On 9/12/2019 3:15 PM, David Billington wrote:
On 12/09/2019 22:51, Bob La Londe wrote:
On 9/12/2019 4:33 AM, David Billington wrote:
On 11/09/2019 23:11, Bob La Londe wrote:
On one of my machines I pulled of the pair of lock down vises I
normally have on the table so I could mount some custom fixtures to
machine a mold that was almost the full work envelope of the machine.

After I finished I had to put my pair of vise back on, align them
and align them to each other.Â* Not that long ago (a few years
atleast) that would have been a daunting task.Â* I have gotten to the
point that I expect them to be within the range of my test indicator
on the first try... and they almost were, but getting the vises
within 50 thousandths is not the goal of course.Â* LOL

I quickly got the first squared up on the table, and proceeded to
the second.Â* Of course I tighten the hold down clamps they shift a
few thousandths.Â* Lightly tapping with a hammer and going back and
forth as I bring the bolts down as far as I dare tighten them
without to much fear of damaging the table gets me within about a
thousandth across 2 six inch vise with a 3 inch gap between them.

One vise.Â* No problem.Â* five minutes any day of the week, and much
faster on a good day. 2 vises... not a "problem," but tedious. Maybe
20-30 minutes.Â* Maybe longer.Â* I didn't really pay attention to how
long it took.Â* Probably also not all that necessary as I use soft
jaws with a premachined step on the bottom so I can fully face them
square to the travel of the machine.Â* Then I add a step in the top
of the jaws, or in this case take a skim cut on the step that is
already there.Â* I can use the step for a high hold or for thinner
parts, and use the entire jaw when necessary.

Anyway, none of that really matters.Â* Just background until I get to
the point.Â* The point is even clamped down as hard as I dare the
vises still can move with only a modestly firm tap with a hammer.
Its only a few tenths to a couple thou depending on the blow, but it
does move.Â* I know a hammer blow delivers a deceptively large amount
of force, but still. It made me wonder how easily those vises really
move, and if there was something I could do or even needed to do to
more firmly affix them in place. I tend to mount a vise or in this
case two vises and only remove them if I have to.Â* Often even
temporary fixture plates are just mounted in the vises.Â* The two I
just remounted on the table were last off the machine over a year
ago.Â* I've cut a lot of parts in those vises. Maybe hundreds.

So what kind of "normal" cutting fores might cause those vises to
move. I put the word normal in quotes, not because I wanted only
include safe cuts that work every time, but also things that can
happen, but maybe shouldn't.Â* I know a crash with a fly cutter could
do as much damage as a hammer.Â* How abut a 1/2 inch mill entering a
piece of hard steel or a face mill banging on the edge of a work piece.

I know about the sheet of paper trick (it does work really well),
but I cut 95% aluminum with flood on that machine and having
something between the vise and the table that can not just hold but
wick moisture is a bit disconcerting.Â* The only other thing I could
think of was to add some stop blocks bolted to the table up against
the vise.


I'm wondering if your clamps may have the threads bottoming out so
not providing the full clamp load to the vice, I've seen it before. I
once did a job with the vice clamp bolts done up finger tight as I
had forgotten to use the spanner to fully tighten them, it did
eventually shift but I did a surprising amount of work before it did.



They certainly didn't bottom out in the table, but I suppose they
could be close in the nut(s).Â* I'll see if I can get a hook tool in
there to see how deep the ends of the bolts are.

Maybe I could have been clearer, all the BP 5/8" T nuts I have are
tapped so the studs won't go all the way through the T nut, the thread
will bottom out in the T nut and not hit the bottom of the slot. I have
experienced situations where the nut will hit the end of the thread at
the top end of the stud and only minimally clamp the vice or fixture.
Worth checking that this isn't happening with your clamping arrangement
what ever it is. If not the case must be some other issue but worth
checking.

RegardingÂ* slot damage I have only seen that on a badly abused
BeaverMill table and then the current owner knew that the previous owner
had been using the wrong sized (too small) T slot nuts which resulted in
the damage to the underside of the T slot.



I understood. I have 7 mills. 6 currently in operation. I have t-nuts
in the slots on all of them. I have also made t-nuts, but when I make
them I tap all the way through. Its a lot easier to make sure you won't
bottom out in the table before hand than it is to make sure you won't
bottom out in a t-nut.

Ok one of them doesn't really count. Its a mill drill that doesn't even
have a fine feed, but it does have a vise bolted to the table. 5 real
mills in operation. LOL.

I have a fairly decent stock of heavy washers, and have made a fair
number of spacers so I could use the bolt i have handy instead of
spending all day looking for one or going to the store. Even when I
don't need one for length I try to use atleast one because it acts like
a thrust bearing and the vise moves less when I torque it down. It also
spreads the load from the bolt a little, so a bolt head is less likely
to damage a cast fixture, angle plate, vise, etc.

One set of six parts cut so far, and the vises have not moved. Maybe I
was just being paranoid.