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Thread: Myth Busted - cutter diameter same as shank

  1. #1
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    Myth Busted - cutter diameter same as shank

    A long while back there was a thread and down in a ways it was stated that a large tool manufacturer stated that it was always best to pick a tool with a shank diameter the same or as close to the cut diameter as possible. So a 1/2" cutter, 1/2" shank, 1/4" cutter 1/4" shank, etc..

    We cut miles of 1/4" MDF and have always run 1/4" or 7/32" 2 flute straight plunge with 1/2" shank. Typically run 22000 at 500IPM and the tools last, well, pretty much forever as I have never tallied how many sheets on a tool but I have cut several hundred sheets on 3 - 4 tools a couple of which I still keep for backup/spares but depending on the material that lands they are dull enough to leave a tiny fuzzy edge and the parts need to come off the machine dead clean with no handwork at all.

    So last tooling order that comment popped into my head and I tossed 4 Amana 1/4" shank x 1/4" dia x 1/2" CL tools on the order. At $13+ a piece I though why not.

    First bit didnt make it 2/3 through a sheet and snapped. Second bit, cut the feed to 350ipm ran the remaining 1/3 and the second and snapped right at the end. A used 1/2" shank, 1/4" diameter 2 flute plunge went back in the holder and ran the five remaining sheets for the job. The two new bits will be relegated to fragile little bird type work.

    Its plainly clear that the large fillet at the top of the 1/4" tool to the 1/2" shank adds a massive amount of strength and rigidity to the tool. It eliminates any stress risers at the top of the brazed portion of the bit, and also due to its mass will carry off way more heat.

    I knew it was just common sense because even with hand routers performance is always improved with 1/2" shank tooling but its always great to do some real world testing even if it costs you 30 bucks and a bit of time re-toolpathing.
    Last edited by Mark Bolton; 10-19-2019 at 1:57 PM.
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  2. #2
    I didn't see the post you are talking about but have heard that before but I always took it that they meant if using 1/2" bit then use 1/2" shank not a 1/4" shank. I never even considered that they might be suggesting what you stated and to use smaller shank on smaller bits. I can believe your test results. I always try to find the bits that I am looking for in 1/2" shaft when I can them. Unfortunately most seem to be 1/4" that I find.

    Thanks for sharing your results. Something to remember

  3. #3
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    Hi Mark,
    Here is what I think is a good article on this topic.
    David


    https://www.thesprucecrafts.com/quarter-vs-half-inch-shank-bits-3536400

    router bit size.jpg

  4. #4
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    The info in that article is all pretty spot on especially for handheld. That said most hand held router operations will never push the tooling remotely close to its limits. I found the comment in the post some time ago odd coming from a tooling manufacturer as in most every application from machining world to the architectural cnc world, the largest shank possible is always desireable which is why I'm happy to have given it the test first hand.

    Roaching two brand new bits was a waste but like I say. Its was worth the 30 bucks lol.

  5. #5
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    It's a dance. At higher feed rates and with a cutting length just long enough to "do the job", I can absolutely see how the larger shank plus fillet can add to the strength of the tooling and allow you to push things a bit. A .25" cutter with a .25" shank doesn't have that advantage. The real bottom line, however, is to use the tooling that's best for the particular job you need to do. Clearly, for what you are doing the larger shank setup is better performing.
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    To do the job is spot on. The proper tool to allow you to run as fast as possible with acceptable results for the job (cut quality, tool life, profitability, etc). There really is no dance when a tool wont pull off a single sheet compared to its larger shank alternative running 100 or more. ;-)
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  7. #7
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    The "dance" was referring to was merely choosing the right tool for the given job...which you clearly have determined.
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    The most expensive tool is the one you buy "cheaply" and often...

