WW1 Thornycroft restoration

[k2lofty]

You guys are amazing-------keep up the good work,---- I find myself visiting here every night before bed, its now a habit, but a good one.

[Old Bill]

The bolts to hold the drums on are very close to the flange where there is a radius. To get them to sit down properly requires a spot face. I had a look to see if I could get anything suitable but the nearest was £70- and not quite ideal for our purpose so I decided to make one up. Fortunately, I have recently been given a bar of 1" silver steel. As the face needs to be 15/16" diameter it was just right! I had never made such a tool before so I thought a quick read-up would be a good idea. I found, in the Model Engineer Magazine for August 28th 1998 an article entitled 'Making Special Cutters' so I followed that.

 

Step one was to turn the shaft to size and drill four radial holes in the end. These are deliberately not at 90° to each other in order to prevent chatter when using the cutter. I would not have thought of that but it was in the article!

 

 

The bar was put back in the lathe and faced off to not quite half of the depth on the hole leaving four cutting edges with a top rake of 5°

 

 

Then back in the mill with the dividing head set over to cut a front rake of 7° on each tooth.

 

 

 

 

Now came the tricky bit, the heat treatment. I have abook about heat treatment written by 'Tubal Cain' and intended for model engineers. He suggests a temperature of 770°-790° held for one hour per inch before quenching in oil. This temperature is between 'blood red' and 'cherry red' so I made a stab at that and held it for twenty minutes as the cutter is only 1/4" thick. I made a brick cave to try to even the temperature out and reduce gas consumption. All a bit 'by guess and by God'!

 

 

Quenched in engine oil and given a bit of a polish before tempering. The tempering, I did at 225° for twenty minutes in the domestic oven. In spite of having no markings on the oven control (long worn off!) I must have got it about right as it came out a nice yellow colour.

 

Final step was to run an oil stone over the edges to bring them right up.

 

 

Finally, I made a spindle from mild steel and pinned the cutter to it.

 

 

All ready to go, the next time I am in Devon. Then it will be the moment of truth. Only 16 holes to do!

 

[Cel]

Excellent work Steve! My brother, who is a gunsmith (in the UK), uses silver steel quite often to fabricate his special cutters although these are a lot smaller than the size you made. When he was still at school, a long time ago, he bought a bunch of silver steel round stock, from 3mm up to 10mm and ever since made most of the tools he needed himself. I got a Ridgid temperature gun as a present from a good friend last year, it has come into use regularly since I have it. But I must admit that the old school method is way more interesting and gives more satisfaction!

 

Regards

Marcel

[David Herbert]

Very professional Steve ! I like the drilled holes to give the rake. I have made special cutters for doing one off jobs out of mild steel, turned and filed / angle ground to shape and then heavily case harden the business end in Kasenite. Then wire brush all over and clean up the cutting edge with an oil stone. I don't bother tempering them as they won't shatter because of the soft core and I usually am only doing one or two holes anyway so can be gentle with them. As you say it is actualy an advantage if the cutting edges are not regularly spaced as long as they are all at exactly the same height so creating them by eye is fine.

 

David

[andypugh]

Now came the tricky bit, the heat treatment.

 

If you think you might be doing a fair bit of heat-treatment then it isn't all that much work to make a muffle furnace:

http://bodgesoc.blogspot.co.uk/2014/11/heat-treatment-furnace.html

 

It's useful for parts that are bigger than a torch can keep hot, though for the 18" seat leaf spring on the Ner-a-Car I had to put two tube furnaces face-to-face.

[Old Bill]

Thanks Cel. I haven't cut any metal yet, though!

 

A furnace would be nice Andy but I don't think I could justify it at the moment. Blowlamp and bucket of water is my usual approach. This is as sophisticated as I get!

 

Steve

[andypugh]

A furnace would be nice Andy but I don't think I could justify it at the moment.

 

I think it cost about £60 and took an afternoon to assemble, so it might be easier to justify than you think.

 

I built mine for heat-treating gears, mainly.

