Spigots

[Judge]

Hello everyone. I am a new convert to the world of woodturning and enjoying every minute I can get into my workshop to use my new Hegner lathe. I have taken the Forum's advice and approached a local club for membership and have had two one day lessons, with more in the future. I have watched countless videos on YouTube and bought Richard Raffan's basic woodturning video......
I am practicing every day, roughing down to cylinders, using the skew to get a nice surface, turning beads, coves, simple boxes, and I've also tried a few bowls...BUT I am having real trouble getting the hang of creating a dovetailed spigot which sits true in my Sorby Patriot chuck.
I would be really grateful if anyone could give me some help.

 

[paulm]

Welcome to the forum !

Sounds like you are having fun and doing all the right things in getting to grips with your new hobby

Could be a number of things going on with the spigots. What type of jaw set are you using on the chuck and how are you going about creating the spigots currently and what kind of size are they relative to the jaws ?

I've got a few thoughts, as others will, but rather than spray a volume of random information at you may be helpful to focus in a bit more first ?

Cheers, Paul

 

[monkeybiter]

Only a few main points IMHO;
the area surrounding the spigot must be flat and true so it can rest against the 'nose' of the jaws, the spigot length must be slightly less than the depth of the jaws for the same reason.
The spigot diameter only needs to be roughly as specified, and don't get hung up on the dovetail angle accuracy, the jaws will close up on the wood which will then compress slightly to conform their profile.
Other opinions may differ, but it's always worked for me.

 

[CHJ]

.....the area surrounding the spigot must be flat and true so it can rest against the 'nose' of the jaws, the spigot length must be slightly less than the depth of the jaws for the same reason. ......

This sketch may help show spigot location as described .

Note:- The Socket details are as used with my Axminster C type jaws, other brands and configuration may not be capable of the additional support as their dovetails protrude some distance from the chuck fixing flange.

 

[paulm]

That's pretty much it ! Didn't 't have time to summarise it so succinctly !

Only other thought is that the jaws should be nearly closed up when tightened on the spigot, or close to the ideal diameter the manufacturer specifies so that they are contacting evenly on the spigot. If the spigot is too wide then only the outer edges of each jaw will make contact and it will not hold as strongly.

Cheers, Paul

 

[Judge]

Thank you to everyone who took the time to reply and the very ggod advice given.

I think I may have been turning the spigot incorrectly in 3 ways!

1. Being overenthusiastic in getting the dovetail accurate.
2. Making the spigot too long so that it touches the base of the chuck, and
3. Not making the shoulders square.

It's the last part which I'm having trouble with, so can I explain how I turn the spigot and you can tell me what I'm doing wrong?

I am using a Robert Sorby Patriot chuck which has the standard 50mm dovetail jaws.
Having roughed down a piece of wood to a cylinder between centres, I use a skew to clean up the ends, trying to make them as square as I can. I use a 6mm parting tool to create the tenon/spigot to the whole depth of the jaws (maybe too deep). I'm assuming that if the parting tool is not exactly 90 degrees to the wood, then the shoulder of the spigot won't sit flat against the edge of the jaws? (That may be error No.4!) I then try to recreate the same angle of the dovetail using the same parting tool.
More often than not, when I insert this into the chuck and restart (slowly) there is quite a wobble. On all the demo videos, the wood always seems to run true at this point!!

Any advice gratefully received.

In the meantime, I shall go off and practice the suggestions so far........

 

[monkeybiter]

1. Err toward the parallel if anything, rather than too tapered.
2. Too long will very likely lead to wobble. If the jaws are 6mm deep make the spigot 5mm.
3. If the shoulders are irregular or 'sweep back' away from the spigot you will probably get wobble. If you can't get the shoulders square then slightly concave will work, even if it's undulating, as long a turned surface can and does touch the jaws all round.

