Member postings for John Purdy

Thanks for the replies.
Jason the rings were bought from Reeves in Mar '93 and were listed as 2" dia. Your 5-7 thou gap is about what I thought would be about right. I'll go for that and we'll see what bore I end up with.
My measuring is quite possibly suspect so I will just slowly open out the bore till the ring just goes in then a little further to get the 5-7 thou gap.

I have been machining the cylinder for the #1 an before I finish the bore I decided to check the rings I have. When I got the castings the piston rings were in multiple pieces so I bought a pair of 2" dia rings from one of the usual suppliers. On checking them I have found that when closed up to 2"dia the ring gap is about 35 thou which I feel is excessive. When closed up to zero gap the dia is 1.975". I have roughed out the bore and it is currently 1.800" so I have lots of leeway to make it whatever. My question is what is the normal gap used for an engine like this? In all probability I'll only be running it on air and not expecting it to do any real work.

Edited By John Purdy on 27/12/2018 21:41:44

Guy

I have made a number of bronze castings using the lost foam method in green sand with no problems. I used the rigid blue close cell foam used for insulation (not the white bead board) and used normal risers and venting. Just stand upwind and don't breath the smoke from the burning styrofoam !

John

ega

According to the table I have whether step drilling is recommended depends on the length of the pin. For a #0 pin only one drill is required if the length is 1 1/2" or less. For longer pins two are recommended. The reason for step drilling is to make reaming easier and quicker when using straight flute taper reamers.  If using helical flute reamers then step drilling is not required and the drill size is the same as the small end of the pin.

John

Edited By John Purdy on 22/11/2018 18:22:25

Michael

I've sent you a PM.

John

Jason
I had checked Stuart Models web site, spare parts section, and had noted that, as you say, the con rods for both now have the same part number so are probably the same casting ( a cost saving move when Stuart Models took over perhaps ?). I don't know when my castings were bought but I think probably late '60s early '70s making them Stuart Turner castings. I have the parts list for the #5 (but none for the #1) and it lists no part number for the con rod and for all the castings that do have part numbers they are totally different from the current Stuart ones.

If no one can identify them positively I think I will use the non rusted one for the #1 as it is the smaller and the finished dimensions of the #1 are smaller all round except for the distance from the pin to the bottom of the foot which is the same (3 3/8" ) for both.

Edited By John Purdy on 08/11/2018 20:15:18

Edited By John Purdy on 08/11/2018 20:15:41

I have a question for anyone who has built either the ST #1 or the #5A engines. A good many years ago I acquired a number of ST castings including a #1 and a #5A. They were out of their original packing, in separate boxes but were essentially complete. The 5A had some machining done ( not particularly well done) but the #1 was untouched. I have started machining the #1 and having finished the big end bearings yesterday I started looking at the connecting rod casting and it seemed to have a lot of excess material to machine away, so I dug out the one for the 5A and comparing them both with their drawings it appears to me that they might have got switched. In the picture the rusty one on the left was with the #1 castings, the other with the #5A.( all the #1 castings had a coating of light surface rust but the #5A were clean) Can anyone confirm which one is for which engine? Thanks.

Luke

The build series for "Scamp" in EIM ran from Apr. 84 to July 85.    The reeves casting set I believe contains only the castings, no steel for the frames, buffer beams rods etc,  you have to source that yourself.  I believe they do show the frame and buffer beam steel in their listing though.

I've sent you a PM.

John

Edited By John Purdy on 11/10/2018 21:22:14

Luke

I built the 0-4-0ST "Gemma" , also a David Malcolm design, which is very similar to "Scamp". In fact the whole cylinder/valve/valve gear is basically identical. It was my first loco build and I found it a straight forward build. The most challenging part I found was the inside Stevenson's valve gear. There are no complex machining operations and as a first build it was of a large enough size that it wasn't 'watchmaking" and also not so large that it was unwieldy with multitudes of parts. I personally feel that if you build something that you like the look of that the chances of it getting completed are that much better. Whether it is the right one for you is only for you to decide!

