Sneaky tip for fiber glass

I had to do some glass repair and found that the rotary knife My wife uses is great for cutting Fiberglass clothe! A sissors frays the ends of the glass cloth alot, Plus it dulls out the sissors. Give your wife a glass of wine and after she passes out you can use all of her quilting stuff for your fiberglass repair! Just put it back before she wakes up!

great tip,
mine also has “fit” when I borrow her quilting tools

Fiberglass ok, but not Kevlar …
You can probably get away with sneaking the wife’s edged tools for fiberglass and returning them without her finding out if she is not a real hard core sewer.

Do not even think about doing it to cut Kevlar. Kevlar really destroys a cutting edge in a hurry!!!

In the shop we had the shears marked “G” or “K”. Had to sharpen the “K” shears two or three times as often.

Take a hint and get your own new cutting tools if you are doing Kevlar.


Or take it one step further
I “borrowed” my wife’s power rotary. Worked like a charm on the fiberglass. When I ordered a new Eastman Chickadee for the application, it didn’t work nearly as well. The key was the blade. A hex shaped blade makes all the difference.

Kevlar is another story. Stick to the scissors there! (Gotta disagree slightly with Mick - the kevlar shears need to be SHARP, 'cause they don’t really cut the fabric - they “break” it. The fiberglass actually dulls the blades faster).

Need to understand this…

– Last Updated: Mar-22-05 2:52 AM EST –

please explain in as much detail as you can...

"Fiberglass dulls the blades faster" vs. kevlar....

Because I need to know why I can only cleanly cut about 40 linear feet of 5oz kevlar but then use the very same non-resharpened shears to mow though over 500 feet of 8.9 oz s-glass 'till my hand is sore? Glass breaks when 'cutting'.

What am I missing or doing wrong?

Not antagonistic.... want to understand that statement.

Did that last night
I had just got done sanding down a couple of new canoe paddles that I thought I might have sanded down a bit too much so I decided to glass them. Couldn’t find a pair of scissor so I broke out my wifes fabric cutting board. I dont think I will bother looking for scissors again! The fabric cutter is the way to go. And I think I will be cutting the next paddles down as thin as possible and glassing them too. I really like the results.

Yeah, me three … Please do explain …

as my experiences are also to the contrary.

We had over two dozen shears in use at all times during the three years I was in the Kruger Canoe shop. We went through them so fast because of the Kevlar that I finally brought a scissor sharpener to the shop to reduce the cost of constantly buying new shears and keep sharp ones on hand. Before the sharpened we all used to hide our current favorite set of shears.

In theory we kept the shears separate, but in actuality we would cut Kevlar until the shear set dulled too much for Kevlar use. Then we would switch them to glass use. We could still use that set for quite a while on glass before it actually had to be sharpened (two, three, or more times as long as it had just been used on Kevlar).

I need help understanding the break of the material you mentioned. It seems to me that the stranded glass (fiberglass) would be the one to actually break as glass is a crystalline structure and breaking is how it fails structurally (cuts, breaks, etc). Therefore it would be much easier to cut than Kevlar which does not break easily, but has a much higher resistance to being cut. If Kevlar actually broke it would not be of much use when shocked as it is when distributing the force of a bullet strike.

Confused here!

Happy Paddl’n!



OK - here’s my best shot
I was also going by experience, but my experiences have been far more limited than either of you. So I went looking too see what I could find on the subject, and here is what I found (from the John R. Sweet Co. website):

“Because of its toughness, aramid is difficult to cut. It requires a high-quality pair of Scissors that are dedicated to cutting aramid and other soft, non-abrasive, materials. Using these scissors to cut fiberglass will ruin them quickly. Since fiberglass cuts easily, even with very cheap scissors, this is a silly and costly error to make. Commercial aramid-cutting scissors are often made with carbide or ceramic blades and are very expensive.” (the way I read this, Aramid is a soft, non-abrasive material and fiberglass is highly abrasive)

As for “breaking” (and I may have used incorrect terminology there):

“Aramids should be used in conjunction with fiberglass in most laminates because their properties complement one another. The weakest aspect of aramid is its compressive strength and that is one of the strong points of fiberglass.”

