SN2 Chuck with 20" x 8" Bowl Possible??

[Adrian Anguiano]

I have SN2, and have a few big heavy chunks of wet wood. The biggest is 20" round, and about 8" Deep. Do you think the SN2 can handle it? Im using a 3520 Powermatic.

2nd, if you think the chuck is big enough, do you thinkall of the following jaws would work fine 100mm, 130mm, or Powergrip jaws?

[Reed Gray]

Use the biggest diameter jaws you have. For a tenon on a bowl that size, you want around 5 inch diameter. Keep the tailstock up against the wood at all times, unless you are coring. It will reduce vibration.

robo hippy

[Roger Chandler]

The SN2 will handle that with the "powergrip" jaws or the 4" bowl jaws. I like the powergrip jaws because of their strength and they allow for a deep tenon, not just a small 1/4" or so. The powergrip jaws have serrations that help hold the tenon. For that size blank, I would recommend an tenon over a recess for sure.

I agree with Reed above...........use tailstock pressure as long as possible on it as well!

[Dennis Ford]

It is certainly possible BUT is it wise? I suggest using a faceplate.

[Pat Scott]

For a 20" bowl I would want a 7" dovetail tenon (1/3 the diameter of the blank). A 7" tenon that is 1/8" deep is much stronger than a 4" tenon that is 1/2" deep. Why? The side grain fibers are longer. I'll take a large size tenon over a deep tenon any day.

If it were me I'd make a 7" tenon that is 1/4" to 3/8" deep. No way would I try and use 4" jaws - no matter how deep the tenon or what kind of jaws it has. Definitely use the tailstock.

[Scott Hackler]

I don't use a tenon for the largest bowls. A mortise using the SN2 in expansion mode would seem to be a lot safer for the large heavy stuff.

[Rob Boesem]

I don't use a tenon for the largest bowls. A mortise using the SN2 in expansion mode would seem to be a lot safer for the large heavy stuff.

I 100% agree with Scott!....I turn 18" bowls regularly with an SN2 and 70mm jaws, but always use a mortise, when the wood will allow.

You should have no problem with any of the jaws you have listed.

[Mike Peace]

I 100% agree with Scott!....I turn 18" bowls regularly with an SN2 and 170mm jaws...

I have never heard of Nova 170mm jaws. Are they called anything else?

Adrian, I would start with a faceplate. I think the Powergrip jaws are about the strongest Nova has but 20x8 is way outside their safe range with no tailstock support. The 20" diameter would worry me less than the 8" depth. That can cause a lot of leverage, especially while roughing. I would use a faceplate with tailstock support to make a large tenon for the Powergrip jaws and shape the outside. Then reverse with the Powergrip jaws but maintain tailstock support until the very end. In other words by hollow while keeping the center cone in the middle intact supported by the tailstock till the very end. Then remove the cone.

[Roger Chandler]

I have never heard of Nova 170mm jaws. Are they called anything else?

Adrian, I would start with a faceplate. I think the Powergrip jaws are about the strongest Nova has but 20x8 is way outside their safe range with no tailstock support. The 20" diameter would worry me less than the 8" depth. That can cause a lot of leverage, especially while roughing. I would use a faceplate with tailstock support to make a large tenon for the Powergrip jaws and shape the outside. Then reverse with the Powergrip jaws but maintain tailstock support until the very end. In other words by hollow while keeping the center cone in the middle intact supported by the tailstock till the very end. Then remove the cone.

Mike.........your response is much more detailed than mine, and I should have given more information, but the process you described was what I had in mind when I responded above..........I have done large bowls and even hollow forms with the powergrip jaws and tailstock support, and then transitioning to a steady rest for support for the hollowing. That center cone idea is one I have used several times, and it works well.

All that being said........a faceplate with strong screws might be the best idea, but even with a faceplate, I would want tailstock support for as long as I could have it, for a large turning like the one being mentioned in this thread.

[Roger Chandler]

I 100% agree with Scott!....I turn 18" bowls regularly with an SN2 and 170mm jaws, but always use a mortise, when the wood will allow.

You should have no problem with any of the jaws you have listed.

Seems to me expansion mode could cause some splitting of the wood.........I have used expansion mode on several bowls over the last few years, but still prefer the tenon...........something about the way I like to finish off the bottoms and I don't have to worry about hitting a spinning chuck to get close on the bottom when turning the outside of the form............I suppose we all have our own way of doing things........and our particular preferences.

[Adrian Anguiano]

I went ahead and bought the 4" Powergrips, They had 5" Jaws, but the powergrips were more beefy. I didnt see anything larger than 130mm aka 5", I definitely didnt see anything as large as 7", which is why I had wondered if I should get a chuck that had larger jaws.

[Rob Boesem]

Sorry folks...I edited my post! I meant 70mm jaws.....I always use the tailstock for support as long as possible as well.

Hahahahaha......170mm jaws would be some bad boys for sure. :)

[Thom Sturgill]

Teknatool has some reference listing on their site:

Jaw ........Expansion...... Contraction
------- ---------------- -----------------
Powergrip... 16 x 6 ......... 8 x 12
100mm ......14+ x 5......... 12 x 4
130mm ......29 1/2 x 3 ......29 1/2 x 3

They generally rate expansion as stronger than compression - just don't use it endgrain as any small crack is prone to open and make sure there is enough meat outside of the mortice. The powergrip is best for tall forms like vases.

[Pat Scott]

Anyone that turns an 18" bowl with 70mm (2-3/4") jaws is asking for trouble in my opinion. Can it be done? Sounds like it! But I never would. Just because you can doesn't mean you should.

