how to hold a big bowl?

[nev]

:wink:
Just attempting my first BIG bowl , 17 x 3 :shock: in sapele. mounted on a faceplate and a bit of ply with plenty of two inch screws, I have turned the underside curved edge and am about to attack the bottom and chucking/ mounting method, but i am unsure as to the safest way to mount it when i turn it around to do the inside.
normally (6-8 inch bowls) it would be a 50mm dovetailed recess, mount in chuck (xt450) and away we go, but i doubt that would hold a bowl of this size.

How do I proceed safely? what mounting method can I use?

suggestions please (hammer)

 

[Bodrighy]

Personally I would be inclined to use a tenon for a bowl that size. I have seen much larger ones done with hot glue but would be wary myself. As long as it uis balanced a tenon should be fine.

Pete

 

[stevenw1963]

Nev,

I have the Dakota XT700 chuck - the biggest platter I turned was approx 20 inches by 2 1/2 inches deep.
I had a dovetail recess in the bottom (I find this safest for me) & turned the speed of the lathe right down ( & had some bags of sand on the lathe bed to stop it bouncing).
Mine turned ok without mishap.

 

[CHJ]

A lot depends upon the wood species and the cutting loads expected.
Dovetail socket or spigot cut to the correct depth and to suit the largest jaws you have should be fine as long as you temper your cutting vigour to suit.
I often stay with my fitted nominal 50mm jaws with thinner platters from more compliant woods but do move up to 63mm or 100mm versions for something that is going to need some heavy cutting loads.

 

[henton49er]

I have 2", 3" and 4" jaws for my Patriot and Nova chucks. I tend to err on the side of caution and use the 4" ones on anything large, provided it does not compromise the foot detail that I want.

I also keep the tailstock in position for as long as I need to make any heavy cuts, particularly at the outer edges of the inside of a bowl/platter.

For example, in last months challenge platter which was 16" in diameter, I kept the tailstock in place whilst turning the rim and cutting a vertical slot for the start of the platter centre to avoid any gouge skids across the rim when starting to turn (not that I've ever had anything like that happen, you understand :lol: :lol: ). I only removed the tailstock when I wanted to remove material from the centre of the platter.

 

[CHJ]

...... I only removed the tailstock when I wanted to remove material from the centre of the platter.

Likewise have done the same in the past, this was held on a 50mm jaw, all I had at the time.

 

[nev]

Thanks for the replies gents,
I went for a deep dovetail with a straight entry to sink my 50mm jaws (the biggest i have bar the coles) into, and went carefully and so far so good with no wobbles whatsoever. It is/was a well balanced bit of timber and didnt even vibrate my bench, which was unexpected. :shock:
Couldnt use the tailstock for support cos the bowls too big to go over the bed on my CL2.

 

[gregmcateer]

That's an interesting thread - thanks Nev for raising the question.

I hope you don't mind if I extend the question - Is there any way of knowing how big a blank the bearings can handle? - I have a Nova DVR3000 and want to turn a big green (ie heavy) bit of olive. If I can, I'd like to get it max size, which may be bigger than the 16" diameter poss over the bed. Would I be unwise to try it without tailstock support? (The Nova manual reckons up to 29", but would this mean a thinnish platter?

Thanks for any advice,

Greg

 

[CHJ]

Any reasonable specification lathe bearings should be able to handle anything you can spin on it, it always helps of course to balance the piece as much as possible before spinning it up.

Just think of you car wheel bearings and how big a load they take when you hit a pot hole with the weight of your wheel.

If a lathes bearings fail because of track break through then there is a greater chance of it being because they are not of adequate quality of material or hardening in the first place, not their size.
As long as they are lubricated correctly and any pre-loading set correctly they should cope.

Things like hammering wood onto Lathe Drive Spigots in situ can do more harm to a ball race than any rotational loads.

 

[gregmcateer]

Thanks, Chas - Much appreciated.
Greg

 

[Richard Findley]

Hi Nev and Greg

Apologies, I'm a bit late on this one!

I turn all my bowls on a spigot and as I only have Axminster "C" jaws that spigot is 56mm diameter and a maximum of 8mm long. The biggest bowl I have turned on these was 18" by 5" deep in burr oak.

When turning any work the size of your grip is determined by your final design and how good your tool control is. It is possible to turn quite large work on a quite small spigot but if you are prone to catches expect it to leave the lathe a few times!

Whichever method you choose the standard safety advice stands:
1- start at a low speed and build up - slowly!
2- Always wear full face protection - there are several people killed or seriously injured each year through large work coming off or exploding and the turner having no more than safety glasses to protect them.

Cheers

Richard

 

[jumps]

three things that don't appear to have been focused on so far -

1. make sure that you are using exactly the right diameter, dovetail and depth for your jaws to have the maximum surface area holding.
2. extend this to ensure that the jaw edges are on a good square surface so that there's a positive location to any spigot as well as the jaw compression on the spigot (if going that route)
3. be careful when expanding into cross grain that you have sufficient wood on the outside of the recess and don't overexpand so that the stressed wood splits under cutting loads (and goes flying as Richard points out!). This is where a smaller recess and jaws can be a better overall solution than the maximum recess the bottom of the bowl/platter would seem at first glance to accomadate.

 

[OldWood]

Any reasonable specification lathe bearings should be able to handle anything you can spin on it, it always helps of course to balance the piece as much as possible before spinning it up.

Just think of you car wheel bearings and how big a load they take when you hit a pot hole with the weight of your wheel.

To back up CHJ on that one, some time back I looked up the bearings that my 6" Wadkins Bursgreen uses and found to my amusement that they were also specified for the front bearing of a Ford car - can't now remember which one.

Rob

 

[gregmcateer]

Richard and jumps,

Thanks for the advice.

Greg