View Full Version : NEW MEMBER: Seeking advice on a CNC setup for (one off) machining carbon fiber plate

03-03-2013, 12:43 PM
I'm a total newbie living in Manchester with a sudden need to get up to scratch on CNC machining. Basically, I'm working on a research project (UAV/drone) which requires components to be cut from 1.5 x 400 x 500 mm and 2 x 400 x 500 mm carbon fibre composite boards using a CNC router. Unfortunately, I've recently found out that a couple of our workshop guys are off on long term sick leave (hopefully not carbon fiber dust! :uncomfortableness:), meaning that there is a several month backlog on jobs on our CNC equipment (this basically kills my project deadline). I do have access to alternative facilities (ShopBot PRS standardCNC), but will only be able to get limited training on the equipment. I realize that CF is not a straight forward material to machine in terms of quality of finish, tool life and health and safety, so I thought I best come to the experts for advice.

The setup does have an extractor and is in a well ventilated area, and I intend to use a respirator with Hepa filters and disposable clothing during operation. The CNC does not have any intrinsic cooling for the end mill as far as I know (i.e. air/water jet) so this may be a concern given the abrasive nature of the material. However my main concern lies in the choice of end mill needed to cut the CF. I know that the pros use diamond coated tooling, but I cannot really justify the expense (I will probably need 1 mm and 2 mm (and possibly 3mm) cutting diameter to cut the different levels of detail in the design [see attached]). Also, given that this is a one off, I don't want to pay 50+ for bits when they could still snap anyway. The cutting run will probably be a few meters max (nb: cutting sheets in the diagram are 400 x 500 mm).

I was thinking of using a carbide two flute end mill (see below) running at 15000 RPM with a feed rate of ~ 500 mm per minute.
Carbide End Mills 2 Flute - Arc Euro Trade (http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Milling-Cutters/Carbide-End-Mills-2-Flute)
I have read that people have had some success using diamond cut router bits and diamond burrs in CF, but have not seen any results close up. I do not mind ruining a few carbide bits, as long as I have enough to complete the production run of two sheets. I do, however, require the edge to be decent (no chips, splinters), and want to avoid clouding the CF with overheated tools.
So in summary, I'm wondering....
What is the best low cost tool to achieve the job in hand and how many will I need to complete it (specific products would be very helpful).
What is the best feed rate-RPM combo to use
Are there any DIY methods to keep the bit cool

To be honest, I would be happier having a third party do the cuts, but I just haven't budgeted for this eventuality (I'm on a doctoral grant which is pretty lean and not being able to use in-house facilities is really killing me).
Apologies for the length of this post, but I would greatly appreciate any advice that members would be able to offer me