andypugh

The tapered socket for the other steering arm was quite corroded as there had been no arm fitted for many years. It appeared to be six degree included angle.

If that doesn't do the trick I found a trick for boring tapered holes with a boring and facing head:

http://www.cnczone.com/forums/vertical-mill-lathe-project-log/109301-cnc-3.html#post1357394

Though that part looks just about small enough to (with great difficulty) mount on a lathe.

I got the castings back at the weekend:

https://picasaweb.google.com/108164504656404380542/Holbrook#6230479127730875154

I don't actually know what the total cost was, I just realised that I haven't paid for them.

Found this one on the web, same model truck?

 

Amusing to see a solid-tyred vehicle delivering a load of pneumatics.

It will be for sale later as a well advanced project.

Is he intending to partially dismantle it and hide various parts in fields around the country?

It looks complete to me, certainly compared to most of the projects on here.

I am still undecided about how to 22" radius into the full length of the front bracket and the top half of the rear bracket. Bend them cold with the press or hot around a timber form I cut out with a jigsaw?

I would do it cold, then there is no rush. It's a small degree of bend. It might still be worth jigsawing the template just as a reference.

You really do not want to know any more, and we are getting off subject.

I think we can be pretty sure that the device being described is Pre WW2.

Almost certainly Pre WW1.

I wouldn't be surprised to find Pre Boer War?

I have experience with a sprag; Had the car I was driving not been fitted with a sprag it would have rolled backwards been written off!

Band brakes by any chance?

Hi Dennis, It is called a SPRAG. It is used to stop the vehicle rolling backwards down a hill

I was told many years ago that they are illegal to use in the UK nowadays. (this makes some sense, poking holes in tarmac is likely to be unpopular). So you can probably have them fitted, but shouldn't deploy them.

Not directly related, but I did a trailer-towing course over the summer, and one useful technique taught there was to deliberately jack-knife the trailer if you are having trouble getting going on a steep hill, so that you can get the towing vehicle rolling and the clutch engaged before the trailer starts to move.

(My job sometimes involves towing special trailers up the highest mountains we can find): http://mustangae.com/products-services/towing-dynamometers/carsuv-tow-dynamometer/?prod=Car%2FSUV+Tow+Dynamometer

Thinking about Barry's pictures of 3D-printed patterns reminded me of another process that is very applicable to the vehicle restoration game.

We actually have one of these machines at work, but I don't get to use it.

Excess capacity on the machine is sold via an intermediary company. When I enquired about Dennis cylinders they estimated around £10k for two cylinder blocks, starting from a CAD model.

Interesting to see when I started this, it seems like months that I have been at this, and it is.

These are the patterns, almost ready for the foundry.

https://picasaweb.google.com/lh/photo/gQuPtDB0J_ZiqVVDHaf8vtMTjNZETYmyPJy0liipFm0?feat=directlink

I don't remember, but it would have been whatever Saftek suggested. Probably on the phone, I can't find an email.

Aha! I found that I mentioned it in the blog post that describes making the brake.

http://bodgesoc.blogspot.co.uk/search/label/Neracar9

This is a transmission brake just like the Thornycroft one, but just a little bit less hefty :-)

(And the answer is 200C)

what temperature and for how long?

I don't remember, but it would have been whatever Saftek suggested. Probably on the phone, I can't find an email.

I bent mine in the oven, as suggested.

I put them in the oven on top of a former, then took them out and pushed them onto the former with a tea-towel.

However, if I was doing it again I would not heat the former, as it took a long and uncomfortable time for things to cool enough to take the set. I think hot material onto a cold shoe would be better.

You can always have a second attempt.

I could have imposed on my friends again for use of a larger lathe but am keen not to become a perishing nuisance!

Now, if only you had just built a nice big shed at the side of your house, then you could put a decent-sized lathe in the end of it.

http://www.ebay.co.uk/itm/181925330600 looks to be shorter than a Dennis is wide (though he does say that the photo is not necessarily of the lathe he is selling)

I originally planned to solder the brass to the steel but felt that with dissimilar metals their relative expansions would distort the covers.

You quite often see brass fitting soldered to steel tanks, so I don't think this is a huge concern, especially in a part that probably doesn't see such a huge temperature swing.

