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cutting bit off the bottom of a mast

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Created by sboardcrazy > 9 months ago, 14 Oct 2010
sboardcrazy

sboardcrazy

NSW, 8355 posts
14 Oct 2010 1:55PM
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Ive just been given a 30% carbon 430 mast but it has a bit of a crack right at the base & its been suggested I cut it off? Is that straightforward or anything I need to know?

h20

h20

VIC, 458 posts
14 Oct 2010 2:07PM
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it will change curve flex.... make sure mast extension will fit as diameter will change if you cut some off.. mistake for new players

sboardcrazy

sboardcrazy

NSW, 8355 posts
14 Oct 2010 3:12PM
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So 2cms off would cause hassles..?

sausage

sausage

QLD, 4874 posts
14 Oct 2010 2:54PM
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sboardcrazy said...

So 2cms off would cause hassles..?


2cms should be fine. Make sure you tape around the cut line and use a really fine hacksaw blade. Better still use a guide of some sort to ensure you get a perpendicular cut. Sand so cut edge is nice and smooth. I also permanently tape the open ends with duct tape or mylar to minimise damage.

PS - I also recoat my masts with epoxy resin where cams and boom have excessively rubbed. This seems to stop the carbon dust staining the luff tubes and potentially eliminates a point of weakness in the mast.

sboardcrazy

sboardcrazy

NSW, 8355 posts
14 Oct 2010 4:04PM
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Thanks..

sausage

sausage

QLD, 4874 posts
14 Oct 2010 3:11PM
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SBC,
Don't forget it's a 428cm mast now

h20

h20

VIC, 458 posts
14 Oct 2010 6:45PM
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yeah it should be all fine. I thought you may have gone taken it down to a 400

sboardcrazy

sboardcrazy

NSW, 8355 posts
14 Oct 2010 7:03PM
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h20 said...

yeah it should be all fine. I thought you may have gone taken it down to a 400


I thought about it but then remembered a previous post re mast bend etc..

Mark _australia

Mark _australia

WA, 23721 posts
14 Oct 2010 7:07PM
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Yeah as per above

But I'd seal the cut end with some fibreglass resin or Araldite 24hr - $15 from Bunnings and it will fill the little tiny cracks between fibres caused by the cutting and is cheap insurance. Taping around the base real tight with cloth reinforced gaffa will not hurt
Actually on second thoughts, fibreglass reinforced tape from the hobby shop even better

keef

keef

NSW, 2016 posts
14 Oct 2010 11:23PM
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Mark _australia said...

Yeah as per above

But I'd seal the cut end with some fibreglass resin or Araldite 24hr - $15 from Bunnings and it will fill the little tiny cracks between fibres caused by the cutting and is cheap insurance. Taping around the base real tight with cloth reinforced gaffa will not hurt
Actually on second thoughts, fibreglass reinforced tape from the hobby shop even better


i'll go a long with mark with the f/g tape ,but do you need to cut the mastsboardcrazy said a bit of a crack if you drill a 1/8th hole so the crack doesn't go any further, then wrap some f/b tape around it then wrap masking tape over it to squezze out excess resin that should fix it

paddymac

paddymac

WA, 943 posts
14 Oct 2010 9:14PM
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It'd tricky to get the cut perpendicular. I used a mitre box to take care of one axis but you need to raise the tip slightly so the mast's centreline is horizontal.

Mark _australia

Mark _australia

WA, 23721 posts
14 Oct 2010 10:25PM
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paddymac said...

It'd tricky to get the cut perpendicular. I used a mitre box to take care of one axis but you need to raise the tip slightly so the mast's centreline is horizontal.


Nooooo
Easy peeezy

get an L-shaped bit of anything stiff and sticky tape a felt tip pen or pencil to the end so you have a big square U shape, with one side of the big U being the pen.
Then place one end of the big square U on the bottom of the mast and the roll it around the mast to it makes a line around the circumference at a constant distance from bottom - if that make sense?

Or even better roll a pipe cutter around it so it juuust scores the surface (not too tight as it would crush / crack the carbon.

Or put a piece of wire bent into an L shape (with the end sharpened) in the vice horizontally. Then butt the mast base up against the vice with the sharpened wire touching it and roll the mast to score a line.



Then cut thru with a hackasaw but keep rotating the mast so you follow the line perfectly.

Paul Yeomans

Paul Yeomans

WA, 66 posts
14 Oct 2010 10:38PM
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I cut 100mm off a powerex skinny, mast damage due to extention breakage, and no probs even if you put a 30cm extention balls deep, so 20mm ll be fine.

sboardcrazy

sboardcrazy

NSW, 8355 posts
15 Oct 2010 8:48AM
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Well its done..before i read the latest posts. I have a fine bladed hand mitresaw for framing and we used that.2 people to hold it while one sawed..didnt check it for square but it should be & sanded it with wet & dry.It didnt look that bad anyway..

racerX

racerX

463 posts
18 Oct 2010 6:34PM
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sboardcrazy said...

h20 said...

yeah it should be all fine. I thought you may have gone taken it down to a 400


I thought about it but then remembered a previous post re mast bend etc..


If you shorten the mast from the bottom it is supposed to get softer, as the top part of the mast is always softer than the botttom. Even a stiff top mast is softer at the top, just not as much as soft top mast. At least thats my understanding.

But if you cut too much extension it won't fit inside properly because of the tappering in an SDM mast, and also you need to watch were the boom attaches as it will be higher and may be away from the reinforced area where is normally attaches. You could take it off in stages to make sure the extension still fits.

www.peterman.dk/mast-imcs-comments.htm
Cutting off material from the bottom makes the mast softer (in IMCS terms) and close to the same (or a little more flex top) in bending characteristics. Putting an extension in the mast makes it stiffer (most with flex top masts, lesser with constant curve masts) or the same (hard top masts) - and very close to the same in bending characteristics. Often you hear sailers say, that they prefer a shorter, softer mast with a long extension relative to a longer, stiffer mast with no extension. However, IMCS measurings tell us, that (in IMCS terms) there is often relatively little difference between the two options at all - at least if we talk about flex top masts or (to a lesser degree) constant curve masts. Putting on an extension stiffens up the shorter flex top or constant curve mast, so that it ends up with close to the same stiffness as the longer mast without extension.

frant

frant

VIC, 1230 posts
19 Oct 2010 4:07PM
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I know its too late for sboardcrazy but the easiest way to cut a carbon fibre mast is with a very thin (approx 1mm) abrasive cut off blade in a 4 inch angle grinder. Mark it square with a wrap of wide masking tape. Wear a dust mask and eye protection.
Alternative is to wrap a bandage around the base of a split spar to retain original length, use the core of a dyneema/kevlar rope as bandage and wet out with epoxy. Buy a pack of surgical gloves at supermarket for skin protection. Wash out with? anyone know if its turps or metho (I have forgotten, damn epoxy thinners fumes must have gotten to me!)


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"cutting bit off the bottom of a mast" started by sboardcrazy



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