2

I am currently repairing table leg pedestal. Legs are pretty snug with the base with a dowel and I cleaned out all the old glue so it should be a very good glue joint on it's own. However I also wanted to put in a screw through the leg into the pedestal, belt and suspenders kind of thing. It's the red lines in the photo.

enter image description here

I do not know what kind of wood this pedestal is made of but I am reasonably sure it is a hardwood.

This is where all the fun started, I have a decent hammer drill with a 1/8 12 inch bit for predrills. Normally it works well but not here. It was smoking a lot I had to make a few passes in and out and eventually the long bit got stuck in the wood so I had to spend good 15 minutes screwing it out with pliers.

enter image description here

The screws with their little #2 heads kept slipping off and it was virtually impossible to drive in the screw.

enter image description here

Than I had the bright idea to increase the size of the pilot hole. The length of the screw required another aircraft length bit so I purchased a 3/16th which was the next smallest step up. A lot of companies don't even make that gradation, for example the company that makes the 1/8th I have jumps up to 3/8ths as the next step up https://www.amazon.com/gp/product/B001AHSVGM/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1

So I don't know what is the next drill bit size up or if it's available in the length to drill 4 inch holes.

3/16ths I got turned out to be significantly thicker than 2/16th (1/8) and after drill it both 8 and 10 diameter screws would freely slide into the hole. Fail.

At this point I gave up with the reinforcing idea and used a whole bunch of clamps to make sure it was a good glue joint and called it a day.

What was I doing wrong? Is there an approach to reinforce hardwood with longer screws like in this repair?

10
  • 1
    Although I can't quite make out how it/they were intended to go in I think screws are the wrong call here. If the glue joint is done properly here as it's a long grain | long grain joint the bond should be the gold standard — stronger than the wood around it. But if you want to further reinforce, probably a good call because this joint was poorly designed from the outset (there's a reason these traditionally use a sliding dovetail), I would add one or more additional dowels. They offer easier installation and better future-proof the repair, so win-win.
    – Graphus
    May 16 '21 at 6:45
  • "I do not know what kind of wood this pedestal is made of but I am reasonably sure it is a hardwood" If it's American-made it could be birch, or one of the maples. If it's built in Asia your guess is as good as mine! I've had a few things in from China where it looks like they used maple, and I'm presuming they don't import maple from North America, so it's either a Chinese variety (and there are plenty of Acer subspecies) or something that looks very similar.
    – Graphus
    May 16 '21 at 6:50
  • "What was I doing wrong?" Well in drilling you could probably have done with 1, much more frequently withdrawing the bit (twist drills are famous for their ability to pack solid with swarf and once that happens forward advance basically becomes impossible, with stuck or broken bits the likely outcome) 2, a more powerful drill (cordlesses aren't exactly known for their grunt). Then for driving the screw lubricating it first (used to be standard advice but now becoming lost) and again using a more powerful tool (e.g. a brace) to drive it. Those are Robertson screws right? So best choice there.
    – Graphus
    May 16 '21 at 6:57
  • I agree it's definitely a nice flat long to long grain so glue is the way to go. I actually ended up using epoxy because I was a little over concerned that when I sanded off the dried up remains of old wood glue I created a bit of an uneven surface. But from my understanding they are both very strong hold. So about the drilling, is 1/8 a good thickness of predrills for 8 screws? It does work well for pine, it didn't work at all here. May 16 '21 at 7:22
  • 1
    Side comment: your robertson bit is probably old and dulled -- a good quality new bit (and good screws of course) won't pop like that. Your 3/16 drill bit might have been a perfectly good clearance hole, but it sounds like you drilled all 3" of the depth. If you had to rehab this, I'd smear a bamboo skewer (like, food skewer) with glue, push it to the bottom of the drilled hole, let it dry for a while and then re-drill just the clearance hole. If that doesn't grab, redrill with the 1/8" bit and add another skewer. Rinse, repeat. May 16 '21 at 14:50
3

What was I doing wrong?

Well in drilling you could probably have done with:

  • much more frequently withdrawing the bit.
  • A more powerful drill. Cordlesses aren't exactly known for their grunt, and many are not the match of an 'equivalent' corded drill.

Twist drills (and many lip-and-spur/brad-point bits, which are roughly similar beyond the tip shape) are famous for packing solid with wood swarf, and the deeper the hole the more and more likely this becomes because eventually there is no more flute for the waste to travel up.

Once the grooves are packed, or completely filled, further progress becomes nearly impossible and stuck or broken bits can result. Prior to this smoking is a warning sign to look out for, although some of that is just the inevitable shaft rubbing against the inside of the hole1

Then once it came time to inserting the screw:

  • lubricating it first; soap, oil or a fat of some kind, grease, and wax have all be recommended for this by one source or another and all work.
  • Again using a more powerful tool (e.g. a brace) to drive it.

