Feed rate and bits breakage.


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Thread: Feed rate and bits breakage.

  1. #1
    Thomas91's Avatar
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    Default Feed rate and bits breakage.

    Good afternoon! I use some bits that break frequently. Now I will try to describe the bits and the speeds that I use.
    At first I used straight bits with a cutting diameter of 1.5 mm and a cutting height of 7 mm at a spindle speed of 21000 rpm and a feed rate of 1500 mm / min, vertical feed of 500 mm / min. I cut 6.7 mm spruce plywood in 1 pass with vertical recess. The bits broke. Then he began to cut in 2 passes. That is, at first, the bit was deepened by 3.2 mm. All the same, the cutter broke. Could it be that I chose too high a spindle speed due to which the bit was blunt too quickly?
    Then I started using a 2mm corn bit. I cut it in 2 passes. She broke too. Used the same feed rates and revolutions. Please advise what can be done? I understand that plywood should be cut with compression mills or corn with the chips down. But so far these cutters have not been sent to me by mail.



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    Default Re: Feed rate and bits breakage.

    Quote Originally Posted by Thomas91 View Post
    Good afternoon! I use some bits that break frequently. Now I will try to describe the bits and the speeds that I use.
    At first I used straight bits with a cutting diameter of 1.5 mm and a cutting height of 7 mm at a spindle speed of 21000 rpm and a feed rate of 1500 mm / min, vertical feed of 500 mm / min. I cut 6.7 mm spruce plywood in 1 pass with vertical recess. The bits broke. Then he began to cut in 2 passes. That is, at first, the bit was deepened by 3.2 mm. All the same, the cutter broke. Could it be that I chose too high a spindle speed due to which the bit was blunt too quickly?
    Then I started using a 2mm corn bit. I cut it in 2 passes. She broke too. Used the same feed rates and revolutions. Please advise what can be done? I understand that plywood should be cut with compression mills or corn with the chips down. But so far these cutters have not been sent to me by mail.


    Hey Thomas,

    i use onsrud end mills for most applications, i also use a chart called "routing material quick reference guide"(from multicam) its a basic refernce but, it shows you should be setting a feed rate of 1250mm/min@18000rpm, , also would help to make sure the work piece is not moving as this can cause bit to break also.



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    Default Re: Feed rate and bits breakage.

    Thank you very much! But where i can get this chart? I searched on google but can't find. And can I use full depth cutters, i.e. 1 pass at this feed rate?



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    Member ger21's Avatar
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    Default Re: Feed rate and bits breakage.

    Very small bits are very fragile, and very intolerant of runout, or any other issues. You probably need to make more, shallower passes, and find a way to clear the chips from the cut.

    Gerry

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    Member routalot's Avatar
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    Default Re: Feed rate and bits breakage.

    I think a part of the problem is attributable to the length/diameter ratio of the 1.5mm cutter.There isn't very much metal in the central web and it is almost certainly flexing a little and each rotation causes a stress reversal and at 21000 rpm thats a lot of stress reversals.We have been advised that there is a cutting height of 7mm and there may well be a couple more millimetres of waisted stem above that giving a very slender projection from the collet.The advice for shallow cuts and good extraction has to point you in the right direction and I would add that you will help yourself by using the shortest cutter that will give a clear cut at the intended depth.



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    Default Re: Feed rate and bits breakage.

    I may need to use bits starting from 3mm. I tried to cut with them, but in this case, the machine starts to rattle. The fact is that I mill plywood plates 38x50 cm and I can fix them on the sides with screws, but it is impossible to fix them in the middle. Moreover, this is milling along the contour, through and through. If I were just engraving, then I would think about vacuum clamps, but alas, even they will not help here. Therefore, I ordered 3mm compression bits and am waiting for them to be with me. I am afraid they will rattle and vibrate when cutting so I will have to find the correct feed rates. I will leave links to the cutters that I purchased.

    https://www.amazon.com/gp/product/B073RKCWGH
    https://www.amazon.com/gp/product/B07DYMFNY2



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    Default Re: Feed rate and bits breakage.

    If the plywood is vibrating as it's being cut, that by itself will break bits, particularly the long skinny ones you're using. As you've noticed, it's hard to keep thin stock flat on the table. What makes you think vacuum won't help?

