Portable Engine Model Engineer Article by Tony Webster

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 drilled 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. The view shows the slidebars at 13/16 centres when they should be 11/16 centres. At the 13/16 inch end the bolts are offset outwards from the slidebar centreline.

Q. The end elevation gives the bracket as 1 inch wide and the slide bars project beyond the bracket.

A. The slide bars should not project outside the 1 inch dimension, they are 15/16 inch overall width.

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. One end of the steam chest should be threaded 3/16x40 for the bush to screw into. If you have already made the valve chest, the blind valve end could be tapped 7/32 x 40 and the thread made to suit.

Saddle and cylinder

Q. Is it correct that the cylinder does not sit centrally on the curved flange front to back?

A. The saddle should be made first and the cylinder clamped to it centrally back to front, i.e. 2 inch and 1 15/16 inch dimensions. It is not central the other way, or not until the Valve chest and cover are fitted. The 1 1/4 dim. is to clear the stud holes for the VC otherwise it would be the same as the other side at 1 7/16 centres. Use the saddle to drill the cylinder. If all saddle holes are first drilled tapping size, it will be easy to the saddle as a drilling jig.

After drilling the cylinder, remove the saddle and clamp the saddle to the curved top part of the horn plates. The 1/4 x 40 steam intake hole should line up with the centre of the large bush (other regulator bush) but make sure that the valve face is VERTICAL. The cylinder is not on the centre line of the boiler. It rarely was on portables or traction engines.

Hi There

Most of the corrections are above.

Some questions deleted as all will become clear later in the series.

regards David

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 drilled 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. The view shows the slidebars at 13/16 centres when they should be 11/16 centres. At the 13/16 inch end the bolts are offset outwards from the slidebar centreline.

Q. The end elevation gives the bracket as 1 inch wide and the slide bars project beyond the bracket.

A. The slide bars should not project outside the 1 inch dimension, they are 15/16 inch overall width.

J. Two things are said to be "correct" but they contradict each other, I will do a sketch as its easier to see the error.

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. One end of the steam chest should be threaded 3/16x40 for the bush to screw into. If you have already made the valve chest, the blind valve end could be tapped 7/32 x 40 and the thread made to suit.

J. Fair enough but any answer on the other end of the chest, there is no gland shown for the 3/16" end of the valve rod.

A. The saddle should be made first and the cylinder clamped to it centrally back to front, i.e. 2 inch and 1 15/16 inch dimensions. It is not central the other way, or not until the Valve chest and cover are fitted. The 1 1/4 dim. is to clear the stud holes for the VC otherwise it would be the same as the other side at 1 7/16 centres. Use the saddle to drill the cylinder. If all saddle holes are first drilled tapping size, it will be easy to the saddle as a drilling jig.

After drilling the cylinder, remove the saddle and clamp the saddle to the curved top part of the horn plates. The 1/4 x 40 steam intake hole should line up with the centre of the large bush (other regulator bush) but make sure that the valve face is VERTICAL. The cylinder is not on the centre line of the boiler. It rarely was on portables or traction engines.

J.So in other words the dimensions on the saddle are wrong as I said, A corrected drawing should be issued and the cylinder drawing altered so that it reads that the 5 holes read "locate from saddle"

J. While we are talking about teh cylinder I think a passage way has been missed off the drawing as there is no way steam can get from the 1/4" brass pipe into thevalve chest, I could be making assumptions but there is no way this engine will run as its drawn!!!!

Hi There

Should have read slidebars, not slidebars and bracket.

I can't see the contradicition.

The other end gland will be shown later.

I don't know if the dimensions of the saddle are wrong.

The hole is there on my original copy but the dotted lines are missing

from the redrawn diagram.

The hole goes from the hole on the bottom right and is angled down towards the brass tube.

regards David

Edited By David Clark 1 on 14/05/2012 20:33:12

Right Lets see who is any good at basic maths.

I one reply Tony says gap between bars is 5/16" and overall width 15/16" but this would put the bars on 5/8" cts, this is the lower of the two sketches.

In another reply Tony says Bars are at 11/16"cts, but this would mean the gap between bars is 3/8" and the overall width 1", He also said earlier that he went out to his shed and measured the gap at 3/8" This is shown in the upper sketch which I think is correct.

Please chose one or the other as both can't be "correct" Click image to see it larger.

Sorry, that is my fault.

Lower is correct.

They were drawn on what appeared to be 11/16 centres, obviously not.

regards David

Edited By David Clark 1 on 14/05/2012 20:39:42

Looks like our posts crossed, yes that is the elusive passageway that I made the assumption was missing, most of my assumptions are right

David is there any chance you could let me know the thickness of the "hornplate" wrapper that the cylinder saddle fits on as I can foresee an issue and it would be nice to preempt it.

I do also have an issue with the position of the valve ports as drawn but as it won't affect running will let it go.

J

Sorry, that is my fault.

Lower is correct.

They were drawn on what appeared to be 11/16 centres, obviously not.

J. But how did Tony measure it at 3/8 about a week ago, I think the top one is right as it works so much better with all the other sizes, the bottom option throws other parts out

Can you post the original sketch, I think that the 3/8 & 15/16 sizes that appeared in the mag against the plan view were meant to be against the side view.

