CNC Question

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ldimick

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I have a chance to buy a CNC machine at a good price.

I have no experience using a CNC and I need some ansdwers. I hope you people can help.

Can a CNC machine do a good job of detailed engraving? How close to laser can it get?

Can a CNC cut bands that are as detailed as the Statesman and Jr Statesman?
 
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swm6500

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As far as I know, CNC is just the control part of a machine. The machine can be a milling machine, lathe or something else. Bruce would probably be the expert on this.
 

wrightal3

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I have a friend who is a luthier making very expensive & sought after instruments. He uses his CNC for almost everything now. Some of his inlay work is so fine and detailed it is amazing. Some of his bits are from the dental industry. If you can program it, the machine can do it.
 

kghinsr

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Lynn
you did not say whether it is a lathe or milling machine.
the cnc machine is only as good as the program running it.
buying a machine at a good price will still require to spend many hours
learning how to get it from the computor to the machine.
as for the laser it is not the same machine as a cnc
you will not get the same output
I have done cnc for 3 yrs now and I'm still learning
ken
western pa
 

Fred in NC

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Lynn, as stated above, there are many kinds of CNC machines. You did not state whether the machine you are looking at is a lathe or a mill. There are CNC machines designed for shops making parts, and some are designed for jewelry, where the piece is very small and a high degreee of detail and precision are required. Roland makes CNC mills for jewelry use. Most CNC jewelry is cut from machinable WAX and the wax used to cast the actual part.

To do engraving you need a high speed spindle. That is what holds the cutting tool, which is like a miniature router bit. Such spindles turn at very high speeds, 25,000 to 50,000 RPM is very common. The spindles that come with most mills run at about 6,000 RPM max. The runout (tolerance) in these spindles is often less than .001".

Of the two types of machines, in my opinion, the mill with 4th axis is the most useful since it can make engraved round parts as well as flat parts like clips.

Using as an example an engraved center band, the first step will be to draw the band using a 3-D CAD program. Then the CAD file is run through a CAM program to set the tool paths. The CAM file is then used to run the CNC machine and do the actual cutting. The prices of CAD/CAM software range from free to thousands of dollars. The problem is that the 3-D software suitable fo jewelry (pen parts) is not the cheapest!

Given the above, even if buying a used machine that is suitable for pen parts, the total expense before you are ready to make the first part will probably be a few thouosand dollars. You will need to learn CAD/CAM to design the parts and produce the CAM files.

Hope this helps. And I hope you can get the machine if it will do the job.

A CNC lathe will cut anything that is round. To engrave around a cylinder, such as a center band, you need a mill with a 4th axis. The 4th axis is a CNC controlled rotary table.
 

Paul in OKC

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Originally posted by Paul in OKC
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(I have a chance to buy a CNC machine at a good price.)

Depends on the machine

(I have no experience using a CNC and I need some ansdwers. I hope you people can help.

Can a CNC machine do a good job of detailed engraving? How close to laser can it get?)

In my opinion, it can not do as well as a laser on things like small lettering. The wood won't support the tool pressure and the center of letters like e and such would most likely break out.

(Can a CNC cut bands that are as detailed as the Statesman and Jr
Statesman?)

With a fourth axis, it can do some pretty detailed work. For just doing some inlayed pockets, you could make a jig to rotate the part at 30 or 45 degrees or whatever. I have done some wood inlays on my big bridgeport at the shop with a .031 end mill and at 3000 rpm. Not as clean as a router spindle at 25,000 plus, but it works.
HTH
 

btboone

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Yup. I have a tabletop CNC 4th axis machine as well as a "real" machining center. The limit for engraving will be the cutter diameter. A laser may have a beam size of around .006", whereas a CNC mill will have a limit on how small of a cutter you can use before it can't get the chips out fast enough and just snaps off. As Paul says around 1/32" is approaching the lower limit. You might be able to get by with .020" in a stub endmill, but it's pushing.

As for software, if it's a table top machine, it might be supplied with some software that can interpret dxf files. You could just draw the letters or designs in CAD and the software writes the G-Code, which is what the machine uses. If it doesn't come with CAM software (computer aided machining, the stuff that writes the code) you would at least need to get proficient in CAD (computer aided drafting) to be able to pick off the coorinates needed to write the code yourself. It's not too bad to learn. I hand write all of my machining center code.
 

Paul in OKC

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As for software, if it's a table top machine, it might be supplied with some software that can interpret dxf files. You could just draw the letters or designs in CAD and the software writes the G-Code, which is what the machine uses. If it doesn't come with CAM software (computer aided machining, the stuff that writes the code) you would at least need to get proficient in CAD (computer aided drafting) to be able to pick off the coorinates needed to write the code yourself. It's not too bad to learn. I hand write all of my machining center code.

There are also some free (or very low cost)downloadable software places that have stuff for G-code conversion.
 

Fred in NC

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Paul, if you find a good free or cheap CAM that can do 3-D, please let me know.

This is machining code: (G-codes)

G00 Z-0.030 ;Position for cut
G01 X0.295 ;Face off
G04 P1
G01 X0.075
G01 Z-0.730 ;Rough Turn
G01 X0.000
G00 Z-0.030

An engraved part (like in some kind of design) can have thousands of lines of code !!!

G01 X0.130
G01 Z-0.770 X0.075 F4.5 ;Rough Turn Angle
 

marjoe

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I ran a CNC mill for 15 yrs. and still do. We have mastercam for Cad software, that cost $19000.00 but for my job it pays for itself. I can engrave any font I can get in my computer even handwriting or pictures. The size is limited to the size of the cutter as bruce said. Also the smaller the cutter the faster the spindle has to turn. I can engrave on an dome but that is limited because the cutter stays vetical. With a 4th axis machine the cutter stays perpendicular to the arc. With a rotary table the cutter stays vertical and the rotary table turns. I use small center drills for engraving and a depth of .005. I do a lot of part #s on the things I make but I have not tried doing a pen yet. I would have to measure the pen corectly to draw it so I could engrave it. The machine cuts in 3d so it follows any surface whether it is tapered, angled, or a radius. I have been thinking of making a pen with it, maybe I will try it.
 

marjoe

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Sorry its not a rotary table its an indexing head. A rotary table holds a part vertical and moves in X and Y and turns 360 degrees. An indexing head holds a part horizontal and rotates 360 degrees.
 

btboone

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I'd still call it a rotary table or rotary axis even for the horizontal axis. An indexing head implies that it only can stop at given increments and not be controlled when driven like another axis. They add a whole level of capability to a CNC mill. A rotary table where the part sits upright is redundant on a vertical spindle mill. To cut a circle, it is easily programmed on the XY table itself, so a rotary table is not needed there. With horizontal rotary axis it would be possible to add engraving around a pen, do helical scrollwork, or do indexed drilled holes or slots. The programming gets trickier, but it definitely is the way to go for pens.
 

marjoe

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You are right a rotary table is not needed on a CNC mill but was needed to do offset or oblong holes or pins before CNC. Not many shops have them anymore with CNC. An indexing head can be manual or CNC and turn parts horizontaly 360 degrees. I was just correcting what I said because I don't call it a rotary table.
 

Fangar

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CNC is what controls the machine. Computerized Numerical Control. This type of term and computerized system is used and can to refer to many machines. For example a CNC Mill like others have stated. There are also CNC lathes, water pressure cutters, and even things like embroidery machines that are all CNC based. But oh what fun one could have for repetion of amazing designs. Ugh!

James
 
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