Hints on drilling straight??

[gtrdude]

Hi Fellas,

I am new to CNC and am knocking together my first rig.

I have a large Baker bench drill. For now I'm trying to set it up so that it drills perfectly straight holes. I can adjust the x angle of the work holder, but the y angle is fixed. It has an el cheapo vice mounted to it. Do you experienced guys have any particular methods that you use to set things as straight as possible?? Or is it just a matter of trial and error?

Also, how do you mount your vice to the work holder? (I know the obvious way is with nuts and bolts but this is a little inconvenient when you want to move it all the time.)

Cheers guys,

Paul

[HuFlungDung]

Well Paul,

Apart from the fact that drilled holes may never be perfectly straight, you can set your machine up with a dial indicator so that it is theoretically possible at least

Mount a dial indicator on a little swing arm held in the spindle chuck. Then, bring it down and swing it around in a circle on the table of your machine. Adjust the table until the scribed circle has a zero out-of-square indication.

Do the same thing within the base of your vise, with the jaws set as far open as possible. If this is out of wack on your prefectly aligned table, then your vise is crap, and needs to be reworked.

If the base of the vise is okay, then check the perpendicularity of the back jaw. Run the dial indicator up the back jaw face with the quill mechanism of your drill. If the back jaw is serrated, then hold something that is reasonable straight in the vise, sticking up where you can get at it with the vise clamped. Actually, this may be the best condition to test under, because the clamping force may distort the vise a bit, anyways.

Drill with sharp tools. Do not drill past a partial cross hole and expect the drill not to wander off. That's about all you can do.

The next step may sometimes be to drill the hole undersize (by 1/64"), and then attempt to straighten it out by redrilling with an endmill. For this, I would recommend that you only drill a shallow pilot hole, because endmills don't reach very deep...maybe 3X diameter. So the endmill should help straighten out the first part of the hole, and if you then switch back to a drill bit that fits the endmilled hole, then you have created a sort of "guide bushing" to drill the remainder of the hole depth with.

[HuFlungDung]

Oh, and I would heartily recommend that you get an XY cross slide table for your drill. It saves you the aggravation of moving your vise around (by unbolting it) for every little adjustment.

[gtrdude]

Thanks so much. This is exactly the kind of information I was looking for!

Paul

[IJ.]

I use Hu's method to set the head on my Mill and it works perfectly!

As with anything adjustable it tends to go out of adjustment from time to time (usually after a crash Doh)

You'd be surprised just how quickly you can get it true again after a little practice!

[DareBee]

"The next step may sometimes be to drill the hole undersize (by 1/64"), and then attempt to straighten it out by redrilling with an endmill. For this, I would recommend that you only drill a shallow pilot hole, because endmills don't reach very deep...maybe 3X diameter. So the endmill should help straighten out the first part of the hole, and if you then switch back to a drill bit that fits the endmilled hole, then you have created a sort of "guide bushing" to drill the remainder of the hole depth with."
1/64 under might be pushin your luck but that method works very well. Also there is nothing more important than a properly sharpened drill bit and using a centredrill to start things off.
By the sounds of your vise setup it is not to high tech. I really like these > http://www.kanttwist.com/c_quick_holddown.html < for quick setup on my drill presses.