Reproduction pressings really are a challenge, no matter how well equipped

I used similar "hybrid techniques" to make some Ner-a-Car parts. The material was rather thinner, I suspect.

http://bodgesoc.blogspot.co.uk/2014/07/neracar6.html

This was simply a laser-cut piece of 3mm plate screwed to some 3/4" plywood. Whilst getting this cut, we also had two blanks done at the same time.

Possibly outside the capacity of your laser-cutterist, but if you had done the whole form in steel plate then that opens up the option of heating the flange with a blow-torch to make it easier to shrink the ripples out.

It isn't like some mild steel discs are going to sit around for long without finding other uses, is it :-)

The "gap" can be taken up by using a slightly thicker brake lining but a decision on that can remain for the moment until other team members have cast their eyes over it!

The fire-engine had had brake linings retrofitted to the shoes, and that meant that the working diameter was wrong.

I changed the radius of the metal shoes to partially correct this (using my dad's horizontal boring machine), then bored out the relined linings to the correct radius to complete the job.

In principle you could remove the drum from the gearbox, set the gearbox up on a boring machine, clock true to the output shaft then bore the shoes to the exact diameter in-situ.

An alternative, though not so accurate, would be to wrap a spiral of emery tape round the drum and apply the brake. The problem is the lack of ideal inelastic zero-thickness emery tape.

Andy,

 

Very interesting clip, did you get much expansion when you took the spring off the mandrel?

Yes, a fair bit. I basically made a spring, worked out how much bigger it was than I wanted, then turned down the mandrel to compensate.

The final springs are here:

https://picasaweb.google.com/lh/photo/u7-LoyIMofVXAlpzdUO_z9MTjNZETYmyPJy0liipFm0?feat=directlink

The mandrel included an attempt to form the bottom loop, as the springs are a funny-shaped motorcycle seat spring.

I quite agree that there should not be any need to heat treat piano wire as it comes ready treated from the factory.

However I tried a few unsuccessful attempts to cold form the spring, but as it was 4mm piano wire it was not too keen to stay in the correct shape without trying to tear my face off when I released the tension.

Ah, yes, it all makes sense now.

I wound some 1/4" springs last year, but there was no way to do those by hand without being maimed, so I improvised:

When I bought the milling machine I was sure I would never use the 45rpm speed.

I also managed to make a replacement spring using the correct diameter piano wire bent round a former and heat treated,

There shouldn't be any need to heat-treat piano wire. It gets its properties from cold-drawing, and heat treatment will destroy that.

The heat-treatment stage of piano wire manufacturing is prior to the cold-drawing (or cold-rolling) process and is called "patenting", where the material is heated to the austenite transition temperature, then quenched in molten lead or molten sodium hydroxide to transform to fine Bainite. Cold working of this then gives a very high tensile strength.

Quenching and tempering will give you reasonable properties as it is high carbon steel, but the chances are that you had a better spring before the heat treatment.

Suspension springs are heat-treated, they have a large section and no scope for significant cold reduction.

(This was my "specialist subject" for 2 years at Leeds)

https://en.wikipedia.org/wiki/Holt_tractor

Seems to suggest that the front wheel was a Holt 120 feature and the 75 was steered by the tracks only. Is this correct? It doesn't necessarily look to be, after googling round the subject.

I suspect that the Wikipedia page needs help, it sounds like it it saying that the front wheel or the tiller were covered, when it probably means that the whole tractor was.

It's SG and I feel quite sure that it will be suitable!

Just checking. Failure of that component could be quite exciting :-)

The new casting is shown alongside the pattern.

What material?

I would be a bit nervous of using cast iron in that application, though ductile iron or ADI would be fine.

(I did some fatigue testing for JCB on ADI in a previous life, and it's amazingly strong and tough)

I tried out the pattern in some greensand and this pulled out easily too.

The advantage of doing it like this is that you can define the draft angle easily for easy extraction from the sand and achieve absolutely consistent wall thickness. Also things like scaling to allow for contraction is just a mouse click away. .

Something else you can do in CAD and not in real life is put your pattern in your core box to test that everything is in the right place (not trivial when everything has had drafts added)

This is the core box lower. I now need to decide how to make it.

Also, you can analyse the overlap between the parts, and that is what the actual casting will be

(I am not sure about the volume calculation, that sounds like a 112kg casting...)