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Unread 05-05-2018, 09:49 PM   #154
GlenL
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Default Tube polishing, cont'd

The next step is to grind the inlet end. The tools are used left-to-right. The half-moon file was rarely employed but helped where the casting line was especially thick.

Which reminds me... I'm curious as to how the tubes are made. I always thought they were cast and there were mold separation lines. I'm starting to think they were cast in two or more parts and then welded together. From the inside, it looks like it may be welded. That'd explain why the "casting lines" are so thick. It might be cheaper to make that way, too. Anyways...

The goal of the grinding was to make the inlet end more circular and wider at the mouth. The tubes don't all line up with the plenum right and opening up the tube and rounding off the lip should help air flow.

The main tool is the barrel grinder. Using that, the inlet gets shaped more into a "V" or maybe a tulip shape. Takes a good while to do especially to make it circular and clean up the two weld/casting lines.

The ball grinder cleans up any unfortunate gouges and bumps deeper in the inlet. It's also good for smoothing down the bends right after the inlet.

The cone grinder is used to smooth the inside after it's been cut back and to shape the lip. The tube, as made, has a fairly square lip and a few passes at different angles makes it a quarter-round.

The rotary sander (110 grit) bit takes out a lot of course grinding marks. It's also good for reaching down the tube to the first bends.

Finally, some sandpaper (220 grit) is used to get the surface smooth. That pie-shaped piece is a section of self-adhesive sanding disk. Quite handy as I'd stick it to a gloved finger and could get some good action with it. All the preceding tools are rotary and this one goes across those. I'd do it on the inlet and then on the outlet where the wire brush left some scratching. The ends are nicely smooth to the touch afterwards.
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Last edited by GlenL; 05-06-2018 at 09:50 AM.
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