Vincent DePillis

Drilling precise holes in Carbon

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For my boom project I need to drill several 15mm holes to take the axle pins for the reefing sheaves.  The holes will be in carbon material that ranges from 10mm to 3mm.  I am thinking that I should drill to just below 15mm, and finish with a reamer to 15mm.  It so happens that McMaster Carr has an appropriate 14.5mm drill bit, and a 15mm hand reamer.  Both are steel, the bit cobalt coated with something even harder.  The bits are spendy-- like $120 each.

Am I overthinking this (as usual)?  Should I just get a 15mm bit and drill some test holes?

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Actually, I can do 12mm holes if I use the sleave supplied with the sheave-- I was going to use the bearing direct on the axle, but 12mm bits are MUCH more available,including in tenth of a millimeter increments.  So the question stands--  Drill and ream, or just drill. 

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If you drill, the hole will not be to size or round. Especially if not held rigidly (like in a milling machine). Maybe it doesn't matter but it would on my boat. Drill and ream will get you much closer to size and round. There is another strategy that will take a little more work, but result in a better job: buy some G10 tube of the appropriate ID for the axles. Drill the holes big enough for the tube. Cut some short pieces of tube and bond them into the holes, with the axles through them when wet - this ensures they are aligned. Sand off any excess G10 tube - there may be value (or just available space) to leaving it long on one side or the other. If so leave a fillet in the epoxy on that side. Stronger, perfectly aligned, electrically isolated from the carbon, replaceable. West Six10 works great for this sort of bonding. 

A tip on the drill: flatten the cutting edges (aligned with the length) slightly, can be done offhand on a grinding wheel. About 0.010 - 0.020 width flats will do. This removes the rake of the cutting edge, and will keep the drill from self-feeding, which they do badly in fiberglass or carbon laminate. It will take more force to cut but won't suddenly plunge through out of control, tearing the laminate apart.

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Make a fixture plate and router the holes, this is how all the mast builds do it.  You will need to determine the offset for the router collet but that is easy to do and you can practice ahead of time.  Also the sidewall may be a little thin in its current state to support a pin in bearing.  I would think about putting a patch or backing plate locally as well

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2 hours ago, Kenny Dumas said:

Hole saw?

Not if you want a hole made to a known dimension and round. 

A router isn't a bad plan, but fixturing it on a curved boom profile will present challenges. 

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12mm 1/2 shank is about $20. (Freud, CMT, Amana) Don’t buy a cheap one figuring you will destroy it even though you will. Cheap router bits break or go dull really fast. 
 

Use a plunge router. Any size will work(1 1/2 - 3hp). Take a piece of melamine or 3/4” cabinet ply big enough you can get some clamps on it. Drill a 1” hole on the drill press with a forstner bit.  Install a 1” collar in the base of the router plate. Position the jig wherever you want, position the router with the collar in the hole and slowly plunge away. 
 

You may find installing a fence to the underside of the  jig helpful for alignment and clamping. 

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One problem with the router idea is that it is unlikely to plunge both sides. You must do another setup for the other side, and keeping it lined up is a challenge. 

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Start small and work you way up.   Run the drill backwards on both sides of the hole to de-burr first.

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6 hours ago, DDW said:

One problem with the router idea is that it is unlikely to plunge both sides. You must do another setup for the other side, and keeping it lined up is a challenge. 

So you are going to take an 12mm x 8” drill bit and go straight thru. I’m confident you will blow out the far side when you come out on the backside. That’s if you can jig the bit so it comes out somewhere near where it’s supposed to be. 
 

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The hole saws I get from the local ship store work really well on carbon, at least for a few holes. I often drill undersized and use abrasive covered hole saws and drill bits to bring the hole to the finished dimension. One can wrap the barrel of a hole saw or a drill bit or rod in adhesive backed sandpaper and chuck it up and go. If the hole needs to be just a bit larger, go to a coarser grit (it's thicker).

Do avoid heat when drilling composites as it can fuck the resin. Drilling a bit at a time with the vacuum hose taped to the part to help cool the bit seems to work.

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18 hours ago, CaptainAhab said:

So you are going to take an 12mm x 8” drill bit and go straight thru. I’m confident you will blow out the far side when you come out on the backside. That’s if you can jig the bit so it comes out somewhere near where it’s supposed to be. 
 

Yes. I've done it many times. You aren't going to do it with a handheld drill and the drill sharpened as it came from the vendor though. 

The very best way I have to do it is to fixture the boom in the open CNC mill, drill through, then ream. Rigidity in tool holding and controlled feed makes a huge difference in this sort of operation. If the sides of the boom are steeply sloped where the hole needs to be, then interpolate the hole with an end mill. 

If everything is to be hand held, then drilling undersize and drum sanding to size (and location) may be the safest way. I'd still drill though with a drill the size of the pilot for the hole saw, that way you have a chance of being close on the other side. There are hole saws with carbide grit instead of teeth, these last much longer in glass or carbon.

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On 8/24/2020 at 8:48 AM, slug zitski said:

Carbon laminates are hard to drill ...typically they are machined 

delamination and breakout  are the issues 

https://www.elevatedmaterials.com/drilling-carbon-fiber/

 

FB2E8E6B-887B-405A-8CF3-DEF661F24986.png

Yep. 

