bosses separately and screw them into the steam chest afterwards which LBSC did sometimes show. The actual steamchest could then be fabricated from brass bar silver soldered together which is a lot easier and cheaper than machining a casting!
Onwards with the steam chests and machining the sides.
The valve spindle had to be the correct distance from the frames so the side of the steamchest next to the frames had to be machined until this was so. I found a length of silver steel that was a good fit in the valve spindle bore and used that to measure the distance from that to the side of the steamchest. The silver steel came from my stock of metric stuff and should have been 4mm diameter but was actually 5/32"! (either that or it was 0.001" undersize)
The casting was set up in the mill vice on parallels with the side to be machined on top.
I could then measure the distance from the rod to the top surface with a depth micrometer and calculate how much needed to be taken off, remembering to allow for the diameter of the rod.
(If there is an L. Biggins out there I've got your depth mic!)
I only had to take 0.023" off the face so there wasn't as much surplus material as I first thought.
This was then repeated for the second valve chest. That one needed 0.046" taking off.
Now I need to machine the other side to bring the steamchests to the correct width to match the cylinders. First though, I need to take a skim off the outside edge of the cylinders to remove the remains of the 'Goodwin' name that was on the castings, otherwise the cladding will not sit flat on the top edge of the cylinders. I should have done this before I suppose but forgot!
I skimmed the outside edge of the cylinders to remove the remains of the cast in name and then machined the other side of the steam chests to give the width required.
The top and bottom now needed approximately 0.10" machining off between the bosses to bring the steam chests to the right thickness. The valve rod is equidistant from the top and bottom faces so it was a case of setting the casting up in the mill and milling off the required amount. Once again, I used the rod as a dummy valve spindle and measured the distance of the face from that with a depth micrometer. Once I removed so much I had to use a gauge block as a distance piece to get over the boss.
This depth mic needs a bit of restoring but it works fine. The top part of the thimble that you unscrew to change the rods was seized solid when I got it from Ebay but I soaked it in very thin oil and it came loose eventually with help from a bit of heat. It came with all the rods but no case and didn't cost very much.
I used the DRO to set the width between the bosses by centreing between the ends of the casting and then calculating how far to go in each direction to bring the width to size, allowing for the diameter of the 10mm endmill that I used. Actually, I had to increase the width cut slightly from that calculated as I think the cutter is a reground one so is undersize.
Because I was cutting to the exact length of the steam chest I got a very thin wafer of metal left on the edges but it just broke off very easily. You have to be very careful when machining gunmetal though as it leaves razor sharp edges on any machined surfaces. It's very easy to cut yourself. One reason I don't like the stuff as well as it machines like cheese unless you use really sharp cutters!
Now it's a case of turning the casting over and machining the other face, then repeating this on the second casting.
It seems to be taking forever to do these cylinders!
The rest of the machining went smoothly so apart from drilling the holes the machining on the steam chests is complete and they fit like a glove.
Before tackling the mounting holes I decided to make the steam chest covers. The originals were no good to fit the new steam chests so I made new ones from some 1/8" brass. Just a case of cutting out a couple of blanks and then milling them to size.
Unless you need a fancy shape for the covers I really don't see the point of using the castings that usually come with a cylinder set. Most of the time all you do is machine the casting until it is a flat plate! Much easier and quicker to use a flat plate in the first place (and cheaper).
I would have liked to round off the outside edge of the covers to make the cylinders look more like the prototype but the outside wall of the steam chests is only 3/16" thick so the fixing screws/bolts will be very close to the edge of the cover, probably too close to allow any rounding off.
I ordered some 4mm stainless bar for the new valve rods yesterday from Reeves 2000. They are not a supplier that I would normally use but with this Covid-19 thing they are offering free postage at the moment. I normally use MacModels but I've already sent them a pretty big order for materials which I'm waiting for. I would imagine they are extremely busy at the moment seeing everyone is spending a lot of time in their workshops!
