Tips/Techniques Eccentric turning advice needed

[Arbutus]

I am starting to build the Eureka form relieving tool from Model Engineer, Volume 168.

This gadget cuts the relief behind the cutting edge of a milling cutter, such as these involute gear cutters.

The drawing shows the mandrel which is a triple eccentric turning. I have double-guessed myself a dozen times regarding the order of operations needed. I have a piece of 2-1/2" CRS and some 1-1/4" CRS. If this is turned from solid, that a lot of wasted metal, so I'm leaning towards a two piece assembly with the larger (45,38mm) eccentrics made from 3/8 plate, fitted to the inner 25mm part.

The challenge is indexing the work in the 4-jaw to set the correct 90deg angle when boring the rotational centre pilot which is offset 0.8mm at 90deg to the A centre.

Any tricks and advice appreciated!

 

[johnnielsen]

That's something I'd like to build also to make hobs.

 

[jorogi]

YT, Inheritance Machining did a video or two on this build. You might find it helpful.

 

[Arbutus]

YT, Inheritance Machining did a video or two on this build. You might find it helpful.

Thanks for that! Lots of questions answered in those videos. How does he make it look so easy?

 

[PeterT]

Cool project. Keep us posted on your build!

 

[jorogi]

Thanks for that! Lots of questions answered in those videos. How does he make it look so easy?

All my work goes so easy too, as long as you let me edit it first
Glad you found it useful.

 

[gerritv]

It's easy until it isn't My first attempt making that from 1 piece ended up as a paper weight on my wife's desk. Second attempt made it from 2 pieces, the 3/8" end piece being #2.

I am not confident that I got the offsets correct, the drawings in the article and the Ivan Law book are not the best at showing the offsets IMHO. I haven't looked at Inheritance's drawings (not a patreon there) but I do have a STEP file for the metric version. Pop that into Fusion and produce a drawing for the mandrel.

I did manage to make 2 cutters using the tool. I do need to redo some parts of the Eureka, my skills at the time (8 years ago) were not 'stellar'.

In use, the biggest issue I found was getting the cutter blank aligned to the timing of the eccentric, and staying there while tightening the nut up. A keyed washer would likely help a lot with that.

gerrit

 

[gerritv]

There are other relieving devices made over time in ME and MEW.
MEW Feb & Apr 1999 had a cross lside type, on an ML7.
ME ran a series by Duplex starting in May 1949 that showed design of a rocking tpe on an ML7.

 

[gerritv]

This is another view of the centres for the Eureka. The longer shaft is for use with making gear hobs. I think it is from this video:

 

[Arbutus]

The longer nose on that design is something I'll incorporate before cutting metal. I was considering making hobbing cutters with this - my lathe is imperial only (no change wheels) so making metric hobs is probably not an option on my machine.

I have modelled the Eureka in F360, for metric parts, but using imperial sheetstock. The dimensions and clearances reflect the available materials. The nose thread is M13x0.5 which should snug things down tightly. Since all my other hobs and disk cutters use a keyway I will include that as well. Your point about the disk slipping is well taken.