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ozhunter
25th October 2012, 09:21 PM
Hello all

I'm in need of some advice.

When turning between centres, if I use a skew, a roughing gouge or a spindle gouge, I end up with a shallow spiral all the way down the work. Not like a spiral catch, just a shallow spiral right down the length.

After not using the lathe for quite a while some things are are a bit rusty. My sharpening seems OK (just ask my finger after I drug it across the point of a skew :o)

The pieces I'm turning are about 400 long.

Any suggestions most welcome.

Cheers

Mobyturns
25th October 2012, 09:55 PM
What diameter is your work piece? Chances are you are putting pressure on the cut, deflecting the work piece or have poorly aligned centres on the lathe. There are other causes of course.

Sawdust Maker
25th October 2012, 10:01 PM
I'd suggest that you are moving the tool too fast down the piece thus cutting a spiral groove. Either slow down the left/right chisel movement or speed up the rpms of the piece.

ozhunter
25th October 2012, 10:50 PM
Thanks for the replies. The piece is on a taper from 43mm to 32mm, I'm traversing downhill.

I tried slowing down the lateral movement, but it didn't seem to make much difference. Speed is about 1400 or so, can't remember without going and looking. One step from flatout on the Woodfast anyway.

I never thought to check the centre alignment, I'll do that tomorrow.

Mobyturns
25th October 2012, 11:02 PM
This is one of those occasions when a bit more speed would be helpfull.

Rod Gilbert
25th October 2012, 11:28 PM
+1 more speed.
Regards Rod

RETIRED
25th October 2012, 11:30 PM
Spindle alignment has little to do with this as the tool is hand held.

The speed of the lathe on that size should be t least 2500 RPM.

I also agree that your traverse speed may be too quick.

When you are using the skew is your cutting edge at 45 degrees to the timber? The closer you get to 90 degrees the less material you are in contact with.

I would also suggest that your tailstock centre may be coming loose by working its way into the timber (the reason I don't use cone centres) or you may have movement in the quill, make sure you apply the lock.

robo hippy
26th October 2012, 04:42 AM
While not a skew man, one tip from a friend long ago: When turning spindles, there is a ratio of 10 to 1 for stability. A 1 inch diameter spindle that is 10 inches long will remain pretty stable when cutting. Going beyond that ratio, the wood can start to 'whip', which means vibrate. Things that make the vibration worse are too much tool pressure, and too much pressure from the tailstock. Finding the balance can be tricky. This is where steady rests come in handy, or if you have a light touch, and can reach under or around the tool rest, your other hand can do the same thing. If your steady rest hand is getting hot, you are using too much pressure, and hand pressure should equal tool pressure, so in other words, very light. To get rid of the spirals, you have to go back to where there are none, and start the cut again, or very gently start where there are bumps, and try to nibble them off till you are down to round.

robo hippy

Mobyturns
26th October 2012, 08:21 AM
Spindle alignment has little to do with this as the tool is hand held.

I would also suggest that your tailstock centre may be coming loose by working its way into the timber (the reason I don't use cone centres) or you may have movement in the quill, make sure you apply the lock.

say it better than I did, this is what what I meant about spindle alignment (poorly aligned centres on the lathe).

Jim Carroll
26th October 2012, 09:11 AM
As others have said you are not running the lathe fast enough, at least 2500 rpm is good for this diameter.

You are also pushing too hard and not allowing the tool to cut properly. The wood spirals and the tool is following the pushed wood.

Is the small diameter at the head stock as it is easier to push down hill towards the head stock, the spurs keep you driving. Also a good cup or pin & ring centre for the tailstock is better than a cone centre as the cone wants to push further into the wood.

To stop some of the vibration in the wood on this small diameter use your hand as a steady and fulcrum.

By looping your thumb over the tool rest and your fingers cup the wood you can then rest the skew against your hand and run along the peice, if it gets hot in your hand you are either pushing the tool too hard or holding the wood too hard, back off till comfortable

ozhunter
26th October 2012, 06:53 PM
Thank you very much for all the replies. It got the better of me last night and I went back to the shed.

Centres line up

Cranked the speed up to 2000rpm, as fast it the Woodfast will go in it's current configuration.

Made sure the tool was sharp

Made a conscious effort not to push too hard

Made an effort not to traverse too fast or push too hard

Much better result straight away.

I use a cup and pin (I think anyway, standard issue woodfast) in the headstock, but until now I've had a cone in the tailstock. I think I have a Woodfast cup and pin live centre, I'll give that a squirt tonight.

Jim, I try to use the finger position method you prescribe as much as possible (although a bit scary when a catch occurs).

Going downhill from tailstock to headstock is what I was doing.

I have the skew at about that 45. I'm making some tool handle and I'm trying to use the skew as much as I can to try and get a handle on the damned thing.

