Dumb CNC questions (probably)

[abitfishy]

Hi all,

I have a couple of queries regarding the CNC machines, if you don't mind, to help me understand a bit more about them. I understand what they do, generally, but not these specifics.

I understand they use a DXF file sent to the controller that tells the router what design to cut, just as a plotter or vinyl cutter does, however how is depth of cut controlled if its just a DXF file? On the same subject, how do you tell it to go so deep to 'engrave' rather than 'cut' all the way through the piece. Is it also possible to have varying range of depth of cut on the one piece to give a type of '3D' type appearance or shading.

I'll probably thing of more.

Thanks

[Dingo745]

I'll try to answer with my limited working knowledge of CNC.
The .dxf file is usually imported into a seperate program which creates the required toolpaths to cut the design.
This is normally outputted in a G-Code file, which is imported into, typically Mach3 controller software.
This g-code file has all the instructions relating to the job. Size, feed rates, depth of cut etc.
These variables are entered into the software that creates the toolpaths.
As for the 3D bit, well generally you would create a 3D model in software, then the g-code file would have 3D toolpaths for the differing cut depths.
Confused ? I am.
I'm sure one of the more learned members can explain better, but that's a start.

[Greolt]

I was trying to come up with an explanation and it was just a load of long winded waffle. :roll:

Yours is much more succinct.

Greg

[abitfishy]

I thought it might be a difficult question.....

You see, I can understand using a program to draw the design, but not how to tell the router how deep to do the design.....

[rodm]

The process is very easy but it is difficult to explain and sounds complicated.
The simplest way of explaining is that a 2D drawing is required and you nominate a cutter and the depth of cut for each line. So lets try an example.
In the first attachment I have some text and I nominated to cut in on the line and to a depth of 0.5mm.
In the second attachment I have the same piece but have added an eclipse and told it to cut outside the eclipse and to a depth of 3.1mm. The material was 3mm thick so you can see it has cut through the piece.

In complex routing where there are multiple changes in the depth of cut (3D) the software does this calculation for you. As Dean had said you run it through a piece of software that does all the hard work for you. This then outputs a file that you take to your machine. Like I said it sounds complicated but it isn't and once you learn a bit of the terminolgy used it is a piece of cake.

[rodm]

And while you were thinking I did the long winded waffle reply. :-)

[joe greiner]

I know next to nothing about CNC programming. But a DXF file created by a CAD program such as AutoCAD is a binary or ASCII text file including three coordinates for each entity. Aside from its native file type (e.g. DWG in AutoCAD), your 3D modelling program should have a command something like "Export to DXF." The toolpath program reads the DXF file and generates another file suited to the CNC machine.

Joe

[abitfishy]

Thanks guys. That does make some sense, although it would be good if my neighbour had one to give me a demo. :U At the low price for the cheap MDF models I'd be tempted myself, then I would FIND things I could do with it. I could imagine some of the complicated designs that this thing would make a piece of p*ss. :D

[WillyInBris]

A piece of , um I would say no.

The reasons are as follows.

One you need to learn how to create what you require and design it in the software I find this the fun part on the process.

What bits are required and what feed rates to use different things like Nylon, Perspex, MDF, Blackwood everything you cut may react differently and require different settings and bits.

The main things you will gain are precision as well as being able to put out the same part a number of times exactly the same dimensions and design.

But its all fun and I enjoy learning how to use a new tool.

[AV Elec]

although it would be good if my neighbour had one to give me a demo.

I intend to build one. No idea when it will be finished though, as all I have done so far is look at different plans...

[WillyInBris]

Sorry guys hope I didn't sound negative on the above post, good to hear AV thats what we want to hear. :2tsup:

The first step is normally accumulation of both Knowledge Design and parts its takes a it of time but you will get there.

[big_gumbo]

Once you got the dxf, from AutoCAD or somewhere, there are special programs for the CNC router. You tell how deep you want the cut, how fast etc etc

http://www.cadlink.com/products/profileLab/pl_prodInfo_pkgs.php

[abitfishy]

A piece of , um I would say no.

The reasons are as follows.

One you need to learn how to create what you require and design it in the software I find this the fun part on the process.

What bits are required and what feed rates to use different things like Nylon, Perspex, MDF, Blackwood everything you cut may react differently and require different settings and bits.

