Author Topic: Stephenson’s Rocket  (Read 7089 times)

Offline Admiral_dk

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Re: Stephenson’s Rocket
« Reply #45 on: October 16, 2023, 09:43:48 PM »
Great looking result so far  :praise2:

Per  :cheers:

Offline RReid

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Re: Stephenson’s Rocket
« Reply #46 on: October 23, 2023, 03:12:44 PM »
Excellent!!  :ThumbsUp: :popcorn:
Regards,
Ron

Offline Bob Wild

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Re: Stephenson’s Rocket
« Reply #47 on: November 04, 2023, 01:37:19 PM »
Splashed out and bought the drawing from the NRM which covered the valve gear and eccentrics. The detail was perfect and legible. After much head scratching and reading Bailey and Glithero's book, I finally manged to work out how it all was put together. I wanted to animate the assembly in Solid Edge so I could be happy that it would indeed fit. So, working out how it worked and how on earth to use animation in Solid Edge  took ages. But I cracked it in the end. For all Glithero's genius, he did not describe how it really worked  (at least to my simple mind), so here is a description and drawing if anyone is interested:

The two eccentrics are keyed to a sliding collar which is free to rotate on the front axle. A sliding fork between them is used to engage one or the other dog clutch which are keyed to the front axle. Each eccentric drives an eccentric rod which is hinged to accommodate the transverse movement of the eccentrics. The eccentrics are connected via a bell crank which is keyed to the countershaft. The countershaft is actually in two pieces; an inner and an outer which is free to rotate on the inner. Two further keyed bell cranks drive the gab rods. Each one has a semi-circular groove which engage with the valve levers. The valve levers are keyed to the valve shaft, but it can be seen that we only want one at a time to be engaged. So there is a keep plate (not shown in the drawing) which can be slid over the semi-circular groove when the gab shaft is lifted clear. Yet another crank transmits the motion of the valve shaft to the valve rod and the slide valve. It must have been a challenge to change gear. The gab rod had to be disengaged from the valve shaft, the keeper slid across, the the other one engaged and the sliding fork moved the engage the other eccentric.

I think this is made more clear in the diagram and the animation. Some very fiddly bits to build. I've no chance of using keyways in a 1/16 dia shaft, so I'll have to think of an alternative means of fastening (any suggestion?). Oh, and I forgot to mention that the NRM drawings are in fractions (down to the nearest 1/128 inch) at 1/8 scale whereas mine is 1/12 scale in metric!

Bob

<a href="https://www.youtube.com/watch?v=QYyMVBAUf08" target="_blank">http://www.youtube.com/watch?v=QYyMVBAUf08</a>


Online Kim

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Re: Stephenson’s Rocket
« Reply #48 on: November 04, 2023, 03:38:41 PM »
Wow!  That's quite the mechanism there, Bob!  Excellent sleuthing work to figure it out. And nice animation too  :ThumbsUp: :popcorn: :popcorn:

I still don't really follow how it all works.  I can see things moving, and that makes sense, but I don't see how it engages and disengages.  Maybe that has something to do with things that aren't shown in the drawing?  And how do you engage the handles when they are moving about all over the place?  That seems kind of dangerous, doesn't it?

I'll keep following along and hopefully as you complete parts it will become more clear how it all works and fits together.

Enjoying your build!
Kim

Offline Bob Wild

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Re: Stephenson’s Rocket
« Reply #49 on: November 06, 2023, 10:11:40 AM »
Hi Kim. Oh dear, that is my fault for not explaining my understanding of how it works. Here's a copy of the NRM drawing of the end of the Gab Rod and Catch (keep). The Gab Rod can be lifted and disengaged when the catch is slid back, and when that is done the catch is slid over the slot to prevent the Gab from engaging. I agree it all sounds very hairy, and the engine driver probably needed three hands. I'm not convinced that my understanding is correct, and I stand to be corrected by any of the experts out there. Another interesting fact is that you couldn't change gear when the engine was stationary. It had to be moving for the dog clutch to work!

Bob

Online Kim

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Re: Stephenson’s Rocket
« Reply #50 on: November 06, 2023, 09:28:09 PM »
That seems like a very complex set of steps for the operator to do!  The drawing does help explain the Gab Catches for sure, thanks for posting it.

Very interesting build!
Kim

Offline Bob Wild

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Re: Stephenson’s Rocket
« Reply #51 on: November 28, 2023, 04:44:45 PM »
Wow!  That's quite the mechanism there, Bob!  Excellent sleuthing work to figure it out. And nice animation too  :ThumbsUp: :popcorn: :popcorn:

I still don't really follow how it all works.  I can see things moving, and that makes sense, but I don't see how it engages and disengages.  Maybe that has something to do with things that aren't shown in the drawing?  And how do you engage the handles when they are moving about all over the place?  That seems kind of dangerous, doesn't it?

