3 Jaw Chucks

[brendan stemp]

Does anyone know why Scroll Chucks for woodturning aren't made with 3 jaws? I had the need to buy a metal lathe to do some of my recorder work and find the 3 jaw chucks to be very good. I assume I could adapt an engineers chuck to put on my wood lathe but was just wondering why the preference was for 4 jaws over 3.

[Big Shed]

Brendan, can't help you with your first question, I have often wondered the same thing.

It is relatively easy to mount a 3 jaw "engineers' " chuck on your wood lathe. Almost all those chcuks are designed for back plate mounting and quite a range of backplates are available, either aready threaded for your lathe, or unthreaded for you to thread to suit the spindle thread on your lathe.

Little Machine Shop (http://littlemachineshop.com/products/product_category.php?category=-1110836144&First=C&Last=C) has a range of backplates, I bought their 4" M39x4 to mount an ER25 collet chuck for use on my 9x20 metal lathe. Not a particularly difficult job, just a bit fiddly.

They also sell a range of chucks, both 3 jaw and 4 jaw.

The other option would be to make, or have made, a spindle adapter so that your metal lathe chuck can be used on your wood lathe.

[Ozkaban]

Weren't engineers chucks used on lathes before scroll chucks were invented? I thought the issue with them was the jaws protruding from the outer edge of the chuck which were very effective at removing knuckles of the person holding the chisel.

Not sure about this as I don't have personal experience going back this far, but I'm pretty sure this is what was related to me.

Cheers,
Dave

[Ed Reiss]

A lot of metal work starts with a rod (cylinder) where a 3 jaw chuck is ideal.
Wood spindle work usually starts with a square of wood...a 3 jaw chuck won't work.

[texx]

A lot of metal work starts with a rod (cylinder) where a 3 jaw chuck is ideal.
Wood spindle work usually starts with a square of wood...a 3 jaw chuck won't work.
good answer , pretty obvious really when you think of it , trick is , thinking of it .

[INVENTOR]

Brendan, A fact often not known by woodturners is that self centering chucks for many decades have been available in 2,3,4, etc jaws. And while generally in the larger sizes the jaw face ( the bit doing the gripping) is removable. Just that they are sold through engineering supplies not wood turning supplies.

So when people 'comment' that a certain wood turning chuck manufacturer 'invented' the idea for the 4 jaw self centering chuck, more likely all they did was scale down an exisitng metal lathe chuck to suit wood turning lathes.

While 3 jaws are often convienient they all suffer from limited gripping and tendency for the stock to move out the space between the jaws. (a bad 'catch' when turning metal or wood will prove this to be the case) So if anything perhaps a 6 jaw wood chuck would be a better option.

There is an article in the latest American wood turning magazine about chucks. However one the interesting comments is that metal lathe chucks are more precise and cost a lot more (or words to that effect) However a quick check of the prices for reasonable quality metal lathe chucks reveals that they are not expensive (size for size etc). So why are the wood chucks priced they way they are given their general lack of 'qauality'???

I hope this answers your questions or perhaps 'adds fuel on the fire of the 'chuck' debate.

As suggested, getting a backplate for a suitable sized chuck to suit your wood lathe is a real possiblity. Have a look at the Tos chuck etc.
I have adapted my wood lathe chucks to suit my metal lathe by making an adapter that has a morse taper to suit the hollow spindle of the metal lathe (with drawbar) and is threaded to suit the chuck. (a cam lock back plate adapter would be another option for metal lathes with cam lock) that way you can take the chuck/piece from lathe to lathe.

Hope this helps.

[brendan stemp]

Thanks to all of you for your input and help.

[NeilS]

We used three and four jaw metal lathe chucks before woodturning chucks were available, but as Dave said they were real knuckle killers. Still have a couple of mine, but only use them now for soft metal turning.

However, my first purpose made woodturning chuck (an early Woodfast) was in fact a three jaw chuck (pic attached).

But, as Ed points out, the need to cater for both 'faceplate' and 'between centre' turners in the one chuck had the four jaw chucks configuration win out. Fair enough! If you can only afford one chuck you want it to do everything.

In contraction mode the three jaw chucks are fine. In expansion mode I think the four jaw chucks have the advantage of allowing for positioning in relation to the end grain to avoid breakout.

....

[colhu]

I wonder if it might be something to do with the shape of the scroll jaws and the number of points of contact when the jaws are opened well beyond the point of the perfect circle? In expansion mode a 3-jaw chuck would only be touching the workpiece at 3 points. I'm trying to visualise whether it would be significantly different from a 4-jaw in contraction mode.

cheers, Colin

[joe greiner]

Like Ed says, 4-jaw chucks are better for square stock.

For my Longworth chucks, I used 6 buttons (~jaws) for more purchase points, and easier to lay out than 4 or 8 (compass only, no T-squares etc.).

For metal lathes, independent (not scrolling) jaws are convenient for offset turning - easier to adjust the offsets than with 3.


