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Posted by Trevor Jones on July 24, 2008, 7:55 pm
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chlessig@aol.com wrote:
> For several years now I have been trying to make my own gear
> cutting hobs. The Eureka relieving device shown in Workshop
> Practice Series 17 is what I started with. They started with a
> picture of the Balzer device and reverse engineered it.
>
> I followed the plans closely because I had no idea how it worked.
>
> My first change was to make it longer so a hob blank would
> fit. The hobs for diametral pitch have a lead which is a factor
> of pi. I used a 42t and a 44t gear together to make 22/7 pi.
>
> This makes the half nuts unusable like metric conversion
> gears do.To do plain turning on hob blanks the tool is pulled
> back and the lathe is reversed with the half nuts engaged
> for the next pass.
>
> The problem with the Eureka relieving device is that it drives
> through a ratchet so it loses place when you reverse it.
>
> I was able to relieve hobs with it but it was very tedious since
> the tool had to be adjusted to pick up the thread each pass.
>
> My solution is to use a pattern thread on the reliever and
> a half nut connected to the lathe saddle to drive the carriage.
>
> Now the lathe is only reversed while cutting the pattern
> thread and half nut. A different pattern and nut are needed
> for each thread pitch.
>
> Plain turning the hob and relieving it are all done with the
> pattern thread so there is no need to reverse the lathe.
> The pattern thread half nut always engages correctly.
>
> A plain arbor that matches the reliever arbor is used.
> Both have a keyway to index the pattern thread and hob
> blank.
>
> There is a better description of the Balzer Relieving
> device at
>
>
http://books.google.com/books?id=iu1IAAAAMAAJ&printsec=frontcover&dq=Shop+Kinks+and+Machine-Shop+Chat&ei=39GISKO5M4bujgGJ8pX_Cg
>
> pages 26 to 28 which seems to be the origin of this
> tool in 1896 or so.
>
> Taylor's 1906 patent 817885 is a paraphrase of Balzer's
> design.
>
> Balzer has a 1895 patent 535127 for a reliever with no
> ratchets and a trick gear but it was not the design that
> he manufactured.
>
> Here is my hob reliever on U-tube. It is not as complicated
> as building a backing off lathe but it can't do small
> hobs for cutting worm wheels.
>
> http://www.youtube.com/watch?v=kJ8kyC_bpHs
>
> So far I can't get U-tube search to find it.
>
> Best Regards Charlie
>
Great video!
That's the best Video of a Eureka style reeiving tool that I have seen.
Nice to see a video that's long enough to get a decent look, too.
If you can, edit the title to something like "A Eureka style gear hob
relieving attachment" so it will get found by guys looking for those
terms, together or in combination.
Same with your description. Use words or phrases that will lead the
search engine in to your video. Few will search for "gears hobbing" but
"gear hobbing" will get them closer.
Suggest the words "gear" and "cutter" get added into the tags if you can.
Nice trick with the master thread to get the pitch for the hob. How
tricky is it to get the master in synch with the hob blank?
Cheers
Trevor Jones
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> cutting hobs. The Eureka relieving device shown in Workshop
> Practice Series 17 is what I started with. They started with a
> picture of the Balzer device and reverse engineered it.
>
> I followed the plans closely because I had no idea how it worked.
>
> My first change was to make it longer so a hob blank would
> fit. The hobs for diametral pitch have a lead which is a factor
> of pi. I used a 42t and a 44t gear together to make 22/7 pi.
>
> This makes the half nuts unusable like metric conversion
> gears do.To do plain turning on hob blanks the tool is pulled
> back and the lathe is reversed with the half nuts engaged
> for the next pass.
>
> The problem with the Eureka relieving device is that it drives
> through a ratchet so it loses place when you reverse it.
>
> I was able to relieve hobs with it but it was very tedious since
> the tool had to be adjusted to pick up the thread each pass.
>
> My solution is to use a pattern thread on the reliever and
> a half nut connected to the lathe saddle to drive the carriage.
>
> Now the lathe is only reversed while cutting the pattern
> thread and half nut. A different pattern and nut are needed
> for each thread pitch.
>
> Plain turning the hob and relieving it are all done with the
> pattern thread so there is no need to reverse the lathe.
> The pattern thread half nut always engages correctly.
>
> A plain arbor that matches the reliever arbor is used.
> Both have a keyway to index the pattern thread and hob
> blank.
>
> There is a better description of the Balzer Relieving
> device at
>
>