Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 13, 2019 18:13:19 GMT
Having reached the goal of getting Blowfly running on air, I've decided to let it sit in the background a bit while I work on something I can actually afford to finish. So I've started on a 3½" gauge Tich (small boiler). It's a design that's fascinated me since I was a child, and with a few exceptions (cylinders being the most obvious), I'm pretty sure I already have most of what's needed to build it (including materials for the boiler). A boiler for Blowfly is wildly out of my budget for a variety of reasons, whereas Tich's boiler is small enough (and cheap enough), that I'm quite happy to build and test one on my own, and if I ever need to I can just make another for club running. I'd considered building a Minnie traction engine, but I just prefer loco's. Thus my general aim is to focus on getting a running Tich, while still being able to fiddle about with fittings and bits for Blowfly as the mood takes me. So I've made a start on Tich. First was the bufferbeams. One thing I'm doing with Tich is redrawing everything in metric - a good chance to learn to use OnShape - mostly this is just a matter of converting an imperial measurement, and changing bolt/rivet/pin sizes to the nearest metric size. There is however, also the odd place where I'm rounding to an equivalent but 'neat' metric value, so the bufferbeams are 20x20x3, which is a little larger than ¾" (19.05mm). I used of a lump of aluminium as a fixture in the mill, then set about drilling holes, and milling the beams to size. Scribbling down the dial readings to help with repeating for the second one. That all went rather well, and flipping them upside down meant I could square up the corner of the angle. The angle I have is a touch over size, which also meant I could square up the bottom edge nicely. A bit more hacksawing and milling meant the bufferbeams were done, with the exception of the coupling holes not being opened out to squares; partially because I'm trying to find the tiny square file, and partially because I might oversize the rear hole for a clevis to couple up to a driving truck with.
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 13, 2019 19:06:41 GMT
LBSC designed Tich with 3/32" (2.38mm) thick frames, but I've opted for 3mm. There's two reasons for this, the first being that it's what I have, and the second being that I figure a little extra weight would be an advantage. The frames are therefore a little closer together, so that the overall width is the same. A bit of elbow grease to cut the frames from some plate, then they were bolted together and put in the mill. The bolt holes at the end were put where they'd be cut off, while the larger ones for clamping to the mill table were inside the horns. Of course, the frames are 327mm long, and I've only got 220mm of table travel, so cleaning up the top edge took two goes and a bit of fiddling with the DTI to get the frames square twice. Then with the dials zeroed to the top and front, the drilling began; this would be easier with a DRO, but as long as one allows for backlash, it's not too bad. First moving to the nearest lower multiple of 10 handwheel turns, means one can use a ruler to check that no miscounting occurred, as any variation is plainly obvious. One of the advantages of drawing the part in CAD first, was that I could then pull the coordinates of each hole out and put them on the drawing, which simplified getting the holes for the cylinders and motion brackets in the right place. I also spotted the top corners of the horns at this stage, as a guide for milling them. After milling out the horns, I removed the sideframes from the mill, and gave them a cleanup. Then hacksawed and filed to final shape, before unbolting them; having put bolts into some of the holes as I was drilling them. Then of course I balanced things in place for a look; onto the angles to actually bolt and rivet things together next. Also, a size comparison, with Tich's chassis on top of Blowfly's chassis:
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timb
Statesman
Posts: 512
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Post by timb on Jan 13, 2019 20:02:12 GMT
Brings back memories Lisa, a good start!!
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weary
Part of the e-furniture
Posts: 290
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Post by weary on Jan 13, 2019 20:26:52 GMT
Hello Lisa,
If you are intending to fit brakes as drawn by LBSC (it looks like you have designed-in the upper hanging pivot holes) then you can save yourself a bit of irritation & faffin' around later-on and take approx. 1/8" depth off a short section of the lower edge of the frames ahead of the rear wheels where the bottom of the brake-hangers will be. If you fail to do this then the brake cross-beams will foul the frames - there is not a lot of space to lengthen the brake hangers as an alternative as the loco is so low slung! There is no issue with the front-wheel brake cross-beam fouling the frame as the cut-away angle of the frames allows clearance in that location. Measurements etc., from memory I'm afraid, but if you take a look at your drawings with specific reference to this location and the brake-hangers then all will become clear as to your options.
