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Charles Lessig
07-26-2008, 02:32 PM
For several years I have been trying to make my own gear cutting
hobs and relieve their cutting edges.

I started with the Eureka relieving
attachment found in Ivan Law's Gears and Gear cutting Workshop
Practice Series 17 which is intended to relieve form cutters.

I followed the plans closely because I had no idea how it worked
except for making it longer to hold a hob to be relieved.

The lead of a diametral pitch hob is a factor of pi so I used a pair of
gears, 42t and 44t, keyed together to get 22/7 pi into the lead.

Like metric conversion gears ,this means the half nuts must stay
engaged and the lathe reversed for each pass. This works fine
for plain turning but is a problem with the reliever since it drives
through a ratchet and loses place when reversed. I was able to
relieve hobs but it was very tedious since the tool had to be
reset to pick up the thread.

My solution is to make the Eureka long enough to hold the hob
and a pattern screw to match the hob. A half nut follows the
pattern screw and drives the lathe carriage.

Each gear pitch needs its own nut and pattern screw but it
always engages correctly.

My reliever and plain arbor are 7/8" diameter with a 1/8" keyway.

The hob is put on the reliever and marked with a tool to show
where the gashes need to be.

Here is a video of a device I made to relieve gear cutting hobs.
It is a modified Eureka relieving attachment.

http://tinyurl.com/6qyxoh

This is the book where I got my plans for the Eureka relieving
device. It is shown on pages 123 thru 130. I bought the book.

http://tinyurl.com/5ey4xz

This is Balzer's geared reliever but it is not the one he manufactured.
It uses a trick gear which I think would work since the odd part
does not run under heavy load.

http://preview.tinyurl.com/5jvngc

This is Balzer's reliever which he manufactured. The Eureka was
reverse engineered from a picture of this. See pages 26 thru 28.

http://tinyurl.com/5cfjup

This is Taylor's paraphrase of Balzer's reliever

http://preview.tinyurl.com/6e6pym


Best regards, Charlie

snowman
07-26-2008, 02:43 PM
awesome

something is confusing me though (it's not too hard to do)

does the hob and lead screw for the cutter pivot on the tailstock??

Charles Lessig
07-26-2008, 03:21 PM
Yes ,
The whole reliever runs on the regular
lathe centers. The shaft inside the arbor
with the hob and screw has its centers
offset .030" to give .060" relief on each
tooth that is cut. This is from the Eureka
design.

John Stevenson
07-26-2008, 03:50 PM
Charles,
Very impressive and a good adaption of logical thought.
I am very impressed .

.

Peter N
07-26-2008, 04:46 PM
Brilliant. Very clever.

Peter

quasi
07-26-2008, 07:13 PM
I always wondered how a relieving attachment worked ,thankyou.

mike petree
07-26-2008, 08:11 PM
______superb!

wierdscience
07-26-2008, 09:46 PM
Very nice,how adaptable is it to other work like milling cutters?

I am working on copying Hendy's design which is an eccentric driven tool post that is timed to the spindle via a change gear set.

http://www.lathes.co.uk/hendey/page11.html

J Tiers
07-26-2008, 09:58 PM
I always wondered how a relieving attachment worked ,thankyou.

Actually, the traditional style is geared from the headstock and reciprocates the crosslide.

The video one is nicer, less hassle.

lazlo
07-27-2008, 12:00 AM
Great job Charlie -- I have no idea how you managed to track down the original Balzer patent (from 1894!), since Ivan Law and George Thomas couldn't find it (according to Ivan's book).

I just printed out both patents, but from glancing at the drawings, it looks like the Eureka is more like Taylor's version than the one described in Balzer's patent.

I really like the half nut you added to advance the reliever -- very clever!

oldtiffie
07-27-2008, 12:41 AM
Thank you, thank you, thank you Charles Lessig (OP).

Magnificent - in every respect. A very elegant solution indeed.

I have just ordered the book - plus another on Tool & Cutter grinding - from Amazon.com

This forum is fabulous the way the people on it turn up such great material.

I've been waiting/thinking about this for years.

The one I used in my younger days (50+ years ago) was hydraulic - and was controlled by a follower/stylus following a cam.

