Portable Engine Model Engineer Article by Tony Webster

[David Clark 13Participant @davidclark13]

I have started this thread to publish any questions, errors found and corrections in Tony Webster's Portable Engine series. Some of the content from this thread may be used in Model Engineer.

regards David

PS Any unsigned posts by me will be replies from Tony Webster.

 

Edited By David Clark 1 on 07/03/2012 14:00:39

[David Clark 13Participant @davidclark13]

The boiler barrel is eight inches long, with 3/8in. cut off the firebox end for one third of the circumference.

I advised not to try squaring up the ends of the boiler barrel in the lathe because it is difficult to hold in the chuck.

Edited By David Clark 1 on 07/03/2012 11:47:51

[David Clark 13Participant @davidclark13]

There are five bushes in the boiler, there is one each side of the barrel at the front so there is a spare for a hand pump.

The holes for the eight corner stays for fixing the horns should be 7/32in. dia. ie. the 1/4in. dia. is reduced slightly in diameter to provide a 'head' to stop them falling through when silver soldering. Head on the outside which makes it a two operation job. Reduce to 7/32in. dia. part off, chuck the other way round to centre, drill and tap 4BA. (It also cleans the bronze surface for silver soldering.)

Edited By David Clark 1 on 07/03/2012 11:48:07

[David Clark 13Participant @davidclark13]

[David Clark 13Participant @davidclark13]

The 7/16in. tube should be 20 swg, standard thickness from your friendly model engineer's stockist. Jason B should be assured that if too thin a wall section tube is fitted, the tube is likely to collapse inwards, in other words flatten. The pressure is on the outside in this case and copper is less strong in compression. This would not cause a catastrophic collapse and would most likely happen when the boiler is tested to twice boiler pressure. This is why boilers are tested to twice boiler pressure. Subsequent tests are to one and a half times boiler pressure.

In typesetting my hand written dimensions for publication, in the end section to the right of the drawing on page 364, the 11/16in. dimension to the first row of stays should be from the top of the foundation ring as shown in the door plate drawing to the left. Also the 1/4in. should be for the foundation ring only and not include the firebox wrapper plate.

The front to back location of the water gauge bush and manifold will be detailed in a further instalment of the series. There is no harm in having a static connection to the water gauge, ie a pressure gauge where there is no movement of steam or water through the manifold. I agree that there must not be a connection to the blower or injector etc. from the water gauge. This would have a misleading effect on the water level in the water gauge.

[JasonBModerator @jasonb]

Thanks David good to try and keep all these things in one place.

A few more questions regarding the boiler drawing in 4425.

1. Depth of flanges to inner firebox and throat plate

2. How far does inner firebox protrude below foundation ring

3. Drawing says 2off regulator bush, where does the second one fit

4. Should there be any thickening pad inside the boiler to mount the crankshaft bearings

5. Should there be blind bushes to mount the firedoor Hinge

6 Confirmation of an available thickness for copper in substitution for the 3/32" and 1/8" thicknesses shown on drawing.

 

Thanks, Jason

Edited By JasonB on 07/03/2012 13:15:54

[JasonBModerator @jasonb]

Cylinder drawing issue 4426.

1. No setting out positions for the 10No valve chest stud holes or will they be detailed with the valve chest.

2. Text says machine valve face back to lines 1 & 2 but drawing shows it at least 1/32 away from them.

3.Length of cylinder and protrusion of end faces not shown on drawing but can be found in text.

4. No depth for steam port slots

5. Brass tube, I'll wait to see what teh text says before commenting.

From the comments in about the last issue I got the impression there was going to be another boiler drawing has this been missed or is it to follow out of sequence? In 4426 it would seem the boiler is "complete " and tested yet the details mentioned two posts above have not been covered??

J

[JasonBModerator @jasonb]

Errors & Ommisions 4427

1. Width of Valve chest given as 3/8" but should be more like 1.5"

2. No length given for piston rod

3. Crosshead, no thickness given, probaly 5/16" to suite the slidebars but the 3/8" spigot is not shown to suit that.

David there are now three issues worth of queries, any chance of some answers?? as you did say this thread would be for corrections!!

Jason

[JasonBModerator @jasonb]

more 4427

1. No depth for piston ring groove

2. No length of 1/4×40 thread on piston rod

3. No depth for cut out in cross head, looks about 1/2"

[David Clark 13Participant @davidclark13]

Hi There

Tony Webster has been away.

I will chase him up Monday but I don't know when he is back.

regards David

[Adam Gregory 1Participant @adamgregory1]

Hi all

Any chance of a few more pictures of finished components or close ups of the finished model, to make it easier to understand some of the text and diagrams.

[David Clark 13Participant @davidclark13]

Hi There

I have a few photos to publish but most are pretty poor quality.

regards David

[JasonBModerator @jasonb]

David if they are a bit too poor for actual printing what about just adding to this thread so those that need the reference have access to them.

Another thing that would help would be to try and syncronise the drawings with the text for example the description of the cylinder covers in the latest issue is very hard to follow but I'm sure once the drawings appear hopefully in the following issue the text will make a lot more sense.