Lubricating screws, especially when being driven in to hardwoods and even more especially with long screws, used to be standard advice but is now becoming lost for various reasons.

While braces may not be really practical for driving large numbers of screws in a production environment for occasional situations they can still be a valuable part of the toolkit. They make exceptional screw-drivers as I briefly described in a previous Answer. You'll probably want to keep at least one brace around, even if only for driving screws, once you've experienced how pleasurably easy2 they make it.

Since you ask about pilot hole sizing in the Comments, regrettably there is no one guideline here. The Internet is lousy with pilot-hole sizing guidelines, some of them reprinted from old shop manuals and the like which would typically have two columns or two separate tables, for hardwoods and softwoods respectively. But unfortunately such tables aren't completely consistent, and perhaps we shouldn't expect this because it's not like all hardwoods and softwoods are the same hardnesses!

So sometimes it's a case of just trying some sizes (assuming you have a range of bits available that are approximately in the right range) and seeing what works best. As a general guideline it's far preferable to drill a slightly undersize hole than one that is even fractionally too large, as an oversize hole leads to a much weaker grip in the second piece of wood.

Where a table is not to hand, the rule of thumb is to match the pilot hole bit to the root diameter of the threads; while you can measure this just eyeballing can be good enough in many cases.

Don't forget clearance holes! If used, the clearance hole should be larger than the pilot (large enough that the threading can't engage at all).

The better fix
There are different philosophies of repair and reinforcement of furniture, and a lot of it is just individual judgement calls. But many pros do their best to avoid screws where they aren't an integral part of the original design, on reason being that over time they have a nasty habit of working loose. Unless they've rusted into place, which is another problem.

Here, you had two quite large long-grain surfaces which potentially make for the ideal glueing situation. So just glueing and clamping could have been sufficient, providing plenty of clamping force could be applied during the glue-up if using a PVA-type glue or foaming polyurethane. Or, as you've done, using epoxy instead if very strong clamping couldn't be arranged and/or the glue surfaces were in any way gappy (because epoxy is a good gap-filler while the previous two adhesives are not).

If further reinforcement were deemed necessary — and given there's no actual joint here, as would have been traditional, there's a strong argument in favour of it — adding one or more additional dowels makes a lot of sense. Dowels have a good assurance of providing a near-permanent solution, certainly outlasting the current owner of the piece all thing being equal.


1 Which I think black-finished bits are more prone to than with other coatings which have lower friction.

2 Just to give an idea of the difference, where I've had a screw become too stiff to comfortably turn with a conventional screwdriver, or just get stuck outright, once I changed over to a brace it would often require no more than fingertip pressure on the sweep handle to finish driving it home.

7
  • 1
    Graphus I literally took notes and will be ordering a ratcheting brace shortly. I am so glad stacks exists and there is people like you to help noobies work through all these issues. There is one dowel in each joint already and it's in great shape. The main issue is that Chinese manufacturers originally covered only around 20% of the workable surface with glue (and it still held for god knows how many years) so I am confident my epoxy fix will be just fine. In the future I am really curious to try again driving longer screws. May 17 '21 at 5:29
  • "The main issue is that Chinese manufacturers originally covered only around 20% of the workable surface with glue" Applying too little glue is really common in commercial furniture! [And not just in Asian-made stuff BTW] The furniture-restoration channels on YT often show how little glue there is in a failed joint.... hence the failure! It's one of the things that has directly led to the fairly widespread perception that dowel joints are weak, when 95%+ of the time it's an issue with fit and/or the amount of glue used. As you say in your case it still held for God knows how long, go glue!
    – Graphus
    May 17 '21 at 7:09
  • Re. a brace, I would highly highly recommend getting a vintage one unless they're just not around in your neck of the woods. In addition to often being v cheap (I've picked up braces that functioned, but needed cosmetic work, for the equivalent of four or five bucks) they're generally better made than modern ones (sometimes much better). Obviously where you are is critical to the availability of secondhand tools, if it would help James Wright (of Wood By Wright on YT) has a page set up to aid people around the world in finding good old tools.
    – Graphus
    May 17 '21 at 7:20
  • Oh that's awesome. I'll look around there is a decent size retired affluent population in my city. I am sure I'll find something if I keep an eye. I did find one in Lee Valley but yea price wise not the cheapest although quality is probably decent given that it's Lee Valley. Amazon..less trust lol. May 19 '21 at 4:57
  • There's another issue you might not have heard about yet with braces, in that old braces almost all have two-jaw chucks, with modern ones having three or four. The modern ones do grip hex and round better but can't use any traditional brace bits, so they then become tied exclusively to modern tooling which is a limitation in the long term. On the other hand most two-jaw chucks grip hex pretty well, unless very worn, which opens up a wealth of bit holding of a modern type..... I have one brace set up exclusively as a driver, with a quick-change hex-bit holder permanently installed :-)
    – Graphus
    May 19 '21 at 6:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.