I have a 24" slide in a 3/4" deep dovetail that the back of the dovetail was
worn after only forty years of use. No warrantee, I checked. I milled the
dovetail 1/8" deeper to get it straight and glued a 1/8" brass strip in with
JB Weld. That lasted 18 months before the JB let go. The brass was worn
.050" in the center and less at the ends.
Is there a better material I can use that the glue will still hold? My
other option is to mill it square and make a gib and bolt it in. It's a
BITCH to jig-up on the mill and there's not a lot of meat to spare so, I'm
inclined to put a new shim in, but not every year.
Any of the hard bearing bronzes -- phosphor bronze, aluminum bronze, or
possibly manganese bronze -- will work-harden on the bearing surface and
hold up much better than yellow brass.
As for glue, you will never have an easy time of gluing a copper-bearing
alloy. But you'll get a reasonable job if you use the "scratch-in" or
"sand-in" technique. Are you familiar with it? I can describe it if you
want. What you need to do is to simultaneously sand through the oxide layer,
apply epoxy, and keep it flooded so that the surface is never exposed to
air. It's actually pretty simple.
If you want to select a bronze appropriate for the job, and if you can order
a piece to spec, check your local engineering (college) library for a copy
of _Metals Handbook_, the nonferrous edition. Or fish around on the Web. It
probably will be a lot quicker.
Do you think I can use the technique to put a strip of "Amco Bronze" in
there? Tough stuff but untill now, I didn't think I could get it to hold.
I'm in no hurry for a change, I have a spare head / dovetail in perfect
Rather than gluing in place, could you silver-braze the ends, or
perhaps silverbraze or bend tabs on the ends and secure the tabs with
machine screws into the ends of the dovetail? Seems like it only
needs to be kept from moving longitudinally because there isn't
anywhere it can go in other directions.
I also looked for continuous flat ground 1/8" cast iron strip but had
no luck in a quicky search. Seems like the original machine was CI
on CI, so a gib made of CI should work if you can find such stock.
Heck, they make piston rings out of cast iron, right? Anyone know
what the gibs in lathes and mills are made of?
Yes, probably. The thing that makes it hard to stick epoxy (or other
high-strength, rigid adhesives) to most metals is that you're gluing to the
oxide layer, not to the metal. On aluminum, stainless steel, or copper
alloys, you can sand off the oxide and it begins to form again, literally,
within seconds. If you get under that oxide somehow and keep the metal from
re-oxidizing you have a fighting chance. That's what the PAA anodizing
pre-adhesive treatment for aluminum is all about.
There are variations on the scratch-in method but basically it's just this:
Clean your metal and sand it lightly. I prefer 220 grade wet/dry for this
and the following treatment, but any fine sandpaper will do. Mix some epoxy
(100% solids, industrial-grade epoxy adhesive is best; I don't trust filled
epoxies like JB Weld for all-out adhesion) and smear a layer on the metal.
Start sanding, right through the epoxy. You don't have to sand very much;
you just have to be thorough. As the epoxy wipes off, glob more on. You want
the metal covered with epoxy. If air gets to it, you aren't using enough
After you've sanded the metal without letting it get dry, take a small rag,
wad it up, and smear a thick layer of epoxy on one big spot on the wad. Wipe
the metal lightly, in one direction only, keeping a wet edge ahead of the
rag. Pour on a little more epoxy if required. What you're doing here is
wiping off the filthy epoxy you sanded with and replacing it with a fairly
You can apply the epoxy-covered part directly to the part you're bonding to
at this point, or wait until the epoxy starts to gel. If you wait too long
you'll have to sand the surface of the hardened epoxy and you'll only get a
mechanical bond, not a chemical one.
Some people like to use the abrasive Scotchbrite pads for this because they
hold plenty of epoxy. I've used it on aluminum and it seems to work fine,
but I've been using wet/dry for close to 30 years with good results.
Despite all the pouring and gobbing, you really don't use very much epoxy
for this trick. You just need enough to be sure no air gets to the metal.
You develop a touch for keeping a layer of epoxy on there.
A couple of other things: copper alloys develop oxide very quickly, and it's
a poorly adhering oxide. You really, really have to be careful to keep the
epoxy covering the freshly sanded metal with copper, brass, or bronze.
Be aware that good epoxies form their strongest bond with a gap of 0.003 in.
to 0.005 in. between the glued surfaces. So if some sanding grit gets left
in the epoxy it won't hurt anything. It may actually improve the bond by
helping to keep a slight gap.
Finally, if you're gluing to cast iron and if there's been any oil on the
c.i., good luck. You can try wiping multiple times with acetone but even
that is problematic. Maybe somebody else has a tip for getting iron clean
enough to bond to. I'd at least scratch-in some epoxy with a Scotchbrite pad
on the iron.
Credit goes to the Gougeon Brothers for this trick, which they used for
gluing stainless steel deck fittings to wooden boats over 30 years ago. I've
noticed that others have picked up on it and used it in a wide range of
applications over the years.
Regarding the tricks for gluing metal with epoxy, I should mention a couple
of other things: Don't clamp the parts. It's easy to starve a joint when
you're gluing metal, and, with epoxy, the peel- and cleavage strength of the
joint will go to hell if the joint is starved.
Experts at metal bonding sometimes place little bits of 0.003" shim stock or
wire in the joint to keep the parts separated while the epoxy cures. You
just leave them in the joint. They don't hurt anything.
I think you will have better luck using a polyurethane adhesive to
glue anything with some oil on it. I am not sure about one part
polyurethane adhesives as gorilla glue, but the two part polyurethane
adhesives were touted for oil tolerance about twenty years ago.
Just "pickle" the surface for a while with a hot strong alkali like lye or
saturated TSP solution.
Most of the oil near the surface will saponify, and be removable with water.
Pre-heating the metal will help draw the lye bath into the pores as the
metal cools. This works slowly with petroleum oils and pretty rapidly with
vegetable oils. Keep the surface wet with the alkali until it becomes
cloudy and filled with soap from the reaction.
If you're worried about leaving alkali residues, you can neutralize with
vinegar, then wash again with clear water.
==================Your might take a look at
apply over the gib? also other dovetail and wear strips at
Let us know how things work out.
Unka' George (George McDuffee)
Only in Britain could it be thought
a defect to be "too clever by half."
The probability is that too many people
are too stupid by three-quarters.
John Major (b. 1943),
British Conservative politician, prime minister.
Quoted in: Observer (London, 7 July 1991).
I just ordered 50' from Garland. I talked to an engineer there and
explained the application. The stuff if $1 a foot. Thanks!
I would think about the same stuff people use on worn lathe beds.
Philadelphia Resins makes one and I think another is Moglich or
something close. Yet another option is Ultra High Molecular Weight
Polyethylene ( UHMW )tape or material. Depends on how think you need
it. They use UHMW to line dump truck beds as it is a lot more
resistant to abrasion than steel. Google on " UHMW poly " and you will
find more sources than you know what to do with them.
Like your original vendor, I won't give you a warrentee. You could put
1/8 thick stuff with countersunk brass screws. It should wear much
better than the brass.
Turcite B, Garlock Multifil or Rulon something-or-other. They're teflon
filled composites that are epoxied to sliding surfaces.
The stuff is expensive, but I have quite a lot of misc pieces. Will
trade for brushes, if you're interested.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.