Monday, 3 August 2020

Boom Gallows Tube Support Blocks | Drilling Holes

When the laminated tube support blocks were fully cured I cleaned them up and gave some serious thought to how I could drill holes for the 25mm stainless steel tubing.

Somehow I had to support each block on the pillar drill table so that its upper face was perfectly level. When drilled out and installed in the locker it must line up exactly with the tube coming down through the seatback deck, providing a perfectly perpendicular socket fitting.

Easier said than done. I settled on attaching each block to a piece of scrap ply with temporary screws, so that it could be clamped securely on the drill table and still hold the upper face of the block level for drilling.

This is what the solution looked like for the starboard block.

In this pic you can see that I have marked in the centre of the centre of the block, ready for drilling. The folly of this will shortly become evident.

I went to great lengths to ensure that the block was flat and level using a level, like this.

Then I clamped the block on the drill table, as here.

So far, so good. I'm feeling pretty pleased with myself at this point, so I drilled the hole to a depth of 1 1/4". Here is the beautifully drilled hole.

I had become so intoxicated with solving a real woodworking problem that I had completely overlooked that there is no reason why the hole will be in the exact centre of the block.

So it was a shock when I test fitted it, and dropped the dowel down through the seatback blocking to see how it fitted. Here is the moment of truth.

The hole is not in the right place. It was immediately obvious that I should have used the dowel to mark where the tube will land on the support block, which would inevitably not be in its centre.

The air turned blue for a few minutes while I thought about how to fix this silly but easily remedied mistake. I would permanently plug the hole with a piece of hardwood dowel, mark it out correctly, and re-drill the hole.

As I resigned myself to more work on this block a thought struck me. What if by some miracle the drilled block was suitable for the other side of the boat, without rework? With absolutely no expectation of success I tried a test fit in the port locker. Here is the result.

It was a perfect fit! What are the chances of that happening? Not one to look a gift horse in the mouth, the starboard block immediately became the port block and we moved on.

It was now time to drill the 'real' starboard block. This time I marked the location of the hole correctly and levelled the piece carefully on the drill table, as here.

The block was clamped in place, drilled, and test fitted.

This was the result.

A perfect fit. Checks with the level showed that the dowel was perpendicular, side to side as here.

And fore and aft, as here.

Finally I rounded over the edges of both blocks with a 1/4" router bit, on the router table.

This is what the port block looked like when test fitted.

I'm happy with that. Job done!

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