New machine build questions

[Nathan Flycuter]

Hello, If this is the wrong forum please tell me.
I have been thinking about building a small cnc mill with a table say
4x10". Would like to make parts out of steel, aluminumand plastic.
And hold a tolerance of .002".

Not sure if I should use box ways or liner bearings. Ball screws or ACME screws with anti backlash nuts.

Speed in cutting is not as important as keeping things with in budget
so for a cut of say .030" deep, what size stepper should I use.

Since I can cast aluminum I was thinking a of making some parts out
of alu. which I would fill with non-shrinking concrete. (Like the saddle
and table. Main frame would be steel, again filled with somthing heavy.)

I have too many questions to list, any one know of a place to look for
answers?
Thanks. -Nathan

[sansbury]

Do you want to build a mill to save money, or because you want to build a mill for the fun of it?

Also, besides the ability to cast aluminum, what sort of lathe and mill do you have (or have access to) now?

[Nathan Flycuter]

I just started working at a machine shop 3 months ago, and I think
they'll let met use some of the machinery. (Bridgeport, B-port cnc
retro-fit and Sharp lathe.) And at home I have an Atlas 10x18" lathe
(it works ok) and an AMMCO 7" shaper.

As for the machine it self, I want to build it for fun. If I just wanted one
then I would save up and just buy it. But I think I will really like being
able to design something to fit my own tastes.

I've been working on an xy table for a little 8" drill press so that I can drill
holes more accurately and maybe use up to a 1/4" end mill for some light
milling. (I put a quill lock on it and let the head slide up and down on the
column so that the table can sit right on the base for more stability.)
Would it be worth putting two steppers on the table (assuming light milling
is possible) and just seeing if I can pull of making a two axis machine?
Probly won't hold .002" but I can at lest see if I like messing with wires,
controle boards and software with out blowing lots of money and time.
-Nathan

[sansbury]

Yeah, sounds like a fun project. Access to a milling machine will make it a lot easier to do things like machine dovetail ways precisely. The Gingery books show you how to do a lot of things the old-fashioned way but there are times when one quick setup and a few passes with a facemill on the Bridgeport could save you hours of tedious work.

Putting steppers on even a junk X-Y table will definitely suffice to work through the electronics and software. One of the EMC (control software) developers uses steppers on an Etch-a-Sketch so that he can test things right by his computer. There is a lot to work through there depending on what your skills are. I was OK with electronics and very good with software so the challenge for me is in making the mechanical parts. Usually everyone has trouble with at least one part getting started!

[Nathan Flycuter]

Thanks for the reply. Funny you should metion the Gingery books,
They are what got me working on this little xy table. Which brings
up a question, can I use cold rolled steel or should I use ground
flat stock for the ways? The rolled steel has a width and thickness
tolerance of+/- .003". While the flat stock has a width tol. of +/-
.001" and a thickness tol. of + .005", - .000" . I think the real
question is how much does each one taper over 14"? (The longest
pice I need.)
Thanks. -Nathan

[sansbury]

How exactly are you trying to build the sliding ways? I've built a wood router using square hot rolled tube, which is hardly the best stuff out there, and it works fairly well. But, the forces are much lighter than a mill, and the needed accuracy much less (wood moves a lot more than .01" with temperature and humidity changes).

I'm tempted to say take either kind of material, and use that manual Bridgeport at the office to square it up nice. But clever designs can take care of a lot of that, as can a scraper, surface plate, marking dye, and a lot of elbow grease. All that said, with a first build, odds are good you'll introduce as much or more error by your own hand than comes from the material, so use the cheap stuff and work from there.

[Nathan Flycuter]

Sounds good, the flat ground stock is more than I want to pay
anyway. I'm doing it just the way the Gingery books say to,
using cold rolled steel. Here is a link to a guy who did what I'm
doing. http://www.tjanstrom.com/drillmillconvertion2.html
Don't worry, found a better way to hold endmills than him.


What brand of stepper driver would you use? I am not very
good at electronics yet so I would like to buy one. Also what
size stepper motors do I need? I'm thinking of buying ~65in. oz.
motors because thats what I hear the little mini mills use.

[sansbury]

I see a lot of people over-spec steppers here. That said, 60oz might be cutting it a little close. If you have them already or can get them super-cheap as surplus, I'd give them a try. Otherwise, the price difference between a 120oz stepper and a 300oz one is often not much more than $10, so better to go a little larger than a little smaller.

Sherline supplies their CNC mills with 130oz-in motors, IIRC. I use the same on the X and Y of my X1, which is well over twice the weight of the Sherline, though 200oz might allow me to tighten things up a tad more or run faster, not that I've felt much of a need for that. I'd probably go with those (~120s) or with something in the low 200s, in case you decide to build something larger.

I have the HobbyCNC Pro driver and am very happy with it. I run a 24V PSU and it goes fast enough to get me in trouble. I've used both Mach and EMC2 to drive it. For CAD I've used the free download from eMachineShop that lets you export DXFs and I use CamBam to generate G-code. You can spend days, weeks, months, or years on any one of these items and only scratch the surface. But if you take each step one at a time you can eventually get through enough of each to be useful.

[asen59]

@sanbury

is yr machine done?pls info
tq

[Radical!]

linear bearings, Ball screws are the way to go knowing what I've gone through now. You'll want all the precision and repeatability you can get. If its in your budget then I'd say, yes go for it. If not just stick with Acme screws and box ways, Its all in good fun.

http://www.cnccookbook.com/img/Other...lete_assm2.jpg
http://www.cnccookbook.com/img/Other...ldIMG_6396.JPG


Nice start for a CNC lathe. Would like to be doing the same but for a 3 axis mill.