Regards, Phil.
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 13, 2019 20:58:21 GMT
Hi Phil, I've only got an incomplete set of plans for Tich, so most of the breakgear is missing. But I'm aware of that issue and have made adjustments while redrawing, so it should all work out. Ta.
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 14, 2019 17:12:27 GMT
I've just been drawing the pump stretcher, this takes a little longer than it perhaps otherwise should as I'm still getting used to OnShape; but learning OnShape is part of the purpose behind this project, so a little time is fine. LBSC suggested bending from a single piece, or using a casting, while another option could be to use plate and angle. I've decided against all three of these methods though, and am aiming for a silver soldered fabrication from three parts, with tabs to aid assembly. I've also drawn in an extra hole for the lubricator drive rod; something I've seen others suddenly notice the absence of when further along in construction.
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Post by Roger on Jan 14, 2019 19:26:17 GMT
I've just been drawing the pump stretcher, this takes a little longer than it perhaps otherwise should as I'm still getting used to OnShape; but learning OnShape is part of the purpose behind this project, so a little time is fine. LBSC suggested bending from a single piece, or using a casting, while another option could be to use plate and angle. I've decided against all three of these methods though, and am aiming for a silver soldered fabrication from three parts, with tabs to aid assembly. I've also drawn in an extra hole for the lubricator drive rod; something I've seen others suddenly notice the absence of when further along in construction. Could this not just be a piece of 6mm thick plate with the holes tapped in the ends?
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 14, 2019 20:12:28 GMT
Could this not just be a piece of 6mm thick plate with the holes tapped in the ends? It could, it could also be milled from 10mm plate. I figure this is a nice compromise between appearance, ease of manufacture, and functionality.
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Post by David on Jan 14, 2019 23:05:51 GMT
It is interesting how people design things based upon their skills, experience, and equipment. I've often looked at a part and wondered 'why on earth would you do it that way?' It might take the designer 5 minutes but take me 5 days to get it machined and put together the same way.
Aside from the times there is a mechanical reason I didn't realise was behind the design I guess the designer would have the same reaction to my idea for how that part would have looked/been made.
Of course sometimes I go down my route and find it's a dead-end and go back to what the designer said because they've built god-knows-how-many projects and knew there was a problem coming!
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Post by cnr6400 on Jan 15, 2019 7:45:48 GMT
Hi Lisa, another "thinking ahead" suggestion: If the hole for the pump were made a slot open at the bottom under the locomotive, getting the pump in and out for service would be far easier. Just food for thought.
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 15, 2019 8:56:51 GMT
I'd worry about that weakening the stretcher, particularly as it's the only stretcher. But it's worth a thought. It would also mean some changes to the pump though, as LBSC intended the stretcher to be threaded, with the pump screwed into place and secured with a locknut. Here's what I have drawn of the chassis so far: It's incredibly useful to be able to assemble it all virtually, and know that parts do actually fit where they should.
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Post by David on Jan 15, 2019 9:41:58 GMT
If you're just learning the software now you're powering ahead with it, great job.
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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 Jan 15, 2019 18:04:41 GMT
Hi Lisa,
The extra slot in the stretcher would certainly weaken it as a load carrier but as a stiffening mechanism between frames I don't think it would make a noticeable difference.
Never tried it mind, but it sounds a great idea from Adam.
Pete.
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Post by cnr6400 on Jan 16, 2019 3:06:38 GMT
Hi Lisa, Your CAD looks great. 3D is terrific for visualizing machines, isn't it? Takes a while to learn but well worth it.
