Rounding bar ends - how?

[cidrontmg]

I know how to make neat rounded ends to a bar, if it has a hole near the end, that will serve as a pivot point, so you can swing the bar around touching an end mill. These were made like that.



But letīs assume there is no hole near the end. How could I fix the bar then? Suction cups (hehe...)? Two needles (on top and below)? Or do I need to build some sort of a jig? If so, what sort of a jig?   

[75Plus]

I use a jig similar to this sketch. Two or three grub screws to hold the work piece and the pivot pin as close to the end as possible. This will allow various radii depending on the placement of the work piece. I have not included dimensions as they will vary depending on size required.

Joe

[Dean W]

That's a good idea, Joe.  I like the 'adjustable' aspect.
I use something similar, with a false rod with a hole in the end beneath the part that needs rounding off,
but it doesn't allow for different radii like yours will.  I think I need to make one like yours!

[Stilldrillin]

Now...... That`s a great idea! 

Thanks Joe.

David D

[cidrontmg]

 75Plus:
Thatīs it!     
Exactly what I was after, just couldnīt figure out how to get there. Grub screws on both sides of the slot, and you could center the workpiece for various widths. Pivot point very near the apex of the vee... Iīm going to start today, and post pictures when done. Thank you! 
 

[cidrontmg]

Done. Thereīs a workpiece in it for testing (a rocker arm), and it works just fine.  I made a small ali "table" whereupon the jig is mounted with a M3 screw, and which can be mounted to the mill vise.



The workpiece is held with six M3 screws, so it doesnīt have to be symmetrical, practically any shape that will fit inside the jig (17 mm wide) can be held tight enough.



Thanks again Joe / 75 Plus!           I will have use for this.

[Rob.Wilson]

Nice one Joe 

Looking good cidrontmg    Whats the rocker arm for ?


Cheers Rob

[75Plus]

I had not considered the "Free Form" aspect of the holder. Yours is much improved over the sketch I made. I do have one small suggestion. To lessen the amount of tension required to hold odd shaped workpieces you might add a back stop to support the back end. Just an idea I sketched. The two pins would drop into matching holes in the holding fixture. The stop screw length would be determined by the size of the fixture.

Joe

[cidrontmg]

Another excellent modification from Joe / 75Plus:       



I fixed the backstop with 2 brass screws. It can stay there "forever", it might get lost if itīs a loose part. If ever I need a round end to a bar longer than 60mm / 2.4", then Iīll just take it off. Otherwise, it not only lessens the tension needed in the holding screws, it also makes very easy to dupli(multipli)cate parts that are supposed to be of equal length and equally rounded. And the end of the stop makes for a bit more sensitive handle. A most sensible addition!

Thank you again, Joe / 75Plus! 

Rob.Wilson: the rocker arm is one of many that I made for an upcoming engine. I sensibly made some spares, and thatīs one which has been subject of all sorts of  tests and experiments, like this one here.

[ieezitin]

Cid.

Nice work. A well constructed jig that will serve you years.


Anthony.

[kvom]

Looks like a 5-cylinder radial from the parts being made.