And one last point, on the “bulletproof vest” comment:

“On the other hand, Kevlar 29 is what you want for ballistic applications, such as bullet-resistant vests, chain-saw chaps and the like. It is generally woven into a much tighter fabric so it does not snag easily. It is cut and penetration resistant, as well as abrasion resistant, to a much greater degree than 49.”

Does any of that make sense? Having limited experience, I’d be happy to stand corrected - am I misunderstanding or mis-stating something here?

This is a case of a nickel’s worth
of knowledge will not get you much…

What you read about the kevlar was just interpreted backwards I guess… What it should be is do not use your fresh shears for glass then use on Kevlar… takes the edge off and it is then even HARDER to cut the Kevlar…

Even the dullest shears will still go through glass all day… especially stuff under 10 oz.

I wish more people knew about the 49 vs.29 … have to explain that all the time to folks…

Have a couple of glasses together…
and forget the fiberglass!



Wait until she tries to use it again
You’re right that rotary cutters work great on fiberglass, but cutting 'glass dulls the cutter badly. You won’t notice it as long as you use it only for 'glass, but if you try to cut fabric, you’ll find out exactly how dull it is. Do yourself a favor and buy her a new cutter wheel before she finds out what you did!

BTW, you can sharpen the cutters by putting a bolt and nut through the center hole, chucking it in a drill press and honing the edge with fine stone or diamond hone as it spins. I haven’t been able to achieve a perfect factory edge with this method, but I’ve gotten pretty close.

Gee, thanks sooo much!
Now I have to go searching for what I’ve done with my other 95 cents worth of knowledge.

Your first statement in this last post was what I was alluding to. You can cut Kelvar with a sharp pair of scissors for a while before they are too dull to cut, but cut fiberglass with those shears just once and you’ll have to resharpen before cutting any more kevlar. That’s where I came up with fiberglass dulling an edge quicker - you just don’t notice it as much if you’re only cutting glass.

Am I up to a dime yet?

Best idea yet!
I’ll get back to you on how well it worked…

(or maybe I won’t!)

Misunderstood. Look at the ideas not the

Well said Onno. I came back to say what was understood from the referenced readings seemed to be taken backwards, but you beat me to it.

As for the 29 vis 49 thing. The point was not which is best for shock, but that Kevlar stands up to shock where glass fails, it breaks. Kevlar distributes the load and glass shatters. The shears break the glass and cut the Kevlar. In actuality both 29 and 49 are good at stopping objects by snagging the object and distributing the energy as they are the same fiber, 29 just has a much better configuration for doing so and is therefore much better at doing it. Now if you want to get into some really interesting stuff look to high speed liquid metals and other self lubricating projectiles. No Kevlar, any other fiber, or even solid metal is effective against these. I spent over 5 years evaluating very nasty anti personnel and anti armor devices. We had to wear very heavy extra thick Kevlar vests that would not even slow down those nasties! But that is a whole nother story and even though some of the work was with ships and boats it has nothing to do with the kind of boats we discuss here.

Happy Paddl’n!



No need to get back…
I already know it works good!

As a matter of fact some of the very wine comes from race bets with Bald Paddler.

Hey Bald Paddler are we on for the upcoming Blackwater River (Edistoe) race?



Hey Mick, what about ballistic glass ?
Heard it was being used because Kevlar was too expensive… stuff looks just like regular woven roving.

We did not come across it, but have
heard of it. The bullet proof materials was not really our main focus. It was just a side interest as we tried to find something to protect our skins while we played with the fun stuff; high speed explosives made to kill!

There is also some very, very expensive stuff the long underwear like suits and even everyday looking clothing are made of. It has been a lot of years and I do not remember the name of the material or the company. You can not even tell the person is armored it is so thin and fits so well, but us commoners will never see it. Way, way, way too expensive!


I expect my wife to stay out of my
tool box, so I had better stay out of hers. Rotary cutter huh?

Here’s a link to one

It’s rugged and inexpensive, but you’ll have to venture into a fabric or craft store to get one. Unless you ask your wife to do it… :wink: