Removing nylon plug from carbon fibre tube

One of my hobbies is racing sailing dinghies. The boat in question has a carbon fibre mast which has a nylon 'heel plug' with a tenon which locates the bottom of the mast in a deck fitting. I need to remove and replace it as it has been fitted incorrectly. The mast has an OD of 50mm and an unknown ID (but probably around 45mm or a little less). The plug is solidly stuck and won't rotate or budge by any means I can fathom.

It almost certainly won't be glued in but I believe nylon absorbs a small amount of moisture over time and swells slightly turning a snug sliding fit into an interference fit.

I've drilled the tenon and put a 8mm bar through hoping I could shock it free with a medium sized hammer but it just bends the bar. I'm reluctant to apply much heat but may try that before giving up and drilling it out.

Before I do has anybody got any suggestions?

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Do you think that would work better then this :-

Hitting the bar with a hammer just served to bend the bar in this case, made no impression at the plug/tube interface.....

Purely out of curiosity who is the boat builder (if it's not confidential)?

Edited By Sam Spoons on 21/05/2020 17:50:39

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No, thats somebody else.........

Makes sense WRT the slide hammer being centred. I'll give that a go if I can cobble something together with what I have in stock. I think I understand what you're suggesting so probably don't need a drawing.

Assuming you mean Alex Thompsons boat or similar it's a little bigger than mine, I sail one of these :-

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Mine is a mk 2 Blaze dinghy (web pic, not me), 14' and 10.4m2 sail. The racks mean that you don't have to hike flat out all the time to stay in front of the Laserati.....

+1 For the slide hammer !

Do you know how far the nylon is in the mast? Could it reach as far as that fitting on the left side of the picture?

Pretty sure it won't be more than about 40mm or so so it's unlikely to reach the swivel block which is 65mm from the bottom of the tube.

As Sam states it will go in approx 50mm, I had to remove mine from my enterprise mast and it was 50mm inside but very good fit - I believe the nylon swells slightly on top of the tap in fit makes it quite difficult to remove but using the taped hole and slide block is the best way as trying to just twist will break 1 of the legs

cheers

Trevor

Forgive the thread creep but I first sailed in an Ent and later taught my kids to sail in one. Lovely boats.

Made a crude slide hammer out of a bit of 12mm Re-bar and a 2lb lump hammer head. Quick try to remove the plug was unsuccessful but will have another, more determined, effort later.

Edited By Sam Spoons on 22/05/2020 14:15:18

Watching just as an interest really - no boat, no mast and not much experience in the way of nylon blocks. I am inclined to think it needs warming for a couple of days, or more, to shrink the plug before slide hammering - or just machine it out somehow. The former is easier less likely to end in damage to an expensive piece of kit - if it works. I would be checking coeffs of expansion, too. Even a few degrees can make a difference...

Yes, I'm thinking a bit of gentle heat required, if the mast was ally then no problem, get it nice and warm and it should almost fall out but will need to research the CoTE of CF tube.

edit :- a brief google suggests the CoTE of CF tube is as near to zero as makes no difference. Heat may affect the bond between the CF tube and the nylon plug (if any) but it isn't going to help release an interference fit.

I'm getting closer to drilling it out and making a new on by the day....

Any suggestions WRT turning tools for turning Acetal plastic (apparently absorbs less moisture than nylon, is harder and nicer to machine, I'm thinking sharp HSS will be better than carbide, I have some cheap Chinese carbide insert tools which work well enough for me on ally and steel but are useless on plastic). And a cobbled together method of machining a tenon on the end of a piece of round bar using only a lathe (with no milling attachments)? I could probably do the latter with a hacksaw but it seems wrong not to at least attempt a 'proper job'.

FWIW accuracy required probably +- ¼ mm will be close enough and finish only needs to be 'ok'.

Edited By Sam Spoons on 22/05/2020 16:18:11

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Thanks, was quite pleased it came together as planned as I'm very much a noob WRT to engineering. Shame it hasn't worked..... yet.....

Will try some heat.

What you need is about half a dozen helpers to hold the mast while you use the slide hammer. I would bet on the thread in the nylon stripping before the plug comes out, a larger thread would be better.

Remember to mark the alignment of the old plug with felt tip before removing it. 

The nylon is very unlikely to be glued, as it involves quite a lot of bother. We used to glue a nylon block onto an aircraft part for Westland Helicopters. The nylon was immersed in a very nasty hydrofluoric acid mix, which etched the surface about 0.001" deep. The etched surface lost all of the normal low friction and glue adhered very well.

Edited By old mart on 22/05/2020 16:25:54

Edited By old mart on 22/05/2020 16:34:54

As a sailing bod using some appropriate knots and low stretch rope to tie it to something immovable (tow bar on a large car sounds favourite) will be the next stage. The mast only weighs around 3.5kg so not much inertia to overcome.

You may be right, that was my concern, I did consider a larger thread, 12mm would have been possible but that would have left nothing on the tenon and I don't know if the plug is solid all the way up or hollow above the flange.

Marking it would be an eminently sensible idea if it was correctly aligned in the first place (but then I probably wouldn't be removing it anyway)