Bench Knockdown Hardware - Misaligned Bolt Hole Advice

[Jeff Posten]

I am using the Benchcrafted knockdown hardware on my bench, and ran into some alignment errors during assembly. The auger drifted or deflected a 1/16" (or two) while drilling, and my bolts don't line up with my barrel nuts. It proved challenging to keep a 13" auger bit completely on track.

My question: Should I drill out the current 9/16" hole with a 5/8" bit, to allow for some wiggle room, or, should I plug the holes with a hardwood dowel, and try again? If I go plug route, do you have any advice on how to keep the bit on target? The bolt is 1/2" x 8" long.


Thanks in advance,
Jeff

[Michael Peet]

Hi Jeff, sorry to hear of your troubles.


Should I drill out the current 9/16" hole with a 5/8" bit

This is what I would do. Good luck!

Mike

[Marko Milisavljevic]

About to do this on my bench build and concerned about the same issue... Why not just enlarge the hole where nuts are? it would seem easier and less error prone. They don't need to be in a tight hole, and won't be visible anyway.

[Jeff Posten]

Thanks for the replies. I wasn't sure if increasing the size of the bolt hole would affect the strength of the joint. Obviously, most of the force is lateral, as the bolt and barrel nut pulls the mortise tight, but I wasn't sure how much difference it would make if there was a slight skew to the bolt, or how much "fudge room" I should allow (i.e. bolt is 1/2", I used a 9/16" bit,... should I have used a 5/8" or even 3/4"?)

One other note: why looking through some of Jameel's blog posts during his "apprentice bench build," it looks as though he actually placed his barrel nut further in from the end of the bolt than I did (meaning, some of the threaded portion of the bolt passes through and sticks out the end of the barrel nut). I tried to center the end of the bolt on the center of the barrel nut, which added unneeded complexity, and increased the distance my bolt hole needed to remain accurate.

I also have an e-mail into the Abraham brothers regarding this, and will post their reply on here for other users.

Thanks again for the help,
Jeff

[Steve Rozmiarek]

Jeff, the old rule of thumb for maximum strength of a bolt and nut is that the bolt should screw completely through the nut with at least half the diameter of the bolt protrusion.

[Michael Peet]

Hi Jeff,

I don't think going from 9/16" to 5/8" should significantly reduce the strength of the joint. I can't remember which one of those I used, but I think it was the latter.

Probably the more threads that are engaged within the barrel nut, the better. I think I tried to arrange mine so the bolt just peeked out the far end of the nut. You could always counter bore the wood at the other end of the bolt end to give you a little more depth in the barrel nut.

Mike

[Jessica Pierce-LaRose]

Are you talking about enlarging the hole the barrel nut sits in, or enlarging the hole the bolt passes through? I can't wrap my head around whether one is better than the other. . .

Another possible option, depending on how far along you are, and whether it screws up the rest of the joinery; could you simply flip the legs around and try again? I'm not even sure I'm correctly imagining how these things go together . . .

[Jeff Posten]

Mike, I was planning on counterboring to bury the bolt head anyway, so I'll just make it a bit deeper to increase the amount of thread in the barrel nut. I will make it deep enough so the bolt passes completely through, with a bit coming out the other side.

Joshua, I was talking about increasing the diameter of the hole which the bolt feeds through, and not the hole which the barrel nut sits in. Also, unfortunately, I'm pretty far along and can't flip the legs. I already have the end assemblies all glued up.

Thanks again for all the help,
Jeff

[Winton Applegate]

To keep bit on track :

Sharpen so both edges (if it has two cutting edges) cut when intersecting a flat perpendicular surface. Meaning be sure one edge isn't higher than the other and that both are sharp.
Lube the bit with candle wax repeatedly.
Drill through a thick block of wood with fine or little grain square to the surface you are going to put against the bench component.
Clamp the block in place and use the block as a guide to guide the bit.

[Winton Applegate]

Not sure about the threads past the nut rule. I have never run across that one. I would think it is so that if the structure comes loose it takes longer for the nut to fall off that way.
Here is a counter bored nut on my planing beam. I machined everything so they all came out flushish and look like this. For a wooden bench I am positive there is enough engagement in a large bolt like this. Usually five threads is a good rule of thumb.


http://i801.photobucket.com/albums/yy298/noydb1/IMG_2561_zps2dbe196f.jpg (http://s801.photobucket.com/user/noydb1/media/IMG_2561_zps2dbe196f.jpg.html)

[Jeff Posten]

Just to close the loop:

Jameel (Benchcrafted) said that an oversized hole has no impact on strength. I ended up drilling my initial 9/16" hole out with a 5/8" auger, which solved my alignment inaccuracies.

I made more errors than I'm proud of, on what I thought would be a simple procedure. Some lessons learned:

1. I would have drawn all my layout lines longer than I thought I needed.
2. Bored my barrel nut hole first, after making sure its center line extended far enough for bolt hole alignment (see above).
3. Counterbored my washer/bolt head prior to drilling for the bolt. I ended up being able to fix this thanks to a drill press, but I could have eliminated this by just thinking through things. It's impossible to use a counterbore bit when there isn't anything to center the bit on... forehead slap!
4. Used a larger (5/8") bit to start, which would have made alignment tolerances slightly less critical.
5. I also would have drilled through the leg, with the base assembled and clamped, to the point where it left a mark on my stretcher. Then, I would have disassembled the base and finished drilling the rest of the way into the stretcher. IMO, my skills weren't sufficient to keep a large (9/16" x 13") aggressive bit* completely on track over 8+ inches. And breaking the hole down into shorter sections limits bit drift/deflection (ash is hard), while also reducing the effect distance has on magnifying inaccuracies.

Hopefully my errors will be of help to others

Jeff

*all 9/16" holes were done with a brace, 5/8" "correction" was w/ cordless