Author Topic: Scissors for Kevlar  (Read 1258 times)

Offline Sam Sloane

  • Newbie
  • *
  • Posts: 16
  • I'm a sharp craftsman!
    • View Profile
Scissors for Kevlar
« on: December 28, 2019, 12:24:56 pm »
Hi all,

I rarely do scissors......read alot on facebook about stylist and grooming shears, but not alot out there on Industrial Shears....

Today I did 27 pairs of shears for a Composite Company......for cutting fiberglass, carbon fiber, and Kevlar.

I could cut the fiberglass, and the carbon, but none of my work was "stellar" when it came to the kevlar.   I was told to set the edge at 25 degrees by someone, but found the best for these was actually less than 15 degrees ( which my tormek gauge cant even measure, because the plastic bulge on the angle indicator actually touches the wheel....look for yourself!)

Does anyone have insight to what would work best for the kevlar??

Also, after doing about 15 pairs, I noticed my SB-250 Wheel was totally chattered.....like little waves running across the face of the wheel.....is this normal?....I have to resurface the wheel a few times to gring them out!

Thanks,

Sam

Offline cbwx34

  • Hero Member
  • *****
  • Posts: 1291
    • View Profile
Re: Scissors for Kevlar
« Reply #1 on: December 28, 2019, 04:54:41 pm »
Hi all,

I rarely do scissors......read alot on facebook about stylist and grooming shears, but not alot out there on Industrial Shears....

Today I did 27 pairs of shears for a Composite Company......for cutting fiberglass, carbon fiber, and Kevlar.

I could cut the fiberglass, and the carbon, but none of my work was "stellar" when it came to the kevlar.   I was told to set the edge at 25 degrees by someone, but found the best for these was actually less than 15 degrees ( which my tormek gauge cant even measure, because the plastic bulge on the angle indicator actually touches the wheel....look for yourself!)

Does anyone have insight to what would work best for the kevlar??

Also, after doing about 15 pairs, I noticed my SB-250 Wheel was totally chattered.....like little waves running across the face of the wheel.....is this normal?....I have to resurface the wheel a few times to gring them out!

Thanks,

Sam

I don't know anything about cutting Kevlar, so I did a search.  Most of what I found seems to indicate that a bit of a "toothy" edge is needed.  Here's a sample quote or two...

Quote
Kevlar has extremely strong, and slippery fibers.    When you try to cut it with normal scissors the fibers start to slip over the edge, and pushes the blades apart.    Extremely sharp scissors may work for a while, but they'll dull fairly quickly.    The trick here, is that I'm putting a rough and random serrated edge on each blade.   These little teeth grab the fibers while the blade slices through the Kevlar quite easily.

Quote
The #2733-A is a specially designed made specifically for cutting Kevlar®, aramid, carbon, fiberglass, and other hard-to-cut reinforcement fabrics. Small teeth machined into the blade allow the scissors to “bite” into the fibers without letting them slip.

It sounds like, instead of compensating with a lower angle... maybe you need a toothier edge?

My only other thought... if you indeed need to sharpen them at 15° per side...can you take them apart and use the knife jig?  15° might be too low for the scissors jig. But I'd look at the level of finish first.

(To be clear... I'm just telling what I found... no actual experience).

Offline RickKrung

  • Hero Member
  • *****
  • Posts: 718
  • Maker
    • View Profile
Re: Scissors for Kevlar
« Reply #2 on: December 28, 2019, 05:37:52 pm »
The little waves are most likely, as you say, chatter.  The scissors jig is frustrating to use for me because of the chatter.  I come from a metal machining background and chatter is never good.  It is uncomfortable for me to sharpen scissors when they chatter.  But, I've never heard, read or found of a way to avoid it. 

Same probably goes for avoiding the chatter from causing that on your stone.  I think the only solution would be to resurface it, as you have found you need to do.  I would probably do that resurfacing more frequently, but lighter each time.  It may not save much stone, but I think this could reduce the amount of chatter that occurs on subsequent scissors. 

Previously, I had only heard of that sort of chatter marks on the stone - caused by the truing.  There has been a bit of discussion on this. I have found it difficult to remove, once it has started.  This is also a reason for retruing more frequently, as it is likely easier to remove when the chatter ridges are smaller. 

What CB says about toothyness rings true to me, although I have never cut kevlar.  You might try making one blade toothy and the other smooth, the former being the "gripper" and the later being the "slicer".  If that isn't enough, then make both toothy. 

Can you get a look at shears used for cutting kevlar that are new, to examine the character of the cutting edges?  That could tell you a lot, it "seams" to me.

I like CB's idea of separating the blades of the scissors to use the knife jig for such shallow angles.

