By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Clarkson's Horiz. Compound

All Topics | Latest Posts

Search for:  in Thread Title in  
John Purdy19/08/2017 21:32:39
194 forum posts
61 photos

Here's some pics of the latest project I am trying to complete, a Clarkson's horizontal compound mill engine (3/4" and 1" bore by 1.5" stroke). Only the crank pins, con rods, and eccentric rods to do, and mount the cyls.. Then figure out what to make for the base and what colour to paint it. Anyone got any suggestions?

I acquired them in Apr. "98 in a job lot from a fellow down the road in Ladysmith BC who had bought them from someone else. It was the complete casting set plus drawings in the original shipping box. They had originally been bought by a fellow in Victoria BC from Caldwell's of Luling Texas on 17 June 1960 for $84.53 (51.86 current UK pounds).

Along with these there was a part built 3/4" scale 4-8-4 Northern loco, tender, and boiler (which is what I had gone down there to see in the first place), a Stuart Turner beam and 5A with reverser and pump, which were partially built (complete castings and materials, but missing some fasteners) and untouched complete sets with plans for ST #1with reverser, ST#9 and pump, ST boiler steam feed pump, #4 cyl casting set, and two #6 cyl. casting sets.

I was really only interested at the time in the loco but he would not sell the items separately and the price he was asking for the lot was less than the then current price for the #1 and #9 so I couldn't refuse.

I found for the most part they machined very nicely (the valve chests and covers were chilled but after a few hours at 1400 deg in the kiln and overnight cooling were OK). Some though required very careful setting up as there was minimal machining allowance, particularly the trunk guides as the wall ended up only .050" thick. Also a number of castings were smaller in the cast state than the finished drawing dimensions. Namely the valve chests and covers, main bearing top caps and main bearing pedestals ( as cast 7/8" tall whereas the finished dim. is to be 1 1/16" above cyl mounting pad.)

These problems were got around but required some extra thought and planning.picture 020.jpgpicture 026.jpg

Edited By John Purdy on 19/08/2017 21:36:14

Edited By John Purdy on 19/08/2017 21:48:26

Edited By John Purdy on 19/08/2017 21:53:40

Phil P19/08/2017 22:15:19
622 forum posts
165 photos

Interesting to see your post regarding the Clarkson Compound engine, there are not many of these around.

I have only recently bought a set of castings and drawings for one myself, the drawings leave a lot to be desired I am afraid, so I have just about finished modelling the complete engine in Solidworks 3D CAD to ensure everything will fit together.

One serious omission was any dimensions for positioning the cylinders onto the bedplates, and I suspect you will be doing it by trial and error judging by the white marking fluid.

It looks like it is turning out very nice though.


JasonB20/08/2017 07:31:31
17849 forum posts
1952 photos
1 articles

You look to have done a good job so far John. As for mounting the engine maybe a flat board with applied tile pattern and a wooden edging, small well cut into the base for the flywheel and take the plumbing down under the base so you can have a discrete connector on the timber edge.

Colour is a personal thing, I tend to go for something a bit different from the usual dark greens and maroons that you often see.

Regarding availability You should be able to get these from Blackgates as they now have the patterns and are gradually making the range available again.. It will be interesting to see how it works as a compound if on air, can also be built as a double high as well as a single.

John Purdy20/08/2017 20:07:50
194 forum posts
61 photos


I found that the two bedplates were different lengths, the LP one about 40 thou shorter, so the con rod lengths will be adjusted to suit so that the cyls. are central on their mounting pads. Also there are a couple of potential problems on the drawings. The piston is shown as being 7/16" thick, and if you add up the dimensions of the cyl., piston and stroke, that gives zero clearance at the ends of the stroke. I reduced the thickness to 3/8" which gives 1/32" clearance at each end. The other dimension that is suspect is the length of the piston valve, shown as 13/16". With the eccentric throw of 3/16" as drawn the valve at the extremes will be 1/32" beyond the inside edge of the inlet ports. For it to line up with the inner edge the eccentric throw would have to be reduced or the valve made longer. As I had already made the eccentrics when I discovered this , I increased the length of the valve to 7/8". If this was deliberate to make it run better as a compound I don't know, but I can always shorten the valve if necessary after seeing how it runs.

As you say Jason it will be interesting to see how it runs on air, as that will probably be the only way I will be running it (not having a stationary boiler big enough to run it). I suspect it will require a higher pressure than if it was a single or double high pressure.


All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Allendale Electronics
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest