# Drilling Accurately Located Holes



## breaknrn (Jun 17, 2007)

Okay, here's a challenge for all you readers out there. I just picked up some aluminum miter slot bars from Rockler and they are tapped for 1/4 20 holes . To attach the bars to the table saw cross cut sled I am building, I need to drill holes through the sled to align with the pre drilled holes in the bars. The screws need to be screwed in from the top because there is no counterbore for screw heads on the bars themselves. I could use a punch to locate the holes to be drilled in the sled, but it is not accurate enough because the punch has a diameter smaller than the hole I need to drill. Anyone have any ideas? Very much appreciated!


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## PaulMCohen (Jan 22, 2008)

I have several ideas, use a drill bit the diameter of the hole in the miter bar (http://en.wikipedia.org/wiki/Unified_Thread_Standard), position the bar when you want it with double stick tape and turn the bit by hand until you get a dimple in the bottom of the sled. Remove the bar and drill the holes.

Use a Insty-bit drill bit/countersink combo, turn the countersink around so that the cutting edge faces the drill, insert the shaft of the drill bit into miter bar and then into the drill chuck. Hold the bar in a vice so it doesn't spin, start the drill slowly and when you pull it away from the miter bar the countersink will countersink the bar exactly in the center of the miter bar holes.

You can find center punches at Sears or Ace Hardware and other places in multiple sizes for $3-$4 each, just buy one that fits the holes, while not elegant it might be the cheapest solution.


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## cloakie1 (May 29, 2011)

what paul has said…i was going to say a counter sink in reverse. it should locate the centre of the hole for you


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## devann (Jan 11, 2011)

A self centering drill bit sometimes called a "vix" bit. you'll have to get one the proper size.


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## PaulMCohen (Jan 22, 2008)

A vix bit will not really help here except to create a pilot hole which would have to be enlarged. The hole size in the slid is actually bigger than the hole in the miter bar.


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## bubinga (Feb 5, 2011)

As devann said: A self centering drill bit sometimes called a "vix" bit,maybe a (5/64" Vix Bit for #3 & 4 Screws) , will mark hole locations,on the sled,through the holes in the miter bar, and will be centered,so you can drill and counter sink your 1/4" holes.
Self-Centering Hinge Drilling Vix Bits

Paul M Cohen: I don't think he has drilled any holes in the sled yet

These highly accurate bits are used for precise drilling of holes for cabinet and door hinges, door butts and *all large and small hardware*. Desired depth is achieved by loosening a setscrew, setting the high speed drill bit, then tightening the setscrew.


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## breaknrn (Jun 17, 2007)

Paul,

Thanks for the tip. it looks like a 7/32" bit fits pretty closely in to the hole size needed to fit inside the 1/4 20 pre tapped hole in the bar. Luckily, I have this size in a brad point bit.

Okay, here's the procedure I ended up using.

1. Clamp the bar to the base of the sled temporarily in their desired locations. 
2. Then I put the 7/32" brad point bit in to one of the holes to make a dimple in the wood. 
3. I repeated for all the rest of the holes along the bar
4. Removed the bars
5. Went back to each small dimple and made a deeper indentation using a punch awl (I love this tool by the way. It's the best 2 bucks I ever spent on a tool).
6. I used the smallest bit I had and drilled a hole all the way through the wood (backing up the wood on the other side of course (wink). The key here is to not lose the reference marks on both sides of the wood. 
7. Flipped the wood over and used a dowel making bit to counter sink for the head of the screw. This plug cutter is the good kind with the spring loaded center pin that keeps it on track. (Note: I did this because I dont have a countersink bit big enough to accomodate the 15/32 head of the screw. If you have a counter sink this big, then just use that instead). I then popped off the plug. 
8. Flipped the wood back over and drilled the 1/4 inch hole in the bottom referencing the small hole created by the drill bit on step 6.
9. I then attached the bars to the sled. Perfect fit.

