Machining Cork

[Allen PaddockParticipant @allenpaddock42703]

I need to turn down some wine bottle corks to fit into the ends of some round 20mm electrical plastic conduit.Do you think a normal cutting tip will work or do you think it will rip the corks to bits.The corks will then need a 10mm hole down the center.Any tips before I go out to the work shop in the next couple of days.

Edited By JasonB on 29/01/2014 16:14:36

[JasonBModerator @jasonb]

[Ian PParticipant @ianp]

Cork in the lathe is not likely to machine well with tools for metal cutting.

Best is to cut with sharp knives. In the case of round holes I would use a short length of steel tube of the correct OD and bore one end with a tapered bore to a very sharp end. If you rotate it whilst pushing it into the cork it will cut a clean hole. You might need to peck at the job and remove the core in stages.

To turn the OD you could use a sanding disk or wheel of some sort to abrade the cork away.

Ian P

[Michael GilliganParticipant @michaelgilligan61133]

I'm almost certain that normal turning tool will rip the cork to bits.

You need something very sharp, set to cut with a slicing action.

… a Stanley knife blade might do the trick

For the holes; use a Cork Borer [sharp tube], which is/was standard School Chemistry Lab equipment.

MichaelG.

.

Edit: Ian beat me to it.

Edited By Michael Gilligan on 29/01/2014 16:38:47

[Rik ShawParticipant @rikshaw]

Having made and bottled quantities of wine and beer in my younger days the best way to get your cork into a tight hole is to pour boiling water on the corks and let them stand a while. This softens them and lets you get them into the bottle / pipe. If they resist simply get the cork in as far as you can, grasp your pipe and push the cork against a rough brick wall (sandface bricks are good) and pushing whilst twisting does the job.

Only problem is that the grades of cork vary so some cork is soft (easily dealt with) and some is hard (more difficult). You can drill cork OK but in the cork factory holes are formed with a punch.

I'd recommend a soft cork up your pipe every time.

Rik

Edited By Rik Shaw on 29/01/2014 16:42:34

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Ian Phillips on 29/01/2014 16:34:30:In the case of round holes I would use a short length of steel tube of the correct OD and bore one end with a tapered bore to a very sharp end. If you rotate it whilst pushing it into the cork it will cut a clean hole. You might need to peck at the job and remove the core in stages.

You might be able to do something similar using a larger diameter tube on the outside.

Russell.

[MikeParticipant @mike89748]

As the maker of many fishing rods, I can assure you that any metal tool, however sharp, will cause cork to rip. The only safe way I found was to bring down the diameter gradually with increasingly fine grades of sandpaper. Use gentle pressure and quite a high speed – and wear a dust mask otherwise you will be blowing the stuff out of your nasal passages for ages.

[dcostaParticipant @dcosta]

Hello Allen.

I'm Portuguese and, as you may know, Portugal is the main producer of cork. Long ago I saw a movie showing a machine cutting bottle corks and as far as I can recall the tube like knife was rotating. In the movie **HERE** you'll see a working machine cutting bottle corks. The rotating movement is not clear. However you can see in the specifications table of a cutting bottle corks machine **HERE** there is a r.p.m. of " Velocidade das facas 1400 r.p.m." meaning knifes speed of 1400rpm. As I remember the knifes look very much like hollow punches.

Best regards
Dias Costa

[mike TParticipant @miket56243]

Hello Dias,

Love the video, It would not do to get your fingers mixed up with that cutter.

"Round and round went the b***** great wheel and in and out went the knife of steel"

Mike

[Jerry WrayParticipant @jerrywray14030]

Hi Allen,

Most chemistry labs. used to be equipped with a 'cork softener', I have not seen one for years, but as far as I know chemistry labs no longer use corks.

The softener comprised of two serrated wheels the centre of the small being offset from that of the larger.

By putting the cork into the largest opening and turning with quite some force the cork was squeezed. On removing the cork it was surprising how small a hole it would fit.

Jerry

[BubbleParticipant @bubble]

Hello Allen

Some years ago I made a complete fuel system for the Avro 504 at Shuttleworth.

One item was a pressure relief valve for the fuel tank. This needed a part-hemispherical cork seal about 20 mm diameter to replicate the original item.

I will skip the details of making this (unless anyone is interested). The main point was that all of the machining of the cork was done using a grinder, with a 60 grit grey stone. This produced a very good finish. Try it with a bottle cork on your bench grinder!

regards

Jim

[MuzzerParticipant @muzzer]

From what has been described above, it sounds as if cork would be very difficult for most of us to machine using single point tools or blades.

I've recently been "machining" some vulcanised natural rubber strips. These are actually snooker table cushions and are very elastic (they need to have a very high coefficient of restitution) and pretty soft. I had to taper them at each end where they merge into the centre and corner pocket areas.

My first thoughts were to try some form of sharp blade (ouch!) but this was clearly not going to work. Even with a very sharp wood chisel and a smart blow, it's impossible to place the cuts anywhere near you need them and blend the surface acceptably. I also tried some very sharp tin snips and the result was pretty awful.

