Questions about building CNC Router

[PortlandGTS]

Hello,

I'm starting to consider building a CNC router for woodworking. I have a major cabinetry project coming up, that looks like a good candidate for a 2'x4' machine. That size would be big enough to cut out virtually all the panels I need, as well as doing rabbets, dados, etc.

I found the Fine Line Automation site from a post on this forum, and am really interested in their FLA-200. Originally, I was looking at the BlackToe from BuildYourCNC, but I really like the idea of all metal parts and 8020 construction. Plus, the price of the FLA-200 is not too much more.

Before I get in too deep, however, I have some basic questions I hope I can get answered here:

- Are there any good books, etc. available on CNC routers? I downloaded the "plans" for the FLA-200, but they consist of a bill of materials and drawings of the completed machine. I'd like to know more about setup, calibration, and operation of a CNC machine in a woodworking environment. I'm also concerned about the things that I don't know that I don't know.

- What are the options for holding down material when cutting out complete panels? I've seen mechanical hold downs, and vacuum systems. Are there other options? What happens with mechanical hold downs when you cut a piece completely free from its surroundings? Can you set up the programming to cut out one side, then shift the hold downs and cut out the other side? Is a vacuum system really the way to go for this type of work? I assume when cutting out pieces, you need sacrificial material to protect the machine bed. Does this affect the hold down mechanism (particularly vacuum systems)?

- Has anyone used a CNC router for cutting the edges of wood, e.g., for dovetails or mortices? If so, is this done by mounting the router with the shaft horizontal, or by mounting the wood vertically with some sort of vise?

- I've gotten fairly proficient with Google SketchUp. Is this a good CAD program for a CNC router? I've found a plug-in that generates DXF files from SketchUp. I was planning on feeding these DXF files to Mach 3. Is this a workable plan?

- Finally, any other words of wisdom for a newcomer to this field?

Thanks,
Tom

[wjbzone]

Not sure about a book. I use clamps on my parts and program stops to move the clamps.
Check out this setup for cutting the edge for dovetails
WJBzone Puzzle Box

[JC50]

As far as cutting completely around a piece which separates it from the outside. All of the CAM software I've played with has the ability to make 'bridges". Basically they are small areas left uncut between the waste material (which is typically clamped, screwed down, whatever) and the area you have machined. This keeps the finished piece attached to the waste material. Once the piece is completed, you remove the whole piece and use a small saw to cut through the bridges. I use a fine toothed thin blade backsaw. You then sand down the remaining portion of the bridge on the edge of the finished piece.

[DonFrambach]

I found it very helpful to look at some of the build logs here on CNCZone.com. There are also a number of very good ones listed here: CNCRouterParts

[ger21]

- Are there any good books, etc. available on CNC routers? I downloaded the "plans" for the FLA-200, but they consist of a bill of materials and drawings of the completed machine. I'd like to know more about setup, calibration, and operation of a CNC machine in a woodworking environment. I'm also concerned about the things that I don't know that I don't know.

I'm not aware of any books, but you might be able to fins some websites with some info.
If you ask specific question here, you'll get then answered pretty quickly.

Not sure what you mean by setup. Do you mean Mach3 setup? It's not too difficult.

Calibration? Again, fairly simple. Move. Measure. Adjust the software settings.
Operation. Here, you may get a lot of opinions. People like to work different ways. Personally, I work in a commercial cabinet shop, so I try to setup my machine so that my workflow is similar to using the $100K machine we have at work.
I have fixed fences to locate my parts, and use a persistent origin for most of my work. A lot of people will mount a board somewhere on their machine, and then set the origin to match the board. Not the most efficient method imo.

- What are the options for holding down material when cutting out complete panels? I've seen mechanical hold downs, and vacuum systems. Are there other options?

There are an endless array of clamping systems in use. Some find that holding the workpiece is the most complicated part of CNC.

What happens with mechanical hold downs when you cut a piece completely free from its surroundings? Can you set up the programming to cut out one side, then shift the hold downs and cut out the other side?

Generally, if you cut a part completely free, it'll be damaged from moving (Unless you use vacuum).

Yes, you can cut half the part at a time, and move clamps, but it wouldn't be my preferred method.

Is a vacuum system really the way to go for this type of work? I assume when cutting out pieces, you need sacrificial material to protect the machine bed. Does this affect the hold down mechanism (particularly vacuum systems)?

