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WW1 Thornycroft restoration


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What type of glue was used please, presuming it wasn't a pva which I have heard can creep over time.

 

Mark uses Cascamite - same as used on the Dennis and the FWD Bows. If you Google Cascamite, you will read that it is highly thought of and is good for exterior woodwork.

 

Tony

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Our normal modus operandi is to think about lots of different items all at the same time. The postings tend to be a bit spaced out as we wait until will have a whole story to tell. At the moment, one of the critical path items receiving some consideration is the fuel tank. We are fortunate in that we have an original but it does have a leakage problem.

 

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The filler neck has survived but the sump, a gunmetal casting, has disappeared, literally!

 

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Interestingly, it has a double skin at the ends.

 

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I spent yesterday on the drawing board working out what it should look like. (Sorry about the photo quality!). I shall get this copied this week and see about getting the ends and baffles laser cut. I shall flange these and then start looking for someone to bend up the wrapper as I just can't see how it was done. Once I have a wrapper, it is just a case of soldering and rivetting the seams.

 

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I made the pattern for the sump some time ago and father took it off to the foundry. He now has the casting back and has started to machine it.

 

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He also found a nice tap at Beaulieu last year so I have cleaned that up and it is ready to fit. Father will cut the thread in the sump to suit!

 

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Next job is to remove the filler neck so that Father can machine the filler cap casting to suit it. In the mean time, however, we are pushing on with the hood frames and the steering column. Never a dull moment!

 

Steve :-)

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  • 2 weeks later...

We have a lot of family birthdays in February so that is an excuse for a get-together which we did last weekend. Still found some time for the Thorny as well though.

 

Dad has completed the sump and drain plug for the fuel tank so that is now safely in store for when I have worked out how to fold the wrapper!

 

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Dad has finished priming the hood bows with aluminium primer so I took the opportunity to shape the ends before fitting the iron work made previously.

 

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As usual, space is limited!

 

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Unlike the Dennis bows which have square ends, the Thornycroft ones are tapered. I created this shape by first sawing off the bulk and then removing the remainder with Grandfather's spoke shave before finishing with glass paper.

 

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The ironwork was screwed on using greased slot-headed screws. No Pozidrives here!

 

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Father, also struggling for space, has primed the areas made bare by me and is currently awaiting some dry days to top coat them.

 

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I need to make a jig to hold them in the correct relative positions so that the canvas can be made. Then we can arrange to deliver them the next time I go down.

 

Steve :)

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We haven't been idle in spite of evidence to the contrary! Dad has set us the very tight target of London to Brighton in May 2018 when they are having a special WW1 vehicle class. This really is going to be very hard to achieve but we are going to have a go. To that end, I have done a critical path analysis of the project and have realised that the three items most likely to upset the applecart are the bonnet, the fuel tank and the canvas hood of which the longest lead item is the canvas. Jim Clark at Allied Forces has kindly promised to do the canvas for us but to do it in time, he needs the hood frames very soon. I have, therefore, been concentrating on the steelwork whilst Father and our joiner pal Mark, are doing the timber bows. Fortunately, we have done all of this before as the Dennis has hood frames made to the same pattern. Whilst I understand how they go, they are still a very tedious job however!

 

There are two steel pieces on each side, two uprights and two J-shaped horizontal pieces hinged to them. I started off by bending the J-shape using the forge at my local miniature railway. They bent and joggled quite well but when I got them home, I felt that one could just do with a bit of adjustment in my press with the result you see below:

 

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It went off with quite bang and just snapped. I was quite surprised about this as it is only mild steel. However, I had heated the parts in a coke fire for an extended period (I am not a good blacksmith!) and then quenched them. The carbon rich environment and quenching had case hardened the steel and caused the breakage. The case hardening is quite evident in the fracture and the edges are razor sharp. I carefully heated and air cooled the second one and then arranged to visit the railway again for another go!

 

In the mean time, I started on the verticals. First task was to turn up some bosses and weld them on.

 

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My welding hasn't improved! I did stick them in the vice and lean on them and they remained attached so I deemed them adequate.

 

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Then there were two thicker boss areas at the top to carry the pivot point. These were turned and silver soldered on.

 

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Then the filing and angle grinding started. This went on and on for hours.

 

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Interestingly, the section changes from elliptical just above the pivot to half-round where the timber bow is attached. Careful filing required but they did work out OK.

 

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I bent up a second bar and this one went a lot better with fewer hammer marks. It looks a bit odd because of the joggle which is not obvious but which distorts one's perception.

 

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Then again endless filing and angle grinding.

