Screw Inserts in Hardwood

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Blog entry by Olaf Gradin posted 12-17-2007 10:26 PM 4459 reads 0 times favorited 1 comment Add to Favorites Watch

I recently posted a forum question and got some good replies on the topic. I thought I’d write my official tactic here with some final thoughts…

(I’ll get a picture posted to demonstrate soon)

The problem I experienced recently was involving the insertion of brass screw inserts into some hard Magnolia lumber. I’m building a simple miter jig for my table saw, and I’m using inserts on the back of the fence to attach to the existing miter gauge. I could only find brass where I was shopping, and I didn’t figure the softer metal would pose any problem to even a dense wood like Magnolia. I was a somewhat incorrect in this assumption. First, I pre-drilled pilot holes smaller than the insert itself. I had thought the wood would give and offer a nice, comfy fit for the insert. I could even get it started because of the “pilot extension” on the insert itself. The hole had to be very close to the same size as the insert in order to seat it properly. I had some bits that were a matter of 32nds and 64ths from the mark, so I eased up to the size very gradually. I attempted to screw the insert in after each drilling to some disappointment. Of course, it got progressively easier as I was putting the insert back into the same hole with grooves already cut each time. As the insert got closer to my intended depth, I would inevitably shear off the top with my screwdriver and have to back it out lest I lose all recoverability.

Some of the options posed to me were out of my reach, so I went with the simpler ones first. I chamfered the the hole (by this time, the hole I had been working on was puckered a bit from the stress) and waxed the threads. I only gave a it few turns and decided that it felt pretty much the same, though there was no more puckering occurring. I then recalled seeing some custom tool in Rockler that I thought was useless at the time. A t-nut inserter. It was just a screwdriver bit with a block in the middle of the bit holder and a machine screw to fit the t-nuts. It got me thinking and I decided to try a similar tactic on the screw insert. I found a short machine screw to drive into the insert all the way without any exposure at the bottom. The machine screw I chose had a socketed head (with Phillip’s inside), which is what I wanted. I then used a socket driver (straight would be better than the traditional, 90° style) to drive it in without the risk of chipping the fragile brass.

The other techniques might have helped here, though I was not limited any longer by the brass’s rigidity and could apply as much force as was necessary to drive the insert all the way home. Worked like a charm! I don’t have one, but it would be nice to find a machine screw with a deeper socketed head for this purpose. Of course, on larger inserts, the screw backing it up would be larger too. At any rate, I know this trick is known well enough because there are screw insert tools available. They’re just a t-handle tool with the appropriate threading on the end and a stop. I didn’t think they were worth anything, but I realize now how wrong I was! The only thing I need to work on now is getting the insert to go in perfectly straight…

-- It takes a viking to raze a village. &mdash Blog'r:

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#1 posted 12-17-2007 10:48 PM

I was faced with a simular delima building a drum sander. I was trying to install 3/8 threaded brass inserts into Oak. Needless to say I learned the hard way that the screw driver was useless (after a little bit the top broke off the brass insert and keeping it straight was a challenge). I ended up taking a 3” 3/8 bolt that had about threads about the first 1 1/2”. I used my grinder and ground off the head, so all I was left with was a 3’ bolt with no head. I then threaded a nut all the way on the threads. I could then thread the brass insert onto the bolt. Using my drill press I inserted the bolt into the chuck and hand turned the chuck while applying downward pressure to start the brass insert driving into my board. When it gets tough to hand turn I use a wrench on the nut to turn the brass insert down in to the board, until it is flush. Once it is flush a quick turn the other way with the wrench and the bolt comes right out leaving a flush threaded insert. – Hopefully that all makes sense. ~ Andy

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