One of the main problems with these "home made" hobbing cutters is that all too often or mostly the profile is set at zero top rake - ie with no "hook angle" (as on wood saws and router cutters) and are inclined to "thump". The "throat"/groove ahead of the cutting face is also not spiral-cut to the normal of the hob helix angle and so one side of the profile face will have an effective positive side rake and the other an equal negative side rake (same as a screwing tool that is cut/set "flat" on a lathe).

But as for the lathe tool - keep it slow and sharp with plenty of cutting oil.

Care must be taken when grinding/sharpening the cutter as the profile of the "face" of the cutting teeth must be maintained - ie the same "hook" or "back-rake" must be maintained.

A hobbing cutter - as this is - will quire often "drive" the "blank"/job which can "free-wheel" without physical or electronic (CNC) connection between the cutter and the work - particularly - where a helix or "worm/wheel" situation arrives. A spur gear is only a spiral gear with an infinitely long helical pitch and infinitely small helix angle after all.

John Stevenson
07-27-2008, 04:48 AM
Very nice,how adaptable is it to other work like milling cutters?

I am working on copying Hendy's design which is an eccentric driven tool post that is timed to the spindle via a change gear set.

http://www.lathes.co.uk/hendey/page11.html

For other work like milling cutters you just lock the carriage and don't use the feed screw that Charles has fitted.

The Hendy one is set for what number teeth via the change hears but for a hob still has the problem that Charles came across in that the travel via the leadscrew has to have the pi ratio in it and you can't disconnect the leadscrew after each cut.

.

Charles Lessig
07-27-2008, 03:13 PM
Thank you all for your encouragement and interest.

If I make another reliever I would follow Balzer's 1896
design with its adjustable eccentric. It is a little more
complicated but more straight-forward to make.

I think the pattern screw should be longer than the
hob and not the same. My reliever has a broad
canvas-phenolic nut that starts and ends half engaged.
The pattern screw is aluminum.

A cast iron, locking, double half nut on a steel screw might
work better. The time to stop is when it gets more
elaborate than a backing-off lathe.

The nut mechanism mounts on my follower rest holes
and is steadied by a cone screw in a center-drilled hole
on the opposite side of the saddle. This is on a 9" South
Bend lathe.

The pivots are all cone-pointed set screws into center
drilled holes. There is very little lost motion.

First I get as much metal removed by plain turning and
milling as I can and I then do the relieving.

The gashes should be as small as practical at first since
the start of the teeth is imperfect as slack is taken up
at the beginning of each cut. Later the bad parts can
be milled off, making the gashes wider.

The tops of the teeth are relieved first with a flat
cutter then the sides are done with an acme shaped
cutter. It helps to blue the hob so you can see
what you are doing better.

It is very satisfying to find other people interested
in this sort of thing.

Charlie

tattoomike68
07-27-2008, 03:58 PM
Thats trick, its fun just to watch it work.

http://www.youtube.com/v/kJ8kyC_bpHs&hl

lazlo
07-27-2008, 04:57 PM
By the way guys, don't forget that John built the Eureka reliever in Ivan Law's book several years ago, and posted the video here.

I can't find the video on John's page, so I just uploaded it to RapidShare:

http://rapidshare.com/files/132919594/MOV01374.MPG.html

John: let me know if you want me to take it down...

aboard_epsilon
07-27-2008, 06:10 PM
what sort of tool steel are you using to relieve these cutters .,..i thought the cutters were very hard ...

all the best.markj

Charles Lessig
07-28-2008, 06:26 AM
Charles,
Very impressive and a good adaption of logical thought.
I am very impressed .

.
John,
You were the first to encourage me when I started
on this project in 2004. It seemed like it would be easy to
just stretch the Eureka and put a hob on it. Then I found
it was not so easy. I tried several fixes then let it sit for
a couple of years.

In May this year the pattern screw idea came to me as
I was running hot water on my head in the shower one
morning and I was back on the project in a fit of fury.

I showed the completed device at meetngs of our local
metal working group, Chesapeake Area Metalworking
Society, but it was still hard to understand. That is
when I decided to post the video.

There is room for improvement in the details but this
first version does work.

Best Regards, Charlie

Charles Lessig
07-28-2008, 06:42 AM
what sort of tool steel are you using to relieve these cutters .,..i thought the cutters were very hard ...

all the best.markj
markj,
I am using high speed steel of the usual type.
My hobs are made of A2 annealed air hardening
steel. It is quite strong and the cutters are broad
with flat tops so I can't take much of a cut.

