Eureka relieving fixture

[Bjorn_B]

Tanglers thread about the myford handwheel got me going on this somewhat obscure piece of tooling for making form relieved gear cutters, I guess few of us has seen one in use, it is allso very seldom mentioned in forums.

Maybe this is partly because the cost of a full set of chinese gear cutters is not beyond the reach of most of us nowadays, the rest is down to that a flycutter does the job just as good allbeit just a little bit slower. than a multi tooth disc cutter. In the near future I will need to cut a few 20DP gears with a 20 degree pressure angle (for a Meek screwcutting dog clutch), never found cutters with that spec at a reasonable cost. Flycutting is a very viable option, but I like toolmaking and a bit of a challange so why not?

After poking around in the odds and ends bin for a while I found enough material to make a start on this. I used the drawings supplied in Ivan Law's book on gearcutting (wps #17).

20160302_175028 by Bjorn Pettersson, on Flickr

[steamer]

Cool!   I'll tag along!

Dave

[Bjorn_B]

First things first, the mandrel. there are 3 excentrics on this. It is allso very important that theese are correctly clocked otherwise this gadget will not work at all.. all 3 centres are marked out on both ends.
20160221_191521 by Bjorn Pettersson, on Flickr

Indicated for the third excentric (centre of rotation of the whole kaboodle) the same method is used for seting up on all ops on this part
20160222_193515 by Bjorn Pettersson, on Flickr

And centre drilled, this is 90 degrees offset to the large excenter
20160222_193749 by Bjorn Pettersson, on Flickr

The spindle is then turned round and the punch mark matching the centre just drilled is indexed true. This is centre bored and the end of the spindle is turned down to about 1 inch dia for a drive dog. (got carried away and forgot to take Pictures, but the setting up for this is the same as above)

Edit: Wrong picture in first setup and some missleading info edited

[Bjorn_B]

The indexing sleeve next. Very easy part to make compared to the spindle. Some care in concentricity and diameters, that is all really.

After the basic shape is done it was transfered to the dividing head and indexed for the 12 rachet grooves to e cut with a 60 degree dovetail cutter. Think not twice, but trice over this as they need to be the right way round...20160227_135312 by Bjorn Pettersson, on Flickr

The finished indexing sleeve
20160227_140732 by Bjorn Pettersson, on Flickr

Next is the rachet and anchor plates, plans call for 5/16 thick steel plate but I only had 1/4 inch plate on hand. I adjusted distances to for this on the spindle and indexing sleeve.

Holes where centre drilled with help of the DRO, no real need for marking out, after going trough all holes with a 5mm drill the large hole was then attacked with my largest drill (this is the rachet plate).
20160227_101757 by Bjorn Pettersson, on Flickr

Then a boring session.., this hole was tested for good sliding fit on the spindle at the later stages. diameter is nominal 1,5 inch
20160227_104304 by Bjorn Pettersson, on Flickr

A groove was milled between the small holes to the left and some work in the (horrible asian) bandsaw begun. After a bit of filing this is what I ended up with:
20160227_133008 by Bjorn Pettersson, on Flickr

Note: Thread on the spindle was later found wrong (3/8 BSF on photo), it is now corrected to a 5/16 40tpi according to the book. Reason for this will be revealed

[Bjorn_B]

Pawls: Details on theese are not very clear in the book, but better get started and correct later...

The only rotary table I have is a useless affair with so much backlash and slop that a better job can be made with a chisel and hammer. I usually clamp the table of my UPT in the chuck of my dividing head (opposed to the rotary table it is of very good quality).

With some care a hefty clamp bolt (M8) in the pivot hole was sufficient for work holding, (the clamp in the picture was taken off for the outer radius machining)
20160227_153116 by Bjorn Pettersson, on Flickr

Trying out
20160227_160300 by Bjorn Pettersson, on Flickr

The anchor plate pawl has to have a countersunk mounting bolt due to clearance issues, time for the Granlunds again..
20160228_090227 by Bjorn Pettersson, on Flickr

Strange setup perhaps, but this small chuck have a shank that I normaly use in the UPT, now it is clamped in the vise and the specially made mounting screw for the pawl above recieves a groove for a screwdriver. The screw have a shank that is too short to hold safely in the vise and the dividing head was allready removed from the table.
20160228_091955 by Bjorn Pettersson, on Flickr

[Bjorn_B]

Found som small niggles:
[youtube1]https://youtu.be/bOmVuEghs6c[/youtube1]
This is very exact, the rachet pawl just reaches the next "cog" and unfortunately misses on the same spot every revolution. Some very careful filing and fitting of the pawls is needed to make this work. Thinking this over at the moment because what is won by trimming the end of one pawl is lost at the other pawl... I now have better springs made from proper piano wire (old bicyckle spoke used in the video). Came to the conclusion that reducing the diameter of the indexing body helped a lot, I have taken 0,2mm of so far, maybe I will take another 0,1mm of. Report to follow.

[Don1966]

Bjorn thanks for posting this as this is the project I am currently working on, and I have the indexing sleeve left to make and it's nut. Nice job and it shows me excactly how it works on the lathe........

Don

[swwi]

Bjorn,  When you actually make a cutter, could you please make a video of the Eureka in action. Thank you very much. Very informative post......

[b.lindsey]

Yes please, at the moment I am at a total loss as to how this works. Even so it looks like you did a very nice job of making it!!

Bill

[tangler]

At the risk of intruding...


<a href="https://www.youtube.com/watch?v=U_kqi3dqr50" target="_blank">http://www.youtube.com/watch?v=U_kqi3dqr50</a>

Rod

[b.lindsey]

That helps Rod. So this is used only to machine the relief angle on the homemade cutters teeth if I understand correctly.

Bill

[Don1966]

Awesome Rod and thanks.........

don

[tangler]

My video only shows a topping cutter in action for demonstration purposes.  With a button tool replacing the topping cutter then relief is applied with the correct profile so that the tool can be resharpened (if you put the nascent cutter the correct way round in the Eureka  ).

I showed some stills of the various stages in my carriage handwheel thread.

Cheers,

Rod

[swwi]

Thanks Tangler,        That helps me to understand what is going on...appreciate the video...

[Zephyrin]

Very nice thread, fascinating tool, but it looks like that not much room is left for a gear cutter cutting tool, rather wide with the buttons.
a great classics from the golden age of ME !
the mechanism reminds me the rachet wheel of my recent gearless engine !