Newbie with Questions on Using a Jig. Help Please.

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Nalapombu

Joined
Oct 26, 2001
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303
Hey all.
I have a quick question. I’ve only ever done kit type “builds” and want to try a REAL knife build and need some basic advice.

Let’s say I’ve got my project into its initial shape and I’m ready to start removing material. I want to use a basic jig to give me a better chance at removing material correctly and improve my chance of having some success.
How do I know what angle to set the jig at to remove material as close to my guide lines as possible? This will be a VERY basic jig made from angle iron like what I’ve seen others using in videos.

I plan on using scrap pieces to practice on prior to starting the actual project.
Thanks
 
You can use trigonometry or look at a bevel angle chart. The simplest way is to take a few strokes with the fil=e and see if you need to raise or lower the jig. It will often require adjustments as you file. Here is a good chart from one of te Shop talk members:
Personally, I don't like jigs, They rarely work well and limit the grinds you can do. It may take a few blades to get it down, but once you learn to file or grind freehand you will be able to do almost any grind easily and much faster.
 

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Nalapombu said:
Let’s say I’ve got my project into its initial shape and I’m ready to start removing material. I want to use a basic jig to give me a better chance at removing material correctly and improve my chance of having some success.
How do I know what angle to set the jig at to remove material as close to my guide lines as possible? This will be a VERY basic jig made from angle iron like what I’ve seen others using in videos.
Click to expand...
I guess you will grind on belt grinder ? If so , you will need to have adjustable angle on jig or on work rest .Set some angle and grind little , see where belt remove steel and adjust angle according to that ..............you will need to do that several times till you grind one side .
It is same procedure if you use file grinding jig ....
 
Check out you local hardware store and see if they have a General Protractor. They're around 9 bucks.

This site is pretty handy.

Online Knife Grind Calculator - D. Comeau

A handy online tool for the knifemaker to determine the angle to use when grinding single or double bevel blades.
dcknives.com
Pick stock thickness, blade width... and it gives the required angle.

Using protractor set jig 90 degrees.
Set your work rest to the desired angle.
Or vice versa

Make micro adjustments to the rest/jig as your grind progresses.
 
That's a good link - too bad the author didn't allow numbers to be entered rather than pre-selected values. While I normally just use the trig method to calculate the desired angle, I'll bookmark the site.
 
When I first started I did gymnastics trying to figure out this exact question.

The truth of the matter is, don’t calculate it before grinding. I would get a piece of angle iron (or other jig) and make sure it’s adjustable for angle. Scribe your center lines and then draw (or scribe) on your knife roughly how high you want your bevels to go.

Clamp the knife to the jig at a fairly aggressive angle (roughly 30-45deg, being exact doesn’t matter) and grind down to your center line. Then, adjust the angle shallower and grind the bevel until you see no marks from the 45deg grinding. Continue this process and you will slowly “walk” your bevel up to the line that you previously drew. Flip over and repeat on the other side!
 
While having a general idea for the angle of the primary bevel is not a bad thing, thinking that you will be able to set your jig to a specific angle and then just grind away is kind of going down the wrong path and will lead to frustration and bad results.

For instance, say I have some 1/8" stock, 1" wide and I want a full flat grind? Plug the numbers into the online calculator gives you 3.6 degrees. But wait! I need to leave ~0.030" on the edge pre heat treat! Now that angle is 2.72 degrees. But wait! my blade width tapers towards the tip so that angle is now off even further.

Is your platen square? Is your work table square?

My basic point is that short of a milling machine you are not going to get anywhere near the precision needed to try and grind everything at a fixed angle. There are too many variables and uncertainties involved.

Go look at David Comeau's YouTube channel, specifically how he describes using a file-jig for cutting bevels. Start at a steeper angle, grind/file until you get near your center line. Drop the angle a bit and grind/file until you reach the same place as before. Lather, rinse, repeat. Note that he never talks about the final bevel angle. Now think about how this approach can be modified for a belt grinder.

Good luck with your project.
 
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