CAD / Perrier - Spinks Britannia

[shmbry]

I am continuing my efforts to verify the Perrier/Spinks drawings using CAD. It is progressing well although having looked at Steve (springcrocus) posts and web page and Jim's 'Boadicea' posts there are numerous areas that need amending. I too have found several areas that either are incorrectly dimensioned or just don't make sense initially. Although I was aiming to create the model as drawn and then to amend where neccesary, I have already incorporated a couple of mod's others have inspired. One of the major things at the moment is a disparity between the heights of the pivot blocks on the loco and tender. This is with the axles of the loco and tender set to the drawing height. I am going over the drawings, again but I wondered if anyone else had encountered this ?

[oldnorton]

This would be a nice thing to see when you are finished.

By 'pivot blocks' do you mean the drag boxes?

If you have got the tender axle boxes in the middle their horns, and the three driving axles in the middle of theirs, do the drag boxes not align? The pony truck (brass) riding pads are always a matter of individual adjustment depending on how much load each main axle is taking. The pony truck axle boxes should be sitting mid-way as well, so adjust those brass round pads.

Norm

[uuu]

Another check (to see if your CAD model has the correct ride heights) could be the buffer heights on the front of the loco and back of the tender - you'd expect these to be the same.

Wilf

[shmbry]

This is the part I am refering to:



The drive axle / tender axles centres are at mid height of their horns in accordance with the drawings. The Loco front and tender rear buffers are at 3 21/32"

[oldnorton]

Yes I think those are called the draw bar rubbing plates, affixed to the outer parts of the drag boxes.

I have not looked at my Perrier drawings to see if what you have drawn compares. But your pony truck axle box seems to be at the bottom of its travel. What does occur to me is that most builders have used the Les Warnett 9F tender drawings, have you also?

Norm

[oldnorton]

OK. I have pulled the drawings out.

The Les Warnett General Assembly (GA) tender sheet shows the tender buffers at 3.72 inch and the drag box centre at 3.52 inch, both above track top, taken from the drawing with callipers.

Perrier does not have a GA sheet so I will give you my actual measurements from my loco which are buffers at 3.60 inch and drag box centre at 3.42 inch.

We won't worry about the 0.1 inch differences.

Your tender drag box at 3.47 inch seems fine, the loco is sitting 0.3 high at 3.78 inch.

GL5 standards for buffer height are 3 5/8" plus 1/16 minus 1/4, so 3.62 inch buffers is what the designers were aiming for in 5 inch gauge.

Norm

[shmbry]

I've done some further checks. My rubbing block was oversize (Height) at 1 3/8" rather than 1 1/4" so this has brought the disparity down to 1/4". I have used the 1" dimension on sheet 1 to give the axle height in the frame, and the driving wheel diameter to give rail height.

The height of my rubbing block was down to the drawing actually meaning 5/8" and not 11/16" as measured. It seems sometimes measuring the drawing is aceptable in this field. Sometimes the dimensions are what is drawn, and sometimes not.

I have also done some preliminary views of the pony frame, drag box and rear beam assembly to try and understand the overall. I can't see how I can get the drag box height to 3.42" using the given dimensions.

[oldnorton]

Glad you are getting nearer to some answer.

I don't think we should assume that the frames are supposed to sit parallel to the track, which is how they will probably have been drawn.

Your fixed points above the track are the buffers front and rear. Then we can assume that the tender should sit with the same axle height in each horn gap. This sets the tender drag box centre and I think you should align the loco drag box to match that. Now put the loco centre axle in the middle of its horns and you have two fixed points that set the alignment of the frames. Now set the front boogie pivot pin height and the pony truck rubbing supports as necessary to centralise those axles. Out of interest, how far from centre are the leading and trailing main axles? I would expect it is less than 0.1 inch.

In the absence of a loco GA drawing I would guess that this alignment of parts was not done by Perrier to set the drag box height? You might be the first to re-draw it all. All builders would have resolved the height of the bogie and pony truck by trial and error anyway. Well, they would if they wanted the spring loads and axle travel to be correct.

