Dovetail Jaw Question

Re: Dovetail Jaw Opinion

Mark Mandell - Gone Round In Jersey

>George,

I use DT jaws on my Vicmarc, but I don't use them in "expansion" mode because of the stress it puts on the bowl. Instead, I cut a tenon on the blank and use the jaws to grip it with compression. I have both the "stock" 2-1/2" and the 5" versions. I feel the larger diameter tenon is more stable, and try to use that as much as possible.

Your mileage may vary . . .

Mark Mandell

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Re: Dovetail Jaw Opinion

George Van

>Thanks Mark,

I want to leave a slight dovetail recess in the finished bowl so I can rechuck them in the future if I want to.

George

Re: Living Dangerously

Mark Mandell - Gone Round In Jersey

>That's fine, George, you can certainly do that, and cut your dovetail recess as part of your final finish turning of the bottom. I'd still suggest that you not use "internal fixation" (expanding DT grip) when cutting (forming/refining) the piece. Sanding or applying finish doesn't impede the spin nor produce the sudden drag of a catch, so you expanding DT can be just snugged tight without putting real pressure on the wood.

Mark

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Re: PS

Mark Mandell - Gone Round In Jersey

>Remember, when you expand the jaws into an internal rescess, they only make contact with your wood at 4 points; one at the outside-center of each jaw. On a face grain piece the expanding jaw will have the tendency to sever the wood fibers at the point of contact just as a gouge might. When you use a compression grip each jaw makes contact with the tenon at 2 points (Unless the radius of the tenon matches the radius of the jaws' curve), and presses against the self-reinforceing "mass" of the tenon.

You'll get arguments on this Mark

TDaniel

>Mark, a lot of people will agree with you and a lot of people will disagree. If the diameter of the pocket is slightly larger than the closed jaws the grip will not be 4 points but will be all the way around. If enough wood is left so that it doesn't break away with the expanding pressure the grip is actually better than tightening down onto a spigot because you are gripping a larger area. Also, when gripping a spigot the corners of the jaws cut into the wood and pulls the vessel off center. Each method has its plusses and minuses, therefore the answer is: Try each until you find what you like. MHO

Re: Opposing Views

Mark Mandell - Gone Round In Jersey

>Agreed, Terry!

George asked for "opinions" and I said his mileage might vary. 'Twas only my "opinion," after all, and was based upon my experience (including blowing out a foot with the technique). Surely didn't mean to forestall any differing opinions; yours and anyone else's.

I take the pieces off the lathe (usually planned) a number of times from finish turning through sanding, finishing and rubbing out. Never noticed them being pulled off center. I do, however, mark and use the same jaw-marks when remounting, so maybe that minimises that issue.

Fully agree with you on the "larger area" grip. That's why I try to use the largest diameter tenon that I can.

You opinion, humble or not, is always good to have.

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Re: Dovetail Jaw Question

George Van

>Thanks Terry and Mark,

You both had good points and I learned a lot about both forms of attachment from you. I never gave thought to the size of the jaws and the ideal size of the tenon or dovetail.

Mark, I like your idea also of marking which jaw is on which area of the tenon so the bowl is replaced in the exact position. I will leave the tail center in position as long as possible when roughing the blank as well as hollowing to support the bowl and keep pressure against the headstock.

George

Re: Dovetail Jaw Question

Brad Vietje

>George,

1. I'm with Mark -- since I often turn burls and chunks with voids and sometimes other imperfections, I also like the idea that the chuck is squeezing the wood together, and not tending to split it apart.

2. My recollection is that the Oneway spigot jaws are pretty tall -- for small objects that can be helpful in getting around the bottom of the turning, but I wouldn't use them for truing up bowls, or larger pieces of wood. For turning a bowl, or re-mounting a rough-turned bowl, you are usually best to mount the bowl twice -- once by the top, and then reversed, by the foot, so the advantage of tool access at the bottom is not of much use unless you're turning small production pieces, where speed is important.

The #2 or # 3 smooth jaws will give you a lot of grab in many applications (I didn't want to say "bang for the buck", as bangs are what you want to avoid !).

Safe Spinning,

Brad Vietje

Thetford, VT

Re: Dovetail Jaw Question

George Van

>Thanks Brad,

I am going to order the #2 Smooth jaws, They will be a good compromise for now.

George