Best approach to making a hole in sink unit?

[Northman]

I need to make a hole for solvent weld pipe, and it needs to be in an awkward part of the sink unit back panel, where a stiffener panel overlaps with the backing. I plan a 76mm hole, and the centre point will likely be just above where the bottom of the panel is. The first photo shows the back of the unit showing where the hole needs to be - the horizontal line is where the bottom of the thick panel is; the rough circle where the hole should be.

From above, you can see the two overlapping panels...

and the inside view...

what would be the best way to tackle this? Would a holesaw from the back have an issue once its through the back panel and is just chomping on the thicker part for half the circumference?

 

[Deluks]

Why not go through the front?

Pilot from the back first.

To help eliminate breakout, do a little bit from both sides, via the pilot hole.
Or clamp a bit of wood on the opposite side of which you're drilling from.

 

[chirpychippy]

Don't over think it just drill a 76mm hole, once the sink is plumbed in you'll never see the back panel with all gumph that gets kept in there.

 

[Northman]

Thanks both! I really should have thought of clamping on an extra bit of wood - that would have worked nicely. Quite right about never seeing it again so I wasn't too worried about finish, just about whether the drill would cope. In the end I needed to shuffle the pipework around a bit, and ended up just shy of the stiffener panel, so came through the back panel in one go. Really appreciated the input.

 

[johnny2007]

Why 76mm?
Basin waste is usually 30mm or 40mm.

 

[Northman]

Wiggle room! Its a 40mm pipe, but putting the unit in position over it needs a little manoeuvring space.

 

[johnny2007]

Wiggle room! Its a 40mm pipe, but putting the unit in position over it needs a little manoeuvring space.

It needs a 50mm hole and a collar after fitting to keep things neat.