Chuck Jaws Calipers

**joe greiner** · 27th November 2007, 01:47 AM

These gauges facilitate checking the size of a spigot/tenon or socket, or selecting an appropriate chuck, for later mounting. Thus, regular calipers are freed for adjustable measurements. On an earlier thread ( http://www.woodworkforums.ubeaut.com...ad.php?t=60883 ), member littlebuddha posted a pic of a spanner used for checking tenons. I proposed a rigid caliper set to contain representations of all four jaw conditions: smallest and largest expansion, and smallest and largest compression. This concept had each jaw condition on the edge of a rectangle, with a rectangle for each jaw set. From the outset, it appeared somewhat unwieldy, at least for the larger jaw set. We'll call that Version 1.

Intuitively (a bit unreliable, as we'll see), my first improvement was to place two conditions on each side of a stick, with another stick for the other two conditions. The sticks were joined by a slotted joint along their centre lines. That was Version 2. Joining the sticks was a mistake, because the tailstock end of the blank is too crowded. Luckily, I hadn't glued the joints. I separated the sets and drilled a hole near the end of each stick for Version 3. I married all of the sticks with a piece of electrical wire; a bead chain could replace the wire some day. Versions 2 and 3 are cut from thin plywood on a scroll saw.

The lump shown for the test isn't the final tenon for the blank. It's just what was left after turning the blank to a cylinder and squaring the ends.

For Version 4, I used the entire jaw profiles themselves, with the expansion and compression ranges combined, and reduced the spine separation to about 1/2 inch. I duplicated the expansion bevel at the far end of each stick; seemed like a good idea at the time. Version 4 is cut from polycarbonate, about 4.5mm thick, on a bandsaw (1/8in blade, 16tpi). Polycarbonate is slightly more robust than acrylic, but neither of them cut very well on a scroll saw, because of melting behind the cut so as to trap the blade. On the bandsaw, some melted polycarbonate piles up below the workpiece. In non-critical areas, I just let the workpiece ride up on the melt; elsewhere, I backed out and broke off the melt. I burned through the lettering on the pattern with a low-wattage soldering iron; a wood-burning pen was too aggressive. A PITA nonetheless.

Transparency may be good for Florida's "government in the sunshine," but it's not so great for calipers. Version 5 has the same patterns as Version 4, but executed in 1/8-inch-thick opaque HDPE instead. HDPE cuts very well on a scroll saw, with almost no need for finishing. It's soft enough to break the corner edges with a thumbnail. It's also less brittle than polycarbonate. At this stage it finally dawned on me that the lettering wasn't needed; I figured that if I couldn't tell which gauge corresponded to which jaw, I probably should take up a less intellectually demanding sport than woodturning. I suppose it'd be different if I had more chucks and jaws, though. Versions 4 and 5 are connected with binding posts for now.

I have no burning desire to commercialise this tool, so the design is free for all. This is the sort of accessory that could probably be provided by the chuck manufacturers. At worst, they'd have accurate measurements of the jaw profiles. I found a chart of some jaw dimensions here:
http://www.cnew.org/tips_techniques/...huck_chart.png

Spigots/tenons or sockets shouldn't be formed at the travel limits of the jaws. Some travel should be reserved for tightening the jaws, and there's usually an optimum setting for best purchase on the tenon or socket, subject to variations for different species of timber, spalting, etc.

Joe

**killerbeast** · 27th November 2007, 01:59 AM

Great looking tool... on the must make list

**MartinL** · 27th November 2007, 03:58 AM

Neat tool, Joe. As a beginner I am constantly getting the tenon wrong and having to change jaws or start over. Come to think of it, it's more likely a function of being a newly retired and just not paying attention.(To any thing, my wife says.)

I noticed that you have a piece of podocarpus in the chuck. I just got two 24' podocarpus trees from a neighbor. They range from 24" to 8" diameter and are REALLY wet. Could you share some ideas on how to prepare and dry the wood? It is currently sealed.

