View Full Version : Need help building a cnc-cutter

Arctic monkey
30-11-2014, 10:50 PM

I am currently working on a group project which has the goal to develop a cnc-controlled cutter for carbon fibre. Since noone in our group has any experience in this matter I'd like to present our current level of knowledge in order to get feedback where we might run into problems and what we can do to avoid that.

The setup we are planning to use:
The hardware will be bought from a supplier which constructed it after our inquiry. This leaves the control of the machine to us.
The hardware we will use to control the cutter is the triple beast found here: http://benezan-electronics.de/shop/product_info.php?cPath=8&products_id=61&language=en&osCsid=003f441d590d4e843158bf069d89ae0a
The corresponding software is mach3.

Tasks we are still unsure about:
-generate g-code out of a .cax-file to cut a 2dimensional shape.
-control the cutter with software and hardware
-We plan to use a rotatory wedge-shaped blade to cut the carbon fibre.

As a postprocessor we found a program which changes a .cax-file in g-code. It is not the best way and we probably need to modify the generated g-code a lot. Which postprocessors on the market provide the same result and are easier to modify? Is it possible to change the g-code via a program written with vba and is the required amount of time to do so worth it?

In theory controlling the cutter once everything is properly wired should be easy. Is there a problem we're missing?

The wedge-shaped blade requires us to modify the postion of the blade with an additional motor for example when it has to cut curves. As far as we know this can be solved by compensation tools available in the g-code. When cutting corners the machine needs to reset the blade. How can this be achieved?

Even though english is not my first language and i probably havent covered all necessary points to evaluate our situation I'd very much appreciate any feedback you can give us.

Thanks very much in advance.

01-12-2014, 09:38 AM
There is a machine on cnczone that does exactly this... I'll find the link

Boyan Silyavski
01-12-2014, 02:38 PM
You can laser cut it too, though you need some additional things to consider like good ventilation, what power you need and so. Seems 50-60w will cut 1mm without problems. the best would be to find somebody to do it first for you so you know firsthand the eventual problems and know what power you need for the material.. But the benefits are quite great, starting from detailed perfect finish/if you manage it/ and practically no consumatives apart from the life of the tube. Plus Chinese machines are quite cheap.

On the other hand you will need vacuum holder, high quality carbide bits. But the good part is that you will be able to shape yourself the molds from different materials.

At the end its up to what is your exact need.

01-12-2014, 04:28 PM
he means raw carbon .... before its had epoxy applied to it


for me the hardest part is understanding the post processor for g-code to turn the head to follow the line its cutting

Boyan Silyavski
01-12-2014, 04:54 PM
Then you need something similar to drag knife, rotating blade as you say. It must be offset from the shank . Aspire 4 is the answer. It can generate drag knife tool paths .
This is done without motorized knife. its very easy to modify the tool path in any program, once you get the grasp of it.


By the way i am exactly now developing a drag knife, which is cheaper and i would say better, meaning more functional than the original one. It seems i have to think also of rotary attachment. Just tomorrow would be going to friends house to do some tests. The normal drag knife with utility blade will cut it, though holding down the material will be a problem. But not necessaryly, cause this will be much cheaper than round blades, if managed to achieve. Will report my findings, though glass fiber cloth, i dont have carbon fibre cloth.n

01-12-2014, 05:05 PM
why must it be offset from the shank ?

Boyan Silyavski
01-12-2014, 05:23 PM
why must it be offset from the shank ?

cause it rotates over the offset point, meanwhile the z is making the corner

01-12-2014, 06:13 PM
i understand having it offset from the center point for a drag knife as this acts the same as a castor wheel on a trolley for example

but for a pizza cutter ?

Boyan Silyavski
01-12-2014, 06:53 PM
The same, just saves you some cash for motorizing it. I have seen the Donek drag knife with this attachment.

01-12-2014, 07:02 PM
you will find it very hard to cut carbon cloth in less it is pre preg, if you are not aware of what pre preg is it cloth that is pre coated with resin on it that you activate by cooking it usualy around 100deg c. Even if you could cut carbon cloth dry it will fall apart as soon as you pick it up or try do anything to it. You can use a method were you use a spray adhesive to stick the carbon to wax paper which you then wet it out on but you will still get distortion and loose any sort of accuracy. Pre preg is nice stuff to work with but it must be stored in a freezer and must be cooked to cure it and it is also expensive.

01-12-2014, 07:59 PM
Artic Monkey, im guessing you have already worked with carbon or even glass cloth. As charlieuk said, i think you will have to come up with a plan to cut it if its not prepreg. I use it in another hobby i do and i use the wax paper trick but the final item is trimmed to size anyway.

I Wonder if a rolling cutter or a laser would be better. In any case with out prepreg or a backing the edges will fray like mad depending on the weave.


Arctic monkey
03-12-2014, 05:57 PM
Thanks for every answer so far.
The accuracy is not that much of a concern for us since the cut has to be finished by hand anyway. Basically at our university theres a small lab where one person works with carbon fiber. He coates the fiber as already discussed in this thread. Therefore he needs to cut the fibre with scissors by hand which is suboptimal because the scissors wear out quickly and the carbon irritates the skin.

I have to check which exact material we use but we ran a few tests and the rotatory blade had the best result.

Thanks a lor for the post with the postprocessors thats exactly what were looking for atm. Are there any other postprocessors which work with rotatory blades and how do they interact with mach3 and the triple beast? As far as i know we need an additional hardware for the beast in order to support that.

03-12-2014, 07:23 PM
if its only for one person a pair of latex gloves and any form of electric scissors is going to do the job and probably with better results trust me I do this for my day job the only time it would be worth it was if you used pre preg. You have to be so carfullt when cutting carbon that you get every thread other wise it all falls apart as soon as you try lifting it. you will probably have to cheque it manually and go over with a knife anyway and if something catches with a machine you could destroy a hole lot of expensive carbon very quick! Back it on paper like said and then electric scissors or a new shape blade cut on a cutting matt will give quick and easy cutting.

Ps the trick with using scisors on glass carbon and Kevlar is you only have the top blade sharpe. Run a file over the lower blade it booth directions to give it a fine but rough texture which stops the fibers sliding along the shape edge.