surface box multiple knockouts align with trunking advise

[Telecoms_man]

Hi Guys,

I have to fit an MK 3 way grid surface mount box below 3" metal trunking and require the use of all three knockouts on the top of the MK surface box. This needs to be repeated for a number of surface boxes.

Cutting one hole in the trunking for a 20mm coupler and bushes is easy, but any tips how I can cut all three so they align?

MK have no details (that I can find) on their web site as to the hole spacing or have any templates.

My initial thoughts are either to measure carefully the surface box knockouts to find the centre & spacing of each knockout & make my own template on a piece of cardboard,

or,

offer the surface box up to eyeball & mark the centre of each hole and drill a pilot hole. Offer the surface box up again and use the knockout to align a Qmax cutter, to punch out the first hole. Fix the box to the first hole with bush& back-nut, then punch out the remaining holes.

or,

similar to the above, but cut the bottom of a surface box to use as a template & use a hole saw without the pilot drill.

Thoughts, help tips appreciated.

 

[Risteard]

Knock them out and then draw a circle in the inside of them with a marker butted up to the trunking. Then drill these out.

That's the easiest way in my view.

I'd also put an extra lockring between the backbox and the trunking if you're not putting couplers in so that you can get the accessory on!

 

[Dustydazzler]

As above its just a case of using a sharpie marker to draw where the holes will go...
cut them out and use a bush and lock ring

 

[ipf]

THINKING CAPS NEEDED, lads.

I'd definitely be getting my tape measure and 90 degree angle out.

 

[Telecoms_man]

THINKING CAPS NEEDED, lads.

I'd definitely be getting my tape measure and 90 degree angle out.

I will be using conduit couplers to space the surface box from the trunking.
Using a bush for the first hole was just to make it easier to cut second and third holes.

The issue is, all three holes have to be drilled dead on centre, else they won't line up.

Drawing round the knockouts with a sharpie will give a circle, not a point to drill. A hole saw has a pilot drill, needing a centre mark. I don't trust myself to guess correctly the centre of each circle

 

[ChrisElectrical88]

??? Come on, drilling centre of a hole int hard, you will get a couple of mm play aswell

 

[ipf]

I will be using conduit couplers to space the surface box from the trunking.
Using a bush for the first hole was just to make it easier to cut second and third holes.

The issue is, all three holes have to be drilled dead on centre, else they won't line up.

Drawing round the knockouts with a sharpie will give a circle, not a point to drill. A hole saw has a pilot drill, needing a centre mark. I don't trust myself to guess correctly the centre of each circle

Good luck then. I'm baffled.

 

[Dustydazzler]

I can’t see an issue with drawing around the holes And using a 20mm hole cutter...

unless you are miles of centre with the hole cutter it will line up well enough to fit the Couplers

 

[R-fur]

Remember the bushes have a reduced area between the thread and the hex that gives a bit of wiggle room and as you are using a coupling you will have the wiggle room at both ends so you should have no problem. Just assemble it all loose before you tighten anything.

 

[hasel5]

Heard it all now