Fair 'nuff Marty.
I get down to detail in electronics stuff where I know my territory.
No qualms about ripping commercial gear apart and redesigning. This
stuff is out of my territory and went counter-intuitive for me so I
figured I'd raise the query.
Later,
John
--- In 7x12minilathe@..., "Marty N" <martyn@...> wrote:
How about we leave it at this..."everyone has his reasons". ;)
Everyone's needs, abilities, wishes and ideas will differ and
perhaps there is no "holly grail" of gibs or any other part for that
matter. Thing is that I've just never experienced a single case in
the world of mechanical devices where attention to what seems like
the trivial pursuits of overly complex to others, excellence to me,
hasn't paid me back in triple with results.
Unrelated example. I have a gearbox of English design from the
40's that uses a stacked shaft arrangement, shaft within a shaft. I
was going threw these at a rate of about 2500 miles per shaft. They
were made from 1045 and through hardened but the finish was rougher
than what you see today and the clearance sloppy but by design but
to print and it used "00" grease as a lubricant. I had the outer
shaft honed "round", something it wasn't before, and smooth, 20 Ra.
Then had the inner shaft ground round and hard chromed then reground
for a clearance of .0015". stock was about .008" average. I switched
lubricants to a polyol ester oil..Redline Shock Proof Heavy.
Everybody and there brother told me that I fit it too tight,
finished it too smooth, lubricant was too light, chrome wouldn't
hold up and was too hard and would abrade the untreated inner shaft
and so on and so on. That was in 2002 and the box hasn't been apart
since. It also does something it never did before, shift cleanly.
Project cost me about $100 in services and parts. Each broken or
seized shaft set cost me that much every few months before that and
meant weeks of down time each and every go at it.
I have at least 20 experiences like that. T'is in my nature to be
overly complex ;) and win being that. Hold over from racing days.
Your right though John, not everyone's cuppa.
Marty
----- Original Message -----
From: born4something
To: 7x12minilathe@...
Sent: Tuesday, March 06, 2007 9:23 PM
Subject: [7x12minilathe] Re: Way Wear, Hard Gibs
Hi Marty,
Gotta go with Roy on this one. You're making things overly
complex.
This isn't a big lathe. The existing plates are quite adequate
once
shimmed properly. I haven't shimmed yet but plan to. I am
temporarily getting reasonable performance from the stock
arrangement once properly adjusted. Admittedly many stuff them
up by
twisting them all over the place because they don't understand
what
they are doing. Agreed they need some thread seal to stay put.
Mine
fell apart during shipping. But gee that's easy.
John
--- In 7x12minilathe@..., "Marty N" <martyn@> wrote:
>
>
>
> I just couldn't understand why anyone would go out of their way
> (poor pun) to use hardened strips and see it as an improvement
> rather than a potential risk.
>
> John
>
> Hi John:
>
> I liked the pun :)
>
> Here's my personal thought on the "why". 1.) The three cap
screws
that hold
> the gib opposed to the two dog points can provide zero preload
to
the
> fasteners, thus they are at will to move, won't hold
adjustment.
This is
> easy enough to take care of with a bit of blue Loctite. 2) The
two
dog
> points are not equidistant between cap screws, thus, even with
the
most
> meticulous setting the gib is bent to an arc if ever so slight
in
the best
> of cases and flat bowed silly in the worst of it. This means
that
only the
> leading and trailing edges are in contact with the ways
underside,
and only
> the outside "points" of that. This makes unit force over area
high
enough
> to, a) pierce the oil film b.) scrap the oil from the way.
This is
a bit
> more difficult to fix. Replacement of the dog points with
shims is
an
> alternative however the material the gib is made of is so soft
that in my
> first attempt at it with the half hard 260 brass I used dented
the
gib as
> easily as a finger nail dents pine boards. I had cut the brass
into two
> pieces, one each side of the center cap screw as the fine
adjustment needed
> here precluded, for me, individually making holes for all
shims in
the pack
> required. This leads to misalignment by the depth of the dent.
Later when I
> lapped the stock gibs it took nearly .004" after local contact
to
remove
> said dents. 3.) Even when a full shim is in play the material
is
so soft
> that it flexes silly under moderate pressures. 4.) When I
lapped
the gibs I
> took .008 of this little critters, after straightening, to get
full contact
> with the lapping plate, wavy, bent, bowed, dented...junk. 5.)
If
your going
> to fix it, then, fix it. 5.) Made from some hardened material,
such as A2,
> makes it stiff enough to loose the center cap, use a shim
without
> perforation where extremely fine adjustment can be made. 6)
Because my
> Southbend uses a gib 10" long held with two cap screws,
is .375"
thick and
> is hardened, ribbed iron and doesn't flex or bow over the
cantilever. So
> it's not a poke in the dark. 7.) On my machine built 5/26/1956
shows zilch
> for wear after 50 years. 8) I'll copy a proven design and
would
down to the
> cantilever if I had enough room :) 9.) Because hard steel on
iron
has 23%
> less friction than iron on brass. And hard chromed (what mine
spec
to) has
> half the static friction of iron on iron and will not gall. In
fact hard
> chrome on iron has about half the frictional coefficient dry
as
brass on
> iron does lubricated.
>
> Just thoughts.
>
> Marty
>
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