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Author Topic: CNC contraption.  (Read 2700 times)

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Offline dunkTopic starter

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CNC contraption.
« on: July 30, 2010, 08:16:25 AM »
hey guys,
so last week i was thinking about making some new PCB prototypes for which i will need to solder QFN packages.
the only problem is there will be a few revisions of the PCB before i get them right.
i also don't have access to a laser printer at the moment so making PCBs with the toner transfer method would be annoying.

so i decided to build the CNC PCB mill i've been thinking about for some time.
i'm out of work at the moment so had very little money to spend. i had to buy the bearings and some threaded bar. all the other parts were either scavenged from old printers or i already had in my parts bin.

it took about a week to get to it's current state but bear in mind i have been thinking about it for a while so i already had a plan for most of the technical issues.
i estimate another week of tuning will get me to the point where i can mill PCBs. (plus the time waiting for my router end mills (cutting bits) to arrive from HK vie ebay.)

the next thing on my ToDo list is eliminate the small (0.5mm) amount of play in the X axis. the Y and Z axis only have about 0.1mm play which should be good enough for 0.5mm PCB traces.

all the control software is an existing open source package so no work to do there:
http://linuxcnc.org/

there is a plugin for Eagle PCB to produce gcode which is an industry standard for CNC machines:
http://groups.yahoo.com/group/pcb-gcode/

here's the first test of my machine:
cnc.mpeg



dunk.

Offline Asellith

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Re: CNC contraption.
« Reply #1 on: July 30, 2010, 10:18:13 AM »
I started my CNC project a few weeks ago. I'm making a 2' by 4' one. I'm probably gonna have a ton of issues with tolerance. My wood working skills are lacking. I should have planned my own. I bought a book and well its less tutorial and more suggestions. I thought I was getting a step by step guide and ended up with a confusing book that says things like the coupler is attached here but never talks about what coupler to buy or where to get it. The book needs a serious BOM with manufacturing suggestions.

Anyway now the my dremel is toasted (probably needs new brushes) I have to finish some stuff at the shop at work. I've got a big learning curve and I hope to get my tolerance low enough to do PCBs. the first revision might now work but after I get the big one done I'm thinking of making a smaller one for PCBs/Rapid Prototyping.
Jonathan Bowen
CorSec Engineering
www.corseceng.com

Offline Hawaii00000

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Re: CNC contraption.
« Reply #2 on: July 30, 2010, 01:47:15 PM »
I read that you can get stepper motors from old dot-matrix printers. What about plain old ink jet?
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Offline MechHead

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Re: CNC contraption.
« Reply #3 on: July 30, 2010, 01:55:12 PM »
For one weeks building thats incredible.  I'm in the process of making a rapid prototyper but it's going a lot slower.

@Asellith: It sounds like what you want is more of just a design than a book about CNCs.  You can buy these somewhere on the internet, I've seen them on ebay.  They should have a BOM and instructions to put it together, but I dont know that it would have manufacturing suggestions.

Offline dunkTopic starter

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Re: CNC contraption.
« Reply #4 on: July 30, 2010, 04:30:36 PM »
I read that you can get stepper motors from old dot-matrix printers. What about plain old ink jet?
so my main X and Y axis motors came from an old Oki 9 pin dot matrix. they are pretty good for the job but still a little underpowered.

all the Inkjet printers i looked at didn't have anything very good.
they seem to use DC motors and high resolution encoders rather than stepper motors. i presume this is because the ink can be sprayed very quickly meaning the printer does not need to hold the print head in position, it just sprays as it goes past.

i did get a big 3 phase brushless motor out of a large office laser printer which would be great if it was bi-directional.
not quite as precise as a stepper motor but it would make up for that with better torque due to it's size.
unfortunately the control PCB is built into the motor chassis and the control PCB only contains circuitry for rotation in one direction.
i did consider completely re-building it but that would take as long as the rest of the CNC machine put together.

the most interesting motors i found in ink-jet printers were the small stepper motors that park the print head when it is not in use.
they are small stepper motors. really nice motors but not powerful enough for my application.
i am having to use one of these anyway for my Z axis in the absence of owning a better motor... (it's the one in the vid that moves the Dremel up and down.)
i saw these on a few different cheap HP printers. presumably other manufacturers use stepper motors somewhere as well.


For one weeks building thats incredible.  I'm in the process of making a rapid prototyper but it's going a lot slower.
thanks!
it helps that i have a friend who has a computer scrapping/recycling business so could get a few broken printers to strip.
i've been planning the build in my head for about a year now though so it really was just a case of cutting out the parts and assembling.
it's still really nice to see that it works as planned though.

@Asellith:
i don't believe it has to be that hard as long as you can come up with a system of rails that only allow movement in 1 dimension.
assemble 3 of these rails and all the rest of the structure can easily be designed on the back of a beer mat. (well, i used Sketchup but you get my point.)

after lots of thought on the matter, finally coming up with a design for rails that could be built cheaply and easily but still with reasonable precision.
then today in a DIY store i saw a pre-made item that cost about the same as the bearings i bought: kitchen draw rails.
they were about 500mm long and very little sideways movement.
if i ever make CNC_contraption_2 i will be using these.

couplers are always a pain.
i'm using pieces of plastic hose. get a piece that you can barely force over the 2 shafts. mount the 2 shafts in their final position so they can only move as they will once in operation then gently heat the plastic hose. while the hose is hot, run the motor.
heating the hose has 2 effects:
1. it shrinks the hose onto the shafts.
2. as you turn the motor and other shaft together it aligns the axis of the partially melted hose with the axis of the shafts being coupled.


anyway, i'm rambling again.
stuck on a ferry bound for Scotland at the moment.
at least ferries have internet these days.


dunk.

Offline Ro-Bot-X

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Re: CNC contraption.
« Reply #5 on: July 30, 2010, 06:06:47 PM »
It seems like everybody is building a CNC these days...

I finished mine last Sunday, after 5 days of work on it (I was in vacation). It was long overdue, I bought the motors and electronics as a package from Hobby CNC about 5 years ago... Relocating in 2 different countries did not help with the build, but the parts traveled with me. Now they are finally working as expected. I did not have a Sketchup model or a drawing, just a few hand made sketches just to add up the dimensions and see how big the machine will be. I used MDF, aluminum angles and roller skate bearings with a washer between them. My design features a moving gantry with a double sled, that means the Z axis moves up and down instead of moving just the cutting tool. I am not sure how big is the play on the axes, but this weekend I plan to find out. I am using a 5/16" x 18 threaded steel bar from Home Depot and long nuts (1 1/2" inch long) and it doesn't seem to have any play, but I'm sure it's there. My first cut was a basso relief picture that took 12 hours to cut (over night, terrorizing the neighbors in the morning), but I had to turn it off before it was completely done. I just threw in a ready made G-code file to see how's going. The motors vibrate at different frequencies, the MDF amplifies them and it sounds like someone practices playing a horn. I need to reduce them somehow...

You can see the machine blogged here: http://letsmakerobots.com/node/21754

A few pictures:




« Last Edit: July 30, 2010, 06:09:21 PM by Ro-Bot-X »
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Offline Hawaii00000

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Re: CNC contraption.
« Reply #6 on: July 31, 2010, 07:38:38 PM »
@Ro-Bot-X
Looks nice!

@dunk
I wish ink jets had nice big steppers. There's so many for free on craigslist.
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Offline dunkTopic starter

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Re: CNC contraption.
« Reply #7 on: August 09, 2010, 03:41:58 PM »
progress pics:

Offline Hawaii00000

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Re: CNC contraption.
« Reply #8 on: August 09, 2010, 05:07:21 PM »
Looks good. What's with the euro? What country do you live in?

Do you have a schematic for your controller?
« Last Edit: August 09, 2010, 05:18:57 PM by Hawaii00000 »
"God chose to make the world according to very beautiful mathematics."
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Offline dunkTopic starter

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Re: CNC contraption.
« Reply #9 on: August 10, 2010, 04:17:29 AM »
Looks good. What's with the euro? What country do you live in?
what's with the Euro?
i didn't have any Chinese Yuan coinage in my wallet which is the most widely used currency by Internet users with around 21% of Internet users living in China.

the Euro is the 2nd most widely recognised coinage on the Internet with around 15% of Internet users in the Euro zone. (17% of world Internet users live in the EU but not all of those countries use the Euro currency.)

but.... this is an english language forum.
as such SORs users are going to be predominantly from english speaking countries.
i'm sure Admin has statistics on which countries SOR users are from but i would hazard a guess that the US has the largest share on this forum (with 12% of world Internet users).
so maybe i should have dug out my US$ wallet.

anyway, i'm making this over complicated again...
the 1cent coin in the picture is 16.25mm diameter.
maybe i should have used a ruler as a scale instead as i've just pointed out, not many native english speakers use Euro coins regularly.

i'm living in Ireland just now. (i'm not Irish, i just live here.)
it's the only country using the Euro where people speak english as a first language.
(it is worth pointing out that irish is the official language of Ireland but english is virtually every bodies first language.)


Do you have a schematic for your controller?
no schematic yet. (although i plan to mill a PCB for this project so i will be making one.)
it's just an ATmega8 watching the PCs parallel port and LM293 s to drive the stepper motors. the LM293 datasheet is fairly clear on how to use it.
there might be better component choices out there but this is just what i had in my parts bin.


dunk.

Offline Hawaii00000

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Re: CNC contraption.
« Reply #10 on: August 11, 2010, 12:29:16 AM »
maybe i should have used a ruler as a scale instead as i've just pointed out, not many native english speakers use Euro coins regularly.

