Author Topic: Turning Balls  (Read 6337 times)

Offline Lazurus

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Turning Balls
« on: November 05, 2015, 08:18:34 AM »
On my last lathe I had a natty little gadget that allowed me to turn perfect spheres, now on the VB36 I am going to have to use "skill". Any advice as I wish to make some balls for a local pub skittle game?

Steve over to you for advice........
Living and working on the Norfolk Broads

Offline desmoengine

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Re: Turning Balls
« Reply #1 on: November 05, 2015, 09:04:56 AM »
was that a self made ,bed mounted ,gizzmo youhad on you last lathe.
if so how about remaking it on a 45mm column to fit in vb tool post.
Dave Willcocks
Dave Willcocks
willcockswoodwercks@virginmedia.com

Offline Lazurus

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Re: Turning Balls
« Reply #2 on: November 05, 2015, 10:02:58 AM »
Yes it was home made, however the local guy who did the metal work / welding has since died and now stuck for a decent engineer, but I think that one sat on the bed bars as opposed to the tool post to give a vertically central pivot point. Not really sure of the geometry to give perfect spheres from the tool post?

All suggestions gratefully received.

Stuart
Living and working on the Norfolk Broads

Offline seventhdevil

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Re: Turning Balls
« Reply #3 on: November 05, 2015, 12:18:32 PM »

Offline desmoengine

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Re: Turning Balls
« Reply #4 on: November 05, 2015, 02:19:31 PM »
the geometery is quite simple ,and can be seen in the linked pictures. the pivot point is aligned to the axis of the machine ,the cutting edge is then set to centre height ,the radiusyou wish to cut is a function of how far you move the cutting edge toward the perpemdicular axis of the pivot point.
so as in the photos the 2 axis's of the pivot and cutter height have to be at right angles to one another to coincise with the centre of the sphere you are making.
there for the whole mechanical setup could be rotated around the machine longtitudinal axis and mounted off of the tool post (as there is no bed to speak of on the VB) this would have the cutter describing an arc lenghtways between centre vertically over the top of the sphere.
i can visualise it ,not sure i've explained that clearly enough.
Dave Willcocks
Dave Willcocks
willcockswoodwercks@virginmedia.com

Offline Paul Hannaby

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Re: Turning Balls
« Reply #5 on: November 05, 2015, 02:58:21 PM »
Perhaps for a toolpost mounted version it would be easier if the axis of rotation of the cutting assembly was horizontal instead of vertical? That way you don't have to centre the toolpost under the blank, you just set the cutter's axis at spindle height.

Offline desmoengine

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Re: Turning Balls
« Reply #6 on: November 05, 2015, 03:25:12 PM »
hi Paul
thats what i was trying to get at without using the vertical and horizontal wording.
the gizzmo i have fits in toolpost and the cuutter describes a horizontal arc over the top of the sphere along the long axis of the machine.
the guy that makes them is on ebay mine will do up to 100mm dia sphere he currently makes the gizmo to do up to 150mm diameter.
Dave Willcocks
Dave Willcocks
willcockswoodwercks@virginmedia.com

Offline fuzzyturns

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Re: Turning Balls
« Reply #7 on: November 05, 2015, 03:48:32 PM »
Paul: you still need to have the axis aligned, otherwise you'll never get to the "poles" of the sphere. Although I can see the benefit of using the banjo with an existing clamping device, I think it'll be a faff to set it up every time, as the banjo moves freely in both directions (laterally as well as longitudinally). It's probably easier to make a new stand for the old gizmo, from plywood, with a central protrusion that fits snugly between the runners of the lathe bed.

Offline seventhdevil

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Re: Turning Balls
« Reply #8 on: November 05, 2015, 04:07:50 PM »
before i had my jig i looked at all that i could find for sale and was depressed by the lack of options in this area. the ones for sale on ebay are very well made but inadequate for turning my skittle balls as they can be up to 6" in diameter and i also thought that the one on ebay looked a bit feeble on the construction side.

the one i ended up designing was done so to overcome any possibility of breaking it as if i did so whilst turning it would not only be dangerous but i would have to disappoint my customers.

mine is a simple design but it does the job and is only 1/16" out of spherical once finished.


for doing variations on a sphere my design is useless but it won't move around like a banjo can and will be in the same place every single time.

Offline georg

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Re: Turning Balls
« Reply #9 on: November 05, 2015, 05:45:28 PM »
 This was made by me originally for my graduate lath with a 1" stem then adapted for my VB inserting it in a 40mm stem, this
 enables  the Beniston adaptor to be locked on the 40mm stem, the 1" stem left loose .... if you start off with 40mm you will
 have to put it in the main tool post & leave loose .... the pillars are 3 1/8 enabling a 6"  ball to be turned it can then be slid
 in & out for smaller sizes . It does take some setting up in center to traverse right round the front for a complete ball
 Regards Tony

 

 

 
"If you always do what you always done, you always get what you always got" 

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Offline TONY MALIN

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Re: Turning Balls
« Reply #10 on: November 05, 2015, 08:29:35 PM »
In a recent demo we were shown a good way to deal with the spigots produced on parting off. He had two jigs with short pieces of 2" dia  plastic pipe glued on. These were slightly chamfered on the inside of the bore. So with one on the headstock and the other held by a running centre the ball was sandwiched between them at 90 degrees to the knobs. These now easily removed. The final sanded finish was done by slacking the tail stock and randomly resetting the ball.


Offline fuzzyturns

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Re: Turning Balls
« Reply #11 on: November 05, 2015, 10:17:57 PM »
Yes, that works, but on soft woods it leaves marks. I have found it better to turn two pieces of wood with an approximately spherical concave shape, then cover them with double-sided tape and stick some rubber mat on. Much friendlier on soft woods, and just as functional. Best made out of moderately soft wood, e.g. sycamore or poplar.

Offline Lazurus

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Re: Turning Balls
« Reply #12 on: November 06, 2015, 07:38:53 AM »
www.paulhowardwoodturner.co.uk

Had some correspondence with the guy above he has and can make a jig specifically for the VB36 - however like most things its quite expensive.

Stuart
Living and working on the Norfolk Broads

Offline Richard Findley

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Re: Turning Balls
« Reply #13 on: November 18, 2015, 12:51:42 PM »
I'm a little late on this one, but I have never used a jig for this, just turn to a template, then use wooden cups to hold the ball. This might explain it better:

https://www.instagram.com/p/-MWIhugSSk/?taken-by=richard_findley

HTH

Richard
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Offline Lazurus

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Re: Turning Balls
« Reply #14 on: November 18, 2015, 01:29:09 PM »
Thanks Richard, very accurate for free hand. There is hope for me yet.  ;)
Living and working on the Norfolk Broads