Can't get anymore revs out of the old girl in it's current form, although I have access to enough bits to put a 3 phase motor on her and use a VFD, should be able to get a bit more pace that way. I'll probably leave that until we get into our new digs sometime next year - cause then I'll have real 3 phase to play with.

I'm going to play some more tonight. I'll report back and again thanks for the replies.

Jonzjob
26th October 2012, 09:00 PM
I had to turn a 6mm elm shaft, about 13" long a short while back. I used a 1" oval skew and a little 3/8" round skew to finish. I supported it with my hand and although there was a little vibration at times it was quite straight forward.

Other times when I have had a spiral it has always been due to vibration of the wood. No real problems and if you arepushed for time and it keeps happening then the spiral sands out very easily :B:B

ozhunter
26th October 2012, 11:00 PM
Spent some more time at the lathe tonight. Using all the tips, I have managed to get probably 98% of the turning free of the spiral straight off the tool.

I think, after tonights effort that vibration is the cause of most of the problem. The piece is 405mm long overall. Too long probably, but by using the finger steady and faster rpm's it's manageable.

I'm going to turn a piece the same finished size except shorter next time I get a chance and see what effect that has.

I did notice that roughing the square down to a cylinder at about 50 mm diameter, the finish was easier to get smooth. Directly related to the aforementioned ratio me thinks.

Thank you for the help.

One question about rpm's, if turning say a bowl that is about 9 inches across, does the same thing apply, faster is better? Or is it just a "feel" thing, experience telling when to slow down or speed up?

RETIRED
26th October 2012, 11:29 PM
One question about rpm's, if turning say a bowl that is about 9 inches across, does the same thing apply, faster is better? Generally, but only when it is round. :D Or is it just a "feel" thing, experience telling when to slow down or speed up?That too, in spades.:cool:

Jim Carroll
27th October 2012, 09:53 AM
Bowls work similar but different.

Always start the lathe on slow then build up the speed to where you are comfortable and the wood is also comfortable.

There is 2 things that control the speed , your ability and the wood.

No good going too fast if it frightens the bejesus out of you.

As you get the bowl blank more into round then you can creep up the speed and get a better cut of the tool.

Again sharp tools help

jimbur
27th October 2012, 10:36 AM
Again sharp tools help
:2tsup::2tsup:
Cheers,
Jim

Jonzjob
27th October 2012, 06:10 PM
Something I meant to say earlier is that when turning long and thin don't put too much pressure on the tailstock or you will push the wood into a slight bow and then it will tend to vibrate more. Just use enough pressure to stop the wood from slipping in the headstock and not move in the tail.

jimbur
27th October 2012, 06:59 PM
I was having this trouble turning some legs for a stool for my grandson. I think part of the trouble was the elm which had soft endgrain (and the length of course). I stiffened the endgrain with a bit of bondcrete and then took lighter cuts to reduce side pressure.
Cheers,
Jim

hughie
30th October 2012, 09:06 AM
[I was having this trouble turning some legs for a stool for my grandson. I think part of the trouble was the elm which had soft endgrain (and the length of course). I stiffened the endgrain with a bit of bondcrete and then took lighter cuts to reduce side pressure.


With soft stuff like that I often use CA to harden up the ends, quick and easy.

Mobyturns
30th October 2012, 09:26 AM
One question about rpm's, if turning say a bowl that is about 9 inches across, does the same thing apply, faster is better? Or is it just a "feel" thing, experience telling when to slow down or speed up?

Lathe speed is about cutting speed at the tools cutting edge. Bigger dia's - slower speeds, very small spindle dia's require flat out speeds. Just like router bits & drilling in various materials, there are optimal speeds on the lathe to obtain the best finish, minimise tool wear, reduce heat & material damage etc but more importantly to be safe.

One thing that we all should be aware of is that a thick walled bowl may be safe at 2500rpm, but when we reduce the wall thickness to say 2-3mm that same speed may be deadly dangerous! It becomes dangerous because we exceed the strength & mechanical properties of the raw material, its ability to flex & move and to recover as we cut it! Reduce speeds as you get thinner.

http://azwoodturners.org/LatheSpeed.pdf gives an idea of cutting speeds.

rsser
31st October 2012, 03:41 PM
Can only add one comment: as one US turner who is a skewmaster said ... the bevel should rub but the wood shouldn't feel it.

ian thorn
31st October 2012, 09:05 PM
Yes rsser its called kissing the bevel:D .tha wall of a bowl can move a lot when its geting thin so if you dont want flying objects in the shop slow it down .And wear you face shield

