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| smfr:
[Moved from homemodelenginemachinist.com] It's been a few weeks since I've managed to get time in the shop (garage!), but I got a few things done today. Here's my setup for the crosshead milling: I have the crosshead on the piston rod in a V-block, because I want the milled parts to be parallel with the piston rod. The angle plate etc. is just there to line things up. I clamped my screwless vise on its side around the crosshead for milling, which made things a little cramped: After doing one side, I had to tear down the setup, turn the part around (making sure that the side to be cut is parallel with the part I just milled out, using the height gauge). Had I been thinking more clearly, I would have had the V-block on its side for the first part, then I could have just flipped it over. Once both sides were milled, the crosshead pin hole was drilled and reamed in the same setup: Here's the result, with its companion connecting rod: Before milling, the crosshead was a nice sliding fit in the standard, but the milling pushed those skinny flaps out (this being bronze), and tightened everything up. A bit of fussing around was required to get it sliding in the standard again. After that I drilled and tapped the boxbed for the studs that hold down the soleplate. The alignment of the soleplate on the boxbed was mostly by eye/feel. I transferred the holes by positioning the two parts under the mill, with the clearance drill bit just dropping into the existing hole in the soleplate. I then switched to the smaller tapping drill size, and drilled down into the boxbed. The 4 holes were then tapped 2BA. One annoyance here is that the stud holes in the soleplate go down the inside corners of the casting, which ends up pushing the drill out of line, and causing the studs to catch. To fix that I milled out some room on each corner, centered on the holes: I'm close to being able to have this thing crank the crosshead up and down! I spent some time fitting the split bearing on the connecting rod to the crankshaft journal, but it still needs some wearing in. I just need to drill and tap the studs for the standard, and make the crosshead pin, and then I can have it turn over. |
| smfr:
[Moved from homemodelenginemachinist.com] Got some shop time in today, since it's a holiday! First up, I marked out and drilled the bolt holes in the standard: and drilled and tapped the soleplate for these bolts. I had left this until now because I was worried about getting the alignment right, and wanted to be able to assemble the crosshead and conrod with the crankshaft to make sure everything lined up. Luckily things fitted just fine. Next up was the crosshead bolt (which I called a pin earlier, but the plans refer to it as a bolt). This started as a bit of stainless from the scrap bin; the first part is a simple turning job, taking care to get a nice 1/4" fit to the conrod and crosshead: Checking the fit on the conrod: It's important here that the nut will bear down on the shoulder of the bolt, rather than the conrod arm, otherwise the nut may loosen when the engine runs. I have a bit to take off the yoke of the conrod by filing, but it's close. Then it's threaded 2BA, with an undercut at the end of the thread so that the nut seats nicely: I flipped it around, held it in a 1/4" collet, and carefully parted off the excess: then turned the head. Almost done: I'm using temporary fasteners for everything so far, hence the ugly nut. Oddly, the fastener set that came with these castings has been blackened. I'm not sure if Stuart shipped them that way for a while, or whether the previous owner did it. Or maybe it's just from storage? There's one more bit on this bolt/conrod to do, and that's a 1/16" pin that prevents the bolt from rotating. This sits right on the edge of bolt's shaft. Here I've drilled the corresponding hole in the conrod: I took care with the setup, using an edge finder on some 1/4" rod situated in the hole, then offsetting to find the center of this pin. I was worried about the teeny drill wandering into the main hole, but it was OK. Without changing the setup, I then dropped the crosshead bolt in, tightened the nut on the other end, and clamped it down to prevent it spinning. Then I could drill a matching 1/16" hole for the pin, and guarantee alignment: Final crosshead/conrod/bolt parts: I need to find a 1/16" pin somewhere. Any ideas? After some more fiddling to fit the conrod bearing to the crankshaft journal, I was able to put everything together and give it a spin on the lathe. It's all pretty tight, so needs a good bit of running in: http://www.youtube.com/watch?v=5z6fSfN6XRc (Sorry about the crappy vertical video.) |
| smfr:
