Well, the interior of the Fast Deer's compression tube wasn't so hot. The ridges and valleys around the cylinder wall were several thousandths deep. Can't imagine how the piston compression could be consistent from shot to shot with gaps like that. Lacking any other evidence at the moment, I've got to assume that these surface imperfections are causing the 240+ fps velocity variation.
We have a couple machines at work for precision honing IDs. This is one of our horizontal hones from Sunnen.
Interchangeable mandrels hold varying diameters of abrasive stones. Each is expandable within a small range. I believe mandrels are available from as small as 0.060" up to 6.500". Bob, our honing department specialist, was kind enough to get me set up and give me some basic instruction so I wouldn't hurt myself--or break his machine.
The compression tube is slid over the mandrel which is expanded inside the bore until it just starts to kiss the inside. The work can be hand held or affixed to a support. RPM, diameter of the mandrel and stroke are all adjustable on the fly. Honing is done with a flood of oil on the part. (turned off for the pic) Here, the mandrel is bottomed in the tube.
And almost withdrawn.
Didn't quite take the tube to 100% clean up. Just wanted to take the worst of the gouges out. Here's a shot fresh from the hone. Bore still covered in oil.
Here's the tube again before the honing.
And after. A fingernail barely feels the scratches now. It looks worse than it feels. The fine scratches trap and hold lubricant--a good trait of a piston bore.
More in a couple days.
If you hand hold the part, doesn’t that cause some areas to be honed more than others? Perhaps it doesn’t matter if the hone is sufficiently fine.
ReplyDeleteNice article, I always enjoy reading them.
I did a quick check and the tube showed less than .0005" variance. I didn't bother to check it with a finer gauge. A highly experienced machinist like Bob can consistently hold .0001--.0002 over 8" using this tool.
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