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Ripthorn

Upcut Or Downcut?

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I am thinking about getting a solid carbide spiral bit for truss rod channels. My question is whether you guys prefer upcut or downcut and why? Do you like a smoother bottom or a smoother top edge? What you all think?

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I am thinking about getting a solid carbide spiral bit for truss rod channels. My question is whether you guys prefer upcut or downcut and why? Do you like a smoother bottom or a smoother top edge? What you all think?

Downcut bits for visible edges because they leave a clean edge.

Upcut bits for trussrod slots because of chip evacuation...

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Is there much of an issue with downcut bits trying to climb out, especially on woods with crazy grain orientations?

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Is there much of an issue with downcut bits trying to climb out, especially on woods with crazy grain orientations?

The main thing to figure out is chip evacuation. If you are making a full cut and not a grove this is not an issue. But if you are doing a trussrod channel you want the chips pulled out of the slot so use an upcut bit.

Downcut bits are best for full cuts where the bit is passing all the way through. In these cases with a really sharp bit climb is not an issue nor are chips (because they have somewhere to go)

One last point. You should never take more than 1/4 the cutter depth (some say 1/2 but I use an 1/8) in one pass anyway so you would step these cuts in small increments. I also try not to remove more than the cutter blade width from the sides using a router. So if the carbide blades on your spiral bit are 1/16" I try not to remove more than a 1/16" for the sides of my cuts.

With smaller increments climb is rarely and issue. Take human bites!

I am by no means a router expert as I hate them. So google your information at will...

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Is there much of an issue with downcut bits trying to climb out, especially on woods with crazy grain orientations?

One last point. You should never take more than 1/4 the cutter depth (some say 1/2 but I use an 1/8) in one pass anyway so you would step these cuts in small increments. I also try not to remove more than the cutter blade width from the sides using a router. So if the carbide blades on your spiral bit are 1/16" I try not to remove more than a 1/16" for the sides of my cuts.

With smaller increments climb is rarely and issue. Take human bites!

I am by no means a router expert as I hate them. So google your information at will...

half the diameter of the tool is using conventional router or twice the diameter if using spiral flute.

there are chip load calcs all over the net but spiral flutes normally need to be run pretty fast..

OP, are you using a hand router ? if so I would be tempted to just use a standard single straight flute router bit.

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I would say neither in terms of smoother bottom or outer edge. They are both fairly easy to achieve unless repetetive manufacture is dictating that work speed is an issue. If it were, i would opt for smoother top edges as the inner is not critical. Adding a cleanup stage to the process slows throughput.

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I've got an upcut spiral bit for truss slots (in a router table). Works well.

Spiral bits "feel" different when you feed the wood, so just let it do its thing and go slow.

When I swapped to using the spiral bit for this I also started making two passed rater than a full pas slike I used to do with a standard bit. The spiral bit just liked it better this way.

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