Vicmarc Jaws

[Burt Alcantara]

I just ordered a VM120 from KMC in Canada. A couple of questions about jaws:
- What is the angle of the dovetail?
- How do you cut your dovetails?
- Vicmarc's site lists jaw sizing by closed/minimum only. Is there a chart that shows min/max?
- What jaws are recommended that are sized smaller then the Standard? By that, I mean a bit smaller not down to pin jaws.
- Can the step jaws be used for bowls? If using the smallest ring, will the bowl base bang against the outer ring? Hard to tell from the photos.

Thanks,
Burt

[Craig Powers]

Burt
I can't answer all of those, but as for cutting the dovetails, I've used and 3/8 round skew. Recently, a friend made me a dovetail cutting tool.
Basically, a scraper with two cutting faces on the end ground to an angle to match the angle of the jaws. As for the exact angle, I couldn't tell you.
The round skew works very good as well. I've become a fan of the VM 120 chuck as well.

[Reed Gray]

As far as the angle goes, I believe it is 7 degrees. This is a standard angle like on your router bits for cutting dove tails. I use a specialized tool that I ordered through one of the magazines. It has the dove tail cut into it. You can easily adjust the angle by touching each face to the grinder wheel, using the face and side of your wheel. For me, I use a recess. I have dedicated dividers/compass that is super glued into place to mark the exact dimentions of the recess (I prefer that to a tenon), then use a plunge cut. Cut just inside the line first, cut just barely take the line, then clear out the rest. To get the angle as close to perfectly matching the angle, I line up the shaft of the tool to the bed ways on the lathe. This is why I never use a skew or another catalogue tool which requires you to hold your tool shaft at about a 45 degree angle to your tool rest (horizontal plane) to get the cut. You get the best hold if your angles match exactly. I don't know exactly how far the jaws open up, probably about an inch or more for the small chuck, and slightly more than that for the big one. Since I use a recess almost all of the time, except for hollow forms or end grain turnings, it doesn't really matter. If I want a bigger grip, I will use bigger jaws. I have a set of the step jaws, and never use them. The other jaws do get in the way. The largest outer jaws work fine, the smaller inside ones do not.
robo hippy

[Ryan Baker]

I cut my tenon with a gouge, then (usually) use a skew to slightly trim it to the dovetail shape. (Cut into the side grain of you do this, not the end grain.) Some day I will get around to grinding a scraper to the right shape. I do have a scraper that will work for a recess, but I only use a recess as a last resort, since it is way too easy to blow up the blank that way. The angle is whatever it is -- 7 degrees sounds about right (never measured) -- just match the jaws.

I agree with the others that the step jaws are nice in theory, but not very useful in practice. It depends, of course, on what you are holding. Most of the time you will have an interference problem with anything but the outermost step.

The rest of the info should be easy enough to come by on the web.

[Burt Alcantara]

I have an old Harbor Freight 1/2" skew. For some reason, this little skew keeps a very sharp edge. The 1" skew wont get sharper then a butter knife. I'm thinking of modifying the angle on the 1/2 to accomodate the 7 degree angle and I'll be all set.

Thanks for the tips,
Burt

[Allen Neighbors]

On hard wood, after I get the tenon to size, I usually take my 1/2" skew, on the side, and use the point to make a small groove for the dovetails to grip. It's usually about 3/64" both ways. That's all I do. If it's soft wood, I do nothing.
I haven't launched a bowl since I don't-know-when.

[Richard Madison]

An alternative is to turn the tenon to approx. size with bowl gouge, make two cuts with a thin parting tool, one perp. to lathe bed to create flat surface for ends of chuck jaws, another from the end at 7 degrees (or whatever). After you have done a few (dozen, hundred ?) you can just eyeball the angle. If it is off one degree or so, the chuck jaws will adjust it to suit as you tighten.

[Reed Gray]

Ryan,
If you are launching things when using a recess, there are a couple of things that you can do to fix it. One, it must be the proper size. If your jaws closed are 2 1/2 inches, then your recess needs to be 2 5/8 wide max. For depth, you want about 1/8 to 1/4 max (on big heavy green bowls). You need an ample shoulder outside the recess. This is kind of like having too small of a tenon on a bowl, like a 2 inch tenon on a 12 inch bowl. For a 12 inch bowl, I want shoulders about 3/4 inch. Also, you can over tighten. Some times you break it right out. Some times you get it almost to breaking point, then a small catch will cause it to fail at the point of most stress. I figured this out through trial and error. I turn and core bowls up to 18 inches with a big Vicmark 2 5/8 inch jaws, no problem.
robo hippy

[Ryan Baker]

Ryan,
If you are launching things when using a recess, there are a couple of things that you can do to fix it. One, it must be the proper size. If your jaws closed are 2 1/2 inches, then your recess needs to be 2 5/8 wide max. For depth, you want about 1/8 to 1/4 max (on big heavy green bowls). You need an ample shoulder outside the recess. This is kind of like having too small of a tenon on a bowl, like a 2 inch tenon on a 12 inch bowl. For a 12 inch bowl, I want shoulders about 3/4 inch. Also, you can over tighten. Some times you break it right out. Some times you get it almost to breaking point, then a small catch will cause it to fail at the point of most stress. I figured this out through trial and error. I turn and core bowls up to 18 inches with a big Vicmark 2 5/8 inch jaws, no problem.
robo hippy

Not launching -- splitting. It is quite easy to split a blank using expanding jaws (much easier, that is, than crushing a tenon). Yes it can be done. Yes it matters a lot what type of wood, dimensions, how thin you turn it, whether you get a catch, etc. Sometimes a recess is the only good option, so I do it that way. Most of the time, either a tenon or a recess will work, so I choose a tenon since I find it easier and stronger. Many other turners also prefer a tenon over a recess for the same reasons. But a recess does work. If you prefer to work that way, i'm certainly not trying to change your mind. It's all preference.

