How would you mount this?

[Skew ChiDAMN!!]

Just after some ideas on turning methods for a project I'm thinking of doing; basically, it's a double-ended goblet. ie. one that has a bowl at both ends and can be used either way up.

I'm planning on rounded, brandy-snifter shaped bowls, about 4" at the widest dia and about 3" deep, with a 2" opening and wall thicknesses in the range of 1/16"=1/8". The stem... well the total distance between the bottoms of the two bowls, will be around 6" long to bring overall height to 12" and will vary from 3/8" to 3/16" in diameter.

I'm sure you can see why I anticipate problems mounting this.

I think I'll start as I usually do, rounding the blank between centres and then mounting in spigot jaws to hollow out the first bowl and shape the top 3/4 of the outside, doing a final finish as I go. Now this is where my planning gets squirrelly... how do I mount it safely so I can end-hollow the 2nd bowl? :? :?

At first I thought about a doughnut chuck to hold around the first bowl, but they're susceptible to lateral movement at the best of times and with the shape of these bowls would really amount to naught more than a ball'n'socket. Not my idea of a "secure" mount, thankyouverymuch! :rolleyes: At the moment the only thing I can think of that would stand up to the stresses of end-hollowing a 12" long blank would be a very deep jam-chuck, (well... sort of) that at least half of the blank sat in.

By "sort of" I mean that it wouldn't quite be a jam chuck, but still a close fit just the same. I'd slot the last couple of inches so that a hose-clamp on the end wouldclamp it tightly onto the unturned section of blank, thus avoiding any marks on the finished bowl from a "force fit."

I'm pretty sure that'd work but I'm a Scot and wasting that much timber to make a jam-chuck for what will be a one off piece of work, well... let's just say it rubs me the wrong way.

Once I have both bowls turned, I'm confident I can turn a plug for each end to turn the stem between centres, being careful of whip & flex...

Ermmm... help? Any other ideas? :?

[Frank&Earnest]

Hi Skew. As you would know by now, I might not know the pointy end of the chisel, but I enjoy these problems and am not afraid of talking from my round end...:D

The solution IMHO is in your last sentence:


Once I have both bowls turned, I'm confident I can turn a plug for each end to turn the stem between centres, being careful of whip & flex...


If you have a chuck with jaws like the Teknatool Supergrip, the roughed cylinder would be within the safety limits they advise. Therefore you could just hollow and finish the inside of both bowls because there should be enough wood left to grip the side hollowed first without crushing it (4"-2" = 1' thick rim - you could build some safety by starting from a slightly bigger cylinder). Then you can proceed as you said for the whole of the outside. For you, should be a piece of cake!

[joe greiner]

Interesting. My first thought was to make the bowls tapered inward on the inside (i.e. not undercut) so you could use a tapered plug with outside filament tape for protection and a hose clamp. Said taper would be flat enough to discourage disengagement. The other end of the taper could be a spigot to fit a 4-jaw chuck. The plug could be duplicated on the second bowl to turn the stem between centres.

For the undercut rim, similar to above, but use an expanding segmented taper like used on tailpipe straightening tools. Bruce Leadbeatter was issued US patent No. 4541465 for an expanding chuck using a similar principle, but the solid taper engages a segmented socket. The wall of the bowl would be pinched between the expanding taper (also cushioned) and the cushioned hose clamp. Would take several attempts at mounting to minimize wobble, but not the first time that would be needed (at least for me).

Joe

[old_picker]

how about doing 2 separate cups and cunningly joining them stem to stem
a little bit of clever design and some very accurate turning
then let em figure out how you done it

[Skew ChiDAMN!!]

If you have a chuck with jaws like the Teknatool Supergrip, the roughed cylinder would be within the safety limits they advise. Therefore you could just hollow and finish the inside of both bowls because there should be enough wood left to grip the side hollowed first without crushing it (4"-2" = 1' thick rim - you could build some safety by starting from a slightly bigger cylinder). Then you can proceed as you said for the whole of the outside. For you, should be a piece of cake!

