Needs Advice - building a small desktop CNC rigid enough to handle metal

Hi guys,

I'm interested to machine small parts from aluminium and steel (precision parts for model making).

After understanding (thanks to fellow forum members) that the chinese made budget CNC machines are not rigid enough for metal working, I understood that i'll have to build one my own.

I'm interested in building a small (desktop) 3 axis CNC machine that will be stiff enough to handle metals.
The key is that it has to be build small enough to stand on a desktop, but build from stiff parts to make it rigid to handle small metal parts machining (small runs, not mass production).
The working area I need from the machine is A4 paper sized working area (this might give you a hint about the size of cnc i'm looking to build)

I've seen on eBay many CNC machine kit parts being sold, But i'm not sure which are good for my build.

I know the best thing is to build the machine frame, rails etc from stainless steel or heavy duty aluminium.
I've heard I'll need ballscrews etc, all rigid and good quality.

I guess that I first need to build and complete the machine body (inc. the 3 axis) and after that fit it with stepper motors, spindle, electronics, psu, etc..

Could anyone list me the basic "shopping list" I need to get for assembling the basic machine body and 3 axis ?

Also, what type of material should specific parts of the machine be build from ?

How do tell between a heavy duty ballscrew and a lower-end cheap ballscrew ?

Do I have to build the machine from from stainless steel as well ? or rigid aluminium could do ?

Any help will be so much appreciated !

You don't have to use stainless, but regular steel would probably be better than aluminum for any parts where its weight's not going to work against you, and it's cheaper too. Most people here are building routers from scratch, but mills are another story; I don't think there are any parts kits to build machines for milling steel. Generally it's easier to convert an existing mill to CNC than to try building one, although if you're into iron casting it might be a good project for you. Often you can get an older CNC mill with good iron but a bad controller for somewhere around its scrap value.You might also look into epoxy-granite frames, which can be quite rigid. There's a huge thread on them here if you look for it.

I don't think you can make linear rails and trucks that would be worth using, unless you already have access to precision milling and grinding equipment.

There are lots of different kinds of ballscrews on the market. At the low end, they're good for opening garage doors and not much else. At the high end, precision-ground screws can cost as much as a whole new milling machine. For a small machine, you don't really need ballscrews at all; Acme screws will be a lot more accurate than ballscrews of the same price.

Look in the Links section of my site for sources of the various bits and pieces you'll need to build or retrofit a CNC mill: ComputerSculpture.com ? External Links

First let me say that if you don't have access to a decent well equipped shop you will better off buying a Chinese machine and doing a conversion. Building a machine from the ground up is not a trivial task. You need a lot of quipment or a willingness to put in a lot of hours doing hand work. That being said even the Chinese mills will need hand work and tuning.

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Originally Posted by dvirb

Hi guys,

I'm interested to machine small parts from aluminium and steel (precision parts for model making).

After understanding (thanks to fellow forum members) that the chinese made budget CNC machines are not rigid enough for metal working, I understood that i'll have to build one my own.

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that depends upon what you mean by budget CNC machine. There are imported mill (not routers) that might do what you need done if something in the $7-$10000 range is OK.

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I'm interested in building a small (desktop) 3 axis CNC machine that will be stiff enough to handle metals.

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It can be done however to fabricate one takes a lot of time, equipment and skill. Depending upon your needs and construction methods the machine itself could weigh in a several hundred pounds.

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The key is that it has to be build small enough to stand on a desktop, but build from stiff parts to make it rigid to handle small metal parts machining (small runs, not mass production).

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can the desk support several hundred pounds? Once you go beyond aluminum the stiffness or rigidity requirements for the mill go up dramatically. Of course if you are working with real small cutters this isn't a severe problem.

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The working area I need from the machine is A4 paper sized working area (this might give you a hint about the size of cnc i'm looking to build)

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Actually I have no idea what A4 is. Millimeters or inches work much better here. If that is close to an 8x10 sheet of paper then you may have issues as that is fairly wide for a desktop bed mill.

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I've seen on eBay many CNC machine kit parts being sold, But i'm not sure which are good for my build.

