[mercaytor]

I will be starting work soon on my 1st CNC mill, and I'm in the design stage now.

My first question is as follows:

Are rails (for X/Y, possibly Z) made from square tubing (1"x1", either steel or aluminum) practical? I have yet to see much information or past builds using this method, so I'm assuming there's a reason.

Any input for a CNC-newb? My intention is for this first build to be smaller, work area of about 18"x18", definitely engraving and PCB isolation routing, and then eventually a 3D printer extruder. I already have a set of NEMA17 steppers, so I know they are small but again for my first one, I need to show my wife I can actually get something built before I spend a lot of money on a larger-scale version!

Here's what I'd mocked up already in AutoCad 2012...

[RicknBeachcrest]

Spend a couple of months reading this forum. There is a wealth of information here, just for the reading. Everyone here who has built a machine has had to deal with the problems your running into.

Just for reference, I am building a machine that will have a work area of about 18" square and I have got about $3500(probably more if you were to add up all the small stuff) into it so far. But also I am using 8020 for the frame, linear bearings, and ball screws. These things get expensive fast.

With the time and money sunk into a machine, it is nice to know that it has a likely hood of working when your finished. Put some time into the design and have things figured out all the way to the end. Try and find a design that someone has had success with and pattern your after theirs.

Good luck
Rick

[mercaytor]

Thanks, yes I've been watching the forum for a couple years now and ready to jump. Has any one had experience with using diy rails made from 1"square steel and skate bearings? Am I asking for trouble with alignment and wear?

I'm looking at this option because it's what I have readily available plus the Mig welder to work with it. And since I'm in rural Canada, shipping kills me on more traditional or ready-made CNC products. Mc Master Carr won't ship to new Canadian customers anymore!

[arizonavideo]

You didn't say how much power the Nema 17 are. Most are too weak to do a good job with a router.

I did just try out a new set of 64 Oz Nema 17's and they just might be big enough. I don't think the smaller 32 Oz steppers will do well.

The 3d printers most all run belts and most printing is done faster than most milling ops. The fast 1 or 2 TPI screws might do good for both but you might want to use slightly larger steppers like 125 Oz or so.

What driver do you have? How much do you have to spend?

For long runs the roller bearing do save money but you can still get deals on THK style rails sometimes. I just got two new 18" 12mm for $41 shipped.

For the Z you should do yourself a favor and buy 2 liner rails. It will save time and money. The short ones are often cheep.

The 1" steel is weak but could work. It does no good having the two main rails 1" apart. They just flex more. I would tack three together or glue them. Small tacks only or it will warp big time.

For screws look at Roton and dumpsterCNC - anti-backlash solutions for home and industrial linear motion

Sometimes nice fast ball screws show up on ebay so keep a eye out.

[DareBee]

I am sure there is a way to make it work.
IMO 1" HSS is very flimsy. We almost always use 1.25 instead, night and day difference in strength.
OTOH it is difficult to guess your scale in your model and if only a couple ft long, 1" should make a decent homebrew router

[harryn]

The big challenge of using a structural element (the tube) as the rail is frankly - what you can buy. When you actually go out and try to buy square tube that is straight and square, it is really hard to find. In addition, building the frame to the needed precision - around 0.001 - with no post build adjustment capability, is beyond most people.

Knowing that your application is pcb milling is very useful, as that is a very demanding application which requires better than normal results. Unlike cutting wood, you don't have the option to "sand out the edges" after cutting. This means that your machine will need to be very stiff compared to wood carving.

There is a special subsection of the forum for people making PCBs, and you will find many have moved to using fixed gantry / moving table designs to optimize the stiffness, even though it makes the machine larger.

The other option is to design with raised side rails like this one: http://www.cnczone.com/forums/cnc_wo...lp_needed.html

The advantage is that it gets rid of the gantry uprights (a major potential source of flex) at the downside of somewhat harder part loading.

If you like, it is not difficult to do a quck estimate of some of the parts of your system to see if they are stiff enough for the application, but be thinking in terms of 1/4 inch wall thickness steel tube for your application and perhaps 2 x 2 inch.

You might consider to use rails such as the pbc.com IVT style V bearing setup if you don't want to use profile rail. Profile rail is nice, but the mounting requires extreme precision.

The motors needed are going to be in the 300 - 400 oz-in range. That probably sounds crazy until you look at the data sheets and find out that stepper motor torque is the inverse of the rpm and they drop off really fast. At operating speed, you will only have 100 oz in or so.

[mercaytor]

Wow, you his are awesome! This is exactly the type of feedback I wanted and needed. I'm gonna rethink my plans and explore those links before I buy anymore material.thank you!

Warren