After a bit of playing with the 3D CAD I decided that if I could move the outside fixing screws for the Steamchest as far in as possible, reduce the two middle fixings to 8BA and reduce the diameter of the heads of the screws, then I could just about get a radius on the edge of the steamchest cover.
The counterbores for the screws along the edge will be covered by the cleading so won't be seen.
Time to drill the holes so I made a CAD drawing with all the hole positions on it so the holes could all be drilled using the DRO.
It was when I came to start the actual drilling that I realised that the back wall of the steamchest was only 1/4" (0.25") thick whereas it really needed to be 5/16" (0.3156") to allow for the hole for the exhaust passage. The write up said the hole was to be 5/32" (0.1563") which was a bit tight for a 1/4" wall. My concern was that the gasket would be very narrow around the hole and could leak. The outside wall of the steamchest was undersize as well so I had to revise my positions for the 8BA fixing screws and move them slightly further out. This is one of the problems with using castings that are not made for the job!
I decided to replace the round 5/32" hole for the exhaust with a narrower but elongated slot which would give more gasket area around it and hopefully seal ok. I also had to move the position of the other fixing holes to take into account the thinner back wall.
The elongated slot is 3mm wide (because I have lots of 3mm carbide endmills) and actually gives more cross-sectional area than the plain 5/32" hole. Obviously, I will have to modify the cylinder block, the steamchest cover and the exhaust fitting to suit. Fortunately, I hadn't drilled any holes in the cylinder blocks yet otherwise they would all have been in the wrong place!
I could now get on and drill the holes and mill the exhaust slot.
The 3mm endmill I used for the slot wasn't long enough to go all the way through the casting so I had to machine as deep as I could and then turn it over and finish it from the other side.
The holes for the outer 8BA screws came very close to the inside edge of the valve chest but I got away with it.
I repeated for the other valve chest and then did one of the steamchest covers by a similar process. By this time I had decided to use countersunk screws for all the fixings as there is not much clearance for nuts or bolt heads under the running boards so the holes were countersunk as well. I'll do the other one tomorrow hopefully.
Time to drill and tap the holes in the cylinder blocks. This was done in exactly the same way using the DRO to position the holes but this time the holes are obviously blind. The holes were tapped using the chuck as a guide as before.
I also milled the exhaust passage but this will have to be revisited once I've fitted the blanking plugs in the cylinder bolting face as they will block off the milled passage when fitted and the passage will have to be milled through into them.
After I had drilled and tapped the first cylinder I tried fitting the steam chest and cover to see if the holes lined up! All but one of the 8BA's went in perfectly. I think the hole for that one wandered a bit in the steam chest. The drill I was using wasn't the best.
I made all the clearance holes in the steam chests and the covers a very close fit with the idea that I could open them out a few thou if things didn't line up properly. I'm quite pleased that all but one screw fitted! I will still ease them slightly to make fitting a bit easier. The screws are a bit snug at the moment!
You'll notice that I didn't countersink the two holes either side of the exhaust passage. These holes will also be used to secure the exhaust pipe flange so will be under the flange.
I've nearly finished the second cylinder block. I've just got to tap the holes.
Because the cylinders will be different from the drawings I've made another 3D model of the chassis which takes into account these differences and any others that come to light. This will probably come in very useful when I try and fit everything back together!
The 4mm stainless rod arrived from Reeves today so I now have that ready for when I get to making the new valve rods.
Keep on plodding on!
Last job on the steamchests (hopefully!) is to drill and tap the bosses for screws to hold the gland covers on. I was going to make these 10BA but chickened out and tapped the holes for 8BA instead. There's plenty of room for the larger heads.
To do this job I used the hole circle function on the DRO after setting up the steam chest in the vice. It was clamped between two parallels because of the recessed faces and set up vertically by making sure the bottom boss was resting firmy on the base of the vice. I did check it with a square as well to make sure it was truly vertical.
To centre the boss on the spindle centre line I roughly set it using a short length of the 5/32" silver steel held in the chuck, centreing it by eye and then moving the x and y axis until the rod slid freely into the valve spindle bore.
