Thread: Stumped! Goblet turning problem

G'day Ern

Sounds like the stem might be flexing. I normally hollow it out before shaping stem. Maybe try a steady if you have one

Have you tried a round bedan? I make mine from BIG old screwdrivers.

I assume that by "outside shaping" you mean the bowl only (leaving the stem for later) and that you're cutting from the middle out to the rim? I only mention it 'cos some people think "it's a bowl, so you cut towards the center" but either forget that hollowing a goblet is usually end-grain work or don't understand why you cut that way.

(Not applying this to you, just making sure it's said for anyone else who reads this post. )

Originally Posted by Skew ChiDAMN!!

I assume that by "outside shaping" you mean the bowl only (leaving the stem for later) and that you're cutting from the middle out to the rim? I only mention it 'cos some people think "it's a bowl, so you cut towards the center" but either forget that hollowing a goblet is usually end-grain work or don't understand why you cut that way.

ta much, i didn't know that but when i try it, i now know.

cheers

G'day Ern,
Am I correct in assuming that the chatter is occuring where the base of the interior melds into the side of the goblet? I experienced a similar problem a little while ago whilst turning a small goblet / vase from Broughton Willow. I think that the chatter occured because I could not get the tool rest close enough to the surface that I was cutting at the time & subsequently had an excess amount of tool overhang. Also, because the tool rest has been rounded on the tool support face, there seems to be minimal tool support as it rests on the tool rest & thereby allowing the tool to move & shudder as it is cutting. This jumping around seemed to multiply on itself the more I cut & tried to stabilize it.
To remedy part of the problem, I fabricated a tool rest from 7/8" square bright steel stock & welded it to a 6" length of 1" Ø round bar stock. I am able to get into the interior of goblets with this tool rest & support the tool much more securely & also get much closer to the cutting area.
Dunno if this is of any help to you Ern, but it worked for me when turning my little fiasco.
Regards,
Barry.

Originally Posted by ss_11000

ta much, i didn't know that but when i try it, i now know.

Stirlo, here's a quick diagram to help you see the difference. No matter what you're turning, you should try to cut so that the grain is supported by the grain beneath it. If you work in the wrong direction you start "lifting" the grain and end up with a lot of tearout. It's the same problem you get with spindle turning, but exaggerated.

It makes all the difference between a simple, easy finish and bashing your head against the wall, needing to spend an hour or six with the 80 grit gouge.

To be honest, 'cos I turn so many goblets I sometimes fall into the same trap and start turning bowls wrong... Habits can be nasty things.

Thanx guys for responding.

DJ, could be ... it's a fibrous timber so could be whipping about. But on a short stem of nearly an inch?

Skew: wouldn't an Oland tool really be a round bedan? Any case, light scrape cuts from the rim down are no prob, end grain cuts from the inside out ditto; yep Barry, wot you said. There's even a knot near the stem but that's not doing it.

Barry: yeah, willow 'resonates', pardon the pun, but there's very little overhang. I've gone 4-5" overhang into hard redgum before getting this kind of high freq catch/chatter. And the opening is too small to get any special rest into it ... well maybe; now you've got me thinking. Might be able to get something in closer. Will have a look

Or will have to settle for removing microns at a time.

[Edit: Skew, it's not grain tear-out, it's full blown chatter]

Unless you have a BIG oland tool (I wish! $$$) there's still a degree of flex in the shaft. As I said, my round bedans are made from big ol' screwdrivers and if they start flexing I know my toolrest will be flexing too!

Mebbe not tearout as such, but it often only takes the merest "grab" of the tip to initiate a major chatter session, especially in the whippier woods. Sometimes tearout is the cause, but you just don't see it 'cos the chatter has taken out the evidence.

But I'm inclined to point the finger at the stem... in my books that's a no-no. The stem is turned last for good reason, even if it is only an inch long. You not only increase the chance of lateral flex in the bowl section, but the reduced diameter of the stem means it can "wind up" which exacerbates chatter (once it's started) in a major way. Basically you end up with both lateral and rotational vibration.

