Good countersink

Questions about tools and jigs you want to buy/build/modify.

Good countersink

Postby Steve Sawyer » Sun Jun 10, 2018 12:34 pm

I'm making wood covers for the control cavities on the current build. I knew that NONE of the countersinks I currently have (and I probably have a dozen of one kind or another) could be relied upon to create a countersink for the screws that would NOT chip the edges of the screw hole. StewMac sells a countersink that would probably do the job perfectly, but they get $36 for it!!

We all love StewMac, but I have to say that while some of the common tools that they re-brand and sell for for lutherie do have some additional tweaks to make them more attractive, or specific to lutherie (a good example is their soft-jaw pliers and the "gunstock" vise that they've re-worked a bit), sometimes they take some generic product and just hang a "for lutherie" spin on it and charge an arm and a leg for it.

I found this 3/8" countersink on Amazon for $11, and just ordered another, larger (1/2") one (for chamfering the finish on peghead holes etc.) for $10. They're double-cut carbide burrs, and they can be spun with your fingers, or chucked into a drill and run at a VERY slow speed to give a perfect countersink. These are 90* burrs, so they're not the 82* that most flat-head screws require, but I've never found that difference to ever cause me a problem with the kinds of materials I use (wood, plastic, etc.).

There is a still larger 3/4" one (an SK-7) that would be nice for output jack holes, but those run about $26.
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Re: Good countersink

Postby John Clifford » Sun Jun 10, 2018 4:54 pm

Cool, thanks. A lot of times, I end up using oversized twist drill bits for countersinks. It works better than the "countersink bit" I have, but this one looks promising.
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Re: Good countersink

Postby Steve Sawyer » Sun Jun 10, 2018 9:33 pm

John Clifford wrote:Cool, thanks. A lot of times, I end up using oversized twist drill bits for countersinks. It works better than the "countersink bit" I have, but this one looks promising.


Yeah, it seems most of the countersinks I have are designed for (and work great) on metal, but as soon as I try to use them on wood, it's clear that the angle of the cutting edge is too obtuse for anything that is softer than something I'd use on a fretboard. Ring-porous woods in particular (e.g. oak, ash) and more open-pored woods like mahogany just don't cut well with those edges.

These cut more like a file.
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Re: Good countersink

Postby Bob Hammond » Mon Jun 11, 2018 12:37 pm

look for a Weldon countersink. It has only one hole and no flutes.
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Re: Good countersink

Postby Steve Sawyer » Mon Jun 11, 2018 1:12 pm

Bob Hammond wrote:look for a Weldon countersink. It has only one hole and no flutes.

Thanks, Bob. I have a whole set of that type, and they can do a good job on wood if the edge if the bore hits the hole in the "sweet spot" that provides a down-shear action. They can also wander leaving a countersink that is off-center, so they are best used in a drill press with the work piece securely clamped. That said, they are my go-to countersinks in most cases.
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there are weldon AKA zero flute countersinks available with pilo

Postby David King » Tue Jun 12, 2018 2:04 pm

There are weldon (AKA "zero-flute") countersinks available with pilot drills so you can drill and countersink in a single step.

Ideally your cover template has the hole locations drilled from the back side so you can locate the holes via a pin in the drill press table opposite the chuck. This is the standard approach to locating holes accurately and repeatably. You make a wood plug, preferably a plywood disc that jams into the hole in the center of the of most drill press tables. You then drill the pin hole and insert the pin. I use 1/8" pins which are just inverted busted carbide PCB drills of which I have an endless supply. They have a chamfer on the back end which makes it easy to locate your jig's hole. You should set the drill depth so as not to drill into the template. Every time you change the table height you need to align the pin with the chuck but this is relatively easy. I push the locating pin down out of the way when not in use and push it up from below when I need it.
Attachments
drillpressjig1.jpg
Here's a jig setup I use for brass string-through ball end holes. You can see the pin in the wood plug and the pin holes are strung together with a shallow channel to make them quick and easy to locate one after another.
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Re: Good countersink

Postby David King » Tue Jun 12, 2018 2:11 pm

The multi-flute countersinks are absolutely worthless in my estimation. One more slight detail -US screws take an 82º degree countersink while metric screws use the 90º.
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Re: Good countersink

Postby Steve Sawyer » Tue Jun 12, 2018 6:47 pm

David - thanks - cool technique.

What I normally do is use a centering pin which is a double-ended pointy thingumbob used to center router bushings. One end is 1/4" and the other 1/2" in diameter. I chuck it up in the drill press, lower the quill until it actually pins the work piece to the table at the point where I want to bore, lock the quill, then use clamps or hold-downs to lock the work piece to the table.

Your approach would work much better for repeated holes.
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Re: Good countersink

Postby Mark Fogleman » Fri Jun 15, 2018 12:08 pm

Before spending any money, try cutting the countersink with your current countersink prior to drilling the through hole. I get much smoother countersinks this way.
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Re: Good countersink

Postby Steve Sawyer » Fri Jun 15, 2018 1:10 pm

Mark Fogleman wrote:Before spending any money, try cutting the countersink with your current countersink prior to drilling the through hole. I get much smoother countersinks this way.

I'll try that. But $20 for two countersinks ain't bad...
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Re: Good countersink

Postby Michael Hampel » Mon Jun 25, 2018 5:12 pm

Read this on the Lost Art press blog. I haven’t tried them, but it looks promising.
https://blog.lostartpress.com/2018/05/2 ... untersink/

Good luck
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Re: Good countersink

Postby Steve Sawyer » Mon Jun 25, 2018 5:25 pm

Michael Hampel wrote:Read this on the Lost Art press blog. I haven’t tried them, but it looks promising.
https://blog.lostartpress.com/2018/05/2 ... untersink/


Yeah, someone mentioned that type above. They work really well on wood depending on the size of the hole, plus they WILL wander, making an off-center countersink, particularly on soft woods so they seem to work best for me chucked into a drill press. If the hole is just a tad too small for the countersink the angle of the edge of the hole will actually be an up-cut, and can cause some tear-out. I use these all the time, but when precision and a smooth cut is necessary on a "show" piece on a guitar, the ones I showed at the start of this thread work beautifully. They aren't fast, but almost work like sandpaper or a file with no tear-out at the edges and they do a good job of staying centered in the bore, and can actually be spun between your fingers if the wood is relatively soft like ash or mahogany.
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Re: Good countersink

Postby Michael Hampel » Mon Jun 25, 2018 10:57 pm

Good info, thanks. I think I’m going to try the double cut carbide, a good deal too.
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