I like the idea of a carbon fiber free float tube, but I thought it might benefit from some vent holes.  Is there anything wrong with slapping it in the drill press and going to town?  Or is that going to compromise the structural integrity of the thing?

Basically, what I'm wanting to end up with is something like this:

without paying the $312 that this thing costs for the carbine length.

Anybody got any other sources for carbon fiber free float tubes?

Drill away... But take it slow. If ya go to fast the back side will splinter when the bit goes through.

Oh and pilot drill all locations first. Keeps the larger bit from wandering.

Quoted: Do NOT breathe the dust created while drilling/sanding. Bad stuff. Brownells sells carbon tubes.

They only have a full length (12") listed.  I guess for $85 I could cut it down if I'm going to be drilling it anyway.

You have to be careful when drilling carbon fiber.
The resulting "dust" has strands of carbon that will get stuck in your lungs, and also on your exposed skin just like fiberglass.

You may want to slightly countersink the drilled holes, just to deburr the surface.
If you do, use an actual countersink, not a larger drillbit.

No disrespect to Mr Mcnasty (i dont know his background) but I would call the manufacter and get there opinion. I think they will suggest a maximum size hole to prevent the risk of splintering and they may also suggest a drill speed.  Ask if a wood bit would work better than metal.

Quoted: No disrespect to Mr Mcnasty (i dont know his background) but I would call the manufacter and get there opinion. I think they will suggest a maximum size hole to prevent the risk of splintering and they may also suggest a drill speed.  Ask if a wood bit would work better than metal.

Unfortunately, I don't really have a manufacturer just yet.  Brownells lists this one
]www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=4998]
from Clark custom but it's a full length.  I'd like to avoid cutting and stick to drilling if I can.

Hydguy;
Good call on the countersinking.

When drilling through carbon, use a new bit (preferably solid carbide), and back up the other side where you will break through with a piece of wood, for a cleaner exit hole. The sharper the bit, the better. Carbon is tough on cutters. And do use a dust mask and gloves, the stuff is nasty to breathe in and can also be a skin irritant.
Any idea what type of carbon weave it is? 282 or 1k?

Quoted: When drilling through carbon, use a new bit (preferably solid carbide), and back up the other side where you will break through with a piece of wood, for a cleaner exit hole. The sharper the bit, the better. Carbon is tough on cutters. And do use a dust mask and gloves, the stuff is nasty to breathe in and can also be a skin irritant. Any idea what type of carbon weave it is? 282 or 1k?

Hopefully I'll know more when I find a source.  three questions:
1) since this is a round handguard, should I get a round piece of wood to put inside the handguard when I drill?
2) the bit.  Should I use a flat bit, or a hole-saw for the larger (maybe 1/2"?) holes?
3) What do those numbers mean, 282 & 1k?  I assume 1k is shorthand for 1000?

Rod at Hiperform says you can drill and even thread his tubes for things like mounts or swivels. His wrench is unnecessary, just use a strap wrench. I've worked with CF in knifemaking. Wear a respirator, glasses, and go slow. I have a PRI. The current batch of "sport tubes" and the PRI tubes are not the same animal. The aftermarket tubes are glossy, first of all, like superbike parts. VF sandpaper should work fine. Second the tube wall is thinner on the other stuff than the PRI.
Hiperform.com has them for $80-$90 for the carbine length, they are all one piece. The barrel nut is machined to very high tolerences. Had one installed for a buddy this past weekend. Went together very well. Light and sturdy. As a second choice the Hiperform looks good.

1.whatever type of wood (dowel or clothesrod) that it'll fit the contour well enough--to prevent or minimize splinters and exit damage, depending on thickness.

2.standard type bit, or 120 degree would work-I would advise against hole saws, it'll produce terrible holes. If possible, get solid carbide bits, at the minimum, a TiN would be ok, although you may use more than one..carbon dulls cutters very quickly.

3. 282 and 1k are common weaves found outside of aerospace now,  as they are getting cheaper. 282 is strong, and has a larger but not very dense weave. 1k is much denser, but thinner, and usually used as a face ply as it looks much cleaner. You may even run across 584, which is a very thick weave, and does not cut as well. I am assuming that most of these are wet layups, and hopefully vacuum bagged--it'd be nice if they were pre-pregs.

