Mechanics and Construction > Mechanics and Construction
My homebrew CNC
vinito:
Yea I'd oblige if I could. Maybe I can borrow and pull that off sometime. However, in operation it looks and sounds (noisy!) just like the few dozen videos of similar machines on youtube.
Here's a picture of a fairly successful test I did last night though. Traces are too narrow but that's a simple matter of adjusting a parameter in PGB-GCODE.
Here are a few particulars:
Softwares:
Eagle for PCB design. It's free for small boards, pay for unlimited (?) size files. Seems to be the industry standard for most folks I run into.
http://www.cadsoftusa.com/
PCB-GCODE for generating G-code from the Eagle file for both isolation milling and hole drilling. It seems to work pretty well. And it's free !
http://www.pcbgcode.org/
This runs "inside" Eagle and it's easy to deal with.
Gsuite for optimizing the code generated from PCB-GCODE. Basically eliminates a ton of rapid moves from what PCB-GCODE generates for whatever reason and does a very good job of it. For a slow stepper motor machine, it's a godsend. It has a couple other handy utilities as well. Pretty neat. Also free.
Gsuite v1.3
Mach 3 for running the machine. About $150 but all I'm doing is running the G-code to the machine and for that EMC2 would work just about as well (some say better) for free. I think Mach 3 is a little overboard for this, but I bought a copy a while back so I'm using it.
Steppers are NEMA 23 and 1.5A, so about as small as this frame gets I think. For the force required for an engraving bit and those little bitty drills, these are more than adequate.
Lead screws are 1:1. Just 5/16-18 threaded rod. I was finicky about picking a pretty straight one and it wasn't too bad. Seems to be plenty accurate enough for the purpose, and dirt cheap. 200 Steps per revolution on the motor (which is typical and easy to find) and 18 tpi gives a nominal positional accuracy of .00028 per step, so more than adequate for me.
I machined the nuts from delrin (yer basic drill & tap) and that makes for a free-turning but close fit. Of course wear & tear will probably loosen things up over time, but they are easy to make and at the moment it indicates zero backlash.
Downloaded the board file in Eagle from here in case you are curious what it is:
http://arduino.cc/en/Main/ArduinoBoardSerialSingleSided3
Soeren:
Hi,
Nice job with the PCB ;D
How long did it take to route it?
Are you planning to route/drill the holes as well?
photomark:
nice job , even more so considering it is a budget home built machine , I have also started on CNC and bought my self a cheap machine from China , I fried the electronics on the first day and even though it was coverd by warranty it just was not worth the cost of me sending it back to them , the company was good about it though and gave me a token $50 refund , I got a new power supply for $50 and a controller board identical to yours for around $60 .
I am running this with Kcam and using Turbocad 17pro and SolidWorks 2010 , for PCBs I found a great program called FreePCB , I also have Ventric Cut3D for generating 3D tool paths .
You got me thinking on just using all thread for the lead screws , I am intending on building a much heavier machine , not so much larger but I have a need for a very heavy duty machine and good lead screws are very expensive to buy .
The best thing about building a CNC anything is that you learn a lot about stepper motors, I had a box full of them ,all sorts and types ,mostly from old record turntables , I have had a lot of fun with them and intend on using them in a lot of future projects .
Well that is if I get some time
MT
vinito:
--- Quote from: Soeren on March 03, 2011, 04:48:27 PM ---Hi, Nice job with the PCB ;D
How long did it take to route it?
--- End quote ---
Thanks for the kudos.
1) My motors were tuned to turn as fast as they could and still repeat reliably, which will move the table at 13 inches per minute. That's pretty slow, but not for steppers (a little over 200rpm).
2) With the parameters in PCB-GCODE set the way I did it for this test, it made three paths around each trace (to achieve the width I "instructed" it to make). That's 6 paths between close traces and with the runout I'm getting out of the crappy Dremel performance which makes the cuts wider than it should, that's way more than it needed. Actually I think it could have been done with a single pass around each trace, which would cut the time to 1/3 the time this one took.
So anyway, it took a bit less than two hours to trace that board out, so a single pass path would have cut it down to maybe 30-40 minutes.
--- Quote ---Are you planning to route/drill the holes as well?
--- End quote ---
Yea that's in the cards, but this was just some double-sided material I had from Radio Hack from years back and I was just testing the trace routing, so no sense doing that to this board. It wouldn't have functioned anyway if I had actually finished it since the other side is solid copper. Anyway, I have run a second test of a smaller board and added drilling. The process worked OK, but the Dremel is in the way again, making a bit of ratty hole at the entrance to each, plus some ripping and tearing. Plus, I couldn't find my selection of drill bits and fudged it with what I could find, which were too large and didn't help any. Obviously a better spindle is also in my future, and was from the beginning. But a Dremel got things kind of going quickly and easily. Some parts are on the way and some I have started making already. It is a little bit "on-the-cheap" too, but will still be tons better than a Dremel and still better than several I've seen out there on the web. Of course having less runout will mean I probably won't get by with single-pass trace routing, but I'll be happy to trade that out.
