Drilling Straight is Hard to Do

I've been obsessed today trying to figure out why I can't drill a straight hole into the end of a one inch dowel.  This isn't the first time I've noticed this problem.  I've been working on wooden track risers and I've been able to drill straight into the face grain of the base and tops, but when it comes to the columns, whether it's dowel or 2" square stock, I just can't drill a straight hole in the end grain.

Checking the Miter Saw

My first thought was that maybe I'm just not getting a parallel cut on my miter saw.  So I checked whether the blade was square to the fence and the table, it was, but I noticed that there was a slight step down from the table to the sacrificial insert.

I removed the insert so I could shim back up to the level of the table. Since it was only low by a few thousands I  traced the insert on some card stock and cut out a shim that I would use under the insert to bring it back up to the level of the table.

I tested the insert with the card stock shim and it seemed to bring it back to even with the table, but when I tightened it down I found that for some reason the insert actually was higher than the table.  What happened was when I tightened the screws on the outside of the insert, it was actually twisting the middle of the insert up. I found that if I just barely tightened the screws past the point they bottomed out, the insert didn't flex.  Of course now I have to watch to make sure these screws don't wiggle loose after a while.

The take away lesson from this is that materials change their properties after they've been cut.  It can be from from internal stresses, external stresses, or both.  In this case, since it was hard board, I assumed the material was stable, but I didn't take into account the external stress of the screws.  I'd never noticed it before because, the only time I ever messed with the inserts was to change the old insert for a fresh one -- yes they do wear out, if you're not careful how you bring the handle down you can slightly move the blade to one side or the other with eventually widens the kerf to the point where it's no longer useful for lining up cuts.

Drill Press Table: The Next Candidate

When I built my drill press table, I designed it with a sacrificial insert under the bit.  That way once it got all chewed up I'd be able to easily replace it.  What I didn't count on was how hard it would be to get the insert to be flush with the table.  It seems not all 3/4" MDF is the same thickness.  The MDF I used for the table seems to be the thinnest in my shop so I have to shave a few thousands of an inch off the insert to get it to fit flush.

This time when I sanded down the insert I noticed something, the insert was flush in the back and high in the front.  I flipped it around and it was still high in the front and flush in the back.  Since I had checked and double checked to make sure there was no debris in the home, the table itself must be the problem.

I made the table by screwing two pieces of 3/4" MDF together.  My current theory as to why the insert isn't sitting flush is because there are no screws holding the two pieces together anywhere near the metal table that's actually attached to the drill press.  I'm guessing the either I warped the table in the process of screwing the two pieces together, or they have moved since I built it.  I'm going to try to put 2 to 3 screws close each edge of the insert hole to try and draw the pieces together and see if that doesn't fix the problem.  Unfortunately I don't have any of the right sized screws on hand right now.

My drill press table doesn't seem to be the problem, or at least the entire problem.  I tried drill the dowel using the metal table and I still drilled a crooked hole.  Of course I checked the table and it is perpendicular to the quill.

The V-Block: The Last Candidate


From the first hole I drilled in the dowel, I used a V-Block to hold the dowel upright.  I thought the V-block would give me a much larger surface area than the dowel so it wouldn't rock.  When I clamp the dowel in the V-block, I make the bottom of the dowel flush with the V-block. Maybe the dowel is slipping in the clamp allowing the V-block to rock.  Another thought I had was that the bit was just following the grain.

----------

I ran out of time in my shop and I've run out of ideas of things to check.  I may try using two V-blocks clamped together for more stability, or I may try clamping the dowel and the V-block in a drill press vice.  I'll eventually get to the bottom of this!

Tools: drill press, miter saw

Tags: end grain

Materials: dowel, hard board

Comments

Vic's picture

I have the same problem drilling through 1/2" dia. x 3/4" dowels for my spiral staircases pictured on my website.  I have batches of 400 of them to drill out the 1/4" hole.  I have tried the drill press and the lathe with no real difference so i use the drill press and a cross vice with a v groove jaw.  I'll just share that slowing down the speed of the feed and using brad point drill bits helped a little.  I also drill through about half way and turn the dowel around and drill the other side.  I also center punch both sides.  This is a lot of extra steps for a quantity like this but it does seem to help.  Results are still nor perfect but not too bad either.  I think you are right about the drill following the grain...

If I discover anything better I'll keep you posted

Good luck

Vic