Source for Invar rod stock

Discussion in 'Clock Construction' started by Dave Barker, Jan 8, 2013.

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

    Dave Barker Registered User

    Aug 12, 2011
    10
    0
    1
    Hi, I've located a Stromberg master clock movement to use in my tallcase clock. I would like to make an Invar pendulum for it but I've been unable to find an online supplier willing to source a single rod. I'm looking for a 1/4 or 3/8 x ~40" rod. Does anyone know of a source?

    thanks,
    Dave
     
  2. glenhead

    glenhead Registered User
    NAWCC Member

    Nov 15, 2009
    1,024
    85
    48
    Telecom Engineer
    Williamson County, Texas
    Country Flag:
    Region Flag:
    The website for invaralloy.com states "no order too small". I've had good success with other specialty metals from calling places like that and talking to a real human. http://www.invaralloy.com/invar-rod-bar-sheet-plate.php

    If you have any success, please let us know what it costs - an Invar pendulum rod may have to be part of the regulator I'm going to build someday soon.

    Glen
     
  3. Allan Wolff

    Allan Wolff Moderator
    NAWCC Member

    Mar 17, 2005
    610
    34
    28
    Male
    Tulsa, OK
    Country Flag:
    Region Flag:
    #3 Allan Wolff, Feb 21, 2013
    Last edited: Feb 21, 2013
    I contacted two vendors regarding purchasing Invar rods. I am looking for 5/16" diameter rod; I think 1/4" might look too thin.

    The vendor that Glen referred to is also known as Ed Fagan Inc. They have a $150 minimum order.
    This will get you 18 feet of .250" diameter rod or 12 feet of .3125" (5/16") rod. Stock lengths are 6 ft. and 12 ft. and they will cut to shorter dimensions to reduce shipping. Shipping is not included in the $150 minimum order. Very nice and helpful people on the phone.

    National Electronic Alloys did not mention a minimum order, but you must buy a full standard length piece. I received a quote of $170 for 12 feet of .3125" rod. They will also cut to shorter lengths and shipping was not included in the quoted price.

    I would need to purchase enough Invar to make 3 pendulums. If we can get 3 of us together, I would be willing to take the lead on a group purchase of 5/16" rod. According to the USPS online shipping calculator, it would cost about $12 for me to ship a 48" rod via Priority mail ($10 standard mail). So it would cost about $62 for each rod. I will need to limit shipping to the US to avoid customs and foreign currency hassles. Send me a PM if you are interested.
    Allan
     
  4. John MacArthur

    John MacArthur Registered User
    NAWCC Member

    Feb 13, 2007
    309
    24
    18
     
  5. Jim DuBois

    Jim DuBois Registered User
    NAWCC Member Sponsor

    Jun 14, 2008
    2,492
    386
    83
    Male
    Magnolia, TX
    Country Flag:
    Region Flag:
    Some years ago I built a pendulum using an Invar rod for a master clock, replacing a true mercury compensated pendulum. I was pretty careful in my construction. When done time keeping was no better than with a temporary pendulum I had built using a wood rod. After some fairly careful analysis a few thoughts come to mind.

    1) the environment our clocks run in is much more controlled today than it was in the past. Today in my house the temperature where I kept this clock did not vary more than perhaps 1/2 degree day to day or from hi temp to low temp. In years past, pre central heat, that number could be 20 to 50 degrees, making accurate temperature compensation much more critical IMO.

    2)in the clock I had the overall accuracy was being limited by other than pendulum temperature compensation, namely gear train and escapement anomalies, as well as vibrations from the structure in which it resided. 1/2 degree of temperature change resulted in virtually no timekeeping change as measured by a Microset in hi resolution using a wooden rod. Invar was about the same/

    3) I believe a number of studies have found both carbon fiber and quartz rod to be more stable pendulum rod materials than Invar. Wood, well treated and moisture stabilized is also nearly as good as...as I recollect carbon fiber is also hydrostatic so it must be sealed also.

    4) using the very best construction techniques in what ever pendulum rod material selected may yield better results than keying on to any particular material. Also the "Q" of the bob material as well as the shape of the bob may limit the accuracy of the overall pendulum more than the rod material. I am suggesting that a perfectly compensated pendulum with a low "Q" clunky form bob will not yield as good of timekeeping as one may desire. A football shaped bob made of a very dense material seems to win the higher "Q" contests. An elliptical bob made of solid gold or tungsten on a quartz or carbon fiber rod maybe? I guess plutonium is out?
     
  6. Dave Barker

    Dave Barker Registered User

    Aug 12, 2011
    10
    0
    1
    Thanks for the message Allan, and thanks Jim for the analysis. I have wondered about the same as what you mentioned. It makes sense; I suspect you're right that other factors influence accuracy more these days. I think the use of Invar would be more for "bragging rights" than anything related to ultimate accuracy.

