Which jaws do I need for larger bowls on a midi?

[Justin Stephen]

Hello all, new turner here on a Delta 46-460. I picked up an SN2 with the default 50mm jaws. I also have a nice pile of fairly fresh cedar logs courtesy of a neighbor, our recent snowstorm and the unforgiving force we call gravity.

I cut out my first blank and started to rough out a bowl about 9" across by 5-6" deep between centers and then turned a tenon knowing that it was unlikely that the 50mm jaws would be able to hold onto an unhollowed bowl that large. I was right (no drama, shut it down before it popped off). So now I am hollowing what will be a slightly more shallow bowl on a faceplate and that is fine.

However, I would like to be able to turn bowls of this size in the future using a chuck. What size jaws do you think I need to do this pretty safely?

[Alan Trout]

Justin, I have done 12" bowls with the 50MM jaws without trouble. While it might not be the ideal jaw it is very capable of it. When I first got started I did not have much money so I really had to make due with what I had.

First size the Tenon correctly. I personally prefer contraction mode but others have different opinions. It should be as close to being closed and still have some compression so that the full surface area of the jaw makes full contact with the tenon also make sure the tenon does not bottom out in the chuck. In reality the tenon does not need to be much longer than 1/4 inch even a little less with the 50MM jaws. Also make sure the angle of the dovetail is accurate. A skew cut at 20 degrees is very close to what is should be.

Next always use a live center against the bowl until is is roughed on the exterior most of the hogging of the interior. By this time most of the weight is gone and you should be able to do your finishing cuts without to much difficulty.

Remember practice and always have proper face and head protection and always stay out of the line of fire. I have seen bowls come off 4" jaws that the tenons did not fit properly.

Good Luck

Alan

[David E Keller]

I agree with Alan... It probably has a lot less to do with the size of the jaws and a lot more to do with the size and shape of the tenon. Take a little extra time when you're making the tenon and get it right. Remember that the tenon should not bottom out in the chuck. I'm not familiar with that chuck, but if it requires a dovetail, try to get the angle right. Lastly, make sure there is a nice flat shoulder where the edge of the jaws meets the base of the bowl.

I hope that helps.

[Justin Stephen]

Thanks guys. I had completed outside roughing and then turned the tenon between centers.

While the tenon was certainly deeper than 1/4", I can say with complete certainty that it did not bottom out in the chuck and the top of the jaws was initially pressed firmly against the bottom of the bowl. I did dovetail slightly the tenon with the edge of a skew but I don't really know from site how much dovetail is needed. I also probably turned the tenon a little large but I didn't want to get too close to the minimum size of the chuck since I might have to take more wood away if the tenon warps later during drying.

With that, the bowl started to come off of the chuck almost immediately after making hollowing cuts. I was not, however, doing any hollowing with the tailstock up. I honestly don't know how as I have never seen that done. In the Grumbine video (if my memory serves) and in the 2 bowl turning clinics I have attended, hollowing was done without a tailstock up. How do you do that?

Thanks!

[Leo Van Der Loo]

Justin IMO you have two things here that contribute to your problem of the bowl not staying put.
First off an approx. 2" tenon on a 9" bowl is rather small, I'd rather go a little larger than the 1/3 rule for a foot/tenon, as I can always make that smaller later, (or turn it away al together) it's a lot easier done than trying to turn it larger ;-)).
The other thing here is the wood you are using, Cedar (Juniper) is a rather soft wood so it will give and come loose pretty easily, some CA soaked in will help a little, and also make sure the tenon is very clean so the jaws sit good and solid.
So what jaw size ??, I'd probably use a recess, but if you use a tenon, I'd go for a 3 to 4 inch size tenon, with more experience and stronger/harder wood the 2" jaws could be used, but the Oneway jaws I use do hold better over a larger size difference than the dovetail jaws will, just play it save and go for a larger set of jaws on your chuck, HTH :-))

Just have a look at the picture it shows were the smooth jaws (dovetail) hold at their best.

[Mike Peace]

You may want to review the manual for your SN2. It states:

"The 50mm standard jaw has a thin lip or shoulder at the front face. This is designed to bite into the timber as the jaws are tightened. DO NOT CUT A RECESS FOR THE LIP TO FIT INTO, AS THIS WILL REDUCE GRIPPING POWER."


It may seem counterintuitive, but you don't make a dovetail cut on a tenon for your dovetail jaws. It you size the tenon right, not too large but max steel on the wood, The 50mm jaws should be able to handle the largest bowl you would turn on your Delta midi.

[Alan Trout]

Justin, When I am hogging a bowl out with the live center in place I use both pull and push cuts. I am not worried about the finish just removing material as fast and safe as possible without any catches. When it is roughed out it will have monolith left in the center that you can turn away when most of the weight is off. It is so much easyer to show than tell. Maybe the next time you get to San Antonio I would be more than happy to show you.:)

I agree with Leo that on soft or punky wood I will sometime harden the tenon with thin CA which will increase durability.

Good Luck

Alan

[Justin Stephen]

Thanks all.

Is an application of thin CA to the outside ring of the tenon sufficient for it to harden it?

[Gary Chester]

Another thought...

I make my tenons as big as I can for the jaws I'm using... that way, when the bowl has dried and warped, I can turn the tenon to true it and still have it fit in the jaws.

[Ryan Baker]

The 50mm jaws can hold a blank that size, but you would be a lot better off with larger jaws and a larger tenon. Get a set of the 100mm jaws, and your tenon will be in the 3.5 to 3.75 inch range.

If the blank is pulling out of the jaws almost immediately, you are doing something wrong with the shape of your tenon. Granted, green cedar is not an easy thing to get a good grab on (all the more reason for the bigger jaws). Make sure your dovetail angle matches the jaws ... and err on the side of less dovetail angle, not more. Too much angle on the dovetail will destroy your grip. On really soft wood, you might be able to get away without cutting the dovetail, but on most reasonable blanks you do need the dovetail for proper grip.

This is a case where the profiled Oneway style jaws grab better than the smooth dovetail jaws. You might also consider using a spigot type jaw, like maybe the PowerGrip jaw.

[Gordon Seto]

If you look at the cross section of the dovetail jaws, the dovetail portion is not all the way extended to the bottom in a straight line.

http://i118.photobucket.com/albums/o83/gbseto/0d0edd87.jpg
Page 13 of manual:http://www.teknatool.com/products/Chuck_Accessories/General/downloads/Accessory%20Jaw%20Manual_Nov07.pdf
If your spigot is too long, the dovetail is not biting critical intersection of the shoulder and the tenon. Also as pointed out earlier, the top face of the jaws making a gap free contact of the shoulder of the spigot is very important.

[Ken Fitzgerald]

Justin,

I have an SN2 and the largest jaws I have are the standard 50mm. I have turned a winged bowl that measured over 13 inches.

Check the tenon.....check the jaws......Something is not right but that chuck and the 50mm jaws should turn anything you can turn on that lathe.

[Jason Clark2]

Ditto what Ken said. The 50mm jaws on a SN2 will handle anything you can fit on your Delta. I regularly turn and core 12+" with the 50mm jaws.

Jason