Hi to all.
After reading an almost 1 year old post from a memberfrustrated with cutting, drilling and edgework of Kevlar laminates, I thought Iwould join your clan and post the solutions I have employed while dealing witharamid.
If you are impatient or easily frustrated, find anothermaterial and read no further!
First of all, if you are using Kevlar, you are probably useFG, carbon and possibly other as well. DETICATEALL OF YOUR MACHINNING TOOLS (SHEARS, DRILL BITS, SANDPAPER, ect) FOR USE ONONLY ONE FABRIC, BOLDLY LABLE THEM, AND DO NOT MIX THEM UP!!! Edgeretention will improve 100 – 300%. Soak / clean them regularly in acetone evenif they are never exposed to epoxy.
CUTTING DRY ARAMIDFABRIC
For hand shears, the best by far are “Kai 7000 series”tailoring shears. Nice micro serrations to hold the fabric from slipping out,and edge retention is 5 times that of any other shears I have used. Well worththe $95.00 I paid for them from Soller Composites. Prices may be slightly lowerat trade shows. I use cheaper ones during lay-up though.
E.C.Cutter. Buy one at any cost, but buy one!!! Ittook me 2 years of doubting the praise of many before purchasing one. Ultralight, cordless, no hand fatigue after 8 hours of pattern cutting. I use it tocut just about everything including perf, bleeder, bag , as well as glass,carbon, and, yes Kevlar. Just order an extra “shoe” blade for each compositefabric and one more for everything else. A second battery is extremely handyalso. Some places charge more than $130.00, but places like Jamestown Distributorssell them for under $100.00.
TRIMMING CURED ARAMIDLAMINATES
Cutting
First of all, to reduce the “Kevlar Fluff” during the trimmingand edgework of an all-Kevlar laminate, consider laying a 1”-2” wide strip ofthin FG in the mold first where each edge of the laminate which will be trimmed.1.5oz style 1080 or 3oz style 120 really help to reduce the fluff and isvirtually invisable. Obviously, the entire first ply could be glass. If thelaminate is comprised of Kevlar and other fabrics, for God’s sake, PUT THEKEVLAR IN THE MIDDLE OF THE LAMINATE!!!
If possible, and rather thin, consider de-molding thelaminate while still a bit “green” and cut to size with a simple utility knife,as long as you purchase replacement blades in boxes of 100. This is especiallyeffective used on flat laminates with straight cuts but awkward and evendangerous on curved pieces. It is impractical for most of my applications. Forthe flat, 11 ply alternating carbon / Kevlar laminate I need to cut in straightlines, I purchased a 10” table saw blade with 126 carbide tipped teeth ground10 degrees negative and make sure the fence is at least .063” wider at the farend to minimize heat buildup in the piece. It may not be the recommended method,but it works for approximately 200 lineal feet before needing to resharpen theblade. Hey, it’s Kevlar.
A band saw with a relatively fine toothed, bi-metal bladewill work but most composites, especially Kevlar, will kill the blade in rathershort order. The finest carbide toothed band saw blades I have found were 7 teeth/inch,and although I have not tried one, I cannot imagine it producing adequate results.
Typically, a standard jig saw with a metal cutting, 30 tpi bi-metalblade produce the best results on the kidney bean shaped tubular end cuts of myKevlar/carbon bear-resistant backpacks. I know the blade will need to bereplaced every 20-25 lineal feet going through the single or double, 8 plylaminate. Hey, it’s Kevlar. A few less tpi is better than more whichproduce more heat, and keep the blade moving as well for the same reason. Thecarbide grit blades might possibly be OK for carbon or FG but are patheticallyworthless on Kevlar.
Sanding
This the most tedious, time-consuming, boring, and generalpain-in-the-ass step in producing an aramid laminate. Hey, it’s Kevlar.
Post cure your laminate as hot as possible/practical. Heatcuring it will help it from softening with the heat generated while sanding andcutting also.
Heat build-up is your worst enemy while cutting, sanding, ordrilling an aramid laminate as it will soften the epoxy and not hold the fibersfirmly enough to be sheared. Instead, they lie over, fuzz and fluff up. Slowspeed and light to moderate feed are key and keep moving around the piece to allowthe high spots to cool. I try to have 5or 6 pieces to alternate while sanding to allow them to stay as cool aspossible. Try to keep the direction of sanding parallel with the edge untilflat then chamfer at a +45 and -45 degreeangle, starting from the surface going toward the edge. This will assiststretching the fibers into the laminate and severing them. NEVER GO BACK ANDFORTH!!! Do not consider using an orbital sander unless using 400 grit orfiner.
Although I was informed silicon-carbide grit was sharper andrequired less pressure than aluminum-oxide, the aluminum oxide seems to performbetter for me. I have been unable to locate ceramic grit discs for my 20”grinderwhich is supposed to be the way to go (other than price). I rarely use anythingmore aggressive 60 grit, then 100, 150, 220 and finish with 320 or 400. Whenall the fuzz is gone, I use a very thin foam roller to apply a coat of epoxy.It’s a lot of work, but Hey, it’s Kevlar.
All edges are exposed on the Wise Backpack, not onlyvisually, but to people’s skin and clothing to get snagged on if left rough. Hopefullyyour project does not require as much attention to the edges.
DRILLING
This is the easy one. Solid carbide, brad point drill bits!They perform best if the laminate is backed up with plastic or maybe even wood.Even if backing is impossible, they produce an exit hole with minimalsplintering. Fast speed with medium speed or firm pressure produces the bestresults for me. I purchase mine from McMaster-Carr. They are expensive, butthey work. Hey, it’s Kevlar!!!!!!!!!!!!!!!!!
Mark T.