J

[David Clark 13Participant @davidclark13]

Hi There

We don't have rights to put unpublished photos on the websites.

Rear cylinder cover drawing is in 4428, front cover in 4429.

regards David

[JasonBModerator @jasonb]

Why can't it be done like the Darjeeling ref photos, none of them have been published, You would only need to Ask Tony if it was OK.

Failing that if I see it at another exhibition I could take a load of photos and stick them in an album

J

[David Clark 13Participant @davidclark13]

Hi Jason

I took the Darjeeling photos.

They are my copyright. That is why they are on here.

regards David

[JasonBModerator @jasonb]

Fair enough.

This wil take anyone interested to the only pic I have of the engine, there is another one on the net that I will dig out the link for when I have a bit more time

Edited By JasonB on 02/04/2012 13:04:00

[David Clark 13Participant @davidclark13]

Hi There

I do have some photos that I took at exhibitions.

I will dig them out.

regards David

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I have put a photo that I took of Tony's engine when on display at Sandown, in my album named Portatable Engine, if anyone is interested in viewing it.

It is similar to JasonB's link, but at a slightly different angle.

Regards Nick

Edited By Nicholas Farr on 02/04/2012 20:55:43

[Mike WainwrightParticipant @mikewainwright87512]

Is there a full set of drawinging available to go with this series that will have all corrections included.

[JasonBModerator @jasonb]

Posted by Mike Wainwright on 07/04/2012 07:26:29:

Is there a full set of drawinging available to go with this series that will have all corrections included.

Sorry could not resist.

It would be nice if a lot of the newer models being published in the mag could be added to the MHS range of plans but somehow I don't see it happening, though most people contemplating a build in the future would likely track down the back issues anyway which would have the drawings in so why pay twice unless they had all revisions.

J

[JasonBModerator @jasonb]

Issue 4428

Slide bar drawing

-Plan view gives width over the outside of the bars and bracket as 15/16

-Plan view gives one end of the bars at 13/16" centers and the other end at 11/16" ctrs

-End elevation gives the bracket as 1" wide and the bars project beyond the bracket which would give the outer edge of the bars as 1.125" or there abouts

– and to be picky the oil cup does not show the hole carried through the slidebar

Cylinder saddle.

– is this the actual view of a developed shape of the curved part.

– 1/8" dimension bottom left is wrong should probably be 1/4"

– the two 9/32" dimensions on teh left seem wrong as the hole will break through the edge, 11/32 would be nearer whats right

– No size given for the 4No corner holes to mount to the boiler/dummy wrapper.

– Is it correct that the cylinder does not sit centrally on the curved flange front to back, or should the 3/4" dimension for the position of the 1/4" hole be 15/32" to allow for the 1/32 projection of the cover faces beyond the cylinder.

Its now been some 6 weeks since the first queries were raised any idea of when and if they will be answered???

J

 

Edited By JasonB on 13/04/2012 15:55:52

[David Clark 13Participant @davidclark13]

Hi There

Cylinder saddle was the wrong drawing. Corrected version in 4429.

regards David

[David Clark 13Participant @davidclark13]

Hi There

The slidebar drawing has been checked and is as supplied apart from the hole which is shown right through.

I will forward the query.

regards David

[David Clark 13Participant @davidclark13]

Piston rod.(Not in 4425) 1/4in dia stepped down to 3/16 and threaded 3/16 x 40 tpi.
To save creating a stress point at such a step, taper at 60 degrees inclusive and
'countersink' the piston with a combination centre drill before drilling tapping size for
3/16 x 40.

Boiler: Height of Backhead 6in.
Height of firebox 4.1/4in. neither is critical.
The wrapper plates are probably overlong and will need trimming to match the flanged plates.
Before fixing the skirt length(see below) check that the lower tubes will fit the lower holes
in the firebox tubeplate, clear of the inside of the barrel.
The important dimension when setting out the tube positions on the firebox tubeplate is that
the top row of tubes should be 11/32in. from the INSIDE of the flange, (or 15/32in. from the
outside of the flange if marking out on the other side of the tubeplate). Do not drill the
7/16in.dia holes until the flanges have been made.
The drawing was redrawn for publication and the tubeplate thickness of 1/8in was not transferred.
The 'skirt' ie firebox below the outer, should be 5/16in..
Foundation ring should be 1/4 square all round but you may be only able to obtain 6mm square.
Use it.
The outer door plate (Backhead / frontplate) and the firebox doorplate should be parallel to
each other and vertical.
The firedoor and the water gauge bush should be on the same horizontal centre line and the
stays should be equally above and below this centre line and maintain the 11/16in vertical
centres. they are offset 1/8in. from the lower ones to place them nearer the centre of the
area alongside the firehole.
Get the blowdown bush as low down as you can, ie. 7/32in. above the foundation ring.

The 1/2in. hexagon for the top water glass connection should not have the 3/16in x 40 tpi hole
drilled and tapped yet. Drill 6BA clear and tap the hole in the boiler 6BA. Fix with a 6BA brass screw.
After the boiler has been silver soldered the screw is drilled out and the outer part tapped 3/16 x 40.
This is for a banjo pipe connection to the pressure gauge

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