Bits for Boring Holes in Laminate

Cabinetmakers discuss choosing a bit to drill lock holes in laminate doors. July 31, 2009

I have to bore a lot of 5/8" diameter holes in plastic laminated doors for locks. What would be the best bit to use considering that the doors are already hung and how quickly laminated plastic dulls bits (especially Forstener or brad-point-type bits with a non-angled cutter)? I use a 1 3/8" carbide tipped Forstener bit in my hinge boring rig, but I cannot seem to find one for 5/8" holes. If I use a regular steel twist bit, I'm sure I'll get ragged holes.

Forum Responses
(Cabinetmaking Forum)
From contributor C:
We have been using Forstner bits from the local hardware store. We made jigs from hickory that can be clamped on with welders vice grips and we just plow away. We get about 40 doors average per laminated doors. We have used the black 90 degree angle lock strike with great success and there is a less obtrusive nylon or plastic extrusion that works well, be we seem to hit them in a b/o situation.

From contributor V:
I always used spade bits for that purpose. Spades are easy to sharpen too. You can grind them so that the outer cutting circle hits first. Itís best with laminate to cut until the circle of laminate comes free and begins to spin. Stop boring and remove the loose laminate circle. Then continue boring until the point of the bit punches through the back of the door/panel. Then bore from the other face and repeat. I usually finish the bore from the face side just for assurance.

From contributor U:
I don't have a good alternative to brad point, or hinge boring bits but I do know that they are both available with carbide tips in either 5/8" or 16mm.

From contributor S:
Contributor V has the right idea. The outside points cut through the laminate so they are the first to get dull. You can touch those points up with a file every few doors. The middle cutter stays sharp longer as it is usually mostly just cutting the substrate.

From contributor V:
Honestly, you are going to get a lot of lock holes bored before needing to sharpen a spade bit. I have never hand filed a spade bit but I suppose I would if I was away from my shop and grinder. I canít say enough good about the humble high speed steel spade bit. Itís so easy and fast to sharpen. You can do no wrong as long as you don't grind the outer edge and change the diameter (I do this on purpose to create special sizes and step drills). It seems a waste to me to use an expensive carbide bit that is designed to leave a flat bottomed hole when you are boring all the way through.

The design of spade bits has changed recently and I suspect the reason is to make them appear more difficult to self sharpen. Some have side spurs and require thin grinding wheels to stay with the factory design while sharpening. So when you select them, try to find a set or single bit that omits the fancy spurs on the outside edge.

Also, if you ever find a used set that doesn't have that little hole drilled out of the center grab it. I may be wrong but I think they drill those holes to prevent you from being able to sharpen any further therefore needing to buy more bits. 5/8" diameter lock holes - interesting, all the cabinet door locks I have ever used need a 3/4" bore.

From contributor C:
The short point on some of these bits are so you don't poke through the facing material in cabinet doors. The brad points also hold the drill concentric. The side spurs on drills size the hole. The cliplifters pull the material up to the gullet, gash or twist. The little hole below the cutting edge on the spade bits is for bellhangers (pulling wire).

From the original questioner:
I never thought about using a spade bit, but what you say makes sense. I think I'll grind one so that it has a spur on the outside edge to score the plastic laminate and allow me to remove that little circle quickly.

Of course, being an old guy, I know how to grind tool steel. When I was apprenticed, grinding and sharpening was taught as part of the trade. For instance, we got shaper steel in bars, cut it into short lengths, and ground our profiles for molding runs. There was no "outsourcing".

I think I made a mistake here in initially asking if a Forstner bit was good for my use. What I meant was a multi-spur bit, which is actually different from a Forstner. Multi-spur bits have teeth around the circumference, while Forstners don't. I think that nowadays the term Forstner is often used for both kinds of bits.

From contributor V:
I know what you mean about the interchangeable nomenclature on that type of bit. At any rate, they can be a problem with laminate anyway because they can jam the laminate cuttings back into the face edge of the bore and cause problems. I am still grinding all my molding knives by hand and eye from corrugated high speed steel bar stock to this day. Before you go through the trouble of grinding actual "spurs" on your spade bit, try just grinding a steep angle from the outside cutting diameter (5/8") to the centering spur (brad point).

That type of grind will still behave like a spur and free a circle of laminate without having to have an actual spur. The new bits I see on the shelves have spurs factory made but this makes them require special thickness grinding wheels to sharpen them with. I suppose a guy could just waste the spurs off on the wheel and turn them into a traditional style spade bit once they become dull.