knapping precut slabs

[Dh88]

Anyone have tips or a video on knappping slabs? I have some novaculite slabs and I can make sharp functional points from them but they always have a pile of little hinge fractures.aggravated would be an understatment

[bubby]

I work lots of slabs, use a handpad with a groove in it, abrade the edges good and push in then down, an ishi stick will help to get the flats off, work around one whole side and check after each flake

[Dh88]

I have no trouble clearing the face on the first pass.my troulbe starts when im trying to develop convexity on the following passes. Thats when the little hinges start to show up

[Jodocus]

I had the same problem and it took me quite a while to solve on my own, a teacher would cetainly have pointed me to the solution more quickly. I'm not sure if this is also your problem, but it sounds like.

In my case, the problem was that the angle on my bevel was too steep (sharp). When raising the bevel, I now try getting somewhat in the 70 degrees range. I lay the bicafe flat on the leather and essentialy push straight down along the edge. After, abrade well.

The reason for having an overly steep angle was mainly reluctance to give up width. Dullening the angle of the edge seems like a step backwards, but it is not. A sharp edge isonly produced when i finish the shape and sharpen the edge in a last pass.

Hope this helps.

[Ghost Knapper]

Do you have any pictures that you could share to show how they are turning out? One thing that helps to cut down on hinges with percussion slabs is removing the square edge first and taking short flakes in the beginning and work in towards clearing the whole face rather than clearing it on the first pass, also as Jodocus stated having a proper platform angle really helps.

[Chippintuff]

I have not chipped much novaculite, but a lot of what I have chipped was prone to step. If you're not having that. Problem on other stone, it may be a problem of needing to make tougher platforms. Also, after running long flakes across a flat surface, the bulb concavities at the start of each flake may need a little cleaning up before running the next series.

WA

[Dalton Knapper]

Dh - are you sure it is heat treated? Glossy or at least some gloss? You may have to zig-zag the edge before you attempt to run flakes across. Good luck.

[mullet]

After each pass grind the edge off so it is slightly rounded. Then grind some new platforms. I also use a rubber pad glued on a piece of wood with different size slots cut in it.

[vinemaplebows]

After each pass grind the edge off so it is slightly rounded. Then grind some new platforms. I also use a rubber pad glued on a piece of wood with different size slots cut in it.

I agree with Mullet. Try to get the video "lap knapping"  by Craig Ratzit (sp) it will answer most of your questions when it comes to slabs.

[mullet]

That's where I got the idea from, Brian. I watched Craig use it at the Dade City Knap-In a few years ago.

[Dh88]

@ghostknapper I have no clue how to post pics from my phone

@chippintuff this is my first time messing with slabs but I dont have problems with hinges when pressure flaking flakes into points.

@dalton knapper the material came from donald jones and is supposed to be heat treated. His material was highly recomended on facebook knapping groups

@mullet I abrade the heck out of the platforms, maybe im going overboard on the abrading part? I use a rubber pad glued to a block of wood also

@vinemaplebows where can I find that video?

Thanks for the replies so far guys.
Dh88

[vinemaplebows]

If you google "Neolithics & flintnapping" you may figure it out.

[flungonin]

What is the notch for in the wood? Is this for the flake being removed? Also I can get a 1/4 to 1/2 long skinny flake, but nothing longer and never anything to go across the surface. I have a tendancy to have turtles(humps). Never been able to get rid them. Also working with debige, so the pieces are really small and mostly I have to use direct pressure. Mentioned earlier you were saying to abrade enough to get the angle for running a flake. So you really abrade past center then push in and down or just down. How far in is the tip of your Ishi stick when applied to the stone? Apologise for so many questions, but this article raised some questions I never heard before. Just trying to learn. Thanks for the paitience.

[bubby]

You can get that lap knapping video at amazon.com

[caveman2533]

I have no trouble clearing the face on the first pass.my troulbe starts when im trying to develop convexity on the following passes. Thats when the little hinges start to show up

I think you are doing it backwards I would not clear the face first. First pass pressure or percussion should be short flakes  Maybe only a 1/4 inch long and spaced  about 3/8 apart. This will create convexity from the beginning. Then go back for the second, grinding it well and in between the original pass.