Stuart 10V

Hi, I am brand new to this Forum. I bought a Stuart 10V Kit (unmachined). I also bought a book "Building a vertical steam engine from castings by Andrew Smith" revised by Pengwern. I notice that the outside dimension of the crank web on the Stuart drawing is 5/8" and in the book it is 11/16". Has anyone else come across this? Also, when the engine is assembled do the outside faces of the crank web run against the inside faces of the crankshaft bearings.

Scott
To answer your last question the distance between the bearing inner faces and the crank webs should be the same plus a small clearance. On my engine, built in the late '70s, I'd estimate that it is a couple of thou. On the plans that came with my casting set there are some build notes and with reference to this it states "The shaft should turn without binding in the bearings but with practically no end play".

In my book, which is "Building a Steam Engine from Castings" by Edgar Westbury, not Andrew Smith, the crank webs are shown as 5/8" wide the same as the drawings. Check the distance between the mounting hole for the bearings in the base casting and the distance between the mounting holes in the bearings and the inner faces of the bearings. They should be the same as the width of the crank web plus a few thou. On my drawings, and in the book, the distance between the holes in the base casting is 1 1/4" and the distance from the mounting hole in the bearing to the inner face is 5/16" so when mounted on the base casting the gap between the inner bearing faces is 5/8", same as the crank width. Obviously there also has to be a small clearance as stated above so the crank can turn freely.
Check these dimensions on your plans, an in the book, and see how they add up.

I'm not sure this has answered your question but I hope it helps.
John

Edited By John Purdy on 21/04/2023 18:44:54

Just measured mine and the crank is 5/8" with just a running clearance between it and the bearings

This build of a 10V by a beginner member is worth a read

Scott welcome to the world of Model Engineering where every set of drawings has errors, no matter how old they are they will not have been corrected.

Hi everyone, Thanks for these replies. They help tremendously. I now understand the importance of the relationship/fit between the web crank faces and the main crankshaft bearings.

One thing I forgot to mention though about the crankshaft bearings. The turned O.D. dimension of 27/64" at either end have lengths of 1/8" and 5/32" I am assuming the 1/8" dimensions are positioned on the inside of the soleplate!!.

Thanks again,

Scott.

No, as John hinted at they face the inside and leave a 5/8" gap for the crankshaft.

If you look at the soleplate drawing it shows the stud holes at 1 1 /4" ctrs

Middle section of bearing is 5/16" so middle to edge is 5/32"

Protruding round section also 5/52"

So when assembled you have 5/32 + 5/32 + 5/8 = 5/32 + 5/32 = 1 1/4

Edited By JasonB on 22/04/2023 07:42:54

OK. The penny has dropped. Thanks everyone for all your help and patience.

Scott.

The 10V is a nice engine. It’s a well documented build and it will teach you quite a lot about fitment. Do you plan to add the reversing? It can always be added later, but there is less repeated work if it is done from the start.

Best of luck with the build.

A 10V as George says is a nice engine but fitting the reversing gear really finishes it off ,I have a D10 with the reversing gear, I polished it all as I assembled it. Noel.

Hi, Sounds interesting but although I am a time served turner/machinist (more years ago than I care to remember) I need to learn to walk before I can run. Actual machining doesn't present a problem but I need to get my head round the build, alignment and workings of model steam engines. I've still to find out the principle of how steam engines work. I'm sure if I manage to complete it I will take up the challenge of the reversing gear.

Thanks Scott.

Hi, I'm considering using an O ring for the piston on the Stuart 10V I am currently machining. Can anyone advise what size O ring I should use. Also what size/depth of groove would be required in the piston.

Scott.

Hi,

I am still machining the Stuart 10V. The valve rod and piston rod specify "stainless steel" on the Stuart drawing. Can anyone advise if it would be OK to use mild steel?

Thanks in advance.

Scott.

The rods tend to be stainless to prevent rusting and stainless is what is suppled in the kits so that would be best. If you go for mild steel then PGMM (precision ground mild steel) would be better than just bright mild steel.

If you do want to use an o ring then a BS113 would be the right size. Groove 0.125" wide and 0.098" deep

OK. Thanks for that.

Scott.

Scott, You must calculate the depth of the groove based upon the cylinder bore diameter. You should not use published o-ring compression recommendations. I would shoot for no more than 5% compression of the o-ring. It should be a easy fit in the cylinder. Rick

My figures of 0.098" give approx 5% compression of the nominal 0.103" section ring I suggested. That is based on the Arnold Throp calculations that can be found in Model Engineer's Handbook and paper versions of Reeves catalogue.

Hi,

Thanks for the resposnses. I'm afraid though that the compression of the o ring and the calculation thereof means very little to me. It's something I need to read up on. In the meantime I shall use the size that you have given and see how I get on.

Thanks again.

Scott.

Hi Scott, If you intend to use an O ring then the finish of the cylinder bore is very important if you want to run the engine. Using a small cylinder hone is one way to get a good finish though there are other ways This then means leaving the cylinder bore slightly undersize, say .025mm, then you hone or finish to size. .I only mention this as your comment above indicates you may not be from an engineering background Good luck. Noel.

My post was not meant to dispute your numbers. I have built quite a few engines and because I am not an expert machinist, often times I have ended up with cylinder bores that are not "spot on". A few thousandths over or under planned dimensions will make a difference on the groove dimension, especially on a small bore cylinder. Another variable to consider is the actual diameter of the o-ring cross section. Rick

With out getting out some books, O rings are available in both odd imperial sections and also metric sections so that give or take one can normally find a ring to do the job. Noel.