Dome building: A new and bigger saw sled.

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Friday: It was soon obvious that my first saw sled was far too small to cut the dome's lower covering panels. So I used up some crappy, 10mm birch ply I had bought in desperation one weekend when I could get nothing else.

The new sled is 90cm wide x 72cm deep, It has larch crossbars top and bottom cut from a scrap of the obs. flooring. The battens are to ensure the two halves of the top board stay flat and firmly together. I haven't glued them on yet but have used plenty of screws while avoiding the saw cut line. Screws can always be undone if I have made another error. Glue makes my mistakes permanent. Try twice: Glue once!

I have yet to make the plywood runners so that comes next. They need to allow full travel of the sled.

The image [above right] shows a later view after the birch plywood runners were cut precisely, propped slightly high, with washers, and then glued. The sled was carefully lowered onto the runners and squared against the fence. Once the glue is dry the runners can be screwed to the top board for extra insurance.

Note how the weights have been aligned directly over the runners to avoid bowing the top board. The crossbars can later be planed hollow, or flat on the bottom, before gluing, if it proves necessary to flatten the sled board.

It has just reached a scorching 75F @ 14.30pm in the shade. But I have none, as I am working outside in bright sunshine under an almost cloudless sky. I really don't like such hot weather! I need dark sunglasses with [reading] power just to see what I'm working on. Of course I don't have any.

Sunday: Much more cloudy and cooler at 66F. I started ripping up the thin, 5'x5' of 4mm birch ply for the dome covering panels. Not very easy due to the floppiness of the sheets. So I set up some support rails on B&D workbenches to keep the sheet as flat as possible during sawing. This is going to be very wasteful! Only four lower panels per sheet!

Once the large sled had been completed I discovered some potential improvements. The packing piece to cut an angle should be placed on the left with the angle reversed. This means the push against the saw blade is more direct.

The large sled is easily supported on the left with a rail in a workbench. An alternative is to fit a 14mm packing piece on top of the fence rack rails after moving the rails fully to the left without the fence fitted.

I had some 15mm square ally tube which would have been perfect but it was slightly too thick and lifted the sled too much instead of merely supporting it.  So now I'm ripping some 1x2 batten down to fit. A little wax will ensure a smooth ride. It did too.

I managed to fit two lower panels before it suddenly started pouring down without any warning. I just had time to throw a tarpaulin over the table saw, grab the loose electric tools and dash for cover. The sled is a revelation in effortless, fine adjustment of angles and saw lines. A hair's breadth, width of cut, is easily possible.

Then one of the runners partially parted company with the sled bottom. More glue and pressing. More dome building hours wasted. I added a dozen screws to each runner before proceeding.

I have also added a support batten on the left with a couple of self tapping screws to hold it onto the fence, rack rails at full left adjustment. This stops the sled from tipping at maximum overhang and reduces friction due to the previous, heavy cantilevering on the left. The sled is now silky smooth in action again.

If I was doing regular work with the saw I'd add a smarter support batten and a remote safety switch. One which can be reached with anything on the table. The tiny DeWalt press button switch is a very long reach from a kneeling position with the sled in use. Plus, the Danish dealer sent me an old model of saw without the later safety switch shown on almost all YT videos. I understand that the switch can be swapped for a later one but wonder if that would affect the guarantee if I did it myself. A foot operated O-volt, kill switch would be ideal. I'm not sure they are even available. This could be fitted in the extension lead rather than modifying the saw cable itself.

When I went out to tidy up before dinner I noticed a deep bulge in the white tarpaulin. The recent storms had filled the area above the observation slit and it had collected. I lifted the heavy bulge with my hands as gallons of rainwater poured down and across the ground. I slipped couple of temporary boards under the tarpaulin to ensure it doesn't happen gain.

Click on any image for an enlargement.

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