Sadly, no. There won't be 1" of thickness to play with, I almost wish there would be. Perhaps this sketch will give you an idea of what I'm hoping to do? All measurements are approximate at this stage... (else I'd be measuring in mm. :wink:)

49609


how about doing 2 separate cups and cunningly joining them stem to stem
a little bit of clever design and some very accurate turning then let em figure out how you done it

I've thought about that, too! However, the idea is for this to be a "wow" piece for other turner's, so I'm trying to avoid the tricks I use for the unwashed masses. One of the problems with trying to impress other turner's is that they're too damned likely to know the same tricks! :rolleyes::D

[Frank&Earnest]

I did not explain myself. If you start from a solid 5" cylinder, for example, the rim would be 1.5" and the weakest point .5". Still think it would be ok.

[Richard Findley]

Hi Skew,

You don't like making life easy for yourself do you!?!:q

Just thinking through the process (knowing me, probably not very thoroughly!) you would want to part hollow both ends so when you're working on the second bowl you only need take light cuts, no heavy roughing and less chance of catches. So...

...part form both bowls, leaving a gripping spigot on the first, but finishing the inside totally and the outside roughly, leaving the very rim as a gripping spigot which can be removed at the end. Then cut a disc of some sort (sorry thats a bit vague:doh: !!) which will sit inside your rim/spigot which will support the gripping spigot, so that you are essentially gripping a solid piece of wood. You can then work the second bowl to a finished inside and rough outside then a final mount between centres as you described:

"Once I have both bowls turned, I'm confident I can turn a plug for each end to turn the stem between centres, being careful of whip & flex..."

You then remove the gripping spigot and final finish the outsides of your bowls. Job Done!!

You would probably need to make templates of some sort as checking bowl wall thicknesses would be hard or impossible in these final stages.

I've probably missed something and/or not discrbed myself very well but I hope it helps... even if only in a small way!

Good luck :2tsup: (you may well need it for this one!!!)

Richard

[Jackson]

What's the end product meant to do/be Skew?

[dai sensei]

After rounding blank, hollow both ends to finished shape using your jaws to hold. Then you could use jam chucks or plugs at both ends to turn the outside.

For extra support whilst turning the cups, you could also turn the stem down slightly, just enough to use a small center steady. This would also assist while finishing the lips of the cup - ie take away the tailstock.

[Cliff Rogers]

What Neil said. :2tsup:

[Frank&Earnest]

After rounding blank, hollow both ends to finished shape using your jaws to hold. Then you could use jam chucks or plugs at both ends to turn the outside.


Isn't that exactly what I said, put in more concise and precise English?:)

[Manuka Jock]

What's the end product meant to do/be Skew?

Raise the bar for the rest of us , eh .:U :U :U

[Frank&Earnest]

One picture is worth a 1000 words.

Pictures 1 and 2 prove that I am a good problem solver :wink: .
Picture 3 and 4 prove that I am a lousy turner...:C .

[Cliff Rogers]

A picture is worth a 1000 words but the 3rd one is speechless to me. :D

[Skew ChiDAMN!!]

What's the end product meant to do/be Skew?

It's for teasing Scots. You offer them the goblet and a full bottle of your best Malt Scotch... then tell 'em "fill it up, and I'll have the rest." :D


One picture is worth a 1000 words.

:2tsup: They certainly do. Good attempt, BTW!

Normally I'd turn & finish the outside of the bowl at the same time as the inside, so I can use the ol' finger-gauge (SHHH! Do as I say, not what I do! :p) to ensure constant wall thickness and flowing curves. Obviously I hadn't given a moment's thought to your way... one of the problems with turning so many "normal" goblets is that I get stuck in the ol' mental rut. :-

As Richard mentioned, it introduces the problem of guessing wall thickness later (as you found out! :D) but he also suggested a practical solution.... templates!

Thanks fellas, now I know what direction I'm heading. I reckon I can wing it from here.


A picture is worth a 1000 words but the 3rd one is speechless to me. :D

Maybe he was giving the camera a "rest?" :rotfl:

(Sorry... I'll crawl back under my rock, shall I?)