[Chuck Jones]

I use a Super Nova 2 chuck and somewhere I picked up that it is best to cut tenons straight; not angled. Since I've been doing that I have had far better success. I'm not sure it's the same for other chucks.

[Reed Gray]

Ryan,
You have me wondering how you are splitting bowls with a recess. I have broken the shoulders off, but don't think I have ever split a bowl. I haven't been able to determine that there is any mechanical difference with strength for tenons or recesses. Hope this doesn't sound rude, but you have presented me with a puzzle, and I am trying to figure it out. I am the curious type.
robo hippy

[Burt Alcantara]

Chuck,
The jaws on Vicmarc chucks are designed to accept a dovetailed tenon or recess. I needed another chuck so I decided to try a Vicmarc and was curious about using the jaws to their maximum efficiency.

I've been using Talons and Strongholds that require a straight tenon. I have no probelms with them but since most jaws are chuck specific I decided to try something different.

Burt

[Ryan Baker]

Chuck,
A SN2 chuck (any Teknatool) uses a dovetail tenon like the Vicmarc (with the exception of the non-dovetailed jaw sets, like the pin jaws). Oneway chucks are meant for straight tenons.

Reed,
Perhaps terminology is adding confusion. You say 'broken shoulders off'. I suppose that is what I meant. When I said 'split', that is in terms of cracking the recess, not necessarily splitting the whole bowl in half. Of course, sometimes the result is the same anyway.

If one is turning 18" blanks, as you indicated, then I agree that one shouldn't have any problem using a recess, as there is plenty of "meat" there to grab. Expanding the chuck in a recess puts the pressure in the direction of splitting the blank apart. A bigger blank has enough material there to resist the pressure from the jaws, so it works fine. A smaller, thinner turning (like I am most commonly using), has a lot less mass there to resist the jaw pressure -- just the 1/4" or so in the plane of the recess. Depending on the type of wood and the dimensions involved, it may or may not be enough to hold together. Sometimes it will hold together, but a slight catch is enough to push it over the edge. With some kinds of wood, it takes very little force on the jaws to put too much pressure on the recess -- you don't have to strongarm it. (Just ask Bill Grumbine.) On the other hand, it is really difficult to crush a tenon by squeezing it too hard with the jaws -- at least to the point of being a problem.

I also find it faster, easier, and more convenient to use a tenon (in most cases, with some exceptions) -- but that's just my opinion.

Like I said, it's just preference. Any method that gets the job done and does it safely is a good method. Use whichever one you prefer.

[Reed Gray]

Ryan,
Now that makes sence. Most of my bowls are utility types, and have a larger foot on them. When I am making the more dainty types with a smaller foot, a tenon is more appropriate.

Oneway does now have dove tailed jaws. I prefer a dove tail to straight. Mechanically, they hold better because of the angle.

robo hippy

[Burt Alcantara]

Reed,
I've seen the smooth Oneway jaws but never stopped to read the descriptions. They state that they do not have the same holding power as the profiled jaws. If you cut a properly dovetailed tenon, in my case, wouldn't they have similar grip?

Burt

[Bernie Weishapl]

Ryan,

Oneway does now have dove tailed jaws. I prefer a dove tail to straight. Mechanically, they hold better because of the angle.

robo hippy

I just bought the Oneway chuck body only with the tommy bars. I got the #3 dovetail jaws for it. It holds 16" bowls and large HF's securely. I would rather have the dovetail than the straight. Never have launched one because of a broken tenon or recesses cracking using a dovetail.

[Reed Gray]

Bert,
My guess it is some thing like why dove tail joints on a drawer hold better than finger joints. There is a mechanical advantage because of the angle. I know the searated jaws will hold better on a straight tenon than smooth jaws. The ridges bite into the wood, and there is a slight advantage of more steel on the wood.
robo hippy

[Wyatt Holm]

Yes, Oneway has dovetail jaws, but from what I have heard they are not very good. They have rounded edges that do not hold too well. I like to make a tenon better than a recess. I use a gouge to cut it.

[Leo Van Der Loo]

Yes, Oneway has dovetail jaws, but from what I have heard they are not very good. They have rounded edges that do not hold too well. I like to make a tenon better than a recess. I use a gouge to cut it.

Where did you hear that Wyatt ??, interesting party likes to know ??

Oh and here are a couple of pictures to show you the looks of the Oneway jaws, + some more info if interested by chance :)