Composite Cutting Tips // TACIT RONIN II Build Preview

Hi all,

Been wanting to make this thread for awhile about some general tips and tricks I've learned after cutting fiber composites and carbon fiber almost exclusively on Openbuilds machines for 2+ years and over 3 separate builds, first a modified OX, then C-Beam, and now finally a brand new custom build, the TACIT RONIN II.

I've put together a short video outlining a few key tips about machining composites as part of our latest project release I've been working on for the last number of months.



I'll elaborate on each of the main points a bit here:

1) Burr tooling seems to give the best results in composites bar none however there are some caveats. Non-burr tools CAN be used to cut fiber composites (specifically PCD Diamond coated routing tools) if your machine is rigid enough. It is certainly preferable to create chips instead of dust, however, even using the top coated fluted endmills, significant secondary dust WILL be created. Some further points about Burr tooling:

• When burr tooling becomes dull, it is very obvious on the bottom edge finish of the cut. Using sharp tools is a must for clean edges and burrs wear quite fast. Typically I use using solid carbide chipbreaker or diamond-cut tools, which can cost as low as $2-3 per unit. A carbide tool will be become dull within two to three 1 sqft. pallets of parts and need replacing. PCD or CVD Diamond coated tools will give tool lives about 3x longer but at 6x the unit cost.
• If production is your game, its best to stick with cheaper carbide burr tools in bulk and replace them more often, than go with more expensive coated tools in the long run.
• If you do mainly one off parts occasionally, then it might be better to go with PCD, CVD or AlTiN coated burr tools.

MY SOURCE FOR BURR ENDMILLS (US BASED)

Some excellent composite machining content I've come across:

Titan teaches on Machining Composite G10 - CNC Machining Education

Successful Machining of Composites

How to Machine Carbon Fiber and Today's Difficult Composites

2) Carbon Fiber and composites tend to like high RPM's from 10,000 and higher. Check out the datasheet put out by Amana Tool, it tough to find real datasheet on speeds and feeds for burr tools, so have a look if you are looking for a reference!

Amana Tool Composite Speeds and Feeds Datasheet

I say, "tend" to like high rpms because, unlike metals, many composites don't follow the same fabrication rules as metal alloys, so what one company calls "carbon fiber" could only be a percentage of carbon with the rest being polyester filler, so ultimately hard speeds and feeds data when it comes to composites is only useful to a point. Nothing will beat empirically derived data from the specific material you are trying to cut as well as other factors the strength of coolant, depth of cut, etc.

Machining Graphite (Check out the RPM's used)

3) I consider flood coolant a must when cutting with burrs due to two factors.

• Clearing swarf and heat dissipation. Small micro flutes have trouble evacuating gritty swarf on their own and the cut will start to pack. Packing leads to rubbing, rubbing leads to heat and, since composites are bound with epoxy, the heat will both destroy the endmill and melt/scorch the material.
• Respiratory hazard. When excessive silica or carbon fiber particles get in your lungs, they don't come back out (silicosis). A flood blast + coolant shoe eliminates both dust and spray. However if you have a powerful shopvac with a very fine dust filter, it will certainly cut but isn't something I would personally play around with. (a highly sealed dust shoe can work to cut CF dry but is is a n o j o k e level of vacuum dust extraction.)

Datron CleanCut Milling Chip Extraction System (check out what is required in terms of dust extraction)






Thanks everyone, looking forward to completing a complete detailed build thread soon!

I'm also working on a playlist compiling the best of the publicly available information on composite machining as the videos can be quite obscure and hard to find, so subscribe to our YouTube channel, or just hang out around here, I'll post it when its ready.

I have a real passion for composites, I believe they are the future in so many industries, so I hope this info can find itself useful to you!

Alex

P.S. If you think you like that Made-with-Openbuilds utility knife, you can check it out here.

 

Hey Glen,

Submerging parts definitely works, but i would only use a DOC (depth-of-cut) of about 1mm. It only uses the bottom tip of the tool which is unfortunate for wear but what you avoid is that nasty swarf packing problem.

The 2nd thing I would suggest is to cut a profile of your part a depth of a couple mm in your waste board before you place your stock material down. That way the tool is able to cut that last pass with minimal deflection. Good luck!