Drill Press Table Not Square to Bit

dusty · Post by **dusty** » Thu Aug 07, 2014 9:27 am

I have just set up to drill a number of holes through 3" stock. My drill press table is square to the bit, when checked with a Wixey, front to back. When checked left to right, it is off .3° to the bit.

How big of an error is that going to create?

"Wild Bad Bob" · Post by **"Wild Bad Bob"** » Thu Aug 07, 2014 9:35 am

How deep are the holes going to be?

"Wild Bad Bob" · Post by **"Wild Bad Bob"** » Thu Aug 07, 2014 9:41 am

One way to figure it out is, on a piece of something, draw a horizontal line, then a vertical line 90* to the horizontal one. Where they intersect, draw down a line .3* the length of your drilling depth and you will physically see the deviation.

dusty · Post by **dusty** » Thu Aug 07, 2014 9:45 am

rbursek wrote:How deep are the holes going to be?

About 3".

When you did this, what did you get?

"Wild Bad Bob" · Post by **"Wild Bad Bob"** » Thu Aug 07, 2014 10:07 am

I did it at 1* deflection, at 3", it was a 1/32" so .3* would be 1/3rd. of that so about 1/96th of an inch.

BuckeyeDennis · Post by **BuckeyeDennis** » Thu Aug 07, 2014 11:11 am

dusty wrote:I have just set up to drill a number of holes through 3" stock. My drill press table is square to the bit, when checked with a Wixey, front to back. When checked left to right, it is off .3° to the bit.

How big of an error is that going to create?

3" * Sine(0.3) = 0.0157" Almost exactly 1/64".

algale · Post by **algale** » Thu Aug 07, 2014 11:51 am

If the Wixey says it is off by 0.3 degrees it could be anywhere from 0.2 to 0.4 degrees in reality given the Wixey's advertised resolution is 0.1 degrees.

charlese · Post by **charlese** » Thu Aug 07, 2014 11:59 am

Rather than using math (wixey) to adjust the table - mount your sanding disk in the chuck and mark the back. Now using that mark hand turn the disk and adjust the table until it just touches a known thickness block. You have an aluminum block that would be perfect for this.

Do this for all cardinal directions because as you adjust the table for sides you will probably change the fron/back .

You use the mark on the disk because disks (like saw blades) are not perfectly flat.

dusty · Post by **dusty** » Thu Aug 07, 2014 12:35 pm

charlese wrote:Rather than using math (wixey) to adjust the table - mount your sanding disk in the chuck and mark the back. Now using that mark hand turn the disk and adjust the table until it just touches a known thickness block. You have an aluminum block that would be perfect for this.

Do this for all cardinal directions because as you adjust the table for sides you will probably change the fron/back .

You use the mark on the disk because disks (like saw blades) are not perfectly flat.

I sorta did this, Charlese. I gave up trying to predetermine the size of shims that were needed by using the mathematical methods or the Wixey.

Instead, I looked to see what sort of shims I had that would fit on the trunnion bolts. Not a whole lot of selection. I had five that were/are .028" and a fist full that are .003".

I decided to give it a shot using two of the .028" (one for each trunnion bolt).

Now I am .1° off in the opposite direction. That is where it stays until it causes me an assembly problem that could be avoided by getting closer. I doubt that will ever happen.

My brain teaser for the rest of the day will be trying to figure out what I am doing mathematically. This is the sort of real life problem that should be used in high school math classes to teach mathematics in a way that sticks.

In the case of the main table, this all gets fogged up because the shims are placed on the trunnion bolts and one needs to know the offset; in this case the distance from one trunnion to the other.

charlese · Post by **charlese** » Thu Aug 07, 2014 12:54 pm

Yeah; the best (easiest) real world problems are ladders leaning against houses and determining height of trees.