Shooting 3/4" studs

By swnorris (****)

Date 01-12-2006 16:31

The galvanized coating on a G90 sheet of decking is three times thicker than the galvanized coating on a sheet of G30 decking. The 30 indicates 3/10 of an oz. of galvanized coating per square foot of surface area decking. The galvanized thickness on a G30 is about .25 mil, while G90 is about .75 on any given surface. I don't know what your decking gage thickness is for your application, but it's pretty much a rule of thumb to add 300 to 400 more amps when welding thru deck studs, along with increased weld time and increased plunge times. I'd say that you need to have around 1/4" to 3/8" more stickout, and just play around with the timer. Watch the stickout, because it can cause the stud end to be melted away as it penetrates the decking. Then, there's nothing left at the end of the stud to fuse it to the beam flange. Also, note that some studs have a sort of tapered base and some have a blunt base. If your studs have the tapered base, that would contribute to this problem because the tapered stud base melts away faster than the blunt stud base. Stickout should be increased more if the stud ends are tapered. I will assume that they're not trying to shoot studs through galvanized decking onto galvanized flanges, which further complicates things.

By jwright650 (*****)

Date 01-13-2006 18:45

Scott,
No coatings of any type on the top flange(thank goodness). [edit: the detailer had mistakenly left off any no paint top flange notes, but our people here caught it in time to fix the shop drawings.] I gave them the parameters that you sent me, and I looked at out machine here which had a sticker on it with the same info written on it. That should give them somewhere to start and they can tune it from there. I haven't heard from them today, so I'm guessing that no news is good news.

Chet,
I don't know for sure whether the guy on the job has the manual for his machine or not. I've been to the stud mfg's website but that was not any help in it's self, but I did get their 800# and will call if the guys at the job call back needed more info. They wouldn't have been in this pickle if they were testing the first few studs like they should. After 3000 are shot and failing, well...., I feel that is a little late to be calling me for help. I'd be a little more sympathetic to their situation if they had only shot a few and they had tested them and found that they had a problem early on.
John Wright

By CHGuilford (****)

Date 01-13-2006 18:04

John,
Usually the gun manufacturer has information in their manuals. I would see if you can find it there. If not, we have fouinf that the stud manufacturers have good info as well.
Chet