Thanks Paul and everyone for their tips.

Note: as Paul said, Sorry, a vix bit won't work here since its tough to get a vix bit with the same outside diameter as the 1/4" hole size. Even if you want to use it to make a dimple in the wood below, you'd have a difficult time making sure it is plum and square to the wood while using the tip as a reference edge because the miter bar wasn't countersinked. Thanks anyways!


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## Bluepine38 (Dec 14, 2009)

Another method would be to use a transfer punch, this is a machinist punch set made in sizes similar to a 
drill bit set, with a needle point punch in the center. The main drawback is that they are expensive, they
are used to mark the metal only, sometimes used with in combination with blue layout ink or paper, then
you remove your pattern and use a regular center punch, or in your case awl to mark the drilling point. If
you want to really perturb a machinist, try using the transfer punch as a center punch. Glad you got your
problem solved, and hope your sled works OK. Another method would be to use a cone point set screw,
which would thread through the threaded hole and mark the wood as deeply as you wanted to tighten 
the set screw.


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## rsdowdy (Aug 25, 2009)

Page 21 of the Lee Valley Feb 2011 Suppliment (http://www.leevalley.com/US/wood/page.aspx?cat=1,43456&p=54892) has a center punch set for 14.95 for a Transfer Punch Set for accurate layout of holes. Not near the same price as center finding drill bits. I have been toying of getting this set but have not done so yet.

Royal


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## NBeener (Sep 16, 2009)

I know I'm missing something *obvious*, but … if you punch the center of the right location, and use a brad-point (or equivalent) type of drill bit, of the appropriate size, why WON'T it be just where you want it to be ??


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## SCOTSMAN (Aug 1, 2008)

Actually drilling holes with a drill press is not an accurate way of making round holes for various reasons.
I think you should look at drilling undersize then reaming the holes using the correct undersize drill and correct perfect size reamer. if I am understanding your question then this should work. Alistair


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## rsdowdy (Aug 25, 2009)

The key is actually punching the exact center of the hole. If you just dot it with a pencil, or other marking device, then you are not on center. By using the predrilled holes as guides, and coloring in the hole, or marking the center of the hole, many of us can't mark the exact center of the hole with a regular punch or hold a pencil exactly 90 degrees and mark the exact center of the hole. Being slightly off just drives some of us crazy! So, using something like this marking set that the punch is the exact same size as the pre-drilled hole, then it will give us a true center. (Then if we don't use a drill press, then our holes are not drilled perfectly.)

Royal


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## tierraverde (Dec 1, 2009)

The way to drill a perfectly sized hole (not location) is to drill 1/64 undersize and then "drill ream" it with the finished size drill bit.
As was said above, the reason a 7/32 bit fit perfectly in the tapped holes (1/4-20) is because that is the root dia. of that thread and that is the proper size drill to use prior to tapping the hole.
Transfer set screws (pointed set screws) are the way to accurately locate the screw holes to the sled. Then drill with a brad point.


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## bubinga (Feb 5, 2011)

I have used drill bits to mark a hole through, another hole hundreds of times 
I didn't suggest that ,I guess because , I think my mind actually functions differently in the house ,than it does in the shop. LOL


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## wildbill001 (Mar 2, 2011)

I've used the Harbor Freight Transfer punch set (paid maybe $5 on sale) A LOT with no problems on both wood and metal. But hey, sounds like the problem was solved and all are happy now….


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## Fuzzy (Jun 25, 2007)

One more simple suggestion …

Chuck up a 1/4"-20 *long* setscrew in your drill and grind/file the exposed end to a point. Clamp the miter bar in place … run the new setscrew into the hole, pointy end first … screw it in until it meets resistance … give it another turn or so, and *tap* it with a hammer. You should have a very accurate center mark which can be drilled to whatever size hole you wish.


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## roundguy (Jan 19, 2011)

Another vote for using a transfer punch. I have a cheap set of them, and seem to use them more than I thought I would.


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