Rick
Quality is like buying oats.  If you want nice clean, fresh oats, you must pay a fair price. However, if you can be satisfied with oats that have already been through the horse, that comes at a lower price.

Offline Jan

  • Hero Member
  • *****
  • Posts: 1289
  • Iron sharpens iron, and one man sharpens another
    • View Profile
Re: Scissors for Kevlar
« Reply #3 on: December 28, 2019, 05:41:52 pm »
Sam, I am sharpening scissors quite often but have no specific experience with kevlar.

A good tutorial entitled “Scissor sharpening” by Steve Bottorff you can find here:
https://www.tormek.com/forum/index.php?topic=2544.msg13186#msg13186

Do not hesitate to experiment with angles 5 to 10 degrees. Two of my scissors were sharpened at 5 degrees and work well. Some scissors blades during grinding strongly vibrate and produce strange howling sounds. To reduce this effect mount the blade in the jig with smallest possible protrusion (2 to 3 mm). Vibrations cause irregular stone wear.

Jan
« Last Edit: December 28, 2019, 05:48:19 pm by Jan »

Offline Sam Sloane

  • Newbie
  • *
  • Posts: 16
  • I'm a sharp craftsman!
    • View Profile
Re: Scissors for Kevlar
« Reply #4 on: December 29, 2019, 05:17:30 am »
Guys,

When I say 15 degrees, thats 75 degrees on the tormek guide......I wonder if there is enough length on the Bar support to get that far away to do 75 degrees!

Offline cbwx34

  • Hero Member
  • *****
  • Posts: 1291
    • View Profile
Re: Scissors for Kevlar
« Reply #5 on: December 29, 2019, 03:16:05 pm »
Guys,

When I say 15 degrees, thats 75 degrees on the tormek guide......I wonder if there is enough length on the Bar support to get that far away to do 75 degrees!

Ah.   (I wondered how you were making 15° with the scissor jig).

I still think "level of finish" may be the answer, (vs. what now looks like trying to make the edge more robust).

Tormek has the new "US-430"...

https://www.tormek.com/international/en/spare-parts/other-spare-parts-and-upgrades/us-430-universal-support-extended/

... if you need additional height.

Offline Jan

  • Hero Member
  • *****
  • Posts: 1289
  • Iron sharpens iron, and one man sharpens another
    • View Profile
Re: Scissors for Kevlar
« Reply #6 on: December 29, 2019, 04:25:19 pm »
Yes, Sam, scissors angles are measured from square, which is called 0 degrees. The picture shows scissors jig adjusted for 0 degrees.

The jig holder has a wedge shape which adds some 10 degrees to the angle of the support plate.

Jan

Offline cbwx34

  • Hero Member
  • *****
  • Posts: 1291
    • View Profile
Re: Scissors for Kevlar
« Reply #7 on: December 29, 2019, 04:54:45 pm »
Yes, Sam, scissors angles are measured from square, which is called 0 degrees. The picture shows scissors jig adjusted for 0 degrees.
...

Except on the Tormek (of course)...



 ;)

Offline Sam Sloane

  • Newbie
  • *
  • Posts: 16
  • I'm a sharp craftsman!
    • View Profile
Re: Scissors for Kevlar
« Reply #8 on: December 29, 2019, 06:39:44 pm »
so, with the nub of the angle gauge riding on the wheel...is this measuring properly???

Offline Jan

  • Hero Member
  • *****
  • Posts: 1289
  • Iron sharpens iron, and one man sharpens another
    • View Profile
Re: Scissors for Kevlar
« Reply #9 on: December 29, 2019, 08:14:55 pm »
Sam, Tormek Anglemaster does not allow to set/measure edge angle larger than 75⁰, what in US scissors terminology corresponds to 15⁰ (90⁰ - 75⁰ = 15⁰).

Scissors were invented in Finland by Fiskars and that is probably the reason that Tormek handbook uses different cutting angle definition than the one used in USA.

Jan

Offline Sam Sloane

  • Newbie
  • *
  • Posts: 16
  • I'm a sharp craftsman!
    • View Profile
Re: Scissors for Kevlar
« Reply #10 on: December 29, 2019, 10:09:15 pm »
Jan,


kiitos minun frind!.......my first wife was Finnish......i had no idea!

Offline Jan

  • Hero Member
  • *****
  • Posts: 1289
  • Iron sharpens iron, and one man sharpens another
    • View Profile
Re: Scissors for Kevlar
« Reply #11 on: December 30, 2019, 09:24:02 am »
Sam, the origin of your first wife gives you the best prerequisites to be an excellent scissors sharpener!  :D

Jan