Wet Core Drill Accessories

Extension bars, and what depth costs

An extension bar sits between the drive and the crown so a hole can go deeper than the crown's own length. 150mm and 400mm cover most of what comes up.

They are straightforward parts with one thing worth understanding: every extension adds a joint, and every joint adds a small amount of deflection. Over a deep core that compounds, so the exit point can be measurably off the line the entry suggested.

The working rule is to use the shortest extension that reaches, set the rig up square before starting rather than correcting mid-hole, and expect a long core through a thick wall to need more care on setting out than a shallow one.

Thread adaptors

Wet drilling runs on two thread standards: 1¼" UNC on rigs and larger crowns, ½" BSP on small diameter crowns.

The adaptors here convert between them in both directions, male and female, which means one motor can run the full diameter range rather than two. If you have ever had a crown arrive with the wrong fitting on the morning of a job, this is the part that saves it.

Looking after the threads

Threads are the weak point in wet drilling, because they spend their life full of abrasive slurry and they are done up under torque.

Flush and wipe the thread every time a crown comes off, rather than at the end of the week. Slurry that dries inside a thread sets hard, and the next assembly then tightens on grit, which is how a joint seizes permanently.

A smear of waterproof grease on the thread before assembly costs nothing and makes the joint come apart again. So does breaking the joint at the end of the day instead of leaving it made up overnight.

For crowns, see wet core drills.