Yes, imo, it is. But achieving that with a reasonable budget may be another story.
Regardless of the holddown system used, a spoilboard is usually used on the machine bed, allowing the tool to cut through the part.
The most efficient (from a production standpoint) type of vacuum system is drawing vacuum through the spoilboard. On industrial machines, this is accomplished with big vacuum pumps, up to 25-40HP. Not practical for a small shop or garage. Shopbot users are using high powered vacuum cleaner motors to build similar systems. Follow the links at the bottom of this page to see some examples.
ShopBot Vacuum Motors
While a lot cheaper than a 25HP pump, you'd still be looking at close to $500. Imo, you'd need two motors to get enough vacuum. Some Shopbot users are using 4 of them.
Even with really good vacuum, small parts are prone to moving with this type of system. One solution is known as onion skinning. You cut most of the way through the parts, leaving a thin "onion skin", maybe .01" thick. Then make a second pass to remove the skin. On this second pass, cutting forces are near zero, so parts are much less likely to move.
Another option is to leave the skin, and trim the parts free with a laminate trimmer, or small router with a flush bearing bit.
Still another is to leave small tabs that can be quickly cut away. A few CAM programs can create these tabs for you.

An alternative vacuum system is a "pod" type system. You use several small vacuum "pods" that hold your sheets up off of the table. These usually use a rubber seal, to get very high vacuum with a much smaller pump.
If you can locate them carefully, you can cut through your parts and around the pods. Or you can leave a thin skin for trimming later.

- Has anyone used a CNC router for cutting the edges of wood, e.g., for dovetails or mortices? If so, is this done by mounting the router with the shaft horizontal, or by mounting the wood vertically with some sort of vise?

Yes, you can do it either way. Careful attention to toolpaths may be required to prevent, to minimize tearout.
A dovetail jig would probably be a lot faster.

- I've gotten fairly proficient with Google SketchUp. Is this a good CAD program for a CNC router?

While quite a few people use it successfully, Imo, no, it's not a good choice. The main reason for me, is that sketchup can not export arcs or circles. So all arcs and circles are made up of multiple straight line segments.
Also, most flat panel routing uses 2D drawings to create the toolpaths. Why use a 3D program when all you need is 2D? This is just my opinion, you may find that it'll work fine for you.

I was planning on feeding these DXF files to Mach 3. Is this a workable plan?

Workable, Yes. Recommended? Not by me.
Mach3 comes with LazyCAM, which converts .dxf files to g-code. The free version included is clunky to use, and feature limited. Buying LazyCAM PRO gives you more features for $75. However, be very aware that it's no longer being developed. Some people use it and like it, but there are much better options. Unfortunately, they usually cost more.

- Finally, any other words of wisdom for a newcomer to this field?

Spend at least 2 months here, reading, reading, and reading.

[louieatienza]

Hello,

I'm starting to consider building a CNC router for woodworking. I have a major cabinetry project coming up, that looks like a good candidate for a 2'x4' machine. That size would be big enough to cut out virtually all the panels I need, as well as doing rabbets, dados, etc.

I found the Fine Line Automation site from a post on this forum, and am really interested in their FLA-200. Originally, I was looking at the BlackToe from BuildYourCNC, but I really like the idea of all metal parts and 8020 construction. Plus, the price of the FLA-200 is not too much more.

Before I get in too deep, however, I have some basic questions I hope I can get answered here:

- Are there any good books, etc. available on CNC routers? I downloaded the "plans" for the FLA-200, but they consist of a bill of materials and drawings of the completed machine. I'd like to know more about setup, calibration, and operation of a CNC machine in a woodworking environment. I'm also concerned about the things that I don't know that I don't know.

- What are the options for holding down material when cutting out complete panels? I've seen mechanical hold downs, and vacuum systems. Are there other options? What happens with mechanical hold downs when you cut a piece completely free from its surroundings? Can you set up the programming to cut out one side, then shift the hold downs and cut out the other side? Is a vacuum system really the way to go for this type of work? I assume when cutting out pieces, you need sacrificial material to protect the machine bed. Does this affect the hold down mechanism (particularly vacuum systems)?

- Has anyone used a CNC router for cutting the edges of wood, e.g., for dovetails or mortices? If so, is this done by mounting the router with the shaft horizontal, or by mounting the wood vertically with some sort of vise?

- I've gotten fairly proficient with Google SketchUp. Is this a good CAD program for a CNC router? I've found a plug-in that generates DXF files from SketchUp. I was planning on feeding these DXF files to Mach 3. Is this a workable plan?

- Finally, any other words of wisdom for a newcomer to this field?

Thanks,
Tom

1- Ahren from CNC Router Parts makes components that bolt on to extrusions, and has some plans as well. A lot of people here are using his stuff with success... Setup and calibration of the software is pretty straightforward. As for books, there's not a lot out there. There was onw advertised here called the CNC Cookbook. There are also plans on sale on eBay for the Momus Design router. While smaller than your needs, I think the author gives some really good information as to construction and design. The rest you could probably get from lurking here!

