I am about to try a compression bit but there is one thing that has me stumped ā¦ how do you enter the work piece? Put in another way, when you enter the work piece, either via ramp or plunge cut, there is a small section where the upcut portion of the bit does the cutting. How do you prevent a rough edge at the insertion point?
I can only see using ālead inā but you canāt do that for slots.
So, is there a trick that is used for the start of a cut?
The first pass on a compression bit needs to be slightly deeper than the upcut portion of the bit. In most cases, this means setting the first pass to .26ā, but some compression bits have shallower upcut lengths, e.g. mortise compression bits. I use a ramp that equals roughly twice the pass depth, or .5 for a Ā¼ā compression bit.
If youāre using a Pocket toolpath in Vectric software, you can add the ramp with no lead in and it will stay within the vector boundaries as it ramps in. Set it to Raster parallel to the slot walls with the Profile Pass set to Last. That keeps the plunge in the center of the slot rather than plunging along the edge.
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Usual preface, Iām with PreciseBits. So while I try to only post general information take everything I say with the understanding that I have a bias.
The short answer is you donāt. Thereās no way to prevent the initial plunge of the up-cut section leaving an artifact if thatās part of your finished dimensions (e.g. slotting cuts, starting the cut on the edge of a pocket).
The long version of this is that compression cutter were originally intended as finishing tools. Not for primary cutting and defiantly not slotting. Itās not that you CANāT do those things with them. But thereās issues with it. The primary one in my opinion is that when slotting you are compressing the chips with nowhere for them to go until they get all the way around the tool. That leads to higher cutting forces and deflection in addition to side wall cut quality issues. More or less depending on how itās ground.
Sorry I donāt have a better answer for you.
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Thank you for confirming my thoughts.