# Two Questions Regarding CNC



## Guitar_Jen (Nov 21, 2010)

Hi Everyone,

i moved this from the introductions section in hopes that someone could answer my questions regarding CNC routing.

I have recently begun working on inlay and stringed musical instrument making (lutherie). I have been a lapidary for many years and earlier in life worked as a cabinet maker in the yacht industry. so becomming a luthier who also inlays her creations with abalone and mother of peral, among other materials, seems like a natural progression.

about a month ago i acquired a CNC controlled router. it has three axis control and runs under a program called "Mach3". Mach3 takes something called "G-Code" which is developed by "CAD", computer aided drafting, programs.

the router is wonderful, can hold a pretty high accuracy, about .003" with good repeatability. Now it is time for me to purchase a CAD program so that i can begin transfering my inlay designs.

I have two questiuons:

First is: Does anyone out there know how to hold a small thin (.050" or so) piece of material like shell on the router table so I can cut it? people in the guitar industry create CNC inlay all the time, so there must be a way.

Second is: does anyone out there know anything about CAD software? i want to purchase a program that will let me "draw" the delicate curves that often go with inlay. most i have looked at are really great at straight lines and geometric shapes comon in industrial drafting, but are a little weak when it comes to generating complex curves. Any suggestions would be warmly welcomed.

Thanks for your assistance. It is nice that there is an active forum just for people who use routers.

Thanks,
Jen :help:


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## Phil P (Jul 25, 2010)

Hi Jen



Guitar_Jen said:


> First is: Does anyone out there know how to hold a small thin (.050" or so) piece of material like shell on the router table so I can cut it? people in the guitar industry create CNC inlay all the time, so there must be a way.


The way thin components are held down is often to have a through-flow vacuum pump drawing dowm through a permeable spoil board - or in other words a very large volume vacuum pump sucking through an MDF spoilboard. To improve efficiency areas not holding workpieces need to be blanked off with plastic film. Alternatively if you are making mainly one-offs you might like to try attaching your materials to a sacrificial spoil board by means of a good quality double-dided tape. I'd recommend All Star Adhesives Jig Tape.



Guitar_Jen said:


> Second is: does anyone out there know anything about CAD software? i want to purchase a program that will let me "draw" the delicate curves that often go with inlay. most i have looked at are really great at straight lines and geometric shapes comon in industrial drafting, but are a little weak when it comes to generating complex curves. Any suggestions would be warmly welcomed.


Whilst that type of CAD isn't my area of expertise I've had success in the past on small pieces by scanning or tracing an original then using software like Corel Draw to edit and smooth out the curves. The resulting bezier files were exported in a CAD-compatible format (e.g. AutoCAD DXF) and then imported into the CAD program for inclusion in a larger component. The main reason for that approach was that I had Corel Draw already and I was already familiar with the Corel Trace application, so it was a no cost exercise. One thing worth noting is that smooth curves like this can result in CAD files with hundreds or even thousands of tiny line segments, so beware big files and slow execution.


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## Guitar_Jen (Nov 21, 2010)

Phil,

thank you for the reply.

I have thought about using vacuum to hold the pieces, but most often they are so tiny the the total holding force exerted on them would be much too small to hold the pieces. At 14.7 pounds pre inch square, assuming an absolute vacuum, the holding force on a piece a few mm's in width and length would not amount to much. 

The idea about a sacrifficial "spoil board" may be the answer. I could use some type of adhesive that is easily dissolved in a solvent that will not attack the shell. This sounds like it may be the way to go. 

To give you an idea of the scale of my craft: I work with shell blanks that often are only a square inch or two in total area, I often can get four or five parts from one of these, even ten at times. It is kind of like making a tiny mosaic.

Now all I need to figure out is what material to use for the substrate, and what type of adhesive to use for attaching the shell. I am afraid that two sided tape is too thick and potentially too elastic for the tiny work i do. If the piece should slip during cutting the entire desigh could be comprimised. Each piece of shell is just one part of a very complicated miniscule "jig saw puzzle", if one piece is misshapen all the others surrounding it will not fit properly.

I think the substrate idea is grand, i will pursue it further. 

Thanks again,
Jen


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## Phil P (Jul 25, 2010)

Hi Jen



Guitar_Jen said:


> To give you an idea of the scale of my craft: I work with shell blanks that often are only a square inch or two in total area, I often can get four or five parts from one of these, even ten at times. It is kind of like making a tiny mosaic.


Wow! That's what I call small. I've rarely machined anything that small in wood or plastics.



Guitar_Jen said:


> Now all I need to figure out is what material to use for the substrate, and what type of adhesive to use for attaching the shell. I am afraid that two sided tape is too thick and potentially too elastic for the tiny work i do. If the piece should slip during cutting the entire desigh could be comprimised. Each piece of shell is just one part of a very complicated miniscule "jig saw puzzle", if one piece is misshapen all the others surrounding it will not fit properly.


