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TT901
27-02-2017, 01:41 PM
Hi

I'm looking at getting a Chinese 3020T (or possibly a 4030) CNC Router for general hobby use, school projects, etc. The main use would be for routing single and double sided PCBs, but I would also like to be able to machine Aluminium and Carbon Fibre sheet.
My question is are these machines generally up to the job? What tools are best for Carbon Fibre and which tools for aluminium? What have you found to work well?
I used to work on control systems for million + machines, and I appreciate this is the extreme other end of the scale. I don't want to waste money on something that isn't-up-to-much and isn't going to be any good for what I want it for, but with limited workshop space (and money) a full cnc mill is well out of reach.

Your thoughts, please.....

Thanks

Zeeflyboy
27-02-2017, 08:52 PM
Problem is that 3020/3040/6040 etc are just generic terms and machines do vary quite a lot in actual details of what is fitted, what electronics are there and so on.

In terms of mechanics, they will do a fine job on PCBs and depending on the machine a fairly decent job on composites like FR4/G10 (which is PCB stuff anyway) and CF.

Unsupported rail type (round rails, typically completely unsupported on gantry) will generally have a stab at light aluminium machining, but results will be variable at best. Proper profile supported rail types will do a fairly decent job with light machining once you've got the hang of what you're doing.

Your experience on control systems will probably be quite useful because most machines are not generally up to snuff on the electronics front, although they are generally a bit better than they used to be imo. Be prepared to do a bit of work in grounding everything properly and personally I think a shielded spindle cable at the least is a must have...

CF is a bitch, it wears out normal tools quite quickly. The best tool i've found are coated fishtail type carbide burrs (http://www.precisebits.com/products/carbidebits/fdrouter.asp) - on the cheaper end you have the uncoated ones, a little more money but worth it for added durability imo are the ZrN coated ones. My personal faves however are the diamond coated ones (http://www.bzt-cnc.de/en/shop/drilling-and-milling-tools/59-diamantverzahnt/300-diamantverzahnt-diamant-beschichtet) but they end up a little spendy perhaps.

There is a lot to be said for making a water tray and cutting CF underwater - it improves the cut quality, keeps your tool alive for longer and traps all the nasty fibres and dust far more effectively than any vac filtration system. To that end if CF is on your to-do list I would definitely recommend you avoid an air cooled spindle and go with water cooled instead - you won't get forced air trying to disturb your water tray.

As for alu, with the high speed spindles and low rigidity of the generic chinese machines you really need either 2 flute or single flute in my experience as you can't push fast enough to stop a 3 or 4 flute from rubbing, fairly light cuts but not too slow is the key to getting passable results out of them. If you intend to do much in alu I would personally say you really need to be looking at a machine with profile rails at a minimum or you'll just find yourself wanting to upgrade to a new machine after a while (exactly what happened to me!).

There is of course the option to build your own since you have some machine experience already.

TT901
27-02-2017, 09:22 PM
Thanks for the reply Zeeflyboy.

Some great info, which is much appreciated and also lots to think about there.

I have been considering a DIY machine but the main issue I have there is that I don't have access machinery to produce the parts. A bit of a chicken-and-egg situation. However I do use Solidworks at work so designing parts isn't an issue. Are there any worthwhile, relatively simple DIY builds that you are aware of?

Zeeflyboy
27-02-2017, 09:29 PM
There's always the option to throw out an RFQ for bits you need machined for you on here. I haven't personally used it yet so no idea what the sort of cost people charge is but I would guess you would get some pretty reasonable quotes.

There are no shortage of DIY builds out there, you could browse the diy machines on here for inspiration - there are some amazing machines guys have built on relatively modest budgets.

If you do decide to go the DIY route then a bit of research on here will give you enough info to get started. Get a design whipped up and then ask for critique on here.

Clive S
27-02-2017, 10:51 PM
but the main issue I have there is that I don't have access machinery to produce the parts. A bit of a chicken-and-egg situation.How about taking a leaf out of Joe's build and you will see what can be done:-


https://www.youtube.com/watch?v=pZo2LVQA9UI&list=PL1FIADAKba_uTgFU5qqS3i705fuSogBXT

TT901
03-03-2017, 02:42 PM
Thanks. Some nice ideas there. Perhaps a little bigger than I had in mind though.

A few of questions:

I appreciate that there is no definitive answer and that part quality, precision & tolerance is down to the choice of components. However taking into account my original requirements of being able to machine PCBs, profile sheet aluminium, and carbon fibre sheet on a machine with a 200mx300mm bed what sort of spec stepper motor (NEMA 23?), spindle and slide rails should I be looking at?

Would I be better off with a 12mm supported round rail, something like SBR12 or a 15 'square' rail with slide blocks such as MGN15 ?

Thanks

Zeeflyboy
03-03-2017, 03:20 PM
MGN is miniature, more suited really to lighter duty machines like 3D printers, laser etc

You want HG really, and HGH20 is a very common size which will be more than sufficient for your needs but easier to grease than HGH15 (15mm).

HGH20 is common on places like aliexpress and available fairly cheap, won't cost much different to MGN15.

As to that vs 12mm supported rail, well that's really up to you. HGH20 will be superior, but it will cost a little more. You have to do a cost benefit analysis on that yourself really... so to answer your question, your machine would definitely be better off with HGH20, but your wallet will be worse off.

Definitely go nema23, nema17's are good for 3D printers but don't have the power to do any decent milling imo and you'll end up chasing your tail and ruining stock with missed steps from motors that aren't up to the job.

Spindle wise, either a 1.5kw or 2kw water cooled spindle will do a good job and you can always move it across to a better/bigger machine later on if you want to. Given your relatively modest requirements there is the option to go cheap on this and use a dremel type router, but I find this to be a false economy as I went through 2 of them in short time on my first machine (and that was proxxon which supposedly had better bearings than dremel) before deciding it was pointless.