Thread: 3/4" Upcut Spiral Router Bit

Good price. Expensive little blighters aren't they. When you look them up on Amazon or Rockler both the pictures they have show a downcut configuration, but they describe them as upcut.
Yours is definitely upcut though, go figure?

Upcut ones are better for plunge cutting as they clear the chips from the hole as you go but for edge work doesn't matter too much.
the better quality ones are soild carbide like mine from carbatec. I used it a lot for mortising until I got a Domino machine.
If you stick one in a router table it becomes a down cut !

Originally Posted by mark david

If you stick one in a router table it becomes a down cut !

No it doesn't.

Originally Posted by aldav

No it doesn't.

Well yes it does, in relation to the workpiece you are cutting if you invert the router.

Originally Posted by mark david

Well yes it does, in relation to the workpiece you are cutting if you invert the router.

Sorry, but that statement is just WRONG! Have a think about it, if you've got the router on some stock in the hand held mode and you turn the router and stock upside down as a unit there is no change in the relationship between the router bit and the stock. The only way an upcut bit can be used as a downcut is to reverse the rotation of the router motor.

Originally Posted by aldav

Sorry, but that statement is just WRONG! Have a think about it, if you've got the router on some stock in the hand held mode and you turn the router and stock upside down as a unit there is no change in the relationship between the router bit and the stock. The only way an upcut bit can be used as a downcut is to reverse the rotation of the router motor.

I am talking about when you don't invert the stock, you would only really be doing edge work with a spiral bit in the router table, I doubt anyone does plunge cuts in a router table, you are just being obtuse.

Aldav is spot on. It doesn’t matter if you face it down, up or sideways it’s still an upcut.

Originally Posted by mark david

I am talking about when you don't invert the stock, you would only really be doing edge work with a spiral bit in the router table, I doubt anyone does plunge cuts in a router table, you are just being obtuse.

Whatever. I'm sure I understand perfectly, and when it comes to being obtuse the shoe is on the other foot. Like many other box makers on here I regularly cut grooves (dadoes) on the router table and very rarely joint the edge of stock with spiral bits. So your assertion that only edge work would be done is also WRONG.

Do you realise how offensive the word 'obtuse' is? Perhaps your intention is to offend?

At least we're giving the OP's thread a good run.

I use downcut spiral bits almost every day in the router table to cut inlay banding channels. Because the cuts are blind (not through to the end of the piece) the workpiece is held against the fence and against the table at one end then lowered onto the router bit, run along to the appropriate point then raised off the router bit.

I agree with Aldav about the relationship of the router and workpiece. Even if you are making an edge cut with a downcut spiral in the router table it is still a downcut at the point where the bit and workpiece intersect at the table. The fact that an edge trim might extend above the top of the workpiece doesn’t make it an upcut bit. It is still making a downcut at the level of the table.

Basic explanations, looking at where the swarf goes, and the propensity for chipping the surface of the material.

Up cut pulls the swarf toward the surface, but swarf exiting the cut and the 'lift' on the flutes can cause chipping at the surface.

Down cut pushes the swarf into the cut, which is generally not good, but with minimal swarf being raised and a downward push from the flutes there is extremely low likelyhood of surface chipping as the forces are directed into the material, rather than outwards.

Compression is a combination of up cut at the tip for a few mm, transitioning to a down cut for the rest of the flute length. These are primarily used for cutting materials with brittle surfaces and direct the swarf into the centre of the cut, protecting both surfaces from chipping. In use, they are normally set so that the tip cuts slightly into a sacrificial surface that the material rests on, so the lower surface is sandwiched between the sacrificial material and the core of the material being cut.

Inverting the router and bit won't convert an up cut to a down cut. That is determined by the direction the spiral is ground into the carbide.

Unfortunately, I have to disagree with Aldav for once also. Reversing the motor direction won't convert an up cut to a down cut, it will convert a router bit into a firelighter, because instead of cutting into the material, the tip and flutes will just be crating a lot of high speed friction and heat in the material.