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Culvan
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Joined: 20 May 2008
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Location: Kansas City, MO

PostPosted: Mon Dec 14, 2009 10:30 am    Post subject: Culvan's CNC thread Reply with quote

I've been very interested in Computer-Numeric-Controlled (CNC) mills recently. Generally the idea is that you can use a computer to control the motion of a router or other cutting instrument then you can cut anything you have a 3D model of. Professional CNC machines generally start at 4 figures and go up (a lot). I found a thorough set of instructions written by Stuart Mcfarlan that said it could be done for around $600. So I thought I would give it a try. There are cheaper options than that, but I wanted something large enough that I could make armor bucks for vacuumforming.

http://www.instructables.com/id/How-to-Make-a-Three-Axis-CNC-Machine-Cheaply-and-/

From a high level, CNC combines three different technical specialties - Mechanical ability (in this case woodworking), electronics to control the motors and Software to give instructions to the electronics. I'll start off with the mechanical side of this. That was the hardest part for me and I've seen recommendations that you start with your weakest area first.

The Stuart Mcfarlan has done a good job detailing the parts list. He has prices to expect built right into it and recommended parts sources for all of them. He even includes a parts list that has pictures of the parts. In general I've found that the prices at Home Depot have gone up slightly but the prices of those same components at Lowes were cheaper in my area. I wish I had paid attention to the cut list because the instructions told me to buy 3 foot of threaded rod and then cut it down to 12 inches. I could've bought 12 inches and saved some effort and money. I did run into a problem where I bought out the entire supply of metric 8mm parts from multiple stores. The majority of the work revolves around cutting the parts out of a 48"x48"x0.5" sheet of MDF.

He provided PDF files of the cut pattern. The easiest one to get ahold of is a set of 35 8.5"x11" sheets of paper that you tile across the MDF. This was the method I tried the first time and ultimately it led to my failure. My problem was that there are no alignment marks on the small pages so it is easy to get slightly misaligned. 1/8" misalignment between sheets is very believable and when it multiplies out over 7 sheets across you can end up with nearly an inch of alignment error. I believe the error needs to be kept under 1/8th inch total. Eventually I found a way to print out the layout in two 39"x 48" sheets. With only one point of alignment it was easy to keep the error low.

However I'll go ahead and present my first try since there are many lessons learned. If you go with the 35 tiled sheet version be certain that you do not allow Adobe to "shrink and rotate to fit" the images. Print off the pages. You will need to trim these down otherwise the natural page margins will cover up parts of the other pages.


The next part of the process is gluing the pages down to the MDF. It probably would've helped if I had measured the sheets then drawn an alignment grid on the board so I would've known exactly where each sheet should line up. Even with that extra work I think this may be too tricky to be reliable.


Here's one of those learning experiences. I glued the pattern down and the bottom left corner was just barely off the edge of my MDF. I cut everything else out and tried to leave as much space as possible around it. I then printed off another copy and glued it to the other side of the board. That was good enough to get the full size.


On my first try I set the board up on sawhorses and used a jigsaw to cut the parts away. This was an exhausting process that led to more slight errors.


In my excitement I forgot to document the processes that followed for quite a while. I trimmed all the parts, I drilled a wide variety of holes, and routed a few channels. I followed the assembly instructions and discovered that the rails wouldn't sit properly in the routed channels, and the whole thing was a little off square. Both of these problems made the system bind up. I tried to use a belt sander to correct as much as possible and even filled in some of the routed channels and re-routed them, but it was a loosing battle. I eventually decided that I'd have to rebuild all the long parts to correct the accumulated errors. I started to harvest parts off the old machine to get the new one going.


More to come...

Andy
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Culvan
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Location: Kansas City, MO

PostPosted: Mon Dec 14, 2009 12:34 pm    Post subject: Reply with quote

On my second try I managed to get the cut pattern layout printed onto two sheets. That eliminated the problem of accumulated error and made one pass at the alignment a breeze. However I believe even this could've been improved. Working with large sheets makes it easy to get air bubbles that can cause various inaccuracies. I flattened mine out and they don't seem to have caused any harm, but there are easy ways to avoid them. I should have analyzed the pattern and found natural parting lines and cut the pattern along those lines into four pieces. That would have made the individual pieces easier to work with and avoid air bubbles.


I cut the MDF into slightly smaller sections with the jigsaw then I mounted my jigsaw in my vice and did the rest of the trimming. I found this method gave me much better control than cutting the parts off from the big board on sawhorses.


