Author Topic: James Coombes Table engine  (Read 420 times)

Offline rebush

  • Full Member
  • ****
  • Posts: 37
James Coombes Table engine
« on: November 15, 2019, 03:55:13 AM »
I've just finished building the James Coombes engine. I used the Stuart Models plans, but machined it from bar stock. This is my first attempt at a steam engine. and I don't fully understand how the cylinder works. There are two 3/32x3/8 ports that go to the top and bottom of the cylinder. There is a port 3/16x3/8 for the exhaust. How does the exhaust evacuate the cylinder? I've assembled the engine and have everything moving smoothly with no drag. When I set it up and put air to it,all I get is air coming out of the exhaust. Am i supposed to drill a 3/16 hole from the exhaust port into the cylinder? Thanks in advance for any light you can shed.
Hopelessly lost but making darn good time.

Offline jeff l

  • Full Member
  • ****
  • Posts: 214
Re: James Coombes Table engine
« Reply #1 on: November 15, 2019, 05:37:01 AM »
When the D valve in the steam chest covers one steam port (say the top one)and the center exhaust port the steam from that port exits the cylinder while steam in the steam chest is going into the exposed bottom steam  port .When the cylinder goes up the D valve exposes the top port while the bottom one is covered and it's exhaust flows out the center port . I hope this helps

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6768
  • Surrey, UK
Re: James Coombes Table engine
« Reply #2 on: November 15, 2019, 07:13:01 AM »
As Jeff says


Offline rebush

  • Full Member
  • ****
  • Posts: 37
Re: James Coombes Table engine
« Reply #3 on: November 15, 2019, 01:53:01 PM »
Jason and Jeff, thanks for the replies. Will go over the engine today and see if I can figure out the problem. I have the piece in the D block that the rod goes thru snug with about .003 clearance to the face of the cylinder. Do i need to have that block floating in there so incoming air pushes it against the face of the cylinder?
Hopelessly lost but making darn good time.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6768
  • Surrey, UK
Re: James Coombes Table engine
« Reply #4 on: November 15, 2019, 01:58:56 PM »
Yes it needs to float so the air/steam pressure holds it to the face, any slight gap will give the leak straight to exhaust

Offline JR72

  • Full Member
  • ****
  • Posts: 44
Re: James Coombes Table engine
« Reply #5 on: November 15, 2019, 03:48:56 PM »
Hi
We would love to see photos if you have any, parts in the process of being made or even the completed engine.
John

Offline rebush

  • Full Member
  • ****
  • Posts: 37
Re: James Coombes Table engine
« Reply #6 on: November 15, 2019, 05:12:21 PM »
Thanks Jason and JR72. Figured out what the problem was. I milled the 3/8 exhaust port in the D block all the way across. Making a new one that is closed on the ends. I had bought the casting kit for the twin Victoria and the light bulb went on and I opened the box and pulled out the D block casting. Their's didnt look like mine. There in lays the problem.
John, will post pictures when and if I can figure out how to do it.
Hopelessly lost but making darn good time.

Offline rebush

  • Full Member
  • ****
  • Posts: 37
Re: James Coombes Table engine
« Reply #7 on: November 16, 2019, 02:56:20 AM »
I'm happy to announce I have a running engine, and a little more knowledge of steam engines. Thanks everyone.
Hopelessly lost but making darn good time.

Online crueby

  • Full Member
  • *****
  • Posts: 9302
  • Rochester NY
Re: James Coombes Table engine
« Reply #8 on: November 16, 2019, 03:23:04 AM »
Excellent! Glad you got it sorted out, it doesn't take much to keep all the bits from working together, great when it all flows.
 :ThumbsUp: