Thread: Wadkin PK Crown Guard.

I was looking at a photo of Auscab's crown guard column - the column with the crank handle at the top to raise/lower the crown guard.

It seemed odd - or at least the mounting hole at the bottom seemed odd.

PK1.jpg Auscab's column (PK 1857 of 1956).

Odd? Yes it's ~9/16" or so diameter. The column is held on by two 1/2" BSW (12tpi) bolts. One goes through the hole, the other in the curved slot (to allow the guard to be pivoted clear of the saw blade). So a ~9/16" hole would be appropriate - but I'm used to the massive hole in mine. 7/8" diameter to be precise.

PK2.jpg My column (PKA 800 of 1945).
So I searched and found a restoration wallace did in 2019. It looks to also be ~9/16" - so I guess mine is the odd hole size .

PK1a.jpg Wallace's column (PKA 628 of 1941).

A friend offered to make me a new pin - with a 7/8" shank and a 1/2" BSW threaded end. But we had no way of machining a hex head, so we opted for a bush - with the head shaped like a Wadkin washer (turned not stamped, and with a chamfer on one edge). OD = 7/8"; ID = 1/2"; flange 1 3/8" x 5/16" thick.

PK3.jpg

Trial fit in the hole.

PK4.jpg PK5.jpg

Remove, coat with oil, reinsert and apply bolt.

PK6.jpg

And while we were at it, a matching washer for the slotted side.

PK7.jpg

Note: the slot is 5/8" wide, which looks to be consistent over the three column bases I looked at.

One disappointing thing is: the bolt isn't OEM Wadkin and out of curiosity I measured the thread. It 1/2" 13 tpi - which means it's been tapped UNC. And I suspect that tapping out a 1/2" 12tpi hole with a 1/2" 13tpi tap is going to leave a bastardised threaded hole . It's holding so far, with no sign of impending failure.

Lucky we didn't make a new pin - with a 1/2" BSW 12 tpi thread !!

Cheers, Vann.