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Post by ettingtonliam on May 11, 2021 22:03:12 GMT
Thanks Don. So we have a strong leaning towards 567 for screwed fittings but that raises another related question or at least confirmation maybe? Lets take items like the steam chests and cylinder covers. I would suggest that the cylinder covers and at least the steam chest cover could do with a gasket method and system that is easy to dismantle? Should they be fitted with paper with some ter gunge or is 574 suitable for those i.e., are the parts easy to 'part' if 574 is used? Sorry for all the stupid questions but I am going through this the first time. Yes I have used liquid silicon on car parts or cork etc many years ago but they can always be tapped with a mallet to get them apart. Cylinder covers on a small engine would be wrecked. You could always follow full size practice and drill and tap a couple (better still, 3) of holes in each cover to take a jacking screw which will break the joint without recourse to more brutal methods.
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
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Post by smallbrother on May 11, 2021 22:15:57 GMT
Paper gaskets and making sure you tighten down the covers evenly; remember you don't need to go mad with the tightness of the nuts on the steam chest studs as they are most likely quite small. I bought a selection pack of paper gasket material from an ebay seller and as Pete says, it will last. I don't use a gasket sealant myself. I've never tried it without the sealant but I could be overdoing it I guess! Pete.
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don9f
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Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
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Post by don9f on May 11, 2021 22:33:00 GMT
Personally I use just flange sealant on the cylinder covers of my 9F, which are cast iron, held on by countersunk screws. When the screws are removed, a sharp tap on the edge with a flat punch has always removed them quite easily without damage. It might be a different story with a softer material like gunmetal and especially if studs are used, as the sealant might get round the studs and make the covers more reluctant to come off? If this is likely, then a gasket could be the better method.
Cheers Don
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Post by philh1aa on May 12, 2021 15:35:10 GMT
Liam,
I don't think the Rob Roy covers will tolerate another 3 holes but I like the idea. Getting 8off 6BA will be fun because the description tells you to take care with the passages obviously but also the cylinder drain cocks and the slide bars. I also need to miss the leading brake hangars with the fixing somehow - maybe a countersunk screw for that bit. The fixings certainly won't be equi-spaced though.
Looks like paper wins the vote. Dare I ask what everybody uses on the ferrules? Is that back to the 567?
Phil H
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JonL
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Post by JonL on May 12, 2021 16:29:45 GMT
I'm probably being a bit thick, which part are you referring to with ferrules?
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Post by philh1aa on May 13, 2021 12:52:05 GMT
The screwed fittings discussed so far include valves etc that have a threaded tail. That threaded tail screws into say a bush on the boiler or the cylinders for the drain cocks.
However, the other end of the valve e.g., a non return valve usually has a threaded section with a female cone. When you connect the pipe, it usually has a silver soldered ferrule backed by a nut. So I would imagine that Loctite 567 would work between the ferrule and the cone and tightened with the nut? I haven't made or got any of those yet but I think if that is also Loctite 567, I will have covered just about every bit of plumbing apart from the occasional 'O' ring.
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
Posts: 2,269
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Post by smallbrother on May 13, 2021 13:12:28 GMT
Phil - you don't need anything on those joints. Nip them up but don't go mad with the spanner.
Pete.
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JonL
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Post by JonL on May 13, 2021 13:58:55 GMT
As Pete says, they seldom give trouble. Its hard to describe a tightness without a torque! If you see one weeping on cold pressure test you can try nipping it up a little more then. Always keep an eye on the pipe though, if it twists rather than spinning inside the nut you can twist the pipe into a corkscrew if you are doing it blind.... as I may have clumisily done when I first started...
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Post by philh1aa on May 13, 2021 18:20:12 GMT
Thanks chaps. I have taken a note and I should be fairly comfortable with the plumbing now.
I had a couple of days wasted with jammed bevel gears on my Myford Super 7 apron. How or why it happened, I have no idea but I have stripped it, fixed it and back to making parts again. I'm still on the cylinder drain cock operating linkage.
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Post by philh1aa on Jun 7, 2021 13:59:42 GMT
I would really appreciate some help with this little snag please;
I have fitted the cylinders onto the frames complete with covers, pistons and piston rods. Unfortunately, I appear to have undercooked the distance between the cylinder centreline and the frames by 0.054" on one side and 0.039" on the other side. I have no idea how I managed that but we are where we are.
This means that the front coupling rod will clash with the main crossheads when it tries to rotate. I guess the unpleasant, messy correction is to add shims to move the cylinders out from the frames to their correct position.
However, even if I correct the cylinder position with shims to achieve the correct frame to centre distance (according to the drawings), the clearance between the moving bits (coupling rods and cross heads etc) is still frighteningly close. To give an example of the breakdown;
Axlebox to back of wheel = 1/16" Wheel thickness = 1/2" Coupling rod thickness = 1/4" Wheel/ axle end float = 1/32" (side to side clearance) Total = 27/32"
Frame to cylinder centre = 1 1/16" Cross heads = (3/16") i.e., 3/16" closer to the frames. Total = 7/8"
That leaves just 1/32" clearance between some very fast moving bits if everything has been made spot on. Is a miss by 1/32" as good as a mile on this or have other builders added a bit more? For example, I could easily add shim to make both sides correct + say another 0.010". The motion plates could easily move over to match.
