Left hand drill to remove broken lag

[PT Doc]

Hi all.

I broke a 5/16” lag in an outdoor stair stringer. Posted about it here.

Enlarging 5/16” lag bolt hole to 29/64”

I was removing a 5/16“ lag bolt in a thick, heavy stair stringer for an exterior railing. The bolt broke and I have about 5/8” depth before the broken screw. No chance to hand drill that out. I plan on using a threaded insert above the broken screw and using a hex head machine screw in its...

www.garagejournal.com

I missed a post that suggested using a left hand drill. I realized I have a left hand set of Norseman drills. Only issue is to keep the drill centered on the angled stringer. I have a Big Gator drill guide that has been helpful with other projects but I can’t clamp this in place. I might be able to screw it in place then still have 2 hands on the drill with left hand drill.

What size left hand drill? 3/16”? I kept the broken head and the diameter of the shank at the break is .240. Based on what I can see it looks like a relative nice flat break Perpendicular to the shank. So I’ll try to center lunch, then center drill, thr use left hand drill in reverse. If it doesn’t work then I’ll place a lag next to it like many suggested in the original thread.

Thanks

 

[Shiftless]

Try to drill it out with a left hand drill bit but I wouldn’t be at all surprised it that didn’t get the broken lag screw out. Once you get a nice clean hole, use an EZ out to remove the screw. That seems like too much work when a guy could just put another screw next to that spot and get on with doing something else.

 

[mogandave]

If you can get a center hole in it, can't you just drill it out, plug it and drill a new hole in the same location?

 

[p00p]

LH drill at the center, but not 100% all the way through. LH tap the hole with LH threads for a grade #8 LH threaded hex bolt with the largest diameter shank that is appropriate for the broken hardware. As the LH threaded hex head bolt goes in the LH tapped threaded hole & bottoms out, it should twist out the remains of the initial problem.

 

[BillK]

LH drill is just a waste of time on a lag bolt. They work great on broken machine screws that arent seized in the threads but thats about it. I would just use a regular drill to get a hole in the center and then try an E-Z out but dont be surprised if it doesnt work

 

[PT Doc]

Thanks. I’ll just put another lag next to it. The broken lag is @ bit more than 1/2l below surface of would. I can’t see nothing!

thanks again.

 

[theoldwizard1]

When using a left hand drill bit to remove a broken screw/bolt there are a few step you should follow. You might be able to "get away" with skipping a few if your attempt fails and you have to go to a large hole that might be off center. Seeing as you are trying to remove a lag bolt, I don't think it can be that critical.

Abom79 has a couple of videos on this topic and I am summarizing :

• The surface of the fastener to be drilled needs to be FLAT !
• Using a good, sharp punch, make a mark in the CENTER. Take your time. This is critical !
• Use a center drill on your punch mark.
• Start with a smaller left hand bit and "sneak up" on the proper drill tap size.

 

[wssix99]

The only luck I have had with this situation is to weld another bolt to the broken bit in the wood and then crank it back out.

 

[PT Doc]

UPDATE:

As many guessed I was not able to use a LH drill to remove. The break was not flat and center punching, then drilling and then LH drill was unable to get a purchase.

So I enlarged the hole in the stringer and put a screw next to it. I used a new screw,to,cut the threads and then remove. The threads on the portion that engaged the broken screw like Acme threads. In them installed the railing with a new lag bolt and all Is good.

Thanks for the help to all.

 

[ShuhornGarage]

fyi for next time you have a broken bolt etc
Take short bolts of all sizes, NC & NF thread & put them in a lathe & drill the corresponding ezee-out drill size thru each so now you have an automatic centering device that can be threaded into the hole, then drill the broken stud, then you can tap in the ezee-out & add a bit of squirrel juice in the hole to hopefully lube the treads a bit, hopefullu enjoy a successful removal

 

[nadogail]

I have had very poor luck trying to remove broken bolts with a left handed drill bit. I think the salesman who demonstrated the technique had lots of practice and almost perfect conditions.
There is no easy substitute for skill and practice.

 

[strutaeng]

The YT channels I watch working on the Rust belt vehicles say the left hand drills don't work. I don't live up there, so I would believe them.

For the things like broken manifold bolts and a stripped transmission drain plug, welding a big 'ol 3/4 hex nut has worked for me. I've never tried this on wood though.

 

[mike93lx]

In the future, I'd strongly recommend moving away from lag bolts and use either grk structural screws or fasten master ledgerlock/headlok/timberlok screws. Much higher quality and easier to drive

 

[PassnThru]

I've had luck with a left handed bit in an exhaust manifold situation where the head broke off because of the stresses over the years - not because it was frozen in place with rust. Sure - there was a certain amount of stuck involved but drilling it produces heat which helps after you soak it with penetrant oil. In the right conditions it will come right out. In other conditions if you broke the bolt head off trying to get it out then a drill bit is infinitely more fragile than that head was.

 

[finn]

In the future, I'd strongly recommend moving away from lag bolts and use either grk structural screws or fasten master ledgerlock/headlok/timberlok screws. Much higher quality and easier to drive

Once you start using engineered fasteners like the GRK, you‘ll never use a lag bolt again.