[Moved from homemodelenginemachinist.com] Guess what I found in the old fixings jar? Not one, but two 1/16" pins :D The newer fixings set that I got recently from Stuart for this engine didn't have any, so I'm glad these castings came with their own fixings set. Made some good progress today. I'd been putting off milling the exhaust steam passage, but did so uneventfully, after carefully marking out the exhaust slot, and the exhaust hole on the side (with the same center height, of course). The two inlet holes were pretty wonky in the casting, and one is a bit wider than the other, so I tried to center the exhaust as best I could between them. Milling was starting with a 3/16" end mill, and finishing off with a 1/8", then the corners were filed square. I probably should have drilled the 1/4" exhaust hole first so I could just mill down until I hit it, but did it the other way around, and it worked out OK. Given that the steam ports aren't quite equally spaced, I wonder how smoothly the engine will reverse once complete. One possible solution would be to make a plate with accurate ports, mill a recess in the casting and silver solder it in, but I'm not keen on doing that unless I absolutely have to. While I had the cylinder set up, I also drilled and tapped the holes for the exhaust manifold thing, and the lagging screws. Interestingly, the older models used a 5BA lagging screw (left side below), and the newer ones a 7BA (right side; the screws are in the exhaust manifold holes; I'm just trying to compare them visually here); I chose 7BA for now. Now to drill for the drain cocks: spot-face, center drill, drill through and tap 3/16" 40TPI: and the cylinder done except for the stud holes on each end: So, lots of stud holes to drill and tap: 6 on one end, and 4 on the other. I broke out my recently purchased 4" Phase II rotary table, centered the table under mill (via an MT2 arbor in the center hole), then centered the cylinder casting on the table. Boy, clamping things on this teeny table is tricky! Once everything was aligned I cranked the carriage along by half the bolt hole diameter, and I'm ready to go! I drilled the top cover and the tapping holes at the same time (the cover was clamped for drilling), turning in 60° increments, then enlarged the holes in the cover to clearance size. Then I went back around the holes for tapping; I found that the rotary table was precise enough that I could accurately return to a hole position, which is nice. I started the taps in a chuck in the mill (turning by hand) to keep things straight. 6 holes tapped, and the moment of truth: does the cover fit? (Spot the odd stud out!) Yay! In fact it fits in any orientation, so I guess I counted the rotations right :D After that I did the 4 stud holes on the base on the cylinder. 4 holes this time, so line things up, rotate 45°, drill, crank 90°, drill, crank 90°etc. I jotted down the angles, and used those to double-check my handle-turning count. Drilling the standard really pushed the limits both of clearance on my mill, and clamping on the rotab. I could just get the drill into the chuck, and don't look too closely at my clamping job here :D I was relieved when all the drilling and tapping was complete without any broken-through holes and broken taps. Now for the fun part, assembly: Wow, this thing is beginning to look like an engine 8) Next up will be the piston rod gland. I'm a bit concerned about alignment there, having read another recent thread here about that. I have the right taps and dies (1/2" 26 TPI), but I wonder if single-point threading would be something to consider, having never done it before? Thanks for following along, Simon |
| smfr:
[Moved from homemodelenginemachinist.com] Dave, the packing gland is screwed in (with a hard-to-find 1/2" 26TPI BSB thread!). I actually made a quick tail post die holder for the die, and cut the thread already: but I did that after reaming for the piston rod, and I'm wondering if it would have been better to tap the bottom cylinder cover, screw it down onto something to simulate packing, and then ream it in place. The risk is that it then only lines up at that particular orientation. I think it's OK for it to be a little oversize though. Steve, I'm pretty happy with the Emco. The main limitation for milling is the tiny table (about 5" by 9", and deep rather than wide). Not even enough room for a decent 4" vice! I wish I'd kept the spare carriage that I had, so I could have ganged the two carriages together somehow. Simon |
| smfr:
[Moved from homemodelenginemachinist.com] I plucked up the courage to thread the bottom cylinder cover for the piston rod gland today this evening. To hold the cover, I put the soft jaws onto the 3-jaw chuck, clamped the jaws down onto a bit of stuck, and cut a lip to fit the cylinder cover, then removed the stock and clamped down on the part. Here I'm checking with the dial indicator; runout was about a thou, which seemed reasonable. Then I put a small bevel on the bore so that the tap would start concentrically: I was concerned about tap alignment, so fiddled around for a bit with shims under the leading edge of tailstock, and the drill in the chuck that I'd use to drill the part earlier, and got the drill sliding nicely into the hole. Then it was replaced with the tap, and tapping started under hand power, with the taper tap: With this size tap it wasn't long before the tap was starting to rotate in the chuck (despite backing out the tap often to clean the chips), so more desperate measures were called for! The steady rest made a handy way to keep the tap straight so I could apply more force with the tap wrench: I switched to the bottoming tap, then back to the taper tap, then back to the bottoming tap, and by the end was using two wrenches to turn the thing (but carefully!), and finally was done. Hey, I can make it finger-tight, and the piston rod still slides through :D The threads in the cast iron look terrible, but I'm not sure how much of that is my fault. These are HSS taps from Tracy Tools in Devon, UK, but they don't seem to cut as nicely as the HQS taps I have from Tap & Die. Simon |
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