Thread: Useful chuck aids

Originally Posted by Tiger

As we all use our chucks on a regular basis, I'm wondering what others use to speed up production. I would like to make a dovetail scraper to match the jaws of my chuck but what is the best way to replicate the angle of the small jaw recess, it's difficult to get a bevel gauge into the small area of the jaws?

Take a jaw off your chuck and use that as your template.

Originally Posted by Tiger

Like to come up with a tool that gives you the minimum and maximum contracting sizes of my chuck but not sure how to do this, I'm thinking of perhaps a thin bit of mdf with 2 semi-circles cut out, one for the minimum contracting size and one for the maximum contracting size, is there a better way?

I'm sure there are many other better ways, but what I do is use my calipers (divider type, sitting on toolrest) to scribe the diameter in the wood... a few test positions soon narrows down the correct diameter that allows the second leg of caliper to match the scribing leg. Be careful not to allow the second leg to dig in.

One day I will acquire enough sets of calipers to not have to reset the distances to match the different jaw sets, but until then a double sided disk that has all the recessed sizes marked is useful.

Neil

The super chuck that comes with the leady lathe is one of the quickest to mount. There is a cutter that mounts in the tail stock with a jacobs chuck. Just advance the cutter and the recess is cut in seconds. No measuring or chisels required. Record power in the uk have a similar chuck. I seldom use the nova chuck on bowls since I got this one. Having more than one chuck is also handy.

Originally Posted by Tiger

I would like to make a dovetail scraper to match the jaws of my chuck but what is the best way to replicate the angle of the small jaw recess, it's difficult to get a bevel gauge into the small area of the jaws?

Like to come up with a tool that gives you the minimum and maximum contracting sizes of my chuck but not sure how to do this, I'm thinking of perhaps a thin bit of mdf with 2 semi-circles cut out, one for the minimum contracting size and one for the maximum contracting size, is there a better way?

for the scraper i would try to grind it by eye first the push it into the dovetail of the jaw to check if it matches, then correct it where needed. shouldn't be to hard i was thinking of making one all you need is an old HSS tool to reshape

the MDF semi-circles sound like a good tool i would make it out of clear Acrylic, should be very useful

thanks for the tips

Patrick

I use a marking gauge like this:
Attachment 100742

You put a slight dimple in the centre of the blank when roughing, put the longer centre line pin in the dimple and it will mark the optimum and maximum diameters for both dovetail and spigot.

To form the dovetail (rarely use one) I use my skew chisel.

Here's a set I made a while back:
http://www.woodworkforums.ubeaut.com...ad.php?t=61540

I measured the jaws as carefully as I could, and drew them in CAD, expressing the range of motion for each jaw type or chuck, then printed full-size, for adhesive attachment to the material. To use them, you must allow room for tightening in either direction. In compression mode, the largest diameter tenon is governed by the distance between opposing points; the smallest by the distance between opposing arcs. In expansion mode, it's the other way around for sockets.

There may be an optimum setting for each type of jaw, depending on other conditions, such as wood species. After finding those settings, a spanner could be more useful. See some of the remarks in the thread.

Cheers,
Joe

Originally Posted by

I use a marking gauge like this:
Attachment 100742

You put a slight dimple in the centre of the blank when roughing, put the longer centre line pin in the dimple and it will mark the optimum and maximum diameters for both dovetail and spigot.

To form the dovetail (rarely use one) I use my skew chisel.

That's a very new looking marking gauge.

Originally Posted by tea lady

That's a very new looking marking gauge.

Couldn't find my old one. It was scrappy any how.

Thanks, folks, some good ideas here.

Joe, like your detail and will probably use something similar.

I don't believe in "minimum & maximum jaw holding sizes"... I believe there is a "best size" - which is when the gripping edge is almost perfectly circular when tightened - and a bit of leeway either way.

To this end, I've made up templates for each of my jaws. They're just strips of thin ply about 6" long and 2" wide, with a cutout on one edge to fit my tenon. Looks a bit like a monkey-wrench. On the corresponding short edge I've trimmed either side until the end is just wide enough to fit into a mortise.

The edges have been rounded over 'cos I tend to use this template while the lathe is running - test-fitting as I go - and I really don't want any sharp edges catching. Purely for the sake of reducing the number of jigs rattling around, I've done the same for another set of jaws on the opposite end.

No photos... I've been looking for 'em for a while but haven't found the right box yet. (The joys of moving house.) I might make another pair instead. So a quick sketch will have to do...

And, like , I simply use a skew to get the dovie angle.

