Puzzle with chip weld, help!


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Thread: Puzzle with chip weld, help!

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    Unhappy Puzzle with chip weld, help!

    Scratching my 50 y/o head once again after I thought I had figured it out.

    I need to CNC several parts from 1/4 inch 6061 aluminum. After days of experimentation and a bunch of broken bits, I thought I got it (with help from folks on this forum)
    My ProBotix Nebula table router (which I know perfectly well is not a metalworking CNC) was churning out parts cleanly one after another.

    Then, on part #8 it all went haywire. Same gcode, same exact sheet of aluminum, same everyhing! But the part started with a bad vibration and a broken bit.
    OK, replaced the bit (same model: Yonoco 1/8inch single flute carbide spiral O-cut) - same problem. Chip weld, terrible vibration sound, HEAPS of cotton-candy-like shavings as the bit gets deeper. None of which was observed before.

    What's going on, any clues?!

    I cant think of any variable that has changed between the parts. I've heard somewhere that bearings on routers go bad, could that be it? The router has worked for 10 hours combined - max at the lowest RPM.

    A little background, I used to use DWP611 router, but it had the minimum RPM of 16,000. I had to push it too fast to have an acceptable chipload, but then the machine was not rigid enough to handle it. So, I adapted Makita, which has the minimum RPM of 10,000 ... Still high for aluminum on my CNC, but it was working very well until now, and I was happy.

    Taking 0.5mm deep passes at 500 mm/min speed, conventional milling (again, it worked beautifully for many sessions ... and now suddenly this).Puzzle with chip weld, help!-cnc-issue-jpg

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    Default Re: Puzzle with chip weld, help!

    You didn't mention anything about cooling or chip removal. When I mill aluminum on my CNC router with a water cooled spindle, the rpm's for an 1/8" bit are 22000 and I use continuous compressed air to cool the bit and remove the chips. Without the compressed air, the bits are destroyed in a short time.



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    Default Re: Puzzle with chip weld, help!

    Yes, thanks for brining up. There is a paintbrush - turned into a blower that constantly blows air at the bit. Its not a super high PSE, but still quite respectabe, fast flow. I constnalty squirt WD 40 on the work piece.

    All that is unchanged between "before" and "now" - same exact air flow, same WD 40 - only now it welds, vibrates, and before it was smooth as butter. Even the work piece is attached the same way (in fact tis the same piece of 1/4" aluminum) - The only variable that's changed is time, really between half a dozen perfect cuts, and now this mess ...



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    Member awerby's Avatar
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    Default Re: Puzzle with chip weld, help!

    It could be the bearings on your trim router - these things really weren't designed to be CNC spindles. It could also be a mechanical problem in the machine somewhere, like the linear bearings going out, or something coming loose. Have you checked the attachment of the nuts?

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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    Default Re: Puzzle with chip weld, help!

    Pardon my ignorance, Andrew, what is the "Attachment of the nuts"? (I am laughing as I type this)



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    Default Re: Puzzle with chip weld, help!

    OK, I give up ... I'll call it "spindle bearings went bad between the parts" and order another spindle ... Maybe this 2-1/4 HP one: https://www.amazon.com/gp/product/B0...=ATVPDKIKX0DER ?

    I recall that when I did pocketing, I used spiraling / down programming, and event when the spindle was new - it was making a not-so-healthy sound and the whole table was vibrating as the bit went down AND sideways at the same time. Maybe I should just use a conventional pocketing (using RhinoCAM) - this way the bit will plunge to the cut depth first, then start moving sideways ... Maybe that's what killed the bearings ... Just a hypothesis.



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    Default Re: Puzzle with chip weld, help!

    You would be better off with a water cooled spindle and a vfd than a router.



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    Default Re: Puzzle with chip weld, help!

    It could be the position on the table. The good part was closer to the left side of the machine. A router will have the most play or flex at the center of gantry travel. For that reason, you would probably want to cut closer to the edge of the work envelop. Also, you really want to get a real chip rather than stringy looking cotton candy.
    That means you are rubbing. Rubbing equals friction. Friction equals heat. Heat equals chip welding.
    Another tip is to use the largest bit possible. Say up to 1/4". It will be stiffer and remove more material faster. Get the chip load in the right ballpark for feed and speed and the heat issue goes away.

    Routers will run hot too, especially at the lower RPM. The heat from it's electric motor combined with the tool heat make it very hard to keep cool enough to cut aluminum correctly.

    Lee


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Puzzle with chip weld, help!

Puzzle with chip weld, help!