Question on thinness?

Hi
DavidL41 said:
The sharpest cut I can get is a scalpel, is it possible to get a long blade to a thinness similar to a scalpel 5mm behind the cutting edge (convex edge). Would the only way to get this done is a hollow grind, with a convex secondary bevel?

Knife on the right.
https://www.reddit.com/r/Leathercraft/comments/560s8f/admiration_for_mr_knipschields_craft/
Click to expand...

Yes its possible,
no hollow grind required as any grind will do
just keep lowering the angle until it reaches your desired thickness
its easier if you have the knifemaker thin the blade to your requirements

You can see guy tune a blade easily as thin or thinner than a scalpel
flat grind edge to 7 degrees per side, make 1000 slices of hardwood ... examine damage ... increase angle ...
 
bucketstove said:
Hi


Yes its possible,
no hollow grind required as any grind will do
just keep lowering the angle until it reaches your desired thickness
its easier if you have the knifemaker thin the blade to your requirements

You can see guy tune a blade easily as thin or thinner than a scalpel
flat grind edge to 7 degrees per side, make 1000 slices of hardwood ... examine damage ... increase angle ...
Click to expand...


The steel is fairly thick 2mm and about and inch and a half of steel to sharpen. I think the steel needs to start at 1mm then I can taper it down to razor thickness?
 
Hi,
DavidL41 said:
The steel is fairly thick 2mm and about and inch and a half of steel to sharpen. I think the steel needs to start at 1mm then I can taper it down to razor thickness?
Click to expand...
Not sure what you mean.
The guy in the thread linked says stock is 1/16" or 0.0625inch or 1.5875mm
Consider that large kitchen/chef knives are commonly made from 3/32" or .1" or 2.54mm thick stock
a full flat grid blade will be 0.005" at the edge or 0.127mm
so while its a bit more work to grind a thicker/larger blade,
its possible, you don't need to start with a 1mm blade

Consider this image, the razor is from ~0.4mm thick stock at ~8 degrees per side
Small+Blade+Geometry+EDIT2.jpg



Also,
Not sure how you're judging performance,
but if you're doing shallow cuts,
like using a head knife to cut leather,
i dont think you really need to have a very "thin" edge
 
bucketstove said:
Hi,

Not sure what you mean.
The guy in the thread linked says stock is 1/16" or 0.0625inch or 1.5875mm
Consider that large kitchen/chef knives are commonly made from 3/32" or .1" or 2.54mm thick stock
a full flat grid blade will be 0.005" at the edge or 0.127mm
so while its a bit more work to grind a thicker/larger blade,
its possible, you don't need to start with a 1mm blade

Consider this image, the razor is from ~0.4mm thick stock at ~8 degrees per side
Small+Blade+Geometry+EDIT2.jpg



Also,
Not sure how you're judging performance,
but if you're doing shallow cuts,
like using a head knife to cut leather,
i dont think you really need to have a very "thin" edge
Click to expand...

The round knife from times will cut thick handles up to 20mm and leathers that are 2-3mm thick.

The thickness 5mm before reaching the cutting edge is important in cutting leather. The standard configuration can work, although the thinner the thickness the less overcut or undercut you will have. Essentially when you cut with a blade with a wider thickness behind the edge the leather will push against the bevel.

Snap off blades with a very thin belly is very straight cutting. I think the round knife might be okay and in the graph the yellow blade is thinner for about 5mm away from the edge.

Do you know at 1/16th stock at say 5 degree convex per side how long would the grind be and how would I measure the thickness say at 2mm or 5mm away from the edge. This is going above what is necessary, knife geometry for some reason is very appealing to me.

Also want to try out a hollow grind I hear the reduction in friction makes it even better slicer.
 
Hi,
DavidL41 said:
Do you know at 1/16th stock at say 5 degree convex per side how long would the grind be and how would I measure the thickness say at 2mm or 5mm away from the edge. This is going above what is necessary, knife geometry for some reason is very appealing to me.
Click to expand...


A triangle calculator , so if you measured angle at 5 degrees per side
5 + 5 is 10 degrees, so
10 degrees and left/right sides at 5 says 0.872 thick
10 degrees and left/right sides at 2 says 0.349 thick

going the other way, measure the thickness with calipers, and the sides, so
2mm sides and 0.349 thick means 10 degrees inclusive (5 dps)

Re: Definition of edge thickness
01PrototypeKnife.jpg
 
bucketstove said:
Hi,



A triangle calculator , so if you measured angle at 5 degrees per side
5 + 5 is 10 degrees, so
10 degrees and left/right sides at 5 says 0.872 thick
10 degrees and left/right sides at 2 says 0.349 thick

going the other way, measure the thickness with calipers, and the sides, so
2mm sides and 0.349 thick means 10 degrees inclusive (5 dps)

Re: Definition of edge thickness
01PrototypeKnife.jpg
Click to expand...

Doesn't there need to be a ratio? If I put a 5 dps edge on a scalpel it will be different to 5dps on 1/16th.

Perhaps I will see if I can get a hollow grind and a convex secondary bevel at 5 degrees. Would probably be more concentrated force with the blade like a triangle from tang to edge.
 
Last edited:
DavidL41 said:
Doesn't there need to be a ratio? If I put a 5 dps edge on a scalpel it will be different to 5dps on 1/16th.

Perhaps I will see if I can get a hollow grind and a convex secondary bevel at 5 degrees. Would probably be more concentrated force with the blade like a triangle from tang to edge.
Click to expand...

Find someone with a wet wheel grinder, grind it very thin and convex or V bevel the cutting edge. The issue with this type of edge is it tend not to track maybe as well as one with a flat grind, and it might bind more once the depth of the concave/hollow is reached. Might also have less lateral stability tho this is a factor common to other knives with the same thickness behind the edge.

On the plus side it can be touched up a few more times than a flat grind before the cutting angle depreciates.

If the stock is very thin to start it will limit the amount of concave the edge will support.
 
Hi,
DavidL41 said:
Doesn't there need to be a ratio? If I put a 5 dps edge on a scalpel it will be different to 5dps on 1/16th.

Perhaps I will see if I can get a hollow grind and a convex secondary bevel at 5 degrees. Would probably be more concentrated force with the blade like a triangle from tang to edge.
Click to expand...

Angle is a measurement of ratio , radius / length of arc ... or rise/run ... or thickness / width

Yes,
there is a difference between
a 5dps on 1/64" stock (utility razor)
and 5dps on 1/16"
see it here 5dps at 1/64" or 0.396875mm (sides 2.277)
5dps at 1/16" or 1.5875mm (sides 9.107)
that is edge bevel only,
and for the first ~2mm of width the blades are identical thicknesses/angles
after the first ~2mm the 1/16" blade keeps getting thicker while the 1/64 blade doesn't
same as in chiral.grolim's picture



There is some math over here on calculating force required for a cut based on geometry and material stiffness Primary Bevel Angles
 
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