2- If you had a vacuum pump you could probably make yor own vacuum hold downs. Another way would be to leave tabs to be cut apart later, or leave a thin skin of material. Yet another way, if you're making paint grade stuff, is to simply pin the work down with a 23 ga. pinner...

3- Search YouTube for videos of CNC dovevtail routing. I've seen it done with a 5-axis router (A/C head) but that's getting a bit crazy. Usualkly the router bed is shortened for a vertical clamping area. A backerboard could prevent tearout.

4- As mentioned before, SketchUp might mot be the most accurate way to design parts for CNC cutting. Though there is a plugin called PhlatScript that will allow you to do basic 2.5d work, and generate g code, right from SketchUp!

5- Read a lot of the builds here. You can learn as much from mistakes as well as successes. You have goals for what your machine needs to cut. Now you need to set goals as to cost.

[PortlandGTS]

Thanks for all the responses. They provided a lot of useful information. Also, I'm finding good information in the build threads.

I do have a couple followup questions:

- By "setup", I meant putting together the CNC router. I've never worked with 8020 extrusions before, so I assume there must be some slop in the connections. How does one make sure that things are parallel, coplanar, etc.?

- What are some low cost alternatives to SketchUp? At this point, I have the cabinetry project I am planning drawn completely in SketchUp, with each piece a separate component. I planned to "pull out" each piece, and convert it to DXF separately to feed to Lazy CAM. Given that I've already invested this much effort into SketchUp, I'll probably use it for this first project. But I'd appreciate suggestions for software to look into.

Thanks again for the help. I'm sure I'll have lot more questions as I get further into this.

Tom

[ger21]

- What are some low cost alternatives to SketchUp? At this point, I have the cabinetry project I am planning drawn completely in SketchUp, with each piece a separate component. I planned to "pull out" each piece, and convert it to DXF separately to feed to Lazy CAM. Given that I've already invested this much effort into SketchUp, I'll probably use it for this first project. But I'd appreciate suggestions for software to look into.

A good, free 2D CAD program is Draftsight. You're going to need 2D .dxf files to convert to g-code, so no sense drawing in 3D. If you do want to use a 3D CAD program, be aware that CAM programs that can use 3D models, will usually be much more expensive.

[Phife]

I just wanted to jump in here and give my opinion in Sketchup.

I use Sketchup pro exclusively. I really like it because its quick and easy to learn.

While sketchup doesnt export arcs, I generally never have issues with it because my CAM program automatically converts all line segments to arcs for me, When I draw a circle in sketchup it will be made of arcs when I open the dxf in my CAM program (I use Vcarve pro and Artcam)

Also, I only draw my models in 2d using sketchup and I export the 2d file in a 3d DXF. My CAM programs have no problem with this. I generally start sketchup and click on the Z view icon (roof of house) this puts it into a sort of 2D drawing mode, I also change the camera from perspective to Parrallel projection. This eliminates the Z axis lines and allows you to view the model in 2D fairly well.

You can draw your cabinets in 3d using sketchup, but you will not want to export a 3D DXF for your CAM program. You only need the profiles, and things like circles for shelf holes and stuff. the CAM program will only look at the 2D info anyways.

I know there are better CAD software out there, but over the last 2 years I have not needed anything other than Sketchup, and it was cheap!

Hope this was helpful!

[ger21]

When I draw a circle in sketchup it will be made of arcs when I open the dxf in my CAM program (I use Vcarve pro and Artcam)

A circle made up of lines will not be automatically converted to arcs when loaded into V-Carve Pro.

If I'm wrong, tell me how it's done. I know you can fit curves to the vectors.

[Phife]

A circle made up of lines will not be automatically converted to arcs when loaded into V-Carve Pro.

If I'm wrong, tell me how it's done. I know you can fit curves to the vectors.

It depends on the size of the circle, small circles under say 1" diameter will show up automatically as arcs in Vcarve pro 5.5 Larger circles you need to change the # of segments of the circle in sketchup entity window to something like 60 (default is 12, I find 60 to be enough for circles as large as 32" diameter). As long as the circle is made up of a lot of segments for its size it gets converted by Vcarve automatically.

For things that didnt convert, a simple selection and a click on "Fit curves to Vectors" works just fine.


*Edit*
I just did a test, and drew about 12 circles ranging from .125" to 36" diameter didnt change the segments in sketchup and exported and then imported to Vcarve. All of the circles were converted to arcs automatically.

[ger21]

I just loaded a 1" diameter circle with 48 segments into Aspire. While it does become arcs, it still has 48 segments, and gives you 48 lines of g-code, vs 1 line for a circle.