Errors on drawings

[jones1972]

Hello Model Engineers,
I am thinking of doing Evan's Ivo Peters, but have noticed that the engine does seem rather wide at 9.750" and valve gear weighbar looks in the wrong position to the pictures of the fullsize in the same articles in M E i know he altered the gear for IMLEC purposes but it don't look right is Paul 1979 out there and could he show me the way he modified his valve gear and any errors on the design please or indeed any help from any builder of this locomotive i need a break from G W loco's!!
S N JONES1972

[baggo]

DIDCOT

Having recently acquired a set of castings and drawings for Didcot I've set about having a look. The drawings are very poor photocopies (as supplied by Reeves I believe- Eric-Jan Stroetinga also commented on the poor quality) so I've decided to produce a set of my own using 3D CAD.

A coupling of errors have come to light so far as I 'build' the loco on the PC:

Stay C for the rear subframes is shown as 1-15/32" deep on the drawings - I assume it should be the same depth as the front of the subframe i.e. 1-21/32".

If you make the weighshaft bracket to drawing, the mounting holes in the frame are in the wrong place - they need to be 11/64" (0.171875) further forward. Alternatively, make the bracket so that both front and back edges are angled with the top edge symetrical about the axis of the weighshaft.

The valve gear as drawn seems to give poor valve events when checked in the simulator so I've redesigned it using Don's spreadsheet. The original has a difference of 13% at 50% cut off although it's a lot better in full gear.

I'll post any more errors if I find them.

John

[dscott]

Baggo,

You could of course do a 517 or as Neville calls her Fair Rosamund. I had been checking the drawings for him after the first big mistake of putting angles all the way along the sides of the frames, plus missing out on any holes for the water pump in the frames, that was until he took a break to get well.

My version is true to scale and a very early model of 1890, I toyed with the idea of bearings but as you only take an engine out occasionally cast iron on silver steel will be fine.

Yesterday I bought a C.A.D. package similar to solidworks but at a fraction of the 4,000 pounds they were asking!!
The wheels were done on solidworks and machined using solidcam, the advantage being that everything can be built up in parts and assembled to check for fits etc.
I had great fun revolving the inner valve chest and changing the size of the inspection holes until I could see the edges of the valves perfectly from underneath. I am using 2 " square lumps of continuous cast iron here as we need as much weight as possible at the front end.

I still use a pencil and ruler etc for the first drawings as I enjoy traditional methods and in 1/16Th's and the good old 32Nd's!
Most of our Design degree students enjoy using inches and we have to convert these to mm for our machines.

David.

[baggo]

Hi David,

Thanks for reminding me about Fair Rosamond - there's probably a few ideas that I can 'borrow' for Didcot. I particularly like Neville's round valve buckles - much easier than the square ones! I shall definitely use the sealed bearings for the eccentrics. (I hope Neville is making good progress by the way).

I'll stick with Didcot as I've got the frames already laser cut and all the castings. I'm waiting on the wheels though as they are at the Derby club at the moment. I'm hoping they are not the same castings as Erik-Jan got from Reeves as the wheel bosses are grossly oversize .

The 3D CAD certainly makes life a lot easier for anyone designing a loco or anything else come to that. It makes finding mistakes pretty easy. It's virtually impossible to check your own work manually which is why If I do find mistakes in drawings it's not meant to be a criticism.

John

[dave254]

Just one I have noticed this evening. The myhobbystore plans shows the centre of the cylinder bore being 1/8" from the top of the cylinder. Its not! it should read 1/4". The original shop notes are however correct.
Ill add anymore as I find them (hopefully not the hard way like this one!)

Regards,
Dave

[dave254]

One more so far (for mollyette)... The plans say the ports on the cylinder should be drilled 3/64" centres. No my friend, 9/64" as per the original articles.

Dave

[davet]

Hi All

Just looking at getting on with the Tich I have had in the cupboard for a long time.

Looked at the slip eccentric design as I am using 3mm frames instead of the 3/32, so something in the valve operation has to be extended to cope with the different thickness of the frames.

In the calc's for the 3mm frames I kept getting what seemed to be the wrong answer, so I went back to the original design and with dear old progeCAD did the drawing for the original.

With the 3/32 frames, to the original LBSC plans and no allowance for movement in the various connections the centre line of the valve spindle to the centre line of the valve rod is 0.031 thou out (exactly 1/32"). The centre of the valve rod is too close to the frames at the 19/32" offset. So make the offset 5/8" and all seems well.

I cannot believe that I am the first to spot this so it is either well known or the 1/32" is the inbuilt machining and fitting allowances.

I started doing the calculations because in Malaysia the imperial sizes are difficult to come by, so time to replace 1/8" with 3mm etc, so the metric slot drills and slitting saws will be getting a work out.

Be interested to hear other peoples thoughts.

Kind Regards

DaveT
Kuala Lumpur
Malaysia

[quest]

Hi all.
Only recently taken up this intriguing hobby. After a lot of thought on what prototype to build (loco wise - still ploughing through a small stationary engine to hone my skills!) I've just forked out £125 (no I'm not looking for sympathy) for Keith Wilson's Bulldog. First thing I did was check the drawings for the bogie only to find an error (or 2) on a drawing - I've only looked at 3 so far, so how many more am I going to find? Not unusual according to a lot of contributors to this thread.

I'm not appealing for any help unless someone out there can help, but I have discovered from one of those useful spreadsheets on the internet that in ME issue 3603 Vol 145 contains info on errors to the Bogie frame and spring support!

My point is that if known errors like that are published then the designer is aware, so is it not too much to expect that after all these years the latest set of drawings would have them corrected and correction notices added to the drawing? I don't think this is asking too much for sold items to be fit for purpose as required by the Trading Standards legislation.