I'm an old hand at machining, but this particular thing is pretty new to me. I'm doing it for several reasons. First, I want to be able to make my own boards of course. Next, I also consider this a prototype concept in which I build my way into a pretty nice servo-driven machine with more bells & whistles eventually - in other words, making my biggest mistakes and fixes now. Sure it's been a few dozen times before me, but I kind of like the process anyway.
And finally (which actually is more immediately applicable to #1 and similar to #2) I want to develop a reliable process for making boards. There are several variables and possibilities to work out. I need to add some stuff to this machine so I can mechanically line up the board on the flip and insure things are in register (alignment) for double-sided boards. I'm still exploring engraving cutters (angles, material, style) to find out which ones work the best and last the longest. Drilling the holes seems simple, but there are at least three ways I can think of to do it and need to experiment to find which turns out the best. Plus each solution tends to illuminate more questions to answer and I'll have to solve those current unknowns as I discover them. It's a good thing I enjoy this process. :D
Interesting that photomark is using a whole different set of software to accomplish this same thing. Just goes to show there's a whole rainbow to choose from. As for all-thread for lead screws, I'm pretty happy with how mine works. That's one of the few things on the machine I haven't had to fiddle with at all - it just worked OK out of the gate and is still working fine. If it was a milling machine and needed to make precision parts, it probably wouldn't be adequate. But for routing PCBs it works plenty well. You just have to check them out when you buy them to make sure they are pretty straight. Just roll them on a table or floor and look for wobble. All-thread from the hardware store is notorious for being bent, so be picky. Usually threaded rod is used to simply hold stuff together so being bent is a non-issue. But for a lead screw you want to minimize that of course. Also, you might look here (click) and maybe it would be a good, inexpensive source for an even better solution. At 4tpi, you'd have to use belts and pulleys to change the motor/screw ratio to get acceptable resolution for accuracy, but that's not a big deal. They'd be beefy and smooth anyway.
By the way, if you want a decent spindle and don't feel like making one yourself, this one looks like a pretty darn good deal:
http://www.angelfire.com/az2/proff/
Soeren:
Hi,
--- Quote from: vinito on March 04, 2011, 07:00:21 PM ---So anyway, it took a bit less than two hours to trace that board out, so a single pass path would have cut it down to maybe 30-40 minutes.
--- End quote ---
That's not half bad - I talked to a science teacher who started a shop with robotics parts and he used a ready bought machine at the faculty to make a similar size PCB in 7..8 hours.
--- Quote from: vinito on March 04, 2011, 07:00:21 PM ---[...] It wouldn't have functioned anyway if I had actually finished it since the other side is solid copper.
--- End quote ---
A lot of HF PCB's are made with one side copper, where a small pad of copper is removed from where the through holes are - makes a great ground plane.
--- Quote from: vinito on March 04, 2011, 07:00:21 PM ---[...] Of course having less runout will mean I probably won't get by with single-pass trace routing, but I'll be happy to trade that out.
--- End quote ---
As long as you have adequate isolation (and not doing anything extremely high impedance), there's no (electrical) reason to remove the in-between islands.
--- Quote from: vinito on March 04, 2011, 07:00:21 PM ---[...] I'm still exploring engraving cutters (angles, material, style) to find out which ones work the best and last the longest.
--- End quote ---
A rod with a splinter of wolfram (tungsten) brazed into a slit in the end and ground to a "slanted V" the shape of most engravers I've seen (I'm sure you know what I mean) is easy to grind into the size you need and is very long lasting.
--- Quote from: vinito on March 04, 2011, 07:00:21 PM ---Drilling the holes seems simple, but there are at least three ways I can think of to do it and need to experiment to find which turns out the best. Plus each solution tends to illuminate more questions to answer and I'll have to solve those current unknowns as I discover them. It's a good thing I enjoy this process. :D
--- End quote ---
Yes, you really have to - to get it done :)
--- Quote from: vinito on March 04, 2011, 07:00:21 PM ---Interesting that photomark is using a whole different set of software to accomplish this same thing. Just goes to show there's a whole rainbow to choose from.
--- End quote ---
Way more than in the early eighties when I first considered making one - perhaps I should get around to actually do it some time soon.
But it would be more for engraving, as I prefer photo transfer when it comes to PCB's.
Wonder if I could find a program to take a bitmap and trace that down on a piece of something, or are they all vector controlled.
--- Quote from: vinito on March 04, 2011, 07:00:21 PM ---As for all-thread for lead screws, [...]
--- End quote ---
Suitable screws can be found in car jacks and in several other places.
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