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Part built Allchin 1.5 inch

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derek blake13/01/2019 15:19:13
327 forum posts
97 photos

Hi All

So I’ve drilled holes to hold valve chest, all went well except when drill snapped but managed to remove.

I’m a little stuck on next move and I’m afraid I’m may have to ask before drilling too many more holes, the attached drawing shows a 7/32 hole to link up with regulator port, now my question is I guess this must not go into the annulus?

Kind regards Derek

0d7635a6-60fa-4dc0-bfba-04deb51e8aa7.jpeg

JasonB13/01/2019 17:13:19
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Only needs to go in far enough to meet the small rectangular regulator port, it's the hole I have marked in red with teh port in blue

reg passage.jpg

derek blake13/01/2019 17:42:54
327 forum posts
97 photos

Many thanks Jason, these will be the next ones I concentrate on.

Please forgive me if I ask further question relating to the cylinder, it’s the first one I’ve ever done and don’t want to drill a hole wrong.

Regards Derek

derek blake13/01/2019 19:50:33
327 forum posts
97 photos

If anyone gets anytime could some direct me to a picture or video that would explain how the steam travels around the Allchin cylinder block and how the holes etc do there job.

I’m keen to learn all I can about what I’m building and how it should work.

Regards Derek

derek blake14/01/2019 11:44:10
327 forum posts
97 photos

Hi Guys

Is SA660 bronze OK to use for the piston, with having the same material for my cylinder?

Thank you

JasonB14/01/2019 12:19:30
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No real difference to running bronze in gum metal

derek blake14/01/2019 12:39:50
327 forum posts
97 photos

OK thanks Jason, id read that you shouldn't use the same material fro liner and piston.

I guess it makes sense that a bronze piston would be fine with a bronze liner, especially on this small engine.

Jeff Dayman14/01/2019 13:16:50
1519 forum posts
37 photos

I would recommend a dissimilar metal for your piston to the cylinder material. A cast iron piston would work well in a 660 bronze liner. Continuous cast cast iron bar is widely available, not to expensive, machines beautifully, and has no sand inclusions or blow holes as sand castings can have. A stainless steel piston would also work well.

If you did use 660 bronze for both cyl and piston, and the lube oil film ever broke down or was lost, the parts could rub together, "pick up" or "gall", which is local surface welding, and seize solid.

Just my $0.02 worth after building a number of engines of various kinds. Standing by for the usual arguments and contrary opinions....

derek blake14/01/2019 13:22:12
327 forum posts
97 photos

Hi Jeff

Thank you for your comment, OK well I'm not expert and will take any advice i can.

so is that the search i should look for Continuous cast iron bar?, any special numbers or types i should look for?

Many thanks.

derek blake14/01/2019 13:31:06
327 forum posts
97 photos

I've found some called (Meehanite Bar) is this OK?

Thanks in advance

Paul Kemp14/01/2019 13:45:30
283 forum posts
9 photos
Posted by derek blake on 13/01/2019 19:50:33:

If anyone gets anytime could some direct me to a picture or video that would explain how the steam travels around the Allchin cylinder block and how the holes etc do there job.

I’m keen to learn all I can about what I’m building and how it should work.

Regards Derek

Derek,

I couldn't find easily a video of a traction engine cylinder steam flow or a decent drawing (and don't have Jason's excellent CAD skills to be able to draw one!). Niether do I have direct experience of the Allchin cylinder so have tried to put in words a general description of how steam flows from the boiler to the chimney, hope it makes sense!!

