Bit breaking and melting on milling


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  1. #1
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    Default Bit breaking and melting on milling

    Hello everyone i am new to the forum and new to CNC as well. I got a basic C Beam Router from openbuilds and today i broke 2 carbide 1/8in bits tryng to mill a 1/8inch deep 6061 aluminum plate.

    Rpm was 13.000 , and feed rate around 700mm/min SFM around 150 and cuts mostly 0.4mm deep. The bit was a good quality carbide bit 3 flutes for aluminum from BitsBits.

    2 of them broke during sloting and it looked like the aluminum was melting into the spoilboard. I put a picture of what happened. The sound was very rough like it was struggling to cut and vibrating.

    I am thinking to increase the rpm to 20K and SFM as well but i am afraid of breaking another beat. The machine is capable of milling this kind of plates as ive seen videos doing just fine. So anyone would suggest something ?

    Thanks for the help !! Mistakes get quite expansive on cnc ????

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    Default Re: Bit breaking and melting on milling

    Quote Originally Posted by Biancolima View Post
    Hello everyone i am new to the forum and new to CNC as well. I got a basic C Beam Router from openbuilds and today i broke 2 carbide 1/8in bits tryng to mill a 1/8inch deep 6061 aluminum plate.

    Rpm was 13.000 , and feed rate around 700mm/min SFM around 150 and cuts mostly 0.4mm deep. The bit was a good quality carbide bit 3 flutes for aluminum from BitsBits.

    2 of them broke during sloting and it looked like the aluminum was melting into the spoilboard. I put a picture of what happened. The sound was very rough like it was struggling to cut and vibrating.

    I am thinking to increase the rpm to 20K and SFM as well but i am afraid of breaking another beat. The machine is capable of milling this kind of plates as ive seen videos doing just fine. So anyone would suggest something ?

    Thanks for the help !! Mistakes get quite expansive on cnc ????
    These will probably do a better job at a fraction of the price, you need some WD40 as well, is you spindle running the correct way for the cuter you are using and yes you where melting it

    Ebay Item # 143404055322 there are many to choose from

    Mactec54


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    Default Re: Bit breaking and melting on milling

    Try this - it may get you slotting aluminum instead of breaking end mills: Use a the shortest possible end mill - with it sticking out of the collet or holder as little as possible. This is to limit the end mill deflection (even carbide will deflect). The following data is for a 3 flute carbide end mill with 0.500" flute length, sticking out of the collet 0.525":

    8000 RPM slowing down the rpm will reduce the net heat generated at the cut. A little more time between each tooth's (flute's) cutting action. And give the chips a little more time to be cleared.

    175 mm/min this reduces the chip load per tooth (flute) too ~0.0009", instead of 0.0021" that 700mm/min creates. More importantly, at the 0.525" stick-out from the collet, a 175 mm/min feed rate reduces the end mill's deflection from ~0.0015" to ~0.0006".

    MOST IMPORTANTLY : use a mist coolant with enough air psi to blow the chips away - you do not want to re-cut any chips. The coolant will help keep the chips from "melting / sticking" (galling) to the end mill. A TiN coated endmill will also help with galling. At the very least, use a constant air blast to clear the chips, and spray the end mill with WD-40 as needed.

    If you still see galling or "melting", Reduce the rpm to 6000 and feed rate to 136 mm/min and make sure the chips are blown out of the cut and use plenty of WD-40 or other suitable cutting lube / coolant for aluminum.

    Another solution I've used for slotting is a trochoidal tool path. For example, with a short as possible, 2.5mm or 3/32" carbide 2 flute end mill, and 0.020" to 0.030" advancement for each trochoid loop, at 170 mm/min. AND keep the chips clear, and the endmill misted with coolant or lube. Intro to Trochoidal Milling - In The Loupe



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    Default Re: Bit breaking and melting on milling

    Hi,
    most endmills which are specialised for aluminum are uncoated.

    TiN, TiAlN etc coatings are all trivalent which is good in iron and other tetra-valent metals but show an affinity for aluminum because its trivalent too.

    If you get really stuck try di-boride coated tools, a bit specialist and therefore expensive, but 'as greasy as a butchers prick' in aluminum. Good in 'sticky'
    1000 series, 3000 series and some of the soft 5000 series aluminum.

    I rely on flood cooling when doing aluminum, in part for the cooling, and in part for lubrication, but MOST IMPORTANTLY for flushing the chips out of the cutzone.
    Slotting toolpaths are bad for re-cutting chips because the chips can't evacuated, any flushing, be it with liquid cooling or air, is a great step in the right direction.

    Some CAM programs offer a toolpath that does a similar job to slotting. Lets say you want a 3mm slot, you'd use a 2mm tool and cut a 'tricoyodal' toolpath. You need a
    machine capable of high accelerations but is a good method of cutting a slot without a tight slot from which you have to evacuate chips.

    Craig



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    Default Re: Bit breaking and melting on milling

    WAY to high on the RPMS. You need to do some testing on the edges of aluminum to find a good balance for nice big chips which help get the heat out. As another said you can get a mister too. They are not too expensive.



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Bit breaking and melting on milling

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Bit breaking and melting on milling