Teflon (plastic) bushing related photos, with wear

Discussion in 'Wood Movement Clocks' started by Jim DuBois, Sep 1, 2015.

  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  1. Jim DuBois

    Jim DuBois Registered User
    NAWCC Member Sponsor

    Jun 14, 2008
    2,823
    565
    113
    Male
    Magnolia, TX
    Country Flag:
    Region Flag:
    #1 Jim DuBois, Sep 1, 2015
    Last edited by a moderator: Dec 31, 2017
    I offer the following photos regarding past discussions of using plastic/Teflon bushings in wood works clocks. I am not certain we can draw many conclusions, other than Teflon suffers from the same wear as other bushing materials, at some rate, perhaps less than some other materials.

    This example is particularly of concern as the shaft is .100" stainless steel, and there is a great amount of wear as can be seen on both ends of the shaft. The Teflon (not certain as to the composition of the bushing, spec sheet does not call out the material) bushing is an insert in a plastic housing. This amount of wear occurred in approximately 4380 hrs of operation, not a clockworks device, but running under a very light load. Total revolutions of approximately 75,000,000 in an uncontrolled TX environment, which certainly includes some very abrasive dust. However, that would equate to nearly 150 years of a clock running with the bushing located in the escape wheel location….so, while wear occurs in plastic bushings its rate may preclude any major concern to us when used in WW clocks lower in the train…… my conclusion, if we use proper plastic bushings wear should not be an issue in our lifetimes…..I still prefer wood, brass, or bone bushings, depending on what was in the clock originally, but a proper material plastic bushing should last a very long time.

    stainless worn .jpg stainless steel worn 1.jpg plastic bearing worn.jpg
     
    glenhead likes this.
  2. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    Jim, those are interesting images. If my fuzzy math is correct that works out to 285 rpm which is a lot faster than anything in a clock turns. Just looking at the damage to the stainless shaft I seriously doubt that this was caused by the Teflon bushing (or perhaps it was Nylon or HDPE which would not matter). I believe it almost certainly had to be caused by some abrasive material hard enough to cut stainless. Given the same speed, load, and environmental conditions, I suspect that a brass, bone, nylon, delrin, HDPE, or almost any other material to fail.

    Regarding bushing worn (wooden) pivot holes in wooden clocks, we know that wood works and has a track record exceeding a hundred years. We also know that wood wears out and that steel pivots running in wooden pivot holes also wear, probably from abrasive dust rather than from the wood. "Plastics" as bearing materials is a relatively new concept and has proven to be do very well in many industrial applications and not so well in others. They generally do poorly under high speeds and loads that can potentially produce heat, but do well at lower speeds and loads especially in areas that cannot be easily accessed for lubrication, and in the food industry where lubrication products could contaminate the product. I think wood will always be an acceptable, or preferred by some, material for bushing wooden movements although there have been differing opinions regarding which type of wood may be best.

    "Plastic" bushings/bearings are the rule in quartz clocks and while we don't know how many will be around for a hundred years, the potential has been demonstrated and "plastics" are improving all the time. I've been trying Delrin-AF in some wooden clocks and so far the material seems to be doing well at about 8-years out. It is perhaps easier to work with than wood, requires the removal of less original material, has a very smooth low-friction surface, requires no oil, and will not corrode like brass. Like all other material, it will wear out in time and cannot prevent abrasive damage. I hope to tear down some of these clocks at 10-year intervals to assess how the Delrin-AF bushings are wearing. So far I have noticed no change in performance and the clocks are run all the time.

    Time will tell, as is ture with so many things.

    RC
     
  3. Jim DuBois

    Jim DuBois Registered User
    NAWCC Member Sponsor

    Jun 14, 2008
    2,823
    565
    113
    Male
    Magnolia, TX
    Country Flag:
    Region Flag:
    The "dust" in the environment hereabouts is extremely abrasive. It has a high percentage of very fine sand, not a real surprise considering much of my front yard is sand, so poor in soil content it won't even grow crab grass. That is how the stainless shafting got cut up to the extent it did. And yes, it rotates much faster than any part in a clock in this operation. I was surprised at the amount of wear on the stainless, not so much surprised on the wear in the plastic bushings. By the way, both ends of the shafting had similar wear on the bearing surfaces. I don't know if the plastic bearing was better or worse at retaining the abrasives than say brass or other harder materials. I suspect that in this application the plastic bearing would be better than other possible choices, but that is only a guess on my part.

