Notice: Complete rewrite and how-to video in progress. Scheduled for February 2018 completion.
The need to remove a broken screw or lag bolt can result from a faulty piece of hardware and / or hardware fatigue from too much resistance.
The range of difficulty varies, there is no one straightforward approach, but more a list of processes to try, hoping one or more works successfully.
Note: Extreme hardwood, hardware lodged in a knot of wood, or sub-par hardware can alter the effectiveness of any extraction.
Option # 1 – Leave It
There may be no need to remove a broken screw or lag bolt if they pose no issue of adding new hardware near the damaged piece. If there is a very small exposed shank you can use a nipper(cutting plier) and/or grinder and file to make flush.
Note: Cutting pliers come in all kind of styles to best suite various goals. What works best will depend on the job and hardware diameter. Manufacturers like Channel Lock or Knipex have detailed information about each product use.
Option # 2 – Grab and Reverse Out
Locking Pliers – You may have the good fortune of the shank being exposed to the point where you can latch on with a locking pliers and turn the screw or bolt out. For this type of work a Knipex straight jaw or similar would work best.
Drill Chuck – You’ll need more shank exposure than a locking pliers. Lock a drill chuck on the protruding shank » set drill to reverse » remove. This process can also be used when other extraction methods eventually expose enough of the shank.
Option # 3 – Screw & Bolt Extractors
The Alden line of screw and bolt extractors can work very well on many broken screws and lag bolts, but if not, a Spiral or Studout™ style like Norseman, or commonly found Irwin (Hanson) extractors can pick up the slack.
Q) How do the Alden line of extractors work?
A) The packaging and information shown on Alden’s website is self-explanatory. (i) One end completely drills, or helps drill a proper hole after using a separate drill bit for the extraction end. (ii) Flip the tool around, and the extractor bites into the broken hardware for removal.
- Contrary to what Alden’s products mention about, “not needing” to use a drill. I find a high quality 135° drill speeds up the process, or is definitely needed in many cases, especially for multiple uses on hardened metal from the actual breaking action of the screw or bolt.
- Left-hand drills can be helpful in trying to extract the hardware when drilling, as the are trying to unscrew the hardware, but they can also be uncommon locally. Using a standard drill for creating an extractor hole is fine.
- A center punch (Dasco) may come in handy and does help if you have walking issues with your brand of drills or Alden extractor. Be careful the punch doesn’t jump off the broken hardware when struck and damage the surrounding area.
Extractor Size & Screw Shank Sizing (not including thread diameter)
#6 = 2.5mm | #7 & 8 = 3mm | #9 = 3.5mm | #10 = 4mm | #12 = 4.5mm | #14 = 5mm
Broken Wood Screw Tests Performed
A #6 (2.5mm shank) wood screw and larger can be treated as a relative bolt size. A #6 screw is the smallest shank size you can use an extractor on and be successful. Even at this size you chance the screw shank wall blowing out with a spiral extractor and losing grip.
- #8 x 1″ – (i) Alden micro #1, safely and easily removed screw.
- #8 x 2.5″ – (i) Norseman EX-1 spiral extractor used with success. (ii) Alden micro snapped quickly under the stress. Too small a diameter tool for the resistance subjected when removing. In Alden’s defense, their site does mention for use with screws up to 1.4″ in length.
- #9 x 3″ – (i) Norseman EX-1 spiral extractor used with success.
- #14 (5mm) x 4″ – (i) Alden #1 ProGrabit, safely and easily removed screw.
Broken Wood Lag Tests Performed
When extracting larger bolts and wanting to use a keyless chuck drill the hex shank of the Alden extractors provided better grip in the chuck than spiral extractors with a round shank, which would slip on longer and more resistive bolts. Considering we had success with Alden, we continued to use them on all the lag bolt tests.
- 1/4″ x 3.5, 4.5, 5.5, & 6″ (pine and treated lumber) – (i) Alden #2 ProGrabit safely and easily removed screw.
- 5/16″ x 2″ – (i) Alden #3 ProGrabit safely and easily removed screw.
- 3/8″ x 1.5, 2, & 2.5″ – (i) Alden #4 ProGrabit safely and easily removed screw.
Option # 4 – Wood Boring Extractors
Other forms of extractors that bore around screws can be found at Rockler and Woodcraft. In my experience they can work for very small and short screws that fall under the light duty title, but not more aggressive framing type of hardware. These type of wood extractors are only suitable up to 2″ deep.
In order to be successful you have to be perfectly perpendicular with the screw, use extreme caution, and have a little luck on your side. Any contact with the screw while boring and the extractors break very easily.
Option # 5 – Wood Plug Cutters, Countersinks, & Counterbores
If you want to get creative there are few tools that can help gain access to broken hardware below the surface. The downside is the difficulty in repairing the hole created.
These tools work similar to a wood-boring extractor, but can create a bigger hole, although you also have a more durable tool. Any of the tools will cleanly bore a hole around the hardware so you can either latch on with a drill chuck, locking pliers, or at least have a clearer view to drill into the hardware, and use a screw extractor.
- The smallest plug cutter is a 1/4″ I.D. x 1/2″ O.D.
- Can create up to a .5″ deep hole.
- Built in shank for easy drill attachment
- Tapered or straight design will depend on if you plan to fill the remaining hole, and with what.
- Easier to find at any home improvement store.
- Diameters down to 1/4″, to create less repair work.
- Countersinks are designed to attach to a matched tapered drill bit, and the drill bit shank attaches to the drill, but we don’t want the drill bit present for this type of work. We only need the cutting abilities of the countersink, so a makeshift shank will need to be made in order to connect to a power drill. One can match and cut a section of bolt shank to the countersink I.D. size (preferably the part that is not threaded) as a safe and secure shank. This way there is no drill bit protruding into the work area.
- Works similar to a countersink, but creates a flat faced hole instead of a taper.
- Once the hole is created and hardware is removed you will be left with a hole that can be filled with a wood dowel.
- Plug cutters are designed for this specific type of work to make custom wood plugs from matching material.