Portable Engine Model Engineer Article by Tony Webster

[David CostelloParticipant @davidcostello75947]

What a complete fiasco this beginners engine has turned out.ME should never have started it.

Dave

[David Clark 13Participant @davidclark13]

I put it off for two years, I wonder why?

regards David

[Ian S CParticipant @iansc]

Oh well ***t happens, I suppose it give beginners some idea of the traps that are set to catch even the experienced modeler. I'm one that gets around the problem, don't use drawings, all mistakes are mine (pleanty of those). Ian S C

[JasonBModerator @jasonb]

All well and good but a beginner won't know that these are errors and may get dispondant and give up the hobby when things don't fit together or work. For example if they don't know how an engine is supposed to work they will end up with slidebars that are no where near parallel !! to use the latest issue as an example.

Is this the attitude we should be encouraging??

[MichaelRParticipant @michaelr]

All these errors are beginning to read like a epistle, there will be modellers out there who don't have access to this forum or even have a computer, who are building the model.

To help those who don't have access to the error information on this site of this particular model, I think the editor should consider publishing free with a issue of Model Engineer a supplement of all the known errors, I fear some beginners may have already thrown their hand in.

Stick.

[Mike WainwrightParticipant @mikewainwright87512]

I think that Model Engineer should print a full set of amended/corrected drawing in the next available issue so that everyone that buy's the magazine is aware of the errors and have something that they can work to now.

It is a shame that there has been so many errors as I was looking at this as a possible project while I was building the Simplex. I have a full set of drawings for the Allchin that I bought on ebay so I will get the constrction book and see if I am able to make that once I have finished the popcorn engine that was run as a series a while ago.

[Sub MandrelParticipant @submandrel]

Perhaps the fairest thing would be to print a message saying a list of amendments is being prepared that can either be found here or send an SAE for a print out?

I have to be honest, I check every dimension from the job anyway, as I don't trust my work to be accurate enough

Neil

[JasonBModerator @jasonb]

The best way to do it would be as it was in the past, at the start of the next part of the article any errors or ommisions were dealt with before the build continued. Keeps it upto date and all in one place.

In ideal place to print these would be in the half column that is left blank under each authors photo, that way no extra magazine space is wasted.

Its a shame errors can't be dealt with like one of the other model engineering mags I subscribe to, if any are found a new drawing is produced with CAD and a pdf version sent to the subscribers. A printed version is also published in the next issue. That way you are not held up waiting for revisions and you know of any errors within days of the mag dropping on your door mat.

J

J

[Ian S CParticipant @iansc]

An errorata column in Model Engineer may be a good idea, hopefully not in every issue, can't remember, but there may have been one in the past. Jason may have the idea. Ian S C

[David Clark 13Participant @davidclark13]

Hi There

We are working to far ahead to get it in the next issue.

We are about to start 4430 and corrections will be in there.

regards David

[David Clark 13Participant @davidclark13]

Just back from holiday.

The 11/16 and 13/16 centres are correct. 11/16 puts the fixing holes in the centre of the slide bars, but to give a little more space for the nuts at the support end the centres are 13/16". I've just been out to the workshop to measure them. The bars are a constant 3/8 between.

[SpringbokParticipant @springbok]

Well David this sounds like a complete disaster of a series but I am sure that you are not personally able to build every single model that is published in ME to find errors. Did the author not build as he was working on the drawings and make changes or notes of errors..

Bob

[JasonBModerator @jasonb]

So are you saying the two bars are on 11/16" centres. If so the end elevation is wrong as that has them sticking out beyong the support bracket in which case the 1" dimension is wrong, the 13/16" dimension to the reinforcing web is also wrong and how do teh bars fit each side of teh support which is 9/16" wide, they would need notching around it???

I think a new drawing is needed as there are just too many anomolies on this one to try and describe in writing alone.

[Sub MandrelParticipant @submandrel]

Tony Webster has been writing for ME for a good 20 years on traction engine related topics. His It's ashame these drawing errors are detracting from what is a really nice looking model that clearly has inspired a lot of people to have a go. models are always good looking and robust, and he's willing to use a few 'tricks' to get it looking right.

I suspect the problem here is drawings made from the model without complete dis-assembly?

Neil

[JasonBModerator @jasonb]

Just been thinking about what I said above and looking at the photo I linked to on the previous page.

If the 5/16" wide bars are on 11/16" cts that agrees with Davids 3/8" between bars. But the bar support is given as 9/16" wide ( this looks in proporting) so the bars would need to be notched out to fit round it making the bar ends 7/32" wide, this would be why the bolt spacing is increased to 13/16 at this end.

Looking at the photo confirms that the bearing surface of the bar is wider tha the end that we can see.

David can you confirm if the front end of the bars are notched and if so why was it not on teh drawings

 

Another greek C**k up that has made it hard to follow is that the 15/16" & 5/16" dimensions shown against the end of the plan view actually apply to the side elevation, the 5/16" being the Horiozontal gap between the slide bars and the 15/16" is just about right for the height of the oval cutout in the support post.

