Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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Knifemaker / Craftsman / Service Provider
- Joined
- Aug 20, 2004
- Messages
- 37,757
I have had a few emails from folks with problems getting their knives and bevels flat when grinding. It is sort of hard to tell someone how to grind in words, but there are a few things that can make the process less error prone. I just straightened out a blade for a fellow who had ground it nicely...except it had a twist ground in it. Each side seemed perfect, but they were composed of several planes ...and no plane was parallel to any other plane.
These instructions are aimed at a maker with a 2" belt grinder and a bit of practice and skills. The same procedure can be applied to a person with only files, sandpaper, and a flat reference surface ( granite plate is best).
1) Start flat to stay flat.
Using PG stock has advantages, but isn't a guarantee of things being straight. After profiling the blank, take a long knife magnet and flatten both sides against the flat platen. Of course, if your platen isn't flat, you aren't going to get a blade flat. A pryoceramic platen liner is a real boon for these tasks.
Once the two sides are both showing a flat grind over the entire blade area, it is time to make it un-flat. Take the time to measure the tang area to make sure it is parallel. The spine and belly sides should normally be the same thickness ( unless you are deliberately tapering the tang toward the bottom side).
About that long grinding magnet. One really valuable purchase is a couple of grinding magnets. A 9" and a 4-5" pair will do most all tasks. The knife suppliers sell then for very little and the easy to grip wooden backing makes use efficient. I couldn't grind nearly as fast or flat without mine. All the flattening and tapering steps are done with them. I use an 80 grit ceramic grinding belt for all the basic steps, and then repeat them on a 120 grit blue Zirconia belt. This leaves a surprisingly flat and smooth surface to start the bevels on.
2) Taper things.
Start on the tang. If it is a full tang, make sure it is perfectly flat and the two sides are parallel. If it is a hidden tang, taper it by at least 25% of the thickness all the way to the guard shoulders. Tapering a hidden tang first keeps the tang from causing problems by getting into the grind later on.
Next, add the distal taper. Don't worry about the bevels yet...just taper the entire knife blade area evenly until the tip is about half the thickness of the ricasso. On a full tang knife, don't carry the taper back farther than the front of the ricasso. On a hidden tang, you can taper it all the way to the guard shoulders, or stop at the front of the ricasso. These places don't need to be exact right now, you can fine tune the grind on the 120 grit belt. Fully tapered blades with the taper from butt to tip or the tang having a reverse taper are advanced skills.
At this point the blank should be shaped like your desired knife, and tapered from ricasso to tip. The tang is either flat if full tang, or reverse tapered if a stick tang. Look things over carefully. If the sides are uneven, or the taper is not complete, it will come back to haunt you later.
3) Taper the bevels, Grind the basic bevels as smoothly and evenly as possible. It won't be flat if it sits still...so keep the blade moving. I use the shorter grinding magnet here to hold the blade only on the bevel area. Holding the blade tang and all can lead to "pushing" the tip into the belt, or rocking the blade at the plunge. neither of these situations will give a flat bevel. Get over the blade and sight down on it as you grind. This helps see what is happening. By holding the shorter magnet on the blade bevel area, you concentrate your attention on this area only. If needed, use a 3" grinding magnet for shorter blades.
4) Go back and touch up the tapers and flats.
After getting the basic bevels ground in at 120 grit, re-do the flats and tapers again with 220 grit. This will tell you where you ground a dip in the spine at the top of the plunge, or where the ricasso is uneven. Touch up what needs to be done before moving on to finish up the bevels and other details. When I am done with touching up the tapers and flats, I has slightly flattened the top of the bevel grind at the spine in a long narrow triangle, with the ricasso as a flag on that narrow "pole". This is exactly what I want. The two sides should have identical triangles. The entire triangle and flag should be one unbroken, smooth and even grinds. If the two sides are the same, and the triangle goes from near the tip to the guard shoulder smoothly....the knife will be perfectly symmetrical. This should make it much easier to finish the bevels and center the edge and plunges.
In all the steps, try and do the grinding evenly from side to side. Remove the same amount off each side in each step. Don't grind one side completely and then move to the other. Also, let it cool a bit between grinds. A dip in a tub of water is always a good idea. Every now and then set the blade on the granite surface plate to check that you aren't grinding things out of flat, or creating a warp. Deal with the warp as soon as you find it.