Edited By JasonB on 14/05/2012 20:50:03

Not all corrections are Tonys.

The centres are not 13/16 inch, they appear to be 11/16 inch but probably not.

The bottom one ties in with the original drawing.

I doubt it matters which but the width between slidebars is definitly 5/16 on the original.

Hornplates are 1/16 inch thick.

The wrapper thickness is not on the drawing but looks the same or slightly thinner.

The wrapper is 1/2 inch higher than the top of the boiler.

How the clinder fits on that I have no idea at the moment.

regards David

Edited By David Clark 1 on 14/05/2012 21:00:20

Edited By David Clark 1 on 14/05/2012 21:17:59

Well looking at the drawing one or the other must be wrong as that plan view shows the wide centre spacing of 11/16 and the narrow overall width of 15/16. I notice that the locating spigot on the cylinder cover at 1" dia is drawn in line with the outer edges of the bars so could well be 1" overall, not that we should work things out like that.

Is that really 11/16" !!!!! thick or 1/16". then there is an error on the cylinders curved base which will mean its scrap. Getting too late now, I'll draw it in tomorrow don't want to make a mistake. With what we have been given so far the wrapper can only be 1/32" thick

I can see how the horns will fit but can't work out how the 1/4" pipe will seal to the large top flange and connect to the regulator

J

Edited By JasonB on 14/05/2012 21:18:15

Hi Jason

Just because it is higher does not mean the radius is incorrect.

No, 1/16 inch thick.

Now you know why it took 3 years to decide to print it.

regards David

Right 1/16" is better and I edited my post while you were posting your reply, yes height won't be an issue but radius is not right.

Radius will be half the overall width over the outside of the horn plates.

Boiler 4"

Twice firebox wrapper thickness3/16"

Twice hornplate thickness 1/8"

thats 4 5/16 so radius 2 5/32"

To this we add the thickness of the saddle at 1/8"

Total radius to underside of cylinder 2 9/32, thats not what is on the cylinder drawing, maybe a thick gasket is needed? May be able to re machine but it will drop the cylinder centre line.

The inside radius of the wrapper is 2 1/4 inch (8/32) + the thickness of the wrapper = the outer radius.

If the cylinder is 2 9/32 that means the wrapper is 1/32 thick.

regards David

No, Cylinder is  2 1/4, Which means radius of underside of saddle is 2 1/8" ,don't think you are getting what I am saying, that's why I will do a sketch tomorrow. But just to say those figures are based on the 4 3/16" O/A firebox width not the (in)correct size of 3 3/8" given yesterday which would result in an even bigger radius.

Edited By JasonB on 14/05/2012 22:24:43

Hi David & Jason, with regards to the slide bar sketch and the question of the 13/16 and 11/16 centres, I believe are being misinterpreted. My understanding of the cross marks these two measurements are referring to are centres of the fixing holes and not of the bars. I do agree that a 3/8 gap makes more sense, in that it makes the 13/16 measurement to be more realistic.

Forgive my rubbish sketch below, but this is how I have interpreted it. At the end where it is shown the 13/16 measurement, there has to be at least 3/32 cut out of the edge of each slide bar to accommodate the loop structure and this would leave 7/32 to accommodate the fixings. If the fixings were to be put in the middle of these 7/32 portions, you would end up with 25/32 centers for the fixings. By adding 1/32 to 25/32 you would arrive at 13/16, which would be a more sensible figure to work to and will give a little more clearance between the loop structure and the fixings.

Regards Nick

Nick thats just about the same as the sketch I did back on page 2 or 3. Great minds think alike

Several of Tony's replys specifically say "bars at 11/16" cts" so its not just teh screw holes nearest the cylinder that are at this spacing. I'm going to show a few of the other parts assembled to the bars and this will show when compared to a photo of the engine that the 1" overall width is the most likely correct, off to work now so will do it tonight.

Edited By JasonB on 15/05/2012 07:38:36

Hi There

I will ask Tony to redo the entire set of drawings.

No point publishing further episodes until it is sorted.

In fact, It will be easier to ask how many people are building it.

If only a few, drop the entire series and offer them a set of the remaining drawings to sort it out themselves.

regards David

Edited By David Clark 1 on 15/05/2012 09:22:03

Looking at the next part of the portable, it looks like there are many more errors.
The question is, do I drop the whole series or wait for Tony Webster to correct everything?
It will help me to decide if I know how many people have actually started to build this engine.

Please let me know if you have started this engine ASAP.

regards David

Its a shame if it comes to that, maybe ask in the mag as well just incase there are builders who don't visit the website. I know we did have a set of finished wheels posted by one member but they have gone a bit quiet lately.

I'm happy to look over any drawings in advance if it helps. Or even resurect it using the boiler and wheels that we have at the moment and rehash what you have of Tonys drawings so far if there is any demand. As I have said its has the potential to be a good model and the next step from stationary engines upto traction engines.

J

I have asked in the mag but that is 3 weeks from publication.

Jason, can you email me at

[email protected]

Edited By David Clark 1 on 15/05/2012 15:21:41