That would probably have been good enough for drilling and tapping the holes but I also wanted to ream the valve spindle bores to 4mm so I 'tweaked' the position using an indicator in the mill spindle. I indicated on the bore for the O ring seals as that was easier than trying to get into the much smaller valve spindle bore.
The bore was then reamed with a 4mm reamer and the holes for the bolts drilled and tapped.
One boss done, three more to go.
With all the bosses drilled, tapped and reamed I moved on to making the exhaust blanking plugs for the cylinders so that I could finish milling the exhaust passage in the port face. The plugs were just a length of brass bar threaded 1/4" x 40 with a shallow hole drilled into them to allow the milled ports to connect to the drilled passage in the cylinder block.
I adopted a similar proceedure to when I made the plugs to fill in the incorrect mounting holes in the frames i.e. I partially parted off the plug leaving a thin spigot so i could use the rest of the bar to screw the plug in after smearing it with Loctite 603. Once screwed in, the rest of the bar was wiggled about to snap it off. This worked fine for the first plug but I must have drilled the recess too deep in the second plug and when I broke the bar off it left a small hole in the end of the plug! I then had to remove it using heat and make another one. This time I sawed the bar off to be safe.
I put the cylinders back in the mill and milled off any protrusion of the plugs above the surface and finished off with a rub on some emery paper.
I could now finish mill the exhaust passage in the port face so that it broke through the top of the plug into the drilled recess. Job done.
I really should have milled the ports a bit deeper to get rid of those dimples in the bottom from the drilling operation. I'm leaving well alone though!
What next? Well, I need to see if the cylinder end covers will fit so that they can be reused. I removed the pistons, rods and gland nuts from the end covers as I had left the crossheads and slidebars etc. all in one piece. The crossheads were retained on the rods by a taper pin so removal was just a matter of tapping that out. When I came to disassemble the lefthand assembly though I couldn't get the gland nut off the end of the piston rod. I thought it was just a burr on the rod to begin with but closer inspection showed that the end of the piston rod was bent. As the rods were going to be replaced anyway I just sawed the bent end off rather than try and straighten it.
I then tried both the left and right rear covers in the cylinder bores and the spigots on both are about 2 thousandths of an inch too big. The original bores are obviously slightly bigger than the new ones. Oh well, it's better than the cover spigots being too small. The problem now is how to remachine the covers to remove such a small amount and keepng the spigot concentric with the bore for the piston rod. The outside edges of the covers could also do with a bit of a clean up at the same time.
I also tried the pistons in the bores and both went in but were a bit tight. If I hadn't had to replace the rods then they could have been reused. As it is, it's unlikely that they will run true enough after fitting them to new rods so I will probably have to make new ones.
It was about this time that I realised I had got confused (easily done nowadays!) over the sizes of the valve and piston rods. It's the piston rods that are 4mm or 5/32", not the valve rods. Those are 1/8". I will probably find that I haven't got any 1/8" stainless bar now!
Not much done in the workshop since the last update due to other things but I did manage to get the spigots on the rear cylinder covers machined to fit the cylinder bores.
To hold them I first tried chucking a length of 4mm bar in the collet chuck, threading the end of it and then putting the cylinder cover on the bar and clamping it against the face of the chuck with a nut with the spigot outwards. Unfortunately, the covers refused to run true and wobbled all over the place so I abandoned that idea. I don't think the outside end of the boss on the covers are true to the bolting face of the covers. I then fitted the gland nuts and tried again but the results were pretty much the same. The gland nuts are probably not square to the bolting faces either!
As a last resort I chucked a length of 1/2" brass bar, machined the end and threaded it 5/16" x 40, the same as the thread of the gland nuts. I then screwed the covers onto this mandrel and, to my surprise, they ran fairly truly. I think this was the best I could do so skimmed the bolting face of the covers using this method and reduced the spigot to a good fit in the bore. This had to done carefully as there was not a lot to take off.
I also took a cut off the outside of the flanges to true those up. They were all shapes and needed quite a bit taking off. I was a bit worried about them ending up too small in diameter but I think they will be ok.
To be continued