[Frank&Earnest]

A picture is worth a 1000 words but the 3rd one is speechless to me. :D

Let's try to speak LOUDER... got it now?:D BTW, this proves that the chucking method REALLY works!:- And, Skew, I was using a template... but my skill level does not suit 1/16 crapiata!

[powderpost]

Skew, I would be tempted to turn one end using dowel, waste block, face plate idea, leaving the stem 20mm thick. Then using a plug in the finished end use TTIT's egg cup chuck concept to produce the second bowl. Finish off the outside with two plugs between centres. Lot of mucking around, but could work.
Jim

[joe greiner]

Assuming this enquiry is still alive, and having seen your cartoon of the final desired shape, I'll jump back in with a suggested procedure.

1. Using crapola firewood, not valuable timber, prepare two cup chucks with multiple fingers and hose clamps. Turn the initial blank for both of these between centres so as to preserve at least one of the divots. Turn spigots at both ends, separate the two halves, mount each in a four-jaw chuck, and turn a more or less rectangular hollow with rounded interior corners. Inside diameter slightly larger than the OD of the goblet bowl, depth about 2 inches (from your cartoon) to reach slightly beyond the equator of the bowl. Slice the walls in about 16 places to make flexible fingers. Use two hose clamps on each cup chuck, with the screws 180 degrees apart for balance. One clamp tightens the fingers, and the other binds the fingers at the base of the cup to avoid flexural breakage. DAMHIKT.

2. Mount the goblet blank between centres. Turn the stem region to about 3 inches diameter, and turn a spigot at one end.

3. Mount the goblet blank in a four-jaw chuck to hollow one of the bowls and turn part of the bowl's outside to a distance beyond the fingers of the cup chuck. Use a steady rest on the oversize stem. Finish the interior and partial exterior of the bowl. Wrap the bowl at its equator with a single layer of masking tape with no overlap.

4. Reverse the workpiece, with the first bowl mounted in one of the cup chucks, itself mounted in the four-jaw chuck. Again using a steady rest, hollow the second bowl and turn its outside as before. Also finish this bowl as before, and wrap the outside of the bowl as before.

5. Loosen the hose clamps of the first cup chuck. Set the second bowl in the second cup chuck, with the tailstock lightly engaging the divot preserved in the first step above. Progressively tighten all hose clamps with light pressure from the tailstock to assure concentricity. Jog the lathe motor a few times to be certain.

6. Turn the remainder of the bowl exteriors and the stem, finishing progressively to avoid excessive side pressure.

Uncle Bob would be pleased.

Joe

[Skew ChiDAMN!!]

Skew, I was using a template... but my skill level does not suit 1/16 crapiata!

Does anyone's? :D


Assuming this enquiry is still alive, and having seen your cartoon of the final desired shape, I'll jump back in with a suggested procedure.

I'm always interested in hearing alternative methods. :) I see you're familiar with the problems of flex in thin-walled bowls and can see how it applies to this project. It's one of my main concerns, hopefully it's just my overactive imagination and when it comes to the crunch it'll only be a minor concern.

Your way is close enough to my "normal" method, as far as the bowls are concerned, that I think I'd be more comfortable using it than working with templates all the way. (I dislike pattern turning with a passion... :-) 'Tis just as well I haven't made a start on the turning yet!

[rodent]

One of these days skew ( probably next century ) you'll actually learn how to use a gouge for a goblet not a scraper . Oh well maybe you'll have to use booger to do the hollowing and shaping just keep him sharp .( booger jess named this tool after i set it's handle and shaft in polly urethane it foamed up pushed the handle up when pushed back in ,it ozzzzed out and she though it looked like a booger ,named though art , tis what it's called ) oh well that's jess for you . When things go insanely south have a laugh .:doh:

[Skew ChiDAMN!!]

One of these days skew ( probably next century ) you'll actually learn how to use a gouge for a goblet not a scraper .

Mate, the day anyone can show me how to do a hollow form (don't forget... my goblets are not just bowls on legs! :D) and use a bowl gouge correctly all the way, then I'll convert. Until then... :p