More info re: repro track
Hello gents,
Thankyou for the public and private messages of welcome and support for our investigation.
I had a look at a couple of carriers yesterday, both for the tracks and to help a friend draw up the front armour plates for reproduction (if anyone is interested in these drawings I will send copies when they are finished).
I also re-measured a couple of brand new links to clarify the pin bores. My measurements would indicate the bore in the link is nominally 0.5mm greater in diameter than the maximum pin diameter.
ie (according to Nigel Watson's text) the new pin diameter is allowed to vary between:
Max 0.437" (11.10mm)
Min 0.432" (10.97mm)
My measurement of a link bore (taken three times) averaged out to 11.6mm. If anyone has a link lying around and can take a measurement to confirm this as a suitable target diameter for the bores - that would be great.
On the topic on pins, I had a discussion with our patternmaker who has contacts at Ajax Fasteners here in Australia. We will ask them for a quote, and have also sent a pin drawing to China.
We have had a number of discussions regarding pin materials and pin retention and would be interested in some feedback from the forum. As was mentioned above, I understand the pins were case hardened along "most" of their length. This would have been done for wear resistance, but still allowing the softer end to be peened over.
Frankly, heat treating pins adds another sub-contract operation which means more cost. We have considered using a high carbon steel like 1040 in an attempt to maintain some surface hardness without adding another manufacturing operation. With the expected use of restored carriers in mind (ie they are not in war service) we propose this will provide a cost-effective alternative.
With respect to pin retention, there are a number of options. The NOS track I inspected today used a small collar on the straight end and appeared to be simply peened over with a hammer. Nigel's book shows factory tracks having a domed, riveted head. There is also mention of "welded caps". Service track sections are joined with split pins. Aussie tracks use lead plugs.
Here are the pros and cons of each (from a manufacturing perspective):
[1] Collar/peened: Pros - cheap and easy, Cons - lots of labour, assumes 1040 high carbon steel can be peened in this manner (we'd have to make a sample pin and try it)
[2] Domed/riveted head: Pros - very strong, Cons - needs special tooling to achieve, would have to sub contract and ship big heavy link sections around
[3] Welded Caps (using a collar as per [1] and TIG welding the collar to the end of the pin): Pros - strong, relatively cheap, Cons - can't think of any
[4] Split pins: Pros - easy to assemble/disassemble, could be assembled by end user, pack tighter in crate for cheaper shipping, Cons - Retention relies on a small split pin
[5] Lead plugs: Pros - can't think of any, Cons - another part, another material, more cost, questionable whether we can reproduce the dimensions and achieve acceptable pin retention.
On the topic of strength using split pins, I don't believe this is valid option. When turning the carrier, the track is curved and hence the forces generating the turn are transferred to the washer and therefore the small split pin is loaded in shear. This would be acceptable for joining service link sections, but I would consider this poor engineering practice if used to join all the links.
My preference is for [3] Welded caps, but interested in the feedback from members. If this was selected and if the repro track manufacturing goes ahead, I would propose service link sections would be pre-assembled and stacked in a custom-built crate for shipping. End users would then assemble the service link sections with split pins as per original supply.
Anyway, enough for today. Would appreciate any thoughts, feedback or comments.
Regards,
Matt McLeod
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