The solution in the end was to hack off the bulk of the material with scissors or snips and then use a belt sander to remove the rest. As you can see from the test piece, you can get a very reasonable result indeed. Believe me, this is a miraculous improvement compared to the first attempts with the cutting tools. Just keep yourself to one side unless you want rubber crumbs everywhere! Of course, this is what the professional snooker table restorers do.

I imagine something similar would work very nicely for cork. If I was planning to "turn" cork, I would probably mount a Dremel tool in the tool post and use a fairly coarse one of those sanding wheels.

Muzzer

[paul raynerParticipant @paulrayner36054]

just a thought for rubber and cork you could try freezing it to make it harder

ive no idea if it works but may be worth a try

Paul

[HughEParticipant @hughe]

Paul is spot on

when I started out in engineering we used to make pinch wheels for tape recorders. the rubber was bonded on to the shaft left in a freezer. Then ground down to the correct size finish was perfect May work with cork!

hugh

[Allen PaddockParticipant @allenpaddock42703]

Thanks guys for all the info,I will certainly try some of the methods out to see which is best,Alterntivly I was thinking of turning down some nylon bar to use,If I dont make a very good job with the cork idea.I am a ham radio guy and I am making a 4 meter aerial using 10mm alloy tube inside some 20mm electrical conduit with out it touching the the sides of the plastic tube,So I need something non conductive to hold the alloy tube central inside the 20mm plastic tube.Any way thanks guys.

[maurice bennieParticipant @mauricebennie99556]

Hi Allen why not use rubber bands ?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by dcosta on 29/01/2014 17:42:05:

… Long ago I saw a movie showing a machine cutting bottle corks and as far as I can recall the tube like knife was rotating. In the movie **HERE** you'll see a working machine cutting bottle corks.

.

Dias,

That is astonishing !!

I can't bear to think what damage that machine would to the operator's hand, if he slipped.

Thanks for posting the link.

MichaelG.

[Ian S CParticipant @iansc]

Little OT, back in my aviation engineering days we used to fit a rubber seal with a hole though it in the fair leads for the tail wheel control wires, the bits of rubber were about an inch long by an inch wide and D cross section, the corners of the D were first cut with a knife, then finished on a wire wheel. When fitted a split pin was passed through the fair lead, and rubber block. Used to prevent the fertiliser etc., getting in and damaging the control cable.

The wire wheel maybe a bit harsh on cork, I'd try the bench grinder. Ian S C

[Phil WhitleyParticipant @philwhitley94135]

Could you use one of the synthetic corks that are appearing in our wine bottles?

[Andy Gray 1Participant @andygray1]

I recently found myself needing to cut some cork into a cone shape, and after attempting to cut it down with a razor sharp knife, I discovered the best way was simply to chuck it in the lathe and, using a normal right-hand knife carbide tipped tool, machine it down with the speed set at the highest. In my case this was around 2650 rpm, this provided quite satisfactory results with all types of cork, reconstituted ones included.

For boring this also works, however as the bit gets smaller the speed needs to increase (obviously) so as to maintain high speeds at the cutting edge, and beyond some diameters this becomes hard to achieve. As a suggestion if this is the case, perhaps a power drill mounted in some fashion on the tailstock could spin in the opposite direction to the lathe chuck so as to increase the relative speeds between the bit and the work?

[Michael Cox 1Participant @michaelcox1]

One of the recent innovation in cork technology is to veneer it into thin sheets. To do this the cork is first impregnated with plastic. It can be veneered into thin sheets that are used to make handbags, purses, wallets, shoes and even skirts. I do not know what process is used for the veneering.

Mike

[MWParticipant @mw27036]

Anyone who's read L.S sparey's "amateurs lathe" book will know he actually devotes a section to the machining of rubber and cork and how to make razor thin cutting tools for it.

I believe the example he used was the machining of rubber feet he made for a friend/client once. I'm now at risk of one of the bookworms tripping me up. I don't know why i bother. 

Michael W

Edited By Michael Walters on 02/04/2016 21:08:01

[Robin GrahamParticipant @robingraham42208]

Ee, I remember the cork borers mentioned by Michael G well! They were nickel-plated brass tubes sharpened from the outside – the sharpening tool was a metal cone with a slot cut lengthways along the face in which a guillotine style blade rode, pivoted at the base of the cone. The borers cut a pretty clean hole without tearing. To my surprise they are still buyable on eBay, but easily made anyway.

I used to (occasionally) machine rubber at work by dunking it it liquid nitrogen before attacking it, but that would take it well below its glass transition point., so it worked like hard plastic, eg acrylic. But I don't think a domestic freezer would get it cold enough.

Of more relevance to the OP's problem though – I'd worry about just how 'non conductive' cork is at radio frequencies.? I'd have thought it would have a significant water content which could cause losses? Some sort of plastic, nylon or by preference PTFE might be better Just a gut feeling based on my experience of listening for the feeble RF signals from atomic nuclei – might be a different ballpark entirely!

Rob.

[Gordon WParticipant @gordonw]

I am surprised nobody has mentioned cutting fluids, unless I missed it. I've found that water makes a big difference in cutting both cork and rubber.

[mark costello 1Participant @markcostello1]

Preach on about using cutting fluids, never heard of it.

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