[ftkalcevic]

A noob question about the down cut tools...

I always thought down cut tools were limited to edge finishing because they push the chips down into the work. Is that not the case?

[louieatienza]

A noob question about the down cut tools...

I always thought down cut tools were limited to edge finishing because they push the chips down into the work. Is that not the case?

The chips will still eject, though not as efficient as an up-spiral. They work fine for mortising and pocketing operations. If your work is held down tight to the spoilboard, though vacuum or clamping, you can achievev a decent finish on the bottom. A downspiral can also be beneficial when cutting thin stock, as it can prevent the stock from lifting.

[ger21]

A noob question about the down cut tools...

I always thought down cut tools were limited to edge finishing because they push the chips down into the work. Is that not the case?

The deeper the depth of cut, and smaller the bit diameter, the more likely chips are to pack into the cut. But if you take shallow cuts, you'll get much less packing.
The other day I cut some red oak with a 1/4" downcut spiral, .05" per pass for 3/4" thick parts. 400ipm, and when the parts were finished (.70" deep), there were no chips in the cuts.

Some advantages of downcut bits:

Downcut bits will tearout much less than upcuts when cutting solid wood.

They'll leave a clean top edge even when they get very dull. Because of this, you can get a lot more life out of downcut bits.

They'll help to hold parts down. On 3/4" parts, I can cut .745 deep without going though, because the bit is pushing the material down. With an upcut bit, it would lift the material up and cut through, allowing the part to move.

[freecncplans]

When I use a 5/32" Centurion Tools down spiral on 3/4" pine, oak or baltic birch ply, I get severe packing. In my case it actually kind of helps as then I can cut all the way through in a single pass without the parts moving. That saves me from sanding the edges from the onion skin or sanding the parts down.

I have had people tell me also that I cannot cut 1/2" deep in a single pass with a 1/8" down spiral bit. We do it day in and day out at 150-175 IPM with the ones from Centurion Tools. I have yet to find another bit to be able to do the same without breaking.

Those are my two main bits that I have experience with.

Sean