[chillydk147]

Hello all, another newbie to cnc here, I'm currently doing some test runs on my cnc3020 using 4.5mm acrylic, I'm running with a feed rate of 700mmpm and spindle speed of 7000rpm, my overcut is set at 140%, I have it set to do multipasses of 0.4mm, I'm using 3.2mm Carbide Endmills, I'm pretty sure they are 2 flute, here's the url for them 10pcs 3 2mm Carbide End Mill Endmill Tungsten Steel Blade CNC PCB Engraving Bit | eBay , anyhow I've done a few test runs from 700mmpm to 1000mmpm, but the finish doesn't look too good, attached is a photo of what I'm getting. Any tips or suggestions would be great.

[rlockwood]

From the picture, those almost appear to be drills. Its hard to truly tell, but they don't appear to have a primary grind along the flutes, and mainly seem to list drilling in the features section. Further, i'd never purchase anything with "I am sure it the right thing you need now." in the title. Perhaps a detailed image of what you're actually using.

Assuming however that they are endmills, acrylic likes to melt, which will cause the finish you're experiencing. The cure is a heavier chipload, and a blast of air can help tremendously. You can achieve a heavier chipload either by increasing your feedrate, or decreasing your spindle speed.

Further, its not uncommon for a router type machine to simply have too high of a minimum rpm, and too little rigidity (either tool or machine) to achieve the desired feedrate necessary for the required chipload. This is why you'll often see single flute endmills used for cutting plastics, as it allows you to maximize your chipload for a given feedrate/spindle speed. They also tend to have excellent chip clearance, and a very sharp cutting edge.

[chillydk147]

So what you're saying is that a high rpm causes the end mill to heat more thus melting the smaller chips to the milled piece? Assuming that, a lower rpm would mean less heat, larger chips and less chance of chips melting to milled piece.

[integymachine]

Make sure your chips are getting away from the tool. Even if they are larger they can get stuck in flutes and "galling" the tool. This is when the previuosly removed material coates the cutting edge causing the tool to stop cuting and just rub the material Generating heat. Lower your rpm. Not you your feed. If that doesnt help. Use airblow or coolant. Try more depth cuts on the z. Lastly be sure your "climb milling" on your finish pass.


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[aarggh]

Are you using good dust extraction?

Because if not, the cutter will simply be re-cutting the ejected chips, which would also give the same results as too high rpm/too low feedrate.

cheers, Ian

[chillydk147]

Thanks guys for the suggestions, I've ordered some single flute endmills "1/8 and 1/16" which should arrive in 2 weeks, hopefully they will give me better results.