My theory is that only the longest parts and the ones that connect directly to them needed to be re-cut.


Once I had the parts cut out, I routed the channels for the rails. I used a routing table that I clamped guide boards to for the small stuff and I used the router on guides to do the channels in the large base. I had a lot of trouble with the bit scorching the wood. I believe the cheap router bit I was using was gathering some of the adhesive spray glue and started burning it. That resulted in carbon deposits on the bit that increased friction and the problem just got worse. I ended up buying a carbide coated bit and I didn't have any more problems after that.


After that I drilled holes. Most of the holes are 1/4", but there are a few others worth mentioning. There are a number of places where a 7/8" hole needs to be cut about halfway through the board. This becomes a ledge that will hold a bearing. I bought a forsner bit to ensure that the ledge would be crisp. I probably could've done this with a spade bit and some caution, but it would've been trickier.


There were also 5/8" holes where bolts and axles would pass through. I used a spade bit for that.


The middle beam is connected together by 1/4" bolts, however the ends of them stick out a bit and can catch on the carrage. To give myself some room to fix that I countersunk the holes a little bit.


There are also holes drilled into the boards where dowel nuts will sit to make the connections and holes drilled into the edges for the bolts to connect parts into those dowel nuts. After some fairly quick assembly with the assistance of a rubber mallet I had the two troublesome axis assembled.


I scavenged parts off the old system and started assembling the carriage.



Andy
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Culvan
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PostPosted: Mon Dec 14, 2009 2:20 pm    Post subject: Reply with quote

Here it is assembled.


I wanted to upgrade from a dremel to a Black & Decker, Rotozip clone. I had to design my own clamps to hold that down. Here it is with the cutting tool attached.


To test it out I attached my cordless drill to it. It seems to have full clearance and doesn't bind up. I later discovered that it's still a little loose and probably should be rebuilt since this is from my first try. The carriage can wobble a little bit. It's especially bad when I'm cutting something like wood. The rotation of the bit against the wood tends to make it want to walk in the direction the bit is rotating. I think that's entirely correctable though.


I'm including this next picture because the instructions never show a picture from the back. There is a timing belt stretched across the back. It's a little hard to see because it lines up with the bottom of the Y-axis rail in this picture. There is a Eyelet on the left that is used to tension the belt. The belt runs over two bolts that are resting in bearings. The timing belt is threaded down and around a pulley attached to the stepper motor.


I used a driver board package kit from Hobby CNC. The package was easy to assemble, my biggest complaints would be that there wasn't enough information provided about it up front. Had I known enough about it I probably would've bought the "kit" version instead of the "package" version. It would've saved me some money since I know enough about electronics to get it up and working without all the extra cables and stuff.


Here's the driver electronics assembled. I purchased a project enclosure to put this in. I'd recommend making one out of wood. It would've been much cheaper. In addition to this it recommends a fairly massive transformer. I opted out of that and chose to use an old PC power supply to power this. There are some unnecessary parts on this because of that change. I really don't need the rectifier bridge or as many fuses as I've got. They don't hurt anything and maybe they would solve a problem I haven't thought of yet.


As I mentioned earlier, I chose to take an old power supply from a computer and use it. Unfortunately my old spare power supplies were not in use for a reason. I ended up doing this three times. The basic gist of the modification is that you put a power resistor between the red and the black wires to make it believe there is a constant load. That keeps it from shutting down because it believes there is a open circuit. The idea of this is mentioned on hobbyCNC's web site, but I found there were many other web sites with better instructions on how to do this. (I've got more pictures of this process, but I'm summarizing here, let me know if anyone wants to see the steps.)


The driver package included wiring instructions on how to wire up all the stepper motors. I deviated from it slightly by adding connectors onto the wires so I could disconnect them if I wanted to. I also bought some cheap knobs to put on the ends of the stepper motors so I could move them by hand. Unfortunately the set screws tend to loosen because of vibrations when it' running. I think most of the knobs have fallen off by now.


Andy
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Culvan
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Location: Kansas City, MO

PostPosted: Mon Dec 14, 2009 2:24 pm    Post subject: Reply with quote

Software is a little more complicated. There are too many options to list out all the possibilities. I will give an overview and the specific versions I'm using. There are three main tasks to accomplish. 1) Some sort of 3D modelling software to make a 3D image to machine. 2) take that image and turn it into a tool path that defines how the object will be cut. 3) Send that as instructions to the CNC machine to make it perform the movements.

