CF Barrel or carbon fiber parts in general

Crash · 06-22-2007, 09:25 PM

Well I picked up a very cheap Stiffi but it is 16 in.
Is there a way it could be cut it down to a shorter length?

B · 06-22-2007, 10:55 PM

Yes it can but it will take a speclided tool to do the job either a lathe or a tubing miter. It will then need to be smoothed crowned and then sealed.

This is not an easy home job.

Railgun · 06-22-2007, 10:59 PM

You can but it requires some careful work with a very fine toothed saw to avoid tearing the fibers out of the matrix. Also once you've cut it down be sure to sand it to a round ended "crown" much like they shape real gun barrel ends. to help avoid any bruising or picking up fibers and tearing them out of the matrix.

You want a fine toothed very sharp hand saw like a Zona hobby saw and you want to keep turning the barrel so you're cutting as tangentially as possible all the way around. It's easy to do but difficult to explain.

Think of it like this. You're going to cut the barrel end on a small fine toothed bandsaw. So you push it into the blade to get started but JUST as the blade comes through on the inside you stop pushing and start rotating the barrel in place back to you. So this way the cut on the inside of the barrel is always pushing the fibers back into the matrix. The problem is that on the outside the opposite is happening. SO to prevent tearout there you can do two things. Run a light scoring cut that only goes into the outer surface but does not go right through. In this case you woudl twist it into the teeth as though it was on the bandsaw but rotating with the top going away from you and into the teeth. Once it's scored all around then cut in further so it cuts through to the inside and rotate the top back towards you.

The outside should also be wrapped tightly with masking tape at the cut line. THis does two things. One it gives you something to mark up for the cut line. Second it will help avoid any fibers that do catch from tearing along and out of the surface.

The trick in the end is to make sure that the aggressive leading edge of the cutting teeth of the saw is always pushing down into the material whereever possible.

I've cut a couple of carbon windsurfing masts and some various sized tubes for my model airplane stuff and using these tricks I've never had any trouble.

Another good saw for larger stuff (just remembered this) is a fine tooth hacksaw blade. Use a brand new one for cutting your barrel. The 24 tpi acts more like a slitting sander and greatly helps avoid any issues. But still use the outer scoring cut and then follow it up with the rotation for the final cutting.

It should go without saying that you want to support the waste portion well during those last few strokes so it doesn't pull and tear out any fibers.

EDIT
The sealing with a bit of epoxy resin is also a good idea as mentioned just above. Some 5 minute epoxy applied thinly and then warmed with a hair dryer to make it watery and soak in is fine. Wipe off the excess before it cools and gets gummy again and use a little bit of alchohal and paper towel to wipe away any that gets on the inside or outer side before it cures.

But you can easily do the marking out without a lathe. Just wrap a sheet of writing paper around it so that it meets itself perfectly with the edge at the desired cut line. VOILA! A perfectly square cut line. This only works for straight barrels of course. If it's tapered then it won't meet up on a square lineup. I'd trust the sheet of paper line before I trust the junky miter box that I have.

And FWIW I've got a lathe and if I was cutting carbon tubing I'd still be doing it the way I describe here. Far less stress to the fibers compared to a single point that is digging into the composite.

Crash · 06-23-2007, 03:45 AM

You mention fine toothed saw what about a diamond blade? Also I will have to take it to work and have one of the maint. guys turn it down so the tip will fit back on anyway.

Tessaract · 06-23-2007, 06:11 AM

why not just use the 16in as is?

Crash · 06-23-2007, 07:25 AM

Quote:

Originally Posted by Tessaract

why not just use the 16in as is?

It was damaged hence the 30.00 shipped price and it is going on a very compact gun. Also I just don't like long barrels!

It looks like the threaded end was crushed and it caused a crack in the CF tube where the two join. The cap has been straightened, now I want to shorten the tube to remove the damaged area. If I can get the muzzle end off I will have both of the aluminum ends and 4 sizing backs annoed with the gun.

Railgun · 06-23-2007, 02:00 PM

Don't do the diamond thing unless you use water as a coolant. The biggest enemy to working on composites with machines is that the heat from the cutting softens the bonding agent (very likely an epoxy resin in the Stiffee) and when the bonding agent is softened it makes it easier for the fibers at the surface to tear out. This applies to any fiber be it glass, kevlar or carbon or even cotton. Yes there are cotton and linen composite tubes and sheet materials out there for specific uses.

So that's all part of why I suggested the hand tools option over any power tool option. With hand tool cutting I have much more control over the amount and direction of the cutting force. Also carbon actually cuts a lot easier than glass fiber and MUCH easier than kevlar. While it's very strong in tensile strength it actually cuts not much more difficultly than pencil lead. But you still don't want to mess up and rip a fiber out of the matrix and have a "run" in the surface. That's why the attention to the cutting direction.

It's really not as bad as it seems. I could easily have cut the end and crowned it in less time than it's taken me to type these answers....

Crash · 06-23-2007, 02:27 PM

Thanks for all the answers! I have a couple of ideas to work with and plenty of barrel to try it on.............off to the Bat Cave.......well once i get off work!

Railgun · 06-23-2007, 05:10 PM

Good point. Since you're wanting to remove 2 inches you've got a good two or three tries to practice with before you end up at the final cut line....

Crash · 06-23-2007, 05:12 PM

Quote:

Originally Posted by Railgun

Good point. Since you're wanting to remove 2 inches you've got a good two or three tries to practice with before you end up at the final cut line....

Two inches.....I'm looking at 6 or 8!

