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Post by joanlluch on Oct 15, 2016 17:38:45 GMT
Roger, I still do not see the point. What you showed modeled in your post above is a different scenario, than my drain valves no? If you seal on a diameter where you remove the thread and on the inside of a pocket, the flange just screws up to the face and doesn't compress the 'O' ring. Ok, that was already obvious. By your initial post I thought you referred to something else. The "flange" (valve) will not necessarily screw to the face, because it must be set at a particular angle before it screws completely. So in order to have some control of the screwing torque to make sure it won't unscrew, the o-ring should still surface a bit over the face, so you still can decide which one is the last screwing turn. My whole point is that the o-ring must prevent it to unscrew, not just seal.
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Post by Roger on Oct 15, 2016 17:56:48 GMT
I don't think that it's a good idea to use an 'O' ring as a friction retainer. I'd use a metal to metal contact done up tightly to hold it in place.
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Post by dampflokfreund on Oct 15, 2016 18:31:31 GMT
Wow, this is such an amazing project. I love how you use modern technology to help build your loco. The chassis looks so complex and well built already, nice job!
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Post by joanlluch on Oct 15, 2016 18:35:12 GMT
I don't think that it's a good idea to use an 'O' ring as a friction retainer. I'd use a metal to metal contact done up tightly to hold it in place. I don't know how to do this. Roger, my question from the very beginning was about sugestions on alternative ways to fix the valve as I didn't like the current way based on o-ring friction. By your answer the solution looks pretty obvious to you, but it is not to me. I actually ask for suggestions that would not rely on the o-ring, not the opposite. Please reread my original post. You are welcome to post a solution if you have any. I don't want to type anything else because my hands hurt very badly already. Thanks.
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Post by joanlluch on Oct 15, 2016 18:45:40 GMT
Wow, this is such an amazing project. I love how you use modern technology to help build your loco. The chassis looks so complex and well built already, nice job! Thanks for your comment. I think the strongest point of this build is that it is different from all the rest in the sense that I attempt to make a (meccano like) locomotive from my own design while most model engineers build a model locomotive based on existing plans or by scaling down a real one. Every approach requires a different set of skills.
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Post by Roger on Oct 15, 2016 19:37:19 GMT
Hi Joan, I see what you're getting at now. I was thinking about the situation where you hadn't already got the threads cut and forgetting that you can't screw them up tight because they would be out of position. I think you may have to use copper washers carefully adjusted to allow them to be screwed down tightly at the point where they are at the right position. You can get them made too long, do them up tight and then see what angle they need to make to end up square.
The easiest solution is to bond them in with Loctite like Lisa suggested. Actually, since they don't go in deep enough, can you carefully tap them deeper little by little so that they end up at the right angle?
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Post by springcrocus on Oct 15, 2016 21:50:50 GMT
OK, Joan, maybe a complete rethink. first, make the valves as you have BUT make the thread into a plain section and add an "O" ring groove near the root. In the cylinder, plain bore the tapped hole to suit the turned section of the valve. At this point, you can push the valve in and it will seal, but steam pressure will blow it out again. Now make a bracket which stretches between both valves and bolt it to the cylinder to hold them in place. I can't draw but this sketch gives some idea of what I mean. Hopefully, it will give you a starting point to come up with a solution.
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Post by Lisa on Oct 16, 2016 5:45:37 GMT
Hi Joan, I see what you're getting at now. I was thinking about the situation where you hadn't already got the threads cut and forgetting that you can't screw them up tight because they would be out of position. I think you may have to use copper washers carefully adjusted to allow them to be screwed down tightly at the point where they are at the right position. You can get them made too long, do them up tight and then see what angle they need to make to end up square. The easiest solution is to bond them in with Loctite like Lisa suggested. Actually, since they don't go in deep enough, can you carefully tap them deeper little by little so that they end up at the right angle? Uh, just to be clear the purpose of the jointing compound I use is to seal the thread, not to lock it in place; the thread can still be unscrewed quite easily, hence the suggestion of a locknut to aid in fixing the fitting at the correct angle. Though some compound on the thread, and carefully tapping it so it tightens at the right place would probably be a better solution than a locknut.
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Post by Roger on Oct 16, 2016 7:03:50 GMT
Another thought is a variation of Steve's idea. You could add a flat on the inside faces of the drain cocks, and screw a bar onto the face of the cylinder like Steve shows. The bar would be flat though, and its length made to be a very close fit. That would stop them from unscrewing, but you'd need sealant on the threads.
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Post by joanlluch on Oct 16, 2016 9:28:51 GMT
OK, Joan, maybe a complete rethink. first, make the valves as you have BUT make the thread into a plain section and add an "O" ring groove near the root. In the cylinder, plain bore the tapped hole to suit the turned section of the valve. At this point, you can push the valve in and it will seal, but steam pressure will blow it out again. Now make a bracket which stretches between both valves and bolt it to the cylinder to hold them in place... Hi Steve. I really like this idea. It's totally in line with the essence of my build. I can think on a bracket design as you suggest that clamps the valves on the cylinder block but at the same time it can feature a flat surface that matches the inner side of the valve, so to prevent it from wanting to turn. Now, this requires re-drilling the female thread on the cylinder block to 8mm and making again the body of the valves. Or turning the valve and add a 8mm OD cylindrical sleeve in the place of the male thread. I will model it as soon as I am able to see how it would look. (my CAD computer is still being repaired) So thanks for that.
