Re: Hypodermic needle drills???


Dennis Storzek <destorzek@...>
 

--- In STMFC@..., "Tom Madden" <tgmadden@...> wrote:

Philip Dove wrote:
New Hypodermic needles for drilling plastic...
Whoa! Let's hear more about this. Are we talking about sharply pointed
needles with the hole in the side of the tapered tip, or ones that
aren't tapered and the hole is in the end? I've used the latter for
drawing liquid samples for analysis, but they've tended to be larger
sizes. And do you spin, or just push the needle through the material?

Tom,

Side, spun.

Actually, piano wire is way cheaper. Just cut it on the diagonal with
a cut-off wheel, then grind on a long flat point. It's an easy way to
make a bastard single lip cutter, but they work fine in soft materials
like styrene and resin.

The real way to make a single lip cutter would be to grind the end to
a cone, the grind half the diameter away. In reality, the conical
point should also have a slight spiral to provide relief for the
single cutting edge, but in soft material it doesn't really make any
difference.

The wire with diagonal points work great in variable speed motor
tools, but cut a bit slowly to use with a hand pin vise. What actually
happens is the point starts scraping away at the material around the
dimple, or pin prick used as a starting mark. As the point goes down,
the cylindrical side of the wire forces the point over, so that when
the full surface of the wire is in the material, it's centered on the
spot the point first entered. Of course, when the full depth of the
point is in the work, there is no longer anyplace for the chips (in
this case scrapings) to go, but typically by this time the point is
coming through the other side of the material, so it doesn't make much
difference. These are not for really deep holes. The only thing to
watch is that the speed of the drill doesn't melt the surrounding plastic.

Dennis

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