"whit3rd" wrote in message
...
On Thursday, December 8, 2016 at 11:16:10 AM UTC-8, Bob La Londe wrote:
I've got to clamp a think brass strip into a slot on a piece of aluminum
bar
prior to finish machining the project. Machinists clamps would work
except
that the screws either [hit] the table or stick up to far and the mill
head
would run into them.

This particular job is a one off custom job, but the task of inserting
the
brass strip (slide gate) is fairly common and I am trying to think of
ways
to make it a little faster and more efficient in the future.

At first glance, it would seem that a vise with soft jaws would be a
better
way to combine the slot and clamping (for sure, it gets rid of the upward
protrusions). Before using loose bits and long clamps, could you just
put
some threaded inserts into the slotted Al plate, and use holddown clamps?
A screw and a bit of U-section up close to the slot is easier on the
holddown arm than the longnose clamp proposed.

Huh? Why or how would a soft jaw vise make any difference? Do you
propose crushing the work piece? That would be counter productive, because
then the brass bar would have to be driven out with a hammer, the slot
recut, and the brass bar recut. Doesn't make any sense to me. Or are you
proposing some form of clamp outside of the main work piece to hold the end
of the brass bar. This isn't a good idea either as it does not hold the
brass bar down into the slot where it needs to, and it could possibley cause
(or allow) it to bow up and get overcut creating a destroyed workpiece.
Also, if you didn't notice the main workpiece is in a high hold in the vise.
It needs to be in that high hold in order to do everything in "one" setup on
the machine

Not sure what protusion you are talking about. The handle for the slide bar
can't easily or effectively be added on later. It has to be there. The
curved corner edges of the brass bar need to stick out above the surface so
it can be machined flat with the rest of the surface. Big voids from the
curved edges would allow all the media to leak out of the mold cavity.

I really don't want to drive a screw into the surface of the mold for the
U-section. Neither in the front where it may create hard spots for detail
maching or in the back where I would have to machine it off or the customer
will complain about the aesthetics. Now I am sure I could put stuff under
the screw you propose and monkey around to prevent damage, but that's
exactly the sort of extra work and time wasted I am trying to avoid. What I
am doing now is working just fine already. I want to make clamps so I can
do this sort of setup faster.

This is a one off work piece, but I routinely do work pieces of this type.
Each one is different in the specifics. The brass slide bar may be at
varying distances from the end of the main work piece and sometimes there
are more than one of them. A long clamp will work because while the part is
machined to be able to move in the slot it is a very close fit. There is
friction. The long nose clamps have the advantage of working on multiple
different setups easily and quickly, and they will not damage the work
piece. It doesn't take a ton of force to hold it in place until the
retaining screws are machined in. The retaining screws are just 10/32 in
aluminum with a shim. They are also adequate to hold against all the rest
of the machining forces to complete the part. I am sure the long nose
clamps will generate as much holding force as that piece of half inch
aluminum square bar under c-clamps at each end.

I just wanted to know if 1018 would be strong enough for my clamp (which
will other wise work) or if I needed to go with a stronger or hardenable
alloy. Do you know?

All the rest was background. I included the background because certain
people in this group won't answer the question you ask without background.

So without further adieu... is 1018 strong enough to last for this
application or should I chose a stronger alloy?