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  1. #1

    Is This Bit Ruined?

    Someone warned me about this on a separate thread just a few days ago but I'm afraid the damage has been done at this point. Running this 3/8" compression bit at 15k RPMs and 30ipm (new to CNC routing and learning speeds and feeds) were probably the wrong settings here.

    I am trying to use a feeds and speeds calculator to optimize feed and rpm for tool deflection but haven't paid much attention to tool life yet.

    20180528_194051.jpg20180528_194119.jpg

  2. #2
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    Don't know what you were cutting, but a quick calculation has your chip load at .001. Normal load for most materials for that tool is much higher - around .017 to .023. Your feed rate is way too slow.

  3. #3
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    Quote Originally Posted by Mick Simon View Post
    Don't know what you were cutting, but a quick calculation has your chip load at .001. Normal load for most materials for that tool is much higher - around .017 to .023. Your feed rate is way too slow.
    Agree. And that causes a lot of heat...
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  4. #4
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    As alluded to above, the heat generated should be carried away with the chip to minimize the heat build-up in the cutting tool.
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  5. #5
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    The information above is all good. But either carbide or hss should be able to stand heat without being ruined. Does it still feel sharp compared to the unused portion up top? At worst it probably just needs to be resharpened.

    IMHO ruining a bit means breaking it, or running into a hard screw or stone.

  6. #6
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    I don't think a wood chip carries away any heat, perhaps aluminum or steel. Nothing wrong with the bit as long as the cutting edge is still sharp. A 3/8 bit should never be ran at 15,000 RPM without either air or fluid coolent.
    I did a quick calculation and I have never used this app before with a chip load of .250 and 60 ipm = 80 rpm? Sounds too slow rpm wise anyway.
    Last edited by Bill George; 05-29-2018 at 12:03 PM.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  7. #7
    Quote Originally Posted by Bill George View Post
    I don't think a wood chip carries away any heat, perhaps aluminum or steel. Nothing wrong with the bit as long as the cutting edge is still sharp. A 3/8 bit should never be ran at 15,000 RPM without either air or fluid coolent.
    I did a quick calculation and I have never used this app before with a chip load of .250 and 60 ipm = 80 rpm? Sounds too slow rpm wise anyway.
    Im not sure where your math is coming from. But if you dont think a wood chip carries away heat you will have to tell that to my chip pile when we empty the drum. If you stuff your hand in the drum its HOT. Im not talking combustible hot, but its HOT. Wood chips, MDF chips, Melamine chips, all of them, absolutely carry off heat.

    The feeds and speeds in the OP's post are way off for us but its a difficult balance between what your machine is able to achieve with regards to your tooling selection.

    I have popped the lid off the drum of the cyclone that feeds the CNC and been met with a burst of warm, wet, air. When I look in and see chips instead of powder (Mdf excluded) Im happy.

  8. #8
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    Quote Originally Posted by Mark Bolton View Post
    Im not sure where your math is coming from. But if you dont think a wood chip carries away heat you will have to tell that to my chip pile when we empty the drum. If you stuff your hand in the drum its HOT. Im not talking combustible hot, but its HOT. Wood chips, MDF chips, Melamine chips, all of them, absolutely carry off heat.

    The feeds and speeds in the OP's post are way off for us but its a difficult balance between what your machine is able to achieve with regards to your tooling selection.

    I have popped the lid off the drum of the cyclone that feeds the CNC and been met with a burst of warm, wet, air. When I look in and see chips instead of powder (Mdf excluded) Im happy.
    Yup, I was way off base confused on the chip load.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  9. #9
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    Clean it up

  10. #10
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    You have a bit of discoloration because it was running within the chips. This is not incredibly uncommon with a compression bit or downcut bit. Such is life. All of us with smaller machines and whimpy DC systems fight this. I have a 5hp DC and that is tiny compared to a proper industrial DC. Check the bit for sharpness with your fingers. I bet you still have a sharp edge. If so, clean it off as suggested. None of us in this thread have machines that can push the bits as hard as one should according to the charts. Gary suggested months ago most of the chart data is for industrial machines with much stiffer heads, and I tend to agree with that. If you want to get closer to the suggested values in the charts you could look at single flute bits. They do make single flute compression bits.

    None of us can really suggest a feed speed without knowing a more about your machine, what you are cutting and the depth of cut. That is dreadfully slow for a 3/8" bit regardless. My guess you are running it as slow as you mention because of the machine stiffness, or your hesitation. If you tell us what you have for a machine that will help.

    Bill, there are tons of bits that can run up to 24k rpm in wood without coolant, you just need the DC that can effectively remove the chips and cut at speeds in excess of 1000ipm.

  11. #11
    Quote Originally Posted by Brad Shipton View Post
    Such is life. All of us with smaller machines and whimpy DC systems fight this. I have a 5hp DC and that is tiny compared to a proper industrial DC.
    We have a 3HP dedicated cyclone with less than 15' of pipe between it an the CNC (smooth and flex combined). It sucks every bristle of the widely adorned Kent CNC dust shoe into the hose other than those behind the spindle. Other than a traveling house there is no more DC that can be applied (nor none needed). We run a 10HP spindle (like you) and other than wide open panel processing, when we are cutting with the shoe down against the work there isnt a chip left in the cut unless we are off the side/end of the work with the shoe.