Not so much of a rant as an observation for my first entry into this forum. Before anyone suggests that I ought to approach the suppliers, in this case MyHobbyStore an email has already been sent to them. Will update if anything interesting happens.

Best regards to all you modellers out there.

Barry

[alanstepney]

In an ideal world, all "our" drawings would be perfect.
Unfortunately, in this world, errors on drawings are commonplace.

(You will find details of some at: www.alanstepney.info/page6.html )

In fact, I suspect that ALL, or almost all, of the usual model designs contain mistakes of some sort or other.
Where they dont, it is often because there are NO drawings for the part concerned.
(Instruction such as "make xxx in the usual way", are common.)

This has been discussed often here, on other message boards, in club-rooms, etc, and
the conclusions are basically, we have to work with what is available, so check, check and check again before cutting metal.

[Shawki Shlemon]

Barry , I built a Dukedog , I still have the engine , I run it every now and then . there are more mistakes, most are minor but one is very important to consider and that is valve gear . The expansion link is of loco type and therefore the output movement is less than input , the valve travel is not sufficient to fully open the valves , by the time I discovered this was too late , I resolved the matter by reducing the size of the valve , hence the lap and that of course reduces the expansion time and the engine is less efficient but it runs well . I didn't want to pull the crankshaft apart and change the eccentrics . I suggest that you check this and run on simulator and correct the amount of centre off set of the eccentrics.

[donashton]

Alan,

Just been looking at valve gear on John Clarke's B4 for a couple of forum members.
Slot radius is given as 7.5" and the offset eccentric pins by 0.5" leaves an eccentric rod length of 7", not the 6.812 stated.
The suspension offset is a bit of guesswork - this should be 0.267". Trim the lifting arm to 2.125"
This little lot transforms the performance figures, but crucial is the eccentric setting not even mentioned on the drawing. The advance angle (from the crank on back dead centre) wants to be 113.337 degrees! Are you still there?! That's simply 0.167" linear advance towards the cylinder. In full forward gear that equates to 2 or 3 thou negative lead. That way the pre-admission and compression don't climb uncomfortably when notching up.

Don

[Smifffy]

Martin Evans' Royal Scot

As I'm working my way slowly through my build, I have created a pate on my website to record the errors that I'm coming across. It can be found here:

www.markfsmith.com/Drawing_Errors.php

Smifffy

[springbok]

Thompson Springbok Class B1 Errors.
These were kindly sent to me by Nigel Field in Canada

Attachments:

[springbok]

Page 2 of errors in the Martin Evans Thompson class B1 Springbok

Attachments:

[springbok]

More Springbok errors
Kindly Supplied by Pete Seager

On checking I find the bogie on Springbok is already 3/8" too long.
Since no rush of satisfied users of locos built to the ME drawing materialized I did my own test on a salvaged piece of 30 ft radius track. The result showed about 1/16" clearance to exist. I spoke with one of our club members who has worked on Springbok. He suggested it just about works but suggested machining the front cover down to 1/8" thick. This I have done and I now have about 1/8" clearance. The attached photo shows the result, I machined the outer 10mm down to 3.2mm thick. (The dark centre is the unmachined centre of the cover not the bore!)
This image can be viewed in the Thompson B1 thread

[Andrew C]

Aug 28, 2011 20:13:07 GMT Smifffy said:

Martin Evans' Royal Scot

As I'm working my way slowly through my build, I have created a pate on my website to record the errors that I'm coming across. It can be found here:

www.markfsmith.com/Drawing_Errors.php

Smifffy

Hi Smiffy sorry I'm a techie

The link to you error page is an error too ;D

www.markfsmith.com/html/errors.html

is what you need. Nice site though the Scot is getting there. Just imagine the feeling the first time it moves under it's own power, priceless!

Andrew

[Smifffy]

Cheers Andrew - I have rebuilt my website since I posted that message, so thanks for pointing out the 'error'

;D

[jma1009]

BOXHILL

despite the quite considerable prototypical errors,
there arent many serious constructional errors by martin evans

1. turn down the front axles between axleboxes to 1/2" dia to give clearance for the slidebars

2. raise the bottom boiler bush for the water gauge.

3. if you must follow the drawings and fit a rear balance pipe for the tanks then you need to drill a hole in the frames for this which isnt shown on the drawings

4. the eccentric throw is too great and causes the valvegear design to be seriously flawed as a result. there is no suspension pin offset shown etc.

5. the valve rod bosses on the steam chest should not be relied upon as a press fit.

6. the axlebox drawings are awful and incorrectly show the axleboxes as being flush with the insides if the horncheecks.

7. the axleboxes as dimensioned allow excessive lateral play on the crank axle. hardly any play (say 10 thou) is required between the outer crank webs and the inside faces of the axleboxes.

8. the boiler IMHO with a 1/16" inner firebox wrapper at 90 lb psi is suspect as is the lack of proper girder crown stays. the inner firebox wrapper ought to be 3/32" and proper girder and longitudinal stays fitted.

cheers,
julian

[brucedouglassza]

Nov 24, 2008 20:05:44 GMT @paul1979 said:

My uncle and I found 5" Maid of kent stephensons valve gear to be totally incorrect, doesn't come close to notching up. The drawing for this gear is still sold by M.E. suppliers (they may well not know the errors are there) so watch out. However the Joy gear is spot on.

[brucedouglassza]

Modification to LBSC's Maid of Kent valve gear .
Model Engineer vol135 #3380 pg 1066 7-20 November 1969.

Cheers Bruce