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Post by joanlluch on Oct 16, 2016 9:37:01 GMT
Another thought is a variation of Steve's idea. You could add a flat on the inside faces of the drain cocks, and screw a bar onto the face of the cylinder like Steve shows. The bar would be flat though, and its length made to be a very close fit. That would stop them from unscrewing, but you'd need sealant on the threads. Hi Roger, I suppose you mean adding a precisely machined flat section, a flat section is already there because of course the drain valves are 'cube' shaped. Still, I like more the Steve solution because it gets rid of the screw thread, which is to some extend the source of the trouble as it prevents the valve from exactly matting the cylinder block face.
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uuu
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Post by uuu on Oct 16, 2016 15:00:11 GMT
Jessie is drawn with a slight taper on the male thread.
Wilf
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Post by joanlluch on Oct 18, 2016 19:56:17 GMT
The reversing gear is made and assembled. Following some pictures: I used a commercially available TR10x2 stainless rod with bronze nut. "Husillo" by joan lluch, on Flickr The rod is left hand threaded because according to my choice I want the locomotive to go forward when I turn the reversing handle clockwise, and it will go backward when I rotate it anticlockwise. The total travel as designed for my loco is 32mm, so this means 8 turns to each side from the neutral position to full forward or to full reverse. Canvi de marxes by joan lluch, on Flickr The provisional handle shown in the picture is the same I will use in the locomotive cabin, connection to the handle in the cabin will be by means of a cylindrical rod with cardan joints at each end which will be assembled at a later stage. And two more pictures showing all the rods and levers required up to the valve gear mechanism. The photos are taken with the gear in neutral position. Canvi de marxes by joan lluch, on Flickr Canvi de marxes by joan lluch, on Flickr
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Post by joanlluch on Oct 21, 2016 17:45:29 GMT
Some more progress has been made. Amb pistons. by joan lluch, on Flickr The above is a picture of the locomotive on a small section of track to allow it to roll. The picture shows the cylinders and pistons already assembled as well as the 3D printed crosshead connected to the main rod. By the way, my Windows computer is already repaired and fortunately everything seems to be on place. It's the one on the left in the following picture. Lloc de treball by joan lluch, on Flickr Also, a newer version of the 3D CAD software has been installed as I had not updated it since It was first installed several years ago. I am now performing online backups of the documents folder to CrashPlan service through a shared folder in my Mac OS computer (shown on the right). I continue performing the local copies to the Mac, which in turn is automatically backed up, as I used to do before (although not as often as I should). My Windows computer is not connected to the Internet, but just to my local network. If I do not find any major issue, I expect tomorrow to assemble the valve, valve piston, valve rod, union link and combination lever on both sides of the locomotive. On Sunday, I will try to get some help to bring the locomotive to the tracks. I want it to roll on the tracks for a while (pulled by an electric locomotive) so that the piston rings fully adapt to the cylinder bore and the locomotive looses some stiffness before it is ready for running on air.
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Post by uuu on Oct 21, 2016 18:22:46 GMT
Are you going to run it in backwards, or forwards? I favour backwards.
Wilf
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Post by joanlluch on Oct 21, 2016 18:32:49 GMT
Are you going to run it in backwards, or forwards? I favour backwards. Wilf Hi Wilf, To be honest, I haven't given a thought on that. In principle I was going to run it forwards (pulled from the front), but for no particular reason. Is there a reason to do the opposite?
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Post by Roger on Oct 21, 2016 23:32:17 GMT
I imagine that a chassis with plain bearings ought to be run in reverse so that the direction of loading is the same as when it's pulling a load. For a chassis with rolling contact bearings, I don't think it makes any difference. I suppose you could argue that the chassis ought to be run with the reverser in both forward and backward positions to make sure that the mechanism is worked in both positions, although it's going to run more in forward gear of course.
I suppose the closest you can get to how it will run in forward gear is to pull it backwards while leaving it in forward gear. Personally, I think I'd do both and also try forward and backward gear to make sure it's all free.
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Post by runner42 on Oct 22, 2016 5:20:28 GMT
Is it simply under running conditions the pistons are driving the wheels, but pulling it along the wheels are driving the pistons so to simulate the driving conditions pulling it backwards is closest to normal operation? LOL
Brian
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Post by uuu on Oct 22, 2016 6:35:03 GMT
I was thinking of the load on the crossheads, mainly.
Wilf
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Post by joanlluch on Oct 22, 2016 7:34:59 GMT
HI all,
Oh, I can see now your points on going backwards, it has a lot of sense. My particular loco has flat sliding bearings for everything except the wheels. Specifically, flat bearings are used where a swing movement exists (connection rod, and baker valve gear mechanism) as opposed to full rotation. So by running the loco backwards these bearings will indeed receive loads on the same bearing surfaces than in normal forwards operation with steam. For this to be right I must set the gear in forward and run the loco backwards. Thanks for pointing that out and your suggestions!!
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