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1914 Dennis Lorry


BenHawkins

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Ben, fantastic ingenuity in the fabrication of this transmission brake arm. How would the time equate from doing it this way against making a pattern and having the part cast?

 

What do the tubes do which you welded in? I should really know the answer to this, but it defeats me at the moment!

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Gravity naturally wants to make the brake shoes rotate on their pivots allowing the tops of the shoes to rub on the drum even when the brake is released. One of the holes is tapped 7/16 BSF so a set screw can be used to limit how far the shoes rotate. The other hole carries a spring and presumably this prevents the shoes from rattling when the lorry passes over bumps.

 

I though the arms would be better in steel. The steel foundry I use is very slow (possibly as long as six months for a casting). The laser cutters usually have the profiles ready for me in 3 working days.

 

In terms of man hours to make the pattern or fabrication they are probably fairly similar in this case.

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Did you have to soak the felt seals in oil before fitting?

 

 

I have had new felt seals punched out for the input and output shafts.

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The input shaft seal is retained by a washer with six 3/16BSW screws soldered in and nuts fitted on the outside.

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Just the output shaft cover and transmission brake to fit.

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I had to stop there and tile the kitchen; the glamorous assistant can have strange ideas about prioritisation. This gearbox has needed repairing for many decades, I have only been putting the tiling off for a couple of years.

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Did you have to soak the felt seals in oil before fitting?

 

I don't think this is essential for felt seals but I always at least dip them in oil before fitting. It should prevent them rusting to the shaft as it could be years between a component being assembled and the vehicle being driven.

 

The welding of the second transmission brake arm is complete so it was all loosely put in place to check I had the alignment right this time. It all looks to be OK.

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The arms then had to be removed for drilling and tapping 1/8 BSP

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To accommodate Rotherham's screw down greasers.

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The brake parts have been painted, the split pin holes cleared out and slotted nuts sorted out for the various components. New adjuster bolts need to be made as the ones I have work out to be slightly too short and the heads are no longer hexagonal.

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The machine shop working on the flywheel called me up. They have uncovered a void in the casting.

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It is probably about 30mm long in total; continuing below the machined surface around the circumference. It will not be entirely machined away and if it was slightly deeper in the casting I would never have known about it.

The void is in the engine end of the flywheel (and therefore the thickest part). Obviously there is a need to balance the clutch but I am unsure if there is any reason not to proceed with the machining and continue to use the casting.

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I cut threads on some 1/2" EN8 rod to fit the clevises.

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This allowed a trial fitting of the bell crank to see if it was all going to work. These parts are off a variety of vehicles and resulted in the mechanism being tight because the eye in the bell crank was not directly above the eye in the actuator arm.

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I turned up a collar to move the bell crank over.

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The brake rod between the bell crank and the foot pedal is meant to have a turnbuckle. There is a double clevis fitted to the pedal to allow for slight misalignment and therefore I needed to make a 1/2" BSW left hand eye bolt. I started with some 1-1/4" EN8 steel, machining it down to 1/2" diameter and cutting the left hand thread.

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The next stage was to fly cut the end.

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I scribed diagonal lines to find the middle.

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After drilling and reaming the hole I fitted the eye to a bolt and milled the outside diameter.

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I had made the turnbuckle from a laser cut profile previously. Unfortunately I ran out of steel so could not thread the final length of rod and fit it all together.

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The 1/2" steel arrived this week so it was fairly easy to make the second brake rod to fit the turnbuckle and the 1/2"BSW left hand nut to lock it off.

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It seems to fit quite well, but I had to take the bracket for the return springs off as there was not enough clearance. The bracket will have to be modified and refitted at a later date.

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I had forgotten that the thread on the brake arm adjuster was corroded away.

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So I made a new one of those as well.

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Whilst working in that general area I removed the gear selector cross shaft that was too long and cut it down.

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After facing the end off in the lathe I refitted it. I will have to finish shaping the drop arm so I can link that up as well.

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The jaw for the universal joint on the back of the gearbox needs machining to 1-1/2" diameter so it can be brazed into the tubular propshaft. I thought I would be able to do this with the boring head on my milling machine but there is not enough height on the machine.

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Plan B was to turn between centres on the lathe so I scribed the ends and drilled for the centres.

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I thought a No 3morse taper sleeve for the headstock came with the lathe, but it was actually for collets.

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I don't remember where I found this 5mt centre but it turns out not to be right either!

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So plan D turns out to buying a headstock sleeve from an internet auction site. It was cheap, and the dimensions seemed right.

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So plan D turns out to buying a headstock sleeve from an internet auction site.

 

My plan A in this situation was to re-machine the adaptor to suit my spindle. But then you have a more common lathe than me, so can probably be more confident in what you will get.

Mine was a stub MT4.5 in some dimensions, but with a more round-number taper.

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My plan A in this situation was to re-machine the adaptor to suit my spindle. But then you have a more common lathe than me, so can probably be more confident in what you will get.

Mine was a stub MT4.5 in some dimensions, but with a more round-number taper.

 

And my plan D didn't quite work either. My headstock taper is 0.624" taper/foot like MT4.5 but a little larger (large end ca. 1.75"). The reduction sleeve that arrived from ebay turned out to be for a Colchester Student/Master 1800 so the same taper angle but slightly larger again. I clocked it up on a cylindrical grinder and reduced the diameter to suit the Colchester Master mk2.