Anyway , back to the slot in the stretcher - I only mentioned it as I have read the Tich book and seen a number of Tich locomotives, and they all seem to have to drop an axle to get the pump in or out. Got to be a better way - pumps do need servicing once in a while. One idea - make a horizontal stiffener flange above to slot to get some strength back. Then fit an angle bracket to the pump, maybe threaded for the pump and nutted as LBSC had in mind. Then use a couple of vertical screws in the horizontal part of the angle bracket to secure the pump/bracket assy into tapped holes in the stretcher flange. If the stretcher is a solid plate you would just tap into the plate edge. Vertical access for any screws or serviceable parts under the loco was not on LBSC's mind but it is on mine! Just food for thought. Good luck with your build.
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Post by Roger on Jan 16, 2019 6:01:19 GMT
Hi Lisa, Your CAD looks great. 3D is terrific for visualizing machines, isn't it? Takes a while to learn but well worth it. Anyway , back to the slot in the stretcher - I only mentioned it as I have read the Tich book and seen a number of Tich locomotives, and they all seem to have to drop an axle to get the pump in or out. Got to be a better way - pumps do need servicing once in a while. One idea - make a horizontal stiffener flange above to slot to get some strength back. Then fit an angle bracket to the pump, maybe threaded for the pump and nutted as LBSC had in mind. Then use a couple of vertical screws in the horizontal part of the angle bracket to secure the pump/bracket assy into tapped holes in the stretcher flange. If the stretcher is a solid plate you would just tap into the plate edge. Vertical access for any screws or serviceable parts under the loco was not on LBSC's mind but it is on mine! Just food for thought. Good luck with your build. I'm not sure why you would want to get the axle pump out unless it's worn out. This is not the sort of locomotive that's going to get used every week, they're more of a novelty. I would have thought the pump would last forever. Even if you do have to remove an axle, is that a big deal on such a simple locomotive?
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 16, 2019 8:14:05 GMT
LBSC's pump design looks rather complex and prone to failure tbh, it wouldn't suprise me if it did need regular removal for maintenance; I'm going to modify it to something I know works well.
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weary
Part of the e-furniture
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Post by weary on Jan 16, 2019 12:24:29 GMT
'Ello,
Looking at your pump stretcher:
The hole that you have shown for the lubricator drive is an elegant solution to the 'as designed' bent drive-shaft passing below the pump-stay and leading axle. However, the hole that you have designed in looks to be on the same line as ("level with") the axle; if you follow LBSCs oil-pump location then you will have to joggle the drive anyway (slightly?) upwards to avoid (and to go over rather than under?) the axle. There is about 20mm between the pump stay and the axle(?). Of course you may have this covered and/or I may have misunderstood your excellent rendition of the plans. Depending on your exact layout and location of the oil-pump the drive-shaft hole may need moving up slightly or, if a significant joggle is still required consideration given to whether it is a worthwhile modification given your concerns about stay strength.
As regards the water pump itself maybe worth considering using a 1/4" or 6mm diameter pump piston which would be more than adequate for the job rather than the as designed 5/16" 8mm item. This would potentially allow you to thread the fixing hole in the pump stay M10 rather than M12 (1/2") as designed. I vaguely recall that LBSC's own Tich had a 3/16" (5mm) pump piston. Of course the size of the pump depends on where and how you drive, how you prefer matters to proceed (quick fill vs slow fill)..... and your attitude toward 'cruelty to small locos' regarding loads to be hauled! LBSCs own personal track was a level oval, so the demands on his locos may have been relatively reduced and he always applied "monkey gland treatment" to enhance the efficiency of his own locos, though I believe that he enjoyed a bit of speeding around! There is a thread on here somewhere about calculating pump requirements I think. If you later decide that you prefer a larger pump then opening out the M10 hole to M12 and making a new pump would be relatively easy, and given the topic heading......cheap!
Plus, if you are carrying out a bit of a redesign around the water pump maybe worth considering a front axle drive? I think that you know already that the original loco that LBSC used as the basis of Tich had this feature. Whilst requiring an indirect drive to the pump itself this would resolve some of the issues around the very limited depth of ashpan and hot, dirty, and tricky to get to location of the LBSC rear axle drive on this particular design.