Jonzjob
31st October 2012, 09:44 PM
I also open the window !! Well, it's only a couple of feet away from any flying object possibility :rolleyes::rolleyes:

http://i47.photobucket.com/albums/f180/Jonzjob/3phasecontrol1.jpg

Christopha
31st October 2012, 10:45 PM
Hey Oz,
There is some good advice here and some silly.... you need to decide...
I sent you a PM ...
Big thing is don't get too technical, just relax, trust your instincts and ENJOY the turning process and then make it fit what you want to turn.
Stopper :B

Watch them prove they have teeth! ;)

robo hippy
1st November 2012, 04:26 AM
rsser,
Who is that skew master? I love that quote, and want to use it, and give proper credit.
robo hippy

Drillit
1st November 2012, 09:21 AM
Hello Oz Hunter,

While I am not for one moment advising contrary to the experts, you may find that it helps to have the tool rest a tad higher that normal. I have found
that using the "skewart" tools to plane on the bevel that a little higher helped a lot, particularly with the bigger skew. I dont know what the experts think
but I have seen others who dont have the skew high enough and that higher level makes it easier to plane at 45 degrees for me. Drillit.

ozhunter
1st November 2012, 08:59 PM
Thank you for all the advise. I haven't had a chance to get back to hte lathe yet, but when I do, I should be well armed.

I'll post the results.

Jonzjob
1st November 2012, 09:47 PM
One up for having the tool rest higher. I always have it almost to the center of the job and it is such a habit I forgot to mention it.

jimbur
6th November 2012, 11:43 AM
It happened to me yesterday. The spirals came, no movement anywhere or so I thought. I replaced the live centre with a solid one just on the off-chance and that was it. Movement in the bearings that I couldn't detect by hand.

rsser
6th November 2012, 11:55 AM
Yeah Jim, have read of that change and improvement mentioned by some fine-spindle-work turners.

Reed, 'fraid I can't recall who originated that skew tip. At a guess Alan Lacer but a quick scan of his site didn't find it.

jimbur
7th November 2012, 09:58 AM
Ern, I made it sound easier than it was. It drove me mad for an hour. I was using an extension on a mini lathe and assumed that wasn't lined up or was loose, then worried about the main bearings, then fantasised that I'd forgotten how to use a skew, then wondered if there was vibration in the rest etc, etc.:C

rsser
7th November 2012, 11:09 AM
Oh Jim, I had you pegged as a problem solving genius :D

jimbur
7th November 2012, 01:14 PM
Oh Jim, I had you pegged as a problem solving genius :D

The only person I fool Ern is myself:C

rsser
7th November 2012, 03:01 PM
The only person I fool Ern is myself:C

A little self-delusion oils the cogs of life.

A lot can end up in millions dying. That's a really bad finish off the tool.

Jonzjob
13th November 2012, 04:25 AM
As far as long and thin are concerned, this crochet hook in bamboo was fun. Got it right though by just using light cuts and supporting it with my left hand..

http://i47.photobucket.com/albums/f180/Jonzjob/Crochet.jpg

The pinch chuck on the drive is part of a set of about 120 year old box wood and brass pinch chucks I was given by a good friend 10 years or more back. Lovely things. The tail stock support is an Axminster multi head tail stock jobbie with the fruit chuck end fitted. A very useful piece of kit!

jimbur
13th November 2012, 07:15 AM
Never tried anything that thin John. Beautiful work.:2tsup::2tsup::2tsup:
ps what speed did you find most comfortable?

Jonzjob
13th November 2012, 08:08 AM
Thank you Jim.

I started off by trying different tail stock pressures and wound it up as fast as was comfortable. I fitted a 3ø variable speed motor to my old-ish Record CL1 a few years back and now I have no idea what the exact speed is. Probably around 1000 rpm? Bamboo is surprisingly easy to turn because it is so hard and strong.

You can soon find out if the tail stock pressure is too much because it whips, if it is too slack then it waves around like a flag in the wind because, until I modified the center of the fruit holder, it had a slight flat! Now it comes to an inverted point.

ozhunter
13th November 2012, 07:23 PM
That looks great John. A real challenge. I think I'll stick to thickere thins for a while.

Jonzjob
13th November 2012, 07:57 PM
Cutting the hooks was fun too

http://i47.photobucket.com/albums/f180/Jonzjob/Crochet6.jpg

But I do have some huge drills and rasps for the job

http://i47.photobucket.com/albums/f180/Jonzjob/Crochet3.jpg

I think that the smallest is about 0.3mm. They used to be used by Silly-cone Valey in the States until they were blunt. Then they were sharpened :C:C and I bought them from Axminster Power Tools. They don't sell them any more though :no:

I have managed to break a couple so far :o

jimbur
14th November 2012, 02:24 PM
just a ps John. Nice to see a Record Power being used. I have an RPML300 for small stuff. Excellent lathes.