I chose GMAX as my 3d CAD software primarily because it is free. I'm familiar with Autodesk 3DMAX because it is used in the FIRST robotics competition and they are fairly close cousins. So my learning curve was already started.

I found a tool called CNCtoolkit that is a plugin for GMAX (or 3DMAX) that is also available for free. The CNC toolkit can convert shapes directly to tool paths. It will then output those tool paths in a variety of instruction sets including G-code. G-code is fairly standard for CNC machines. Learning the best way to machine a part is tricky. This is where professional machinists earn their keep. I don't expect to stumble in and understand how to do this right off the bat. There is a discussion forum that is a good resource for CNC and machining questions at CNCZone.com. There is also a discussion forum for CNC toolkit. You have to sign up for the forum to get the toolkit at: http://groups.yahoo.com/group/CNC_Toolkit/

The last part of this is the ability to use the G-code instructions to move the CNC machine. I'm using software called Mach 3 by Artsoft. The free demo version will execute 500 lines of G-code. The full version costs $175 (or $120 with an educational discount last time I checked). I probably could've used linux's EMC2 (enhanced machine control 2) software for free to get this done, but I really didn't want to switch operating systems between the CAD and the CNC software. I ended up buying this software to help streamline my process.

As a quick test I tried cutting a dome with it. I hadn't properly calibrated the steps size at this point. I had some set screws loose so there was some slop in one axis. I have since corrected those and my results are much better than my very first attempt as shown here


After I had the full software, and had corrected the problems mentioned earlier I headed over to www.scifi3d.com and downloaded a model by JJ Palomo. Scifi3d's web site indicates that they offer the models for free but they request that the artist be given credit (as I have just done). I made the following out of pink house insulation foam and it is about 3 inches tall.


I made the head as two halves and then glued them together. Based on the way it was interpreted it should be 1/8 of an inch too narrow. The software put the center of the cutter on the surface of the model. This means the edge where it was cutting was constantly 1/16th of an inch off. As you can see it's not too bad on a 3" model, and it will be less noticeable on anything larger. Still, it's relatively easy to fix by stretching the model out.


Andy
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jdougn
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PostPosted: Tue Dec 15, 2009 7:55 am    Post subject: Reply with quote

Culvan, this is great stuff!! Thanks for posting your build progress and all the information about the experience that you've had along the way.
Question, when you get the final 3d model CNC'd out what will you do with it?
DougN
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Culvan
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Location: Kansas City, MO

PostPosted: Tue Dec 15, 2009 8:10 am    Post subject: Reply with quote

jdougn wrote:

Question, when you get the final 3d model CNC'd out what will you do with it?
DougN


A good question. I'm still trying to figure out all the capabilities. Ideally I'd like to be able to use this to fabricate parts quickly. My original idea was to make bucks for vac forming. The machine has a little trouble with wood (that I believe I can fix) so I'm not doing that yet. Another direction is to make molds and then make resin parts. I just picked up some machineable wax from Mcmaster Carr. I haven't done anything with it yet, but I should be able to cut that accurately. The CNC->mould->resin process is slower and more expensive, but should be quick and capable of some good stuff.

I think I can make bucks for vacuum forming if I use either hydrostone or resin with metal powder in it. I think silicone has very good heat tolerance, but will deform under the pressure.

Anyone have any experience vacuum forming cast materials?

Andy
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danipe70
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PostPosted: Thu Jan 07, 2010 2:04 pm    Post subject: Protect foam with epoxy resin. Reply with quote

Im walking in the same way as you:

1.- Made my own cnc machine.
2.- Cut sheet of blue foam 3 cms depth. Wood or MDF are slow to machine. I use Rhinoceros with a pluging Rhicam to make the G Code.
3.- Join the sheets together to make de mold.
4.- Because of the heat and pressure of plastic in the vacuun forming melt and deform the foam, is not a good mold. After look everything in the web I think the best way to protect de foam is apply a coat of epoxy resin without fiber glass. Not used poliester resin because it will melt the foam.

Im still in the third point, and improve my cnc machine to cut faster a deeper.

This is my first answer, and I dont konw how to post photos to show my machine and some models.

[/img]
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danipe70
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PostPosted: Thu Jan 07, 2010 2:30 pm    Post subject: Photos of my cnc machine and first test of a helmet mold Reply with quote

My CNC machine and some first part of a stoormtropper helmet.