    I posted this mostly as I found it interesting and based on past discussions I thought others might find it to be of interest also. By the way, I procured a new part and the replacement part no longer has an inserted bearing. It is all one piece of cast plastic. I suspect this one will not last even 6 years, just a guess on my part. I could be wrong. I will do a post mortem on the new part when it fails and report the same.
     
  4. glenhead

    glenhead Registered User
    NAWCC Member

    Nov 15, 2009
    1,121
    163
    63
    Telecom Engineer
    Williamson County, Texas
    Country Flag:
    Region Flag:
    I believe this was a great test, Jim. Steel on Teflon has a coefficient of friction of about 0.04; the only other combination I could find that even came close was hard steel on hard steel with grease. Every other F[SUB]c[/SUB] I could find was at least five times that amount. Yes, running it at a higher speed will generate a tiny bit more heat, which will increase wear a tiny bit, but all that does is provide further proof of the efficacy of a Teflon bearing surface with a steel pivot.

    Fascinating results! Thanks!

    Glen
     
  5. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    There is no question that Teflon if great stuff for low friction bearings. It does tend to be rather soft which is not great where the contact area is small and the load high. I considered trying it in a wooden clock but never did. Perhaps someone has? Delrin-AF is Delrin (an Acetal polymer) with I believe about 12% Teflon fill. I also considered a moly disulfide impregnated Nylon material. Got some but never tried it.

    RC
     
  6. MartinM

    MartinM Registered User

    Jun 24, 2011
    3,050
    101
    63
    Male
    Medical Insurance Systems Analyst
    El Dorado, CA
    Country Flag:
    Region Flag:
    I was having problems with urethane suspension bushings in my mini-buggy, so went to Nylon and they worked MUCH better; But, still needed replacing after a couple of years. I went with the moly-impregnated Tecamid and never had another problem. As far as heat goes, it machines just like Nylon, so melts much more readily than Teflon and has a service temp of about half that of Teflon or ~250 degrees.. And, I'd be careful using it in a regular clock as Nylon does have a tendency to hold water. In a wooden clock, it may not be a factor.
    Here's an opinion piece with some of the plusses and minuses for a few materials.
    http://info.craftechind.com/blog/bid/259158/Top-5-Materials-for-Plastic-Bearings-Used-on-Metal-Surfaces
     
  7. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    Tecamid MDS - Molybdenum Disulfide Filled (MDS) is an extruded "moly" filled nylon 6/6, which is gray in color. The 1/4" rod that I purchased seemed a bit more flexible then the Delrin-AF. It would be interesting to try sometime if I can pick up a wood movement for near nothing. For sure it has interesting propertied. The Delrin-AF that I use is brownish in color but I believe Delrin comes in various colors.

    RC
     
  8. David S

    David S Registered User
    NAWCC Member

    Dec 18, 2011
    7,195
    245
    63
    Male
    Professional Engineer - Retired
    Brockville, On Canada
    Country Flag:
    Region Flag:
    Hi folks I know this is an old thread but I thought I would try and add some more information.

    A few years ago I ordered some polymeric bushings from a company called IGUS. They have all sorts of materials depending on the application. I was interested in finding bearing material that doesn't need lubrication, since lubricant can trap the dust and dirt in the atmosphere.

    Well it is only recently that I decided to try and see how they may work. Now I am a metal clock guy and not a wooden movement one. I am somewhat reluctant to post in my clock repair forum since the purists may want to lynch me.

    Anyway I contacted my rep here at IGUS to discuss our tribology situation. That is pretty much stopped shafts, some reciprocating. This is one of the worst tribology applications.

    The representative recommend some of their pre made bushing M250 and for custom machining their J series.

    For my experiment I have an old OG T&S movement sitting around with no weights and missing parts, and worn pivot holes on T2 and E/W. I have previously replaced the bushings on both front and back with KWM bushings and it ran ok. For this experiment I push them out and opened up the holes to 3 mm by drilling followed by a 3 mm reamer since the M250 bushings I had were 3.1 mm OD. For T2 F&B I machined the 10 mm od J bar stock to make 3.1 mm od bushings.

