Ebay Chinese Routers (CNC3040) - anyone purchased one of these machines recently?

[Jonathan]

do you have any alternative suggestion bearing in mind that £700 is all we have available?

I doubt it, the £700 limit is unfortunately too low unless you make it yourself.

This, for example, would be a good start:
(Not suggesting you should buy any of these parts yet, clearly you will want to first draw the whole machine to work out exact sizes)

http://www.ebay.co.uk/itm/3-SBR20-se...#ht_942wt_1087

That's a bit bigger than you're after however you can ask the seller for different lengths if that's a problem.
Add to that 3Nm stepper motors, drivers, breakout board, PSU, wire and 50V drivers and you'll easily get good feedrates fort around £210 in total as long as you don't get all that from England. Once you add on the price of a spindle and the frame it's over £700 and probably more like £1000. However since the machine has supported rails, ballscrews and a good control system so it will be out perform the CNC3040 by much more than that price difference implies. Plus from making the machine yourself you will learn, as I did, a lot more about how it works and be able to troubleshoot it much more easily.

I have cut acrylic on a similarly small low power machine and obtained a good finish. So long as the chipload is correct and the depth of cut is not so high as to cause significant tool deflection the finish should be good.

One thing that helps here is single flute tools:

http://www.ebay.co.uk/itm/5x-157-Car...ht_2855wt_1037

(That's just the first one I found, shop around for the cheapest and get the smallest flute length you can safely use as that reduces the tool deflection, resulting in a better finish.)

Since the feedrate is proportional to the number of flutes on the tool, the rpm, diameter and chipload, if you use a single flute tool the feedrate is proportionately lower than with 2 or more flutes. Similarly if the rpm is low, which it has to be as your spindle on that machine says it only goes up to 9500rpm the feedrate is also low. The relatevely low rpm is not so bad as the surface speed is lower, causing the cutter to heat less reducing the chance of melting the acrylic. Chipload is the 'width' of the chips, or put another way the distance the tool moves per revolution divided by the number of teeth.

According to Gwizard feedrate calculator (google it) the chipload for a single flute carbide tool in acrylic is about 0.1mm for 6mm tool and 0.06mm for a 3mm tool when limited to 9500rpm. That gives 600mm/min for 3mm or 1000mm/min for a 6mm tool. If you got a better spindle and used a 6mm tool at the reccomended rpm (12700rpm) the feedrate is 1400mm/min, still well within the 2500mm/min reccomended in the eBay listing, assuming that rating can be trusted!

So in conclusion I'm confident the machine is capable of cutting acrylic with a good finish, but still I would not let that persuade you the machine will do you need. You will have to take shallow cuts, so the overall time to cut a given thickness will be greater than for a more rigid machine. If you really want a good finish on acrylic then get a laser cutter, but that'll cost a teensy bit more than £700 and is not as versatile! Alternatively look into other ways of finishing, such as buffing the edges to get an optically clear finish.

It would cut aluminium, but nowhere near fast enough for it to be worthwhile so it's hardly worth mentioning. Similarly I cut titanium sheet on the router at school (roland camm PNC2300A, probably weaker than the CNC3040) and yes it worked, but prematurely wore out the machine and took forever! It was worth it as a one off as I really wanted the part but it would be foolish to try it regularly.

Saying 'the machine can cut material x' isn't saying much, whatever the material is unless you know how fast it can cut it (i.e. material removal rate, often measured in cm^3/min).