Locating Mounting Holes

[tomp]

Getting ready to replace the (8) 8' double-tube fluorescent fixtures in the shop with LED's as I'm tired of fighting flickering or dead tubes (and it could possibly be corrosion on the contacts after hanging on the shop ceiling for 30 years). Because of the cost, and the ability to hang them without needing help as I did for the 8 footers, I'm going to replace each 8' fixture with (2) 4 footers, installed end to end. The fixtures I've (pretty much) decided on have keyhole mountings on the top surface so I need a way to mark the hole location for the screw anchors in the drywall. Saw this tip this morning, looks like a pretty straight-forward method so going to make a template out of a strip of scrap paneling.

Locating Holes.jpg

It may be worthwhile to grind the ends of the bolts to a point so there would be less effort needed to make a clear mark in the surface.

I have the existing fixtures hard-wired but planning to change that over and have a duplex outlet next to each pair of new fixtures as they have individual power cords, plus a pull chain so I can turn off individual fixtures if needed - the existing fixtures are wired 4 each on two separate circuits so I have to run either 4 or 8 at a time..

[Nickp]

Good idea, Tom...I usually take out the ole folding rule and go center to center...mark the wall (level) and get out the chain saw...er, drill. Same for picture frames.

Gonna have to try this...thanks

[DaninVan]

Tom; do NOT hang ceiling fixtures from the drywall only. Find the framing above, or if it runs parallel to the fixtures length move the fixture position to attach to it properly.
Here's another suggestion if the fixtures run in the parallel orientation. cut a rectanglular hole in the drywall, large enough to accept the fixture...joist to joist, and assemble 3/8" or 1/2" plywood boxes to fit between the joists (2'x4' x 3 1/2' deep. Install them so the fixtures are now recessed into the ceiling.
When I did mine I just cut plywood panels to drop onto the tops of the joists and put 2x4 blocking across the ends, then drywalled the interiors. A lot of work but worth it.

[Cherryville Chuck]

Despite the fact that I sheathed my ceiling in OSB I don't really trust it to hold screws forever so I drilled holes through the lights where the joists crossed. You do have to be a bit careful when tightening the screws. Because there are parts projected out on the backside you can torque the frame out of square sometimes if you over tighten. If they run parallel to the joists I think I would just turn them 90*. It is a shop after all and orientation usually isn't as important as overall light intensity except directly over a bench. There is also the option to screw a piece of 3/4" ply to the ceiling and screw the light to that. I had to do that when I mounted my ceiling air filter. If you paint it the same color as the ceiling it's not that noticeable. Which reminds me I didn't do that yet. As you can tell I'm more concerned about function than looks.

[kmealy]

My method is to put a sheet of paper on the back and secure with some tape. Then run a pencil sideways across the holes/slots. The outline will show where the holes need to be drilled. If you also smudge the edges you can use that to determine level/plumb.

[tomp]

Dan and Chuck,

Sorry to take so long getting an answer back, been a little hectic here lately. I hear you about hanging something from drywall - although the existing fixtures have been hanging from the ceiling for almost 30 years now, although they are hanging from toggle bolts. I was going to use Molly bolts because of the need to adjust the head stickout from the surface - and these 4' LED fixtures are way lighter than the 8' 2-tube fluorescents that are up there. But I looked at what's there - the ceiling trusses run in the same direction as the lights, and are on 24" centers, so it looks as if I can screw the mounting screws into the bottom of the trusses and get the spacing that I want. It's been a while, but I thing one of the reasons for the toggle bolts was so that lights were between the trusses and I could just feed the wire into the open space.

[Cherryville Chuck]

I used to use the toggle bolts but I always hated the large hole you had to drill. And if it ever got unscrewed it was usually impossible to get the bolt back in it. Lately I've been using the ones that mushroom the end when you tighten. One drawback with either one is that if the drywall ever got wet, either from a leaky pipe or roof, the lights might pull the anchors right through. I think Dan and I are of the same mindset, attach to something solid and then forget about it.