As an aside "Gemma" performs very well on the track with very few teething problems from the start. It will easily pull two adults (+me) and quite often runs for 2 to 3 hours at a time. The only major fault was that the lower boiler tubes would plug up. This was cured by the addition of a stainless steel arch in the firebox. I imagine that "Scamp" would perform similarly as mechanically it is almost the same.

John

Jason

Thanks, I'll try the higher temp and see if that works any better. The thickest section in these castings are about 1" so the two hours should have been enough, but as you suggest the temp may not have been high enough. Let you know if it works any better.

Ron

As Jason says chilled cast iron is the result of cooling an iron casting too quickly. What happens is that when molten, the iron contains carbon in solution with the iron as iron carbide. On cooling slowly the carbon participates out as flakes of graphite (pure carbon) in a matrix of pure iron, but if cooled quickly the carbon doesn't have a chance to participate out and remains as iron carbide which is extremely hard and quite shiny being next to impossible to machine with normal HSS tooling.

   As mentioned above it is not always a disadvantage , being done deliberately sometimes to produce a very hard wear resistant section or part.  plow shares being a case in point.   This is done in the foundry by placing  a large mass of  metal, called a "chill" in the mold buried in the sand close to the area that is to be chilled.   This has the effect of cooling that area faster than the rest resulting in being turned into chilled iron ( "white iron" ).

John

Edited By John Purdy on 07/10/2018 20:35:04

Edited By John Purdy on 07/10/2018 20:35:41

Edited By John Purdy on 07/10/2018 20:36:15

The reason I asked the question is that I have had chilled parts before and have tried putting them in my wood stove for an hour or so then leaving to cool overnight. That made no difference. When I made my Clarkson's compound (just finished ) there were a number of castings that had chilled areas. I placed them in my kiln and heated them to 760 deg. C (1400 F) for an hour and let them cool over night. After this treatment they machined nicely. I've now started on a ST #1 and when machining the box bed with a carbide insert end mill I found it did not machine like soft grey iron but like it was partially chilled. The machined surface was quite shiney and the noise was more of a "ting ting" on the intermittent cuts instead of the more normal "shee shee" of soft iron. So I put the rest of the iron castings in the kiln and soaked them for two hours at 760 and let them cool over-night. On machining the bed plate yesterday it was no better so was wondering if the soaking time was not long enough due to the much larger mass compared to the Clarkson castings.

Jason, the colour at 760 in my kiln is slightly oranger the your picture so probably a little hotter than you show.

John

A question for the metallurgists here. What is the ideal temperature/time to soak chilled iron castings to get the chilled areas converted back to gray cast iron so they can be easily machined?

John

not done it yet

Thanks for the link. After reading it I vaguely recall having read it before and that is probably where I got the dimension. Don't know why I didn't note it at the time though. Thanks again.

John

On going through my book by E. T. Westbury on the building of the Atom Minor, I notice that I have an annotation next to the 1 43/64 (1.672 ) inch dimension of the connecting rod centres saying that it should be 1.703", but there is no reference as to where I got this figure from. Can anyone clarify where this dimension might have come from and which one is right?

To everyone, thanks for your complimentary comments. As far as compounding goes, as I suspected, and as most of you have pointed out, since the exhaust air has very little work energy in it as compared to steam, the HP cyl. is basically just motoring over the LP cyl. against friction with little assistance from the HP exhaust. Hence the higher pressure required.

As far as problems with the castings, besides the bearing pedestals mentioned earlier, the valve chest castings had insufficient machining allowance on both height and thickness so when just cleaned up to a flat surface they were smaller than the drawing dimensions in both height and thickness. As well the cast inlet boss was oval to the point that the 1/4" tapped hole would have broken through on the sides so were milled off and replaced with turned bosses threaded into the valve chests. The trunk guides were decidedly oval so after some work with files to get then close to circularity, they required very careful set up for boring to ensure that the bore didn't run out the side of the casting. As it turned out when bored to the stated 5/8" dia. the wall thickness was only about .045". It would have been easier to change that 5/8 bore to 9/16 which would have given a thicker wall and made setup that much easier.

