Ellsworth dimentions

[pointer2null]

First a quick "Hi" - this is my first post. After many years of thinking about getting a wood lathe I boough a second hand one on the spur of the moment. It's an old Draper WTL90 and seems to be in good condition. Needs a new belt, but thats all. Didn't quite realise at the time that the tools would end up costing many times that of the lathe lol. Oh well. Still enjoying it.

Which comes to the point of the post. I bough a 1/2 inch bowl gouge and hand ground a passable Ellesworth/Fingernail grind on it. It's not the bext but got me started. Now I need a proper jig to improve things.

There are a milltion images off the Ellsworth jog out there and since they're all copies they all seem to have once critical measurement missing - the length of the arm on the tool holder.

I've highlighted it yellow in the diagram (which was signed by Ellsworth himself) atteched as

image link doesn't work.

 

[NazNomad]

7 inches ...

https://www.youtube.com/watch?v=g-49cFjCRCg

https://www.youtube.com/watch?v=ir2hlwVr84M

It's not an exact science, you can fiddle with all the measurements to give different grinds.

 

[davem62]

Hi
As I see it , the length of arm is dependant on the length of mounting block and its location in the block , as long as the overall length from pivot point to wheel is 7" it doesn't matter
David

 

[pointer2null]

Not sure about this - Maybe I'm missing something, but changing the length of the arm changes the angle the tool is presented to the wheel.

 

[NazNomad]

Keep the angle between the red and blue lines at 45°.

Keep the other geometry as close to the 2-4-7 given above.

You can tweak those measurements slightly to suit whatever grind you find you prefer.

 

[Wildman]

all dimensions also depend on the dia of the wheel, a bit of trigonometry required or simply measure the resulting angle from a test grind. Or as my old maths master used to say fiddle adjust and wangle.

 

[CHJ]

As others have said there is no fixed definitive dimension or angle with any setup.

There are so many variables that result from machine specification, wheel diameter jig positioning etc.
The only way you are going to achieve jig settings to match a preferred profile is to experiment with the various adjustable settings.

As there are so many variables with this type of jig I suggest you find a reasonable ball park setting for your grinder setup and fix one or two of the variables and adjust any tool nose angle and wing sweep profile just by tool extension in the first instance and only consider adjusting the pivot point of the jig or jig arm length or jig elbow angle if you really need to get a profile for a specific task.

In the following images from the Tormek manual you will see that in all but one nose angle they achieve the various profiles by fixing the tool extension and moving the pivot point and altering the jig elbow pivot angle.

Dependant upon your preferred profile and wheel diameter etc. you can achieve similar results, and maybe all that you need by fixing the jig elbow angle and changing the tool extension and or the pivot point.

But the actual profile will vary dependant upon Grinder spindle height, wheel diameter and jig mounting location so it's a case of experimenting to establish which settings give you the profiles you prefer to use with the minimum of change to jigs. The more of these variables you can eliminate and meet your needs the easier and quicker it will be to touch up a working edge consistently.

 

[NazNomad]

... make an adjustable one - https://www.youtube.com/watch?v=sfmIv0iXjis

I have two of these and they aren't difficult to make (they can't be if I did it twice) :-D