    First let me say that the J bar stock machines beautifully with HSS tooling and even facing with carbide inserts.

    I drilled a pilot hole for the pivot in the lathe, parted it off, pressed it in and drilled to size with sharp carbide pcb drills, trimmed the excess bushing with single sided razor blade, and chamfered the ID both sides.

    If I had to do it again..and perhaps will I wouldn't use the M250 pre made bushings since their coefficient of friction is higher.

    IGUS readily provides small quantities. I ordered three 10 mm diameter 300mm long pieces of J bearing stock and they were only about
    $3 each.

    My purpose for posting is to start a conversation and perhaps suggest an alternative for those that want to replace bushings in movements and not worry about lubrication.

    J machined for T2.jpg M250 for Escape wheel.jpg

    I have no idea how this movement ran before, so really can't compare or attest to whether these are better or worse than plan brass. However it is running. I haven't installed the strike side.

    When I was working in design I am aware of teflon, and delrin bearings, but this is the first time I have experimented with engineered polymeric bearing materials.

    I would be interested if anyone else has tried some of the newer bearing materials that don't need external lubrication.

    David
     
  9. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    Thanks for posting this information. It will be interesting to see how your project holds up over time. I'm wondering is this wouldn't be best as a new thread as the "old" title doesn't give much of a clue of the topic? Probably would get more reads in the "clock repair" section as your project is not specifically for wooden movements, although it has implications for both. Ironically, wooden movements have been using "self-lubricating" bearings for over 200 years!

    I'm not sure exactly what "engineered polymeric bearing materials" is? I looked on the IGUS website and didn't find anything about the specific properties of their material other than that it released bits of "solid lubricant" and their "sales claims" for the material. I'm wondering how this material compares to Teflon, Nylon, Delrin, etc.?

    I've used Delrin-AF in wooden movements where I machine a groove or notch in the OD where glue is used to keep the bearing in place. I'm wondering how you were able to retain the IGUS bearings in the brass plates of that old OG? Most "plastics" tend to deform under pressure over time. I'm not sure how well a "friction fit" will hold up. It seems that the properties that make a good bearing material (low coefficient of friction etc.) would also make it difficult to retain.

    RC
     
  10. David S

    David S Registered User
    NAWCC Member

    Dec 18, 2011
    7,195
    245
    63
    Male
    Professional Engineer - Retired
    Brockville, On Canada
    Country Flag:
    Region Flag:
    #10 David S, Jul 7, 2016
    Last edited: Jul 7, 2016
    Hi RC,

    Your concerns in your last paragraph are also mine. For starters I decided to just make an interference fit of about 0.1 mm for the J bar stock. The initial press fit "felt good", but we shall see. The plate is only about 1.4 mm thick, so indeed I am concerned about retention.

    And yes the IGUS site takes some getting used to, however there is considerable information there other than the typical marketing how great they are stuff,if you can find it.

    Hopefully this link works for you as an example of the stuff I am trying.

    http://www.igus.com/contentData/Product_Files/Download/pdf/J_1.pdf

    Here is a more complete list of other materials with properties and machining information

    http://www.igus.com/contentData/Product_Files/Download/pdf/Barstock%20brochure%202015.pdf

    The reason I posted here is because the wooden plates are much thicker and I know some here have used polymeric bushings in this application.

    However as I do a bit more, I think it is a good suggestion to start a new thread, mainly so I can get more dialogue going and hopefully learn faster. When I talked to the applications person here in Canada they couldn't give me any applications where these were being used in instruments...perhaps that says something in itself.

    David
     
  11. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    Thanks for the PDF link. I'll look that over when I find a few free minutes. When you are in contact with the representative again, could you ask if there is any adhesive or bonding system that can be used to hold these bushings in place? If these bushings work out in your brass movement they should also work in wood if we can keep them in place.

    RC
     
  12. David S

    David S Registered User
    NAWCC Member

    Dec 18, 2011
    7,195
    245
    63
    Male
    Professional Engineer - Retired
    Brockville, On Canada
    Country Flag:
    Region Flag:
    I emailed the rep and here is the reply.

