Piece spinning while roughing

[Dino]

When I am roughing a new piece, still square.

My gouge could do with sharpening but I'm fairly sure it's to do with the way I am putting the bit into the wood. I'm also pretty certain I'm cutting into the wood correctly as well.

I don't have this problem when I use a chuck, but this piece was too big to fit into the chuck to rough.

 

[Grahamshed]

So what sort of drive centre are you using ?

 

[CHJ]

...My gouge could do with sharpening ...

In all honesty this is not a phrase you should ever use, a spindle roughing gouge takes a matter of seconds to sharpen and you are asking for trouble if you start splintering the wood as opposed to cutting it.

As Graham says it's down to poor drive centre engagement. If the timber is hard you may have to drill a shallow pilot hole to aid drive centre penetration,
Are you driving the drive centre into the wood off the lathe with a decent mallet to ensure you have deep drive slots?

The fact that the wood is slipping may be a good point if your gouge is not sharp, better than splintered wood flying about.

 

[Dino]

The gouge is sharp but not clean off the grinder sharp. I think it's more to do with the drive.

I'm using a mallet but the holes created by the slots are not penetrating deep enough I think, though I am unsure how to fix that. I'm using quite a hard wood right now and I noticed as I inspected the piece that when it began spinning it caused a groove to be formed around where the prongs are.

I'm using a 4 pronged drive centre.

 

[swb58]

I don't think you're the first to encounter this problem. You can usually get more penetration into the wood with a two prong centre. Or try cutting small slots (x) in the blank for the for the four prongs to locate into.
I think having properly prepared blanks with perfectly square ends can make this problem worse.

 

[JimB]

All the above plus very fine cuts to begin with and/or at least take the corners off with a plane or spokeshave.

 

[MMUK]

I tend to chamfer the corners to make an octogan before I mount a piece for turning. It makes life so much easier, a few swipes with the circular saw.

 

[Grahamshed]

If you have a bandsaw then it is only a few seconds work to make a cross in the end of the wood for the prongs. Failing that, if you don't mind spending about £40 isn then a stab centre is a good alternative.

 

[MMUK]

Failing that, if you don't mind spending about £40 isn then a stab centre is a good alternative.

Can you get them to fit onto a threaded spindle rather than morse taper? I think mine is a 7/8" or 1" thread.

 

[Grahamshed]

Failing that, if you don't mind spending about £40 isn then a stab centre is a good alternative.

Can you get them to fit onto a threaded spindle rather than morse taper? I think mine is a 7/8" or 1" thread.

Not that I am aware of but you can get them to fit in a chuck. That is what I have.

 

[NickWelford]

No, but you can get them that fit in a chuck......

Deja vu strikes again........

 

[NickWelford]

Hmmmm... Clamouring to answer.........

 

[Grahamshed]

Go on then Nick. Tell MMUK that they are available in 3 sizes at Toolpost

 

[steadyeddie]

Hi Dino,

What condition is your drive centre in? It might be worth tickling the blades with a file to make them a bit sharper.

Dave

 

[Phil Pascoe]

Dino - get a two prong centre. Guaranteed to be a better drive than a four prong, as you can be sure that both prongs engage properly in rough sawn wood. Sometimes in hard wood you've only the point and one prong engaging on a four point one.

 

[Spindle]

Hi

If you are using a four prong centre and the end of the blank is square, (ensuring that all four prongs are in engagement), then the slippage is down to either tool sharpness or your technique.

Knocking the corners off the blank will reduce the effects of bad technique but it's better to address the issue of tool presentation. You are almost certainly trying to take too much material off in a single pass, this coupled with the intermittent contact as you begin to rough down a blank will shock load the centre out of engagement.

Tool edge quality will also have a significant effect, a roughing gouge used enthusiastically will have a relatively large length of edge in contact with the work and consequently, if this edge is not good, the resistance to cutting is high. An edge straight from an 80, or preferably, a 100 grit wheel will be fine but do keep it in good order by regularly visiting the wheel.

When I started turning I was advised to use a ring drive centre - advice I followed. Using a ring drive centre teaches you delicate presentation, (otherwise the drive slips), - if you have one I'd suggest practising with it. If not, ensure your tools are sharp and take lighter cuts.

Finally, Stebcentres are very good in my opinion, however they will not address the issues you are suffering - they will just cut pretty rings into the end of your blank when they slip. One downside with a Stebcentre is that once it has slipped subsequent re-engagements are less efficient.

Persevere with the presentation - you'll get there sooner than you think.

Regards Mick

 

[Spindle]

Hi

A couple of points on two prong centres:

A two prong centre produces less 'grip' than that of a four prong one when they are correctly used. The ends of your blank should always be cut square to their length to ensure full centre engagement, this applies whatever type of centre you are using. Using a two prong centre rather than squaring your blanks is poor practice in my opinion.

Two prong centres act like wedges and can cause the blank to split.

I've turned for 15+ years and have never owned a two prong centre for the above reasons - they are not the answer to your problem.

Regards Mick

 

[Tazmaniandevil]

I may as well throw my hat in the ring here, being a relative novice to the turning world.
I changed from a 2 prong to 4 prong drive centre because my over-eager ham fistedness split a few too many blanks. My most used 4 prong drive centre fits in the chuck, although I also have a morse taper drive. Very hard wood is much harder to engage the drive centre in than softer or green wood. I tend not to hammer the drive centre in these days, preferring to drill a pilot hole and cutting a pair of perpendicular saw drifts. It takes a few minutes, but saves plenty time in the long run. Make sure your lathe is running at the slowest speed to begin with, and present the tool on a low tool rest with the handle down so the bevel is being offered to the work rather than the cutting edge. The temptation to remove loads of material quickly should be avoided at all costs.
Very slowly lift the tool handle until the slightest of cuts take the rough edges away.
In terms of sharpness, I sharpen my tools before starting to use them on a project, and often re-sharpen them halfway through. I find that working this way means I only need to give the edge a very quick touch up. I always re-sharpen before the finishing cuts on the work too.
I know next to nothing about turning, relatively speaking, but believe tools can't be too sharp.

 

[Random Orbital Bob]

all good advice Taz. You may be new but there's a lot of wisdom in those words that camouflage any newness

 

[Dalboy]

Yes I agree with the idea of cutting a cross in the end of your work to help engage the prongs. Not that I have ever done this I tend to use a suitable hammer to hit the drive into the wood, once fitted to the lathe put the lathe on the fastest but safest speed for the size of blank that is being turned. you will also find that you can get a better finish on the wood like this as well as find it easier to rough the blank down.
And like all that have mentioned it keep your tools sharp this may mean sharpening little(depending on the wood) and often especially with harder woods