Z axis gib tightness and gib lock
I posted a message a while back about the head on my Micromark mini
mill moving when I tighten the gib lock. I lapped the gib and 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 the lock.
My next question is how tight should the gibs be? I've gone back and
tightened the gib screws some more on the assumption that they 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 not
binding. There is still a little movement when I tighten the lock. I
think the torsion spring counterbalance design is flawed because it
creates a moment on the head which tends to cock it some small amount -
that and it's not a great design to begin with. I'm tempted to order
an air spring kit from LMS. Any thoughts?
- 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