There are many steps and tricks past this point, but if you don't start out with the proper distal taper and flat surfaces, you won't be able to get them easily later on.
These instructions are aimed at a maker with a 2" belt grinder and a bit of practice and skills. The same procedure can be applied to a person with only files, sandpaper, and a flat reference surface ( granite plate is best).
1) Start flat to stay flat.
Using PG stock has advantages, but isn't a guarantee of things being straight. After profiling the blank, take a long knife magnet and flatten both sides against the flat platen. Of course, if your platen isn't flat, you aren't going to get a blade flat. A pryoceramic platen liner is a real boon for these tasks.
Once the two sides are both showing a flat grind over the entire blade area, it is time to make it un-flat. Take the time to measure the tang area to make sure it is parallel. The spine and belly sides should normally be the same thickness ( unless you are deliberately tapering the tang toward the bottom side).
About that long grinding magnet. One really valuable purchase is a couple of grinding magnets. A 9" and a 4-5" pair will do most all tasks. The knife suppliers sell then for very little and the easy to grip wooden backing makes use efficient. I couldn't grind nearly as fast or flat without mine. All the flattening and tapering steps are done with them. I use an 80 grit ceramic grinding belt for all the basic steps, and then repeat them on a 120 grit blue Zirconia belt. This leaves a surprisingly flat and smooth surface to start the bevels on.
2) Taper things.
Start on the tang. If it is a full tang, make sure it is perfectly flat and the two sides are parallel. If it is a hidden tang, taper it by at least 25% of the thickness all the way to the guard shoulders. Tapering a hidden tang first keeps the tang from causing problems by getting into the grind later on.
Next, add the distal taper. Don't worry about the bevels yet...just taper the entire knife blade area evenly until the tip is about half the thickness of the ricasso. On a full tang knife, don't carry the taper back farther than the front of the ricasso. On a hidden tang, you can taper it all the way to the guard shoulders, or stop at the front of the ricasso. These places don't need to be exact right now, you can fine tune the grind on the 120 grit belt. Fully tapered blades with the taper from butt to tip or the tang having a reverse taper are advanced skills.
At this point the blank should be shaped like your desired knife, and tapered from ricasso to tip. The tang is either flat if full tang, or reverse tapered if a stick tang. Look things over carefully. If the sides are uneven, or the taper is not complete, it will come back to haunt you later.
3) Taper the bevels, Grind the basic bevels as smoothly and evenly as possible. It won't be flat if it sits still...so keep the blade moving. I use the shorter grinding magnet here to hold the blade only on the bevel area. Holding the blade tang and all can lead to "pushing" the tip into the belt, or rocking the blade at the plunge. neither of these situations will give a flat bevel. Get over the blade and sight down on it as you grind. This helps see what is happening. By holding the shorter magnet on the blade bevel area, you concentrate your attention on this area only. If needed, use a 3" grinding magnet for shorter blades.
4) Go back and touch up the tapers and flats.
After getting the basic bevels ground in at 120 grit, re-do the flats and tapers again with 220 grit. This will tell you where you ground a dip in the spine at the top of the plunge, or where the ricasso is uneven. Touch up what needs to be done before moving on to finish up the bevels and other details. When I am done with touching up the tapers and flats, I has slightly flattened the top of the bevel grind at the spine in a long narrow triangle, with the ricasso as a flag on that narrow "pole". This is exactly what I want. The two sides should have identical triangles. The entire triangle and flag should be one unbroken, smooth and even grinds. If the two sides are the same, and the triangle goes from near the tip to the guard shoulder smoothly....the knife will be perfectly symmetrical. This should make it much easier to finish the bevels and center the edge and plunges.
In all the steps, try and do the grinding evenly from side to side. Remove the same amount off each side in each step. Don't grind one side completely and then move to the other. Also, let it cool a bit between grinds. A dip in a tub of water is always a good idea. Every now and then set the blade on the granite surface plate to check that you aren't grinding things out of flat, or creating a warp. Deal with the warp as soon as you find it.
There are many steps and tricks past this point, but if you don't start out with the proper distal taper and flat surfaces, you won't be able to get them easily later on.
I'm just offering my unwarranted $0.02 on how this could help those fellas out a lot more. :foot: 