Phil H
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mbrown
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Post by mbrown on Jun 7, 2021 17:27:07 GMT
Plenty of Rob Roys seem to have been built successfully to the published dimensions - and certainly in 2.5"G a 1/32" clearance between the crossheads and coupling rods etc would be more or less normal.
You best bet, IMHO, would be to make up thin doubler plates to embrace the whole frame opening through which the steam chests go, then you are only dealing with one part per side rather than lots of odd bits. The additional material in front of and behind the cylinder is of no consequence provided it is not excessively long. Given the odd discrepancies on either side, I would be tempted to make the doublers out of 1/16" plate and machine a little more off the cylinder where the discrepancy is only 0.039" so that both are even. That would give you an extra 10 thou or so on either side for added clearance if you feel you need it, and you can stick with the proper length of crankpin and thin down the connecting rod a little on the outer side, or lengthen the con rod to suit. Saves traying to make shims to precise thicknesses which is much harder than machining the cylinder flanges a bit more....
But no doubt others here will have other views - probably equally valid.
Good luck.
Malcolm
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Kevan
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Post by Kevan on Jun 7, 2021 17:29:06 GMT
I think this is a factor of the design. The Rob Roy I got as a part build has similar clearance issues and had been shimmed, however this compromised the valve rod alignment. Originally it had been put together without gaskets just hematite red sealer.
It is on the way back together with gaskets and without shims. I modified the front crank pin arrangement so that the screw head is fully flush with the rod face and I probably have about 15thou clear between crosshead and coupling rod.
Shimming the cylinder from the frame also means shimming the slide bar bracket or remaking them to allow the slide bars to sit out by the width of the shim.
Best of luck figuring out the most advantageous compromise for your locomotive.
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Post by philh1aa on Jun 7, 2021 18:46:13 GMT
OK,
Thanks Kevan and Malcolm. I've not heard of this issue before but knowing that 1/32" is at least not abnormal for small locomotives, I will proceed with simple shims for the cylinders.
Quickly looking up gauge sizes - it just so happens that 16g should work for one side and 18g for the other and I have those sizes in brass plate. I will just machine and drill two strips (one for the top and one for the bottom of each cylinder). These sizes will push both cylinders out by the same amount i.e., the correction plus 0.008".
I haven't fitted the angle to bolt the motion plates in position so they can be lined up to suit. Luckily, I haven't milled the slots in the cross heads yet either - so that is another way of getting everything lined up.
Kevan - I am expecting the 'cranked' valve cross head anyway - I was close to getting it lined up without the crank but it doesn't look difficult to make a slightly cranked one.
Thanks for your comments.
Phil H
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JonL
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Post by JonL on Jun 7, 2021 20:22:16 GMT
I didn't say anything earlier as i wanted to see what the more experienced people said, but i agree that the clearance you state doesn't seem abnormal.
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Post by philh1aa on Jun 8, 2021 14:21:08 GMT
Thanks Nobby.
I will finish off the crossheads with a central slot for the slide bars then dismantle everything to add the shims, gaskets and PTFE piston rings etc. John Baguley very kindly gave me some guidance on PTFE piston ring sizing - so no excuses now.
Very slow progress but the number of challenges (excuses) are starting to melt away.
Phil H
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Post by philh1aa on Jun 20, 2021 16:12:13 GMT
Opinions on this please. I have finished the cross heads and need to pin them to the piston rods. The design calls for a taper pin using a tapered reamer of course. They are a ridiculous price so I guess I could make one from silver steel?
However, for main brake operating spindle which is also 3/16" diameter. I just cross drilled and tapped a hole in the spindle at 8BA and used screws to hold the various pushing/ pulling bits onto it. It appears to have done a really good job. Is the tapered pin superior to that approach. Do I really need to make a tapered reamer?
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stevep
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Post by stevep on Jun 20, 2021 16:46:03 GMT
My Rob Roy crosshead is fitted with roll pins. They only need a parallel hole of the nominal diameter drilled through, and the roll pin hammered in.
Being hardened, I suspect they will have a superior shear strength to even a taper pin.
I wouldn't like to trust a screw threaded through.
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Post by philh1aa on Jun 20, 2021 18:27:57 GMT
Steve,
Thanks, that is a nicer option - or maybe even a close fitting parallel bolt rather than a screw.
Phil H
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stevep
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Post by stevep on Jun 20, 2021 18:53:40 GMT
Still prefer a hardened pin to a mild steel bolt.
Of course, you could follow full size and make a tapered cotter pin! :-)
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Post by philh1aa on Jun 20, 2021 19:33:43 GMT
Ah yes but we are then back to an even more complicated hole aren't we? :-(
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