This platter is all I have made so far.

Thanks

Martin

**hughie** · 27th November 2007, 06:28 AM

These gauges facilitate checking the size of a spigot/tenon or socket, or selecting an appropriate chuck, for later mounting. Thus, regular calipers are freed for adjustable measurements. On an earlier thread (

Joe what a great idea

It has set me thinking why not a adjustable graduated caliper to do inside and out...not unlike a vernier. One tool to do every chuck.

**wheelinround** · 27th November 2007, 07:15 AM

A top Idea Joe

**joe greiner** · 28th November 2007, 12:02 AM

Welcome aboard, Martin. My podocarpus (a type of yew, I've been told) was from a similar source - next-door neighbour in February 2007 IIRC. I haven't sealed it, but it never hurts. We get a lot more rain here than in CA though. Most of my stash is only about 8" diameter, and hasn't shown any checks as of this morning; very much larger could be another story. The only mishap I've had was when trying to touch up a bowl rim after overnight warping. I've found about half of the pieces, but the rest will have to await a complete cleanup of the shop. That could happen with any green timber. I don't have enough patience, or enough WIP's, to do the rough-turn-and-wait-a-year drill.

Hughie, a lot of us use the vernier calipers to check tenon sizes. The objective here, though, was to free them for other measurements. I'm not convinced these are very much better than littlebuddha's spanner wrench, cited earlier. The only suggestion I might add would be to bevel the throat of the spanner to match the jaw's dovetail requirements.

Joe

**artme** · 28th November 2007, 12:20 AM

Welcom to the madhouse Martin.

What a BGI Joe but youknow what it means? ABTTM! I'm behind already!

BGI= Bloody Great Idea
ABTTM= Another Bloody Thing To Make.

**hughie** · 28th November 2007, 06:28 AM

a lot of us use the vernier calipers to check tenon sizes. The objective here, though, was to free them for other measurements. I'm not convinced these are very much better than littlebuddha's spanner wrench, cited earlier. The only suggestion I might add would be to bevel the throat of the spanner to match the jaw's dovetail requirements.

Joe,

Yep me to. I was thinking of adding bevels to the vernier and marking it with various chucks numbers/sizes etc. Keeping it as simple as I could to avoid more complications. I figured I would be scratching around for the various gauges etcs and would have to make new ones from time to time.

Anyway it is still a darn good idea you came up with, irrespective where I end up with my ramblings

**MartinL** · 28th November 2007, 07:31 AM

Thanks for the information, Joe. I'm with you on the hanging about while stuff dries. I think I should make 200 things, put them up to dry, and then take a looooong cruise and finishing them when I get back.

Podocarpus is known as Yew Pine (according to the Western Garden book we have) and can be used to make long bows

Martin

**littlebuddha** · 29th November 2007, 12:06 PM

Nice go Joe, see your head has been working, i like it, but not enough to tempt me away from my ply spanner, i might do a double ended spanner, i just find that they are a bit quicker for me and as i had said about rounding the opening that bit means i can still be running the lathe with no real problem, if im doing a bit of mass product just saves that bit of time, and have been using them for awhile (old dog new tricks). But great to see i sparked something of for you, and most like a few guys will be making yours and or redesign them as well, info idea's arn't they great..cheers Joe..LB

**joe greiner** · 30th November 2007, 10:13 PM

Thanks LB. This was one of those notions that seemed like a great idea at the time, then took on a life of its own. Like I said earlier, maybe adding a bevel to the throat of your spanner would be helpful. Tell the truth, I've used expansion mode only once, and that was a special situation (grabber for the back of one of my Longworth chucks). While the brain cogs are coasting back to idle, I suppose a tapered throat to the spanner, marked at each extremity of compression mode, would better express the range of choices, although the overall size of the gauge could get huge. But for production work, your fixed size is the way to work it.

Joe

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