Given all the reading I do, you'd think I'd be able to find the words to explain it clearly, wouldn't you?

Skew- you are so "eloquent" in your advice!! As is everyone else. And RSSR, realy good of you to post these questions for all of us out here in wood turning land.
I get so much from this forum- Particularly since I have not turned a goblet yet, but intend to, just for the challenge- if nothing else!

Originally Posted by Skew ChiDAMN!!

Unless you have a BIG oland tool (I wish! $$$) there's still a degree of flex in the shaft. As I said, my round bedans are made from big ol' screwdrivers and if they start flexing I know my toolrest will be flexing too!

Skew would you mind posting a photo of your improvised Screw driver/s!!
I'm running out of ???:eek: And I love your improvisations! I am about to tackle the international leaf springs with the thin angle grinder wheels for my scrapers.
Cheers

Here's the top & profile pix I posted elsewhere on a similar thread. Apologies for the quality, but I'm a turner, not a photographer... and I hate my camera.



That particular one was originally a small phillip's, but my main ones are made from mechanics' flats with about 12mm shafts; which also had a hex section near the handle for using a shifter.

Originally Posted by cedar n silky

Skew- you are so "eloquent" in your advice!!

If that means it takes me a 1,000 words to say "yes" then I plead guilty as charged, yer honour!

Appreciate the photo's. thanks

K, tried Barry's suggestion of getting a rest in close (overhang maybe three quarters of an inch in old money), used the normally trusty 5/16" Oland tool (pretty similar to your screw driver Skew) and got better results but still a long way off what I'd expect or need.

The 1" btw was the stem diam.

Think it must be the timber flexing. Done this kind of thing before with soft or medium density timbers without drama.

Guess it's micron ribbons or nothing. Not up to a steady rest at this stage. Might manage some steadying fingers.

Hollowing the inside first is real 'mess with my mind' stuff but I guess it could be drawn on paper and a template produced.

Maybe flex in the brainbox is the real issue

Originally Posted by rsser

The 1" btw was the stem diam.

My mistake. I should've realised that's what you meant. If the flex is that bad, it may be time to resort to [gasp] the 80 grit gouge! :eek:

Hollowing the inside first is real 'mess with my mind' stuff but I guess it could be drawn on paper and a template produced.

Maybe flex in the brainbox is the real issue

At least it keeps you on your toes, mentally.

Some people like to hollow to depth, then shape the walls from there; I can't work that way. I shape the top 3/4 or so of the outside of the bowl, then hollow the inside shaping and finishing (inside and out) the walls from the rim down. This way I can get the walls down to almost transparent thickness without major headaches. Once I've started hollowing past what I've already shaped on the outside I'll start switching back'n'forth between inside and outside, completing perhaps 5mm of the wall at a time.

This allows me to get the transition right while still keeping the walls nice'n'thin. It also means the "stem" section gives the maximum support it can to the area I'm working. Sounds fiddly, but it's really quite quick.

"The 1" btw was the stem diam."

Yeah, sorry 'bout that Ern. I forgot to mention that.
Have you tried setting the toolrest above centre when cutting with scraping tools ( when performing internal cuts )? I've found that toolrest height can sometimes alter the cutting position of the tool enough to stop chatter etc. Plus, use Rooolly, rooolly sharp tools. I know that I'm preaching to The Boss, but I thought that I'd just run it by you just in case.
Sounds like it may be a harmonics thing, so what you could try is wrapping a bit of firm foam rubber etc. around the exterior & securing it in position with masking tape, electrical insulation tape or racer tape. This may give added support to the goblet in the critical area & move the harmonic frequency to a different level & reduce / stop the chatter. I've always been going to try this myself but never actually gotten around to it - not because I don't get tool chatter with my turning. I think that I actually invented it! :eek:
Could you work the tool with one hand & support the exterior surface with the other hand, you know just letting the fingers rub against the goblet?
This may help as well.
Regards,
Barry.