I've been doing some work with wenge recently. A few thoughts:
-- It's a fairly brittle wood, so be cautious about tearout at edges. If you do any router trimming, you might want to think about down-spiral bits and slow feed rates. Also good dust collection, because it creates a fine dust, almost as bad as padauk.
For most of the above one typically wants an
up-cut spiral bit. An up-cut spiral both pulls the router (whether handheld or table) firmly against the wood (rather than trying to push the two apart) and draws the waste into either the router or router table where dust collection can easily capture the majority of the dust (
provided, in the case of handheld use, that the router incorporates a dust collection port).
Down-cut spirals on a handheld router will push waste towards the floor, where it’s usually difficult to capture in real-time and on a router table it will launch the dust upwards and into the air. Down-cut spiral bits also tend to generate lift that tends to want to separate the router and wood from one another and requires more careful control (particularly if the bit catches on some stubborn grain as either the router or wood can forcefully kick upwards very suddenly, a type of vertical kickback not ordinarily encountered when using routers with other bit styles so something to be aware of).
However,
if one has no means of real-time dust collection when using a router freehand then such is about the only time one ordinarily wishes to consider using a
down-cut spiral since then the waste is pushed down to the floor where you can vacuum it later. However, the up-cut spiral bit is usually a far better investment as they excel at so many types of operations, including the routing of blind holes (such as mortising) and also work best with dust collection, both freehand and in a router table.
For clarity, the label of “up-cut” or “down-cut” is relative to the router where up-cut draws waste towards the router body and down-cut pushes waste away from the router body. This is one of those terms that can be easily confused because the directions of “up” versus “down” becomes inverted when switching between freehand routing and a router table, but if you think in terms of the router body being “up” — or think of it in terms of freehand router use — then it is easier to remember what the two terms reference. Or at least that has long been my memory aid.
Hopefully this adequately covers the pros and cons associated with both up-ciput and down-cut spiral bits so one can choose whichever will work best for their intended projects.
In a high-wear (high silica content) wood one will want to invest in a good quality carbide spiral bit and the greater the diameter the better as the greater the diameter the less tear out one will incur because the bit shears more perpendicular to the wood than a narrower bit would have. A good general purpose spiral bit would be the 1/2” carbide up-cut spiral bit both in terms of price and applicability to general projects (a 1/4” up-cut spiral is the next most useful size in terms of general use in my experience).
For cutting the circular shape one may also use a bandsaw or jigsaw with a circle cutting jig. It’s pretty essy to make a circle cutting jig for the bandsaw that makes cutting large diameter circles easy without throwing a lot of dust in the air. Routers also work very well with circle cutting jigs. As with most things in woodworking there are multiple ways to get the job done so use whichever works best for the individual or project.