newbie router bit question

[Ben Davis]

Two quick questions on router bit selections:

(1) When would I want a downcutting spiral bit vs. and upcutting bit?

(2) Why would I want to by a three fluted bit vs. the standard two fluted bit? (I'm looking at the Whiteside catalog and notice they have a few select sizes available in the three flute flavor.)

Thanks!
Ben

[Greg Hines, MD]

Two quick questions on router bit selections:

(1) When would I want a downcutting spiral bit vs. and upcutting bit?

(2) Why would I want to by a three fluted bit vs. the standard two fluted bit? (I'm looking at the Whiteside catalog and notice they have a few select sizes available in the three flute flavor.)

Thanks!
Ben


I don't have any three fluted bits, so cannot comment on that, but generally, the feeling is that more flutes will last longer.

As to upcutting vs downcutting. You want to use an upcutting bit for mortising, or any plunging cut, as it will have a tendency to bring the chips out of the cut. You want to use a downcutting bit when routing along the edge of a piece, particularly with plywood or other manufactured pieces. The downcutting action will prevent lifting the top veneers and keep a smoother edge.

Personally, all of my spirals are upcutting. When I rout an edge rabbet, I use a rabbetting bit.

Doc

[pat warner]

Spiral: See no.12. (http://patwarner.com/faq.html)

3 fluted bits: Indeed for slotters, but an unnecessary expense otherwise; nuthin' to be concerned with.

[Bill Huber]

Remember, an up cut in a handheld router is a down cut on the table and a down cut on a handheld is an up cut on the table.

I still have to think it though every time I use them in the table.

[Prashun Patel]

If you had to get one, I say get a down cut.

The only reason to get an upcut is for deep mortises when handrouting. The upcut evacuates the chip from the mortise. However, you can still accomplish this with a downcut bit; just use shallow passes or pause to blow out the slot every now and then.

The downcut on the otherhand, will leave a cleaner cut on the top edge vis-a-vis an upcut, which can flay the top edge on some woods.

Either way, invest in a good carbide bit.

Then there's the bearings to think about...top, bottom, both, none...But that depends on what type of work yr doing. I'd get one with a bottom removable bearing.

[Ben Davis]

If you had to get one, I say get a down cut.

The only reason to get an upcut is for deep mortises when handrouting. The upcut evacuates the chip from the mortise. However, you can still accomplish this with a downcut bit; just use shallow passes or pause to blow out the slot every now and then.

The downcut on the otherhand, will leave a cleaner cut on the top edge vis-a-vis an upcut, which can flay the top edge on some woods.

Either way, invest in a good carbide bit.

Then there's the bearings to think about...top, bottom, both, none...But that depends on what type of work yr doing. I'd get one with a bottom removable bearing.
Why that bearing selection? Just curious.

[Prashun Patel]

That choice is personal.

I don't think they even make em with a removable bearing (wishful thinking). I choose a bottom bearing because for me they're more versatile.

On a table, a bottom bearing reaches far enough above the table to allow pattern routing; a topmounted bearing can't be used on a router table w/o a collet extender.

On a hand router, a top mounted bearing is nice because you can rout with the pattern on top (which gives me best visibility). But it's not necessary; if you trust the bearing, you don't really need to see the pattern to flush trim against it.

A bottom bearing is also used to flush trim edge banding, which I do frequently. A top bearing can't do that.

The downside of a bottom bearing is that it can't be used for plunge routing. That's huge, I guess, but I do sufficiently less of this than the above stuff such that I can use a bandsaw and cheaper straight bits when I need to take the plunge.

[Tom Esh]

(1) When would I want a downcutting spiral bit vs. and upcutting bit?

Downcut is especially nice for inlays because it leaves a very clean edge at the top of the cut. Sanding out tearout or rough spots would alter the fit.

[Ben Davis]

Good to know! I don't think I'm anywhere near good enough to start inlays though.

[Tom Esh]

Good to know! I don't think I'm anywhere near good enough to start inlays though.

I think you'd be surprised. I sure wouldn't want to cut them by hand, but with a router and templates they're way easier than they look. I started with one of those inexpensive "includes everything" Milescraft kits. Followed the instructions and got perfect results first time. I was hooked.:D

[Prashun Patel]

Note that if you get an inlay kit, you'll likely use bushings so you don't need a bearing on the bit.