how does this ball turner work ?

This topic has 14 replies, 8 voices, and was last updated 29 November 2016 at 03:07 by BW.

Viewing 15 posts - 1 through 15 (of 15 total)

Author

Posts
14 October 2016 at 08:38 #260980
BW
Participant
@bw
Has anybody made the ball turner described by David Fenner in the 25 year anniversary special edition ?

I've read the article a couple of times now and I don't "get it", I don't understand what the piece attached to the back of the cutter is for and why its connected to the other arm that comes out of the back of the main block.

Its a repeat of the article in volume 127 July 2007

Photo on this page its the article that starts on page 80.

model-engineer.co.UK/editorial/page.asp?p=1278#
Advert

14 October 2016 at 08:38 #8327
BW
Participant
@bw
14 October 2016 at 09:11 #260985
Chris Evans 6
Participant
@chrisevans6
I have found the picture from the link but am no wiser. It looks like a version of the Steve Bedair type but what the bit on the back is a mystery. Maybe a mod could provide a better link to the article ?
14 October 2016 at 10:17 #260992
Hopper
Participant
@hopper
Your link does not work for me. But I remember scratching my head for quite some time when I read that article in the 25 year special edition. This was my conclusion after much head scratching. It may be right, IDK. But it is my theory:

It seems the source of confusion was a poorly composed photo (page 87 in 25 year SE), the one showing the "Tool Block Assembly" .

The block you see as attached to the rear of the cutting tool is in fact not. It is attached to the 8mm round rod sticking out of the tool block behind and slightly below it. Because the two are aligned in the photo it looks like the block is attached to a rounded off section of the tool bit. Not so.

That block is actually the "Rod End", basically a clevis with round brass insert with a hole through it. It goes on the end of the 8mm round rod and a threaded adjuster runs through it, into another block, the Fulcrum Block, Sketch 7. This block is attached (never did figure out exactly how, bolt? Pin?) to the "Swing Plate".

The main pic of the complete attachment (page 80 in the 25 year SE) also is confusingly composed. It looks sort of like the square aluminium Fulcrum Block is attached to the back end of the cutter tool bit. Not So.

Nothing at all is attached to the rear of the cutter tool bit. That tool bit could be cut down to half its shown lengthe without affecting the workings of teh attachment at all.

Adding to the confusion seems to be that the design has two pivot points. First the main pivot point, the brass hex fitting, about which the whole shooting match pivots turn the ball. Second, the ToolBock pivots about that upright stud with teh hex nut on top, adjusted by that confusing assembly of the rod, rod end, fulcrum block, knob and threaded stop. This second pivot point is used to vary the radius of the ball to be turned, or to increase the depth of cut as you go, depending on which way you read it or choose to use it.

It's on my list of "to build" items but havent got that far yet. Maybe someone who has can provide video of it at work? Or clearer pics.
14 October 2016 at 11:06 #261005
BW
Participant
@bw
Thanks for replies.

Corrected link

http://www.model-engineer.co.uk/editorial/page.asp?p=1278 look through the index and see the photo labelled page 80

Hopper, I've looked at the photos again and your comments make sense to me. Will now read the article again and with this new understanding the photos and the drawings will make more sense.

Will try to better understand the two pivot points as well.

Thanks again.

Bill
14 October 2016 at 11:30 #261011
Hopper
Participant
@hopper
Ah yes, the photo in the index on your link is the overall main photo in the article I referred to. It looks like that square block is attached to the rear end of the tool bit, but its not.

I'm glad you are having this problem too. I thought it was just my being a bit thick that made the article confusing to me when I read it.

Edited By Hopper on 14/10/2016 11:32:21
14 October 2016 at 13:03 #261038
Neil Wyatt
Moderator
@neilwyatt
Yes, just a trick of perspective.

Neil
14 October 2016 at 16:17 #261086
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Wyatt on 14/10/2016 13:03:27:

Yes, just a trick of perspective.

.

May be worth mentioning on your "What makes a …" thread: **LINK**

http://www.model-engineer.co.uk/forums/postings.asp?th=121113&p=1

MichaelG.
14 October 2016 at 16:30 #261093
not done it yet
Participant
@notdoneityet
Possibly hunt through the many U-toob items for that suitable search. Likely become apparent from one of them, if not more?
27 November 2016 at 01:16 #268567
BW
Participant
@bw
See first photo in this article. Not the same tool, but a similar idea, and much easier to understand.

http://www.haythornthwaite.com/133%20Spherical%20Turning.pdf
27 November 2016 at 20:58 #268680
Howard Lewis
Participant
@howardlewis46836
My understanding of all Radius Turning Tools is:

That the cutting tool is on the centre line of the workpiece, and is rotated about a centre point, which is located somewhere within the workpiece.

As the job rotates, the cutting tool is fed towards it, in small increments, whilst the Cutting Tool Holder is rotated about the centrepoint within the workpiece, until the required radius or ball is produced.

Have I got that correct?.

Howard
27 November 2016 at 22:04 #268703
Chris Evans 6
Participant
@chrisevans6
Yes Howard that is about it. I made one earlier this year and it works well, I based mine loosely on the design by Steve Bedair.(Google will find the plans) Mine is all cast iron from odd bits lying around the workshop, I did fit the sliding tool holder into is base with a dovetail to prevent it lifting in use. I used a 14 degree dovetail cutter from the woodworking router box, carbide tips had no trouble cutting the cast iron.
27 November 2016 at 23:05 #268717
BW
Participant
@bw
Posted by Howard Lewis on 27/11/2016 20:58:34:

My understanding of all Radius Turning Tools is:

That the cutting tool is on the centre line of the workpiece, and is rotated about a centre point, which is located somewhere within the workpiece.

Have I got that correct?.

Howard

There is a useful variation that is well worth knowing about and is shown in the first photograph of my previous post.

If you are cutting maximum possible sized balls then the pivot point must be vertically beneath the lathes axis, but the cutting tool does not have to be anywhere near the axis. See photo above

If you crank the cutting tool around so that relative to the pivot point it is at 45 degrees to the left of the pivot then you are better able to cut a full ball without fouling the chuck (or the steady rest if you are using one). See photo above.

The critical thing is the distance of the tool from the pivot point, it doesn't have to be aligned axially.

In order to understand how they work I've been doing some doodling using the ball cutter linked below, having a go at making chess pieces. Its been very interesting cutting bobbles on the end, and coves into the sides of the pieces with the pivot point well outside the workpiece. Cannot figure out how to attach photos.

Interesting that I was able to use a shear tool to get a nice finish.

**LINK**

Bill
27 November 2016 at 23:34 #268722
Frances IoM
Participant
@francesiom58905
Bill – it is easy just read
http://www.model-engineer.co.uk/forums/postings.asp?th=103028
the simplest thing to remember is put all the photos you want to use into your album
Posting google links doesn’t work for many
29 November 2016 at 03:07 #268901
BW
Participant
@bw
Thanks Frances,

See proof below that I understood the instructions. Blackened pawn achieved by heating and dunking in engine oil. Am always pleased and amazed when I read something, try it …………. and it works ! Yeeha
Author

Posts