Duncan.e
Member
- Joined
- Aug 25, 2011
- Messages
- 17
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Hi,
An old, but newbie here - first post - from the south east of England. I have only just found the forum and have searched through it and read lots - It looks a great place to learn!
I want to build a twin cylinder, double acting, oscillating steam engine ultimately to fit into a 1:13.7 scale coffee pot loco for the garden railway I'm building (slowly).
I have to say straight away that I am completely new to steam engines, but have some machining skills. I'm designing the engine myself, but paying a lot of attention to existing plans.... I want to make it out of 316 stainless steel, with bronze (or brass) inserts in the valve areas to prevent frictional and pick up problems.
I was discussing the piston with an engineering colleague and explained that a lot of people use PTFE tape twisted into string to pack the grooves in a brass piston. He looked at me and said that that seemed daft, why not just make the piston out of PTFE.... This has got me wondering if there is any reason why I shouldn't do just that.
I have looked at the coefficient of thermal expansion of 316 stainless and PTFE and the two are similar, with the 316 being slightly greater, so there shouldn't be a problem there. The working temperature is well in excess of a steam engine's heat, so again no problem.
Can anyone suggest any reason not to try this?
Also, I want the engine to be reasonably small - height max ~ 2.5" and be slow revving but have pulling power, so I presume I need a longer stroke with a smaller bore to give me the torque I require. Can anyone recommend what sort of bore and stroke I should go for? My thoughts are perhaps ⅜" bore and ⅝" stroke (10mm x 16mm), but I really have no idea....
Any insights will be gratefully received....
Thanks!
Duncan
An old, but newbie here - first post - from the south east of England. I have only just found the forum and have searched through it and read lots - It looks a great place to learn!
I want to build a twin cylinder, double acting, oscillating steam engine ultimately to fit into a 1:13.7 scale coffee pot loco for the garden railway I'm building (slowly).
I have to say straight away that I am completely new to steam engines, but have some machining skills. I'm designing the engine myself, but paying a lot of attention to existing plans.... I want to make it out of 316 stainless steel, with bronze (or brass) inserts in the valve areas to prevent frictional and pick up problems.
I was discussing the piston with an engineering colleague and explained that a lot of people use PTFE tape twisted into string to pack the grooves in a brass piston. He looked at me and said that that seemed daft, why not just make the piston out of PTFE.... This has got me wondering if there is any reason why I shouldn't do just that.
I have looked at the coefficient of thermal expansion of 316 stainless and PTFE and the two are similar, with the 316 being slightly greater, so there shouldn't be a problem there. The working temperature is well in excess of a steam engine's heat, so again no problem.
Can anyone suggest any reason not to try this?
Also, I want the engine to be reasonably small - height max ~ 2.5" and be slow revving but have pulling power, so I presume I need a longer stroke with a smaller bore to give me the torque I require. Can anyone recommend what sort of bore and stroke I should go for? My thoughts are perhaps ⅜" bore and ⅝" stroke (10mm x 16mm), but I really have no idea....
Any insights will be gratefully received....
Thanks!
Duncan