    I have my movement in the clock running with the original Stromberg pendulum, and my thought now is the pendulum is too short from an aesthetic viewpoint - it's a 1 second pendulum and movement but the case is very tall. Now I'm considering trying to make a "longer" 1 second pendulum - that is, one with an effective length of 39.1 inches but with a longer rod, a lighter bob and another weight somewhere along the length of the pendulum to keep the same period. I'm curious if anyone has done something similar and what the effects are on accuracy. Anyone?
     
  7. Allan Wolff

    Allan Wolff Moderator
    NAWCC Member

    Mar 17, 2005
    610
    34
    28
    Male
    Tulsa, OK
    Country Flag:
    Region Flag:
    Just a quick update. I have received commitments from 2 other members, so we have enough to meet the minimum order which I will be placing next week.

    John,
    Both vendors I contacted stock inch-diameter rod. If you want 1/4" or 5/16", just let me know.

    Jim,
    I agree with you on the points you make. My house varies by no more than 5 degrees F which does not seem to be enough to affect my modern Howard Miller grandfather clock enough to be noticeable. Of course it has a stamped steel fake gridiron pendulum, so I would expect a high degree of accuracy.;)

    Dave,
    I did something similar on the much shorter pendulum of the Pinwheel Skeleton Clock to give it a longer look but still run at the correct rate. I was not going for extreme accuracy though, just enough to get it within a minute or so between windings.

    Allan
     
  8. John MacArthur

    John MacArthur Registered User
    NAWCC Member

    Feb 13, 2007
    309
    24
    18
    Thanks Allan -- I'll pass for now. I should concentrate on "real" work for a while more, anyway.
    Johnny
     
  9. Allan Wolff

    Allan Wolff Moderator
    NAWCC Member

    Mar 17, 2005
    610
    34
    28
    Male
    Tulsa, OK
    Country Flag:
    Region Flag:
    #9 Allan Wolff, Feb 26, 2013
    Last edited: Feb 26, 2013
    Out of curiosity, I calculated the change in rate of a 1 second pendulum due to expansion of the pendulum rod. I did not try to take into account changes in the suspension, bob or any other components.
    These formulas are in "Excel-like" format so I don't have to mess with special symbols.

    Pendulum period =2*PI()*SQRT(L/9.80665); where L is the length of the pendulum in meters and 9.80665 is the acceleration of gravity.
    Given a period of 2 seconds (1 second beat rate), L is found to be .99362139 meters (rounded to 8 decimal places)

    dL = (a/1000000)*dT*L
    where dL=change in length due to temperature change, a=coefficient of linear expansion x10^-6 per degree Celsius, dT=change in temperature in C, L = original length of pendulum in meters.
    Wikipedia lists the coefficient of linear expansion for steel as 11 - 13 (I used 12) and Invar as 1.2

    Plugging these into an Excel spreadsheet yields the following results for a 1 degree C (1.8 F) temperature change.

    Material dL rate sec/day sec/week sec/month
    Steel.00001192352.000012-.518398-3.6287891-15.5519533
    Invar.00000119242.000001-.05184-.36287999-1.55519953


    Of course the bob and other pendulum components will be affected in various ways by the temperature change, but this give an indication as to the contribution of the pendulum rod. About a half second per day, or 3 minutes per year for a 1 degree C change for steel. An Invar pendulum rod will affect the rate by .05 seconds per day, or 18.25 seconds per year for each 1 degree C temperature change.
     
  10. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
    13,666
    63
    0
    Calif. USA
    Why not use quatrz rod. it is 1/4 of invar.
    There is another post talking about quartz rod.
    Tinker Dwight
     
  11. Allan Wolff

    Allan Wolff Moderator
    NAWCC Member

    Mar 17, 2005
    610
    34
    28
    Male
    Tulsa, OK
    Country Flag:
    Region Flag:
    I have been following the thread on using fused quartz rod with interest. I even obtained a quote from a company for a section of 10 mm solid rod, 48 inches long for $21.88 Since I have never worked with, I had them quote machining costs to cut it to 40 inches and drill a 1/8" cross hole near each end for a pin to fasten mounting hardware. Total cost was $72 which I think is reasonable. However, I have decided to use Invar for several reasons.
    I have no experience working with fused quartz and am afraid I will end up braking it.
    It is a type of glass and although you reported that it is pretty tough, it is still not as forgiving as metal.
    I don't think the clear rod will look appropriate in the clock I am building, maybe next time.
    I sincerely hope that someone who actually uses it will report on their experience in this forum so I don't have to figure it out on my own.
    Allan
     

Share This Page