Hi friends,
So I use a flattening bit from SpeTool. Specifically this one: https://spetools.com/en-eu/products/spetool-4-flutes-spoilboard-40mm-dia-x-8mm-shank-router-bit-with-4-blades
In the beginning the results were pretty good. But lately the bit shows ‘lines’ on the wood after milling. They are quite hard to sand off.
This is how it looks like:
My question is; is the bit worn, do I have to rotate the cutting blades on it? Or is my SO5 Pro not trammed correctly?
If the machine has not mechanically shifted, then a worn cutting tool seems the most likely culprit — one thing which hand wordworking has taught me is that your tool is never as sharp as you think it is/want it to be after the first couple of strokes and that folks just don’t sharpen enough.
Cue Abraham Lincoln’s commentary on axe sharpening and cutting down a tree… (which like many good quotes lacks a solid attribution)
…the instance of the lumberjack who said that if his life depended upon his ability to cut down a tree in five minutes he would spend three minutes sharpening his axe.
In that regard, could this (see images) also be a result of dull blades on the bit?
It seems to really pull out strands of wood/fiber instead of cutting it to pieces. Resulting in the mess not going towards the vacuum but more going towards a fire starting…
Also; I have once seen an old guy putting his bits into a plastic cup with some solution of spirits(?), resulting in dissolving all the caked-on residues from the bit. Seemed like witchcraft at the time to me! What could this possibly be?
That would seem to be cutting along the grain of stringy wood — I always cut across the grain of red oak and bamboo where/when possible — but a sharper tool may help simply because it’s more likely to cut the material rather than push it off to the side.
Oven cleaner is what I use to remove the accumulated wood resin and/or burnt on gunk from my chop saw and table saw blades, should work the same for these cutters.
I have a 5 gallon bucket kept in the shop with CMT blade cleaner. The 5 gallon bucket is wide enough to get a 10 in blade inside and I have it poured deep enough to get router bits submersed. For regular router bits with a bearing remove the bearing before submersing. This stuff works very well for a lot of blades and bits getting resin off. After removing the blades/bits from I use a nylon brush to get things really clean. Dry it thoroughly. I dont lube router bits because that could make them slip in the collet. There are many home made brews but the CMT is not really expensive and made for the purpose.
Excellent! I tried this and it did the trick. Easy and cheap solution. Will do this with all other bits too.
Makes sense to not lubricate bits. But I’m wondering if only lubricating the cutting parts a little will work to protect and/or prolong the life of the bits? A bit of WD40? Or will only drying suffice?
For some reason I thought it’s better to always cut along the grain. Guess not! Learned something today. 
It is mostly good to cut with the grain. But when roughing very stringy wood, cutting cross grain will prevent long fibers.
I clean most of my tools with a toothbrush and TapMagic, a very thin oil/lubricant. It helps chips from sticking. Only the flute / cutting portion of the tool. Yes, you want the shaft clean & dry.
A good sharp cutting edge, and coated flute should usually suffice, but a little lube helps. “Hawk Tuah, spit on that thang!” 
I should have expanded on that to note that I cut stringy woods cross-grain when roughing (so as to break up the fibers and not have long strands clog up a long cut) — finishing passes are made with the grain where possible as @Tod1d noted.
I first need to learn which wood is stringy and which isn’t… LOL
I am not sure on the Spetool surface cutter, but the McFly cuts much better when you remove the bottom face cutters per @wmoy suggestion.
I have actually wondered what the difference between these bits are. What is the advantage or disadvantage of those bottom cutters?
Edit: I asked AI and it explained me very well what the difference is. TLDR; the bit with two vertical and two horizontal carbide inserts is generally supposed to give a better finish with minimal ridges and tear-out. I might try such a flattening bit soon.
I removed the bottom cuts and got much better results from the McFly
But then you only have 2 cutting inserts that do the work; thus wearing out the bit twice as fast…?
But you have twice as many bits to replace them with 
All I know is the sound while cutting and the finish when done were much better.
You can turn the inserts to extend the life spans,
Carbide inserts last a loooooong time. You can resharpen carbide inserts by placing them on a fine diamond stone and swirl them around. I use a honing solution from Smith
This works well and when done I use a paper towel to clean the diamond stone. If your stone get clogged you can use a rubber eraser to clean it. They make specialty cleaners as well but the rubber eraser works just as well.
You can get several sharpenings from a carbide insert. The trick is not to let them get completely dull before sharpening/honing.
I keep a small container of goo-gone on my table with 8th inch holes and quarter inch holes drilled in the lid. When I’m done with an end mill, I stick it in the goo-gone and when I take it out, I just simply wipe it off in the bit stay very clean
