On Tuesday 24 May 2016 10:14:17 Todd Zuercher wrote: > Anyone know the root cause of tool marks like this? Or better yet how > to prevent them? The lines are not in a straight line or consistent > angle, in fact there are places on this piece where they wave up and > down. > > The tool is a 1/4inch solid carbide down spiral, cutting at 200ipm > turning 17,000rpm cutting 1/2" MDF in a single pass. In the picture > you can see about a half inch long section of the cut where the cut is > nice and smooth, this is where the ramp in point is (start of the > cut). The machine is a very large (5ftx10ft) moving table fixed bridge > commercial router (Komo) with a 14KW spindle and HSK63F tooling. > > It does kind of give the piece a sort of simulated wood grain look. > I've playing with the amount of tool sticking out of the collet can > make it better or worse, finding the sweet spot is a bit of trial and > error, and 0.050 can make a big difference. You can hear the > difference in the sound when you get it right, the cut is very quiet. > If it gets bad enough the tool will snap. Also playing with the RPM > can somtimes make it better. > > It is hard to believe that a carbide tool or collet could flex that > much, but something sure seems to be vibrating.
At 200 IPM, even at 17K RPM's two questions come to mind, first being tool breakage, related to debris removal to keep the bits cutting flutes clean. That looks like the usual 3/4" MDF that we would buy here, but yours is likely sized metric, say 19mm thick. Is this a straight cut thru the MDF, or a one side of the tool only edge trim? In either case tool breakage would be encouraged by in-sufficient debris vacuuming. When I was cutting out the bits of ebony for the blanket chests, truly microscopic compared to this, in ebony nominally .275" thick, I had to rig a vacuum right beside a .03125" tool to keep the groove clean ahead of the tools motion, and do loops only about .035" of depth increment in order to stop breakage of the tool, which had a .250" length of cutting edge. In other words, I had to keep the flutes from packing full of debris. If I saw debris buildup in the slot, the tool would break in the next quarter inch of travel, max. But with the vacuum, I cut out the last 140 of them with the same tool. As for the pattern, vibration of the gantry crossbar, a resonance between the pulse of the cutting flute and the RPM's seems like a good point to check, you said changing the RPM's helped or changed the pattern, as would I'd expect changing both the number of flutes, and the spiral angle, somewhere it seems like there ought to be a sweet spot. What does bolting another 20 lbs of something to the back face of the crossbar do to the pattern? That would change the resonant frequency. Is that crossbar sealed? In which case I might try filling it with play sand, about 4/5ths full and sealing the ends. The theory being that the play sand would absorb and deaden the vibration until it was down to face powder from wear. That should be several years to achieve. Endways vibration of the gantry risers might also be involved, in which case a box of sand, 15 lbs or so in a 20 lb box, attached to the outside face of the risers might dampen it. But I'd start with a good vacuuming setup to keep the trench clean, and a different tool bit, even a 4 flute or a 3 flute if using 2's now. Positioning a cheap webcam, separately from the machine so there is no chance of the camera vibrating with the machine, where it can watch something on top of the crossbar, might show you more precisely which direction it is vibrating in as the image focus would be blurred and elongated in the direction of the the major vibration. I would do that if changing the tools angles and flutes fails to reduce it sufficiently. I made a sort of a cyclone separator out of common PCV plumbing that caught 99% of the debris in a 5 gallon bucket sitting beside the $23 vacuum with its costly hepa filter. Easy enough to make and nearly as efficient as an Oneida Dust Deputy at nearly a hundred dollar bill. There are some pix of it on my web page below. The end of the central pipe connected to the vacuum, is placed about 2" below the angled entrance pipe which is plumbed to the pickup point, carried by the head as it moves up and down. The separating swirl being generated by the angled entry. And I control it with an M8(on) or M9(off) in my gcode scribbles. That gates a 500 hz pulse, and a charge pump does the switching to drive a 10 amp relay. I hope something here helps TomP. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Mobile security can be enabling, not merely restricting. Employees who bring their own devices (BYOD) to work are irked by the imposition of MDM restrictions. Mobile Device Manager Plus allows you to control only the apps on BYO-devices by containerizing them, leaving personal data untouched! https://ad.doubleclick.net/ddm/clk/304595813;131938128;j _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
