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Tank Tracks

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Stub Mandrel24/06/2011 20:59:14
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Musings on a possible subject.
 
Since I was a boy I've had a soft spot for the 'Bren Carrier' (I know that's not the proper name) and the Vicker's Light Tanks.I have some simple GA drawings and plenty of good contemporary pictures and pics of the MKIV at Bovington.
 
These share the same suspension and look to be practical subjects for a small working model, and less costly than a King Tiger...
 
The suspension and tracks are common to all, the suspension units look reasonably easy to fabricate, but the idea of producing a hundred or so track units is a bit scary, at least if they are hewn from the solid..

Has anyone got any experience of other methods of fabicating tracks like these. I imagine some sort of simplified construction, using a jig. But what materials and methods to produce working tracks (at say 1/6 to 1/4 scale)?
 
Neil
David Clark 124/06/2011 21:43:05
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Hi There
I saw an article on simple injection moulding on the internet somewhere.
This gave designs for a tank track.
regards David

Edited By David Clark 1 on 24/06/2011 21:43:19

Clive Hartland24/06/2011 22:30:17
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Tank tracks are made from Chrome Molybdenum steel and are cast.
The track pins make excellent chisels, tough and durable.
They have to be very durable as they carry vehicle wieghts of about 60ton on all types of terrain up to speeds of 40mph.
Tank tracks are of two types, 'live' and 'dead'.
The 'live' type have rubber bonded links that spring the track, hence the term 'Live'.
To keep the tracks flat the pins are hexagonal so as the track goes around the hubs it flexes on the rubber bushes of which there are about five or six in each link.
The 'Dead' type of track was the type used on Russian tanks and laid itself flat on the road wheels as it was carried around the hubs. The links were like flat cast slabs and had round pins.
For model purposes the requirements are not so severe as the model is small and light. Modelling the 'Live' track will be very tedious as the links would have to be joined with rubber bushes to be lifelike.
The Bren Gun Carrier had quite light tracks of steel and because of the type of springing involved the track was quite loose.
I think perhaps it would be possible to do die castings of track in a white metal, remember you need two or three hundred. Then using a jig, drill them and fit the pins.
Pins are retained with ring clips that are sprung over a taper on the pin into a groove.
There is a washer with a groove that the ring clip sits up against. This helps to retain it in place.
A very tedious project making tracks!
 
Clive
John Stevenson24/06/2011 22:58:09
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Dare I mention CNC ?
 
John S.
blowlamp24/06/2011 23:04:00
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Posted by John Stevenson on 24/06/2011 22:58:09:
Dare I mention CNC ?
 
John S.
 
 
Get thee behind me, Satan!
 
Martin.

Edited By blowlamp on 24/06/2011 23:04:23

JasonB25/06/2011 07:39:20
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I would have thought lost wax casting would be the way to go, can't see how you could easily machine the hollow area inside the triangular pins even with home CNC. You then only need to make one master.
 
Good diagram of a track here
 
J

 

Edited By JasonB on 25/06/2011 08:07:00

Richard Parsons25/06/2011 08:40:11
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Stub the contraption you want is “a universal carrier”.


Long ago (and now far away) there was one stuck in a ditch for many months until ‘Ole Farmer’ hauled it out with a crawler tractor to get at the petrol left in its tanks. Local copper went ‘round the twiddle’ because it was blocking the road. Eventually some folk came with a Scammel transporter to take it away. They took it away (none too steadily) well it was hot work getting the thing on to the Scammel. And the locals were only too happy to get rid of the dregs of last year’s ‘Zider’ for 1/2d (real money) for a gallon or so of the stuff. They seemed quite sober but this tackle induced a narcosis and sort of paralysed their muscles –they seemed and were wide awake but nothing (arms, legs etc) worked. That were, as the locals said, a drop of ‘good’.


Now you want to make a working track. On this one I would ‘cheat’. I would probably cast the guidance lugs (the things which stop the tracks from derailing from the bogie wheels) as pairs and the tread plates (the bits that run on the road) in a hard low melting alloy. I would go ‘skip diving’ for bale/case strapping (not the metal ones but the sort of stringy stuff). I would hunt up an ‘elastoma’ type resin (try ‘Strand Glass usual disclaimer) and build the things that way. I will try and make a sketch for you and load it.


Rdgs


Dick

JasonB25/06/2011 08:46:14
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The problem with using strapping would be getting the tracks to sit right, you would end up with a large scale engine looking like its got poly tracks on it like you got on the 1/35 AFVs. they are way too springy and don't droop over the top guide wheels.
 
I think casting and then making a jig to consistantly drill the pin holes would be the way to go, you could omit the plugs that retain the pins and just deform one end of the pin so it holds tight in the hole.
 
J
Jim Nolan25/06/2011 09:07:02
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The trouble with this is the amount you need versus the cost time skill or equipment you would need to make the tooling yourself.

I would get or do a 3D drawing and squirt some out by rapid prototyping. Tracks hardly need to be jewellery standard and so you don’t need to go mad on resolution. Someone like Engineers Emporium use a powder process machine (by Z corp. I think) which will be fine for a track pad. The foundry can then use the pad to make a LW mould

Dependant on the cost of course it would also be possible to squirt out multiples making the casting process quicker. It would probably be best to agree with a foundry what pattern they wanted to fit the flasks they have.