I'll keep following along and hopefully as you complete parts it will become more clear how it all works and fits together.

Enjoying your build!
Kim

Kim, ignore my previous explanation of how it works. It's rubbish and all wrong. I have finally cracked it. Like all good engineering the beauty is in it's simplicity and elegance (once you have got your head round the drawings!).

The eccentrics are mounted 90 degrees apart on the sliding sleeve. The left eccentric drives the left cylinder and the right eccentric drives the right cylinder thus the two cylinders drive the two driving wheels separated by 90 degrees. The right eccentric drives the inner countershaft via the eccentric rod, and then the gab rod drives the valve lever and inner drive shaft (not shown in my original drawing and hence the right cylinder. Similarly the left eccentric drives the left cylinder with the outer shafts a sliding fit on the inner shafts. Thus the gab rods are permanently engaged. The key to reversing is the relative angle of the driving dogs which are keyed to the axle. They are offset so that the valve opens from one dog at just the right moment to drive in a clockwise direction, and the other dog (when engaged) opens the valve at the right moment to drive in the opposite direction.

Goodness only knows how I will get all the angles right in my model. I can't key them in place due to the small shaft sizes, so I'll figure out hoe to make then adjustable. We wil see. I'll soon have something to post as the eccentrics are almost finished.

Bob

Offline crueby

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Re: Stephenson’s Rocket
« Reply #52 on: November 28, 2023, 04:48:32 PM »
Great that you got it figured out!   Perfect time to make some sketches and notes to remind yourself a month or two from now how its supposed to work - nothing worse than coming back later and going, Wait, What?

Online Kim

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Re: Stephenson’s Rocket
« Reply #53 on: November 28, 2023, 05:53:36 PM »
Wow!  That's going to be a fascinating mechanism, Bob.  Glad you got it figured out before implementing too much of it. Looking forward to seeing it all work!  :popcorn: :popcorn:

Kim

Offline Bob Wild

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Re: Stephenson’s Rocket
« Reply #54 on: January 10, 2024, 11:03:41 PM »
Having finally got my head round the drawings, started on building the bits. Here are the eccentrics complete with reversing mechanism. Also the shafts and linkages for the lower half of the assembly. I have tried to follow the design as near as possible. However the drawings show some very intricate parts at the scale I am using. For instance using keyways in a three mm shaft is way beyond my skill and ability.  Additionally there are wrought iron parts with many sculptured outlines - much too hard for me. But I’ve ended up with a working mechanism that is dimensionally correct. Next up the valve mechanism 



Offline crueby

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Re: Stephenson’s Rocket
« Reply #55 on: January 10, 2024, 11:15:26 PM »
Thats looking great, some very detailed parts.   :popcorn: :popcorn:

Offline RReid

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Re: Stephenson’s Rocket
« Reply #56 on: January 11, 2024, 02:39:30 AM »
You've made an excellent start! Watching with interest. :ThumbsUp: :ThumbsUp:
Regards,
Ron

Offline Bob Wild

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Re: Stephenson’s Rocket
« Reply #57 on: March 16, 2024, 04:26:45 PM »
Another major milestone reached today. Got the whole valve mechanism built. Very fiddly and I spent ages getting all the links working correctly. Had to remake a few parts because they were a sloppy fit. When you look at the number of moving parts, you can see that all the clearances stack up and lose quite a bit of movement. Anyway they do all fit together, and the valve openings look OK for now.

Next up are the pistons and crossheads. Big issue is how on earth to make the slots in the crosshead that the guides fit into. Not only are the guides a square section, but the are also at 45 degrees to the normal. Any suggestions would be most appreciated.

Bob

Offline Bob Wild

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Re: Stephenson’s Rocket
« Reply #58 on: March 16, 2024, 04:28:24 PM »
Had a bit of trouble with the attachments, so here they are (hopefully)

<a href="https://www.youtube.com/watch?v=B5qcVMKzkno" target="_blank">http://www.youtube.com/watch?v=B5qcVMKzkno</a>

<a href="https://www.youtube.com/watch?v=x0BrOJ0X1Sg" target="_blank">http://www.youtube.com/watch?v=x0BrOJ0X1Sg</a>

<a href="https://www.youtube.com/watch?v=AH8CKkbdu3A" target="_blank">http://www.youtube.com/watch?v=AH8CKkbdu3A</a>
« Last Edit: March 16, 2024, 04:36:49 PM by Bob Wild »

Offline Admiral_dk

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Re: Stephenson’s Rocket
« Reply #59 on: March 16, 2024, 09:28:43 PM »
A lot of tiny part that takes a (relative) long time to make - but they look good  :ThumbsUp:

Per  :cheers:

 

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