[rog8811]

I struck lucky many years ago when a company decided to dispose of its optical pyrometers and I "inherited" one:)

A very useful non contact method of taking the guesswork out of red heat temperature checking.

 

If you have never come across one it is basically a light bulb filament in a low power telescope and a variable resistor with a temperature scale around the knob.

Look down the tube and turn up the power to the filament until it disappears/is the same colour as the hot surface. You then just read off the temperature on the scale.

 

This is still one of my favorite threads, keep up the good work!

[flandersflyer]

I struck lucky many years ago when a company decided to dispose of its optical pyrometers and I "inherited" one:)

A very useful non contact method of taking the guesswork out of red heat temperature checking.

 

If you have never come across one it is basically a light bulb filament in a low power telescope and a variable resistor with a temperature scale around the knob.

Look down the tube and turn up the power to the filament until it disappears/is the same colour as the hot surface. You then just read off the temperature on the scale.

 

This is still one of my favorite threads, keep up the good work!

 

 

i like that....

[Old Bill]

Thanks Rog. I wondered how they worked. It is nice that you have salvaged something and are making use of it!

 

I have acquired the drawing office planimeter from work which is a lovely thing to behold. Obsolete now computers do the drafting but I still use it very occasionally and take great pleasure in so doing. It was going to be thrown out. Sacrilege!

 

Steve

[paul.norton]

Interesting comments regarding steel temperature during hardening.

 

I was told by Fred S of Taunton Model Engineers that he uses a magnet on a wooden handle - when the magnet no longer "sticks" to the workpiece the hardening temperature has been reached.

 

I have never tried this and assume there must be some restrictions on its accuracy e.g. "soaking" etc.

 

Regards,

Paul N

[andypugh]

when the magnet no longer "sticks" to the workpiece the hardening temperature has been reached.

 

To harden steel you need to get it to transform to Austenite (which has a higher solubility for carbon) and then transform it quickly back to ferrite. How quickly you do it, and to what temperature, controls how the carbon precipitates out, and what carbides are formed. (Pearlite, Bainite)

If you quench very fast you get martensite rather than ferrite, and that is the super-hard but brittle stuff.

Martensite is metastable at room temperaure, and warming it back up again converts some of the martensite back to ferrite to bring back some of the toughness at the expense of harness.

 

Austenite is not magnetic, which is how the magnet trick works. However there is a bit of a wrinkle as iron becomes non-magnetic at the Curie temperature too (770C) and at low or high carbon concentrations the Curie temperature is less than the critical temperature. http://www.calphad.com/iron-carbon.html

[Great War truck]

There has been a bit of a pause of late – Steve has been on holiday and is also busy at home with a building extension, Tony has been on holiday and all of us have been rather tied up with other commitments! But with our thoughts turning again to getting the back wheels on now as soon as possible, we have been looking at the brakes and the braking system. Steel 1mm Blanks have been laser cut for the new dust covers which go inside the back wheels over the shoes and springs and they still have to be finished off at the Leicester out-station! New brake pads have arrived and await riveting to the brake shoes at base in Axminster.

 

The original handbrake compensating gear was still fitted to the chassis recovered from under the Shepherds Hut – it was bent and corroded and there was no way of recovering the actual tube and shaft from there to use again so it had to be cut. It consists of a 1 1/2” diameter steel tube which can turn on a 1” steel shaft which runs through it, as the hand brake is activated and to the tube are brazed two arms. Although the arms were also heavily corroded, we hope that we can recover these and that they will prove to be be good enough to be used again.

 

The levers, with some of the original shaft left on them to hold them by for machining later on, were first of all sand-blasted, just to clean them up and so that we could see what exactly we had there. At that stage, the original brazing becomes very clear to see.

[Great War truck]

The arms were set up in the Milling Machine so that the remains of the original shaft could be bored out – that proved to be successful. The final picture in this sequence shows the two arms placed on an off-cut of the new 1 1/2” diameter sleeve, just to ensure fit.

 

If we decide to use these arms again, then they are ready to be brazed to the new sleeve.

