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Thread: Compression bit selection

  1. #1
    Join Date
    Aug 2018
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    7

    Default Compression bit selection

    I have been searching on here and centurion cutters seem to be very poplular. I want to try some just cant decide on the plunge end or the FEM(flat end mill) end. Any suggestions? I have been using whiteside 1/4" compression bits in my 2.2kw spindle so far but want some 3/8" cutters.

    On a side note what would be a suggested feed/rpm, cut depth for a 2.2kw spindle on a machine similar to a prt standard? Its actually a cnc routerparts pro with nema 34s and an atc spindle. Right now I can run a single pass in 3/4" maple plywood at 350ipm and 13,500rpm with the 1/4" compression. I want the 3/8" for a better edge finish.

  2. #2
    Join Date
    May 2014
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    MA
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    I use those same bits and I really like them. Do one pass like you're doing now, but leave an onion skin and make the part about .005 larger (you can do this in Aspire). For the last pass come in the opposite direction and tight to the part (no offset) and you'll get great finish quality on plywood.

  3. #3
    Join Date
    Dec 2011
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    Piedmont, SD
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    Point #1 Having plunge end is in harmony with the plunging of the bit into material. Unless you ramp your cuts, Flat end mill will be stabbing straight into material, heating faster and hastening it's demise. Centurion refers to this geometry as a mortise compression bit.

    Point #2 - What Eric said, though I recently switched to 3/8 for general plywood cutting, simply to reduce number of passes. On a 4x8 sheet full of cutouts, this makes a noticeable reduction in processing time. As for better edge finish, I think you'll find as I did that the difference is not very perceptible. Others will note 1/4 bit allows you to squeeze more parts on each sheet. I've not had any such problems since up-sizing to 3/8, though sometimes that 1/8" wider kerf can add up.

    As for brand, I've been happy with Centurion, especially with pricing. Recently purchased a 3/8 of theirs and equivalent in Onsrud, and they appear almost identical. Time will tell if any difference in longevity, though they are both the "extended" / "Max Wear" varieties. Note part numbers in image.

    Pay attention to length of up-cut tip on your compression bits. Image shows a regular 3/8 compression at the bottom, with the Onsrud and Centurion above. Note the top two have half the length of up-cut tip. This is ideal for plywood, as you're less likely to plunge too shallow, resulting in tear-out of veneer , or worse yet, melamine face.

    .375 compression comparison.jpg


    Jeff

  4. #4
    Join Date
    Dec 2008
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    Diamond Lake, WA
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    A very important thing to consider with compression bits is that the upcut portion will cause chipout until it gets below the surface of the plywood. Because of this, you need to plunge a compression below the depth of the upcut portion then start your ramp. I've worked with 3/8" and 1/4" compression bits. I cut hundreds of sheets of plywood a year. The 1/4" does allow more parts per sheet, but at the cost of speed. You can run faster with a 3/8" bit because there is less bit flex. But, if your machine is not REALLY tight, the 3/8" bit can cause more machine flex. I compensate for this with 1/4" bits by making my first pass a climb leaving a 1.32" skin. The second pass is a normal direction cut. I plunge the bit 1/4" down then ramp all the way thru the material cutting 1/32" thru. This leaves a very clean edge ready to go straight to the edgebanding machine and the second cut is dead on the line.
    Don
    Diamond Lake Custom Woodworks, LLC
    www.dlwoodworks.com
    ***********************************
    Life is not a journey to the grave with the intention of arriving safely in one pretty and well preserved piece; But to skid in broadside, thoroughly used up, worn out, bank accounts empty, credit cards maxed out, defiantly shouting "Geronimo"!

    If you make something idiot proof, all they do is create a better idiot.

  5. #5
    Join Date
    Jan 2004
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    iBILD Solutions - Southern NJ
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    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  6. #6
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    May 2014
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    MA
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    Brady, how much better are those than something like a Onsrud, Whiteside or a Centurion? I tend to get a long life out of my Whiteside compressions... Is it just the time that they last, or is the cut quality that much better?

  7. #7
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    Dec 2008
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    I've been using RBTools compression bits for several years. I went from getting 20 sheets of 3/4" plywood to 25 sheets before I had to change bits. I also went from 5IPS to 6IPS with the same cut quality. The tool seems to last longer then others I've tried (Onsrud, Centurian, Whiteside, Amana). The cut quality is VERY good over the course of 25 sheets. After that, it starts to degrade a little. I donate my "duller" bits to the local highschool woodshop for two reasons, one, the kids are very hard on these bits and drop them on the concrete floor and slam them into screws and nails. Two, at the rate they butcher bits, giving them my used bits saves them a LOT of money. I do the same with 1/4" two-flute down cut spiral bits. I use lots of these bits too.
    Don
    Diamond Lake Custom Woodworks, LLC
    www.dlwoodworks.com
    ***********************************
    Life is not a journey to the grave with the intention of arriving safely in one pretty and well preserved piece; But to skid in broadside, thoroughly used up, worn out, bank accounts empty, credit cards maxed out, defiantly shouting "Geronimo"!

    If you make something idiot proof, all they do is create a better idiot.

  8. #8
    Join Date
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    iBILD Solutions - Southern NJ
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    The Vortex bits give a cleaner edge and last about 3x longer than the Centurion ones in my testing. If you crunch the numbers, they are a little bit cheaper if you gauge the linear cutting distances of each...but let's not forget that the edge quality is better, regardless of life.

    A friend of mine with a Thermwood recommended them years ago and his machine, being a real CNC (aka not bolt together aluminum), can blaze through material with the Vortex bits - way faster than an Alpha with 5hp spindle could. I was only able to average about 60-70 sheets max. He could get in the neighborhood of 90 sheets on his machine since it doesn't flex, bog and can run a heavier chipload - which means the bit stays cooler and isn't rubbing more than it has to.

    For most people, the Centurion ones are fine...they are a good bit for the price. Like any consumable...find something that works well for YOU and your material...and stop buying your tools from Ebay, Amazon and TToday. You'll get better tools and pricing from a tool dealer you establish a relationship with. That message is for the professionals...who probably already know that. If you are a hobbiest - it doesn't matter because you aren't really building tooling costs into a paying job. Just as a yardstick...TToday had an Amana bit for $137.00...my dealer's price for the same bit was $87. Do the math. That's money back in your pocket.
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  9. #9
    Join Date
    Aug 2018
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    7

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    Thanks for all the info. Right now the vortex cutters are a little bit steep for this machine, but when I outgrow this one Ill be into a lot heavier machine and then new level of tooling to match it. Tempting to try a couple right now though and see how they last under my conditions. All I have been using is the plunge style cutters so far, any issue plunging a flat end mill style around 1/4" before ramping to depth? Or should they be ramped in the entire way? Cutting maple veneer plywood for cabinet parts, no melamine.

  10. #10
    Join Date
    Nov 2016
    Location
    New Mexico
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    We cut 3/4" plywood with 1/2" straight fluted bits from Lowes ($17 each).
    We ramp with 5 passes at 60 ipm and 16k rpm.
    Great results!
    We are not creating edges which require superior finished cuts. More like rough cutting.
    Our most important shop tool is the pencil sharpener!

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