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loz
18th October 2005, 01:53 AM
This has probably been asked hundreds of times but I shall ask again anyway.

I enjoy turning goblets but have a lot of problems with chatter when turning the inside. I have an ancient but very solid Tough lathe and an excellent screw cup chuck so the basics are there, the wood is held very firmly. I always turn the inside and then work my way down the outside towards the base.

I often use a large spade bit to remove the bulk before turning to shape with a combination of a long gouge and various scrapers. Recently at the perth wood show I was dissuaded from buying a ring tool by a member of the wa woodturners assoc. who advised me to buy a piece of square section HSS and make a rounded scraper profile on the diagonal so that the face presents at 45 degrees to the stock. Did that but it doesn't seem to remove much material or reduce chatter.

The gouge produces the least chatter but I cant seem to achieve the internal profile I want with it

Can chatter be eliminated completely and if so how?

Laury

Utuk_Xul
18th October 2005, 01:02 PM
I use a detail gouge to hollow endgrain. You may trying making a Hill Shear scraper out of an old roughing gouge if you have one you don't use. How long is the piece? The longer the piece the more vibration.

Dean
18th October 2005, 04:49 PM
What about something like this?
http://www.mik.com.au/layout/productDetail.asp?productID=2400&model=A2400

Note the last photo in particular. A tool rest extension (basically flat bar) that sits inside the end grain hollowed section to provide tool support deep into the end grain?

rsser
18th October 2005, 06:32 PM
Yeah.

Sorry to ask but you are leaving finishing the stem til last?

Otherwise, couple of fingers on the outside to steady it and light cuts inside.

What kind of wood are you turning?

Mike Jefferys.
18th October 2005, 11:20 PM
End grain turning is nearly always a pig of a thing to do - no disrespect to pigs I've known my share of nice pigs. A couple of suggestions - be sure your scraper is as massive as is reasonable but has its contact with the work optimised which generally means minimised. With side grain face work such as bowl bottoms a massive 38mm wide x 10mm thick scraper with a lot of tool engagement works just fine but end grain is intrinsically more challenging. Try a scraper with a lot of cross section when end grain hollowing. You may not be aware of it but most standard scrapers - say the standard 6mm x 19mm or 25mm - actually flex when end grain hollowing hence they dive and cause chatter. The ideal might be a 12mm square HSS bar shaped so that about 6 or 7mm max is actually in contact . Then experiment with the sharpening angle - I work with about as little as 4 or 5 degrees undercut. If you have a more agressive angle it tends to dive into the cut conversely a blunt angle tool is tamer which you want with end grain. Finally use a handle high presentation with contact on or below centre and work with a trailing cut, negative angle region if this makes sense.
Finally whats wrong with crystal for goblets? We gave up drinking out of wooden cups about 500 years ago - what is this obsession with wooden drinking vessels? Would you seriously prefer to drink a good red out of a wooden goblet or a nice glass? Not that I want to start a fight or anything but there is maybe a fitness-for-purpose argument here.
Mike Jefferys

Mike Jefferys.
18th October 2005, 11:29 PM
Another point. A screw chuck might give you the impression of a secure fixing but it is really only held on centre by a single screw and will flap about in reality even though it may look like it's well held. You might be much better to try a scroll chuck which grips the piece further out typically at the four jaw points and is inherently more secure. Did you happen to catch the ultra slow mo cricket shots in the latest test? The ball hitting and flexing the bat is an interesting comparison and indicates what we might be able to see in a turning situation if we applied the technology. I suspect the work piece would be flexing and reacting to applied tool pressures in a way we might never be aware of.

Mike Jefferys

gatiep
19th October 2005, 08:35 PM
I have an ancient but very solid Tough lathe and an excellent screw cup chuck so the basics are there, the wood is held very firmly. I always turn the inside and then work my way down the outside towards the base.

The gouge produces the least chatter but I cant seem to achieve the internal profile I want with it

Can chatter be eliminated completely and if so how?

Laury

Mike. Loz is using a Screw Cup Chuck, not a screw chuck (totally different )according to his post.

Loz,
I use a 13 mm Hamlet spindle gouge ground to a finger nail shape. ( 10 mm spindle gouges often have too much flex which will lead to unnecessary hassles ).Set the tool rest so that when the tool is held horizontal the bottom of the flute is on the centerline of the work. Keep the tool horizontal and on the centre line for the whole cut. Keep the speed up high and take light cuts. Cut with the gouge on it's back or try by rotating the gouge so the the bevel rubs against the side. With this combination one can do any shape you like inside the goblet. Finish off with very light cuts using a round nose scraper, in negative angle in the bottom or tilted to the left when scraping the sides, only if really necessary. Be patient and scrape the sides from the rim towards the bottom. Going opposite and creating chatter can shatter the thin sided goblet.

I teach goblet turning as part of one of the courses and find that I very seldomly use a scraper in turning the inside of goblets, bowls, boxes or platters. Presevere with the gouge, soon you'll find that you can get a finishing cut with the gouge and then just a bit of abtasive before applying the Shellawax.

Skew ChiDAMN!!
19th October 2005, 09:26 PM
When left to my own devices, rather than working to order, I turn goblets more than any other thing. Probably something to do with the pile of old redgum posts in my shed and the dearth of any cured billets. ;)

As most of my goblets are a partially closed form, ie. like a brandy snifter, the form dictates against the use of gouges except for the initial cuts. I've made a set of tools specifically for this job, mainly from old scrapers but some I designed to cut on the angle, much like a skew designed to fit inside curves. These are tools that basically do the job for me I don't know if anyone else would use 'em. [shrug]

Mike J is spot on with his suggestion of thicker tools, the thicker the tool the less chatter. The thicker steel can mean difficulty on tight inside curves but it doesn't take much to thin the 1" closest to the cutting edge. I've also found that when scraping near the centre of the inside, notching the RPM up a bit helps. BTW, lowering the RPM can enhance the chatter
and give some startling effects. (If I can't eliminate it, I make it a feature! :D)

I assume you're not turning the stem until last? After rounding a blank I'll rough turn the outside of the bowl, then the inside, then completely finish & polish it. I then fit a turned plug into the mouth and bring up the tailstock, before turning the stem & base. This leaves maximum support during the heaviest working...

Apart from that, sharp tools and a light touch...

loz
29th October 2005, 12:00 AM
Gents

Thankyou for the varying but informative opinions. In answer to a couple of questions, yes I do the stem last. I turn the inside and then shape the outside from the top down to the base. My scrapers are quite heavy- yes I know I will be branded a heathen for this but they are made from LARGE old files. I am aware of the risk involved with using files for this purpose but they are heavy enough not to be put at risk of shattering by my lathe. Mike - I make goblets from wood because I enjoy making them - I prefer to drink my single malt whisky from a crystal tumbler!

I have promised my sister a cubby house for her rug rats but once that is done, I will put some of your excellent tips into action.

Laury