Horizontal Boring: Getting the holes centered in the edges of boards

algale · Post by **algale** » Sat May 07, 2011 8:05 pm

Okay, I'm going to be using my Mark V in horizontal boring mode to drill dowel holes for edge joining some pieces of 3/4 inch ply for a project. So far I've been experimenting with some scraps of the same boards. I try to mark the middle of the edge and adjust the the table height until it seems like the drill bit will hit the mark but it has been a hit or miss (mostly miss) proposition with the boards ending up about 1/32 to 1/64 offset when I put the dowels in. Anybody have any tricks or advice for getting the hole bored in the exact center of the edge of the board?

Thanks,

Alan

JPG · Post by **JPG** » Sat May 07, 2011 8:27 pm

algale wrote:Okay, I'm going to be using my Mark V in horizontal boring mode to drill dowel holes for edge joining some pieces of 3/4 inch ply for a project. So far I've been experimenting with some scraps of the same boards. I try to mark the middle of the edge and adjust the the table height until it seems like the drill bit will hit the mark but it has been a hit or miss (mostly miss) proposition with the boards ending up about 1/32 to 1/64 offset when I put the dowels in. Anybody have any tricks or advice for getting the hole bored in the exact center of the edge of the board?

Thanks,

Alan

Exact centering is not required. Exactly the same for all boards is. Care must be taken to ensure the board is flat against the table. Also make sure the intended 'top' is always facing up(or always down).

Bit wander is another thing that can cause inconsistent hole location.

I prefer using a router bit for that operation. Flat face!

This is not easy with plywood!

algale · Post by **algale** » Sat May 07, 2011 8:42 pm

Thanks. It makes sense that exact centering isn't important as long as one consistently references off the same surface. I will experiment some more and report back.

damagi · Post by **damagi** » Sat May 07, 2011 8:48 pm

A few things here:

1) if you want better centering, you should make sure you are using a brad point bit so you can make sure that you hit your line more accurately.
2) consider using a marking guage rather than pencil
3) make sure you always drill with the same side up and you don't need to worry about 1 & 2 as much. That's assming your two boards are the same thickness. doing so means that in relation to each other they are both off center the same ammount.

algale · Post by **algale** » Sat May 07, 2011 8:53 pm

Great tips, thanks.

8iowa · Post by **8iowa** » Sat May 07, 2011 9:07 pm

You might consider geting the adjustable stop collar (555937). This accessory enables you to lower the table just a few thousandths at a time.

michaeltoc · Post by **michaeltoc** » Sun May 08, 2011 7:56 am

The biggest problem with horizontal boring is table flex. When you press down on the board the table will flex a little bit. Press a little harder or softer on the next piece, and your holes are not lined up. It doesn't take much of a difference in pressure to be off by 1/32nd.

There is a Sawdust Session that explains the problem and provides a solution if you have a 510/520. If you have a 500, then use a table support leg, or a piece of 2x4.

algale · Post by **algale** » Sun May 08, 2011 9:02 am

Great point about table flex. I have a used 520; I'll check out the Sawdust sessions.

algale · Post by **algale** » Sun May 08, 2011 1:13 pm

Well, after all the helpful comments, I decided to see if stabilizing the main table of my 520 by putting an extension table in the tail stock and connecting it via the extension tubes would help. I have to say that it does seem to have made a difference as the sheets now line up without any noticeable offset. Thanks everybody. Now, if there was only an easy method for making sure the holes in the mating pieces line up horizontally......

beeg · Post by **beeg** » Sun May 08, 2011 1:19 pm

You are drawing a line across both the boards? On the spot where ya want the dowels to go.