More steel advice.

you won't be able to do it with a drill alone, however, the way i'd go about it is to work out where you wan't the slot, and use the drill to put a hole at each end (drill size same as required slot thickness e.g. 10mm drill for 10mm slot), then just use a 4" grinder with a 1mm cutting wheel to connect the holes, it will make the sides of the slot - 2 cuts per slot
Go slowly, and mark everything out well before you start, scribe the lines and punch the holes well.
If the slot is a lot smaller than the grinder disc can cut, like 3" or less, drill the holes the same and use a decent jigsaw to join the holes - go slow and use cutting fluid and allow a bit of metal to clean up with a file.

Take it someone who can do it properly, last thing you want is crooked lines and rough cut outs.

We use a Plasma Cutter to do stuff like that.

Back in the days of steam radio ..... we used to drill lots of small holes close together just inside the cut line. Then clamp a thick bit of steel just below the line on both the inner and outer sides. Now take a good cold chisel and whack it against the cut line and you will be surprised how easy it is to sheer the steel off with the cold chisel. Finnish with a file - not hard at all. Try a small bit of steel in a vice to get the hang of it, use the top of the vice as the sheer guide. Up to 6mm no trouble at all

KK.

Howz about a 4" angle grinder- just a cheapie from Bunnings.
Cut the hole a 'pubic hair' undersize and claen it up with a file..!!

Gday,
What size slot?
What thickness material?

OK. all good advice..

The slots I wanted to mill are into 7 mm thick mild steel.

I wanted them to be blind slots i.e. not thru the metal all the way, say 4 or 5 mm deep is all so using a jigsaw is out.

I could use the 4 inch angle grinder and 1 mm cutting disc for the long cuts and the drill bit for the ends... thinking the slot will need to be about 5 mm wide or whatever width the LED strips are when they arrive.

How does one get rid of the metal left in the middle once you have your two parallel cuts either side of the slot?...more grind8ing with a disc?...say a wider cutting disc?....

I want to insert the LED strips "flush" into the bar and maybe even epoxy over them flush, to seal them in against the weather.

The milling attachment for a drill sounds neat - I'm not bad at making jigs for tools to follow... Will search the net a bit and see what I can find.

Thanks everyone for the ideas - I'll see what I can come up with.

Still making progress - got some welding and grinding done today / tonight until the Mig Gas ran out.

Managed to cut one of the swing arms down 70mm and move it to the left to make the wheel not lap past the centre.

Will have a go tomorrow at duplicating/ mirroring the arm for the RH carrier, bye bending up some 50 mm pipe to the same angles (reversed).

Still a lot of hours left in this build but it is starting to actually "look" engineered specifically for the job as we work on beautifying the basic unit.

Will try n get more pics uploaded and another description thread posted soon as I can.

Cheers
Cheers

Yea short of putting the bar in a mill and running a slot drill along it, its gonna be hard to do without going all the way through, even an attachment for a drill would need to be clamped to the bar and use a guide as theres no way you'd be able to make it straight by hand.
Either do what the guy above says and tack a plate behind or just don't make stots and put the lights on the bar without slots, then bend up a surround out of 20x4 flat or something and weld it on to protect the lights.