What Drill Bit for This Job?

[Jon Farley]

On an upcoming project I will be required to drill a hole right down through the center of a couple of 18-3/4" long oak posts. I plan to drill from both ends and (hopefully) meet in the middle. the holes will be 1/2" or 9/16". I plan to do it on the drill press.

Anyway, was wondering what the best bit for this application (drilling through 9 inches of end grain oak) would be. My first inclination was an auger-type bit, but I've come upon some research that flatly says "never use an auger-type bit in a drill press!" Why is this? And again, what bit should I use? Spade? Regular twist bit?

[tod evans]

jon, if possible cut a saw kerf down the center 1/8x1/8 then glue the blank back together. the kerf will guide the drill bit and keep it from following the grain....02 tod

[Steve Clardy]

Auger bits are self feeding. Thats why they are a no-no on drill presses.

[Jon Farley]

jon, if possible cut a saw kerf down the center 1/8x1/8 then glue the blank back together. the kerf will guide the drill bit and keep it from following the grain....02 tod

Tod, this is a good idea, but it will be too late, as the ornate pillar-type posts I will be drilling will have already been turned on a lathe.

Okay, so the auger bit is a no-go. How about spade vs. regular bit?

[Barry O'Mahony]

What's the hole for? Running wires, or something else? If it's for wires, it doesn't matter that things meet precisely in the middle. In that case, using twist drills from either side should be Ok.

[PeterTorresani]

I believe the preferred option is to use a "centerless" holder in the tail stock on the lathe and a long drill bit. My high school shop teacher called them bell hanger bits because the phone company guys used tehm all the time (useless aside). This method (I've heard) ensures you stay on center when swapping end for end.

[Dave Richards]

Where's Bob Smalser when you need him? :D

I'd guess he would say to use a barefoot auger. A bell hanger's bit is likely to wander as is a standard auger bit with a pilot. You could get a barefoot auger from Jamestown Distributors, I believe.

Edited to add the barefoot auger would be the boatbuilder's choice for boring long holes for things like rudder shafts and shaft logs.

[Andy Hoyt]

Jon - Put it back on the lathe held with a scrollchuck. Mount a plain old twist bit of the right size and at least half the length of the column in another chuck on your tailstock. Drill, reverse stock end for end, drill. I've done 32" with this method. I don't suggest a pilot hole as the thinner bit will deflect. A decent 1/2" or 9/16" bit should not deflect - or not enough for it to matter.

[Jon Farley]

I guess I should have mentioned that I don't actually have a lathe....yet:rolleyes: and that I am having a local Amishman turn the posts that I will be using. I suppose I could talk to him about the lathe methods.

The reason I need to have these holes is to run threaded rods which will then be used to bolt the posts to both the base and top of the two-legged altar I am making. While the holes don't have to be perfect for this, I don't want too much slop in them either. By the way, the posts are 4-1/4" in diameter at the bottom and 3-3/4" at the top.

[Don Baer]

Jon,
Does the threaded rod have to go all the way through the post's. If it were me I just drill the hole a little snug and get a metal tap the size of the threaded rod and thread the hole for the rod sise. I'd think a few inches of threaded rod would be enough for what you want to do.

I do this all of the time with drawer pulls when they are made of wood and it works great. I don't know why it would work for your use.

Here is a thread where this technique is discussed.
http://www.sawmillcreek.org/showthread.php?t=28466

[Dave Richards]

You could also use hanger bolts for this. A lag screw thread on one end and machine screw on the other.
http://img.alibaba.com/photo/50448356/Hanger_Bolt.jpg

[Barry O'Mahony]

I'm a big believer threaded holes in wood (I started the other thread), but I'm concerned about them holding in end grain. A threaded insert might be the way to go.

Too bad you don't have a lathe; I understand that's the recommended way to do deep boring. For metal, there are special drills with oil journals that allow you to deliver oil at high pressure directly to the bottom of the hole.

If you can turn the DP table 90 degrees (vertical) and carefully bolt the piece to it, you should be OK with that method. At 9" deep for a 9/16" drill, it should not deflect too much.

[Dave Richards]

Just bore the hole a little oversized for either the hanger bolt or a couple of inches of threaded rod, fill the hole with epoxy and thread in the metal. That'll be plenty stong even in end grain.

[Mike Cutler]

Jon - Put it back on the lathe held with a scrollchuck. Mount a plain old twist bit of the right size and at least half the length of the column in another chuck on your tailstock. Drill, reverse stock end for end, drill. I've done 32" with this method. I don't suggest a pilot hole as the thinner bit will deflect. A decent 1/2" or 9/16" bit should not deflect - or not enough for it to matter.

Andy's on the right track. the only thought I would add is that I have seen a lathe tool that is for boring holes through lamps. It looks like a really long fireplace poker with a bit on it, and it bores from the tail piece to the head.
I think you need to find a friend with a lathe to really do this properly

[Andy Hoyt]

That's a Lamp Auger Mike. And yes, they're run into the workpiece after passing through the tailstock (assuming it's hollow, and some aren't); but the issue I have with them is them they're typically too thin for this fellow's specs and inexpensive; hence you'll likely get deflection. And I've never seen a lamp auger long enough to get through a 19" piece and the tailstock.

[Andy Hoyt]

....will have already been turned on a lathe.... This factoid escaped my notice earlier. Since nothing yet has been turned, let your friend do the drilling. If this was my project, I'd drill the hole first (on the lathe as described earlier) and use the resultant hole for proper centering and alignment of the stock for all subsequent turning.

This is now a complete no brainer.

[Jon Farley]

Andy, you make a good point. I never gave much thought to doing the hole prior to the turning, but since I have no experience at a lathe, I guess I didn't really think the whole process through with the right perspective. Unfortunately, I "put in my order" for these turnings yesterday and the guy said he'll have them done real soon, so he might have already started them. I can't just give him a call, as he is Amish but if I can find the time tomorrow I'll try to drive out to see him.

Someone asked why I plan to use threaded rods the whole length, rather than the threaded lag bolts. This project is a two-legged alter that is going to be quite heavy. The key to the stability of the whole structure is going to be these two posts. Though it might seem like a bit of overkill to use the long threaded rods, I'd like to use them "just to be sure" and also for my own peace of mind.

I'll try to post a pic tomorrow of my scale model of the project.