Author Topic: Trevithick  (Read 8650 times)

Offline crueby

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Re: Trevithick
« Reply #210 on: October 18, 2020, 08:10:07 PM »
Brian, looks like you are well on your way to your next project of a steam saw ;)

Ooh, love that saw! Do you know what model/plans it is? Your build?

Offline Brian Rupnow

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Re: Trevithick
« Reply #211 on: October 18, 2020, 11:21:37 PM »
I've tried all of the tricks in the "Rupnow Magic Hat" and I am not able to get this thing to run using the 4 way valve. It is one of those engines that wants to run so badly that you can almost taste it, but it isn't happening. I have tried all of the different settings that I can think of, and have pinched my fingers so badly that I cried like a baby, but this just isn't going to run for me. This is not to say that the project is abandoned--Just that it isn't going to run with this 4 way valve. I can salvage most of the parts and make a Trevithick engine that runs with a more conventional slide valve. I hate to admit that I haven't been able to get this to work, but I have tried everything I can think of. Weirdly enough, I can make the model look more like the original Trevithick by using a conventional slide-valve than I could of if the 4 way valve had done the job.
« Last Edit: October 18, 2020, 11:28:40 PM by Brian Rupnow »

Offline crueby

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Re: Trevithick
« Reply #212 on: October 19, 2020, 03:39:20 AM »
Thinking through the valve motion, and remembering some things from the videos of the full size engines - had an idea. The way the driver had to manually run the valves during startup makes me wonder - if the motion of the piston rod and the slider is not quite enough to run the valve all the way to admitting steam in the other direction, but it depends on the speed of the hit from the tappet to drive the valve farther along to open the steam port in the other direction.... That would give you just that little bit of lag in the operation of the valve to let the crank go past the TDC/BDC positions....
Does that make sense? Need to go back and watch the video of the reproduction full size engine again to see the stopping point of the slider/tappet against the valve crank.
 :thinking:

Offline Jasonb

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Re: Trevithick
« Reply #213 on: October 19, 2020, 08:19:41 AM »
Ooh, love that saw! Do you know what model/plans it is? Your build?
[/quote]

It's one of Torsen's designs, though photos not showing at the moment
https://www.ts-modelldampfmaschinen.de/gussteilesaetze-modelldampfmaschinen/modelldampfmaschine-dampfsaege.html
« Last Edit: October 19, 2020, 08:39:05 AM by Jasonb »

Offline Zephyrin

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Re: Trevithick
« Reply #214 on: October 19, 2020, 09:27:46 AM »

I would say that the valve is not involved in this reciprocating movement, but it seems to me from the video (post #204), that it's the stroke of the connecting rod that is too big for the length of the cylinder...and can't go through the dead points. With a shorter piston or a shorter crank it will do it ...

I like the mood of your posts, very pleasant to read, thanks to share.

Offline Brian Rupnow

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Re: Trevithick
« Reply #215 on: October 19, 2020, 03:39:20 PM »
Boys, we're going to start down a new path today. I'm very disappointed that I didn't get this engine to run with the 4 way valve and I really, truly thought that I would. Ah well, so much for unbridled optimism.  The change of course is going to involve a more conventional steam slide valve on the cylinder. Due to restrictions based on everything having to fit inside the boiler, I am going to have to gear the crankshaft to a "camshaft" and mount the eccentric strap and eccentric on the camshaft. (it will revolve at the same speed as the crankshaft.) This means that the steam-chest will hang from the underside of the existing 3/4" diameter x 3" stroke cylinder, similar to the way it did on the Stephenson's Rocket. I will be getting rid of all of the exterior valve control rods and guides, and the rings with built in rod guides will revert back to being just simple rings around the ends of the boiler. The only visible difference is going to be at the smoke-stack end of the engine, where it will be possible to see the extra set of gears to operate the cam shaft, and different method of mounting the crankshaft and cam shaft. If this sounds like a lot of extra work, well, yes, it will be.-However, it's Covid time. Can't visit friends, can't go out for entertainment, can't even see my grandchildren nor take out good-wife for a restaurant meal. I'm just happy to have something fun to do!!!

« Last Edit: October 19, 2020, 03:48:07 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Trevithick
« Reply #216 on: October 19, 2020, 08:21:52 PM »
Just finished the big three hour "clean-up, slick-up, put all my tools away in the correct place" dance. I try and put my tools away as I use them, but when I get into the final lap of building something I get so excited that nothing gets put away properly. When I walk into my little machine shop and the floor "crunches", I know that it's about time for a sweeping and vacuuming.  My apologies to everyone who hoped to see this run with the 4 way valve.---I did too. My apologies to anyone who I may have snapped or snarled at on the forums. I'm not normally like that. This project hasn't stopped. Very little of my work will be lost, even the cylinder will remain the same. The 4 way valve gets tossed, and I gain a cam shaft and conventional slide valve to control the cylinder. Don't go away please. There is more to come, and I promise, it will be interesting.---Brian

Offline Brian Rupnow

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Re: Trevithick
« Reply #217 on: October 19, 2020, 11:18:58 PM »
Two 25 tooth gear blanks turned and that's all she wrote for today. O.D. and hubs are turned to size from 1144 stress proof steel. Center hole has been drilled and reamed to 5/16" diameter. Next time you see them they will have teeth cut and be mounted in place.