Hand machined mechanical pencils

Air inlet guide (Dec. 2009)

The pictures below are pretty self-explanatory. To allow air to enter the front of the machine, the lid is raised up slightly (about 1" or so) by a couple of blocks which are screwed to the lip of the main casing. Because the lid is raised up, it no longer triggers the interlock switch so there's a block of wood stuck under the lid to trigger the switch. Air can now enter the machine through the gap left between the two spacer blocks at the front. Make sure that there are no large gaps between the left/right edges of the lid and the case - if there are, sit a short length of square stock material on the case to block them up.

The air is guided down to near the surface of the table using various sheets of ply and wooden blocks. These form a tunnel to direct the air. These bits do take up some space and reduce the Y-travel of the gantry by a few inches, but I haven't found that to be a big problem. The entire air-guide assembly is wedged between a thumbscrew on the top of the bed surround and just under the lip at the front of the machine. It's then relatively easy to remove, if the full Y-travel is needed.

The overall effect is a sheet of air flowing over the surface of the cutting table. The end of the nozzle is immersed in this and any smoke generated is swept away and out the extraction fan at the rear. It's a massive improvement compared with before, when air just entered the case through any cracks or fan vents it could find.

Spacer block to keep lid up

Showing how spacer block is screwed to lip of case

Both spacer blocks in position

Lid closed, leaving around 1" gap

Block of wood glued to underside of lid to trigger interlock switch

Air guide - two pieces of ply separated by wooden blocks

Closeup of guide

Guide in place. It is wedged underneath the lip at the front and is prevented from sliding down with a thumscrew into the table surround.

View looking into guide

View from inside the machine, showing the thumbscrew which holds the guide in place

The small piece of wood (with the red tape) slips down between the cutting table and the machine surround. It prevents smoke from gathering in that region, and also prevents tools etc. falling down and getting trapped under the table.