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Thread: Compression bits - better cutting tip

  1. #1
    Join Date
    Jan 2012
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    Compression bits - better cutting tip

    This may be common knowledge amongst you CNC guru's but I just figured it out today. I don't research cutting profiles and tips often - ok, rarely - and it would probably be in my best interest to do so from time to time.

    However, assuming this little issue is one you've encountered or not thought of then this little tip will save you a bunch of time and a fair amount of sanding.

    My normal cutting profile on 1/2" BB (12mm) for Longworth chucks is to cut the slots in a rough pass climb cut leaving 0.007" on the side walls (radial) and 0.020" on the bottom (axial). Then I come back and clean up each slot with a conventional cut at full depth and that has left a very clean slot. Except for the bottom face veneer sitting on the spoilboard. That has splinters/fibers/fuzz and I have to hand sand those. All this is at 175 ipm and 18k rpm.

    Now this may not be a big deal if you're cutting one Longworth chuck. But on days like today, where we had a 16" going to the UK and three 12" sets for the States, then that adds up to 64 slots! That's way more hand sanding than I want to be doing on these given the low cost we charge and I don't want to increase the cost just because I feel the need to do some sanding to make a better product.

    However, time is money and as I was cutting the plates today I began to finally think about how I can eliminate the fuzz. It dawned on me before I cut the final of eight plates that I need to cut the full depth in one pass rather than leave 0.020" because what's happening is there's nothing to support the upcut of the compression bit in that final 0.020". So I quickly modified the cutting profile in Fusion 360 and cut the final plate.

    Turns out my thinking was correct, albeit 7-8 months late (we've cut over 270 Longworth chucks and I've had to sand slots on most of these). So now I can't wait to cut more chucks and NOT sand slots! LOL! In thinking about why this worked I realize it's something that just makes sense and I should have thought about this a long time ago.

    Leaving 0.020" for final pass -
    001 - Fuzz, leaving 0.020 in bottom of slot on first pass.jpg

    Cutting to full depth in one pass -
    002 - No fuzz in slot, cutting full depth in one pass.jpg

    David
    David
    CurlyWoodShop on Etsy, David Falkner on YouTube, difalkner on Instagram

  2. #2
    Join Date
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    Yes, that really helps with cutting sheet goods with compression tooling...the singular downside is that you need to project the bit a little deeper into the spoilboard that you might normally prefer to do to expose the upcut enough for best effect. With good feed/speed, the cut can be amazingly clean!
    --

    The most expensive tool is the one you buy "cheaply" and often...

  3. #3
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    Right now, the way I cut these, I am only lightly touching the spoilboard and not cutting into it. But now that I'm not leaving that 0.020" for a clean up pass the slots are coming out perfect. I was told about these Amana Mortise Compression bits and I may give one of those a try some day.

    David
    David
    CurlyWoodShop on Etsy, David Falkner on YouTube, difalkner on Instagram

  4. #4
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    The Whiteside .25" compression cutters I have have the shorter up-cut portion, too. I really like the format because they are usable in thinner material which is more typical for the kinds of things I cut.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  5. #5
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    I'm using the Whiteside UD2102 and it has an upcut section that's about 0.200". Is that the same one you're using, Jim?

    David
    David
    CurlyWoodShop on Etsy, David Falkner on YouTube, difalkner on Instagram

  6. #6
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    That sounds about right. I always try for at least a 6mm/.2"+ initial pass for that reason if I'm doing multiples.
    --

    The most expensive tool is the one you buy "cheaply" and often...

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