[img]http://i765.photobucket.com/albums/xx299/danipe70/P1010235.jpg
[/img]
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danipe70
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PostPosted: Thu Jan 07, 2010 2:47 pm    Post subject: Reply with quote

Photos of my first test mold. It was to small and will be resized.





Sorry about the size of the photos. Tell me about your progres.
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TK 109
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PostPosted: Fri Jan 08, 2010 1:20 pm    Post subject: Reply with quote

WOW.

THIS is REALLY cool stuff, man. VERY good work! Shocked


This is TOO cool, man! WOW. Just... WOW!! Shocked Very Happy
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danipe70
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PostPosted: Fri Jan 08, 2010 1:54 pm    Post subject: Reply with quote

Thank you, for you support TK 109.

I don't know if you could help me?. I need the real measures of the helmet to scale my autocad file, Do you know where could i find it?

Thanks to all that make possible this forum.
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LaughingCheese
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PostPosted: Sun Jan 17, 2010 12:30 am    Post subject: Reply with quote

Awesome work so far!

I was going to build this machine:

http://www.instructables.com/id/Easy-to-Build-Desk-Top-3-Axis-CNC-Milling-Machine/

But its been frustrating finding some of the parts because I'm a first timer and newbie at tools as well.


Therefore I was thinking about building a gantry machine like this, but the total cost is way too much for my budget.

I'm trying to keep it under $200, like the machine in the first link, so I'm thinking of something like what you're building, from the same plans.

Could I keep costs down if I build a smaller machine? I'm thinking of something with a footprint of about 16" x 18", maybe a tad larger.

I'm torn between the two designs. If I knew the gantry type could be cheaper if I made it smaller I would go for that one.


Thanks

LC
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stormtrooperguy
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PostPosted: Mon Jan 18, 2010 9:46 pm    Post subject: Reply with quote

this is great! i was just reading about desktop 3d printing and home cnc in the current issue of make.

as far as saving money by scaling up / down... i don't imagine much of the cost is size related. a 4' x 8' sheet of mdf is only around $30. i suspect the cutting tool, motherboard, etc... is where the cost lies.
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Culvan
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PostPosted: Thu Jan 21, 2010 10:35 pm    Post subject: Reply with quote

I need to stop in here more often. Sorry about the slow response.

Danipe70 - That looks awesome. It also looks like you have stacked layers of foam to make deeper parts. I've been considering doing that. I've found that the spray adhesive eats a little bit of the foam away. I'm probably going to use watered down wood gloe or watered down white glue. What have you used so far?

I was trying to cut the foam, then pour silicone right over it, but the voids from the spray adhesive filled up with sillicone and the mold didn't work. The sillicone also locked down on the foam. It was easy to remove with Acetone. However that destroyed the foam original.

LaughingCheese - stormtrooperguy is correct the cost of the wood around $40 for twice what I needed. The biggest single cost was the electronics. I think it was $280-ish for the stepper motor controller kit and stepper motors. $30 for bearings and most of the rest was spent on nuts and bolts. One of the things that drew me to the plans I listed at the beginning of this was that the author had listed all of the costs of the components up front. He left off the cutting tool and software. I re-used an old tool that I wasn't using otherwise. There is lots of free software, but I did break down and buy the machine controller. It was much easier to use than the free stuff. There appears to be someone selling kits for all the wooden parts for something like $200. That makes the wood cost 10x more, but almost any estimate of value for my labor would have made that a good deal. I ended up taking nearly two weeks off work to get all this done. (I couldn't cut any of it while the kids were sleeping)

I ran into a Machinist at my local harbor freight. After an hour conversation I've got a lot more confidence in what I'm doing. It sounds like I should be able to cut wood (albeit very slowly). I need to order some different milling bits too. I also think I'm going to use some demo software for the CAM part. I'l have to see how that goes. In addition to all that, I picked up some Machinable wax. It has properties similar to aluminum, but is easier on the tooling. Best of all I should be able to melt the chips down and reuse it. I'm a little nervous about that though. It sounds like it gives off fumes if heated to hot that can induce flu-like symptoms.

Andy
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danipe70
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PostPosted: Wed Jan 27, 2010 6:29 am    Post subject: Reply with quote

You are right, i used watered down white glue.
To do the mold, try to protect de foam with a layer of epoxi resin or poliuretane resin (not poliester resin), then sand the resin and paint it.

See this videos, they could help you.

http://www.youtube.com/watch?v=VWkch-QEGkI
http://www.youtube.com/watch?v=1WMuLBNthk8
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