 

[Harry 48]

Just a thought are your head and tale stock aligned I've had problems with wobble when I did not swivel the headstock back to the correct position it then makes the spigot of centre. (homer)

 

[Rlewisrlou66]

I might get told off for this but I make my dovetails with a skew.
I know you can buy special tools that should cut a perfect dovetail every time so long as you have it straight but I can't afford one.

 

[Dalboy]

When cutting a spigot for the sorby chuck it need to be just short of the depth of the step. All the things that CHJ said still apply regarding the work piece being tight up to the outer edge of the jaws.

The profile is not an exact match but gives the idea

 

[monkeybiter]

I might get told off for this but I make my dovetails with a skew.
I know you can buy special tools that should cut a perfect dovetail every time so long as you have it straight but I can't afford one.

Me too sometimes, on it's side as a scraper, or more often with the spindle gouge.

 

[procell]

I ground down an old scraper so it can be used to create the dovetail profile on the inside of a chucking recess. I suppose I could also grind the other side so it will work for spigots too.
The advantage is it can also be used to smooth the bottom face or the shoulders of the piece.

This is used with the tool rest parallel to the base of the work. Obviously the angles should correspond to the angle of the jaw dovetails. It also acts as a depth gauge for the spigot/recess

 

[paul-c]

I might get told off for this but I make my dovetails with a skew.
I know you can buy special tools that should cut a perfect dovetail every time so long as you have it straight but I can't afford one.

i always create my dovetails with a skew chisel - thats how i was taught.
best of luck
paul-c

 

[CHJ]

To form the rough taper I plunge the skew in on its side, I did grind myself a scraper with both tapers as shown above but it's spent most of its life on the back shelf.
As said by monkeybiter, if in doubt aim for undercut face to get max diameter support rather than worrying about strict right angles..

This is an exaggeration, 1/2mm is enough, but does mean that the jaw face contacts on the max diameter possible.

 

[Judge]

Everything they said about the woodturning community is true - I am blown away by the response to my query! Thank you all very much for the time and effort you have put into helping me out!

First practice with a shorter spigot and squarer shoulder produced hugely reduced wobbles. More practice I am sure will make me a "true" woodturner!!

Not being very confident with the skew yet, does anyone have a particular recommendation for creating the dovetail?

Thank you all again - superb forum!

 

[CHJ]

.....
Not being very confident with the skew yet, does anyone have a particular recommendation for creating the dovetail?
.

Using the skew laid flat on the rest as a scraper is a pretty safe low risk process as long as the contact point is on centre or below, (that way if it catches it's pushed into fresh air not digging into wood.)
It does not have all the skill/judgment calls associated with mastering the tool for planning cuts.

Re:- the spigot dovetail, often you could get away with just a small undercut at the base of the spigot if you have a thin parting gouge.
In fact the Axminster C jaws are designed for just such a groove, something I personally rarely take advantage of, but turners making accurate box assemblies often prefer this type of fitting.

 

[woodfarmer]

I might get told off for this but I make my dovetails with a skew.
I know you can buy special tools that should cut a perfect dovetail every time so long as you have it straight but I can't afford one.

Me too, so far, that and using it as a scraper is the only use I have managed to get from it

 

[Rlewisrlou66]

As for getting it right just practice practice practice. I grabbed a piece of scrap and made a tenon/spigot with the jaws sat on the workbench, I just kept testing it in the jaws till it was right then parted that one off and started again.
It might seem a long process but it helped me massively.
After my first failed attempt and lucky escape when the wood wobbled then flew past my face and bounced of the ceiling I needed to do what ever I could to make sure it didn't happen again.

I use callipers to get the size and then make the Dovetail once you have made it a fair few times you will know when it is right by eye.

 

[CHJ]

Consider making a couple of simple gages based on your regularly used jaws, that way you have quick and instant marking aids for anything clamped in or on a chuck without having to resort to callipers or verniers.
Here's one idea Measure once and forget forever.

Likewise simple mdf or thick card calliper serves for spigots on a spindle piece between centres where you can't draw a witness mark.