I know this method has been posted or suggested before, but just wanted to support its ease of use.
I have tried cutting nice straight lines in fuselage or composite items using diamond wheels on Dremel type power tools, fixing a straight edge to the item and then either taking chunks out of the straight edge or the workpiece - either way the slot is never really straight, and often wider in places than others......
So tasked with cutting two slots in some BVM drop tanks for a fin i used the 'hacksaw' blade method. Trim a junior hacksaw blade down to say half its length (makes two cutters then), make a handle to protect your hands from the teeth - I strap two wooden coffee stirers to the blade and wrap electrical tape around them, leaving about an inch of blade exposed. Using a Dremel and a cut-off disc cut the tip at an agle and then on the teeth edge grid a small angle sloping back towards the teeth making sure you leave a tooth exposed at the leading edge.
Depending on the blade a cut will occur on either the forward or backward stroke.
Using a piece of stiffish material, flexible ruler, or as I find best thin glass board, tape this to the workpiece to line up with the slot you want to cut. Mark your extremities of the cut and then using light stokes only run the blade up and down the surface keeping light pressure on the straight edge. The blade will slowly cut through the gel coat and cut into the material, sooner or later (later with carbon layups!) the blade will break through in a spot or two, if you widen the slot big enough to get the blade in you can then use a sawing action to cut the slot open along its length - the groove already made helps keep the slot straight. Each end can be cut to meet your end points without going too far.
Hope this helps some, and sorry if its bored others!

marcs.

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In the BVM manuals I have built from they suggest the same but using a razor saw with the back removedinstead which give a really fine cut on things like gear doors on the Bandit. Good tip though. Thanks

Jason

Good tip, Thanks

Good idea....

Jus to add to the above, I have in the past heated a #11 blade using a torch and this allows the blade to cut a very fine line in FG. Towerhobbies also has a soldering gun that has a special fitting where one can attach a #11 blade to achieve the same as above...works great for LG doors and hatches...

Ehab, tried that and found it very slow going, really had to work the hot blade to make any progress. It certainly did not like anything with cf reinforcement which is often the case in areas where cut-outs are required.
Jason, found the blades blunted real quick on those razor saws, with the small hack saw blades just re grind the tip when it looses its bite and away you go.
Often wondered if there was a miniature version of those 'cutters' they use to remove plaster casts from broken limbs, might be useful in our game!

marcs

Just to reinforce and clarify what Jason said, the razor saw method leaves a gap thinner than the Dremel cutoff wheel. Perfect for applications where the cutout piece is kept in place, such as with hatch covers and as Jason said, gear doors. Accurate to control as well.

Craig

Those "cast saws" you are referring to, would more than likely not work.  I use one frequently to cut bone.  One nice thing is that they will not cut tissue, so unlike what you see in the movies they will not whack a guys head off with blood spurting everywhere (although they will cut thru a skull pretty quickly).  They primarily operate by vibrating a blade, similar to a hacksaw blade, but with bigger teeth, in a back and forth type of motion.  The high frequency ossilation will cause the hard substance (ie, bone or cast) underneath to disentergrate beneath the teeth of the blade.  My guess is that on a structure such as the plane airframe it would just crush the glass or make an irregular cut.  The hacksaw or razor saw look like the best thing out there right now.
Just my two cents.

Mmmm, Craig not having a go at Jason, I know the razor saw will produce a thinner cut than a Dremel cut off wheel, thats not really what I was getting at, more about a neat straight cut of equi-thickness all along. Incidentally you can get diamond tipped wheels which are the same thickness as a razor saw blade if the truth be known - just not easy to use! A razor saw blade looses its sharpness very quickly when using it on composites so where there is carbon reinforcement you can go through a fair few trying to cut the slot. The junior hack saw blades are cheap and the 'cutting' tip renewable with a quick grind off.
Doc cheers for the update on the cast saws, had no idea how they worked and guess following your explanation totally unsuitable for our purpose.

marcs

</p><div style="margin: 0cm 0cm 10pt"><span style="font-size: 9pt; line-height: 115%">marc s,

not sure what razor saw you have been using but the Exacto one I have been using since 2001 is still sharp enough to cut through composites and occasionally my finger too

Jason</span></div>

Its an Exacto one too, but the blades don't seem to last long when cutting through fuselages

marcs

Marc hi

Slightly off topic but can you give me a little detail on making tanks........

ie what type of foam to use for the blank and what cloth &amp; resin you recommend

Ta

Phil.

Very true. It's necesary to frequently snip off the end to have sharp cutting teeth.

Thanks for that graphic description Tommy. I think I'llgo have breakfast now.

Craig

Nice tip and description Marc.
Did you finish your composite hatch latch system ?

You're welcome Craig...I threw that last part in just for you.......LOL

Olnico, the samples were made but yet to find a man with a cnc machine who can cut the pieces in bulk for me, I have tried seanrit but he has gone off the radar and is not returning my skype calls
If you need a few let me know and I will send them in the post.

marcs

Well Marc, my best friend here in Dubai has a CNC milling machine and might be interested in helping you on this project.
He is the man who has worked on the F-22 raptor for a long time ( still in progress ):
http://www.rcuniverse.com/forum/m_3189695/tm.htm

In between I'd happy to get a couple of these for my Me262.

Maybe this is similar to what you were thinking. Dremel's version of a "Tommy Saw" . Ijust picked this up 2 days ago. 1/2 price so Icouldn't pass it up. Thenew stock ones had a bonus blade in them but I'll keep the $50.

( Home Depot if you guys are looking, Its clearance season and you never know what you may find. I also picked up a Makita grinder half price. Most of the stores have the arc welders and small air compressors on clearance. Other stuff are one of kind items. Istop at every Home Depot I see now LOL.)

I haven't tried it yet, but it sounds like it would be perfect for the job you describe. These normally are $99, at least for this kit combo (Dremel 6300-01) that also has a triangular sander attachment.
Mark