One mistake I made when machining the cyls. was to use my usual practice of using the as cast radius of the flanges as the datum to define the cyl centres (always worked well before). This resulted in that when the cyl. was  finished, and the cavity in the valve chest was centred on the steam ports, the top of the valve chest sat proud of the top of the flat as cast surface of the cyl where the exhaust boss is, by about 1/16" with the result that there was no room for the top row of valve chest studs in the cyl. After some head scratching (and a few choice words!) the solution was to lower the valve chest to the point were the studs could be fitted and to offset the valve on the spindle so that it was centred on the ports (as can be seen in the photos the valve chest is still slightly proud of the cyl).   In hind sight( wonderful thing that) I should have used that as cast flat surface were the exhaust boss is as the datum to define the cyl .centres and filed back the flanges to suit. There was plenty of meat on the bottom of the casting for the cyl. centres to be lowered. As it was I machined off about 1/8" to bring the cyl. vert. centre to the 1 1/16" height required.

As Jason says, this engine was basically two of Clarkson's horiz. singles with and extra mirror image bedplate and a large casting for the rope drum. The ends of the rope drum are just the horiz. singles flywheels reduced in dia. somewhat. As the cyl castings weren't cored it could be made as a two cyl. high pressure of 1" bore or a compound with 3/4 and 1" bores. I chose the latter.

John

Edited By John Purdy on 29/08/2018 19:52:20

Edited By John Purdy on 29/08/2018 19:58:32

Edited By John Purdy on 29/08/2018 20:01:33

Finally finished the Clarkson's horizontal mill engine. Ran each engine on air individually at about 250 RPM to bed them in, then connected them up as a compound. As I suspected it required considerably more pressure to get the same speed in the compound configuration. Individually, at 150 RPM, the HP required 4 PSI and the LP 3 1/2 PSI. But in compound it required 9 PSI. Also the lowest sustainable speed singly was just under 100 RPM but in compound it is 135 RPM.

The engine was built using a set of original Clarkson castings and drawings I acquired many years ago. I found some of the castings had no machining allowance at all. The worst was the main bearing pedestals on the bed plates. They are to finish 1 1/16" above the cyl. mounting pads but the rough castings were less than 7/8" above. This necessitated a complete re-design of the main bearings. The others were got around by adjusting some of the dimensions, with the consequent problem of then having to adjust others.

Clive

D.A.G. Brown did a series in ME on injectors and In the last installment (7 Apr. 2000) he describes injector testing and includes dimensioned drawings of the test valve based on Bill Carter's design that you are looking for. I've sent you a PM.

John

Edited By John Purdy on 23/08/2018 18:45:53

Jason

Thanks for your reply Jason. The reason I'm looking is I've been given a set of plans and part machined castings but the carb and flywheel castings are missing. I guess it will be fabrication time. The crank case, main bearings, cylinder, liner, con rod, and crank are all finished, and the machining appears to be of a high standard. The only problem is the crank appears to be slightly out of true and will require, I think, some judicious straightening.

John

Does anyone know if there are any suppliers of castings for Westbury's "Phoenix" 15cc engine? I've checked all the usual suppliers (that I know about) without success.

John

Duncan

When I built my 5" 0-4-0, which has gunmetal cylinders and pistons, I used standard Buna-N "O" rings (I couldn't find Viton at the time) on the pistons (#212) and all the glands. It has run since being completed in the the spring of 1991 with them with no problems. About 5 years ago I found a source of "Viton" rings so decided to change them all over. The original piston "O" rings when removed showed only minimal wear.    The cylinders when made were not lapped in any way just bored to the finest finish I could get (between centres boring bar). So that was 20 + years with minimum wear for the Buna-N rings. So from my own experience, "O" rings for piston seals in gunmetal cyliders are perfectly satisfactory. I found the "O" rings also have an added benefit in that they start to squeak when the lubricator runs out of oil !!

John

Edited By John Purdy on 07/08/2018 18:38:47

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Edited By John Purdy on 07/08/2018 18:42:00