    "Glad to hear that the samples arrived and you've had a chance to try them out.
    The 0.1mm interference is fine and because of the interference fit, you won't need any adhesives to retain the fit."

    We shall see.

    David
     
  13. gleber

    gleber Registered User

    Jun 15, 2015
    1,732
    193
    63
    Male
    Underwater Robotics Expert
    Downingtown, Pennsylvania USA
    Country Flag:
    Region Flag:
    I think if you chamfered the hole with a shallow chamfer to a point in the middle of the plate and pressed the bushing in, even if the bushing deforms over time, it would be hard to fall out. A convex chamfer in the bushing and matching concave chamfer on the hole in the plate seems like it would work to, but be harder to make.

    Tom
     
  14. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    The down side of what you propose is that without parallel sides in the hole there will be less friction to grip the bushing so it may be more inclined to come out. It will be interesting to how David's clock holds up over time.

    RC
     
  15. MartinM

    MartinM Registered User

    Jun 24, 2011
    3,050
    101
    63
    Male
    Medical Insurance Systems Analyst
    El Dorado, CA
    Country Flag:
    Region Flag:
    Actually, a case could be made that there is more contact area. Kind of like the concept that grooved brake rotors on a car actually have more surface area usable for applying friction.
    Maybe just increasing the interference by a small amount would assure that it doesn't ever move.
     
  16. David S

    David S Registered User
    NAWCC Member

    Dec 18, 2011
    7,195
    245
    63
    Male
    Professional Engineer - Retired
    Brockville, On Canada
    Country Flag:
    Region Flag:
    Guys I appreciate the discussion. Let me know if we should start a new thread or perhaps even rename this one (if it is possible) to keep all the polymeric bushing experiences together.

    Retention is my concern as well. Prior to just doing a plain interference fit I was thinking of all sorts of ways to put features in the bushing for retention.

    It would be nice to come up with an accelerated life test. I was wondering about some temperature cycling and then doing a push out force. Trouble is I have no idea what temperatures would correlate to life in the application.

    BTW I have no personal interest in IGUS. I happened to find them on line, they didn't mind small quantity orders and I felt the J bar stock was very reasonably priced.

    David
     
  17. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    The amount of friction is going to be dependent on the surface area and the force applied. My guess is (and it is a guess as one would need more information and some math that's beyond my pay grade to demonstrate a proof) that increasing the interference beyond a certain point will cause the plastic material to yield and deform rather than increasing the grip. The empirical test of a bushing is to see how much force is required to remove it.

    RC
     
  18. FDelGreco

    FDelGreco Registered User
    NAWCC Star Fellow Sponsor NAWCC Diamond Member

    Aug 28, 2000
    2,018
    94
    48
    Male
    Retired chemical engineer
    Novelty, OH
    Country Flag:
    Region Flag:
    Actually, friction is independent of surface area. When I was in my college physics class and the professor said that, I questioned him but he was right.

    See http://physics.info/friction/

    Frank
     
  19. David S

    David S Registered User
    NAWCC Member

    Dec 18, 2011
    7,195
    245
    63
    Male
    Professional Engineer - Retired
    Brockville, On Canada
    Country Flag:
    Region Flag:
    Just to be clear my reasons for rejuvenating this thread are to see if there have been any improvements in polymeric bushings that could give some advantages regarding longevity of replaceable bushings. I like the idea of no free lubricants that could collect dust etc.

    Regarding the comment on friction, I feel that has to do with a mass on a surface. And yes the force of friction is not dependent on surface area. However we are talking about a press fit in this application. And I believe that the push out force..or retention force if you will.. is going to be proportional to the amount of interference.

    Again I want a discussion to find out if anyone else has had experiences with polymeric bushings in clock applications.

    David
     
  20. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
    10,236
    835
    113
    Male
    Trappe, Md.
    Country Flag:
    Region Flag:
    I should have said force applied per square inch. That's why trucks have larger brake shoe surfaces than cars. Place 5 lbs of brick on a 4 sq ft piece of plywood on the floor and try to pull it. Then make it 50 lbs of brick and try. It will be obvious there is a lot more force required to pull the board.

    RC
     

Share This Page