I was discussing wood working with a metal worker the other day. I said I did not like the idea of routing a slot by starting with it about a 1/4 deep, then a pass at 1/2 and then the final pass at 3/4" because the first 1/4 of the router bit did all the work and dulled while the rest of it remained sharp. (I Think)
He said that with a milling machine you slow the bit down and slow the feed rate way down and cut the entire 3/4's in one pass. I know not if he speaks the truth for I have only seen milling machines from a safe distance and never operated one.
Does it seem there might be some application of this for routing in wood?
I don’t know if that works for all size bits in metal, but in wood, which isn’t as even textured as metal, we are dealing with another animal all together. As the bit moves through the wood, the cutting edge starts in against the grain, then straight across the grain in the middle of the cut, and finally down the slope of the grain on the other half of the grain. That first half of the cut is pulls hard on the bearings and can induce lots of bit deflection especially in smaller diameter bits which flex more, have a wider sharpness angle and has more trouble clearing the chips in a deep cut, which generates more heat, and quicker dulling. Uncut spiral bits ought to negate some of those issues.
I cut all mortises with either 3/8” or 1/2” solid carbide, upcut, spiral bits. They will plunge full depth just fine, but my router will howl like a banshee if I try to move it forward. I cut all mortises, indeed all deep cuts, using the step method you describe.
I have broken carbide bits by attempting to route full depth. Best to do it in increments. You also get a smoother cut by doing it in steps. Also the grain does change as you go down - wood was once living material.
I cut dadoes and grooves using 1/8" steps. Especially with 1/4" diameter, any deeper and the bit breaks. You're right that the end if the bit dulls, but that's how it goes.
Metal working mill has advantages in coolant, machines that weigh tons, huge shafts, bearings, and collets. Only thing in common is making chips and chip loads with both. Everything else is different.
Apples and oranges, totally different materials, operations and tools.
In metal working if cutting with a small bit, I used to mill by lowering the bit into the stock to full depth (using the mill stop), raising the bit, moving the stock a bit, and repeating until the majority of the material in the slot was removed, then and only then moving the bit through the slot with it fully lowered.
The milling bits are called "End mills"!
Almost all of my wood bits have carbide cutting surfaces, so the "dulling" you speak of is not a major factor in normal woodworking.
I normally cut slots on my router table (as you do) if possible, or using a guide on the rotor or clamp on guide on the material. If I have a lot of repetitive cuts I sometimes use my table saw with a Dado saw blade.
Yeah. What he said. My Robland's slot mortiser actually uses standard end mill bits and the "plunge, move, plunge, move,...., clean out" method is exactly what they recommend for all of its mortising functions regardless of bit size. The big advantage of the slot mortiser over a router is that the work is attached to a massive cast iron table and moved precisely with long levers and limited by stout stops.
Materials are very different in how they need to be handled. Just look at the speed chart in/on your drill press to note the speed difference between wood and metal.
Another related point to feed rates is that feed on a mill is more steady and of a consistent rate due to the use of the cranks on the mill. Much steadier than the humans can ever be.
The router will probably not benefit from milling machine techniques, as they are nowhere near so inflexible and stable as a mill.
I've cut a lot of wood on a milling machine, and you can get away with stuff you'd never try with a router. The bit spins much slower, at least in the one I was using, max speed was about 3,400 rpm. So you could then slow the feed down without burning the wood. Due to the lead screw feed and usually a very consistent power feed as opposed to hand cranking, you could take heavy cuts without unduly loading the bit so there was no deflection to speak of. They also have true hp motors that routers do not - a 3 hp mill is vastly more powerful than a 3 hp router.
Most of what I was doing was using a 7/8" ball cutter designed for wood. I've not used so many bits designed for metal on wood, but a carbide endmill intended for aluminum work should have similar cutting angles as for wood.
So in a nutshell, stick with the step cuts with the router and don't worry about wearing the bit unevenly. The important thing is the results of the cut, not getting maximum and even wear out of the bit - bits are cheap compared to wood, at least out here where the wood has to come across the country.
Before I got the big Domino machine I often used end mills on a router, though making multiple passes. They made good clean mortises. If you have a Festool 1400 router, you can get a 3/8 inch collett for a 3/8 endmill. Endmills, unlike routers, are one size top to bottom, not different sizes for shank and cutter.
There are two nice advantages to endmills - 1)they come in a large variety of lenths so you can make deeper mortises and 2)they cost much less than equivalent router bits.
And, yes, put your router on its slowest speed.
Caveat - probably not a good idea for a production environment, but it worked well for me in my hobby shop.
I have a Festool 1400 router and before I got the smaller Domino I used it exactly as you suggest. Bought some 3/8" end mills and routed a lot of mortises for loose tenons. I also have a box of 3/8" tenon material. A lifetime supply. Then I got the Domino and there is not 3/8" cutter for it. I looked into having one made out of a 10mm one but then decided it was easier and cheaper to reduce my tenon stock to 8mm. the end mills are really nice and I highly recommend them. I don't remember running them slowly, but I may have.
I don't really know what is "normal" speed for a bog-standard end mill. My Robland chucks them to the end of the jointer/planer drum which spins at 3500RPM IIRC. Certainly way slower than any router I ever used but it has a massive "real" 3HP motor doing the spinning and can hog out serious amounts of wood when it needs to but I still wouldn't try slotting a 16mm mortise 100mm+ deep which is certainly within its capability -- to scary -- so I always use their plunge then clean out method