Traction engines, particularly English ones do not normally have a dome to collect 'dry' steam from the boiler like a railway loco. The dome on a loco provides a space where steam collects and is drawn off for use that will hopefully not contain entrained water. So on a traction engine the cylinder casting usually performs this function. The casting is generally hollow around the liner so steam gravitates from the boiler barrel into the the space in the cylinder casting around the cylinder bore, this achieves 2 things, it gives a space seperate from the boiler barrel for the steam to be drawn off for use and because the steam surrounds the cylinder bore (in your case liner) it keeps the bore warm reducing condensation of the steam inside the bore when the engine is running. As you are fitting a liner to create the steam space in the cylinder casting and this space will be directly connected to the boiler and at boiler pressure the seal between the liner and the casting needs to be leak free. Any leak can either get into the bore via the end covers bypassing the slide valve which will lead to reduced or non existent performance or will be blowing to atmosphere! Steam is then taken from the steam space via the regulator to the valve chest via drilled or cast passages. The regulator is arranged so that the high pressure (boiler) side acts on top of the sliding regulator valve, so keeping the regulator on its seating face. It is a good idea to make the regulator port under the valve a pear shape so as the regulator is opened the area of the port exposed to high pressure steam progressively increases, this makes the engine easier to control. The passages for the regulator must not break through into any other passages! Once the steam is in the valve chest it is directed to each end of the cylinder by the valve. The steam ports (outer two ports) and the drillings to the ends of the cylinder again must not break through to any other area or drilling. The exhaust port (wider, centre port) is connected to the steam outlet flange for the blast pipe on the exterior of the cylinder casting again by drillings or cast passages and again these must not break into any other passage or area. So you have four areas that must remain isolated from each other within the cylinder block, the high pressure steam space around the liner, the regulator passages and valve to the steam chest, the steam ports to each end of the cylinder and the exhaust arrangement. You will also likely have cylinder drains which are drilled directly from the external boss where the clave will be fitted to the bottom of the bore and usually a steam take off for the steam blower that will be drilled from a point on the front face of the cylinder 'block' directly into the high pressure steam face surrounding the liner (with your engine it will probably turn 90 degrees down and connect with the space in the saddle.

1000 words when a decent picture would do!

As to piston material, bronze as Jason said should be fine. Remember 'technically' the piston does not run on the liner as it is supported by the rings although in practice that is a moot point. Full size generally have cast iron cylinders and pistons, another example of a material running on itself if you like.

Paul.

Clive Brown 114/01/2019 14:07:12
234 forum posts
7 photos

I would guess that hundreds of model Allchins, inc. mine, and similar have been built with gunmetal pistons and cylinders, as supplied by the trade.

Bear in mind that iron for either or both components requires more careful storage of the model to prevent possible rusting, more especially for one used only very occasionally.

JasonB14/01/2019 14:14:35
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Infact the book says the liner can be GM or bronze and the piston is from Bronze.

Myself I'm a bit of a fan of aluminium pistons as they keep the weight down more in keeping with what the original hollow CI pistons weighed.

Jeff Dayman14/01/2019 14:39:33
1519 forum posts
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Meehanite would be a great brand if cont. cast CI to use Derek, I try and get that when I am buying CI. Good luck.

Andrew Johnston14/01/2019 15:02:45
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Posted by JasonB on 14/01/2019 14:14:35:

Myself I'm a bit of a fan of aluminium pistons as they keep the weight down more in keeping with what the original hollow CI pistons weighed.

Ideally one doesn't run similar metals together, cast iron is one of the few exceptions. However, for a model which only runs once in a blue moon it probably doesn't matter.

Of course you could always make prototypical hollow cast iron pistons, although in such a small scale they probably wouldn't have any weight advantage over aluminium. My main objection to aluminium is the clearance needed to allow for differential expansion.

Andrew

derek blake14/01/2019 15:09:26
327 forum posts
97 photos

i really appreciate everyones input and its a real learning curve, so lets look at what I have.

ive machined the liner from SA660 bronze and its worked great, I now need to do the pistion.

I was supplied with bronze from the supplier but it was undersized so ive sent it back, id like to purchase a new material and I was hoping that the SA660 bronze would be good as I have some.

however some says that's risky as it may lock which is what google says, and another to use Cast iron which sounds good also.

Jason you are right about the book, I do want to use O rings and not graphite packing.

so I guess the question is do I go with Cast iron or bronze frown

JasonB14/01/2019 15:16:19
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Derek, are you intending to steam the engine regularly when it is complete or will it sit as a display model that jets the odd whiff of air from a compressor.

There is the slight risk of iron rusting to be taken into account if the layer of steam oil breaks down.

derek blake14/01/2019 15:19:00
327 forum posts
97 photos

good question, I guess id like to get use in summer but display in winter.

I can keep it oiled and serviced of course.

but id like to make it so it correct basically and best I can.

derek blake14/01/2019 18:44:28
327 forum posts
97 photos

I have a piece of cast iron and SA660 bronze, so I guess it’s decision time.

I will make both types, as it’s practice for me on the lathe.

derek blake15/01/2019 08:46:15
327 forum posts
97 photos

I think once the engine is built if I ever see my boiler I will keep it looked after and oiled up.

so I will make the piston from SA660 bronze as that's what I have at home, I cant see that being a huge issue from what I've read from everyone.

The original should be GM or bronze and piston bronze, only thing is the piston maybe a different type of bronze but the drawings don't say,,,

Regards,

Del

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