    If cutting with a 3mm bit causes your machine to rattle, that's indicative of a major rigidity problem, which also can break bits. What kind of machine are you using? If you push on the spindle when the motors are locked up, can you detect any deflection, and if so, how much?

    [FONT=Verdana]Andrew Werby[/FONT]
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    Default Re: Feed rate and bits breakage.

    I think you may regret 3mm compression cutters.In part because the multiple cuts necessary will have the first cut using just the upcut portion of the cutter and you will very likely have splintering of the top veneer.They will also have very shallow reliefs between the cutting flutes,although you may have more edges doing the work.As has been said,more information about the machine would be useful.I find the mention of spruce plywood interesting as I have never encountered such stuff and it could have some interesting uses.



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    Default Re: Feed rate and bits breakage.

    My machine is CNCest, Chinese CNC. Spindle 1,5kw 110v. I checked that the design of the spindle mount is very rigid and there is no backlash or swinging, no matter how I press. The only problem is attaching plywood to the table. I fix it on the sides and it vibrates in the center. And I know why, because the bits I use are with upward discharge of the shavings, they lift the plywood and make it beat. I hope with the bits that I ordered there will be no such problems. For they are either compression, that is, they will not push the plywood up or down, or they will press it against the table. But nevertheless, I would like to know the feed rates and spindle speeds for these milling cutters ... I cannot find an adequate calculator ...



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    Default Re: Feed rate and bits breakage.

    Believe me, a small chip in the top layer of plywood is not so scary, especially if you compare it with what is happening with me now) Chips around the entire perimeter. And by the way, I also use birch plywood, birch plywood is simply tougher and stronger than spruce. Spruce is more suitable for decorative purposes.



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    Default Re: Feed rate and bits breakage.

    I think what you need is a downcut spiral form of cutter.Unless the compression cutter is intended for material of the thickness you are using and run at a depth where the upward forces balance the downward forces it may not be the answer.Is it possible to use double sided tape to attach the plywood to the table?



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    Default Re: Feed rate and bits breakage.

    I tried to attach it with tape, but this is possible if I do not make through cuts because in this case the cutter is covered with tape and starts to burn ... Fortunately, I found out that the tip of that compression cutter goes deep enough to collect chips .. anyway, if it is not if it works, then I will have corn cutters with chips dumping down ... in this case, problems should not arise, but I still do not know how to calculate the feed rate (



  13. #13
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    Default Re: Feed rate and bits breakage.

    The chart on this page may help you to establish a starting point https://carbideprocessors.com/pages/...oad-chart.html



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    Default Re: Feed rate and bits breakage.

    are these diagrams suitable for all diameters? I think they can be used in conjunction with the formula



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    Default Re: Feed rate and bits breakage.

    Use them as a starting point and maybe take a look at this other chart to see how chip load changes with diameter. https://www.cutter-shop.com/informat...oad-chart.html .You may need to take into account the brittle nature of the alloy the tool is made of.



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    Default Re: Feed rate and bits breakage.

    You are asking a lot for that little tool. Slow your feed rate down you are way to fast, cut it in half. Do multiple passers. I use a 4mm up down cut in 1 pass on 12mm plywood at feed rate of 50mm sec plunge rate 20mm sec . So a 3mm bit has to be slower then that. Also do you have quality bits????



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    Member coc9's Avatar
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    Default Re: Feed rate and bits breakage.

    Hello,
    Firstly there's no perfect reference table or a calculator ever made for feed and speed calculation. Sometimes we are into so much detail that we forget basic things, so just for confirmation your bit has the correct rotation direction as it should be ? Another thing is i prefer to have the pass depth which is always less the diameter of the bit. This may be the reason for the breakage plus 18000 rpm would be better considering the bit dia.

    Plywood is one of the toughest material to machine and tool gets wear out easily. In order to get desired machining you may fix your sheet onto another waste or a particle board so that you get through and through cut very easily without damaging the base or chipping at bottom face. you may use double sided tape or simply nail both the sheets (careful place nails atleast 20-30 mm away from machining portion).
    Regards



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Feed rate and bits breakage.

Feed rate and bits breakage.