Jim

Andrew Johnston25/06/2011 11:55:38
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I can't resist it; whatever method you choose, it'd be only too easy to get distrackted.
 
Regards,
 
Andrew

Edited By Andrew Johnston on 25/06/2011 11:55:55

Edited By Andrew Johnston on 25/06/2011 11:56:45

Ian S C25/06/2011 12:35:56
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I,v got a mate how is building a model of a D 11 Cat dozer, its about 30" long. For the tracks he obtained some roller chain with lugs on the links, to which he has rivited mild steel plates. The result is not what I would have used but I,m not the builder. The dozer is powered by two windscreen wiper motors through right angle gear boxes.
From what I know of bren carriers the tracks give a fair bit of trouble in full size. After the war, a company here in NZ thought they would make good tractors, they didn't.
Also the saying in North Africa during WW2, if you want to find a Kiwi mechanic, look under a bren carrier.
You know that you'll have to build a Ford V8 motor for it, well perhaps! Ian S C
    The NZ railway workshops built quite a few for the army during WW2

Edited By Ian S C on 25/06/2011 12:40:17

JasonB25/06/2011 13:19:07
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The Caterpillar type tracks do suit that method as they were basically a chain with plates on them, bit like this model of a Holt 75. I believe the plates were done using a homemade die to press the profile and the links machined from solid.
 

And there are a lot less links
 
J
Stub Mandrel25/06/2011 13:25:06
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Blimey that question woke a lot of folks up! As many suggestions as there are links in the track - perhaps making one each way would cure boredom. Thanks for so many ideas.
 
I'm going to go and study my pictures and see if I can post a sketch of how the real ones are made up.
 
The problem is that the large number make casting/attractive but that could be a lot more costly than fabrication. The scale I choose and how closely to approach 'true scale' are issues too.
 
I'll be back,,,
 
Neil
JasonB25/06/2011 13:31:29
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Stub, my link above shows how they are made up.
 
 
J

Edited By JasonB on 25/06/2011 13:32:44

Clive Hartland25/06/2011 18:36:51
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Ill jump in again here, I have in my time used a lead melting pot to cast bullets and have used high values of Antimony and Tin to make harder bullets.
I think if I was to make track links I would diesink a mould in two parts and cast them with the hardest alloy of Antimony, tin and lead I could make up.
Then they could have their Brinell hardness raised by cooking them in an oven.
I have the details of this and would be happy to pass it on if Stub wants to go that way.
The quality of the casting is very good with full detail and if the die is cut using a slight taper cutter which I know are available then the item will release OK.
I have made bullet moulds to my own design and they worked fine.
It only then requires a jig to drill through for the pins.
The wieght of these cast links would satisfy the requirement to sag onto the road wheels and stabilize the running gear.
It also means that if any are worn or damaged over time then they are easily replaced by casting another set and re-using the old track links back into the pot!
I always ended up with more lead than I cast by salvaging the spent bullets from the sand bank.
With a quarter or a sixteenth scale then the track links are going to be quite large, maybe more than a inch width.
Just my thoughts.
 
Clive
Stub Mandrel25/06/2011 18:44:12
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At 1/6 scale the model would be a managable size, or at 1/12 it would be small but do-able:
 
Vickers Light Tank MkV1a/b

Bogie wheels 22" dia = 3.67"
Sprocket wheel 22" dia + teeth 3.67"
Track width 18" = 3" "
LOA 160" = 27"
Height = 84" = 14"
Width = 80" = 13.33"
 
Track segments ~ 156 per side
Model size - from 3" section of 3/4" x 1/4 bar.
so (160*2)/4 feet of bar required = 80 feet...

Teeth about 3/4" high 5/8" wide, 3/16" thick.

Could get 24 from 12" of 3/16" x 3/4" bar

(160*2*2)/24 = 27 feet of bar...

So a lot of bar stock and a LOT of hacksawing. So castings start to sound appealing!
 
I've sketched out this very basic drawing of a link (I've missed out the ridge on the underside in two of the views):

 
It's a simple enough shape, although the teeth are surprisingly deep in relation to the size of the links. Here's a sample pic (not by me) and there are some more in my albums.
 

Unlike the track itself, that suspension unit looks like a pleasant thing to make just four of, and no hidden horrors, you can see exactly how it works from the picture.
 
I'm inclined towards the 'hard low melting point metal' suggestion. White metal would be relatively straight forward and allow meto use a silicone mould. But would it be strong enough?
 
Neil
Stub Mandrel25/06/2011 18:50:35
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Thanks Jason/Clive
 
Your messages appeared while i was composing my previous message. The isometric drawing is very useful.
 
Neil
Gordon W25/06/2011 19:39:37
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Just a thought- would it be possible to make an extrusion, then saw the tracks off ?
JasonB25/06/2011 19:53:35
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Are you sure those tracks are 18" wide? more like 8"
 
And the teeth are nothing like 41/2" tall if you compare them with a 22" dia wheel, they would be more than 1/3rd the radius
 
Jason

Edited By JasonB on 25/06/2011 20:05:05

JasonB25/06/2011 20:01:30
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Looks like someone has already made one
 

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