Drilling a BATH with a diamond holesaw drill bit to make a hole for taps etc using Porsadrill from 365 drills

Drill or drilling a steel or cast iron bath

How to drill a hole in a bath

This article is written by 365drills using a porsadrill diamond to start the hole into a bath for a customer

Plus a remgrit holesaw (not supplied by us) to grind into the cast iron and finish the hole.

Tools Required:

  • 1 x drill with a standard chuck
  • 1 x diamond drill kit by 365drills
  • 1 x remgrit holesaw for cast iron

drill bath

This is a steel bath (you can cut cast iron baths as well) but steel is lighter.

The customer didn’t want the hole on the tiled wall but was afraid of chipping the enamel

drilling a bath

This is the bath corner he selected for the hole to be drilled.

bath hole

When we examined the bath this is the overflow hole and you can see how poor the finish is.

This hole above is not our work!

365 drills

We measured the bath tap which was a 40mm monoblock with a standard 35mm inner bore

monoblock tap
These bits are what go underneath the bath to tighten up the monoblock

bath tap

And this is a shot of the monoblock without all its fittings.

guide plate

Find the position of the hole using the 365drills guideplate. We used a 38mm drill because there is plenty of room under the tap ring to hide the bath hole.

drilling a bath tap hole

Same shot of the 365-drills guide plate but show from a slightly different angle. Once you drill the bath the hole can not be changed. Simple I know but there is no going back after.

diamond drill ennamel

First cut has been made with the 38mm diamond drill. As you can see the edges are perfect with no major chipping of the enamel protective bath coating. Large chips at this stage are a disaster so we use diamond crowns to wear down the paint with a fine grinding action.

hole drills bath

The hole has been cleaned of debris and the collar fitted to check for fit. As you can see we went slightly inside the 40mm diameter choosing to play safe and drill a 38mm ring. That way any fine chipping is held within the fitting and cant be seen.

cutting a hole in a bath

Next we drill a basic pilot hole for a remgrit holesaw to fit through.

We do not supply the remgrit holesaw

Doesn’t have to be perfect and can chip because its within the perimeter wall of the predrilled hole. But best to be careful!

holesaw bath
Stage one of the actual grinding. We set back the inner circle because that’s how the plumbing goes inside the tap.

monoblock tap

Can you see everything is offset rather than in the middle.


It takes about 30mins to grind out the hole with a grit edged holesaw. WARNING Everything GETS VERY HOT and messy so please go slow and try to cool it all down. If you use a battery drill to bore the hole in the bath then expect three battery changes. This project will drain the life of a battery drill very quickly. So be sure your kit is fully charged.


This is the back of the bath (or the underneath) you can see some sharp metal which must be removed by pliers and filed down. To prevent this we drilled from the underside for 2mm but you cant stop it all from jagging.

tap hole bath

And this is the finished result.

35mm hole in a bath

We tested all pipes into the bath tap to make sure it worked.

contemporary bathroom

bath pipes 365


diamond drill bits


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