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=iu1...M4bujgGJ8pX_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

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=iu1...M4bujgGJ8pX_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

Thanks Trevor, I will try to get the search terms better. Even the
exact
title did not show up.

After the plain turning is done the the hob blank is blued and
put on the reliever and marked on the end with a cutter bit as it
turns.
The pattern screw is marked so the two parts can be put on the
reliever the
same way they were during plain turning. Both arbors have a keyway.

The mark on the hob blank looks like a circular saw. This shows
where to put the gashes. Since the beginning of the teeth are
not perfectly formed as slack is being taken up at the start, the
gashes should be as small as practical. Later the odd parts will
be cut away and the gash made wider.

The tops of the hob teeth are relieved with a straight cutter first.
I blue the hob blank to be able to see how the cutting is going.

Then the thread relieving cutter is adjusted to pick up the thread
once
and then stays in synch. Small adjustments can be made on
the pivot screws of the follower that carries the nut.

This is the first time for me on U-tube. Charlie

Very impressive project. I remember reading about the eureka and thinking it
was too big a job for me to take on. Do you know about how many hours you
spent on construction?

Karl

Karl,
The original Eureka was said to have been made in four days. My first
longer
version was done over a period of two weeks. The plates were made
using
a rotary table and boring head a lot while following the plans
closely.
Holding the parts is the hardest thing to do.

The main arbor has three offsets that make it tricky. I used extra
length at
the ends so two sets of centers could be milled off and the relieving
centers
then drilled. The offset is only .030" so it must be done later.

The Eureka described in Workshop Series 17 has the curves of Balzer's
1896 reliever that inspired it. My second version with the pattern
thread
just needed still longer parts and used the Eureka mechanism to drive
it. My half nut carrier has no curves at all.

The Balzer has only one ratchet and uses friction washers to keep it
from freewheeling when not being turned by its ratchet. The Eureka has
a second ratchet that seems like an after thought to do this. I have a
cork friction washer and Eureka's ratchet on mine.

I am cutting A2 steel with broad flat topped cutters making my hobs
so I can't take much of a cut. They have a 7/8" bore and a 1/8"
keyway.

Charlie



On Jul 24, 10:24*pm, "Karl Townsend"
wrote:
Very impressive project. I remember reading about the eureka and thinking it
was too big a job for me to take on. Do you know about how many hours you
spent on construction?

Karl