    Quote Originally Posted by Brad Shipton View Post
    None of us in this thread have machines that can push the bits as hard as one should according to the charts.
    I dont really feel this is true. You and I have similar machines. I can outrun (and easily break) a 1/4" compression. I can (and do daily) crowd a 3/8" compression. I can run a 1/2" compression wide open (rpms arent and issue as there are more to spare), but feed is the limiting factor. 550IPM and a 1/2" compression is laughing at me. 3/8" its winking at me to ease up on it a bit. 1/4" would be crying out for a few seconds of peace before it went bye bye. I would never do that to any cutter in my shop.
    Bill, there are tons of bits that can run up to 24k rpm in wood without coolant, you just need the DC that can effectively remove the chips and cut at speeds in excess of 1000ipm.[/QUOTE]

  12. #12
    Thanks for the feedback gentlemen. Thanks for the detailed responses I will have more time to go thru them this evening but saw some comments regarding machine details, and I really should have it all posted in the signature but I'll get there. The machine is an

    Axiom AR8 Pro+ with
    3 HP spindle and
    200 ipm max rapid.
    2' x 4' x 6" work envelope

    It seems rigid enough but I say that with limited experience. I'm cutting 18"-23" monogram letters in 0.5" baltic birch. Not trying to get back to my other post but that's where this is headed

    Again cutter is 3/8" Amana 46171. Cut depth is 0.2"-0.25" first pass and 0.1"-0.2" following passes to cut thru.

    DC is 2 HP harbor freight with Wynn 222 nano filter.

  13. #13
    Quote Originally Posted by Casey Thomas View Post
    Thanks for the feedback gentlemen. Thanks for the detailed responses I will have more time to go thru them this evening but saw some comments regarding machine details, and I really should have it all posted in the signature but I'll get there. The machine is an

    Axiom AR8 Pro+ with
    3 HP spindle and
    200 ipm max rapid.
    2' x 4' x 6" work envelope

    It seems rigid enough but I say that with limited experience. I'm cutting 18"-23" monogram letters in 0.5" baltic birch. Not trying to get back to my other post but that's where this is headed

    Again cutter is 3/8" Amana 46171. Cut depth is 0.2"-0.25" first pass and 0.1"-0.2" following passes to cut thru.

    DC is 2 HP harbor freight with Wynn 222 nano filter.

    I dont know how the Axiom specs are written as to whether your 200IPM rapids relate to feeds or only rapids. The issue you will have there is unless you can slow your spindle speed your going to cook your bit if you try to meet any given cutter spec's. I would be looking to how slow you can run your spindle before you land in the fall off of the power curve for your spindle and then base your depth of pass on those two fixed parameters. If your trying to save/prolong tooling life your best bet may be to lower your RPMS as low as possible and reduce your depth of cut (ditch the compression all together) to a point where you close to your desired chip load. The answer may well be that you dont run a compression at all and opt for a different bit that allows you to take better advantage of your spindles speed range, HP, and your machines max feed.

    I dont believe in babying tools regardless of cost. Investigate tooling options that allow you to run your machine at 80%+ of its capacity. Its there to work, not may talcum powder. Put the hurt on it.

  14. #14
    Quote Originally Posted by Casey Thomas View Post
    Someone warned me about this on a separate thread just a few days ago but I'm afraid the damage has been done at this point. Running this 3/8" compression bit at 15k RPMs and 30ipm (new to CNC routing and learning speeds and feeds) were probably the wrong settings here.

    I am trying to use a feeds and speeds calculator to optimize feed and rpm for tool deflection but haven't paid much attention to tool life yet.

    20180528_194051.jpg20180528_194119.jpg
    Based on some of your other posts you many need to make your bit choices differently. Your initial start may be what is your max feed speed, and what is the HP of your machine. Those two factors may tell you that even though you can run an aggressive cutter your machine doesnt have the power or feed to handle that specific tool. You will have to find the sweet spot where your running at your machines peak speed of feed and HP.

    There are cutters I would love to run but when I realize the point at which they would be profitable to run on our machine they will either have to be run to slow or with other issues that make them a bad fit for our capabilities.

    I would agree that your bit shows no major issues. Color shows a bit of heat, seems like there is a traditional nick that happens on the lower upcut part of the compression (we deal with this a lot). But a re-sharp will bring it back to life.

    Evaluate what your max feed is, and your known HP. Dont exceed either with your cutter choice.

  15. #15
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    Mark, I agree we can push a 1/4" double flute bit close to the chip loads, but a 3/8" or 1/2" diameter we are going to be very low compared to what the industrial machines do. Your machine has a 600ipm max +- and mine is 400ipm. Industrial guys push those diameter bits to 1000ipm+ in melamine or other sheet goods. I use 3/8" and 1/2" frequently for thick stock and the chip loads I cut at are always much lower than suggested taking into account the mass of my machine and what it can do reliably.

    I know you are not one to BS, but I would need to see pictures after your first pass of a full width plunge cut. Given our low hp table vacuum I suspect you onion skin your sheet goods like I do. I can see the chips left in the groove with a compression bit or downcut after the first pass. Downcut is by far the worst because it tries to pack everything at the bottom. On the clean up pass the chips are extracted, but at that point they have already caused a problem for excess heating of the bit. I finally tried the kinetic dust extractor I picked up, and it works awesome for chip extraction. Problem is it works too well, and my DC will not grab all the chips once they have reached the speed they do after going thru a 10-20,00rpm turbine. That process pulverizes the chips and they get stuck to everything. I have an idea to fix my dust boot, but it will take some time to 3D print the parts needed. The big boys solve this with big HP on the DC.

    The Kent boot is an ok idea, and is practical, but is a poor design technically. It is basically a bristle holder for an offset pipe. The air flow is good right at the pipe inlet, but it drops off dramatically near the cutter where it is important. Kind of like trying to use your shop vac holding the end up off the floor.

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