[nz2]

The arms were set up in the Milling Machine so that the remains of the original shaft could be bored out – that proved to be successful. The final picture in this sequence shows the two arms placed on an off-cut of the new 1 1/2” diameter sleeve, just to ensure fit.

 

If we decide to use these arms again, then they are ready to be brazed to the new sleeve.

Was there photos to be with this?

Again I see no images. I know this problem has occurred before. From other threads I receive the images. Are others experiencing similar problems?

Doug

[Sean N]

Doug, I see the images in their entirety, both in the original post and in your quote of it.

[11th Armoured]

Doug, I see the images in their entirety, both in the original post and in your quote of it.

 

Same here...

[nz2]

And this morning I can see them!! Computers work in strange ways.

[David Herbert]

I could see them all along. Maybe photos travel slower than text and need to stay the night somewhere on the way.

 

I think that I would be tempted to build up the brake levers with some weld as one in particular seems to have gone a bit beyond having aquired extra character over the years. I am amazed that they were brazed onto the cross tube, and that it is a tube rather than solid.

 

David

Edited June 5, 2015 by David Herbert

[mammoth]

Nothing wrong with brazing when used appropriately, in this case a pure shear force. Similarly Velocette used soft solder to assemble the front forks in some of their motorcycles.

Likewise, if you had to carry a 11/2" thick wall tube any distance you would begin to think it was over-engineered. They knew what they were doing, just that the accountants had yet to move in.

[gritineye]

Nothing wrong with brazing when used appropriately, in this case a pure shear force. Similarly Velocette used soft solder to assemble the front forks in some of their motorcycles.

Likewise, if you had to carry a 11/2" thick wall tube any distance you would begin to think it was over-engineered. They knew what they were doing, just that the accountants had yet to move in.

 

Looking at the cast in bosses on those arms, I would hazard a guess that earlier versions had cotter pins that fitted a flat in a solid shaft, as in push bike pedals, very liable to work loose and fail. So maybe to improve reliability and save costs brazing was a much better method.

Edited June 6, 2015 by gritineye

[Minesweeper]

[QUOTE=gritineye;444145]Looking at the cast in bosses on those arms, I would hazard a guess that earlier versions had cotter pins that fitted a flat in a solid shaft, as in push bike pedals, very liable to work loose and fail. So maybe to improve reliability and save costs brazing was a much better method.

 

 

Possibly too, that the arms were just a standard part bought in, that were designed for any one of a multitude of purposes - but with this one purpose here, cotter pins were not deemed necessary with brazing preferred instead so in which case the arms were never drilled.

[dgrev]

I eagerly await the next update.

 

In the meantime, sorry to hijack your thread: but I need to contact someone who replied to either your Dennis or Thorny thread.

 

IIRC he was restoring a very large old engine.

 

He mentioned that he was reproducing data and serial plates. I need to get some done but only have photos to go on.

 

Can anyone identify and provide contact info for the gentleman concerned please or for anyone else who makes good

reproduction plates?

 

Many thanks

Doug

dgrev@iinet.net.au

[andypugh]

who makes good reproduction plates?

 

It isn't all that hard to do it yourself.

If you can create the artwork in a graphics program then you just need to print it on to Press-and-Peel PCB paper, then etch it with Ferric Chloride.

 

http://www.ebay.com.au/itm/Press-and-Peel-PCB-Etchant-Film-/181754940614?pt=LH_DefaultDomain_15&hash=item2a51704cc6

 

http://www.ebay.com.au/itm/Ferric-Chloride-Powder-1L-Bottle-/111617956958?pt=LH_DefaultDomain_15&hash=item19fcf2dc5e

 

Here is one I made this way near the bottom here:

http://bodgesoc.blogspot.co.uk/2014/11/the-last-bits-and-pieces.html

[David Herbert]

Sorry to continue this diversion but if you search "photo etching brass" on YouTube you get some quite usefull tutorials on how to do it. The problem in the UK seems to be finding a supply of the photo resist film. Ebay can only offer it from China or Germany. The chemicals seem much easier. I have fancied having a go at this for years and you may well have given me the push I needed.

 

David