Cheap CNC router to use with 3D printer toolchain

I learned to use a Bridgeport Series 1 CNC mill back in the late 1970s, and have done a lot with such mills, but I don't have one now. I do own a MakerGear M2 3D printer, which has been a joy to work with, but now I'm looking for a small and cheap CNC router/mill/engraver that I can use to make mostly wooden parts to integrate with 3D printed stuff made on the M2. The M2 build area is 200x200x250mm, so I'm looking for at least a 200x200mm bed workspace and the ability to machine hardwood at least 3/4" thick. Most of my designs are done with OpenSCAD, and I would like to be able to render select components using a CNC without having to tweak the design files by hand; I'm willing to write code that would extract slices from OpenSCAD files and render G codes if no existing tools can do that. Alternatively, OpenSCAD can generate STL files, which I'd want to generate G code from.

So, the question is how feasible would it be to do this using LinuxCNC to drive a cheap CNC mill like, for example, the 3020 router/engraver? Suggestions?

I'd really like to keep cost under $800, and the 3020 seems to be as low as $500 or so....

Thanks.

That is the sort of thing Linuxcnc is probably used for the most.

I didn't think LinuxCNC could take OpenSCAD or STL files into G code, but that is definitely part of the toolchain I want, so I was hoping to hear some "I use this for that" type comments.... PyCAM looks interesting; I'm downloading the .deb now. I'll play with that and anything else open source, but I suspect I'll end-up writing my own G code toolpath generator and make it freely available. I built my first 3D-model-to-CNC-toolpath compiler back in 1977-1979 to run on a NorthStar Horizon generating code for a Bridgeport Series 1, so if I could make it work under those constraints, I doubt I'll have too much trouble making one work now.

My primary concern is actually the lack of limit switches, etc., on the 3020 in particular. Is this asking for trouble? How reliable is LinuxCNC with an open-loop system like the 3020? I assume I'd be setting home position by jogging to the desired spot?

Is there a different comparably cheap system I should check into?

BTW, I'm also guessing that for 3/4" wood and the tiny tools being used, I can probably get away with having a sacrificial 1/8"-1/4" board fixed to the bed and simply use 3M double-sided tape to secure most parts for machining (a trick that used to work for many wood & plastic parts even on real CNCs). I'm thinking I might also 3D-print some custom dogs for the 3020 bed. Any other clamping issues I should know about?

Thanks again.

1. Overall part dimensions are usually good to about 0.1mm, but large flat pieces coming near the heated bed edges will often contract and slightly lift the corners as the print lower layers cool, resulting in up to 1mm or more warp in the bottom flatness of the part. Incidentally, because this warp happens during printing, dimensions near the top of the part are rarely affected by the warp -- the hot plastic gets forced to the right spot despite having a warp under it.


2. PLA (and other easily extrudable plastic) starts to soften at relatively low temperatures, so parts that have to hold shape while being subjected to heat (e.g., bearing surfaces subject to frictional heating) are problematic.

I'd highly recommend a vacuum table for milling wood and other soft items.

Are you talking about a vacuum clamping system or vacuum dust removal?

I'm very serious about hoping the 3M double-sided tape will suffice for clamping many pieces. Hey, it worked for smallish wood/plastic parts on an old Bridgeport Series 1... and that was using huge tools compared to what the bits for this CNC will nibble away.

I'm definitely thinking in terms of making an enclosure of some kind and having some dust removal mechanism, but haven't really thought it out yet. If I ever cut metal, I'm assuming I'll want coolant too, so I'm thinking maybe add a removable coolant collection tray and manually filter and reuse the coolant. It shouldn't be hard to design and 3D-print add-on parts to attach a shop vacuum or a bottle rigged for dripping coolant (for that matter, what coolant does one normally use with this class of machine?).

The 3020 I'm looking at is more like this model,

You really have to shop around on Ebay, dozens of people are selling the same Chinese stuff at hugely varying prices, some with huge P&P costs to bump the price up

In the UK, Portsmouth seems to be the centre of Chinese imports by Chinese living over here.
There are similar centres in US (CA) and Australia as well
They usually sell without P&P

For instance this 3040, which is cheaper than your 3020, but exactly the same build and even the picture is almost identical.

www.ebay.co.uk/itm/PROFESSIONAL-CNC-3040...&hash=item4d0a0601f1

If general 'rip-off Britain' criterea apply, I would be surprised if you could not get a 3040 for the same dollar price as the £ price here and have a bit more flexibility in terms of what you can machine

regards