Pakpaul's Workbench

[JimG]

Paul,

To turn to cosmetic nuts, which could be either square or hexagonal, I think the bet approach is by CNC milling or engraving of styrene or other plastic such as ABS or acrylic.

Below is a photo of 1/32nd scale 7/8" whitworth bolts in styrene.

View attachment 44688

The size is roughly 1.5" by 2.5", and the spacing is determined by the diameter of the parallel engraving cutter used. In the case of the above sample the central hole dot was made with an engraving cutter, and this has resulted in the .55 mm drill used to cut oversize, or as can be seen to jump out of the dot. Future production will use a centre drill to mark the hole position which should avoid oversized or misplaced holes.

If you are CNC milling the nuts, then peck drill the holes using CNC with a slot drill of the appropriate size, or profile mill the holes with a smaller diameter slot drill. Then you avoid the problems of locating a drill in a subsequent operation.

Jim.

 

[JimG]

Paul, or Jon,

Do you have data on the actual diameter of bolts used on wagon and coach construction? Since this topic started, I've checked back through all my official GA drawings of stock, or books and articles in magazines - like Chris Croft's article in the early MRJs - but I can't find any statement of the particular screw sizes used.

Jim.

 

[Jon Nazareth]

Jim

I'm sure Andy B has the relevant information for Midland wagons. I assume that it would be pretty much universal.

Jon

 

[pakpaul]

If you are CNC milling the nuts, then peck drill the holes using CNC with a slot drill of the appropriate size, or profile mill the holes with a smaller diameter slot drill. Then you avoid the problems of

Jim

The supplier I used for my miniature carbide slot drills did not do the range of sizes that are available from others, which I found out after reading your comment. I agree the more the machine can do the better and the less chance of mistakes or errors once we have got the instructions right!

Paul

 

[pakpaul]

Nut and Bolt sizes

Jim

With regard to actual bolt sizes used, it does depend on company and type of wagon, and in some cases it is difficult to find the data from an individual GA. If you have a series of GA's available for one company such as those published in Wild Swan's wagons of the LNWR you can build up a picture of the bolt sizes they used.

Also in general where a hole diameter is quoted to receive a bolt the the bolt size used will be 1/16" smaller than this hole size. For example the hole in a brake block for the bolt for the hanger is 15/16", the bolt size is 7/8". In the case of the brake push rod, the hole size is 13/16", bolt size 3/4".

In general axleguards are held onto the solebar with 7/8" bolts but Midland 8 ton wagons used 3/4"; Brake V hangers with 3/4" bolts.

RCH wagons have the side strapping held by 1/2"bolts and nuts, but end strapping is held with 5/8" bolts and nuts.

LNWR 1/2" square nuts sides and ends (but 5/8" for coupling plate), buffers 3/4" hexagon head.

Underframe tie rods are usually 1'' or 7/8".

Where the GA's are reproduced to the 12mm to 1' favoured by Wild Swan in their magazines and books, I find I need a watchmakers eye glass to be able to read the bolt sizes. I prefer to scan these GA's at high resolution and enlarge them on the computer screen. this way you can also measure the drawings a/f size of a known nut or bolt, and compare this with an unknown one. I know you should not scale from a drawing, but if there is no other option?

I hope this rather rambling response may be of some use, perhaps another approach could be to draw the wagon in a CAD program, and play with the size of the fasteners until they look right in comparison with a photograph.

Paul

 

[JimG]

Paul,

That information is excellent. I model mainly Caledonian and I think they used square head nuts and could well have practices similar to the LNWR with whom they had a close working relationship. I warn you that this forum can be a tough place regarding nuts and bolts. I had to re-machine the nuts on two S scale cylinder covers to get the correct AF measurement a year or two ago.

Jim.

 

[pakpaul]

Jim,

I had a quick look at my copy of Calendonian Wagons and NPCS, and for a 7 ton mineral wagon all nuts seem to be square ones, 5/8" on body and strapping, 3/4" for axleguards and 7/8" for tie rods.

Paul

 

[JimG]

Paul,

Thanks for that. I believe that there is a supplement to Mike Williams' wagon book coming out soon but it will be as part of the new coaching stock book. I think the publishing date is geared up for the Perth exhibition (in Scotland ) which is the last weekend of this month. I've been waiting on this coaching book for a long time.

Jim.

 

[JimG]

Paul,

I also dug up this web site which gives details of AF dimensions, etc., of square head bolts, and nuts, I presume.

http://www.globalfastener.com/product/detail_2742.html

Jim.

