Sharpening router bits--alteration of size?

[Chris Yarish]

If one is to sharpen a router bit (roundover or flush-cut specifically), do you not also alter the precise dimension of that bit?

I have been experimenting with some layered plywood projects like this bench.

What is required is a lot of use with a flush cut router bit. I have opted to buy new ones everytime, but think it is more economical to sharpen them....will their dimension/accuracy be compromised as a result?

[Dick Strauss]

Chris,
If you only take two or three light swipes on each flat carbide face, the dimension won't change much at all (a few .001 max).

[glenn bradley]

I'm with Dick. I sharpen (touch up is more like it) mine with a swipe or two across the flat face. I do not de-burr. If a flush bit had reached a wearpoint where I could not just touch it up, I would expect it to come back from the sharpening shop a little undersized which would make it worthless to me. Any good sharpener should be able to tell you if they can salvage the bit or not.

[Jamie Buxton]

In theory, the diameter of a router bit must change when it is sharpened. How much it changes depends on the design of the bit and the choices made by the sharpener. In practice, you may not notice the change. That said, sharpening services don't often sharpen router bits. By the time they handle them, set them up in a machine, sharpen them, send them back to you, and generate the bill, they've consumed more money than you'll spend just buying another bit.

[Scott Whiting]

In theory, the diameter of a router bit must change when it is sharpened. How much it changes depends on the design of the bit and the choices made by the sharpener. In practice, you may not notice the change. That said, sharpening services don't often sharpen router bits. By the time they handle them, set them up in a machine, sharpen them, send them back to you, and generate the bill, they've consumed more money than you'll spend just buying another bit.

Your theory of what must happen is correct. Because of the relief behind the cutting edge when it is reground it changes size.

Where an operation exists that require no change in dimension there are bits with replaceable knives that you change out instead of regrinding. The upfront cost is high but in many cases the replacement knives are less than regrinding.

As far as regrinding bits, sharpening services do that all the time. And at a cost far less than the price of a good bit. Just as with any tool, if you are having to pay for shipping both ways it is a good idea to save up several items so the shipping doesn't eat up the cost savings.