Crane Arrangements

An Eccentric Anomaly: Ed Davies's Blog

After last Sunday's lovely weather Monday and Tuesday weren't so nice and all I got done on site was preparing two more rafters to go on the north side.

However, I have got a digger organised (probably) for next Monday. Hire is quite a reasonable hourly rate but having to pay for a whole day (but that does, at least, include transport) means it's worth getting as much done in one go as possible.

Accordingly, on Wednesday I had a go at fit checking the one south-side rafter I've got prepared (from the little photographic experiment).

With easy access to the ridge the first thing I did was simply measure the length it should be by stretching a tape down. The discrepancy was only 12 mm which I'm pretty happy with though a bit concerned it might actual be out a bit more as I later found that that glass fibre tape needs to be pulled tighter than I thought to match my metal tape.

Next I went back to my “field-expedient” crane to lift a rafter in the middle to push it into place.

That looks like it should push up into place. The problem is that until the bottom is all the way up and slotted on to the ring-beam properly the top end is dipped down a bit so catches on the ridge beam.

The rafter needs to be lifted higher, so that its middle is well above the purlin. My “crane” board is long enough that I could probably get that height but in this case I ran out of travel on the chain hoist I was using. I should have started with the rafter higher in the first place. Actually, with the rafter resting like that I slackened the chain hoist and pulled and retied the rope to get a bit more travel but it wasn't quite enough and the rafter was then no-longer on a stable resting place to repeat the trick, and it was getting late, so I gave up at that point.

This wouldn't be a general trick for lifting other rafters at it starts with the rafter to be lifted lying level, parallel to the purlin and next to the posts. If there was a neighbouring rafter up already then it would block the lift. Hence the need for a crane of some sort able to swing the rafters into place.

Still, I'm moderately confident of the fit so today, between the wet start to the morning and the spreading of big shower over the site mid-afternoon, I prepared the tops of two more rafters for that side. If the weather cooperates Friday or over the weekend I'll do another to make it a set of four.