Defective bottom cleaning bit?

[dttworld]

Guys,

I bought the following 1" diameter "bottom cleaning bit" from Grizzly to use for surfacing my spoilboard. However, the bottom of the flutes aren't flush and horizontal to the cutting surface. I have a pic with the gap circled in red attached. Do you'll think this is defective or is a bottom cleaning bit not considered very precise?

Gizzly link:
http://www.grizzly.com/products/Bottom-Cleaning-Bit-1-2-Shank-1-Dia-/C1259

I found this forum link for another surfacing bit but it also doesn't look flush on the bottom:

http://www.magnate.net/index.cfm?event=showProductGroup&theID=136

I'm thinking of just buying this .75" 2 flute steel endmil from Enco for $11. Only concern is I don't see a max RPM rating.

http://www.use-enco.com/CGI/INSRIT?PMAKA=PL320-2850

The ShopBot book recommended .75" to 1.25" diameter bits. Anyone have recommedations for an entry level spoilboard bit?

thx

[Ajcoholic]

In my experience, many cutters (including the spiral end mill type router bits) do NOT have the bottom of the cutting edges ground at 90 degrees to the body of the bit.

When you plunge with an up or down spiral, there is a very slight disk that is made when exiting the material (sort of like a Forstener drill bit without the rim).

With the larger, two cutting edge bits I have (one Onsrud, One Dimar), I know the Dimar 1 1/2" is not flat across the bottom. This also reduces drag, as the cutting edges do not stay in contact with the board at all times. The leading edges of the cutter and the sides are what are doing the work, as the cutter travels along the board.

This is the bit I use.. Dimar BC838 It is a very high quality bit, and the edges are slightly sloped up from the outer edge to the center.

AJC

[myxpykalix]

Danh,
I've used the magnate bit for years for my spoilboard and years earlier on my legacy manual mill. I would consistently get a smooth finish on things i was turning on the legacy with that bit. It is a good bit.
I seem to recall that for some reason it had a 1 degree taper on it, not sure of the reason but for what you want it for it is a good bit.:)

I have had them take a bit that cracked on me back after 6 months so they are pretty good about standing behind their product.

[Ajcoholic]

Again, my idea for why most router bits or milling type cutters are not "flat" across the bottom...

If they were, flat that is, the cutting edges would be in contact with the material you are cutting 100% of the time. And woodworkers know, that cutting edges like to have some sort of a break once and a while. :) Most cutting tools do not have the cutting edges in contact with the material 100% of the time.

With the bottom edges tapered, even 1 degree, as the bit moves across the material, the channel left is still perfectly flat and true (it has to be, as the cutter is turning in the same plane as it is moving )but the edges are not in contact with the material unless (a) it is moving, and (b) only for as long as it takes to clear the chips away.

AJC

[gene]

what you are trying to say is that with a bottom that is NOT flat it reduces drag on the cutter as the outer edge does the cutting , Correct?
also I have been using a 1.75 magnate cutter for years and it has served me well

[mark_stief]

GENE
He's right on the money I grind knives for moulders and shapers for custom profiles and resharpen them also any knife that cuts at 60-90 degrees to the wood you grind a 10 degree relief into them or they'll burn the wood or start fires like you said you only want the tip of the knife or cutter doing the work or cutting the wood

[dttworld]

......

With the bottom edges tapered, even 1 degree, as the bit moves across the material, the channel left is still perfectly flat and true (it has to be, as the cutter is turning in the same plane as it is moving )but the edges are not in contact with the material unless (a) it is moving, and (b) only for as long as it takes to clear the chips away.

AJC


Thanks for the sanity check. I get it now. The gap in my Grizzly bit doesn't matter because the bit is turning and the lowest cutting edge will be the depth of cut as the bit traverses over the spoilboard - kind of like a fly cutter.