Bearing material for a dovetail shim

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.

Reply to
Tom Gardner
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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.

-- Ed Huntress

Reply to
Ed Huntress

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 shape.

Reply to
Tom Gardner

=================== Your might take a look at

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over the gib? also other dovetail and wear strips at bottom.

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).

Reply to
F. George McDuffee

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apply over the gib? also other dovetail and wear strips at

Oh, I LIKE that! I'll talk to them to see if it's oil resistant.

Reply to
Tom Gardner

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?

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Reply to
Don Foreman

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.

Dan

Reply to
dcaster

Turcite B, Garlock Multifil or Rulon something-or-other. They're teflon filled composites that are epoxied to sliding surfaces.

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The stuff is expensive, but I have quite a lot of misc pieces. Will trade for brushes, if you're interested.

Ned Simmons

Reply to
Ned Simmons

I would first check the oiling system and then glue in a piece of turcite or rulan for a length of about 8 inches on each end. The turcite will hold up better than brass and has a lower coeficient of friction. After you put it in you should cut oil grooves in it.. in fact you should do that to the brass too if you use it.

John

Reply to
John

The bearing material comes in all different thicknesses and sizes. It is easy to use and many new machines use it under their ways.

John

Reply to
John

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 epoxy.

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 clean layer.

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.

-- Ed Huntress

Reply to
Ed Huntress

Taper gib with a screw to force it into the taper to take up the slack .

HF 7 by 10" lather has not taper gibs , a pain to adjust ,

but all the larger China stuff uses taper gib . It is high carbon cast iron alais Semi-steel , the carbon lubs the ways and slides ....

Reply to
werty

Taper gib with a screw to force it into the taper to take up the slack .

HF 7 by 10" lather has not taper gibs , a pain to adjust ,

but all the larger China stuff uses taper gib . It is high carbon cast iron alais Semi-steel , the carbon lubs the ways and slides ....

Reply to
werty

Bondable Teflon sheet from MSC. Relatively inexpensive, easy to install, and durable. Working very well in my rescraped Bridgeport ways.

Reply to
Richard J Kinch

Actually, the slide is hard, doesn't make sense does it. The new heads have bronze alloy front and back and inserts in the base.

Reply to
Tom Gardner

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apply over the gib? also other dovetail and wear strips at

I just ordered 50' from Garland. I talked to an engineer there and explained the application. The stuff if $1 a foot. Thanks!

Reply to
Tom Gardner

If it's cast iron/steel sliding against cast iron, then use gauge plate or carbon steel shim stock held on with Loctite 603. The 603 is oil resisting and the steel stock will have very similar thermal expansion to the iron or steel that it's bonded to. It's worked for me on old, oiled cast iron.

Mark Rand RTFM

Reply to
Mark Rand

Great, give me a call, toll-free 888-411-3265 after noon, before 7:30 PM EST

Reply to
Tom Gardner

I'll call next week. In the meantime, if you can give some idea of what size and thickness you need I'll rifle thru the box of pieces. I believe I have mostly 1/32 and 1/16 thick, but there's also some 1/64 and 1/8" in there.

Ned Simmons

Reply to
Ned Simmons

Or, rather than bending, attach separate tabs. The "bearing" could just float. Randy

Reply to
Randy Replogle

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