Making a large cork

**BobL** · 23rd September 2019, 10:38 AM

Although the product is not wood related the process does involve wood working.

I have a 20L glass bottle with a 30 mm opening that I lost the cork stopper for and replacing it turned out to be harder than I thought. I would basically have to buy an oversized one and then try to shape it to fit. Anyone that has tried to shape cork know that is.

So this is what I did.

Determine size of cork.,
Find or make up a piece of wood that is a about 10mm thicker than the length of the cork is long - mine was 45mm long
Mount wood onto lathe face plate.
Using the lathe, drill a hole through the wood that is as wide as the narrowest end of the cork (mine was 25mm) - I used a Forstner bit
Turn a truncated cone in thef wood by enlarging the accessible end to be as large as the fat end size of cork - mine was 35 mm.
Make sure you sand the hole smooth so you end up with a smooth cork finish.

I will call the piece of wood with the truncated cone in it a mould - see below.
Former.JPG

Take as many old corks as you think you will need plus a few more
Chop in food processor on highest speed (it works better if you use 3-4 times more cork than you will need) for about 30 seconds.
Pieces should be ~5mm or smaller - the chopped cork in the above photo is still a bit large.

Lay out a 30 x 30 cm piece of cling wrap on bench.
Place mould in middle of piece of cling wrap with large hole uppermost.
Fill with chopped cork plus about 30% more than you need
IMG_3983.JPG
Lift up mould and allow chopped cork to fall though to middle of cling wrap
Make a small depression in the middle of the pile of chopped cork.
Add a good “gollop" of silicone sealant - about 1/4 of the volume of the cork.
Cover Silicone with chopped cork from the edges of the pile
Gather up edges of cling wrap forming a bag with the chopped cork and silicone
Twist edges of bag forming a loose ball and thoroughly fondle the bits in the bag.
Don’t worry if all the silicone seems to disappear - you can add more if you think it's needed

Screw the mould to a piece of wood and liberally oil the inside of the mould with linseed oil - this stops the silicone from sticking to the wood.
Empty the mixed cork and silicone into the conical hole - be firm. Even after squishing it you should still have a bit of a domed top.
Cover exposed cork silicone with a small piece of cling wrap
Place a wooden disc that can fits inside the top of the cling wrap that will enable you to further squish the disc and cork/silcone mix into the old.
Use a clamp or a press to press the disc into the hole.
IMG_3984.JPG

Leave to cure.
I really squished mine in hard so I had to use a press to ease out the cork.
Although the surface is smoother than it looks, below you can see the cork could have been chopped up a bit more but this is good enough for what I want it for.

Final.JPG

In a subsequent tests I used a piece of 18 mm thick MDF with a parallel sized hole the same diameter as the top of the mould and screwed that to the top of the mould.
Then the wooden disc fit neatly into the parallel sized hole and enable a more even pressure to be applied to further compact the cork/silicone mix into the mould.

**Tonyz** · 24th September 2019, 09:49 AM

Bob I could solve the problem. Is this what they called a carbouy? I'll buy it off you.

**BobL** · 24th September 2019, 10:52 AM

Originally Posted by Tonyz

Bob I could solve the problem. Is this what they called a carbouy?

Is "what" the cork or the "glass bottle"?

I'll buy it off you.

Buy what?

**LanceC** · 24th September 2019, 11:54 AM

Bob, you recently tested the Cork-Rubber on your bench vice. Assuming you had some left over, did you consider tightly rolling some of that into a conical shape?

I do like your solution. Were you concerned that by needing to compress it to set in the mould, it wouldn't have enough spring left to squash in the bottle? Obviously it worked well for you though.

**BobL** · 24th September 2019, 12:07 PM

Originally Posted by LanceC

Bob, you recently tested the Cork-Rubber on your bench vice. Assuming you had some left over, did you consider tightly rolling some of that into a conical shape?
I did try that and no luck. It's a lot harder than it sounds.

[QUPTE]I do like your solution. Were you concerned that by needing to compress it to set in the mould, it wouldn't have enough spring left to squash in the bottle? Obviously it worked well for you though.

When removed from the mould it sort of expands a little and turns out to have heaps of squish left. More than real cork which is surprisingly non-squishy.

**Tonyz** · 24th September 2019, 02:23 PM

Dear Bob..
The carbouy is the hidden glass container, Id love to get my hands on a decent sized one

**clear out** · 29th September 2019, 08:41 AM

I was interested in your latest project Bob and wondering how strong the end product was.
The reason being Bandsaw wheel rubbers.
Bandsaw wheels have been covered with cork in the past.
I have some long strips that I may use with a scarf joint but your mix is interesting.
Although by the time I make a mould around the wheel I might as well just source an appropriate urathane and be done with it.
H.

**BobL** · 29th September 2019, 10:15 AM

Originally Posted by clear out

I was interested in your latest project Bob and wondering how strong the end product was.
The reason being Bandsaw wheel rubbers.
Bandsaw wheels have been covered with cork in the past.
I have some long strips that I may use with a scarf joint but your mix is interesting.
Although by the time I make a mould around the wheel I might as well just source an appropriate urathane and be done with it.
H.

I will make another cork and do a destruction tests.

One of the key aspects of the cork I made is the amount of pressure needed to compress the cork into the mould needs to be quite high - much higher than you think. If this is not done then there are still too many voids and it will be considerably weaker. I know this because the first two I made were like this. Only when I started using a press did I get enough pressure to compress everything together to get the final product.

Another factor for using a belt mode of cork/urethane rubber belt is the distribution of the sizes of the cork pieces, it will need to be a lot finer for a belt, ie grind old corks for longer.
Making mould and applying the required pressure sounds tricky for a BS belt/tyre like object.

I note two part urethane rubber can be purchase for ~$40/kg and applied with a brush for making moulds for things like concrete products. For a BS wheel I'd be looking to brushing it direct (no cork) onto a BS wheel while it is slowly rotating.
eg Flexible Polyurethane mould making material
.

**Pagie** · 29th September 2019, 11:07 AM

Large corks are available at pottery supply places

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