On 05/26/2010 10:38 AM, Lloyd E. Sponenburgh wrote:
I've got a tough-dog clamping job to do.

I want to mill my lawnmower blades, rather than grind them.

The blades must be mounted at an angle to the table (tilting the head
just wouldn't work well in this app, because my Y travel isn't enough),
and the jig/workholder must be "indexable" in the sense that I must flip
the blades end-for-end to grind both ends, yet get the same position from
center each time.

No problem on the indexing, but has anyone a good idea for a very simple
way to clamp the blades at a "tilt", yet still hold them well enough to
reduce the chatter? There is a requisite overhang of about 6" from the
jig to the end of the blade, because there's nothing on the ends you can
clamp to -- little "lift wings"& turbulence slots get in the way.

Ignoring the more important issue (why???), are those turbulence slots
wide enough to get a bolt through, to use for clamping? 6" of overhang
is going to guarantee chatter -- possibly deathly to the milling tool --
regardless of the rigidity of the thing that's holding your springy
piece of metal that far from where the cut is being attempted.

How about casting a zinc or lead (or solder!) bed for the blade, and
clamping to that? Cast it over the back side of the blade, using a
suitable method* to keep it from sticking, then mill its bottom side to
the angle you want. Then use some sort of "reach over and push hard"
clamp to hold the work.

You definitely want something that snubs the metal up tight to the
working surface of the blade, or the darn thing will vibrate like a reed.

* Note that I don't know the best way to do this -- really wanting it to
stick generally works quite effectively when I'm soldering, but that's
hard to apply here.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com