Lotus Elan

DIY Bobbins

PostPost by: mikealdren » Tue Apr 02, 2019 12:40 pm

I have a few scrap bobbins and need a some replacements. Has anyone tried re-casting bobbins? Is the realistic? Does anyone know what the material is and what its melting point is?
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PostPost by: USA64 » Tue Apr 02, 2019 3:28 pm

I would say no, no, aluminum and why would you bother? They are available with and without holes. If you just want a challenge beyond Lotus:

Fahrenheit (f) Celsius (c)
Aluminium 1218 659
Brass 1700 927
Bronze 1675 913
Cast Iron 2200 1204
Copper 1981 1083
Gold 1945 1063
Lead 621 327
Magnesium 1204 651
Nickel 2646 1452
Silver 1761 951
Steel 2500 1371
Tungsten 6150 3399
Wrought Iron 2700 1482
Zinc 787 419
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PostPost by: alan.barker » Tue Apr 02, 2019 3:41 pm

Why are the Bobbins scrap, is the thread damaged as you can fit Wire Thread Inserts
easily.
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PostPost by: mikealdren » Tue Apr 02, 2019 4:56 pm

I want to replace the bonnet bobbins in the front wings and I tried thread inserts some time ago but they were too short so I have damaged (possibly ruined) the original bobbins. I could drill out and use a larger thread or use new ally bobbins but they are made from hex bar and don't look right (I will however probably go this latter route.)

In the meantime I have considered using the old metal. Most of the bobbins that I have as scrap really are that (old door bobbins etc.) I suspect they are Mazak, the material used for most castings in the 1960s and that has a melting point of 380C.
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PostPost by: RichardHawkins » Tue Apr 02, 2019 6:14 pm

Mike,

Thread inserts, often referred to as "helicoils", are available in different lengths.

Hope this helps,

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PostPost by: nmauduit » Tue Apr 02, 2019 7:52 pm

it may be beneficial to try full inserts (e.g. Time-Sert or equivalent) rather than helicoil, since the supporting material is very soft and a bit sticky, full inserts may have a better way of keeping the shape of the final thread. You may want to make a setup to ensure both inserts are concentric for a durable operation.
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PostPost by: USA64 » Tue Apr 02, 2019 8:59 pm

I'd like to hear back if you make you own. Am I using graded bolts in pot-metal castings?
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PostPost by: Elan45 » Wed Apr 03, 2019 3:56 am

I handmade a bobbin from Stainless bar stock in 1983 or 4 to replace the front bobbin for my S3's battery hold-down. It didn't end up being a perfect oval, but I bonded it in place and its been holding well for many years now.

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PostPost by: alan.barker » Wed Apr 03, 2019 6:22 am

There are also solid Inserts larger o/dia than wire inserts. I think they are "keyserts" and once fitted you drive the Keys in that lock them in place. They are very solid and in stainless steel
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PostPost by: 661 » Wed Apr 03, 2019 8:28 am

RDent sell them, but they are $20 a piece!

I think Miles Wilkins may have some 5/16 ones but no 1/4"
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PostPost by: JonB » Wed Apr 03, 2019 11:24 am

Miles has a big box full of bobbins, I saw them last time I visited.
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PostPost by: rgh0 » Thu Apr 04, 2019 9:19 am

Col at Elantrikbits was casting up new bobbins a few years ago. I dont know if he still has them but worth asking.

cheers
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PostPost by: Lotus14S2 » Thu Apr 04, 2019 11:39 pm

If the bobbin itself is OK, then you can use an insert in it. There are a bunch of different inserts, by different companies. They come in a number of thread sizes, and lengths.
I don’t know where you live, but if you check the McMaster-Carr on-line catalog, you will find a number of styles, and most of them are far less than the prices charged by race car and collector car parts dealers.
McMaster supplies parts to industry; as an engineer, I have used them for close to 50 years, and they have had the parts in stock, and ship fast, and as cheap as anyone else.
If you use the key locking style, you will need to buy an installation tool, but they aren’t that expensive. The length of the insert will be long enough to meet the strength requirements of the threaded fastener you will need to use.
As an example a 5/16” thick wall insert which is 7/16” long, will cost about $4.70 each, and the installation tool will cost about $12.80.
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PostPost by: mikealdren » Fri Apr 05, 2019 8:18 am

It's all about the challenge, financially the answer is buy a new bobbin.

As I said earlier, I have already fitted thread inserts that are too short, at the time some years ago, I didn't know longer inserts were available. Now I'm not sure how to get the old inserts out.....

I will then use 2.5D inserts, the 1/4 bobbins are 0.6" thick.
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PostPost by: TeeJay » Fri Apr 05, 2019 9:07 am

Hi Mike.
In the past I have removed wire inserts by using a pointed pick to lift out the 1st part of the insert. Then with pliers pull the insert out rotating your hand as it’s pulled out.

There is also a removal tool which has a triangular head. See the YouTube video link below; which explains all about installation and removal, the tool is at approx 6.5 mins into the video. The tool could be made DIY.

Link:- https://www.youtube.com/watch?v=C1gptYa-OMM
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