Thread: I keep dulling bits cutting fiberglass sheets (Honeycomb Composite panels)

**animuL** · 10-26-2007, 06:42 PM

Not really sure what forum to post this in but I am running into an issue while cutting composite Norbond and AAR brand panels. These panels have .010-.020 thk fiberglass face sheets and a phenolic honeycomb core (1 inch core on these particular ones). The machine is a Thermwood router. Basically I can get about 100 inches or so out of a bit before it has a notch in it from the fiberglass. Once this happens it doesn't cut so much as just beds the face sheet up. At this rate I would have to go thru as many as 20 bits a day. What I am using right now are 3/4" diameter 2 flute up-shearing end mills. They are custom made in town and cost about $25 each. The guy says they are solid carbide but I kinda wonder about that because the price seems WAY cheap. Either way, I have cutters I KNOW are solid tungsten carbide and they dont last but a few thousand inches. I am running a spindle speed of 18k and a feed rate of 200 ipm. Anybody have any input on how I can make a bit last longer here?

**awerby** · 10-27-2007, 10:06 PM

Fiberglass is abrasive stuff, so it's not surprising it's killing your tooling. There's a new process that actually deposits a thin layer of diamond over a carbide endmill, which enables it to hold an edge a lot longer. People use them for graphite and other abrasive materials; they aren't cheap but will save a lot of aggravation. There are insert solutions as well, if that works for you. Here's a supplier: http://www.sp3inc.com/sp3-ct.htm

Andrew Werby
www.computersculpture.com

**ger21** · 10-27-2007, 11:00 PM

Look at the "Think Composites" .pdf here:
https://www.onsrud.com/xdoc/composites

Also, I think your rpm's might be too high. I don't cut composites, but I cut wood at 200-300ipm and about 14-15K rpm with 3/4" tools.

**animuL** · 10-29-2007, 06:38 PM

Thanks for the replies. I am about to try cutting one at 15k rpm to see how it reacts. I also bumped up to about 400 ipm feed rate and it seems to do fine. It looks like I just have the wrong cutter probably. The ones in that catalog that are specifically for fiberglass look WAY different than any tool I have.

**harryn** · 10-30-2007, 01:49 AM

I actually know the SP3 guys pretty well. While my machining experience is below novice level, I have seen some of the testing they did on carbon fiber composites and on general life testing on Al.

Diamond cutting tools are definitely going to help. I have no idea if their diamond tools are better than the next guys diamond tools.

One of the very interesting discussions we had over coffee one time was "how do you measure quality control on tooling that takes weeks machining large billets of Al into shavings to get a measurement ?"

**K&Y** · 01-29-2008, 05:51 PM

Originally Posted by harryn

I actually know the SP3 guys pretty well. While my machining experience is below novice level, I have seen some of the testing they did on carbon fiber composites and on general life testing on Al.

Diamond cutting tools are definitely going to help. I have no idea if their diamond tools are better than the next guys diamond tools.

One of the very interesting discussions we had over coffee one time was "how do you measure quality control on tooling that takes weeks machining large billets of Al into shavings to get a measurement ?"

One way how to measure "quality control" of a specific tool vs. another is straight-forward.......tool-life.

Another, is finish. It's the design of the diamond tool in question that will determine if you reach your target goal. Price isn't always indicative if a tool will do the job either, as most of you already know. Diamond tools are definitely an investment, and the initial cost may seem high. Taking into consideration that they will outlast anything in the carbide, or coated carbide range, and if you do the match associated with replacing worn tooling, down-time, etc., it more than makes sense to make the initial investment. You won't be sorry that you did.

**K&Y** · 01-29-2008, 06:01 PM

Originally Posted by animuL

Thanks for the replies. I am about to try cutting one at 15k rpm to see how it reacts. I also bumped up to about 400 ipm feed rate and it seems to do fine. It looks like I just have the wrong cutter probably. The ones in that catalog that are specifically for fiberglass look WAY different than any tool I have.

Here's an example of some Endmills (dimensions), as well as speed and feed rates. Hopefully, this will give you a clearer idea of what can be accomplished with the PCD-tipped Endmills/Routers when it comes to machining composites in general.

**Geof** · 01-29-2008, 06:22 PM

Is your cutter long enough and do you have enough room to vary the depth of cut? You are notching the cutter just at the fiberglas layer but if you can have the cutter cycle Z up and down through 0.2" while the other axes are moving you spread the wear over this distance on the cutter. It is possible to get much longer cutter life doing this, but it can be really tedious adding all the Z moves to a program.