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Posted by Martin Whybrow on July 17, 2008, 1:47 pm
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>
>> I'm currently fixing a number of issues on my recently acquired
>> Colchester Bantam 800 lathe; one of the problems I've found is that the
>> gear on the thread dial indicator has a tooth missing. I don't think that
>> it's repairable as it's some form of white metal (Mazak perhaps?) so I
>> need to make a new one. I've read of people using a tap as a hob for worm
>> wheels and it occurred to me that this might work for this application
>> but I'm wondering if it's going to be difficult to cut with an Acme form
>> tap; the second problem would be where to get a 1 1/8" x 4 TPI Acme tap
>> for a reasonable price.
>> The gear is 16 teeth and circa 1 1/4" in diameter.
>> Martin
>> --
>> martin<dot here>whybrow<at here>ntlworld<dot here>com
>>
>>
> Those gears work okay even when badly worn or misshapen and I am not sure
> it would not work properly with a tooth missing. I have seen straight spur
> gears used which did not fit the leadscrew at all well. It does not take
> much contact to rotate the thread dial. I have not tried it but I suspect
> you could cut a new gear from soft material by gashing a short section of
> the leadscrew at the end and using it as a hob. Otherwise you might get
> any kind of 4TPI tap or bolt and use it as a hob.
>
> Don Young (USA)
Thanks Don but I don't fancy gashing the leadscrew and I can't think of a
lashup that would enable me to use it to cut the gear anyway, the through
bore of the headstock is too small to try getting in the lathe! I'll dig
around for a 4 TPI tap but they are a bit thin on the ground in my workshop,
maybe I'll find one on fleabay.
Martin.
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martin<dot here>whybrow<at here>ntlworld<dot here>com
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