Driving and Counterboring Big Lag Screws
Thoughts on tools and methods for fast setting of long half-inch lag screws in a production setting. October 27, 2009
Question
I have a project coming up that requires me to put .5" x 5" (galvanized) lag screws into 6" thick pt wood. What is the best drill/driver that can do this at fast speeds without burning out? We were 1" paddle bitting, then pre-drilling, then putting in the lag. This is a low pay piece of work. Any suggestions would be greatly appreciated. Hilti, Neumatic are options although I’m not sure which would be the best. Do they make a 1" w/(.25" drill bit) countersink drill bit that produces a flat screw bed, not coned?
Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor M:
You should try a 1/2" electric impact gun. There is lots of power to drive those lags.
From the original questioner:
We have an electric Dewalt impact and it takes about 15 seconds per bolt. I’m looking for 4-5 seconds though. Hilti must have something. Has anyone ever seen a flat countersink with the pilot bit?
From contributor U:
I have a Hilti impact driver and it is a great tool. It also has a high and a low speed. I have never used it to drive the bolts you mention. Five seconds might be pushing it for 5 inch lags.
From contributor K:
W.L. Fuller Inc. has them as well as counter-bores up to 1 1/2". Their type B&X would work. The type B allows for a stop collar. I'm looking at their catalog and they have a 1" with drill sizes 1/4"-1/2". So B74 is 1" counter-bore, 1/4" drill size, 11901000 is a 1" I.D. stop collar. 1/4" is too small for a 1/2" lag pilot hole, isn't it? They also have long length tapered drills.
From contributor A:
I second the motion of an impact driver. The old school corded ones would eat that project for lunch. I would see if you could get a decent 18 volt cordless impact gun. If you buy a kit with a 6 1/2" saw the prices are very reasonable. Panasonic is number one. Also look at Bosch and Makita.
From contributor R:
If Pnuematic is an option, then why not just go with a mechanic's impact gun? They are big, heavy duty, not too expensive and can run those big lags all day long without burning out.
From contributor G:
We used a Miller dowel bit for a similar situation and the bit was perfect.
From the original questioner:
Contributor K has found the step bit I was looking for. I have not called them to confirm but the picture on their website looks perfect. Not sure if the countersink will drill deep enough to flush the lag head even, but it looks close. We used an 8 amp drill and it smoked it pretty fast. Our Dewalt impact driver is just ok. I'm thinking Hilti will have a drill speed driver for this. We even have the long Dewalt with a clutch and smoked that too.
From contributor S:
If you can get away with using "TimberLok" screws you will find that any good drill/driver will set these easily - no pre-drilling required. They are not 1/2" but I would consider using a few extra TimberLoks over driving 1/2' lags. I don't exactly know what you are building so this recommendation may be off base.
One other consideration, and I don't have the specific limitations at my command, is that the new PT formulas require the use of stainless fastenings or specially formulated screw alloys. Galvanized is no longer acceptable for long term use in PT. My understanding is that TimberLoks meet the requirement except for use in salt water applications.