 

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On these, the pivot boss is generated by filing only. I bolted a washer to the surface to give me a guide.

 

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Main pivot point drilled out and the screw holes were countersunk.

 

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Pivot pins turned up.

 

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Job complete.

 

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Now we are waiting for the timber to finish the job. Pleased to see the back of that one!

 

Steve :-)

chances are you've been forging it too cold Steve....And it's work hardened
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chances are you've been forging it too cold Steve....And it's work hardened

 

I respectfully disagree. That's a brittle fracture due to quench-hardening. I am not sure if it is actually due to accidental case-hardening in the coke, you would normally have to actually try to get a significant case depth, or whether the steel used actually has a reasonably high carbon-equivalent content. Do you know the actual steel grade, Steve?

 

You would need a lot more strain (shape change) than that for significant work hardening, but I am actually basing this opinion on the colour of the fracture surface.

 

(In a previous life my job revolved around heat-treatment, cold-work and fracture mechanics research)

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Wouldn't a fracture due to cold forging happen at the time of hot working the material, rather than after cooling (note Steve's description of breaking it when trying to tweak it in the press)? A cold fracture suggests some undesirable metallurgical transformation.

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The steel suffered a brittle fracture whilst I was trying to bend it stone cold. My impression is that I have hardened it by quenching in water which removed all of the ductility. I did not expect that to happen as I did not think that it had enough carbon in it. I did order 'mild steel' though, so precisely what we got I am not sure! The case hardening is a bit of a red herring. That again was a surprise to me but a proper blacksmith would have been aware of it. Heating the steel for a long period in a carbon rich environment is bound to cause that and my quenching made it glass hard. I should have heard the warning bell when I tried to drill it as that certainly took some doing!

 

What do you actually define as 'cold forging'? Would that be at room temperature or just below red heat? I am a very poor blacksmith so my temperature control is a bit variable but I don't generally hit it unless it is glowing to some degree.

 

Always something new to learn!

 

Steve :-)

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A little more progress. These are the hood stowage brackets to mount on the sides of the seat box. They are a simple fabrication using my favourite silver solder to put them together.

 

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After a good clean up, they had a trip to the Devonshire paint shop and are now ready to fit.

 

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Fortunately, a quick rummage turned up a pair of period wing nuts to go with them and they look rather nice.

 

Steve

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Something else we have been pressing on with is the steering column. This consists of three concentric tubes. The inner one carries oil to the steering box, the middle one is attached to the wheel and does the work and the outer carries the throttle and advance mechanism. The middle one is shown on page 231 but before we could fit it, we had to complete the inner. It is just a piece of 1/2" tube pushed into a hole in the top of the worm shaft. with the top located in a similar hole in the spigot at the top. It puzzled me for a while how I was going to put it together and get the top end into the hole! A look in the parts book clarified things and showed a collar at the top. I turned one up and pressed it down the tube and we were ready to go.

 

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Inner tube in place.

 

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Middle tube simply slid over the top and located on a key in the worm shaft with a tubular clamp over the top to hold it all together.

 

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Now we turn to the outer tube. This one has four castings associated with it in that there is one top and bottom to carry the throttle mechanism, a quadrant mounted on the top one and a steady bracket at the bottom to anchor it to the dash plate. I started off with the patterns for the two to carry the throttle lever mechanism. As usual, they are fabricated from MDF.

 

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I create fillets by filling with Isopon and cutting back with glass paper and the Dremel. Not perfect but seems to work adequately.

 

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Then onto the top one. This is more complex as it carries the pivot point for the hand throttle and advance levers and also a quadrant to control their position.

 

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The kit of parts and also my surviving original. Sadly, it proved to be beyond salvage.

 

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More Isopon!

 

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Into the paint shop for two coats of Bondaprime.

 

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Father picked up the castings on Friday.

 

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Perhaps I should have cored the centres but for just a single casting in each case, I felt it was not worth the effort. With the big mass of iron, they shouldn't have any chilled spots. Father will machine them this week and then they can be soldered onto the outer tube. I am currently working on the pattern for the steady casting and a pal is doing the one for the quadrant.

 

Watch this space!

 

Steve :-)

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T Heating the steel for a long period in a carbon rich environment is bound to cause that and my quenching made it glass hard. I should have heard the warning bell when I tried to drill it as that certainly took some doing!

 

What do you actually define as 'cold forging'? Would that be at room temperature or just below red heat? I am a very poor blacksmith so my temperature control is a bit variable but I don't generally hit it unless it is glowing to some degree.

 

Always something new to learn!