Quoted: Rod at Hiperform says you can drill and even thread his tubes for things like mounts or swivels. His wrench is unnecessary, just use a strap wrench. I've worked with CF in knifemaking. Wear a respirator, glasses, and go slow. I have a PRI. The current batch of "sport tubes" and the PRI tubes are not the same animal. The aftermarket tubes are glossy, first of all, like superbike parts. VF sandpaper should work fine. Second the tube wall is thinner on the other stuff than the PRI. Hiperform.com has them for $80-$90 for the carbine length, they are all one piece. The barrel nut is machined to very high tolerences. Had one installed for a buddy this past weekend. Went together very well. Light and sturdy. As a second choice the Hiperform looks good.

Ok, at the risk of hijacking my own thread...

Is it possible to index the thing so I can be sure of where the top-center of the tube is?  In other words, if I install it, and mark the top-center, will that still be the top-center when I re-install it after drilling?
I'm just not at all familiar with how these things go together.

Quoted: 2.standard type bit, or 120 degree would work-I would advise against hole saws, it'll produce terrible holes. If possible, get solid carbide bits, at the minimum, a TiN would be ok, although you may use more than one..carbon dulls cutters very quickly.

Would keeping it wet while cutting help at all?  Oil? water? I'd think the water would at least help keep the dust down, just so long as wetting it wouldn't actually HURT the material in some way that I can't think of.

I have never used any cutting fluids or water (nor have I seen anyone else do so), in fact, never really thought about until now. Doing it dry is just fine, and I do not know if oils or fluids will damage it over time. There's differing opinion on speed and pressure while drilling carbons, but if it's thin enough (as I suspect), you should be able to apply some good pressure, cut at a fairly good speed, and not too much dust should be created. I'd pay attention to your arms and hands--you DO NOT want that crap to touch your skin.

I'd definitely consider getting someone with a flood coolant system (not a mist system, has to be flood to keep the fibers from going airborne) to do it, I had an internship the summer after high school where we fabricated carbon fiber panels for the Navy.  You knew if a carbon fiber got on your skin because it burned and itched like hell.  If you got a splinter, the only way to stop the pain was to dig it out with an Xacto knife, because trying to use tweezers would break the strand in two and it was actually the ends of the strand that caused the pain (so a broken strand was twice as painful).

Imagine that happening inside your lungs, and having to live with it for the rest of your life.  

We wore coveralls, goggles, high quality dust masks (I would have preferred a respirator and hood due to fibers settling on our necks and foreheads), latex gloves and duct-taped our cuffs to our boots and gloves to prevent fiber infiltration whenever we cut a finished and cured panel.  We had an entire machine shop dedicated solely to cutting cured panels, with an identically equipped machine shop in the next room for cutting whatever else we might need to work with (metal, plastic, wood, etc).  Only a single person would be in the fiber machine shop at a time if we could help it to limit exposure to the airborne fibers.

Carbon fiber is neat stuff, but the little fibers on their own are nasty little buggers.

Kharn

Get a bit designed for drilling C/E laminate.  Don't even try a hole saw, it will just rip the fabric apart.

Go slow, and use fairly light pressure.  Try to back up the inside of the tube to minimize splintering and delamination when the bit breaks through.

I suppose water to control the dust wouldn't be a bad idea if you don't let the handguard soak in it; C/E and Gl/E laminates absorb water, although it occurs over a period of months when simply exposed to the atmosphere.  The mechanical properties of epoxy laminates take a large hit under hot or hot/wet conditions, but this is a consumer product, not a fighter aeroplane.

Watch the dust and the splinters - they hurt like hell.

If you get (when you get) delaminations around the holes, mix some 5 minute epoxy with some of the carbon fiber dust you saved and squeegee it into the delam's for a cosmetic fix.  Sand to suit.

Kharn, did you guys use a coolant system?

I can vouch for EAFB in Bldg 1600-Composites (and also subcontractors-USAF Plant 42, Lockheed Martin Aeronautics and Boeing) that no coolants of any type were used, but PPE runs the gamut of nitrile gloves, Tyvek sleeves and bunny suits when the situation required. Come to think of it now, distilled water (not very much though) is used to do a waterbreak verification prior to bond, but if hyd fluids get on it (such as a line leak) it is cleaned up pronto!