Which is better - expansion or contraction? That's best left for another thread, but that's also not what Adrian is asking. I always use tenons for bowls, as does Mike Mahoney, Glenn Lucas, and Jimmy Clewes that I have trained under. The only time I use expansion is when turning plates and platters.

I think the more important thing is that the tenon/recess is sized properly for the piece. I subscribe to the school of thought that a tenon (or recess) should be 1/3 of the overall diameter of the piece being turned. Which is why I say don't use 4" jaws to turn a 20" x 8" blank. Using the 1/3 rule (or guideline), then 12" is the biggest that 4" jaws should be used on.

I also core my bowls. If you try and core a 20" blank that is held in place with 100mm or 130mm jaws, be prepared for a lot of vibration and don't be surprised when it comes flying off the chuck.

I have Vicmarc chucks with 4", 5", 6", and 7" jaws for my VM120 chucks (105mm, 128mm, 148mm, and 173mm respectively). Vicmarc makes 8" and 9" jaws if you want bigger.

[Ryan Baker]

Tenon vs. recess isn't really the issue -- more a matter of preference. Either can be used if done correctly. The important thing with a recess is that there is enough material outside of the jaws to keep it from cracking through.

I wouldn't really want to turn a 20" blank with 4" jaws. Yes, you can likely do it without incident if you are gentle. I don't really find the Powergrip jaws to be much more secure either, frankly. I would use the biggest jaws I could get. (This is a case where I would pull out a Stronghold with some big jaws.)

Whatever you use, be sure to make a perfect fit with the jaws, and keep the tailstock in place as long as possible (that makes a huge difference). Get the blank as close to round as possible before even mounting it. If you are going to core it, you will need an even better grab. The sooner you can get it spinning true and the bulk of the mass removed, the better.

[Thom Sturgill]

Agreed, if the OP hadn't already bought, I would have recommended a Titan or V120 or similar and 7" (or better 8") jaws if he planned on turning in this size range often. Or better still - use a faceplate even if he has to sacrifice a little depth. You want the BEST bowl, not necessarily the BIGGEST. I would start between centers and make a very slightly dished area for the faceplate so that it sets even at the rim. Mount the faceplate and use the tail-stock until the piece is rounded and relatively balanced at a minimum. If coring, mark your starting grooves before removing the tail-stock.

I believe that a faceplate gives the maximum for both diameter and distance from the headstock if not using the tailstock.

[Adrian Anguiano]

Let me say that, my question is really for coring.

I normally use a screw chuck with tail stock support, because its simple, and fast. In this case, I have no problem using a faceplate for turning the outside, and making a tenon/recess.

My question is really for coring out the inside. Thom, after its balanced, and outside is cut, would you still suggest a 7 or 8" or at that point could I use smaller?

[Thom Sturgill]

Adrian, I'm not a coring expert. I do have a Kelton corer but have only used it twice with limited success as I don't often get piece of wood suitable for coring, though I have a couple now just waiting for the Drs to clear me to get back in the shop after a pacemaker/defibrillator was installed two weeks ago.

I just reviewed Mike Mahoney's video and he used 5" jaws on a 12" bowl - about 40% of the outside diameter. So for a 20" blank that would be 8" jaws for 40%. There is tremendous side pressure on the tenon, so a large base is needed. BTW his 12" bowl was fairly shallow. I stand by my statement that a faceplate is the strongest hold in general. Not quite so good in endgrain as the screws can pull out. I also use screw chucks, just make sure the base is large enough when using them on something that size as a larger base again changes the direction of the forces applied. A screw chuck would require that the face be smooth, which is where starting between centers has its advantage.

Turn safe, I would hate to read of another turner injured when a piece flew off and hit them.

[Adrian Anguiano]

I guess I shouldnt have said coring since that has an infered meaning. I really meant just hogging out the inside with a gouge.

I did a piece last night that was unbalanced and 20" in one spot, 16" in another.. faceplated it. It turned to about 15", then I made a 4" dovetail for the powergrips. It was about 5" deep. It seemed to hold it pretty well. I used tail support for about half of the hogging out the inside, and the whole time for the outside.

Worked well, but I guess it sounds like I will need another chuck brand, since Teknatool only goes out to 5"

[Reed Gray]

I use the Vicmark chucks. I have turned and cored 18 inch bowls using my larger ones with a recess. The jaws, closed are 2 5/8 inch diameter. The 18 inch diameter pretty much maxes out the chuck for this type of turning. With 4 inch jaws, it would be very secure. You can put 4 inch jaws on a smaller chuck, and on a larger chuck. There is a huge difference in stability if you do it on the larger chucks. If you feel your grip is minimal, keep the tailstock engaged and leave a pillar in the center of the bowl. Once is is mostly hollowed out, then remove the tailstock and tower. Biggest problem here is the walls of the bowl will start to vibrate with minimal tool pressure. "The bevel should rub the wood, but the wood should not know it." Easiest way to remove the tower is with a scraper, about 1 inch wide and 3/8 inch thick, and plunge straight in. The gouge can do it also, just roll it on the side, and cut more with the wing.

robo hippy

[Thom Sturgill]

Yes, hollowing and coring can be very different. Hogging the inside of a bowl can be done such that most of the force is applied toward the headstock while the coring blades push to the side. Care in cutting can keep you stable as you "hog out" the inside once the bowl is balanced outside (not always possible with burl and NE bowls). Jimmy Clewes demonstrates a technique where he makes a series of stepped cuts from outer edge toward the center as he works down the inside. He occasionally removes much of the center to lighten the bowl but keeps some mass there for stability rather than cutting out the center and working toward the edge as you would tend to for a hollowform.

If the forces are kept in line with the ways there is much less stress on the chuck. This is the technique I've used but then again, the largest bowl I've made were much smaller - one 14" x 4" and a few in the 10-12" x 6-8" range.