Finishing knife handles.
Sanding
Knife handles are a difficult thing to finish. They will be handled, so soft finishes are not viable, and even the highest mirror sheens will dull with use. Knife handles are also often made of extremely dense, oily, figured or stabilized woods. These types of wood offer different finishing issues to other applications.
From shaped to finished, Sanding is the most important part of finishing.
One major factor to remember is to keep the wood cool. Just as steel can overheat and ruin its temper, wood that gets too hot will scorch, crack, check, twist or change in color. For handle work, i highly recommend buying the very cheapest AO belts and paper and changing out relatively often, always using fresh, sharp grit to lower the risk of these issues. Its also important to wait a little while sanding to allow the mass of the wood to cool down and for the heat to travel within the piece. Uneven heat causes cracks and checks. This can also be improved by using a machine sander at ~25-35% speed. A variable speed sander makes getting a good finish much easier than going by hand or at a high speed.
A good finish starts with good sanding. After the handle has been shaped, you must remove each layer of scratches carefully and completely before progressing up the grits. Left over scratches will be almost impossible to remove at higher grits.
Assuming handle shaping ended 60-80 grit, The first step should be to go over the handle with an 80-100 grit belt to make sure there aren't any deep scratches from the initial shaping stage. This is also a good time to apply thin CA glue to any small cracks, checks, pin holes, voids, soft spalted areas and anything else that is vaguely worrying. My favorite brand is https://trugrit.com/product/insta-cure/, its a water thin CA glue and will wick into any size gaps. I strongly recommend buying the debonder as well, https://trugrit.com/product/un-cure-debonder/ If you have not worked with water thin CA glue before, it is amazing how fast you can glue your fingers together. Run a thin bead over any areas of concern and allow to cure. Depending on the depth of the crack, you may see bubbles as the superglue is wicked into the voids. I recommend laying down multiple thin layers. By filling the crack once or twice with CA, and if it still wicks glue down allow 10-15 min to cure before adding more layers. While this does add time, it prevents cracks from spreading, and will yield a much more attractive and consistent final product.
Once the handle is at an even 100 grit, progress up the grits as normally, common grit steps are grits of roughly 120-150 to 180-220. At the 220 stage you are really finishing the handle. Stray grits or pieces of sawdust can scratch the wood or damage the finish. I recommend rinsing the wood by hand in warm water, just to remove any dust or bits of leftover grit before finer grits are used. Strong compressed air or a tack cloth can both also be used, but i find a quick rinse is the most effective.
Continuing to sand to roughly 320-400 finish. At this point, i recommend stepping down a grit to ~300 and sanding the handle by hand. Examining the piece all over, you may find scratches that had been missed. It will be incredibly difficult to remove these scratches moving forward, and if they can not be easily removed with the 300 paper you may have to re sand the piece at 220 grit and work your way back up.
From here, you can continue jumping up the grits until you reach your desired finish.
Depending on the fineness of the grain of the wood, different woods can be sanded to different levels.
Large pored woods like walnut, oak, or wenge can be sanded to ~400-600 grit before no real improvement is made.
Medium pore woods like stabilized Maple, koa, acacia and afzelia can be sanded to ~800-1500 grit.
Very fine pore woods like ebony, rosewood, or desert Ironwood can be sanded to 2200-5000 grit.
With a well sanded handle, the next step will often be buffing. Buffing allows a much glossier finish on wood and can make a huge difference. Many of the same rules from sanding apply to the buffing process.
Buffing
SAFETY
The very first thing is that buffers are dangerous. Almost certainly the machine tool most likely to cause a lethal injury to a knife maker is the buffer. There are a variety of reasons behind this danger. A large part of which is simply how harmless the buffer looks. It has soft cotton wheels, not abrasives or moving blades. The fact that it is also one of the last tools used in the knife making process means craftspeople are often tired or excited to finish a piece when they start to use the buffer. Its important to be focused and present while working on the buffer.
The danger of the buffer is its ability to throw items at incredible speeds directly at the groin and thighs of the maker. A sharp knife can easily cut a major artery, and this is probably the most common lethal accident knife makers have suffered.
To lessen the risk of this, there are several steps to take.
1. the first and most important step is being focused on the task at hand, and never using the buffer distracted.
2. a heavy apron of leather, thick canvas or other tough material can add a layer of protection. Thin cloth aprons for protecting your clothes will not offer much protection.
3. Always wear safety glasses or a face shield, buffing compound is fine grit mixed with wax and if it gets in your eye can do some SERIOUS damage. It will also damage glasses like prescription classes, marring the finish. Sacrificial safety glasses are strongly encouraged.
4. When using a buffer, use only the front, lower quadrant of the wheel, so the spin is always down and away from you. This reduces the risk of catches, and makes them much less dangerous if they do happen.
5. Be aware of the edges of your work. The buffer will grab on to an edge ledge, causing the force exerted by the buffer on your work suddenly increase, ripping the item out of your hands. Do not present sharp edges aimed up into the spin of the buffer.
6. Use only gentle pressure. Gentle buffing passes improve not only the quality of the finish but also makes using a buffer much less dangerous. Catches will be less likely and if they do happen the item is more likely to drop out of your hands rather than being thrown at high speed.
Cleaning the buffs and the wood
Before you start buffing, I would recommend thoroughly cleaning the handle. Compressed air, a tack cloth or a clean soft brush would all work. You must make sure the wood is completely clear of abrasives or leftover sawdust which could get caught in the buffing wheel and damage the finish.
Buffing wheels should be kept covered, if on the machine putting a shower cap over them when not in use works, otherwise being kept in a drawer or bags also work. You can also blow down the wheels with compressed air. Grit and dust that settles on the wheels will be present and mar your materials finish.
Be gentle, soft wheels, low speed and fine compounds.
Use slow speeds if possible, 750-1000 RPM is best. Higher speeds make both damaging the finish and throwing the knife much more likely.
I recommend using a soft, unsewn buffing wheel Dense, spiral sewn buffing wheels can damage the wood and the finish.
https://trugrit.com/product-category/buffing-etching-sharpening/buffing-wheels/ I recommend the 40 or 60 ply loose, fitted to your buffers arbor, speed and Hp.
Practice good wood buffing technique. Apply a small amount of compound and recharge often.
Avoid overloading the wheel with compound. If you apply too much compound to the buffing wheel, it will become clogged. It will stop effective polishing and deposit a layer of the compound onto the handle, often filling pore or staining part of the wood. Use a buffing rake to clean the wheels as needed,
https://trugrit.com/product-category/buffing-etching-sharpening/buffing-rakes/
When buffing, take short, slowly moving passes to keep the buffing action even. Buffing a cutting action, just like sanding. If you linger too long in one position, you will carve into the wood slightly, heat up one area and lead to other issues.
If you see scratches, you will NOT be able to buff them out. You will have to return to sanding and remove any scratches by progressing through the grits again, cleaning well with compressed air before returning to the buffer.
Picking what compounds
I like to start buffing using a brown tripoli compound
https://trugrit.com/product/tripoli-compound-d-14/
To go over and establish a nice shine and make sure there aren't any leftover scratches. Using slow, short passes on the buffer go over the wood until you’re happy with the finish.
For most handles, this can be the end of finishing. A high grit and tripoli buffed finish is often incredible. If you wish to continue however,
The next compound to use would be a blue moon or pink scratchless.
https://trugrit.com/product/blue-moon-buffing-comp...
This is a finer finish and should have its own wheel. The only downside is that the compound is much more sticky, and can deposit in a thin film on some open pore woods. This can be cleaned afterwards, but it is something to consider.