Help milling holes in fiberglass

Surprisingly I found some work here in Dayton, Ohio. Most shops still have old auction flyers still littering their empty parking lots.
I've been asked to mill holes in 4" thick fiberglass on a light duty CNC router. The 8000rpm spindle is 1/2" max capacity collet system and there is no coolant system on the machine, just air (if needed) and a vacuum. Can we cut this stuff dry? I've been told that carbide will work but will dull much sooner than diamond coated, any recommendations? The holes are usually either 7/8" or 1.25" in diameter. If 4" is too deep for a 1/2" cutter to circle mill, I thought of going in 2" on one side and then flipping it and going in the other 2" from the other side. Or find larger cutter with a reduced shank. This is a new beast for me, I'm used to cutting stuff that sticks to a magnet. Anybody out there milling fiberglass that can steer me in the right direction? Tooling? Speeds and feeds? Any help is appreciated.
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What accuracy is req'd? If not super accurate, how bout a deep hole saw, carbide tipped? My buddy just dropped off some nice ones, Milwaukee-style arbors, proly not cheap, but proly no more than decent carbide mills. He in fact did a job in steel with these holesaws, with pretty good accuracy.
You might have to lengthen the l.o.c., by cutting and welding in a tube splice to get 4", but you might be able to get them 4+ inches from the gitgo. And indeed, 4" x 1/2" is pushing the envelope. 2" seems to be the trad'l max,altho you might find it as a specialty.
The carbide tipped hole saw is Relton, altho Starrett and Lennox, Milwaukee may make them also, with arbors by the same names.
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On Fri, 12 Dec 2008 23:32:43 -0500, "Proctologically Violatedฉฎ"

Diamond coating would be better for fiberglass.
http://www.c-cuttools.com.au/productsinfo.php
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-JN-

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wrote:

Thanks for the link. Interesting product. Upon further research I found something called "core drills" that seem the same but have a couple notches in them to allow the "swarf?" to be rinsed out by water/coolant. We have to cut this fiberglass dry as there's no coolant system on the machine, just air and vacuum. Seems a diamond coated endmill would be more of an open environment for an air blow or vacuum system to prevent re-cutting. But heck, I've never done this before, willing to try anything once. Regards.
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Thanks for the input. The holes are just clearance for big bolts so accuracy isn't that critical. There's no coolant system on the router, just air and vacuum. Would you recommend peck drilling the saw to clear the shavings/dust? I wonder how the saw will perform cutting dry. They talk like we'll be making thousands of holes over the course.
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Ahm no 'spert, but with core drilling/hole saws, the notion of pecking is proly not quite the same as with an end mill/fluted drill.
It's more a matter of ejecting the plug/slug captured in the saw. You might have to modify the tool for efficient ejecting, You proly won't need a pilot drill like portable drill hole saws, so if the plug does not come out easily, you might make a stationary drill fixture or sumpn, to drill/pull the plug out. Or make push holes on the back of the hole saw.
I would imagine there's all kinds of fiberglass, and there is no doubt about its abrasiveness, the Q is, How *tough* is it? It's certainly not tough like steel, not even aluminum, more like plywood, ie, some heterogeneity in the structure.
To the extent that some *tearing* (albeit microtearing) would be involved in the cutting process, you might could get away with cheaper saws, mebbe not even carbide! Mebbe a very coarse tooth.
You'd have to calc out the cost of the tool, vs its lifespan, vs the cost of changing, vs the feed/speeds. John Scheldroup posted an excellent ditty some time ago on this very subject, the actual calculations. Unless the endmills were like $1,000 each, the tooling that allowed the highest speeds/feeds yielded the highest revenue for the machine -- cost of the tooling, change time were incidental, unless of course you had to change the tool every second cut.
The dust and "chips" may indeed be a big deal. Some shops refuse to machine cast iron for this very reason, or have a dedicated machine just for this purpose. You may want to hook up a *bank* of wet vacs or sumpn -- or at least numerous hoses arranged 360 deg, with really good filtration, to keep the dust in check -- off you, and off the machine, and out of the air.
Boat builders do fiberglass. Mebbe a ng/forum on this would have people who do this.
How bout DIS:
A hole saw, but instead of teeth, a razor edge, and you punch/slice out a core??? Could possibly to that from both sides. Mebbe a very low rpm, or even zero. And, you could have a few, just resharpen on a lathe, and swap out.
If forces weren't too great (ie bending torques), you could hold the "cutting tube" peripherally and offset the tool from the true spindle, so the plugs could just come out top of the tool! ie, one plug would eject the other. Like if you had a really big hollow spindle.
Textiles often use razor bands for cutting. Man, you don't want to get nicked with DAT stuff....
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Roger wrote:

Roger:
    Some things to be aware of. Fiberglass often has a surface gel coat that a drill or end mill may chip on entry and exit. As others have said, the glass fibers are VERY abrasive and hard on tooling, even carbide. Diamond coated tools are definitely recommended.     Fiberglass dust is likely to get EVERYWHERE in your shop, especially from an open machine such as the average router - even with a vacuum. And the ways of your machines may not appreciate the abrasive dust.
    You say THOUSANDS of holes? Have you considered getting quotes from Waterjet shops?
http://www.paradisewaterjet.com/why_waterjet.htm
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Roger,
See https://www.onsrud.com/xdoc/ThinkComposite
They make router bits specifically intended for cutting dry in fiberglass. I would circle mill the holes with a smaller bit.
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Dan

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Yep, use that PCD tipped cutter listed there. Carbide goes away pretty fast cutting fiberglass. Use some air on the tool to keep the tool and the fiberglass from overheating and vacuum on the part to keep the dust from going everywhere. Circlemill down in small pecks from both sides, ramping on each peck. Diamond core drills work well on glass, ceramic or concrete but tend to load up in fiberglass because of the resin.
Fred
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Found this:
for fiberglass: http://www.cnc-west.com/cncwgen/Mall%20data/Fiberglass%20Machining.htm
for waterjet: http://www.cnc-west.com/cncwgen/Mall%20data/Waterjet%20machining.htm
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Thanks for everybody's input, I'm glad this group is alive and well. I just got a quote for 50 flanges, 4 inches thick................ to put 8 holes that are 1 inch diameter the price would be $80 to $100 per flange. These are just round disks so there's no fancy fixturing. They did recommend a test cut to see if the laminate layers would deteriorate, and if so, I'd have to provide a "pilot" hole.
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