 

Edited By JasonB on 29/04/2012 19:17:28

[JasonBModerator @jasonb]

Further to the above this is the "drawing" as ME click both to enlarge

And based on Davids Measurement, looking at photos and applying a bit of common this is a quick sketch of what I think it should look like

 

 

J

Edited By JasonB on 29/04/2012 20:38:37

[JasonBModerator @jasonb]

Posted by David Clark 1 on 13/04/2012 15:53:11:

Hi There

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

regards David

Well the "corrected" drawing that has been published in 4429 STILL HAS ERRORS, lets hope someone will be third time lucky when the second revision is published.

Also hope no one has made the valve chest yet as the tail rod bush detailed in 4429 may be a bit of a loose fit, I find drilling a 3/16" hole does not give much thread engagement on the specified 3/16×40 thread!! The 1/4" hex on the bush has also been drawn as 1/4" across corners not AF

Couple of 1/16" dimensions on the valve block would also help beginners.

Edited By JasonB on 01/05/2012 19:45:22

[David Clark 13Participant @davidclark13]

Hi there

the blind bush clearly states 1/8 inch.

Where is the 3/16 hole dimension? It appears to have been left off my issue.

The 1/4 inch Hex is given.

Nowhere does it state corrected on the the cylinder saddle drawing.

It says the incorrect drawing was printed and this is the correct one, not corrected one.

Where would you like the 1/16 dimensions, in the corners of the cavity or on the recessed edges of the valve?

Either way, who can say if they are 1/16 or not.

What errors are there on the cylinder saddle drawing?

It was corrected by Tony.

 

Edited By David Clark 1 on 01/05/2012 22:55:20

Edited By David Clark 1 on 01/05/2012 22:56:08

[JasonBModerator @jasonb]

Off out to work but will reply later. to drawing errors

"Nowhere does it state corrected on the the cylinder saddle drawing.

……………………………………………….

It was corrected by Tony."

 

I think you just said it yourself

 

J

Edited By JasonB on 02/05/2012 07:55:52

[JasonBModerator @jasonb]

Blind Bush.

1. This is shown with a 3/16×40 male thread. if you look back at issue 4427 the valve chest that this is meant to screw into is shown with a plain 3/16" hole at each end. That is why I said that I hope no one has made the chest as it should obviously now have had one end threaded 3/16×40 for the bush to screw into.

While correcting the valve chest Its worth pointing out that there is no form of gland shown on the rod side either so may be worth sorting that out at the same time.

2. the drawing may well say 1/4hex but that is not what the drawing shows. If you look closly at the hex part it is drawn with one of the flat faces facing the viewer which means there are two of the corners of the hex top & bottom in line with the 1/4" dia of the end of the bush. This would show that the bush is made from 1/4" round stock and the hex is machined into that so the max AF hex size you could get is 0.216"

If the 1/4 hex dimension shown on the drawing is correct as you say then the part will need to be made from 1/4" hex stock and the larger distance across the corners should be shown on the drawing.

Valve

1.Yes 1/16" should be on the recessed edges of the valve. "Either way, who can say if they are 1/16 or not." This is exactly why the dimensions should be there we should not have to make an educated guess or in the case of a beginner an uneducated one.

Valve rod

Would have been good to show the flat on teh 1/8" reduced dia part but as its in the text I'll let that one go.

Drawing of the corrected saddle to follow. Any thoughts on that sketch I posted on the guide bars? as the 3/8" dimension you measured would throw a lot of other things out.

Edited By JasonB on 02/05/2012 14:11:45

[JasonBModerator @jasonb]

Cylinder saddle issue 4429

As said above I feel this drawing is still wrong, the reason being that the position of the 1/4" steam feed hole and two of the 4 mounting hole are dimensioned at 3/4" and 3/8" in from the edge respectively. They also have the same dimension in from the end of the inverted cylinder plan that was in issue 4426. The problem is that the base of the cylinder is only 1 15/16" long but the saddle is 2" long so no allowance has been made for the 1/32" difference at this end but it has at the other because the holes are shown at 9/32" which is the 1/4" + 1/32".

Click on the pic below to get a larger view of what I feel is correct in black and what the drawing in 4429 gives is shown in red.

Comments from Tony or David awaited

Jason

[JasonBModerator @jasonb]

Just back to the valve again.

The valve chest is shown with a cavity 3/4" wide yet the drawing of the valve has the 13/16" dimension fitting into this 3/4" space

EDIT when the valve is assembled with the nut this will increase the whole assembly by another 1/32" giving an overall width of 27/32 which is an even more impossible fit into the 3/4" space

Edited By JasonB on 02/05/2012 16:36:34

[JasonBModerator @jasonb]

Any comments yet on the errors I have raised that were in 4429, would be nice to get an answer before 4430 drops on my mat.

Oh and of course all the other queries over the last six weeks.

J

[David Clark 13Participant @davidclark13]

Hi There

The following will be published in ME 4431.
Some changes will be made if I get the information in time. Comments are welcome. This text is an attempt to get it into order.

The drawings for the portable engine have some errors and omissions. After discussion with Tony Webster, we have come up with some clarification and corrections.