As far as I care, you can even use Euro in a pic you want ;)


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Offline dunkTopic starter

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Re: CNC contraption.
« Reply #11 on: August 13, 2010, 07:29:21 AM »
wow. i was of on a bit of a tangent there.
don't know what i was going on about...

anyway,
progress is going ok.
the rails are better than i expected. very little unwanted play.
but my motors are way under powered meaning i have to move them slooowwwly.

i'm supposed to be getting another pile of broken printers from a friend but don't know if i'll get any stronger stepper motors without buying them.
i've asked him to keep an eye out for old dot matrix printers because i think that is my best bet.

so,
like i say, it's slow but it works.
if i try to run the motors too quickly i get the occasional missed step which leads to accumulative position error.
the picture of the PCB below demonstrates this. (PCB_errors.JPG)
the traces were cut at a slower speed than drilling the holes.
while there are a few overlapping traces, the drill holes are all over the place.

the other pics are of an airfoil template for my UAV project.
i had to run the CNC motors so slowly that it took a few hours to cut the template
but the results are fantastic. far more accurate (and still quicker) than cutting such a template by hand.
it was my first time hot wire cutting so i'm pretty pleased with the results.


it's really nice being able to design something on a computer and then have a machine cut it out.
i don't think i would have been able to make such an accurate job of that airfoil template with hand tools.
i can't wait until i get stepper motors that are up to the job.


dunk.
(who's just landed a job so will be able to buy the bigger stepper motors before too long.)

Offline awally88

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Re: CNC contraption.
« Reply #12 on: August 14, 2010, 08:22:44 AM »
One of my friends recently made himself a CNC recently and he had the same trouble as you with it missing occasional steps which was caused by incorrect switching on the stepper motor drivers he made himself. After he purchased off the shelf drivers it worked perfectly. I think it was something about momentary short circuits when it was switching directions. I can't really remember, I'll speak to him on Monday and try and find out what the exact story is though.

Offline dunkTopic starter

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Re: CNC contraption.
« Reply #13 on: August 14, 2010, 12:38:06 PM »
[deleted whole post because i was typing nonsense.]

so i had posted about steps being overlapping each other but i was having a blond moment so deleted it.

@awally88
it's just my motors are not powerful enough.
even with the motors stopped they don't have much holding power.


dunk.
« Last Edit: August 14, 2010, 03:46:22 PM by dunk »

Offline dunkTopic starter

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Re: CNC contraption.
« Reply #14 on: September 05, 2010, 06:51:29 PM »
so while my mill has been working well i was having problems finding any inexpensive (ie, free) software to create G-code for it.
(G-code is the language CAD files for CNC machines are written in. they are essentially just a list of coordinates to move the cutter to.)

so i wrote a little SketchUp plug-in to output G-code.
the idea is you create an object in SketchUp then run the script and you get a G-code file for your CNC machine to make the object you created in SketchUp.

so far it's working for cutting 2D shapes out of sheet material.
full 3D to follow.

https://sites.google.com/site/sketchuptogcode/


dunk.

Offline Hawaii00000

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Re: CNC contraption.
« Reply #15 on: September 06, 2010, 01:13:25 AM »
Awesome, I use sketchup so I might end up using that some day...
btw I like the picture with all the coins... never noticed that before
« Last Edit: September 06, 2010, 01:15:46 AM by Hawaii00000 »
"God chose to make the world according to very beautiful mathematics."
-Paul Dirac
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Its Hawaii Five-O. Get it?

Offline Ro-Bot-X

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Re: CNC contraption.
« Reply #16 on: September 06, 2010, 06:27:09 AM »
Dunk, amazing job, I'll give it a try this week. I'm gonna cut parts for a robot chassis from acrylic. I have to test out the speed so it doesn't melt, I'll report my findings here.

Thank you so much!
Check out the uBotino robot controller!

Offline Asellith

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Re: CNC contraption.
« Reply #17 on: September 06, 2010, 06:41:22 AM »
Dunk your making me want to finish my CNC build. Outta cash to buy the electronics so I was working on other potentially profitable projects but with promises of sketchup -> gcode and a new plug in I found for sketchup -> STL I might have to finish it sooner. Don't really have time to learn a bunch of new software but I already know sketchup.
Jonathan Bowen
CorSec Engineering
www.corseceng.com

Offline dunkTopic starter

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Re: CNC contraption.
« Reply #18 on: September 06, 2010, 10:32:31 AM »
it's worth pointing out the competition:
PhlatScript is able to produce 2D G-code for cutting shapes out of foam and similar thin material.
http://sketchuppluginreviews.com/2010/04/30/phlatscript-google-sketchup-plugin-review/

my script is meant more for anyone who needs to make multiple passes along the same path (and eventually mill out 3D shapes).


dunk.

Offline Oller125

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Re: CNC contraption.
« Reply #19 on: September 06, 2010, 11:45:21 AM »
Nice CNC you got there. It is a little slow but you explained why. I think I might build one in the future as I don't want to be using my school cnc :)

 


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