skew chatter

[Woodmonkey]

Having problems with the skew. I can get a lovely clean finish, but suddenly the to will start chattering and I'll end up with spirals like this

Seems to do it more as I get further away from the head stock end, the bit in the picture is about 300mm. Doesn't seem to matter what speed I've got it on, the tool is nice and sharp, any suggestions?

 

[Richard Findley]

It's unlikely to be anything to do with how far from the headstock you are, because you have your tailstock in place, so the work is well supported. More likely it's related to body movement.

You will be stood comfortably to start the cut at the left hand end (you must be left handed?) as you cut to the right you are not moving yourself evenly across the length of the wood, which means you are either over reaching or twisting yourself and so probably end up applying too much pressure on the last couple of inches of work.

Move yourself to the right a little, start with your weight over your left leg and as you cut, transfer your weight to your other leg, keeping your movement as smooth as possible.

Hope this is of some help

Richard

 

[Mark Hancock]

+1 for what Richard has said.

In additional make sure you on putting pressure with your steady hand down onto the tool rest and not onto the work. Let the tool and lathe do the work.

 

[Spindle]

Hi

In my experience, barley twists such as these are best avoided by supporting the work with your non tool holding hand by wrapping the fingers that aren't guiding the tool around the work. Cutting from the opposite direction is the easiest way to remove the twist and varying the speed will reduce the chances of a re-occurrence.

I will however try Mark's advice re loading the tool rest next time I produce a barley twist, (I've tried to produce them to order but can't).

Regards Mick

 

[Woodmonkey]

Thanks fellas I will have a play around with stance and pressure on tool rest. It's fractions isn't it, just moving a few inches or applying more or less pressure in the right place makes all the difference

 

[Jonzjob]

Two's up for the fingers round the wood. It damps out most of the chattering. Light cuts too. I'm with Richard on moving your body and try to keep your hands as steady as you can..

Practice makes perfect too.. Failing that sanding works :mrgreen: :mrgreen:

 

[Richard Findley]

While I agree that supporting the work with your front hand is a very useful and valid technique (one that I use often), it is usually only needed for long and/or thin work. The example in the photo looks like it shouldn't really need it. One thing I have noticed though is a knot in the wood in the centre of the spiral.

Knots can cause problems in several ways but the thing to remember is that they are only wood, so they will cut. They may be harder than the surrounding timber but with care, they can be cut as if they aren't there at all!

Best of luck with it, and let us know how you get on!

Richard

 

[Spindle]

Hi

I think what happens when barley twists are formed is that the skew is bouncing on the work. In this case the knot or some other anomaly has made contact with the bevel and caused the bounce which then continues as the bevel contacts the result of each bounce.

The effect is more often experienced on thin unsupported work because not only will the tool bounce but the work will flex also.

Supporting the work by wrapping your fingers around it reduces the tendency for both tool bounce and work flexing by effectively coupling the work to the tool.

Well that's my theory

Regards Mick

 

[dickm]

Have often had similar problems, especially when in a hurry . So one question - using the "hand behind the spindle" technique, how do you avoid getting very burnt fingers????

 

[Woodmonkey]

I can see how supporting the work piece would help on very thin pieces but in this case it was around 2 inches thick so don't think it would've made a difference.

 

[Jonzjob]

Have often had similar problems, especially when in a hurry . So one question - using the "hand behind the spindle" technique, how do you avoid getting very burnt fingers????

Light pressure and to realise when it's getting too hot :mrgreen:

But I agree, on a spindle that thick the vibration shold not be a problem..

 

[Neil Farrer]

While I agree that supporting the work with your front hand is a very useful and valid technique (one that I use often), it is usually only needed for long and/or thin work. The example in the photo looks like it shouldn't really need it. One thing I have noticed though is a knot in the wood in the centre of the spiral.

Knots can cause problems in several ways but the thing to remember is that they are only wood, so they will cut. They may be harder than the surrounding timber but with care, they can be cut as if they aren't there at all!

Best of luck with it, and let us know how you get on!

Richard

Richard,

Can this be caused by cutting with the skew near the centre and not the lower quarter?

 

[Spindle]

I can see how supporting the work piece would help on very thin pieces but in this case it was around 2 inches thick so don't think it would've made a difference.

Hi

Please re-read my post - the work doesn't have to be slender to produce barley twists, I've had them on 3" oak.

Regards Mick

 

[Richard Findley]

As Mick says, it's possible to get chatter marks of one kind or another on all sorts of sizes of timber, for all sorts of reasons. In this case it seems unlikley its the wood flexing, most likely body movement, too much pressure on the wood with the bevel/heel of the tool and/or the knot.

Using the wrong part of the skews edge can result in the tool kicking, if you stop it before it catches it will leave a mark, but its unlikely to cause such a nice even spiral pattern.

The technique of using your front hand to support the work is usually used on slender work, in which case its only small (like lace bobbins for example) so doesn't burn you, or its running at a lower rate of rpm, so again less of a problem. Of course a good callous on your hand from years of doing it helps to reduce the burning sensation! Centre stedies are of course another option which helps considerably on long thin things like stair spindles, but I think I should reiterate that I think this isn't the problem in this case - especially with the spiral happening so close to the live centre support.

All the best

Richard

 

[Woodmonkey]

Hi Mick
I was agreeing with you, in this case the twist was not caused by the workpiece being slender so supporting it from behind wouldn't help. If it was the knot causing it then not sure what the solution is as I tried taking the lightest cut possible and it didn't help

 

[Spindle]

Hi Woodmonkey

The point I was trying to draw your attention to was that by supporting the work with, in my case, my left hand which is also in contact with the tool tip I create a coupling with my hand between tool and work. In my experience this reduces the tendency for the tool to chatter. That technique plus varying the lathe speed works for me

Regards Mick

 

[Woodmonkey]

Cheers mick I'll give it a try next time I'm in the workshop.

 

[JimB]

Looking at the picture the chatter seems to have begun at a flaw in the wood. Once it's there practically anything exacerbates it - worn bearings in a live centre, a bit of flex in the tool rest etc. My first reaction is to put on a shorter rest and go for my most delicate skew (a half inch Marples carbon steel). It means I have to take very fine cuts and usually have to change my stance. I also feel I can get it sharper (for a short while anyway) than HSS. If this doesn't work I put on a solid centre.
All the advice above is excellent especially putting fingers behind the work - it seems to help you present the skew better as well as damping out any vibrations from whatever cause.

 

[Dalboy]

Have a watch of this where he discuses ridges with the skew Near the beginning

Understanding catches

 

[JimB]

Watched that once before. It gives me the creeps to see him doing it deliberately.