Great War truck Posted July 18, 2015 Author Share Posted July 18, 2015 I think this was mentioned in the forum before, but there was a problem with Thorny back axles breaking during the war and JI Thornycroft was sent out to come up with a measure to strengthen them. Roy can probably add more to this. Quote Link to comment Share on other sites More sharing options...
nz2 Posted July 18, 2015 Share Posted July 18, 2015 I have a Thornycroft rear axle of the type Gordon describes. The axle castings are bolted directly to diff housing, giving a five piece rear axle. That does have a tensioning strip underneath, however it comprises of two steel rods passing under the diff. These then come together at either end to plate with a separate single rod passing through and mounting to the brake castings. This design is pre war with the chassis I have being imported to NZ around 1913. Aside from the one I have, I am not aware of any other Thornycroft diff housings of this pattern. Doug Quote Link to comment Share on other sites More sharing options...
andypugh Posted July 20, 2015 Share Posted July 20, 2015 Cast iron is tremendous in compression, less so in shear, which is what those flanges would be seeing lots of without that strap. The major loads are contained inside the spring-pad and brake pivot casting. The static loads in the actual diff casting are fairly small. However I wouldn't care to guess the dynamic loads in the axle case when the wheels are busily bouncing about in shell craters. The 1916 Dennis I play with has a rod in the place of the Thorny strap. It isn't especially tight, and I think that they are there as a safety restraint in the event that something unexpected happens to the diff (like landing hard on a rock) Quote Link to comment Share on other sites More sharing options...
flandersflyer Posted July 22, 2015 Share Posted July 22, 2015 The major loads are contained inside the spring-pad and brake pivot casting. The static loads in the actual diff casting are fairly small. However I wouldn't care to guess the dynamic loads in the axle case when the wheels are busily bouncing about in shell craters. The 1916 Dennis I play with has a rod in the place of the Thorny strap. It isn't especially tight, and I think that they are there as a safety restraint in the event that something unexpected happens to the diff (like landing hard on a rock) it`l be to do with what Gordon says. Cast has poor shear & tension strength....very good on compression. lets not forget that the iron used in this diff will not be of the same grade as you can get now either.... Quote Link to comment Share on other sites More sharing options...
andypugh Posted July 22, 2015 Share Posted July 22, 2015 Cast has poor shear & tension strength....very good on compression. It does OK in tension too, up to a point. You would imagine that an axle would be designed with the right amount of metal in the right places. BS 1452 described grades of cast iron by tensile (not compressive) strength, currently the grades are 220, 250 260 etc. 250 is 250N/mm2 tensile strength, or 17 tons/square inch. There are a lot of square inches in an axle casting. lets not forget that the iron used in this diff will not be of the same grade as you can get now either.... It might be better. The Dennis axle appears to be a semi-steel. I re-bored the spring saddles once and it came off in curls rather than normal cast-iron swarf. Quote Link to comment Share on other sites More sharing options...
flandersflyer Posted July 22, 2015 Share Posted July 22, 2015 It does OK in tension too, up to a point. You would imagine that an axle would be designed with the right amount of metal in the right places. BS 1452 described grades of cast iron by tensile (not compressive) strength, currently the grades are 220, 250 260 etc. 250 is 250N/mm2 tensile strength, or 17 tons/square inch. There are a lot of square inches in an axle casting. It might be better. The Dennis axle appears to be a semi-steel. I re-bored the spring saddles once and it came off in curls rather than normal cast-iron swarf. so...you think its a form of ductile iron then? Quote Link to comment Share on other sites More sharing options...
andypugh Posted July 22, 2015 Share Posted July 22, 2015 so...you think its a form of ductile iron then? No, I think it is semi-steel. https://en.wikipedia.org/wiki/Semi-steel Quote Link to comment Share on other sites More sharing options...
mtskull Posted July 23, 2015 Share Posted July 23, 2015 When you see the size of the axle casting and the flanges, you would wonder if the tie bar would possibly ever make any difference? Barry. This subject has generated some very interesting responses by some very knowledgeable people, each argument with its own merits. In this case though, I feel that perhaps there is a tendency to over-analyse the matter, which probably just comes down to that short and simple phrase: Belt AND Braces. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted July 26, 2015 Author Share Posted July 26, 2015 The Brake Drums were finally completed yesterday with the holes for fixing bolts to the wheels “spot-faced” using Steve’s home made Spot Facer to do the job. A slow speed is needed for this job and the Minor Mill was used for this as the slowest speed on the Bench Drill was not slow enough. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted July 26, 2015 Author Share Posted July 26, 2015 Spot-facing completed! The Brake Drums were offered up to the wheels and bolted down. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted July 26, 2015 Author Share Posted July 26, 2015 And given a coat of Primer prior to final painting. Quote Link to comment Share on other sites More sharing options...