I have absolutely nothing to add to this discussion.  

I just wanted to say that I'm highly impressed with the level of technical knowledge possessed by our members.  

you really need to know what type of drill, and the speed to get started with, and be careful dude, hey did you know carbon fiber is a conductor of electricity

I'm kinda groggy with Captain Tripps right now but Yes, I think so. It has holes in the barrel nut for the gas tube. Indexing should be a breeze. PRI sells its' mounts after market BTW.

Thought I'd resurect this, as I'm back on this kick again.
I realized I wasn't very clear before.  I DON'T want the rails on the pic in the opening post. All I want is a CF tube with holes in it for cooling.
Take the tube in the pic, and remove the rails, and you'll have what I'm looking for.
I'm now thinking I will go Dissipator length, by buying a lightweight 20" barrel from Bushmaster & having Kurt cut it down & tune the gas port.
Start with a barrel like this
[img]http://bushmaster.com/shopping/barrel-assemblies/Images/abbl-20a2a.jpg[/img]
and have Kurt cut it down rigt to 16.1" or as close to 16" as I can legally and comfortably get.

As AeroE said, you MUST seal the edges after drilling or cutting CF. We have a devil of a time on our rocket parts with fraying and delaminating. There will be a shiney circle around the hole when the epoxy dries. This can be brought to a satin finish with sanding. I dont do the drilling; thank god, so I cant tell you how to right now. I will however talk to some of the techs on monday and get you some info from people that do this kind of shit everyday. If you can wait or even are interested, that is. I think they use a highspeed(26,000rpm)cutting wheel on a die grinder but don't hold me to it. Indexing it to orient properly when assembled is no big deal. Fit it up as it will be when finished and mark it with a tape overlay. Then make your marks on more overlays.

Good luck.

... pinged for later, this is right up my alley

Couldn't you rig a shop vac up so that it sucks in as much of the powder as possible? Duct tape it in the correct position as to not move the carbon tube with the suction, then flip it on and start drilling?

Any info you could give me would be awesome.  I don't even have the tube yet, so I can definately wait.


Even if they sold the tube I pictured without the rails, it's still damn expensive.  I can get a Briley tube for $85 shipped.  Much better deal.

We back up all of our C/F parts with a thin layer of fiberglass.  This helps reduce splintering.  You could use a block of wood.  Make sure that you minimize the gaps between the backup bar and the workpeice.  We run all of our drills at between 3,000 and 4,000 RPM's. Our feed rates are usually about .001/.002 per rev.  You would need to feed kinda slow. We use Solid Carbide.  They have a special point grind for C/F material.  They are a 8 facit point grind.  They look like the facits on a diamond. This also helps reduce splintering. We pre drill all of our holes before opening up to full size. You could use a standard carbide drill.  Make sure that you have a enough on hand.  C/F really eats up drills even carbide.  As they get dull the splintering problem gets worse.

We also drill with power feed equipment.  When we do we use water to flood the cutter and remove the shavings.  When we do not use powerfeed equipment we just use a vacuum attachment to the drill.  



We also use hole saws.  All of our hole saws are diamond impreginated and we also have diamond drills.  So this is not an option for home use.  

... [b]batchman[/b] saved me a lot of typing!

... Next to high pressure waterjet cutters with an 80 grit garnet, the best tooling for carbon/epoxy laminates are polycrystalline diamond cutters, but you most likely won't get the surface feet per minute needed to sustain clean cuts w/o breakout on the diameter of hole I imagine you're drilling.

... Yes, carbide is your best, all around, bet. Use a dagger or spade bit (McMaster-Carr) and intimately back up your laminate to minimize delamination. Don't exert excessive feeding force, flood with coolant (nothing exotic unless you're planning on secondary bonding) and wear a particulate mask. Watch out for splinters, they bite and hurt like hell.

... Remember to measure twice and cut once.

... Post pictures when done!

Diamond coated tools are best for composites because they do not overheat the matrix and cause splintering. We use them durng repairs of F-22 composite parts.