What kind of railings?

[ipodman1991]

Im starting my CNC machine (first one!) and im wondering what kind of railings I should use. Should I use ball-bearings (or something of the sort, something that rolls on the support rail), or could it be sufficient enough just to cut a hole with the circumfrence of the support rail and have it just slide along?

Note that this is my first CNC that i am designing, so i'd like it to be cheap and easy to use.

[mechsiah]

Cheap and easy to use are sometimes at odds with each other. I have built 1.5 machines (the first one was too inaccurate to do the type of work I wanted and the second is being built more carefully). I am still a n00b myself, so take my recommendations with a big bag of salt. I would defer to any of the venerable members of this forum.

1) How accurate is good enough? If you are cutting wood and you don't need precision, you can get away with all sorts of stuff. No adjustment bolt may work fine if your bearings are loose and you don't need the rigidity for precise cutting. If you have greater ambitions - cutting metal or cutting to exact dimensions, do yourself a favor and spend more on the right parts to start with. THK rails or supported linear shafts or a well built JRGO type machine.

2) Size matters. If you only want to do a small machine you don't have to worry so much about the flex in unsupported beams. JRGOs machine had 42" (?) X-axis and he used 1.5" drill rod, which had a little flex, but not much. If you want to build a precise machine, build it only as big as you need it. It will be easier to work on, cheaper all around, and provide you with a tool to precisely build your next one - and you will build another...

3) Care. I am not a detail-oriented person and it hurt me at every turn. The only reason I got any where on the first one was because my retired father was interested in the whole project and he is VERY detail-oriented. When you build your machine, take your time and do it right. Every minor mismark or cut will haunt the machine for the rest of its life.

Perhaps not entirely on-topic, but there may be something worthwhile in my rambling...

[ipodman1991]

I plan on using the machine mainly for PCB milling, so i imagine it would have the rails would almost have to be perfect. I dont plan to make the area it can cut out any bigger than about 40cmx40cm anyway, so it should be pretty accurate. Bearings seem better to use, but probably harder to set up than just holes.

I kind of have an OT question, how small a trace can a home-made cnc machine produce (approx.)

Incase anyone didnt understand, by bearings i mean something like http://www.lumenlab.com/forums/index.php?showtopic=5960 this CNC machine has.

[mechsiah]

Ah - you want bearings. Also, check out ebay for cheap, short rails and blocks.

[ipodman1991]

So i guess its bearings then? Alright. How can i set those up pretty easily? The ones used in that site i linked to before seems to hard for me to make without a prebuilt CNC machine, and it seems there is a little welding/soldering involved too. Is it possilbe to?

[mechsiah]

The JRGO style bearing that run on hardened drill rod require a drill press and some patience. New drill rod isn't exactly cheap, either, just cheaper that factory rails.

Since you only want to do PCB milling and your size is small, you could definitely do something like what is shown on that lumenlab post. You will only be milling off bit every pass, so the dremel won't have to apply too much force. Precision wouldn't be threated by the "push-back" of cutting a larger area per pass.

Of all the tools you may need, a drill press should be way up on the list. Borrow or buy one if you don't have one and use jigs to make sure you drill consistently.

[ipodman1991]

Thanks for you replys mechsiah, theyve been a great help!

I have a drill press attachment for my dremel. Its pretty precise, so i guess you could say I have a drill press.

I actually finished designing my machine in Sketchup. Its similar to the one i linked to but the gantry doesnt move, the base does. I think it should work fine. If not my backup design is going to be like the 2nd design on the bottom of this page: http://cq.cx/pcb-router.pl Which one do you think would be better?

Youve mentioned a JRGO machine a couple times. What is that?

EDIT: re-reading this post... Im surprised that you didnt say that a table saw or band saw isnt the most important. i think ill be cutting more than drilling.

[Zumba]

"I have a drill press attachment for my dremel. Its pretty precise, so i guess you could say I have a drill press."

mmmm... no. Not precise and it's way too small to drill anything useful.

As for the JGRO (not JRGO) design, forget it. That machine design was meant to be built on a budget, at the expense of time and labor. Unless you have access to a machine shop, it's unlikely that you'll be able to build it accurately enough to drill PCBs.

I would recommend buying a ready-made machine like a Taig. I'm not trying to discourage you, just trying to save you some time and effort. You just can't build a CNC with a dremel and a tablesaw.

[austin.mn]

over the years i have built many cnc machines, and have learned a bit about different techniques and methods. the one thing that i have to say is "keep it simple and go with what you know." if you are used to working with wood, go ahead and use wood for your first machine. linear bearings are very nice to use on a your homebrew machine, but can be a bit pricey. i built my first couple of machines using ball bearing drawer slides and a peice of allthread for a lead screw, that machine worked alright and topped out at 7 inches per minute. i probably spent $250(including motors and drives) to build that machine, and it was a valuable learning experience. it may be a way to go for you to get a start with things, there is a lot to learn. i would not expect that machine to make pc boards perfectly.

once you have a handle on creating toolpaths and good understanding of the dynamics of machining, then open your wallet and shell out some hard earned cash and buy something premade. "widgetmaster" on the forum, has been building some very nice machines for sale at an excellent price. you still have to add your own motors and drives, but from the pictures he has posted it looks to be a very accurate machine. soon as i have hidden enough money from my wife i plan on buying one.

but as i said already, there is a lot to learn, these things aren't like a printer, you can not just plug it in and hit a go button. once you have a handle on it though, you can make stuff that would be almost impossible to make any other way.

good luck

[ViperTX]

Take a look at the pcb milling machine that Paul at cnconabudget.com did.