[Jewelry making - Article 00096] - Re: [Orchid] Cavallin vs. Durston Rolling Mills

[James Binnion]

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    I have both Cavllin and Durston mills and up until recently I would
    have said either one would be fine. However on my Durston D4 158
    (purchased new in 2000)  I just had one of the helical gears that
    drive the flat rolls break a tooth off at the root of the tooth. The
    flat rolls on this mill do not get much of a workout (we use the
    wire rolls every day) as I have a 100 mm Cavallin power mill that is
    used for most flat stock but I needed a wider section of stock the
    other day and was using the flat rolls on the Durston . In the
    process of rolling this flat stock there was a noise of something
    hitting the floor and I thought that something had fallen off the
    bench next to the mill, all of a sudden the crank on the mill
    stopped and would not continue forward. I backed the stock out of
    the mill and tried to turn the crank forward and it stopped again at
    the same point so I thought that there must be something wrong with
    the gears and pulled the cover of the reduction gear first and
    started to disassemble it to look for what could be wrong. During
    this process I did not find anything in the reduction gears that was
    causing the problem but did see something that truly disturbed me.
    The gears are coupled to the various shafts in the mill with key
    slots in both the shaft and gear and keys that lock the two
    together. One shaft has two gears on the same shaft and sharing a
    key. The outer gear appeared to have been misaligned when it was
    assembled and the person who assembled it forced the gear on the
    shaft rather than align it properly. this resulted in a galled gear
    and a offset key. 

    After further inspection of the reduction gears I determined that
    the problem was not in the reduction gears and pulled the cover on
    the drive gear side. Here the broken tooth helical gear was obvious.
    I then looked on the floor for the thing that had made the falling
    noise earlier and found the tooth from the gear. In removing the
    broken gear from the shaft I found it to be almost impossible to
    remove. It required a great amount of force on the gear puller to
    separate it from the shaft.Once I had it off the shaft the reason
    was obvious the key was not filled to fit the key slot of the gear
    and the gear had been forced on the shaft in such a way as to wedge
    a piece of key between the shaft and the id. of the gear next to the
    key slot. I am not certain of the distortion of the gear caused by
    this brute force assembly process is what caused it to fail but I
    would not be surprised if it was a contributing factor. This lack of
    care in the assembly of a precision and expensive machine disturbed
    me as the Durston is supposed to be a top quality mill and the lack
    of care in the assembly process does not fit in with this
    perception. I am still awaiting a replacement gear for my mill right
    now so it is still out of commission. I have not had any gear
    problems with my Cavallin mills but I did get a bad flat roll (it
    had an area of sub surface porosity in it that showed up after the
    initial use of the mill) on my manual Cavallin it was promptly
    replaced by the vendor and it has worked fine for 15 years. 


Jim
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
http://www.mokume-gane.com
jbin AT mokume-gane.com
Member of the Better Business Bureau


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