# Boring Into Edge of Birch Plywood



## jbeuckm (Nov 2, 2011)

I need to bore a 3/8" hole a foot or more into the edge of 3/4" birch plywood. My current idea is to build a horizontal mount for an air drill (it has a round cylinder body for mounting) that can be solidly mounted above a mitre slot. Then I build a section of plywood that slides in the same mitre slot toward the drill. The sliding section has a 2" hardwood guide fence along the edge facing the drill. I first use a regular sized bit to drill a support hole through the fence. Then I clamp my workpiece onto the sliding section up against the fence and chuck a long boring bit. The hardwood guide should keep the bit level while I move the piece into the bit.

Does this seem workable and that it will produce a straight hole? What type of boring bit should I use?

Thanks!
Joe


----------



## mrg (Mar 10, 2010)

Why not use a fostner bit chucked in your drill and a square. To drill a hole in 3/4 ply straight should not be that big of a challenge. I could see going to extremes for drilling through a 4×4 because you wont go staraight but through 3/4 you should be able to drill a straight hole.


----------



## DS (Oct 10, 2011)

You could use a self-centering dowell jig to center and align your bit to the edge of your work. 
Use a longer drill bit through the jig to get your depth.


----------



## jbeuckm (Nov 2, 2011)

Thanks for the idea, DS251. I forgot to mention that I need to drill into a curved edge so there is not a good place to attach the dowel jig that would keep it steady. Also, I wonder if the short length of guide on the dowel jig would be effective enough the keep the hole straight for a foot or more? What kind of long boring bit is best for this?


----------



## HerbC (Jul 28, 2010)

mrg,

I think you misunderstood the task. Joe wants to bore into the edge of the plywood, centering the 3/8 bit/hole in the 3/4 thickness of the plywood and wants to drill a hole that is 12 inches deep into the plywood.

I don't know any better way to try it than you've described. I'd have to do several successful practice runs on scrap before I'd try it on the actual project…

Good Luck!

Be Careful!

Herb


----------



## jbeuckm (Nov 2, 2011)

You explained it better than I did, Herb.

After a bit of reading I think that a regular twist bit is the way to go for the long one. When the jig is perfectly parallel to the mitre slot, I'll drill a smaller hole with a normal twist bit before beginning the larger hole.


----------



## mrg (Mar 10, 2010)

I totally misunderstood. Now it make sense why you would do it the way you explained.


----------



## Loren (May 30, 2008)

I believe you are tilting at windmills attempting this cut with a drill.

If the work can tolerate it, it would be simpler and a faster set up
to excavate a stopped dado with a 3/8" core box bit and plug the 
hole with a filler strip milled to concave on one face with the same
bit.

No 3/8" drill I am familiar with will resist deflection in such a deep 
cut. The glue lines are harder than the wood and the drill will start
to deflect after after perhaps 4 inches even with a perfectly straight
bushing guiding it. By the time your cut is 8" deep I'd expect to see
the bit blow-out through one side or the other, if not before.

Remember you only have 3/16" of room to play with on each face. 
At 12" long you can only tolerate about 1/64" of deflection towards
a face of the work per inch. Once a bit starts to deflect, it continues
deflecting in the same direction as the cut goes deeper.


----------



## muleskinner (Sep 24, 2011)

I might try it if I could find a 1/8 or 3/32 bit long enough to act as a pilot. If like Loren says the glue lines are harder, if you could pilot in one ply the glue might act to counteract the deflection especially if your drilling with the grain of the ply. Once you had your pilot hole you should be on the straight and narrow. Damned if I know where you'd find a 15 inch 3/32 bit though.


----------