Just a few off the top thoughts - hopefully not too intrusive to your current considerations.
Are you missing any currently crucial dimensions and/or drawings? You mentioned that you did not have the full set of drawings.....
Regards,
Phil
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JonL
Elder Statesman
WWSME (Wiltshire)
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Post by JonL on Jan 16, 2019 12:39:11 GMT
Followed with interest.
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 16, 2019 16:08:40 GMT
The hole that you have shown for the lubricator drive is an elegant solution to the 'as designed' bent drive-shaft passing below the pump-stay and leading axle. However, the hole that you have designed in looks to be on the same line as ("level with") the axle; if you follow LBSCs oil-pump location then you will have to joggle the drive anyway (slightly?) upwards to avoid (and to go over rather than under?) the axle. There is about 20mm between the pump stay and the axle(?). Of course you may have this covered and/or I may have misunderstood your excellent rendition of the plans. Depending on your exact layout and location of the oil-pump the drive-shaft hole may need moving up slightly or, if a significant joggle is still required consideration given to whether it is a worthwhile modification given your concerns about stay strength. Yeah, this occurred to me when I assembled it all in CAD, I've since moved the hole up a few millimetres so that the drive shaft clears the front axle. As regards the water pump itself maybe worth considering using a 1/4" or 6mm diameter pump piston which would be more than adequate for the job rather than the as designed 5/16" 8mm item. This would potentially allow you to thread the fixing hole in the pump stay M10 rather than M12 (1/2") as designed. I vaguely recall that LBSC's own Tich had a 3/16" (5mm) pump piston. Of course the size of the pump depends on where and how you drive, how you prefer matters to proceed (quick fill vs slow fill)..... and your attitude toward 'cruelty to small locos' regarding loads to be hauled! LBSCs own personal track was a level oval, so the demands on his locos may have been relatively reduced and he always applied "monkey gland treatment" to enhance the efficiency of his own locos, though I believe that he enjoyed a bit of speeding around! There is a thread on here somewhere about calculating pump requirements I think. If you later decide that you prefer a larger pump then opening out the M10 hole to M12 and making a new pump would be relatively easy, and given the topic heading......cheap! LBSC's pump ram/piston is an odd shape with multiple sizes, I think a plain ram of 6.5-7mm would probably be equivalent to his design, in terms of volume pumped. So 6mm would work nicely... on the other hand, I have some leftover 8mm stainless steel from Blowfly's piston rods, so we shall see. Plus, if you are carrying out a bit of a redesign around the water pump maybe worth considering a front axle drive? I think that you know already that the original loco that LBSC used as the basis of Tich had this feature. Whilst requiring an indirect drive to the pump itself this would resolve some of the issues around the very limited depth of ashpan and hot, dirty, and tricky to get to location of the LBSC rear axle drive on this particular design. I like the simplicity of the rear axle drive, though the front axle drive has its advantages as you say. Probably the simplest option would be to just turn the pump around, and use an oval-shaped follower on an eccentric on the front axle; something akin to how a lot of mechanical lubricators are made. This would also simplify the lubricator drive, as it wouldn't need to pass through a stretcher. Worth a ponder I think. Just a few off the top thoughts - hopefully not too intrusive to your current considerations. It's all food for thought. Are you missing any currently crucial dimensions and/or drawings? You mentioned that you did not have the full set of drawings. I've got scans of most of the original articles, which gives me everything to make a working loco, but I'm missing most of the brakes, and only have the GA to go by for the cab and tanks.
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Lisa
Statesman
Posts: 806
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Post by Lisa on Jan 17, 2019 19:02:18 GMT
Milling the tabs on the pump stretcher is taking a while, but I think (hope!) it will be worth it when it comes to assembly. I'm making them all from one strip that's been milled to the right height, then cutting in each piece and the tabs, leaving about 0.2mm to hold it all solid while machining. I'm aiming to make it about 1mm over length, so I can then mill it square and to length, then hole drilling will come last.
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