First Build - Desktop PCB Milling

[Reed92]

First of all, this is my first post. Hello everybody. I am a freshman in college, EE major.

I decided this last weekend that I want to build a CNC for quick prototyping of circuit boards. It was my intent to do an hour or two of research, find a plan, and build it. Well...it has turned into a bigger uptaking than I thought. So far I have done in the neighborhood of 20-30 hours of research and still have no idea what I'm doing.

I have no previous experience with CNC's other than watching them work in my high school metals room, so some of the mechanics are still a little foggy for me.

So far I have decided on these requirements:
12"x12"x4" Cutting area
MDF frame for vibration damping
No less than .001" precision
All for less than $500

How feasible does this seem?

OH and I have a friend that is an experienced CNC operator, so having custom parts cut for this build is no problem.

I do need some questions answered, though:
What parts are worth machining/Which am I better off buying

How do all the parts of an axis(linear slide table?) fit together? I have not found a good explanation of what goes into these. It's really the biggest question mark on my project right now.

[MrWild]

No. You will not get .001 accuracy for $500. You can blow $500 on motors, drives, and power supply. Tight tolerances need accurate slides, and lead screws. Ball screws can go $200 with bearings. Couplers go for $30-$60 (for the project). Three good zero backlash lead nuts for acme lead screws can run $60. A good lead screw can run $45.

The sad truth is, this is one of those hobbies where if you buy cheap, you get the frustrations of buying cheap. You lose so much time trying to work with low grade/under power systems, you might give up before you got off the ground.

If you are stellar at scrounging, if you find the best deals, if you accept middling performance, you might get away with $800. the basic problem is that a 12 x 12 uses all the expensive bits a 24 x 24 or even 24 x 48 uses.

I've heard some claim it's cheaper and easier to just pay for then fast prototypers,

[RedskinsJBS]

I would take a look at John's thread here:

http://www.cnczone.com/forums/diy-cn...p_machine.html

He builds small desktop routers pretty cheaply that have surprising accuracy.

You could really penny pinch and attempt to build a copy of one of his machines for less than he sells them for... or you could simply buy his machine and be ready to make some parts in a week.

While certainly possible, the cost of .001 accuracy can be a bit out of budget for budget builds. If you build a completely dedicated pcb mill, say with a mill volume of 12" x 12" x 1", you can get away with smaller motors than would be required on a general purpose router.

As I learned recently, precision ACME screws are normally only accurate to .007" per foot. This means that for every foot you move along an ACME axis, you must expect you real world position and your theoretical position to differ by .007". And its additive. So after a 4 ft travel on an 4ft axis, you should expect to be .028" away from where you wanted to be.

On a small machine, this isn't much of an issue because the error can't build as quickly.

A budget-build at $500 normally results in a thin-walled MDF machine with threaded rods from the hardware store as lead screws. If you are looking to build PCBs with this mill, you are going to have to come up with a better design and bigger budget than that.

I'd say for $1000 and under you *should* be able to build a nice router that you will be happy to use.

[Reed92]

Originally Posted by RedskinsJBS I would take a look at John's thread here: http://www.cnczone.com/forums/diy-cn...p_machine.html He builds small desktop routers pretty cheaply that have surprising accuracy. You could really penny pinch and attempt to build a copy of one of his machines for less than he sells them for... or you could simply buy his machine and be ready to make some parts in a week. I'd say for $1000 and under you *should* be able to build a nice router that you will be happy to use.

I've already checked out John's thread. I actually planned on modelling his machine pretty closely.

I only made it to about 20pg's into the thread before I got tired of trying to find useful information amongst all of those lithophane posts.
It sounds like he was selling the small ones pretty cheap.

Do you know if John ever set up a website?
or should I PM him?

[RedskinsJBS]

Just go ahead and PM him. He seems to be on almost every day.

If he doesn't get back to you after say 3 days, then I would make a post on his thread.

I can't recall if he has a website or not (I'm pretty new to this CNC game myself).

Where do you go to school?

[Reed92]

Originally Posted by RedskinsJBS Just go ahead and PM him. He seems to be on almost every day. If he doesn't get back to you after say 3 days, then I would make a post on his thread. I can't recall if he has a website or not (I'm pretty new to this CNC game myself). Where do you go to school?

Alright, I'll try that.
I attend UW-Platteville.
How about you?

[RedskinsJBS]

U of Maryland. Technicaly I am a freshman, but I took a couple years off from school. And I went to community college classes throughout that entire time.

My router that I am working on is a bit larger than what you are investigating, however I'm not quite sure of it's real world accuracy.

I'm thinking that I may have to build a second router specifically for pcb milling operations . . . and FDM extruding.

I am looking in to a build volume in the neighborhood of 8" x 8" x 4" for my desktop mill. However, I'm thinking it will be a long way off for me since I haven't finished my current build.

I will certainly try to help you on your venture. I've done a lot of searching in the area already, so I've built up a bit of a knowledg base.

Jay

[Reed92]

Originally Posted by RedskinsJBS I'm thinking that I may have to build a second router specifically for pcb milling operations . . . and FDM extruding. Jay

This was mostly my plan too, haha. The possibility of adding 3D printing capabilities is the reason for my relatively long z-axis.
I was originally planning on following the build at MultiBot, but the aluminum extrusions don't seem as stable as mdf. Besides, his machine has been in the build phase for 6+ months, who knows when he'll finish.

[Iron-Man]

Found this link last night.
The most affordable CNC DIY Kits for the professional and hobbyist

Hope this helps,

Iron-Man

[RedskinsJBS]

Trying to make a multi-functional CNC machine requires compromises. Either compromises in performance or compromises in cost. In example, I could easily build a PCB mill with .001 accuracy inexpensively if I didn't care how long it took to mill a part and I was only going to use it to mill circuit boards. However, to build a machine that will also be capable of FDM, the axes' all have to be able to move at a much higher rate, and the Z-axis needs much more clearance.

This multifunctional machine would cost much more to get the same performance as 2 seperate specialized machines. I'm not sure if it would cost more than building 2 individual machines, but maybe nearly as much.

My reasoning behind eventually building a second machine is because my first machine is in my Dad's house. I'd like to be able to use it, but I think that I will one day get more utility out of a smaller machine that I could keep around in my dorm room. For this reason, my circuit board machine will be an 'Ottoman' machine. As in, I will build an enclosure for the machine and a vacuum, all of which will fit in a 2'x2'x4' ottoman.

Zen Tool works looks pretty neat. However, I haven't ever heard of them, nor have I heard any reviews of their products. I'd be interested to get more specs about their motors and their lead screws. All in all, a 7"x7"x2" build volume delivered complete to your door for $500 sounds almost exactly like what Reed is after.

Jay

[harryn]

Hi, for a small machine with good accuracy at modest cost, I would strongly consider a fixed gantry based design. They tend to be a bit larger footprint for the same capability, but also tend to be rock solid.

[Reed92]

Yeah, I'm going the (semi)DIY route because it's no fun just to buy one. haha.
I did plan on doing fixed gantry, Thanks for the advice.