The main things you will gain are precision as well as being able to put out the same part a number of times exactly the same dimensions and design.

But its all fun and I enjoy learning how to use a new tool.

Fair enough mate, maybe a bad choice of words. :(( However being in IT I can't say I will have too much trouble with the software once I take a look, I hope, and I guess sample pieces are the go before plunging (pardon the pun) into the deep end. :2tsup:

[AV Elec]

Although it was done with a mill, the concept is the same. Imagine making a supercharger turbine with a CNC machine!

http://www.sherline.com/images/RosenTurbine.jpg

[WillyInBris]

Fair enough mate, maybe a bad choice of words. :(( However being in IT I can't say I will have too much trouble with the software once I take a look, I hope, and I guess sample pieces are the go before plunging (pardon the pun) into the deep end. :2tsup:

lol good pun, After spending 12years in the industry I left two years ago will never go back.

lots of good software around and I haven't had many problems nutting it out so I don't think you will as well, bit of a learning curve to start with then all is good.

so what do you think you would use the Router for do you have any aims etc?

please tell me your a sharks supporter and what part of the shire you live in.

[abitfishy]

Hey Willy,

Yes, I absolutely hate IT nowadays. I got in when IT was DOS, Windows for workgroups and Novell. It its the pits now, but no idea what to do, my woodwork skills would see me living off welfare real quick. :)

To tell the truth, I have no idea what I would use it for. :) I have no doubt I could find plenty suitable projects that one would be ideal for. I'm absolutely no good at hand holding anything, so I can imagine it would allow me to do a lot of things much easier than I could otherwise, or too complicated a design for me to do manually. Having said that, its most likely a thing that is on a very long list of things I'd like and will probably never get around to.

Actually, I'm not really a football supporter actually, but I live in Sutherland which is Southern suburbs with a move this year further north. Yes, I'm leaving gods country, god forbid. :(

[WillyInBris]

Nooooooooooooooooooo Don't go lol.

Born and bread shire boy I am, from Cronulla left about 9 Years ago came to Brisbane for a IT job with NEC left after paying off most of my house and looking to move to Coffs its getting a bit busy up in Brisbane :(( starting to turn into a mini Sydney.

Well building one of these machines can be a hobby in itself and I ain't the best with tools either but do love my lathe but its been gathering dust so I will be selling it.

you may have seen my post on the green man? you can do so many fun things with a CNC well I find it fun anyway,

All is good when ya ready or want to talk more the guys on this forum have a crap load knowledge and you will see it build over the months.

Sean

[gator3535]

Actually CNC's are very simple. 3axis machines only move in 3 directions x, y ,z. X and Y are north, south, east west and z is up, down. A dxf is created and tool paths are assigned, tools are set-up etc. This info from the dxf (or the design) is then passed through a "post" program that converts all this info into code (g-code usually) specific to the machine. Most machines will come wil some with software that you can use to do this manually too.

Nesting has taken cabinet manufacturing to the next level by having all the parts from the design software carry intelligence that will assign operations to the parts (such as a dowel hole or a dado or adjustable shelf holes) and all the operations from all the parts get assigned automatically and the parts are "nested' onto the correct material. This means they are places on the material ready to be cut out to achieve the least amount of waste possible .. it will look like a jig saw puzzle. There is NO MORE manual programing needed. The software does it all.

This programing cannot be achieved manually within a reasonable amount of time. In the old days we would put single parts on cnc's for processing and a programer would program each program for each part.

Please feel free to fire any questions at me you have ... :U

Bruce

[WillyInBris]

Hi Bruce welcome to the CNC forum,

Can you give us an idea on what type of bits you use whom you buy them from what you cut them with etc.

Also what do you Cad Cam packages do you guys use in the trade to create your work?

Thanks in advance

Sean

[gator3535]

Hey Sean. Onsrud seems to have a good selection but there is so many tool suppliers out there .. I cant keep up with them all. With the work I am involved with we use drill bits, downspiral cutters, compression bits ( for outline cuts) and profile bits for making doors.

There are quite afew Software packages out there .. but very few good ones. I have many years experience with Planit software . but I know there are other good ones out there. The key is to have "seamless" movement from design to cutting.

I have worked with and integrated most of the main nesting cnc machines you will find out there. They are not that different for each other.. just how the controller works.

I am actualy in the process of moving back to Australia and and looking for work right now.