06-22-2007, 09:25 PM	#1 (permalink)
Crash MCB Member Join Date: Mar 2006 Location: Texas	CF Barrel or carbon fiber parts in general Well I picked up a very cheap Stiffi but it is 16 in. Is there a way it could be cut it down to a shorter length? __________________ Later, John MY Want To Buy: Black 45 slider frame with internals Cheap 2k pump kit My feed back: http://www.mcarterbrown.com/forums/s...ead.php?t=1021 Carter's Commando Texas Division: http://www.mcarterbrown.com/forums/c...-division.html

06-22-2007, 10:59 PM	#3 (permalink)
Railgun MCB Member Join Date: Oct 2006	You can but it requires some careful work with a very fine toothed saw to avoid tearing the fibers out of the matrix. Also once you've cut it down be sure to sand it to a round ended "crown" much like they shape real gun barrel ends. to help avoid any bruising or picking up fibers and tearing them out of the matrix. You want a fine toothed very sharp hand saw like a Zona hobby saw and you want to keep turning the barrel so you're cutting as tangentially as possible all the way around. It's easy to do but difficult to explain. Think of it like this. You're going to cut the barrel end on a small fine toothed bandsaw. So you push it into the blade to get started but JUST as the blade comes through on the inside you stop pushing and start rotating the barrel in place back to you. So this way the cut on the inside of the barrel is always pushing the fibers back into the matrix. The problem is that on the outside the opposite is happening. SO to prevent tearout there you can do two things. Run a light scoring cut that only goes into the outer surface but does not go right through. In this case you woudl twist it into the teeth as though it was on the bandsaw but rotating with the top going away from you and into the teeth. Once it's scored all around then cut in further so it cuts through to the inside and rotate the top back towards you. The outside should also be wrapped tightly with masking tape at the cut line. THis does two things. One it gives you something to mark up for the cut line. Second it will help avoid any fibers that do catch from tearing along and out of the surface. The trick in the end is to make sure that the aggressive leading edge of the cutting teeth of the saw is always pushing down into the material whereever possible. I've cut a couple of carbon windsurfing masts and some various sized tubes for my model airplane stuff and using these tricks I've never had any trouble. Another good saw for larger stuff (just remembered this) is a fine tooth hacksaw blade. Use a brand new one for cutting your barrel. The 24 tpi acts more like a slitting sander and greatly helps avoid any issues. But still use the outer scoring cut and then follow it up with the rotation for the final cutting. It should go without saying that you want to support the waste portion well during those last few strokes so it doesn't pull and tear out any fibers. EDIT The sealing with a bit of epoxy resin is also a good idea as mentioned just above. Some 5 minute epoxy applied thinly and then warmed with a hair dryer to make it watery and soak in is fine. Wipe off the excess before it cools and gets gummy again and use a little bit of alchohal and paper towel to wipe away any that gets on the inside or outer side before it cures. But you can easily do the marking out without a lathe. Just wrap a sheet of writing paper around it so that it meets itself perfectly with the edge at the desired cut line. VOILA! A perfectly square cut line. This only works for straight barrels of course. If it's tapered then it won't meet up on a square lineup. I'd trust the sheet of paper line before I trust the junky miter box that I have. And FWIW I've got a lathe and if I was cutting carbon tubing I'd still be doing it the way I describe here. Far less stress to the fibers compared to a single point that is digging into the composite. __________________ Model airplanes are cool too! Last edited by Railgun; 06-22-2007 at 11:06 PM..

06-23-2007, 03:45 AM	#4 (permalink)
Crash MCB Member Join Date: Mar 2006 Location: Texas	You mention fine toothed saw what about a diamond blade? Also I will have to take it to work and have one of the maint. guys turn it down so the tip will fit back on anyway. __________________ Later, John MY Want To Buy: Black 45 slider frame with internals Cheap 2k pump kit My feed back: http://www.mcarterbrown.com/forums/s...ead.php?t=1021 Carter's Commando Texas Division: http://www.mcarterbrown.com/forums/c...-division.html

06-23-2007, 02:00 PM	#7 (permalink)
Railgun MCB Member Join Date: Oct 2006	Don't do the diamond thing unless you use water as a coolant. The biggest enemy to working on composites with machines is that the heat from the cutting softens the bonding agent (very likely an epoxy resin in the Stiffee) and when the bonding agent is softened it makes it easier for the fibers at the surface to tear out. This applies to any fiber be it glass, kevlar or carbon or even cotton. Yes there are cotton and linen composite tubes and sheet materials out there for specific uses. So that's all part of why I suggested the hand tools option over any power tool option. With hand tool cutting I have much more control over the amount and direction of the cutting force. Also carbon actually cuts a lot easier than glass fiber and MUCH easier than kevlar. While it's very strong in tensile strength it actually cuts not much more difficultly than pencil lead. But you still don't want to mess up and rip a fiber out of the matrix and have a "run" in the surface. That's why the attention to the cutting direction. It's really not as bad as it seems. I could easily have cut the end and crowned it in less time than it's taken me to type these answers.... __________________ Model airplanes are cool too!

06-23-2007, 02:27 PM	#8 (permalink)
Crash MCB Member Join Date: Mar 2006 Location: Texas	Thanks for all the answers! I have a couple of ideas to work with and plenty of barrel to try it on.............off to the Bat Cave.......well once i get off work! __________________ Later, John MY Want To Buy: Black 45 slider frame with internals Cheap 2k pump kit My feed back: http://www.mcarterbrown.com/forums/s...ead.php?t=1021 Carter's Commando Texas Division: http://www.mcarterbrown.com/forums/c...-division.html

06-23-2007, 06:11 AM	#5 (permalink)
Tessaract Active Member Join Date: May 2007	why not just use the 16in as is?

06-23-2007, 05:10 PM	#9 (permalink)
Railgun MCB Member Join Date: Oct 2006	Good point. Since you're wanting to remove 2 inches you've got a good two or three tries to practice with before you end up at the final cut line.... __________________ Model airplanes are cool too!

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