The scroll chucks provide a lot more movement than the required leeway from "best." And to know the "best," we'd need to know the width of the cutter used to separate the round things into jaws. The jaws should be numbered before cutting, because the cutting might be done on other machinery, which may not be as perfectly centered. Thus, even cheapo chucks can work well enough if you mark the workpiece with jaw numbers in case of slippage or remount.

The minimum diameter, plus a little leeway, is probably optimum for expansion mode (socket). For compression mode (tenon), the maximum diameter (less tightening leeway) might be better than "best," because the eight corners are more uniformly distributed on a larger lever arm. As usual, it depends on the situation. I suspect the chuck manufacturers considered these things, before they made them as complicated as they are; I doubt it was merely to boost the price.

After you discover what's best for your situation(s), dedicated calipers/templates will be the bee's knees.

Cheers,
Joe

It's simple matter to determine when the jaws are forming a true circle... you don't need to know the size of the mfr's cutters, just a small ruler.

Measure across the middle of the chuck, from the centre of one jaw to another. Then measure, again across the middle, from the end of one jaw to it's diametric twin. Adjust the chuck until these two measurements are the same.

That is the position at which those particular jaws will obtain their best possible grip.

The outside dia. of the jaws gives the width of the hole when used in expansion mode, the inside dia gives the width of the widest part of the spigot dovetail in compression mode.

(Note: these measurements should be taken from the base of the jaw's dovetail, not the "top" of the jaw. 'Cos that's the part that corresponds to the "face" of the blank when transcribed over. )

Originally Posted by joe greiner

For compression mode (tenon), the maximum diameter (less tightening leeway) might be better than "best," because the eight corners are more uniformly distributed on a larger lever arm. As usual, it depends on the situation.

I'll argue against this. (I's feeling argumentative. Plus, you're wrong. ) It may hold true for Cole Jaws or similar that holds with buttons, but to say "all eight corners" implies that you're only gripping with the corners.

With std. dovetail jaws, this is not true. The best grip is provided when the entire length of the jaw is in contact with the wood... not just the corners or the middle of the jaw. Dovetailed jaws aren't about evenly spacing the "contact points" around the blank, they're about maximising the contact area of the jaws!

In contraction mode on a spigot, if the spigot is too small then the middle of the jaws make contact before the corners. If it's only slightly too small, then you can crank the pressure on the chuck, tightening it until the corners also touch, but this crushes the fibres in contact with the middle and actually reduces the holding strength there. (You could almost say they're gripping pulp. )

If the spigot is too large, the ends of the jaws contact first. The same reasoning applies... overtightening can make the middle contact the wood, but it's crushing the wood at the corners.

The reverse is true in expansion mode (Too small a hole, the ends of the jaws touch first. Too big, the middle first.)

Ideally, when you dismount a piece from dovetail jaws there should be no marks whatsoever as a giveaway to where the jaws were positioned.

I agree entirely about the best grip, Skew. The difference is in the larger lever arm provided by the maximum diameter. Force times distance provides resistance against dislodging. In some situations, a small force times a large distance, can be just as effective as a large force times a small distance. Crushing should always be avoided.

Across the entire spectrum of diameters, jaws, and species available, I hope the manufacturers have done enough testing to justify providing such a large adjustibility in the chucks. It seems wasted otherwise.

Of course I could be wrong. I've refined being wrong into a high art. And I get better at it every day.

Cheers,
Joe

Originally Posted by joe greiner

I agree entirely about the best grip, Skew. The difference is in the larger lever arm provided by the maximum diameter. Force times distance provides resistance against dislodging. In some situations, a small force times a large distance, can be just as effective as a large force times a small distance. Crushing should always be avoided.

Spoilsport. I was hoping for a nice, heated debate.

Across the entire spectrum of diameters, jaws, and species available, I hope the manufacturers have done enough testing to justify providing such a large adjustibility in the chucks. It seems wasted otherwise.

If dovetail jaws were all that's available, so much adjustability would be a waste. But there are pin jaws, spigot jaws, cole jaws, etc. that don't rely on a dovetail for grip and do take advantage of the full range of movement.

Of course I could be wrong. I've refined being wrong into a high art. And I get better at it every day.

Hehe. I know how that goes; I seem to be becoming more flexible as I age... probably from inserting foot in mouth so frequently.

Originally Posted by Skew ChiDAMN!!

... I believe there is a "best size" - which is when the gripping edge is almost perfectly circular when tightened - and a bit of leeway either way.

If you use your dovetail jaws in expanding mode on the completed foot of a bowl, then the jaws need to be very close to round to avoid marking/bruising the completed foot.

Neil