I know the best thing is to build the machine frame, rails etc from stainless steel or heavy duty aluminium.
I've heard I'll need ballscrews etc, all rigid and good quality.

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Honestly I think you need to step back a bit and bone up on the subject. Find a machine shop to introduce you to a small CNC machine and then a small manual mill like a Bridgeport clone. In a machine shop a Bridgeport is considered a light mill.

As for your machine the only realistic choices are steel or cast iron. The steel would likely need filling. Again it does depend upon what you are doing but just surfacing that A4 sheet would require a large cutter or possibly a fly cutter.

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I guess that I first need to build and complete the machine body (inc. the 3 axis) and after that fit it with stepper motors, spindle, electronics, psu, etc..

Could anyone list me the basic "shopping list" I need to get for assembling the basic machine body and 3 axis ?

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Seriously don't. Don't try to build a machine from scratch without a decent shop or access to one. Instead buy a small Chinese mill and think of it as a casting set. Then do a conversion. This will eliminate a massive amount of work for you. There are many build threads in these pages. The big problem will be getting coverage on that A4 sheet. The problem is the Y axis travels on most of the mills suitable for a desktop are too short to cover A4. So careful selection is needed or you need to re figure your working area.

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Also, what type of material should specific parts of the machine be build from ?

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in a perfect world the structure would be cast iron. You can do steel but it often needs damping.

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How do tell between a heavy duty ballscrew and a lower-end cheap ballscrew ?

Do I have to build the machine from from stainless steel as well ? or rigid aluminium could do ?

Any help will be so much appreciated !

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If you go the stainless route I want to see pictures. ������ You don't need to use stainless, steel will do just fine.

Thanks for the input and all the tips and info :)

It's correct - even though I do have access to a basic workshop I am pretty sure I don't have all the machinery required to build a machine for the ground up (maybe only by starting from. A "kit" ?) and that's one of the reason why I'm trying to find a solution to make a Chinese cnc stiffer enough (so I would buy a stock machine and make the rigidity upgrades to it). I remind that this machine is not for a commercial use for machining hundreds of parts per month, more like a hobby machine to make a few dozens of parts each month.

In case I get a Chinese machine as a base, what should I upgrade? Motors? Rails? Bearings? Reinforce the frame and axis?

Many thanks!

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Originally Posted by dvirb

In case I get a Chinese machine as a base, what should I upgrade? Motors? Rails? Bearings? Reinforce the frame and axis?

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The entire machine.
These low cost chinese machines are lightweight routers for cutting wood, and there's nothing you can do to make then rigid and strong enough to cut steel. If you want to cut steel, you need a mill designed for cutting steel. Nothing less will work.

The problem I see is your work envelope. While most benchtop mills can handle the 12" or so X, not many can do the 8"+ that you want for the Y. If you can relax that requirement some, there are several candidates.

A Taig mill is small and can cut steel albeit slowly. You can get a CNC ready version and DIY your controller or buy a ready to run controller box/motor kit from a couple of different vendors ( Soigeneris, deepgroove1 .....). It is a good machine to cut your teeth on and it retains is resale fairly well.

For conversion, a Grizzly G0704 is probably the most popular right now. There are many threads here covering the conversion. I suggest you read a few to see what it entails. As well some vendors sell kits to make life easier for you.

Good luck!
bob

You might also look at the ACT Desktop Machining Center III. It has a working area about 12" x 8" and it can cut steel, although it won't do very heavy cuts. It's a fairly heavy machine for its size at over 200 lbs, and it uses ball screws and square profile linear rails. It comes ready to run (even the computer is included) so you can start making your parts right away, rather than get bogged down in a retrofitting process.

Buying a mill as suggested is the only way to go if you want to routinely do anything harder than aluminium. You need the power, mass and rigidity of a small mill, and then you can cnc it with a kit off Ebay. You'll find this avenue far easier, and a much more realistic target than building a machine from scratch, which will probably till the 22nd of never, and end up costing more than a small car. Check out the hoss2006 threads on his conversions here, loads of really useful advice there and he also has plans for sale cheap if you want to make your own conversion kit once you have a mill.

cheers, Ian