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

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 hole sizes for the bushes can be obtained from the bush drawings.

The holes for the eight corner stays for fixing the horns should be 7/32in. dia. i.e. the 1/4in. dia. is reduced slightly in diameter to provide a 'head' to stop them falling through when silver soldering. The head is 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.)

The overall width of the firebox is 4 3/8 inch. The inside width of the horn plates is 4 3/8. Clearly there is no room for the head of the corner stays.

I think the stays go right through the inner and outer firebox side with the inner side holes being
7/32 and the outside being 1/4 with the outside of the stay flush with the outer firebox?
Also, can you supply a sketch of the corner stays to help clarify this?

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, i.e. 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.

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.

Boiler: The height of the backhead is 6 inches.
The height of the firebox is 4 1/4 inches, neither is critical.
The wrapper plates are probably overlong and will need trimming to match the flanged plates.

The 7/16in. boiler tubes should be 20 swg; a standard thickness that should be available from your friendly model engineer's stockist. The tubes rise towards the front of the boiler.

Continued in next post.

[David Clark 13Participant @davidclark13]

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.
When the drawing was redrawn for publication the firebox tubeplate thickness of 3/32in was not transferred.
The 'skirt' i.e. the firebox inner wrapper should be 5/16 inch below the outer wrapper. The foundation ring should be 1/4 inch square all round but you may be only able to obtain 6mm square which will be fine.

The outer door plate (backhead/front plate) 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, i.e. 7/32 inch above the foundation ring.

The drawing says two off regulator bushes, as far as I can see one fits the top of the barrel and the other goes on the backhead.

Q. Should there be any thickening pad inside the boiler to mount the crankshaft bearings? A. The Crankshaft is mounted around the boiler by a strap so no thickening plate should be needed.

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

Q. Confirmation of an available thickness for copper in substitution for the 3/32 inch and 1/8 inch thickness shown on drawing. A. Go slightly thicker not thinner.

Q. Will the cylinder stud holes be detailed on the valve chest drawing? A. The positions for the 10 off valve chest stud holes are detailed with the valve chest.

Q. For the cylinder drawing the text says machine the valve face back to lines 1 and 2 but drawing shows it at least 1/32 inch away from them. A. Machine to the line as the text says.

Q. The length of cylinder and protrusion of end faces are not shown on the drawing? A. They can be found in the text.

Q. There is no depth for the steam port slots. A. They must not beak into the cylinder bore.

Q. Width of valve chest given as 3/8 inch? A. This should be 1 3/8 inches.

Q. No length is given for the piston rod. A. I am awaiting the length.

The 1/4in piston rod dia. should be stepped down to 3/16 inch and threaded 3/16 x 40. 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.

Q. Crosshead has no thickness given. A. 3/8 inch should be fine.

Q. No depth for piston ring groove. A. Make deep enough to take packing or alternatively use O ring charts to fit an O ring.

Q. No length of 1/4 x 40 thread on piston rod. A. Make to a length to screw into the crosshead as far as the slot, approximately 5/16 inch.

Q. No depth for cut out in crosshead. A. 9/16 inch will be OK to clear little end.

Slide bar drawing

Q. The plan view gives width over the outside of the bars and bracket as 15/16 inch. A. This is correct.

Q. The plan view gives one end of the bars at 13/16 inch centres and the other end at 11/16 inch centres? A. This is correct; you will have to relieve the slide bars at the left-hand end, as drawn, to clear the oval section.

Q. The end elevation gives the bracket as 1 inch wide and the bars project beyond the bracket. A. The bars should not project outside the 1 inch dimension. I think the 1 inch is also related to the 1 inch diameter that enters the cylinder.

Q. The oil cup does not show the hole carried through the slidebar. A. It goes right through the top slidebar.

The valve chest

The blind valve end is shown with a 3/16 x 40 male thread, if you look back at issue 4427 the valve chest that this is meant to screw into is shown with a plain 3/16 inch hole at each end. That is why I said that I hope no one has made the chest as it should obviously have had one end threaded 3/16×40 for the bush to screw into.

While correcting the valve chest it’s worth pointing out that there is no form of gland shown on the rod side either so may be worth sorting that out at the same time.

Cylinder saddle.

Q. Is this the actual view of a developed shape of the curved part.

Q. The 1/8in. dimension at the bottom left is wrong, it should probably be ¼ inch.

Q. The two 9/32 inch dimensions on the left seem wrong as the hole will break through the edge, 11/32 inch would be nearer what is right.

I feel this drawing is wrong, the reason being that the position of the 1/4 inch steam feed hole and two of the four mounting holes are dimensioned at 3/4 inch and 3/8 inch in from the edge respectively. They also have the same dimension in from the end of the inverted cylinder plan that was in issue 4426. The problem is that the base of the cylinder is only 1 15/16 inch long but the saddle is 2 inches long so no allowance has been made for the 1/32 inch difference at this end but it has at the other because the holes are shown at 9/32 inch which is the 1/4 inch + 1/32 inch.

continued below

Edited By David Clark 1 on 11/05/2012 19:08:05

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