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Vicmarc step jaw use

M

Michael Toivonen

Joined
Oct 29, 2012
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Location
Redwood Valley,Ca.
I have a VM 120 and bought the step jaws with it after reading Raffan. I have found them to be rarely useful because my bowl profiles are usually not steep enough to avoid having the sides interfere with sitting appropriate jaw size of the set on the tenon shoulder. Since Raffan seems to have developed the step jaw for production work I decided he must be doing something different.
Reviewing his books it appears to me that he has his tenons, which are or nearly are finished before remounting for hollowing bottom out in the jaws and it looks like they have little or no effective shoulder to register against. He mentions carefully flattening the bottom outer edge and having the rest slightly hollow which would be neccessary if the tenon is going to bottom in the jaws.Since each step jaw section is much shallower than found on a single jaw size jaw set bottoming out seems almost imperative to get much engagement with the tenon.
My question is this: is this method of mounting as safe as mounting to a similar depth and bottoming on a shoulder, or is it adding risk to the process for the purpose of production speed? I would like to get more use out of these jaws and the idea of being less fussy with my tenon sizes so they will fit standard jaws is very appealing ( somehow I often seem to end up with a tenon size that is in the gap between the other jaws I have, and I have several and even if it does match I might have to still change jaw sets......and I have other chucks besides the Vicmarc)
 
The main use for my Vicmark step jaws is as dust collectors, unless I want to use the larger outside jaw for expansion.

robo hippy
 
I bought a set also thinking they would be useful but have never used them. Maybe someday but mostly they are dust collectors.
 
I think the "shoulder" in the step jaws is the bottom of the step. The tenon size is pretty critical, should be first point of circularity for lots of wood/metal contact. Further, this is the one place where you want your tenon to bottom out firmly. Small diameter work shouldn't be too much of a strain, but I wouldn't go much beyond the size of the largest step, because leverage will build fast, looking to dismount.

California Finn? More Makis in our local book than Smiths!
 
I can’t imagine how bowl turners manage without step jaws because they make life so much easier, especially when you’re roughing out a number in one session and marking the foot doesn’t matter. If the jaws can’t grab a bowl foot, in most cases I reckon the profile needs to be steeper or the foot wider for that bowl, but then I never see the point of a small foot on a flattish bowl as it tends to render them impractical.
I wrote a piece on chucks in the AAW Journal December 2010 edition, vol. 25, no.6. that shows a number of ways in which you can use a range of chucks. With the crisp dovetail jaws you get from Vicmarc and Oneway and Nova now also offer some without irritating chamfers or teeth, you can grip on small beads and the jaws fit right into corners.
I rarely have a foot bottoming out in a chuck when completing a bowl because crisp jaw rims grip quite happily on less than 1/8-in. If you turn the foot or tenon you’re gripping to the original diameter of the jaws or slightly less, the jaws won’t mark the wood. If you’re turning the foot away, I’d have thought anyone would find step jaws far more useful than jaws offering a single diameter so I can’t imagine why they should gather dust. My observation is that few turners seem to use their chucks as much as they could, and far too many continue to use the 2-in standard jaws when a wider set would make life so much easier.
 
Thanks Richard!

I was not an AAW member when that article came out so missed it. I read it online just now and it was very helpful. I look forward getting back into the shop soon and putting the step jaws to work!
 
I saw one of Richard Raffan's tennons at a demo and I was amazed how little he used to grab with the step jaws... way less than 1/8" It resembled a line from a thin parting tool. It was quite impressive! I don't think it would work for turners like me that still make mistakes on a regular basis, though!

Greg
 
bowlman said:
Well said Richard, well said!
Click to expand...

It's no more time involved to open and close any jaw set. If you use dovetail pattern, you get a superior wedged hold for the same time investment. Only thing you have to do is go standard size or own more than one preset chuck/jaw combination if you want to go too far in diameter from one piece to the other. Then you have a chuck to remove and replace. Most of us are turning against a mental image, not the clock, so even that's not much trouble.
 
You can go with less than 1/8 inch with both tenon or recess. I won't do it with green wood because it warps, and you won't be able to remount without turning another recess or tenon. Getting proper fit is critical, and having a dove tailed set of jaws that are sharp, and not with a bunch of nicks in them really helps as well.

This skill is "professional driver on closed course, DO NOT ATTEMPT" for most turners.

robo hippy
 
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