It's pretty obvious that mechanical clocks turn clockwise because they were invented in the Northern hemisphere, to mimic the shadow motion on a sundial. A deeper question is



















Why are alphabets in alphabetical order?:D

Cheers,
Joe

[brendan stemp]

Thanks Neil and Colin for your input. The picture is being filled in very well for me thus far. My initial question stemmed from the fact I do a lot of re-centreing of stuff for the recorder making and find the 3 jaws are a lot more accurate on more occasions than the 4 jaw, even when I am careful to make sure the jaw marks in the wood match up to the same jaws on the 4 jaws and not so careful with the 3 jaw. I am enjoying the 'knuckle cruncher' but have to admit the jaws have caused me some grief on 3 or 4 occasions. I have a design for a guard for the jaws in my head so must get onto making it. Has anyone seen such a guard?

[powderpost]

Good memory recall is not a function of advancing years.. :no: However from what I remember, a spindle for an egg cup or goblet, had to be turned round with a tenon on one end, this was then held in the three jaws. The point of contact by the jaws was relatively small and caused much damage to the tenon and it was prone to slipping.
Probably the earliest spindle chuck, was the bell chuck. It had a slow taper inside, something like a morse taper, only much bigger. In the hands of a competent turner, these were very efficient but often with poor technique and blunt tools the job would develope a wobble or worse, leave the lathe. But it didn't crush the end of the wood. :)
Sorby produced the 6 in 1 chuck that really needed a degree in engineering and four hands to apply and operate, although it was quite efficient. It catered for both "spindle" and "face plate" work.
Technatool from New Zealand produced a four jaw chuck that was based, not on a worm drive, but two tapered surfaces. It also operated in a compression mode and expansion mode. This allowed for both "spindle" and "faceplate" work also. This one was developed by Technatool for green bowl turning and was fitted with bronze jaws so that there was no black stains caused by the reaction of sap and steel. The jaws had some movement to cope with the distortion of the timber caused by drying. I think it was Technatool that first fitted "jaw plates" to a four jaw scroll chuck. Later steel jaws were blackened, I think with the same process used on gun barrels to prevent rust.
It was about the same time, or a bit earlier, that Woodfast came up with the Super Chuck with a disc of aluminium cut into three sections, expanded by means of tightening a cone in the middle of the plate, about the late 80's. It was designed by Bruce Leadbeter.
In amongst all this the spigot chuck appeared, I think from Sorby and one from Richard Raffan, also the screw spiggot and screw cup chuck appeared.
All these chucks, according to the sales pitch, "will hold the timber securely without crushing the fibres", which was the original problem with the original three jaw chuck borrowed from the machine shop.
I have one of each in my workshop and still like and use the spiggot chuck. It's main problem is that the tenon size is critical.
It has been interesting watching the developments over the years, driven mainly by the market created by the explosion in numbers of recreation wood turners.
Jim

[issatree]

Hi Brendan, & Others,
I wouldn't touch a 3 Jaw, if my life depended on it. Why, well you can't hold a square piece of timber successfully in a 3 jaw, without first Turning it Round.

To the " Knuckle Grazer ", get a piece of car tube, cut it wide enough, cut it to length to go around the Chuck, & tighter rather than loose, & use Loctite 401 to glue the overlap.
If you make it to loose it will most likely come off, because of the rotating speed.

That's my bit.
Regards,
issatree.
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[rsser]

Another knuckle protector tip I've read is to get one of those stretchy terry towel wrist bands that tennis players use and slip it over the jaws.

[INVENTOR]

Brendan, from your comments, I would check a few things. Are you comparing the precision of a 3 jaw metal lathe chuck against a 4 jaw wood lathe ( which has 'questionable' precision) ?
Also you may find that the longer contact length of the 3 jaws ( assuming you are using the standard jaws and not reversed jaws) is what is helping you get a better re centre. Are the 4 jaw chuck jaws as long?

I wonder if its 'better' to be a metal lathe owner first (that becomes a woody) rather than the other way round. As you get a more healthy respect for chucks. Especially when you see what 'some' woodies do with their hands and revolving machinery.

This said , generally the more jaws the better. more contact ( provided the chuck is good quality)

[hughie]

As Inventor has outlined, that is pretty well what it is. Essentially wood turning chucks are a copy or adaption of the engineering chucks.
It seems the wood turning industry is many years behind the metal turning fraternity. As and example we now see TCT and other exotic tool steels being employed for cutting tools. When they have been around in engineering circles for and around 1/2 a century.
The major difference between wood and metal chucks is than that the metal are capable of far greater compression or holding power, so great care must be used when tightening them up on wood. They can darn near crush Lignum Vitae. :o

[NeilS]

Powderpost - Nice chuck history. PS - I think the bell chuck is also called a cup chuck.

Brendan - smaller motorbike inner tubes will also fit nicely over extended jaws. I also ground over the leading edge of my jaws.

.....

[Manuka Jock]

So when people 'comment' that a certain wood turning chuck manufacturer 'invented' the idea for the 4 jaw self centering chuck, more likely all they did was scale down an exisitng metal lathe chuck to suit wood turning lathes.


Not that Teknatool even hint at that , all they say is this

"In 1988, Teknatool designed and introduced a self-centering four-jaw chuck with circular jaws which revolutionised woodturning. The chuck makes holding wood on a lathe so much easier and enables a wide range of projects to be completed. This style has since become the chuck standard in woodturning."