Author Topic: Trevithick  (Read 27065 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 ;)

Not a valid vimeo URL
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:

Online 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.

Offline Brian Rupnow

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Re: Trevithick
« Reply #218 on: October 20, 2020, 03:34:30 PM »
Doing something a bit new and different. Normally, when steam-chests are used with a cylinder they are either both machined as one part from the same piece of material or soldered together, and all of the steam passages are internal inside the walls of the cylinder. In my case, I am retrofitting a steam-chest onto a cylinder which was previously operated by my 4 way valve. The steam lines are going to be external to the cylinder. I will solder brass "hose barbs" into the steam-chest and run flexible neoprene lines from the steam-chest to the cylinder ports. ( I know I cautioned against doing that but needs must.) I have never seen that done, but I can't think of any reason that it won't work.

Offline Brian Rupnow

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Re: Trevithick
« Reply #219 on: October 20, 2020, 09:43:08 PM »
It feels like I must have been taking "slow pills" today. I managed to work all day and make only one part. This is the sub base for the new slider valve. The four shcs in the corners attach it to the cylinder. The four tapped holes are where the steam-chest bolt to it. The tapped holes in the ends are drilled galleries that needed to be plugged after the fact, so they were tapped and #10 set screws threaded in to act as plugs.   There will be three tubes soldered into the block, two on one side and one on the other side.

Offline Brian Rupnow

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Re: Trevithick
« Reply #220 on: October 21, 2020, 06:26:02 PM »
So far today, I've got a stem-chest and a steam-chest cover. I might have the internal slider by the end of the day. I'm anxious to see this controlling the cylinder.

Offline Brian Rupnow

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Re: Trevithick
« Reply #221 on: October 22, 2020, 12:12:23 AM »
I did finish all of my slide valve business today. This is the slider, the nut, and the actuating rod. The brass steam-chest is not shown in this picture, because I managed to drill four holes in the wrong place. The holes are not in a critical area, and brass is about the same price as gold around here, so they have been filled with J.B. Weld and the steam-chest has been set aside to cure for 24 hours.  Tomorrow I will make the eccentric and it's mount.

Offline Brian Rupnow

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Re: Trevithick
« Reply #222 on: October 22, 2020, 01:59:32 PM »
Last night I lay in bed reviewing what I had done yesterday, and came to the realization that I needed to get steam (air) into the new steam-chest. It already has 3 outlet tubes--One to go to the front of the cylinder, one to go to the rear of the cylinder, and one to go to exhaust. This morning I added an inlet tube to the steam-chest cover.

Offline Brian Rupnow

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Re: Trevithick
« Reply #223 on: October 22, 2020, 04:17:39 PM »
Okay, we are back up and headed for assembly. One trick I'd like to show. In the center of the brass steam chest you will see two .093" reamed holes. Dowels will fit thru them into 0.093" holes in the adapter plate below, (or it could be into a cylinder). They will not extend up beyond the top of the steam-chest. Why are they there?---Because, when you are setting these engines up to run, it is very important to know just where that slider is in regard to everything else. If you take off the steam-chest cover so you can see the slider, then it all falls apart in your hands and you lose all track of where the slider was in reference to the steam chest. With these dowels in place (loctited into the adapter plate or cylinder) you can remove the steam-chest cover plate and the steam-chest remains in place, so that you can see where the slider is in regard to the steam-chest.

Offline Brian Rupnow

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Re: Trevithick
« Reply #224 on: October 23, 2020, 06:54:55 PM »
Today we have something to show. I have removed the 4 way valve which I copied from Trevithick's original engine ( I couldn't get the engine to work with that valve on it), and replaced it with a more conventional slide valve which will be driven by an eccentric cam on a countershaft, which is driven at 1:1 ratio by the crankshaft. The attached video shows the operation of the cylinder when I manually move the slide valve control rod with a pair of pliers. This is very encouraging, and I will now move on to the countershaft and eccentric which attach to the engine end-plate right below the crankshaft. The air hissing noise you hear is due to the fact that I haven't lapped the face of the slider to the steel adapter plate it slides on yet. Sometimes you get lucky and don't have to do that, other times you do.

<a href="https://www.youtube.com/watch?v=kWgNeR_SWhQ" target="_blank">http://www.youtube.com/watch?v=kWgNeR_SWhQ</a>
« Last Edit: October 23, 2020, 09:33:54 PM by Brian Rupnow »

 

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