CNC machining honeycomb nomex core

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#1

Hi all, First post but some great discussions here.

So i’m interested in machining honeycomb nomex core. I’m looking at the various machines and a 3 axis is much simpler and cheaper than a 5 axis machine. But I"m wondering how I can machine the core to shape and then chamfer the edgers using a 3 axis. There are various router bits available that have a 45 degree or some angle, but I don’t think they’re designed for core and I could see issues arise by using them.

How does one cut and chamfer core using a 3 axis machine? Your insight is appreciated! :smiley:

#2

Honeycomb is very rough after machining. I always chamfer with a da and high speed angle grinder after machining. I also go over the whole piece and the blow it with a air gun.

For setup I machine on aluminum plate with double sided tape holding the nomex. Same with aluminum honeycomb.

There may be another way but this is how I do it.

For complex cores… I always start witha flat piece of core… Then cook it to shape. Rough it in and back in the oven with a reinforced adhesive film that holds its shape. Final trims and such after.

#3

That probably works great, hand shaping is fine but, the volume of core I’m gonna have to shape is going to require a cnc for speed, accuracy, and reproducability. I’m sure a 3 axis cnc router can do the trimming to size. I’ve worked with one for a while but, I’m not sure how to get good edge chamfering. I thought an angle bit would probably work but, I’ve never done it and I’m curious if anyone had experience with this?

I guess the other option is to buy a 5 axis machine, but its a bit more expensive and complicated.

#4

The 5 axis is the best bet. That alows you to use wheel cutters (saws on a stem). Also cut the core much faster.

#5

Agreed if you have a 5 axis. I have 3 axis. Works ok… not the best or fastest. 1/8" is the hardest to cut. Seems to work ok with .25 or larger. The higher PCF density cores also cut nicer than lighter. I wish there were more cutting bit options but, seems like only one size in ball end mills for core.

#6

Can´t you use a V-shaped mill bit to chamfer the edges for 3-axis milling. Depending on the angle required. I´ll bet there are companies, u could even make custom diamond end bits with your requirements and shope and size.

#7

Tried it… doesn’t work.

Maybe a diamond bit, but havne’t had one made.

The standard v bits don’t cut well. I’m cutting 1/8" thick core and it’s the hardest to cut. It’s possible that a custom diamond bit might cut kevlar/nomex but I haven’t had much luck with anything but, the onsrud honeycomb cutting bits so far.

I might try to get a diamond bit and see how it cuts, if it does, before I have a custom bit made. There must be a better solution than what I have so far?

#8

If you are willing to shell out for a 5-axis machine, what about going with an NC ultrasonic cutter (we call them “Sonic Knives” at work.). I believe it’d be close to what you’d pay for a 5-axis, but cuts core quite quickly.

If you are doing more than edge cutting (as in, you’re trying to surface the core), then you may need a mill, but for just edge cutting, a sonic knife works very well.

For simpler cuts and varying thicknesses, a drill press and a routing bit go a long way. Many a helicopter have used core cut this way.

#9

LMT ONSRUD is the place you need to look for core cutting tools they will have a very good solution for you.

#10

We got a remgirt (http://www.disstontools.com/rg-continedge-bsb.html) bandsaw blade for our bandsaw set the table to an angle and never looked back. I had tried milling it before but the blade was a lot faster and left a perfect finish.

#11

we have been using the table saw, seems to work ok for straigh but curves can be a pain.

No, I actually thing I figured it out. I just needed to use a different CAM so I could output a downcut spiral code. My last test seemed to do well and I think I got the 1/8" core down. The 1/8 is the hardest to cut cleanly.