 

[AndyB]

Paul,

I also dug up this web site which gives details of AF dimensions, etc., of square head bolts, and nuts, I presume.

http://www.globalfastener.com/product/detail_2742.html

Jim.

Jim,
But don't forget the other discussion here and on your original thread here about A/F sizes and the change in 1940 - so sizes quoted on modern fastener sales sites will not be accurate for early c.20 models.

Andy

 

[pakpaul]

Jim,

This is a Chinese marketing site.

The standard referred to in the example you gave is for partly machined bolts, and in imperial sizes, the site seems to quote head a/f sizes for BSF bolts with Whitworth thread, and less than the usual standard head height. I think the railways would have used normal standard nuts and bolts in most locations.

(posted before seeing Andy's response)

Paul

 

[JimG]

Jim,
But don't forget the other discussion here and on your original thread here about A/F sizes and the change in 1940 - so sizes quoted on modern fastener sales sites will not be accurate for early c.20 models.

Andy,

It was one of the few sites that showed dimensions for square bolt heads. Did Whitworth square bolts and nuts have the same AF measurement as the hex heads and nuts, or were there different dimensions?

Jim.

 

[pakpaul]

Jim

Square and hexagon nuts and bolt heads both have the same across flats measurement, one of the reasons for showing the diameter of a circle to contain the head size in the fastener sizes and scale equivalents dimension tables. Nuts have the same across flats dimension as the bolt, and the thickness of the bolt head is approximately 88% of the nut thickness.

Paul

 

[JimG]

Square and hexagon nuts and bolt heads both have the same across flats measurement

Paul,

I suppose that should have been obvious or else they would have needed two sets of spanners.

Jim

 

[Len Cattley]

Hi Paul, where did you get the BA14 and BA16 dia's from?

Len

 

[pakpaul]

Len

My dimensions for BA fastenings came from "The Model Engineers Handbook" third edition published 1996. It is still in print and available from
http://www.myhobbystore.co.uk/product/212693/model-engineers-handbook-by-tubal-cain . Current price is sterling 8.95.

BA thread dimensions and tapping drill sizes page 4.6, hexagons,nut sizes etc page 4.13. He also gives the formulas for calculating all of the dimensions of the BA thread series. There is a lot of other useful information in this book, such as speeds for drills and machining.

Paul

 

[JimG]

This thread encouraged me to have a look at what I might be able to do in 1:32 scale. I had had a few thoughts about it. My hip took a bit of a bashing at the sailing on Saturday so I needed a day or two's rest to let it recuperate to I've been messing around on the mill, and I think I got somewhere at last.



This was my first attempt - trying to cut 100 nuts. The cutter was supposed to cut right through and leave two tags per nut to hold it in place but the tool wasn't set deep enough and it became too difficult to get the nuts out. I had used Seklema Multimat to hold the Plastikard for milling and it always gives me some problems with getting cutter height exactly right. I had more goes using two or three types of double-sided tape with different levels of tack, but with not very good results, primarily because it was difficult to clean the nuts up due to the adhesive residues. Also being Scottish and trying to cram as many nuts into the square inch as I could gave problems with cut nuts staying in place during the cut.



So it was back to the drawing board this morning with the drawing re-done to half the number of nuts in the area. I went with the Seklema Multimat again and this time is got the tool depth slightly too deep, so there were no tabs. I noticed this during the cut and started rescuing nuts from the nearer two rows before the got lost in the swarf. But it meant a dig around in that pile of swarf to find the rest of the nuts.



...and here's the result with a lot of swarf still attached. I managed to get 22 of the intended 25 - they ping very easily under the tweezers and are lost forever thereafter.


Here's a shot of the failed attempts yesterday on the Seklema and the double-sided tape.



I threaded the nuts on to a bit of 0.45mm brass wire and cleaned them up with a stiffish brush. They are just under 1mm AF and are intended to be 5/8" Whitworth but would probably also do for 3/4" Whitworth since the difference in the AF measurement is very little.



A nut is threaded onto 20thou Plastikard rod and locked with a dab of Mekpak.



...then the rod is fed into a 0.5mm hole in the body and locked with a touch of MekPak. I'm using the original Slaters rod and I could do the old George Slater trick with his ever-lit cigarette and form a mushroom head on the end of the rod to make the coach bolt head, then feed the rod through from the inside and feed the nut on, then lock everything with a dab of Mek. Then you would be reproducing the bolt heads on the inside as well.

This is quite a good job for the mill since it will use up all the small odds and ends of 30 thou Plastikard that I have accumulated over the past few years.

Jim.