  8. #8
    You mention a brazed cutter, which means that the smaller 1/4" shanked versions are extremely weak at the top of the cutting edges and the base metal of the shank is mild steel. If you had tried a solid carbide 1/4" bit, I suspect you would have had completely different results.
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

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    Quote Originally Posted by Brian Lamb View Post
    You mention a brazed cutter, which means that the smaller 1/4" shanked versions are extremely weak at the top of the cutting edges and the base metal of the shank is mild steel. If you had tried a solid carbide 1/4" bit, I suspect you would have had completely different results.
    Hi Brian,
    Forgive me is I missed it, but I didn't see any mention of a brazed cutter in this thread - but it must be there. I don't think Mark mentioned if these were solid carbide or HSS cutters - but for the price he paid - they would almost have to be HSS (not solid carbide). I agree with you on the point about the solid carbide 1/4" bits.
    David

  10. #10
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    I also missed that they were "straight" bits which generally changes the game.
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    The most expensive tool is the one you buy "cheaply" and often...

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    Correct, brazed tooling. There really isn't a good solid carbide option for this work or thats what we'd run.

  12. #12
    Brazed tooling is notoriously weak, especially in smaller sizes. I'm coming from the metal machining world and we use solid carbide for pretty much everything. I have been woodworking for probably 35+ years now and use mostly metal cutting end mills for routing. With the advent of the special "compression" bits, I would assume cnc routers would run solid carbide most of the time also.

    As a second note, I buy solid carbide end mills in 1/4" size for around $10 each, so they might be cheaper to test with too.
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

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    Solids are only available for the most part in spirals. We buy 80-100$ solid carbide compressions a dozen at a time. They are no good for this material/work nor is a spiral. The grindinging geometry for the brazed is identical on the 1/4" shank and the 1/2" shank. I'm not insinuating the 1/4" shank tool should have held up... I knew it wouldnt. And the post I'm remembering may well have been speaking to solid carbide. But basically the same tool, with the two shanks is the difference between less than a sheet and hundred sheets or more.
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  14. #14
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    Mark, I think that the key difference is that with a .25" braised straight cutter, your effective "core" is smaller than .25" and hence, potentially weaker. The braised cutters certainly will help with that, but I really wonder if they are as strong as a .25" spiral. The flare from a .5" shank will certainly help and I do believe that if you must run these straight cutters, the larger shank is going to help.

    I'm curious about why the straight braised cutters, um...cut better...than carbide spirals for your MDF production? I know it's abrasive, but what makes them work better for you? Really...just curious and want to learn.
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    The most expensive tool is the one you buy "cheaply" and often...

  15. #15
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    The down shear packs the cut full of chips and leaves too much of a mess (too much time) for cleanup when unloading. If I crank up the DC to pick up the chips, the dc will pull parts off the spoil board. These sheets will have a lot of small odd shaped parts nested, sometimes 50-75 parts on a full sheet. An up shear will also fight the vac and try to lift parts and the instant they begin to wear they raise a ragged edge on the top of the parts which is no good. To get these on, cut, and packed out the door, I want zero cleanup when they come off. No sanding off fuzzies, nothing, staight in the boxes and out with hopefully as little dust to pickup when emptying the table. The other big problem with thin material and spirals is they generally have a fairly long cut length so youve got a lot of bit that will never get used when I can run a 1/2" or 3/4" cutter length with the straight cutters. If the chips and the work holding werent an issue and I had a Dbit grinder I could lop the ends off and keep shortening them but again, the chips and the lifting with the spirals are the issue.

    No disagreement about the brazed (or any small tooling) being very narrow at the core. The part that is impressive to me is that the two bits are identical until the fillet begins (perhaps .020" above the flutes) and the larger shank adds that much strength. I have literally never broken a 1/2" shank tool with a 1/4" or 7/32" cutting diameter even pushing them at 500ipm when they are dead dull. The cut just goes to pot but they keep on cutting. Even in the metal world with solid carbide tooling and pre-forms you will see very large shank diameters reduced down to a smaller tool, Im sure for all the same reasons, rigidity, heat, collet holding.

    I can often come across 7/32" (undersized ply) bits at really good prices and use them for all sorts of mortising and dados on drawer boxes and so on where we need a snug 1/4".
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

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