 

Steve :-)

 

Steve,

Mild steel is just that, not enough carbon to make harden-able. You would not have been able to introduce enough carbon to make it brittle (otherwise, it would be a known technique for making harden-able steel!). So the only thing left is forging too cold!

 

Still following along and enjoying the ride! May be see you in Brighton next year! All the best, Matthew.

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Mild steel is just that, not enough carbon to make harden-able. You would not have been able to introduce enough carbon to make it brittle.

I agree with you up to here.

 

So the only thing left is forging too cold!

But this seems to be excluding a number of other possibilities.

Perhaps it isn't actually mild steel? It would be instructive to do a heat and quench on on un-forged offcut to find out. Perhaps they gave you some EN8 by mistake?

 

It is possible to get brittle fracture of mild steel when the section size is very large[1] and there is a starter-crack. It is just about possible that a combination of a crack in a hard case, a borderline material and a fairly large material section conspired to cause this fracture.

 

I don't see that this can be a "work hardening" problem as I understand the term. I would rather expect it to be possible to bend the material into shape shown by cold-forming without fracture, if it was possible to apply the loads required to achieve that. It isn't a very large shape change.

 

I know much less about deformation in hot metal than I do about cold metal. I would be interested to learn what the issues are with hot forging at too low a temperature. I would anticipate that there is likely to be problems with weakening grain boundaries that are not then re-formed on transformation.

 

[1] https://en.wikipedia.org/wiki/Fracture_toughness is sensitive to geometry. In applications such as pressure vessels with very large wall thicknesses it is necessary to perform tests with specimens of a similar scale to the proposed wall thickness. This can require some truly enormous tensile testing machines because you can't simply use a lab-scale specimen and multiply the numbers. AEA Risley had a machine capable of testing 500mm wide CTS specimens.

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I agree with you up to here.

 

 

I don't see that this can be a "work hardening" problem as I understand the term. I would rather expect it to be possible to bend the material into shape shown by cold-forming without fracture, if it was possible to apply the loads required to achieve that. It isn't a very large shape change.

 

 

 

Andy,

Properly forged, (Sorry Steve!) it would have been possible to open up the bend a little bit without cracking, had it been hardened any form of carbon steel would have broken not cracked.

 

Regards, Matthew.

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Is the attached photo of any interest to you.

Not the Horse drawn thing in the front but lurking at the back.

Photo taken in 1930 in the London area probably near Liverpool st station or Kings Cross.

No knowledge of any history of the photo it just turned up in a bag of rubbish for recycling.

Cart 2.jpg

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This looks like a post-war civilian version of the "J" with a low level radiator - and not a former military one. Notice that the Starting Handle passes through the radiator and is not underneath the radiator as on the military version with a high level radiator!

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Military style body though. I guess it could have been bought after the War and had the cab built in the railway workshops. The radiator could have been a later fitment bearing in mind that the LNER and LMS didn't come into existence until 1923.

 

Nice picture though!

 

Steve

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We have made some good progress this week. Dad has been steadily completing the finishing of the paintwork on the hood frames and what an awkward job it has proven to be. They are not heavy but really cumbersome and we just don't have the space. Anyway, in spite of that, all are now complete so I spent yesterday making up a simple jig to hold them in the correct relative positions ready for the canvas to be made.

 

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Father and I took the lot up to Jim Clark at 'Allied Forces' for him to have a look and, hopefully, agree to make up the hood for us. This, he is going to do along with the main tilt to go over the back, the seat cushions, and the cab doors. We left some photos for him to mull over.

 

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"What have I taken on here?"

 

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That is one job off my critical path and it is back to the steering column for a while.

 

Good luck Jim! (And thanks!)

 

Steve ;)

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As we mentioned before, Father has picked up the throttle control support castings from the foundry.

 

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This week, he has machined them on the Colchester lathe.

 

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Quite straightforward really although this one was a bit trickier to hold.

 

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He had cut off a length of column tube to try in the hole to get the fit right.

 

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The spindle holes were then drilled.

 

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Followed by a good clean up.

 

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The castings are secured to the tube using soft solder. Unfortunately for me, Father's tin of Baker's Fluid had corroded through and been disposed of. I therefore went to the local builders merchants and bought some 'soldering paste'. This looked rather like vaseline and, to be honest, I didn't have much confidence in the stuff

 

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I had a go but could not get the solder to run. This could have been the solder which, I believe, was of the lead-free persuasion. I don't have much confidence in that either. Can anyone offer any suggestions on using this combination?

 

Anyway, I cleaned it all up and used good old leaded solder paint to tin the joint and then fed in some electrician's solder which I knew was the proper stuff.

 

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This worked well so I used a rod to align the two castings and soldered the second.

 

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