Part 009: The Filter Cover

I decided to start the engine here, as I await the delivery of a nice supply of necessary stock from Online Metals, an excellent source with good prices. I highly recommend the metal "Packs", which really give you a lot of metal for the money. You save considerably buying in bulk.

This small disk holds a very finely meshed SS screen, and is used behind the compressor to filter the air which helps cool the bearings, and keep them free from grit. The operations sheet from the plans has this thin (1mm) disk turned from a piece of sheet aluminum bolted to a plywood face in the lathe. I elected to turn it from round stock so as to more easily locate the holes, via coordinate drilling using a DRO, in my mill. This way too I can make several at once.

The 2024 is turned to size, and the interior bored using in my case a nice carbide shanked boring tool to minimize chatter. I made the stock 1.5" in length which will allow me to part away up to 10 of these covers.

Long experience in the construction of the radial engine has proven to me again and again the excellence of using a DRO and mathematically derived coordinate holes to locate the necessary drilling spots. The cover has 16 holes spaced evenly on a 48mm bolt circle, 8 of which are 4mm and the others being 2.5mm.

Here, a centering device is being used to locate the stock exactly centered beneath the mill spindle. This widget can easily and repeatably center to within .0005". At this point, the DRO is set to X0, Y0, and a drill chuck is installed.

The 16 holes are started with a center drill, and preliminarily drilled about .010" smaller than the final diameters. Deep drilling in aluminum is very tedious. The drill must be withdrawn frequently to clear the chips. After the holes are started, the correct drill is used to open up the holes to their final dimensions. Any attempt to drill the holes to size in one pass is doomed to drill an oversize hole due to the accumulation of chips and abrasion as the drill is inserted and withdrawn repeatedly.

Back in the lathe, the covers are parted with an ISCAR blade...

...and the holes, as well as the ID and OD are deburred. An ultra-fine wire brush gives them a nice, satin finish.

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