I have a newbie question regarding bit evaluation. Recently, I carved out a tray in soft pine and found that some of the finer inlay cuts had a bit of a “tearing” look on the pine. It got me to thinking about the sharpness of my bits. Since my whole S4 rig is fairly young, it’s a new topic for my work. Overall, things are working well but knowing when a bit has reached its end-of-life would be very helpful.
Also, what does one do with spent bits? Can they be recycled?
When a tool doesn’t cut as crisply as need be, I relegate it to roughing passes only — when it won’t cut well enough for that, it goes in the spent tool drawer.
Yes, carbide can be recycled, and tools can be resharpened, and specialty sites such as carbideprocessors will pay by the pound, but it’s hard for a hobbyist to generate enough spent tooling for it to make economic sense.
I snap mine off or grind them down to get hinge pins, or miniature chisels and so forth.
Take a brand new, sharp bit, and run the edge along your thumbnail, like you are trying to shave off a bit.
Note how it behaves, and what it feels like. It should dig in & not move, or shave some nail off.
If later you try it again & it just slides over the top of your nail, it’s dull.
I sharpen a lot of my own. I have a flycutter, and a surfacing bit (Like a McFly) that I’ve had since the 1970’s. I just keep resharpening them when the get dull.
You can save them up, then send them out to be sharpened. I’m sure there is a break-even point on how many are needed to make it economical.
Consider it a badge of honor… It took me a LONG time before I ever retired a bit because it was dull, rather than retiring it because I did something stupid which resulted in it breaking.
Have yet to break a bit but I’ve come close trying!
Thanks for the guidance. I can compare my older bits to a fresh one using the finger nail test and also like the rough vs finishing bits idea.
Over the years I have sharpened some drill bits but hesitate to even contemplate sharpening end mills or surfacing bits – no need to start flinging metal bits at high speed if I screw things up.
Carbide router bits are good for a long time. Pine is notorious for fuzzing because it is a soft wood. Whenever you cut across the grain it will be worse but even with the grain it will fuzz.
The principal is like petting a cat. When you pet from head to tail the fur stays nice and neat and the cat likes it. When you pet from tail to head the fur is all roughed up and the cat does not like it. That is very much like cutting wood. With the grain it behaves nice but go against the grain it it gets riled up. Grain direction is also important but uncontrollable when using wood in a cnc. Whenever possible cutting with the grain produces the smoothest cuts. When manually routing flat sawn wood the grain is in two directions. One side you are cutting slightly against the grain the the other with the grain. When cutting against the grain the wood fibers are unsupported and tend to fuzz more. Alternately when cutting with the grain the underlying fibers are more supported and you get better results. When cutting across the grain the fibers are unsupported and tend to fuzz more. Pine is a good choice for prototypes but not really a good choice for good work. Pine is soft and the grain structure tends to have wide gaps between the growth rings. Pine grows very fast in the summer months and slowly in the winter resulting in wide soft grain with hard small growth rings in the winter. If you take flat pine board and start sanding and just keep sanding it will soon look like a wash board. The soft growth rings will wear away and the hard part of the growth rings will stay and you get a bumpy surface. So sand pine just enough to get it smooth and no more. So when the surface gets bumpy people think that more sanding will fix it and just the opposite happens.
A carbide bit can be sharp but feel dull because of the build up of pitch and sawdust. So clean the bits by soaking them in a tool cleaner and give them a good brush down with a nylon brush. Do not use brass and definitely not steel brushes. The steel will dull your bit and the brass will rub off on the bit making it feel dull.
Here is a picture of a pine log. You can see the wide lighter color rings and the darker smaller rings. So during the growing season the wood grows fast and is soft. During the winter the tree still grows but very slowly so the dark rings are harder.
You can see that the rings at the center are wider and as the rings go out they get thinner. The tree grows very fast in early life. However the out rings are thinner but bigger so they get smaller. The pine trees grow at about the same rate each year but because the rings bet bigger you see they get smaller but if you add up the volume of each ring they are close to the same. So depending where your board is cut out of the tree you can get harder pine on the outside of a flat sawn board and much softer when cut out of the center. It is a crap shoot when you get a pine board but when ever possible look for rift sawn boards because they will be more stable than the flat sawn boards from the outer edges of the tree. The out areas tend to cup and warp more. Rift sawn means the grain in the end of a board is from 45-90 degrees to the face grain of the board.
