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Drill bit drift

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Forum topic by pariswoodworking posted 06-10-2012 04:38 AM 1399 views 0 times favorited 10 replies Add to Favorites Watch
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pariswoodworking

380 posts in 1136 days


06-10-2012 04:38 AM

Hi everyone, I’m currently making a set of grips for a friends pistol, but I’ve run into a problem. When I try to drill the hole that would allow the screw head to sit flush with the wood, the drill bit drifts. How can I get it to stop? The hole as to be extremely exact, or the screw will not sit into it correctly.

Thanks.

-- Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein


10 replies so far

View Pete_Jud's profile

Pete_Jud

423 posts in 2404 days


#1 posted 06-10-2012 05:01 AM

Brad point or forstner bits in a drill press have no or very little drift. Don’t use simple twist drills.

-- Life is to short to own an ugly boat.

View rance's profile

rance

4132 posts in 1811 days


#2 posted 06-10-2012 06:42 AM

Neither a forstner bit won’t get you what you want for a flat-head screw. You’ll need to countersink them.

But first, you need a bit with a 118 degree tip as opposed to the one you are probably using with a 135 degree tip . The 118 deg. tip will eliminate most all of the drift.

Once you have the hole drilled, then follow up with a countersink to accomodate your flat head screw. Use a countersink that includes a drill bit to keep it centered in the hole you already have. At this point, you’ll only be cutting with the countersink. The drill part is only used as a pilot.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

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pariswoodworking

380 posts in 1136 days


#3 posted 06-10-2012 08:08 AM

The screws are roundhead. I just want the get the wood flush with the edges. Also, they do not have a sloping side like regular screw heads, their edges are at a 90 degree angle. Do you know where I could get a countersink that would work for this? (the head dia is 9/32”)

Thanks

-- Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein

View Brit's profile

Brit

5146 posts in 1493 days


#4 posted 06-10-2012 09:49 AM

You don’t want a countersink at all. What you are doing is called counterboring. You can do it with two Forstner bits, one to drill the counterbore for the head of the screw and one to drill the hole for the thread. You must drill the larger hole first and use a depth stop to get them all the same depth so the head ends up flush with the surface. Without moving the wood you are drilling, change to the smaller bit and drill through the wood. The hole for the thread will then be on center with the counterbored hole.

-- Andy -- Old Chinese proverb say: If you think something can't be done, don't interrupt man who is doing it.

View Charlie's profile

Charlie

1017 posts in 937 days


#5 posted 06-10-2012 09:53 AM

Use a 5/16 forstner and see if that gives you the screw head clearance you’re after. A lot of pistols used a domed head, often with an allen head. Some are slotted head and more rounded. Some, like a Beretta use an extremely flat-topped allen head. Almost like a truss head. If the 5/16 doesn’t look tight enough, you can try a 19/64, but good luck finding one that’s not part of a set.

For the flatter or shallow dome head screws, after you drill the hole, find yourself a “smooth taper” to just burnish the edge of the screw hole. You don’t really chamfer it as mush as you break the edge by burnishing it. An easy way to do this would be to get something like a 3/8 button head allen screw and chuck it up in the drill press, head down, and bring it down to touch the edges of the screw hole. It should more or less polish the edge break rather than grinding it away.
Those grip screws should be smooth. No edges. Where the screw is there should be no sharp breaks, but it only takes a small amount of burnishing to ease the edge.
My dad was a competition shooter when he was on the police force. His hands were so big, all of his competition pistols required custom grips.

View paratrooper34's profile

paratrooper34

760 posts in 1603 days


#6 posted 06-10-2012 12:57 PM

Paris, one trick that works for me to ensure I get holes to end up where I want them when accuracy is critical is this:

I use an awl to set a small dimple exactly where I want the hole. I then take a brad point bit or a forstner bit (without the bit being under power at this point) and bring the bit so it just sits in the hole I made with the awl. Once I have the bit in there, I give it power in REVERSE. This action does two things: it confirms that is where I want the hole and it defines a very sharp and untorn entrance into the the wood. This small action to prior to drilling the hole coupled with cautious drilling if it is wood with funky grain, ensures you have a hole in the wood where you want it to be.

-- Mike

View rance's profile

rance

4132 posts in 1811 days


#7 posted 06-10-2012 02:40 PM

When you said “flush with the wood” I assumed you had a regular flat head screw. Yeah, a forstner would do the trick. If you can’t find the size you need, you can make a D Bit for this one application. Google it. You’ll want a flat bottom one for the final operation though.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View Loren's profile

Loren

7539 posts in 2299 days


#8 posted 06-10-2012 04:58 PM

This is fussy work, isn’t it?

You want perfection in a small thing like this that will get
handled and examined frequently.

I would drill the recess for the screw head first using
a forstner, brad point or a modified standard twist drill
which I regrind to a shape similar to, but less pronounced
than a brad point. You may want to avoid big cutters
on the edge of the bit because they can scribe around
the hole deeper than needed. The cutters on the
edge of the bit in any of the 3 bit styles I described
make a clean entry into the wood and leave a hole
in the middle which you can use to guide your drill when
you make the hole for the screw shank.

You may want to go a step further and experiment
with bottom-scraping the hole with something like
this:

http://www.amazon.com/Shank-Double-Carbide-Shape-SB-51/dp/B0007OV6PM

-- http://lawoodworking.com

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MonteCristo

2097 posts in 839 days


#9 posted 06-10-2012 06:50 PM

Twist drills are good in endgrain (although one with a parabolic nose is even better) and metal and should be reserved to that sort of drilling unless the hole’s accuracy is not very important.

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

View pariswoodworking's profile

pariswoodworking

380 posts in 1136 days


#10 posted 06-11-2012 08:32 AM

Thanks for the advice everyone, I’m going to order a forstner bit tomorrow, so I’ll let you all know how the grips turn out.

-- Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein

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