+ Reply to Thread
Results 1 to 8 of 8
  1. #1
    Join Date
    Mar 2009
    Posts
    10

    Default How to bore large holes, plumb

    I need to drill 7/8" holes, perfectly vertical through 6x6 (5.5" depth) pressure treated beams for a retaining wall. (Don't ask - I'm already way too far in to change course!)

    The ideal solution would be a drill press with a 6" throw, which I thought I had access to, but it turns out I haven't found one that can do more than about 4". (I have 6-8 holes in unique positions in each of many beams, so flipping them over to drill through from the back isn't a practical solution.)

    I've built a jig to try the trick of reflecting the bit across two mirrors set at 90 degrees from each other, but it's relatively clumsy to use for holes this size and depth, and is too easy to get off course since it's all controlled by hand anyway.

    Without a drill press this size, I'm likely going to use a heavy duty hand drill. I haven't been able to find a jig to physically hold it plumb when dealing with bits this size, but hope that maybe someone here knows of one, or has some other good trick!

    Thanks,
    Allen

  2. #2
    Join Date
    Aug 2007
    Posts
    6,481

    Default Re: How to bore large holes, plumb

    First, the proper bit will make ALL the difference. Invest in auger bits, these have a screw at their tip to help draw the bit through the wood, which means they travel a little straighter and remove the material MUCH MUCH easier than with a spade style or twist bit.

    As to drilling plumb holes, I'd recommend drilling a size larger than what you need so that you've got a little bit of play to work with. If you're driving a 1/2" rebar through the hole, then a 5/8" bit will be perfect. 5/8" rebar would use a 3/4" bit, and so on. To do all this by hand, use a plumb line and a square with a helper. The helper holds the tools while you drill, then both of you sight the centerlines of the drill to be true with the tool guides.

    You can purchase a drilling jig, possibly from Harbor Freight for drilling such holes OR you can make your own jig. Use a drillpress to bore a hole through a 4x4 (easy task for most drill presses ). Use the hole in the 4x4 to locate and guide the hole being drilled through the larger 6x6. You'll probably want to install some guide chalks so that the 4x automatically centers on the 6x.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  3. #3
    Join Date
    Jan 2010
    Location
    Northern Virginia
    Posts
    975

    Default Re: How to bore large holes, plumb

    Drill as far as the drill press quill will permit, then raise the table of the press with the workpiece in place and resume drilling. Time-consuming, but doable and with a massive workpiece, safe enough.
    Casey
    Remove not the ancient landmark, which your fathers have set.

  4. #4
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,381

    Default Re: How to bore large holes, plumb

    a variation on the above, insert the drill bit up into the chuck as far as possible. Drill down the 4", back up with the drill, loosen the chuck, drop the bit 1.5", tighten up and finish the hole. When done, you have to raise the drill bit back up as high as it will go to remove the piece.

    Or drill the holes all 4" deep, then finish with a hand drill using the 4" deep hole as a guide.

  5. #5
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,361

    Default Re: How to bore large holes, plumb

    Or use a drill press to drill 4" deep. Then use a handheld drill to go the rest of the way -- the 4" hole should be sufficient to guide the bit.

    (What Keith said.)
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  6. #6
    Join Date
    Mar 2009
    Posts
    10

    Smile Re: How to bore large holes, plumb

    Thanks for the ideas! I spent a couple more hours researching, and I think I found another answer that might be a little faster than some of the drill press ideas, and more steady than my hand...

    For $50/day, I can rent a mag drill, which I'd never heard of but is for drilling into metal beams etc. It's basically a compact drill press with an electromagnetic base, so you can position it on a metal surface, flip a switch to lock it into position, and drill up to an 11" deep hole! (Doesn't do wide bits like hole saws, since it was really made for metalwork.)

    I was concerned about rpm, because they are pretty slow, but the one I'm looking at does 600rpm (unloaded), which I've also found quoted as the top speed you should run an auger bit through wood. Nice, I'm hoping that either it has variable speed or that simply adjusting the pressure gets me in the right speed/torque range to make it work in wood. I'll have a buddy man a shop vac to minimize the amount I have to retract the bit to clear the hole.

    I'm going to get a 5" x 24" piece of scrap plate steel that I can clamp to the wooden beam, then position the mag drill and lock it into place. It's a bit heavy to move around, but probably still easier than setting up the loooong table extension I was considering for these 16' beams.

    Aside from the extra effort of moving the plate, it's a nifty portable drill press with a really long stroke, so appears to be just what the doctor ordered!

    I'm going to haul my steel scrap and a test beam section down to the rental store to check it out. I'll post a follow up if it has any complications or doesn't work, but I hope I've found my solution.

    Allen

    PS - Drill presses with 6" or greater stroke start around $900, jump quickly to several thousand, and are big, floor-standing non mobile shop units. It seems like someone could use the 11" stroke-depth rack and pinion mechanism used on this mag drill, add a way to attach a heavy duty drill (probably the most complicated part) instead of providing a metal drill motor and chuck, replace the expensive mag lock base with a flat easily clamped base, and have a pretty handy tool you could get for under a couple of hundred bucks. Or maybe there just aren't that many times people need really true, very deep holes drilled. Would you find a rig like that useful?

  7. #7
    Join Date
    Mar 2009
    Posts
    10

    Default Re: How to bore large holes, plumb

    Quote Originally Posted by A. Spruce View Post
    First, the proper bit will make ALL the difference. Invest in auger bits, these have a screw at their tip to help draw the bit through the wood, which means they travel a little straighter and remove the material MUCH MUCH easier than with a spade style or twist bit.

    As to drilling plumb holes, I'd recommend drilling a size larger than what you need so that you've got a little bit of play to work with. If you're driving a 1/2" rebar through the hole, then a 5/8" bit will be perfect. 5/8" rebar would use a 3/4" bit, and so on. To do all this by hand, use a plumb line and a square with a helper. The helper holds the tools while you drill, then both of you sight the centerlines of the drill to be true with the tool guides.
    Thanks for the info - I had just about determined that the auger bit was the right choice, and your comment cements that decision.

    I've got 3/4" galvanized threaded rod buried in a 2' concrete knee wall that come up 18", and will be drilling 7/8" holes in the PT beams and locking down the first 3 courses to the kneewall with large galvanized washers and nuts. That 1/8" isn't a lot of wiggle room for 16.5" of vertical rod, ergo the need for really plumb holes ;-)

  8. #8
    Join Date
    Aug 2007
    Posts
    6,481

    Default Re: How to bore large holes, plumb

    Sounds like a project. Take some picks and show off your work during the build and the finished results.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •