Re: Z axis gib tightness and gib lock
If you think on it, if the dovetail contact side of the gib is
perfectly flat assuming there's no burrs or sharp edges on either the
gib itself, the column or any other inteference fit, it shouldn't
matter where where the adjustment screws or locking lever screw make
contact with the gib.
Offhand, the only way i can see how the gib is rocking as you
mentioned is if its belly shaped or warped.
I'm not saying its impossible that the adj. screws somehow aren't the
root cause. I just find it hard to believe that could be the problem
assuming everything else was machined properly from the factory.
The ball bearing idea would either prove or disprove all this.
What i would try first before any major surgery is performed and
since the gibs are on backorder is to pull the gib, coat it with
layout dye or permanent marker and run it over a piece of fine sand
paper laid out on a perfectly known flat surface to check for
flatness. If hi/low/warpage/belly-shape is evident then relap until
the contact edge of the gib is perfectly flat.
The way i lap and polish gibs is to lay a sheet of say 400 or 600
grit wet sand paper on a hard known flat surface (preferably thick
steel plate) and then lightly coat the sandpaper with oil. I also
tape the sandpaper taut to the flat surface to keep it from moving.
Then press down on the gib using a light to moderate pressure and run
it over the sandpaper in one direction being very careful to keep an
even pressure to prevent rounding of the edges or bellying. If there
is severe warpage or any other problem, i'll use a coarser sandpaper
and work my way up to a finer one.
You might also want to try as an experiment to reverse the gib or
trying to use either the X or Y locking lever as the Z lock to see
what that does.
"kylejoiner" <kylejoiner@...> wrote:
> I think a new gib will be next on my list. I am suspicious of the
> quality of the original and the location of the indentations for
> screws. I do believe that the lock screw indentation in the gib isit
> not aligned with where the screw it pressing. I'm also planning to
> try placing a ball between the tip of the lock screw and the gib so
> that I can apply more even pressure and not have the screw dig into
> the gib.
> I took a look at the LMS site for the gibs but they are backordered
> right now. Has anyone made a gib out of brass?
> --- In GrizHFMinimill@yahoogroups.com, "moparado" <kenwm2@> wrote:
> > Kyle,
> > are you sure you're adjusting the four gib tensioning screws
> > and making sure they're secure by tightening their individual
> > nuts? The way i adjust mine is to tighten each screw just enough
> > where i feel it adding a slight minimal resistance, then i back
> > off just before the resistance threshhold starting with thecenter
> > screws and working my way out. Then i repeat the procedurewithout
> > backing off until the resistance is where i want it all the whiletightened.
> > testing each adjustment my moving the head up and down. Sometimes
> > takes a bit of trial and error after tightening the locking nuts
> > get it right.
> > Where is the movement coming from exactly? You should be able to
> > locate the 'play' which is allowing the head to move.
> > You did mention the gib rocks when the locking lever is
> > This should be a big clue as to whats going on. Either the holegib's
> > locking lever threads was drilled off center relative to the
> > verticle center line or the gib is belly shaped, not flat orthe
> > ground at the wrong angle from the factory. As someone suggested
> > if it were my machine, i'd order a new gib from LMS to eliminate
> > possibility, it can't be that expensive. If you order a new gib,
> > might want to also order a set of their excellent after market
> > locking levers also. The original locking levers are pure junk
> > were the first things to break on my machine, all three of em in
> > How about the machined dovetails on the other left side of the
> > Can you see any play there?
> > -Ken
> > ---------------------------------------
> > "kylejoiner" <kylejoiner@> wrote:
> > > Ken,
> > > I'll go back and set the gibs using your method and a block of
> > > to relieve the pressure from the torsion spring.
> > >
> > > The first time I observed the gib, it would rock slightly when
> > > tightening the lock screw. The lock screw had also kicked up a
> > > burr. I've seen mention in another column of placing a ball
> > between
> > > the tip of the lock screw and the gib. That might help with
> > > burring since the screw tip is not grinding away at the backof
> > thedown.
> > > gib.
> > >
> > > As far as the movement goes, it's both lateral and up and
> > > When I tighten the lock, the head rotates counterclockwisewhere
> > > at the front of the machine) slightly so the spindle moves to
> > > right and up slightly since it's at the 6 o'clock position.
> > >
> > > I've tightened the gibs a little more and I'm to the point
> > > will get stiff if I further. The resistance varies somewhat as
> > go
> > > up and down the column. I think I'll apply some blue to the
> > > surfaces and look for wear patterns to see how things fit up.
> > >
> > > Kyle
> > >
> > >
> > >
> > > --- In GrizHFMinimill@yahoogroups.com, "moparado" <kenwm2@>
> > > >
> > > > Kyle,
> > > > i remember your original post. I checked the head movement on
> > > mill
> > > > and there is zero movement even with the lock loosened.
> > > > I think there's something going on thats not obvious.
> > > > can't see how the tensioning mechanism can be a problem. The
> > > > should be secure spring pressure or not.
> > > > The gibs should be just tight enough to let the head move
> > > > with minimal resistance. If remember correctly, i suggested
> > > > adjust the gib set screws with the spindle pressing against a
> > > piece
> > > > of wood on the table to relieve any affect the tension spring
> > > might
> > > > have. If nothing else it might provide some further clues.
