Test the curves

[Frank Kobilsek]

I keep reading about long flowing continuous curves make the best turned shapes so I have concentrated on this in developing shapes of bowls and vessels. Regardless of how a piece feels when mounted on the lathe things looks different when finished in your hand or on the shelf. So I have been trying to develop tests for flats and bumps. I have come up with two methods to inspect for small shape irregularities.
1) on convex surfaces I take a plastic membership card (credit card) and 'roll' it up the hill. You can feel and find the tiny-est flat spot.
2) roll a marble or ball bearing under your hand accross the surface to feel for bumps. I think it amplifys them so you can find them. This method is not a good as the card on the outside but I have myself talked into that it works on the inside of a bowl.

My tip of the month
Frank

 

[john lucas]

Frank My friend Joe Looper told me to run your hand from the lip of the vessel down toward the foot. You can feel the curve better. I've also heard that you can take a flat ruler and gently rock it from top to bottom. It will pause on any areas that are flat.
With either of these methods you can still have an ugly piece. There are a lot of variables that make a piece nice and only experience will tell.

 

[KenN]

As Protagoras taught us so long ago: "Man is the measure of all things" - or something similar. Three or four fingers touching each other and lightly run over a curve will tell you when it is "fair enough". It should be done with the lathe stopped. Visual acuity and tactile sensitivity are amazingly tuned.

 

[DennisM]

Shape and Form

Frank;
The topic next Monday night at the Central Illinois Woodturners meeting is "Shape and Form". The presenter - me - would love to have you share your knowledge with the club. Besides, from the look of my notes the program may run a little short and a second speaker should get it to about the right length. Or, is your shedule still conflicted for another month or two.

Dennis

 

[sifugreg]

Another thing a great turner taught me once was to stop the lathe, walk away from the item and give your eyes a short rest. Then view from several different angles from different positions in the shop. This will change background shading and sometimes content. You'll be amazed what you see as slightly undesirable curves or high spots.

 

[Andy Coates]

curves

I don't think you can better removing the bowl or form from the lathe (whilst still held in the chuck) and placing it down, stepping back, and looking at it.

 

[Frank Kobilsek]

Dennis, I'll be there in September, I promise, but you are scaring me a littel with be a presenter on my first visit. Bloomington right?

I've been playing with alot of things to find 'flaws' in both vision and shape. After your numbers get up I think it is natural to slow down a little a try to find that next level of quality. Andy I'll have to try removeing the chuck with the piece still mounted and walking around in different light etc.

Maybe the Card (or ruler) idea will help somebody.

Frank

 

[john lucas]

Turn it upside down. That often helps evaluate a shape although I'm not sure it will help find flat areas. A good shape looks good upright or upside down. It's also very hard to evaluate a horizontal on the lathe. Standing vertical with a clean background behind it really helps.

 

[TurningDog]

i am of two minds when it comes to shape and form. There are two markets for me locally one will buy only what looks right i.e. have angles in some relationsip to the golden mean. I never make all that much on these., probably because every other local turner is making bowls and hollow forms with the same lines and in the same sizes,

Where I really make the money and get attention locally are my odd ball sizes and shapes. They tend to look horrible wrong and mishapen, like aborted projects left on the clay wheel. The more wild and offsetting I can make them the more I can charge. The wilder the finish I can incread the price even more. I suggest everyone try a series of off putting shaped pieces once in a while

 

[Sean Troy]

You can test for flat spots using a PVC coupler. Size of the coupler depends on the size of the turning. Move the coupler around on the turning (open side to the wood) when you see gaps, you've got a flat spot. The rounder the turning, the better this works.

 

[MichaelMouse]

The eye will give better gross information, the hand better fine. No need for external devices if you examine it for fairness against a contrasting background, then run your fingers over the surface to find any ridging.

Machinist friend of mine says we can feel in the thousandths with our fingertips. I believe him.