New Chinese mill vs old high quality mill

There is a bit of confusion going on here. There is more than one material called "Turcite" (brand name). There are dozens of Rulon varieties, involving PTFE with more or less other things. Turcite A appears to be acetal-PTFE copolymer or blend (like Delrin AF brand), which sounds like what you are describing. Another (Turcite B) is what I suspect is PTFE alone, which is what the manufacturer suggests for machine ways (they also call it "Slydway").

Plenty of evidence in the mfr literature. Polymers have certain properties that improve life vs cast iron ways. Just lowering the coefficient of friction significantly has to improve wear dramatically. Since you have the metal underneath a thin layer of polymer, you get the best of both, strength and rigidity of metal with lubricity and wear of the polymer.

But the blockbuster benefit is that the cast iron components of the bearing just doesn't wear at all, just the polymer layer, at least in our lifetimes. When the polymer layer wears out of alignment, it is replaceable in a relatively simple process. Compared to having to rescrape and realign metal, that is an *immense* economy.

By the way, this is what I've been testing, MSC item 32017774:

This 0.03125" thick and bonds with ordinary epoxy. At $27 for 2 sq ft you have plenty to do a Bridgeport saddle with several retries.

No. I've attempted to use teflon for small bearings, with poor results.

Another reason to stay away from pure teflon is, it is very tough to bond it using any regular adhesives.

Probably most commercial engineering polymers will show mechanical properties somewhat similar to teflon, though not the friction co-efficients, obviously.

My best guess would be to use teflon-loaded delrin available inexpensively from mcmcaster carr. It will exhibit pretty much the same slide characteristics as pure teflon, but will not cold flow.

Jim

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You can't be referring to the MSC item I cited, which is treated on one face to be bondable with ordinary epoxy.

Delrin (trademark for acetal, capitals, likewise Teflon for PTFE) AF (presumably abbreviation for "anti-friction", namely acetal with PTFE component) does improve the structural properties, and comes close to pure PTFE for dynamic friction, but does not come close to pure PTFE for the static friction ("stiction"). Getting down around 0.04 static COF would seem to be a huge improvement for CNC movements like tangents of curves that have minimal motion in one axis vs another, where stiction causes staircasing. From what I read this is what many CNC machine ways use for just that purpose.

I just discovered this MSDS from the mfr which states the Turcite B is indeed just PTFE:

I don't see it saying Turcite B is just PTFE. True, in section 2 it lists nothing besides PTFE (polytetrafluoroethylene) and Chromium III Compound (0.5% by wt.) as hazardous ingredients. But in section 8 it says "This compound contains Chromium III compounds [...] and 25% Cu metal".

-jiw

MSDSs are government (regulatory) documents and you have to be careful interpreting them for physical facts . There is just a tiny bit of the metallic portion (0.5% total stated on the first page). This I suspect is just the very thin coating on one face made by converting the pure PTFE to a thin bondable layer. This is what makes the product glueable with epoxy. Otherwise, nothing sticks to PTFE. It helps to have seen this stuff, snow white PTFE on one face, a muddy brown on the other (the uncolored MSC version).

The "25% Cu" appears to be a misprint. It should have been enclosed in the parenthesis just preceding. That is, of the 0.5 percent chromium III compounds, 25 percent of the weight of those compounds consist of Cu.

The point is, the bulk polymer is pure PTFE, not acetal, or something else.

See my earlier comment on the specific gravity of Turcite B. The higher density would be consistent with a metal filled PTFE.

Ned Simmons

Right, I was confusing another's comment citing "turcite" as if it were a single thing.

You did say they were filled or reinforced PTFE. I found one reference today that identified one Rulon as ECTFE.

See my earlier reference to the MSDS, which doesn't list any metal content in any proportion that would increase density.

But if you're right, then that would require about 10 to 15 percent metal by volume, depending on the metal.

No, I said "copolymer or blend" (too lazy to check which). You're correct, it is the latter.

So what is it, then?

They claim that is actually a benefit, that particles embed at or below the surface so as to encapsulate and not wear the opposing metal.

And of course this is a problem with metal/metal bearings. There was a deep score in the Bridgeport knee way I'm rescraping, and I eventually discovered (only by the disassembly and scraping process) a single tiny grain of carbide or diamond had been embedded in the opposing surface.

Say, have a look at:

Turcite T47 == Bronze-filled PTFE w/ sp gr 3.02 to 3.14.

Lots more here:

Seems the trademark "Turcite" applies to anything, pure PTFE, UHMW-PE, bronze-filled, graphite-filled, carbon fiber, etc.

But isn't the ability of softer way sliders a plus? Then the abrasive particle will simply embed deeper as time goes on, whereas in cast iron/cast iron systems, it will embed in something *hard* and keep on wearing the bed ways?

Has anyone created bed sliders out if, say, brass or bronze? If not, the reason probably is that they get charged as a lap does, and will wear the harder bed rapidly.

Jim

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-Rulon 142 not an insulator

-It's "TURQUOISE in color with a bronze tint."

-"Rulon ® is the Saint Gobain Performance Plastics tradename for a family of reinforced proprietary PTFE compounds."

-It's specific gravity is higher than any plastic I'm aware of.

All admittedly circumstantial evidence, but I'd have to say it's most likely a metal filled PTFE. Taking into account the color and the Turcite B MSDS, probably a copper based filler.

Ned Simmons

Makes you wonder why they're right out front with this and there's so little info on the composition of Turcite B.

That's not too unusual. One of the best references on the common engineering plastics I have is put out by Erta. They list properties of acetal, various nylons, PET, etc., but they're all called Erta(something).

Ned Simmons

I've heard this claim for many different bearing materials over the years, and while it makes sense to me that if the offending particle is hard enough to wear a bearing surface it's likely to be hard enough to embed in the mating surface. And it makes sense if you're going to have an embedded particle, it's better to have it stuck in a softer rather than harder matrix. Nevertheless, it always troubles me.

Quite a few years ago I was in the marine hardware manufacturing business. One of our product lines was stuffing boxes and stern bearings. We used a composite plastic bearing rather the traditional rubber cutless bearings in our stern bearings. Initially, most of these were installed in lobster boats here in Maine where deep water and muddy bottom is typical. When we started selling more into southern New England, where shallower water is the norm and sandy bottom more common, we started getting complaints about excessive shaft wear. I never got a definitive answer, but always assumed that the sand was embedding in the plastic bearing, rather than flushing thru like the rubber bearings. I realize this isn't a very good analogy, but it's always made me leary of this sort of claim.

It looks like the company now offers a composition specifically for conditions where sand is suspended in the water.

I'm quite sure my old Rathbone chucker had bronze bushings running on round ways, but that was a pretty unique machine. It was a clone of a Hardinge chucker in that it used the same turret and spindle tooling, but looked more like the Monarch chuckers. In any case, having round ways made it easier to exclude crud from the way bushings, so the bronze didn't seem to be a problem. It was 40 years old when I sold it, and it could easily work to a few tenths.

Ned Simmons

I could also *highly* recommend a book called "Engineering Polymer Sourcebook." By, umm... hmm. Forgot the author's name. If there is interest I will post it up in the morning, from work.

Jim

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Wasn't the abridged version in _The Graduate_?

I'm loving those VFD's... Felt like Merlin himself when I hooked the latest one up and it really produced 220 three phase from an 115 one phase household current outlet... Sure seems like magic.

So much of single phase motors for me.

:^)

"Engineering Polymer Sourcebook" by Raymond B. Seymour, McGraw Hill, ISBN 0-07-056360-8.

Jim

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