Norm

Norm

[shmbry]

Norm

At present all three drive axles are at the same height, at the axle centre line prescribed on sheet 1. Are you implying the frames should slope down to the rear to align the rubbing blocks ?

I've been trying to get a copy of the original Perrier drawings. For two reasons, firstly I have read a lot of errors were introduced in the re drawn drawings and secondly the height disparity may be because the current drawings use a tender from another source. It would be intriguing to find out what the differences are between the two tenders.

I have also ordered the 'Oliver Cromwell' line drawings from Blackgates although I am yet to find out if this is a Perrier or Spinks or completely disparate drawing.

I'm also making enquiries with NRM to try and get the Derby GA drawing.

[ettingtonliam]

If it was mine, I'd just adjust the height of the rubbing blocks to match, and move on.

[shmbry]

I'm waiting to see if the pont frames need adjusting as the rear beam / cab floor dimensions don't make sense either. Plus the pony truck spring pin is a corresponding 1/4 too short for its hole to line up with the pony truck return spring cross shaft axis.

[oldnorton]

Mar 17, 2023 8:12:52 GMT shmbry said:

Norm

At present all three drive axles are at the same height, at the axle centre line prescribed on sheet 1. Are you implying the frames should slope down to the rear to align the rubbing blocks ?

No, you are not following my suggestions in my last post. I  said that you have a fixed height above the rail for the drag box centre, then put the centre driving wheels on the rail with their axle box centred, by rotating the frames. They are going to shift one degree or something.

Just as ettington says, now adjust the rubbing blocks on the bogie and pony truck and 'move on'.

The Blackgates drawings are attributed to N Spink who got them from Perrier.

If you want proper scale drawings then get the Doug Hewson ones from Steam Workshop. He has done all the work scaling from originals and you won't reinvent a better wheel than the one he has made.

Norm

[shmbry]

A. We appear to be talking about different parts. The part you are refering to I believe is the Pressure Pad. I am refering to the Coupling Blocks casting No. 30

B. Unfortunately I can't afford a Hewson model, nice as it is however I do have most of the Spinks castings and the set of Spinks drawings.

C. I have bought a couple of sheets of Hewson drawings but unfortunately they have very few dimensions and I can't see how the parts could be made without measuring the drawing.

Thank you for your patience in answering my previous questions.

[92220]

If it is any help. I have the B.R. detail, and arrangement, drawings for the B.R. Standard tender frame assemblies, fitted to 9Fs and Britannias. I don't have the drawings for the Britannia loco, but the drawbar position will be exactly the same height as on the tender drawings. The fullsize height of the drawbar centreline from the surface of the rail, on the B.R.Arrangement drawing, is 3' 5.1/2". This scales out for 1.1/16" to 1' (5" gauge) at 3.673", so neither model drawing drawbar height, is shown at true scale height. Just for information, the quick way to scale fullsize B.R. dimensions to suit 5" gauge, is to multiply the fullsize dimension x 0.0885 Example:- 3' 5.1/2" = 41.5". 41.5 x 0.0885 = 3.67275 (3.673")

Bob.

[shmbry]

Many thanks Bob. I'm not intending to create hyper accurate scale drawings or model, virtual or otherwise, I'm just trying to ascertain if I have read the Spinks drawings correctly.

[ejparrott]

There's a classic error in Les Warnetts 9F drawings, showing the radius on the inside of the brake blocks to be something like 1 25/32"....for a wheel diameter of 5 5/16".....does happen

[shmbry]

Mar 29, 2023 13:48:59 GMT ejparrott said:

There's a classic error in Les Warnetts 9F drawings, showing the radius on the inside of the brake blocks to be something like 1 25/32"....for a wheel diameter of 5 5/16".....does happen

Many, many thanks. It's little pieces of information like this that are invaulable. Having searched the net and read numerous posts / pages I'm am gradually picking up the in's and out's of the Britannia.