> > > you
> > > > tried this?
> > > >
> > > > Some things to check if you haven't already:
> > > > -Did you also check the column dovetail for burrs or sharp
> > > > -Did you check the head/column dove tail on the opposite side
> > > the
> > > > lock lever side for burrs and fit? My hunch is something is
> > > on
> > > > there on the other side.
> > > > -Where is the movement originating from and is it lateral or
> > > up/down?
> > > > -Did you check the fit between the gib and the column
> > It
> > > > could be the gib itself and/or its mating column dovetail or
> > > > dovetails on the otherside were ground at the wrong angle
> > thegone
> > > > factory. That wouldn't surprise me in the least.
> > > > -Ken
> > > >
> > > > -----------------------------------------------------
> > > >
> > > > --- In GrizHFMinimill@yahoogroups.com, "kylejoiner"
> > > > wrote:
> > > > >
> > > > > Hello,
> > > > >
> > > > > I posted a message a while back about the head on my
> > > mini
> > > > > mill moving when I tighten the gib lock. I lapped the gib
> > > > removed
> > > > > burrs from it and reinstalled the gib in the mill. It's
> been a
> > > > couple
> > > > > of weeks and I'm still seeing some movement when I tighten
> > > > lock.
> > > > > My next question is how tight should the gibs be? I've
> > > back
> > > > and
> > > > > tightened the gib screws some more on the assumption that
> > > > should
> > > > > pull the opposing dovetail aginst the column to locate the
> > > head.
> > > > The
> > > > > gib is tighter, and the head movement is tigther, but it's
> > > > > binding. There is still a little movement when I tighten
> > > > lock. I
> > > > > think the torsion spring counterbalance design is flawed
> > because
> > > it
> > > > > creates a moment on the head which tends to cock it some
> > > > amount -
> > > > > that and it's not a great design to begin with. I'm
> > to
> > > > order
> > > > > an air spring kit from LMS. Any thoughts?
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Kyle
> > > > >
> > > >
> > >
- Randy you're right. In my last paying job, one of my projects was to
design a new Telco interface transient protection circuit for dial up
modems as the old MOV only design just wasn't cutting it. It was a
tough job getting a new and 'improved' circuit especially for foreign
applications approved by the FCC's, UL's and foreign PTT's rigorous
design and test standards... which is the reason the old design was
kept for as long as it was. But increasing fried customer returns
changed all that.
MOVs have been the mainstay of very cheap surge/transient protection
for years now. They work great if they don't have to work!
Their reaction or turn-on time is also not the best of choices as
compared to other suppression components.
As you say once they start conducting and shunting transient currents
to reference ground they degrade and depending on the magnitude of
the surge hit, they'll fail completely especially the cheaper ones.
Also they are typically spec'd in to turn on at roughly 50 volts
above the peak AC line voltage. If the AC line is prone to surges
and/or the device the MOV is protecting has a heavy inductive load
such as a motor, its turn-on clamping voltage will slowly degrade to
the point it'll actually start conducting during AC line voltage
peaks leading to eventual total failure.
Another potential problem is that MOV's are in the family of shunt
surge suppression. In order to protect a piece of electronic
equipment, the MOV shunts the transient energy to reference or earth
ground. The problem with that is a PC mother board, modems, etc. are
also referenced to earth ground. In essence, its completely possible
a portion of the transient's current will travel through all these
ground paths especially if there is a relatively high impedance to
earth ground due to extremely long extension cables, long distances
to earth grounding rod, loose ground connections, corrosion, etc.
And if the earth ground is very poor to non-existent due to faulty
wiring or using a ground lifter, the suppression energy can find its
way through to the Telco data line reference ground. In the least
this can cause noise-related data errors and in the worst fry telco
and other equipment including the PC mother board, again depending on
the amount of transient energy.
First thing i did when i purchased my home PC was to get a decent UPS
and then connect a 10 gauge copper wire to both the PC's chassis and
the UPS's ground connection to my well's metal water pipe which is
buried 4 feet underground.
One thing to keep in mind, no known surge protection system that will
fit in a PC or related equipment at least, will protect against a
direct lightning hit to a local power or telco line.
In fact electrical storms are apparently so prevalent in South
Africa, their regulatory board demanded we spec in a large gas
discharge suppressor in the product we shipped to them.
--- In GrizHFMinimill@yahoogroups.com, Randy Smith <randyrls@...>
> Ken; I would not use a MOV in this application. These are
> used in surge suppressors, and after a certain number of surges gothru
> them, they fail. Kind of like a solid state fuse.need
> The purpose here is to prevent mill controller damage or outage. I
> to take a look at my mill. The fan in the control box is makingodd
> noises. Fan may need replaced. If I can get one locally, I will,if
> not Grizzly will get an order.suppressors
> In the company where I worked, we got out a case of surge
> after an electrical storm because we knew that we would getcalls. "My
> PC won't turn on!"if
> The servers were on a motor-generator setup with our mainframe.
> Later.... Randy S
> Practice random kindness and commit senseless acts of beauty.
> moparado wrote:
> > Hi Harvey,
> > I really need to look at that controller schematic one day to see
> > there's any transient or spike protecion such as a MOV, transorb,these
> > etc. I've got this gut feeling there is none which could be why
> > controllers have somewhat of a failure rate.
> > -Ken