[laserdog]

Hello,

I am having a problem with my upper edges fnish. I am using a one flute upcut spiral end mill (i know, that upcut is bad for upper edges finish). The problem ussually increases as the end mill getting more blunt through the time. But the main issue is, that i have a a big difference between horizontal and vertical cuts finish. Ussually I am roating square shapes, if the mill goes in vertical movement (isolated Y axis movement) the edges are perfect, but if it goes horizontal the edges are bad (fluffy) (isolated X axis movement). I am roating birch plywood most of the time, using convetional milling for countours and climb for slot cutting. Can anyone suggest what could be the problem here? I was wondering maybe the spindle is not perfectly square in one axial direction, which is possible, because i used not perfectly flat spacer for new spindle couple of weeks ago in terms of 0.2 mm cca.

Please see attached picture for clarification.

Thanks anyone for any suggestions.

[ger21]

That's due to the grain direction of the face veneer. If you want it clean, use a downcut bit.

[laserdog]

Yeah but why is there a difference when it changes the direction of milling? I thought it should be bad in both directions using upper cut mill.

[nlancaster]

Again, it has to do with the grain of the wood. Along the grain it will sheer even with an upcut bit. Accross the grain it will tear with up or downcut, but the important thing is with a downcut it can sheer even endgrain because the grain is suppored by everything below it. If you want good finish on both top and bottom use a compression bit, as long as the upcut portion of hte bit is below your top surface you will get awesome edge finish on both top and bottom.

[LeeWay]

As mentioned, it is a characteristic of woodgrain. It can do the same thing even with a very sharp tool depending on the wood type. Harder woods will shear better than softer ones. Birch is a hardwood, but is relatively soft compared to other hardwoods.
Compression bits work very well.
Something else you might consider is to chamfer the edges if the product will allow it. That will usually clean up all the top edges even with a tiny chamfer.