Model Forum / General / Models / December 2006

Someone posted that last week in RCM. There are strips (out of PTFE)
available with a calibrated thickness that stick on one side. The brand
was ... wait ... here it is:

The discussion started here:
Message-ID: <yAqdh.2682$Ga1.2150@newssvr12.news.prodigy.net>

HTH,
Nick

    Attaching a strip of shim to the existing gib will probably work,
but only after a fashion, and a poor one at that.  Even assuming that your
gib is evenly worn along its length (very unlikely), the problem I found
when I tried attaching shim to the worn gibs of my Elliot mill, was to
produce an effective adhesive substrate of constant thickness.  A few thou
out here or there and I was as badly off as when I started!  I spent hours
experimenting with brass and stainless shimstock, superglue, epoxies and
rollers before playtime was abandoned and I called in the professionals!

    Unless you can get your gib built up with Turcite, or one of the
other PTFE-based materials, and reground, your time would probably be
better spent producing new gibs, not too difficult, especially if you have
access to  a surface grinder.

    Suitable cast iron strip is readily available and College
Engineering Supplies  (www.collegeengineering.co.uk/Materials/castiron.htm)
will cut to size.

    HTH
--

Chris Edwards (in deepest Dorset)      "....there *must* be an easier way!"

Not long after getting my mill many years ago and being dissatisfied with
the play on the long axis of the table I stripped the gib down to see what
was what. It was, like yours, at the end of its adjustment and no easy way
to solve it. Needing to use it again fairly soon I regret to say I folded up
some newspaper and stuffed it behind the gib. It's been like that quite
happily ever since. I did use a quality broadsheet though. Financial Times I
think it was :)

If I ever get the bumper sized box of roundtuits I need I might have a go at
fixing it properly one day. There's always something more pressing to attend
to though.
--
Dave Baker
Puma Race Engines
www.pumaracing.co.uk
Camp USA engineer minces about for high performance specialist (4,4,7)

Tim Hi,

Once in position the shim will not move far as Dave's newspaper shows.
In the past I have used brass shim stock which I cut to match the gib
strip including the adjustment slot (about twice as long as cutout to
stop shim crumpling when adjusting gib) and bent at >90 degrees a small
location strip (2-3mm wide) along the top edge (just clips over the top
edge of the gib (between non sliding contact face and casting) as there
is normally enough clearance between gib strip top and the moving
slide). I just clamped the shim between the gib strip and a length of
steel and folded the location edge over with a length of wood and a
hide face. This was belt and braces really just to stop any possibility
of the shim sliding down and out of the open dovetail. I used about 10
thou shim if I remember correctly and it worked fine for several years
until we shut the workshop down and I moved on.

I've also seen Paxolin used with great success as Andrew suggests. This
offers the advantage of being very slightly resilient so that the slide
can be adjusted at the worn area and the slide will tighten but not jam
at the non worn area, within reason of course. It will not compress
enough to overcome heavy wear but will allow for a few tenths.

By using thicker shimming at the non-wearing face it allows you to take
a lick with the surface grinder to remove any uneven wear on the
sliding contact face of the gib strip. Got to be worth a try before
making a whole new gib strip. Tim, I have to declare that these
"repairs" were both on milling machines but I don't see any great
difference to your setup although I don't know the DSG at all. Us
"youngsters" were never allowed to use those top class machines and had
to make do with the Harrisons and Colchesters, I think you had to be
there at least 20 years before being considered for such trust when
someone died! Those were the days, they keep telling me.

Best regards

Keith