On 4/14/2013 9:53 PM, Bruce L. Bergman (munged human readable) wrote:
On Sun, 14 Apr 2013 13:56:06 GMT, Doug White
wrote:

Tom Gardner Mars@Tacks wrote in
:

snip
The flexing -- that is, the spring rate without taking a set -- is
the same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).

My cousin told me that, I was hoping he was wrong. I could make it
out of Ti and/or go from 5/8" to 3/4" or a scooch more.

I'm a little rusty on this stuff, but for a simple rectangular bar, I
believe the stiffness goes up as the cube of the dimension. You
shouldn't have to add much to make it significantly stiffer. 5/8" to
3/4" would almost double the stiffness (halve the deflection). Adding a
rib could do a lot, if there is room.

A rib, or better yet use U-Channel so the face and stiffening ribs are
all one integral piece, and a chunk of thick bar at the top to bolt
your inserts to - go as physically big as you can. Modify the machine
to make room if need be.

If this is one of those gidges you have mentioned in the past where
you're using the carbide inserts as a hard-faced guillotine and
anvil-blade to chop wire to length, don't count on the machine and
mount rigidity to keep it aligned...

I'd have a finger from the upper jaw extend below the lower jaw where
they overlap, and a few roller bearings with a fine-threaded gap
adjusting method. And a jam nut to keep it there.

Physically keep the upper and lower blades from crashing, even if the
machine gets out of alignment.

-- Bruce --



Yep, you must have seen it! The cutter uses a 1" shaft riding in Timkin
tapered roller bearings that this arm is attached. I use 3/4" square x
1/4" thick, coated HSS inserts. I've tried every grade of carbide, even
custom made they get tiny chips and and they all self destruct in very
short order. The HSS works great and they are only $5 and I get 8
cutting edges on each.

I think the arm sometimes gets too much pre-load pressure from the
mechanism that tightens the stationary blade. It gets readjusted every
time we do a blade change.