More bit flex in downcut bits?

[knight_toolworks]

since I have been measuring my cuts more I have seen a lot of oversize cuts. I have been using mostly downcuts so I get clean cuts and i wonder flex they flex more.
I was cutting some ply with a 1/4" compression cutter. I think the first pass was a climb cut at 4ips and maybe .6 or so deep. the cuts actually had curves on the straights. this did not matter as the cleanup final pass was a regular cut. but thats the first time I saw curves over just oversized cuts.

[Gary Campbell]

Steve...
Are the edges of the cut square with the surface or angled?
Gary

[knight_toolworks]

you know that's a good question. it would be hard to check without messing up the part so you could measure it unless you cut it in one pass. but i will check. I do notice marts tend to be .01 to .02 too small with a regular cut and right on or .01 too large with a climb cut.
I just put on new pinions because the problem was worse.

[paul_z]

Steve,

I had the same problem and finally convinced myself that it was bit flex. I changed from 1/4 to 3/8 bits and the problem has virtually disappeared.

I use compression bits from BAM Tools. The are extremely sharp and last a long time. They are so sharp that I have cut myself letting the bit drop into my hand ... and that was after cutting about 500 linear feet!

Paul Z

[Gary Campbell]

Steve...
As Paul says a 3/8 tool will virtually eliminate bit deflection at the speeds we usually cut hardwoods.

The reason I asked about the square edges is, if the bit is deflecting it cannot still be perpendicular with the surface. There will be more deflection at the bottom of the bit than at the top. A machinists square along the edge held up to the light should clarify. This is very hard to determine when using shallow passes.
Gary

[john_l]

I had the same trouble with some laminated plywood parts I was cutting with a 1/4" down cut. At first I thought it was lack of hold down causing it. I clamped some sample cut parts every which way and had the same thing... and I did notice angled sides of the cuts.

In my case.. After switching to an upcut the problem went away.