The next step is to put the hobs in stainless steel
bags and heat treat them in a little electric furnace.

The idea is to preserve the machined surface as
much as possible.

lazlo
07-29-2008, 12:12 AM
It seemed like it would be easy to just stretch the Eureka and put a hob on it. Then I found
it was not so easy. I tried several fixes then let it sit for a couple of years.

Charles, I'm in SC this week so I don't have access to my copy of Ivan's book, but I seem to remember it was designed for a 7/8" hob -- did you upsize it to a 1" hob?

Do you have the upsized dimensions for the plans in Ivan's book?

Thanks,

Robert

Mcgyver
07-29-2008, 12:14 AM
Charlie, that is just fantastic, way to go.

Charles Lessig
07-29-2008, 07:55 AM
Charles, I'm in SC this week so I don't have access to my copy of Ivan's book, but I seem to remember it was designed for a 7/8" hob -- did you upsize it to a 1" hob?

Do you have the upsized dimensions for the plans in Ivan's book?

Thanks,

Robert
Robert,

My Eureka is stock, made according to the plans except
for the spindle and arbor length. The original has 7/8" and 5/8"
features which I just extended. The arbor is 7/8" diameter with
a 1/8" keyway. The spindle is 5/8" in diameter. The end nuts
were adapted to fit. I forget the nut sizes and threads just now.

The hob is 1 and 3/4" long and the screw is the same with a
3/4" keyed spacer in between. The screw was an aluminum
practice blank the same as the hobs I was working on.

The pattern screw needs to be longer since the nut starts
and ends half engaged. It works but is not tidy.

My arbor and spindle were a close fit so sometimes the
anchor plate pawl would miss its notch due to freewheeling,
which it was supposed to prevent. I think Eureka's anchor
plate pawl was an after thought when freewheeling showed
up.

The 1896 Balzer used
friction washers and had only one pawl. I put a cork washer
behind the locating ring and added more set screws to the
ring to clamp the washer. It will work without the anchor
pawl but I use both since it is there.

An improvement would be to thread the ring and have
a way to clamp it in place.

Balzer's 1895 geared reliever patent has a spindle that is
partly tapered. This might be a good way to make it so
you can adjust the fit for wear. Some other pictures show
this part as a step like the Eureka.

Stephen Balzer was very interesting. He did a lot of work
developing Professor Langley's radial airplane engine and
patented count wheel devices such as odometers use or
did use. He lost money on the aero engine and went to
making cutter relievers to stay in business.

I have pictures posted on the yahoo group mwmills2
if anyone here goes there.

Best Regards, Charlie

FPV_GTp
01-11-2011, 05:31 PM
Robert,

Stephen Balzer was very interesting. He did a lot of work
developing Professor Langley's radial airplane engine and
patented count wheel devices such as odometers use or
did use. He lost money on the aero engine and went to
making cutter relievers to stay in business.

I have pictures posted on the yahoo group mwmills2
if anyone here goes there.

Best Regards, Charlie


Hi Charlie

Sorry to bring a old thread/post back to life , Charlie could you post a direct link(s) to the suggested section in the yahoo group please in relation to the topic " Charles Lessig's Hob Reliever Eureka Balzer Gear Cutting"

Would be greatly appreciated

CHeers

John Stevenson
01-11-2011, 06:37 PM
Not sure if non member can see these but here's the direct link to Charles's photos.


http://groups.yahoo.com/group/mwmills2/photos/album/1286132389/pic/list

.

Jaakko Fagerlund
01-11-2011, 11:29 PM
Not sure if non member can see these but here's the direct link to Charles's photos.


http://groups.yahoo.com/group/mwmills2/photos/album/1286132389/pic/list

.
No love without registration :(

wierdscience
04-08-2011, 08:09 AM
For other work like milling cutters you just lock the carriage and don't use the feed screw that Charles has fitted.

The Hendy one is set for what number teeth via the change hears but for a hob still has the problem that Charles came across in that the travel via the leadscrew has to have the pi ratio in it and you can't disconnect the leadscrew after each cut.

.

John,sorry for the slow reply:),but there is no need to disconnect the leadscrew on the Hendey attachment since it is leadscrew driven and doesn't rely on a ratchet.It's no different than turning a metric thread you just leave the halfnuts engaged and reverse the spindle.