I've used the double-sided tape on delicate wood and plastic components in the past with some success, but I fear that you might have a problem dealing with any glue residues. In terms of substrate/adhesive would something like birch plywood substrate with a hide glue not work? The bond is very good once the glue has set (hide glue used to be used in some forms of glass etching) and the hide glue can be easily softened by the application of gentle heat. In terms of slippage the only advice I can give is to reduce the feed rate and us a technique called "onion skinning" where one or more passes is made to define the component without piercing the bottom surface, the feed speed is then reduced considerably for the final pass at full depth. BTW if you do use plywood as a spoilboard make sure that you make a surfacing run with a spoilboard cutter because plywood is never truly flat


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## Noob (Apr 18, 2009)

Guitar_Jen said:


> Hi Everyone,
> 
> Second is: does anyone out there know anything about CAD software? i want to purchase a program that will let me "draw" the delicate curves that often go with inlay. most i have looked at are really great at straight lines and geometric shapes comon in industrial drafting, but are a little weak when it comes to generating complex curves. Any suggestions would be warmly welcomed.
> 
> ...


I can't help you with the first question, but for 2D CAD, download the FREE Draftsight program from Solidworks/Dassault Systemes. It is a fully-working program, the only catch (not much of one) is that they will want you to register your name and email. Just make up a new one in Gmail or Yahoo if you don't like giving out your personal email.

If you have ever worked with AutoCAD, you can use this program. For your inlays, if circles and arcs don't work for you, then use splines.

Draftsight LINK


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## Guitar_Jen (Nov 21, 2010)

Thanks Noob, i really appreciate your input.

I have explored Draftsight and other Freeware based CAD applications. they just do not have the bells and whistles i want. I am still leaning towards the V-Carve product. although Vcarve is not the best for drawing complex curves it has many good features. You can preview what a finished part looks like in 3-D, a single drawing can be used for both parts of an inlay (the part and the recess) because it automatically calculates offsets based on the tool you select and can export directly to usable G-Code.

I am not worried about price, within reason, what i am really looking for is advanced functionality. If I could import a drawing, specify the tool and thickness, push a button and have G-Code come out i would be a very happy camper. 

My day job is applicatioons programming. the last thing i want to do is futz around with software more than i have to when engaging in my hobbies


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## thermwooddriver (Nov 30, 2010)

If the material you are wanting to hold is flat, a vacuum table works great, provided the piece being held has sufficient area to produce the force necessary. Some people use double sided tape but this can cause problems in that the "sticky" adhesive will build up on the cutter and usually cause a problem. 
As far as a CAM(computer aided machining) program, one of the most popular is Mastercam. This is a very good program, but is pretty pricy. There are lower priced systems out there, but I dont have any exposure to them. Google computer aided machining and see what is out there.
Tom


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## royce (Nov 7, 2010)

Jen

In the pool cue industry we do small surface inlay all the time.

There are a few methods commonly used to hold the work when cutting the parts.

1. Golf grip tape. This is the two sided tape you are talking about, but is very strong and sticky. The only real drawback to this is if you cut into the tape, which you most likely will, the glue will get stuck in the cutter and clog it up. When you are using small cutters like we do, .020" diameter, they break real easy and are expensive.

2. Just don't cut through, and use a thickness sander to remove the parts. I like this the best. If I can have my material to be about .150" thick and cut my inlays to .125" deep and just sand away the back. 

3. Glue it down as mentioned above. I haven't used hide glue, but I know that guitar makers have used it in the past. I have used contact cement and then dissolved it with mineral spirits. Just throw the parts and backup board in a bucket and they will fall off the board when the glue lets go.

By the way, if you are having trouble holding tolerances tighter than .003", then you will most likely have issues with glue lines around your inlays. I like to have backlash under .001" as a minimum. This shouldn't be too hard depending on how your machine is designed.


As for software, I recommend Bobcad. I use 23, but they have just come out with 24 and I'm not sure the differences yet.

Bobcad is a cam software that will let you draw in 2d or 3d, import images and rastorize them, and create G code to run in Mach3. Don't let the price on the website scare you, they will negotiate. If you download the trial version on Thursday, they will call you on Friday, which is the best day to haggle with them. 

Email me if you have any questions.

[email protected]

I hope that helps!

Royce Bunnell
OB Cues


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## Roy R. (Dec 7, 2010)

*Cad software*

Jen - i don't cnc the delicate parts you are doing however the programs we use for our production are Corel Draw and SignLab (to do the drawings) and EnRoute 4 (for the execution of the cutting (the tool pathing). Hope this helps, Roy


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## jeremy budgen (Oct 9, 2010)

Jen

What i do for my guitar inlays is to glue the shell to a spoil board with supaglue, then do the routing with my biesse cnc machine and then when i am finished i soak the whole thing in water and that softens the glue a little so that you can put a flat palette knife under the shell to lift it off the spoil board.

The software that i use for my designing is autocad then send it to biesseworks for tool path creation..

PM me for details on autocad.


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## bgardner46 (Jan 8, 2010)

Jen,

I know this thread is several days old but I would like to recommend Inkscape for drawing. I have started using it recently and have only begun to scratch the surface of what you can do with it. It is open source software so the price is right also.

Besides drawing from scratch you can also import bitmap drawings and convert them to vector drawings where you can modify them before ultimately sending the m to your CAM software to convert to Gcode.

Apparently, since I have not posted previously, I cannot post links but you can find it at inkscape.org

Hope this helps.

Bob


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