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Unfortunately plan E was a failure too, a 3mt dead centre fitted to this bush then didn't reach the centre drilling in the universal joint before the jaw hit the catch plate. On to plan F; make the right tool for the job. I took some steel I had under the bench, turned the OD down at 3 degree included angle and then finished it off on the cylindrical grinder (just for a change I anticipated this event and had not reset the angle).

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With the new centre fitted to the lathe I turned the outside diameter down and machined a 60 degree point on the end. Then it was necessary to bolt a piece of steel to the catch plate to provide drive to the jaw.

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And finally the jaw set between centres ready for machining.

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Turning the outside diameter down.

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Machined down the 1.5" diameter.

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You might question why I left so much material on the casting. On my 1908 Dennis the jaw should be brazed onto a 1.5" diameter solid propshaft but on this one it is a brazed into a 1.5" ID tube. I didn't want to make two patterns.

 

Hopefully putting the holes in for the drive pin bushes will go to plan!

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Whilst I was machining the UJ jaw the shaper was removing some of the excess material from the gear selector drop arm. I should really have turned the vice through 90 degrees for the sake of efficiency.

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And then tidied the taper off on the mill.

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The next stage will be to heat it up and bend it.

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How did you cut the keyway, Ben?

 

Steve

 

The keyway was cut with a broach in the press. That was all the way back on post 380; perhaps I should learn to finish jobs rather than starting more!

 

I have warmed it up and put the first bend in the selector arm. The second bend has to be much tighter but at least it has a smaller cross sectional area at that end.

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The other job for this week has been continuing with the universal joint jaw. I started by machining the faces to the right dimensions.

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I then used a Dial Test Indicator to find the centre of the part before tilting the head on the milling machine and putting a pilot hole through. Unfortunately the holes do not line up perfectly so I need to have another go at setting up as I obviously got something wrong!

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The error on the centre point of the universal joint was down to small errors in the milling machine amplified by taking the knee and saddle near to the full extents of their travel. I corrected for the error and proceeded to bore the holes out until they were a little under size. The plan is to finish the holes with a reamer once the universal joint has been brazed into the prop shaft tube.

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I have had another couple of attempts at bending the gear selector arm. It is now close to the right shape but it shows up that I cut the shaft slightly too short so I need to make another one!

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One evening I had a trip down to Cheltenham to pick up some more planks of mahogany for the cab build. These were purchased cheaply from an online auction site but the ash for the framework will have to come from a timber merchant. Some horse hair for the seat has been delivered as well.

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I have been studying the parts book, general arrangement drawings and manuals as the action of the transmission brake did not seem ideal. It turns out there should be set screws to keep the brake arms centred. As the false frame rails are new it was just a case of drilling and tapping the rails; I should be able to pick up some set screws this week.

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Some models had an extra clevis to account for the sideways motion of the brake rod as the actuator arm travels through an arc. I decided to make one.

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But when I tried it in place I may have worked out why it was not fitted to all model. There is not enough clearance between this part and the handbrake equaliser; it limits the travel so I will go back to the previous arrangement.

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  • 2 weeks later...

We have been on holiday so there has been a lower level of progress, but before we left I managed a couple of small tasks.

 

A bit more bending of the gear selector arm appears to have made it the correct shape. We should now be able to trim and shape it.

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There are two props that support the weight of the canopy. These are mounted on the bulkhead so the props have to spread out to meet up with the corners of the canopy. I bolted a few bits of scrap together to make a jig to bend the props to the correct radius.

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Then it was just a case of warming the steel rods up and bending them around the jig.

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  • 4 weeks later...

Sorry for the lack of updates; we have been away a lot recently and also entertaining relatives. However, we have started to make a little progress again. I have been to see the machine shop and the cone clutch side of the flywheel has been finish machined but it has to wait for another slot on the lathe for the front face to be finished.

 

A couple of weeks ago I submitted a cutting list to the timber merchant and they delivered on Thursday.

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I painted all the ash for the framing with a timber treatment and the douglas fir with thinned "extremely pink" wood primer.

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The boards for the back of the cab were originally 12" wide but I could not source any of these so I have glued pairs of 6" wide boards together. I will sand them flat before applying another coat of primer.

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The rear bearer for the cab has to clear the mountings for the transmission brake shoes. I marked out the centres for the bolts and cut through with a hole saw.

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Then using a saw I joined the holes up.

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Before marking through the existing holes in the chassis and drilling the bearer to suit. I need to tidy up the cut out a little with a plane and make some more appropriate 3/8 BSW bolts to hold it down. The bearer is perpendicular to the chassis rails and lines up with witness marks in the chassis so I don't know why the holes are so far from the centre line of the bearer.

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We have been to Beaulieu autojumble this weekend. We picked up what appears to be a Dennis lamp bracket but for a 3 ton; it has been a bit butchered but nothing that can't be fixed.

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And a selection of general parts for the shelf including an exhaust whistle that is a bit too small for a lorry.

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On the metalwork front I have made four bolts for holding the cab bearers to the chassis; I took this design from a coachbuilders catalogue. They seem less likely to split the grain than a countersunk version.

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