David Negaard wrote:
Now that the other parts of my M4 seem solid, I’m trying to dial in feeds and speeds.
I am seeing varying guidance in a variety of venues as to what an appropriate
step-down is. The SpeTools Spiral Router Bit chart row for 1/4 inch bits calls
for a stepdown equal to bit diameter at 18,000 rpm with feeds north of 180
in/min (where does the M4 top out? Well south of 180 in/min, I assume).
Elsewhere I see a thumb-rule with stepdown equal to 1/2 of bit diameter.I am not sure where to even start my testing. I would like to begin somewhere
likely to be reliable and fairly clean. I’m cutting plywood in varying
thicknesses, mostly with a 1/4 inch compression bit, but will use a 1/8 inch
compression bit for 1/8 inch luan.
There are a lot of threads here on feeds and speeds, I won’t try to re-hash them
all here, but I will give a couple of comments.
If a bit recommends 18k rpm 180 in/min then the same bit will work at 9k rpm 90
in/min, and a bit with 1/2 the number of flutes would work at 9k rpm 45 in/min
the determining factor is how much material each flute removes on each rotation.
With the maslow, you generally want fewer flutes and lower rpm.
the key thing is that you want to make chips, not dust when cutting
beware of compression bits. They are a combination of an upcut bit at the bottom
and a downcut bit further up. If you don’t step down far enough, your cut
through the top surface is only done by the upcut but, so it provides no
advantage over a cheaper upcut bit. They are good for a finish pass where you’ve
cut down far enough with another bit that you can bring in the compression bit
and do a full depth pass.
Dvid Lang
