Tips regarding DIY 3 axis CNC Mill

[Spille]

Hello everybody!

I found my way here a couple of days ago when searching the web for good places to find info about how to make your own CNC mill.. So I thought I would make a post here to get as much help from you guys as I possibly can! Im working as a design engineer so I know my way around machines alittle atleast..

So what is it I want to make? The goal is a 3 axis cnc mill that can handle aluminum, copper, plastics and wood in sizes up to 600*400*150mm. Could it be possible to have a repetable precision of something like 0,05-0,1mm?

Any special hardware you guys recommend? Im thinking stepper motors, ball screws and linear slides..

The part Im most worried about is the electronics.. What functions are needed or very good to have?

I would be very greatful for any tips at all!

//Kristofer

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[awerby]

Most of the people here are building routers, not mills. Routers are good for cutting wood and plastics, but not metals, since they lack the requisite rigidity to do a good job at it. And they don't have the precision you're looking for either. Mills of the size you're talking about tend to be made from cast iron and weigh tons. The mass helps damp vibrations that otherwise would produce a poor cut and break cutters.

My suggestion would be to find a used CNC knee mill with a bad or obsolete control and retrofit it with a new PC-based control system. Mills like this can sometimes be found quite cheaply, as the shops that own them need the floorspace and will often let them go for something close to their value as scrap metal. If you find something like this, it can have good ballscrews and other parts already mounted and ready to run, making it a lot easier than building something from scratch (even if you are set up to cast iron).

As for what electronic control system to use, wait until you've purchased the retrofit candidate to get all that. It may be that the motors it comes with can be re-used, which will save some money. In any case, it helps to know the loads you need to push around. If you're putting together a servo system, then you may need different equipment and software than if you're building a stepper system.

Andrew Werby
www.computersculpture.com

[Spille]

Hello Andrew!

Just to clarify, the sizes Im talking about is just how far reach the machine need.. Im not going to put that huge alu blocks in it! But maybe wood..
Correct me if Im wrong, but most routers can handle aluminum pretty good? I was thinking of having a cast iron surface block as base and then build the whole thing on top of that, should be able to do the trick?

[awerby]

Sorry Spille, but most routers handle aluminum pretty badly. They're really best at wood and other soft materials that don't need to be cut with extreme precision. A cast iron surface block is a nice thing to have in your shop, but I don't see how it would work as the base of a router. Your best chance of building a router that will handle aluminum at all is to use a moving-table/fixed-bridge design. But moving a table that's a large solid lump of cast iron isn't going to be easy - its inertia would work against you and cause lost steps on direction changes unless you fitted it with very powerful motors, like knee mills use. You generally want a spoilboard under your workpiece, so you can have a sacrificial surface to cut into or attach things to, but mounting that onto your surface plate would be difficult. I'd suggest looking at a wide range of designs to see what other people have done, and what sort of precision they achieve in which materials.

Andrew Werby
www.computersculpture.com

[Spille]

Ah okey.. The idea I had with the surface block was to have it as a base for the entire machine. Maybe something like these in the size 700x500mm, and have a fixed bridge bolted down at each end of the plate with the Y-axis mounted in between. And have the X and Z axis on the bridge.

And was thinking a T-slot alu plate,like this, as a moving table for easier fixation. For the fixed bridge it could be good to use angle plates as "legs" and have alu profiles in between to mount the X and Z axis. Is this a bad idea?

I'll see if I can make some quick CAD model of it this weekend perhaps

[JPX2000]

Not to steal your thread, Kristofer, but I'm in the same boat here. I like what Andrew had to say. It helps, but I still don't really have a clue what will work for me. Woods and plastics (12"W X 16"L X 5"H max part size, but thickness 1/2" and under mostly), and aluminum (1/4" max thickness, with some 3D contours) are what I'll be machining. Not a lot of room and not a big budget right now (maybe $1500). The routers I've seen are OK for PCB work and craft stuff like carvings and such. I would like something that has some precision to it. And yep, I've been Googling, lurking, and reading everything out there on this subject, but nobody mentions 3D capabilities unless you get into a software site. Then they neglect to mention materials, feeds, speeds, etc.

Advice of any kind would be appreciated.

Joe

[nicjac]

If I may jump into this "pool"...I have designed this CNC Desktop Mill. I know there will be a lot of if's and why's on it but my idea was to build a small machine that I can use to cut small parts and gears from brass for clock making. Most of the end-mill cutters that I will be using will be 1mm & 2mm diameter. The machine have a table size 500x200, the frame is made from 152x76 steel channel and will be cast full of epoxy granite something similar to help dampen any vibrations.

It can be downloaded from GrabCAD (https://grabcad.com/library/desktop-...ling-machine-1)

Nico

[hanermo]

I built a mill with moving table, in steel.
A tiny nema 23 stepper moves the 300 kg table effortlessly, at 1:3.
Table is 1600 mm wide, 500 mm deep, and 60 mm thick on ribs.
THK 25 mm slides.

Multiple preloads.

[awerby]

That looks like a nice design, Nicjac, but it's manual so far. Have you thought about the CNC components yet? Is that tiny little motor some high-speed brushless thing with an incredible amount of torque for its size? Also, maybe it's an optical illusion, but it looks like the Z axis is at the bottom of its stroke, but the spindle end is nowhere near the table. If you're really using 1mm tools, they usually don't have that much reach.

[nicjac]

No...I do have handwheels on also but on the opposite side of the table, the back of the frame and on the top the stepper motors are located.
It is sometimes quicker to do a small modification to part manually, rather that to try and set it up accurately enough to do a cnc operation.
I'm using 12mm x 3 pitch trapezium thread for all the lead screw. I did plan for ball screws but they are expensive and I don't think necessary for such a small table.