Caddy Posted August 11, 2015 Share Posted August 11, 2015 I heard of junkies greeting going cold turkey, think I'm going cold thorney Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 11, 2015 Author Share Posted August 11, 2015 Sorry. There will be lots more to add soon. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 11, 2015 Author Share Posted August 11, 2015 Followers of this thread may remember that we said that it was our ambition to install the engine and gearbox into the chassis now as soon as possible but that it would be necessary to have the chassis back on all four wheels so that we could manoeuvre it under the chain block, thus being able to lift the engine and gearbox comfortably and under control to drop into the chassis. There was still some work to do to the axle and brakes before the wheels could go on but this has all now been done with the exception of making the two Dust Shields for the Brake Drums. Steve has this in hand but has been rather diverted this summer with other things that he wished to do – and these included the construction of a Lorry Shed adjoining his home which could comfortably take the Dennis – with its canvas erected and which would be its permanent home. The shed has been completed apart from the Doors and wiring it and these final things are under way. The shed or “Motor House” is a magnificent structure and we will leave Steve to post a picture of it if he so wishes! So then thinking about the engine mountings, this is what we were faced with. The engine is designed to sit on two pieces of 3” x 3/8” angle attached to the inner sub-chassis. The angle on the off-side – or right hand side is firmly bolted to the chassis with two clusters of five, 1/2” bolts whilst the angle on the other side is attached to the sub-chassis by one large “Pin” on which the steel angle can rotate slightly, fore and aft, to compensate for any twisting in the chassis in service. The engine is bolted to these two steel angles with two 3/4” diameter bolts in each angle. So this arrangement is designed to eliminate any stress on the feet of the engine through its four bolting points – if it was all totally solid, then there would be a possibility of damage to the engine with any twisting of the vehicle in service with the worst scenario actually being a break in the engine casing and its bolting feet. The only part of the original engine mounts remaining under the Shepherds Hut chassis was the “pin” mentioned above so we were faced with making new parts. Turning first of all to the “off side” angle, then this was quite straight forward to make. The Bolting holes were picked up from the original holes in the sub chassis and caused no difficulty. Many years ago, Steve was working in Portsmouth and was living in a Flat there– this was during his student and post-student days and at that time, the Thornycroft J Bus now with the Hampshire County Museum Service in Basingstoke was stabled in the commercial bus depot nearby. With the blessing of a very helpful and co-operative garage foreman, Steve spent many evening crawling all over the bus, sketching and measuring everything in sight and it is those sketches and measurements from all those years ago that now prove to be invaluable. From this information, we could see exactly what the layout should be of the mounting angles and what the shape of the cut outs are and where they should be in the angles. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 11, 2015 Author Share Posted August 11, 2015 The “pin” was removed after quite a struggle and we initiaily though that it was beyond recovery. It was inserted through the sub chassis from the back and was fixed to the chassis with four 1/2” countersunk screws, nutted on the back. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 11, 2015 Author Share Posted August 11, 2015 We decided not to give up on the old “pin” – it was put in the lathe and skimmed, the badly corroded 1” Whit thread was cut off, the body of the “pin” was drilled to take new steel which was firstly threaded 1” Whit as the replacement. Quote Link to comment Share on other sites More sharing options...
jpsmit Posted August 12, 2015 Share Posted August 12, 2015 Amazing - thank you Sent from my iPad using Tapatalk Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 12, 2015 Author Share Posted August 12, 2015 Turning now to the female part of coupling which has to be bolted to the inside of the nearside (left side) angle, then of course we had no original. From all the research completed, we knew what it looked like and how it was attached to the angle. The first task was to make a pattern so that it could be cast – in SG Iron. This is the pattern on the right in the photograph – the left one is the gearbox mounting pattern. The casting was set up in the lathe, machined to size, ready to fit to the angle, and bored through to take the “Pin” from the male part. The male part was offered up to the casting before it was removed from the chuck to ensure that we had an acceptable fit. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 12, 2015 Author Share Posted August 12, 2015 A hole was drilled and then opened up by boring in the angle to take the casting which had to be a firm press fit. Further machining to the casting also completed at this stage to ensure that it fitted inside the angle in its correct final position. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 12, 2015 Author Share Posted August 12, 2015 Continual easing and trial fitting until we were content that the fit was good. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 12, 2015 Author Share Posted August 12, 2015 Because the right angle inside the two sides of the angle is not sharp – it is curved around, then the casting must be machined to accommodate that curve as well so that the casting can sit cleanly and firmly against the two sides. Quote Link to comment Share on other sites More sharing options...
Caddy Posted August 13, 2015 Share Posted August 13, 2015 Thank you for the fix i have a question though: is that piece of angle the size of a 40' trailer or is it on a miniature railway track? Quote Link to comment Share on other sites More sharing options...
Minesweeper Posted August 13, 2015 Share Posted August 13, 2015 Thank you for the fixi have a question though: is that piece of angle the size of a 40' trailer or is it on a miniature railway track?That made me laugh! We have a 7 1/4" Gauge Railway in the Garden - runs just past the workshop door so it does get caught up in one or two pictures from time to time! Tony Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 13, 2015 Author Share Posted August 13, 2015 The casting was then held firmly in position and drilled through the angle in two places, into the bolting flanges to take 1/2” Whit Csk Machine Screws. The heads on these stock ones seem to be too big – these are the only ones that we have at present and they are not long enough – should be 2” and these are 1 1/2” and must be changed – and the heads properly countersunk. A further retaining bolt – 7/16” Whit goes through the other face of the angle into the bore. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted August 13, 2015 Author Share Posted August 13, 2015 More trial fittings! Quote Link to comment Share on other sites More sharing options...
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