A wobble in the bead?

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A wobble in the bead?

Postby ericgoodson » Mon Oct 28, 2013 5:32 pm

A question for more experienced turners:
Below the core and the mandrel in the following image you can see where I am chasing a bead down, and yet in just one part of the bowl the bead is sort of wavy, and only in that portion. I was working hard to hold my tool steady, but maybe I was not working hard enough. What has caused this?
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Re: A wobble in the bead?

Postby gavin » Mon Oct 28, 2013 7:47 pm

ericgoodson wrote:A question for more experienced turners:
Below the core and the mandrel in the following image you can see where I am chasing a bead down, and yet in just one part of the bowl the bead is sort of wavy, and only in that portion. I was working hard to hold my tool steady, but maybe I was not working hard enough. What has caused this?

Look closely at your tool-tip. It will vibrating harmonically - for you have a wave on your work.
This is caused by some combination of
    1. flex in the shank of the tool
    2. movement in the tool rest
    3. movement in the crutch that supports the tool rest

If you can get A N Other to operate the lathe and turn whilst you observe, you'll learn a good deal. Failing that, video yourself as you work from multiple angles and you'll rapidly diagnose your problem.

Once you have such a wave in your work, you need to concentrate on removing only the crest i.e. the tops of the wave with your hook.
Report back!
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Re: A wobble in the bead?

Postby woodness sake » Tue Oct 29, 2013 12:07 am

differing wood density
same start and stop position
different start and stop position with too much pressure on the tool
dull tool
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Re: A wobble in the bead?

Postby gavin » Tue Oct 29, 2013 8:35 am

woodness sake wrote:differing wood density
same start and stop position
different start and stop position with too much pressure on the tool
dull tool

And I'd agree with those suggestions too. I would not have credited different wood density as a possibility BUT if you were turning wood that was not fresh or half-seasoned, you could have rotten soft bits. ( Why you would turn such I don't know - but there is logical possibility you may be...?)

Once you get a wave or a wobble it tends to self-reinforce. As a next step, I'd aim just to remove the tops of your wave.
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Re: A wobble in the bead?

Postby ericgoodson » Tue Oct 29, 2013 3:37 pm

Many thanks Gavin and woodness sake. Great points.
I will check the tightness of the rest and the crutch holding the rest up.
If there is flex in the tool, I would be amazed, and if there is, I am out of luck as these are the only tools I have.
I have never experienced it before, so maybe it was caused by some unique property in the wood. Interesting possibility. I will see if it comes up with the next bowl.
I had not considered the start/stop position possibility. If I see it happening again, I will try moving the strap a bit. Maybe I was pushing too hard in the midst of a press on the treadle, and that was causing it.
I was able to lop off the crests of the waves, but they just kept coming back, for a while. Once I had chased the bead further down and got closer to the bottom of the bowl, the problem went away. Maybe it had something to do with the angle of the tool or how far the hook was projecting out from the tool rest.
Dull tool? Yes, a definite possibility. I am still learning how to quickly sharpen the hooks. I can get them quite sharp, but it takes time.
Again, thanks for the pointers!
If I figure anything out, I will be sure to post.
Best,
Eric
"Use it up, wear it out, make it do, or do without."
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Re: A wobble in the bead?

Postby gavin » Wed Oct 30, 2013 9:33 am

ericgoodson wrote: these are the only tools I have

Did you make them? Did you buy them?
They are not hard to make - once you have made 10! Making the first is a challenge, but if you can locate a forge and anvil and an old car spring (aka OCS) preferably 14 or 16 mm diameter ( from a jeep or land rover is good) you can bash hot iron which is always fun. You'll need a linisher or grinder to form the edge. Ben Orford supplies such hooks - google him. He can show you how to make them too - but you are in US and a trip to England may not suit your pocket or your carbon footprint.
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Re: A wobble in the bead?

Postby TonyH » Wed Oct 30, 2013 11:06 am

In a cross grain bowl, there are always a couple of patches where you're cutting at a less favourable angle with respect to the grain. Careful inspection of a finished bowl can usually show whether it was turned right or left handed because of the positioning of the slightly rougher spots that it causes.

It is hard to judge scale from a photograph, but perhaps it is a matter of just trying to take too heavy a cut on each pass ? Too much force will inevitably make something flex and judder.
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Re: A wobble in the bead?

Postby ericgoodson » Wed Oct 30, 2013 6:29 pm

Gavin, I bought my hooks from Ben Orford. I am about to take a metalworking class and hope to learn to make hooks. I am very curious about how larger and smaller hooks cut differently, as well as external bevel and internal bevel. I like Ben's hooks, and don't think they are flexing, but what do I know.

Tony H, thanks for your input. I do think I was taking too aggressive a cut, so that could be part of it. I will try to be more delicate. Pretty ham fisted these days. I have noticed that two patches are always rougher where I am cutting up hill against the grain. Still trying to keep the plucking down to a minimum (keeping tools sharp, letting wood dry out a bit more).

Again, thanks to you both for some feedback. It is really helpful. I am trying to figure this out on my own here. No one I know does this sort of thing.
Eric
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Re: A wobble in the bead?

Postby Steve Martin » Thu Oct 31, 2013 5:03 am

Eric, Have you tried to meet up with or contact Peter Follansbee at Plimouth Plantation. Although furniture and spoons are his "things", he has been seen using a pole lathe. I bet he could also put you in touch with other PLT's that are closer than I am in North Carolina. He has a blog which covers a lot of interesting stuff and he has a definite greenwood approach to wood working. Good luck!
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Re: A wobble in the bead?

Postby ericgoodson » Tue Nov 05, 2013 7:12 pm

Steve Martin wrote:Eric, Have you tried to meet up with or contact Peter Follansbee at Plimouth Plantation. Although furniture and spoons are his "things", he has been seen using a pole lathe. I bet he could also put you in touch with other PLT's that are closer than I am in North Carolina. He has a blog which covers a lot of interesting stuff and he has a definite greenwood approach to wood working. Good luck!

Thanks Steve!
Yes, I have spoken with Peter a few times. He was my initial inspiration to turn toward greenwood carving and away from power tools. After making the switch and carving some bowls, cups and spoons, I visited him this September to share a few samples. He has always been very approachable and interested. He says he is offering a spoon carving course this winter up in Maine, so hopefully I can pick his brain there more. But you are right, I should ask him if he knows of other PLTs in the area. Thanks.
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