At a minimum you should use a burr tools to pilot the hole. then drill if you must.

The best method would be a 12mm hole template and a burr tools AKA rout the hole...   

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The picture is the result of using a bit sharpened for steel in laminate. You cannot expect perfect results. It's like not knowing which end of a screwdriver to hammer with. 

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I've never seen  a dagger drill , but looking at the panamerica tool website I found a sealant cutter that can be chucked in a tool and cut out thick caulking without harming surrounding material. And its $6 bucks. 

It was worth logging in here this am, I learn so much stuff

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Carbide bits that look like steel cutting bits work great in carbon. McMaster has decent prices on them and I've been happy with the quality.

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11 hours ago, crankcall said:

I've never seen  a dagger drill , but looking at the panamerica tool website I found a sealant cutter that can be chucked in a tool and cut out thick caulking without harming surrounding material. And its $6 bucks. 

It was worth logging in here this am, I learn so much stuff

there is nothing better in carbon, in my opinion, than a dagger bit

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In small sizes, the dagger type bit is available at HomeDepot etc. It'll be HSS not carbide, but will last a few holes and they are easy to sharpen offhand. 

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I think these are the ones I use: https://www.mcmaster.com/drill-bits/drill-bits-5/carbide-tipped-drill-bits-10/

I have bought both the 118 degree and the 135 degree tips and I'm not sure that I can tell the difference. I buy them separately as I only use 5 sizes and go through a few of those sizes a year doing production carbon parts.

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You can get carbide tipped hole saws in small sizes.  The electricians on the ships like them for SS boxes as they are alot quicker than knockout sets.  Think we usually get from Ballard industrial, Green Lee and maybe Milwaukee or Bacho.  They certainly take alot of abuse.

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With a hole saw , To get a clean  hole with no laminate breakout , you need to drill from both sides 

Only use a hole saw on laminate if you can access both sides of the component 

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i would use a forsner bit.

cuts the fibers clean as it makes the hole.  centering spike keeps you dead on point.

Best if you can get the boom to a drill press...

Using Forstner bits instead of hole saws - Home Improvement Stack Exchange

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What about brad point bits? The spurs always produce the best, cleanest hole when I've drilled.

But - I've never drilled carbon laminate.

image.png.6b4030b05e2decce7516bc3dec8786ce.png

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3 hours ago, SloopJonB said:

What about brad point bits? The spurs always produce the best, cleanest hole when I've drilled.

But - I've never drilled carbon laminate.

image.png.6b4030b05e2decce7516bc3dec8786ce.png

I use these a lot , but they don’t cut the carbon fibre cleanly.  I drill undersized holes, then die grind the laminate up to size, epoxy the bore and redrill to finished size with a standard point. The reason I use a standard type drill is it centres itself , unless I can use my drill press, then brad point drills are fine. This is assuming the article has a core, to epoxy into. The boom may not, so sealing the fibre may present its own issues.hope this helps. 

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6 hours ago, Raked Aft\\ said:

i would use a forsner bit.

cuts the fibers clean as it makes the hole.  centering spike keeps you dead on point.

Best if you can get the boom to a drill press...

Using Forstner bits instead of hole saws - Home Improvement Stack Exchange

Have you ever used a forstner bit? They only work in drill presses. They get full on trashed if you drill anything but wood. 

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???

Forstner bits work fine in a hand held drill motor. They do dull very quickly in glass or carbon. Also in laminate, they can be "catchy" because when the flute penetrates a layer of laminate it can peel it up suddenly. 

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Forstner bits are best for wood using a drill press as mentioned above. They will tear up your carbon bits, new or sharp, doesn't matter.

 

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On 8/25/2020 at 1:12 AM, DDW said:

Not if you want a hole made to a known dimension and round. 

A router isn't a bad plan, but fixturing it on a curved boom profile will present challenges. 

I have not tried this, but, what about 3D printing a router fixture to fit onto the surface of the mast? Then use hot glue to hold the fixture in place, along with fiberglass strapping tape. 

As an alternative, I have seen a CNC guy use blue tape as the foundation for crazy glue to mount material to fixture plates for CNC machining. 

Bam Miller 

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A 3D printed fixture would probably work great, you could even just fabricate something from some plywood. Or pourable foam/urethane etc. It is just an extra step, might have to be repeated for each hole if the boom profile is tapered or changes. You can use hot melt glue to hold them in place, as long as you aren't too rough with it. The hot melt peels off afterwards. 

I've 3D printed fixtures for a lot of things. I've also printed male and female molds for fiberglass parts. MarkForged main business for their carbon printer seems to be tooling. 

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You simply need a way to hold a piece of 3/4” ply or melamine at the tangent(perpendicular) to the hole. You should be able to cut a block of wood or ply to fit the mast. Ideally you want to jig it so you have the base on both sides at the same time. Let’s say it’s a round piece of 3” pipe. You should be able to take (2) pieces of ply, (2) pieces of 2x4 ripped to 3” and bolt/screw it all together. You need to shape the 2x4 a bit to keep it from rotating .

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