On 13/09/2019 15:49, Bob La Londe wrote:
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. 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.Â* I have 7 mills.Â* 6 currently in operation.Â* I have
t-nuts in the slots on all of them.Â* I have also made t-nuts, but when
I make them I tap all the way through.Â* 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.Â* Its a mill drill that doesn't
even have a fine feed, but it does have a vise bolted to the table.Â* 5
real mills in operation.Â* 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.Â* 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.Â*
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.

Now I feel inadequate as I only have 3 lathes and 2 mills but they pay
their way and always useful, the small CNC mill is a work in progress. A
mate down in Cornwall mentioned recently he met a guy down at the local
mine with 30 lathes, then largest being 12' diameter capacity and a 30'
bed, I guess he has the need, space, and connection to the national grid.