Screw chuck

Re: Screw chuck

Dennis in Southern Oregon

Faceplate?

Re: Screw chuck

Jorge Castañeda

Yes, that is what I normally do, the down side is that I get only 3 bowls out of a core, instead of 4. Just wondering if there is a "better screw chuck"

Thanks Dennis

Re: Screw chuck

Dick Coers

Oneway Stronghold chuck with the 2" woodworm screw really holds well.

Glaser

Screw chuck bearing surface *LINK*

Doc Green

The capabilities of a screw chuck depend as much on the diameter and surface finish of the bearing surface as upon the diameter and length of the screw. A rough,large diameter bearing surface is far better than a small, slick one.

The screw inserts that work with scroll chucks suffer from two disadvantages when you pushing the limits. One is that the diameter of the jaws is relatively small, and second, the front of the jaws are slick. Both of these factors make the screw more likely to strip out of the wood. This is especially true for green wood, which is inherently wet and slick.

Here is an article that explains more than you ever wanted to know about screw chucks. In it I show a picture of an 8" diameter screw chuck made of plywood and a Woodworm screw.

http://www.docgreenwoodturner.com/screwchuck.html

~Doc


http://www.docgreenwoodturner.com/screwchuck.html

Re: Screw chuck

Frank Joseph

3 inch jaws, hard wood wast block turned to fit jaws, add 6 inch 3/4 inch. Ply disk with a 11/2 inch 3/8 lag screw = Big screw chuck. Will hold big wood,, if you need insurance add 6 #10 screws though disk like a face plate,, as per Doc. Greens book...it's a great book

Re: Screw chuck bearing surface

Frank Joseph

Wish I had seen and read Docs. note before posting mine lesson learned go back and check before .

Re: Screw chuck

robo hippy

I have the Vicmark 120 chucks with 2 5/8 wide jaws. I drill a recess with a forstner bit, and expand into that. With the tailstock engaged, no problem with 16 inch bowls. Not sure about 20 inch bowls, but it should still work. Since I use a recess, I would be totally done with the outside before turning it, I would make sure to retighten the chuck before removing the tailstock, and I would turn the speed down. Nice thing about the forstner bit recess is that the core is already centered, every one if you core like I do by taking the biggest one first.

robo hippy

Re: Screw chuck

Dick Coers

I thought I would add that I prefer the big bite center from Oneway now compared to the screw. It lets you adjust the blank to work with the blank and profile compared to the one time shot of the screw.

Re: Screw chuck

Dale Bonertz

I use the vicmarc screw in a vm120 chuck that has 5" or 6" jaws. The larger jaw surface helps hold the bowl steady and sturdy. I core from smallest to largest blank though so that may not help you. Screwing the screw in more than twice is risky for hold. I would suggest to learn to core from smallest to largest since it is faster and more efficient.

Re: Screw chuck bearing surface

Jorge Castañeda

Thanks Doc, as usual your articles are very clear and to the point.

Re: Screw chuck

Jorge Castañeda

Thanks Reed,

I had a dismount the only time I tried to turn a big chunk at expansion. It was norway maple, very green and it just broke and gave me a glancing blow that scared me more than hurt me. I should try it again, but I am so used to work with tenon.

Re: Screw chuck

Jorge Castañeda

Dick,

That is a thought, I should get that big center and experiment with it.

Re: Screw chuck

Jorge Castañeda

Dale,

I will have to try your method, I am so used to get out the biggest core first. It sounds like it should save time taking all the cores making just one initial tenon.

Re: Screw chuck

Dick Strauss

Jorge,

Another optionis to use #3 or #4 jaws instead, you move the pivot point that much farther and increase surface area (top jaw surface) to drive your blank!

If you don't have #3 or #4 jaws there is a bit of a compromise that can be used. Others may disagree, but one option that I have used with screws is to open the jaws of my stronghold as wide as possible to change the leverage by changing the pvioting point. So if the screw is at 0 inches and the pivot is at 2" (chuck jaws edge when completely closed) and you have a 16" blank, you have an 8:1 ratio. If the jaws are opened to 4" (fully open) the same 16" blank only has a 4:1 ratio, etc. The jaws when fully opened are still stronger than a 4" wooded disc added to the top of the chuck and you get more screw penetration in your blank without the additon of a 1/2" thick disc. You also have an interrupted surface (jaw and no jaw) that if rotated where the jaws are in the in low points of the blank, it can give some additional drive force and stability.

I grew tired of normal spur drives spinning on heavy roughing cuts. I just had a buddy turn down some 1" set screws to a point for me. These set screws mount on a 6" faceplate that that has threaded holes across its surface. You can adjust for uneven blanks and it drives really well.

I like having lots of options and gadgets!

Re: Screw chuck *LINK*

John Kaner

Have you seen the Bestwoods Tools big Texas Drive Centers? The body screws on the spindle and has a large insert. Various models.

TEXAS SPUR DRIVE CENTERSTEXAS SPUR DRIVE CENTERSThese giant Texas size spur drives are available with 2, 4, or 6 flutes, in either Fixed Point or Adjustable/Recesable Point Styles, to give you the greatest versatility and holding power available and they won't slip under heavy turning loads. Click on the image for complete information and pricing.




http://bestwoodtools.stores.yahoo.net/tespdrce1.htmlhttp://

Re: Screw chuck

Jorge Castañeda

Thanks Dick,

I like options and gadgets too!

I have #3 jaws for the Stronghold, 4" to 5" range, and usually make the tenon around 4 1/8" and it works for me most of the time. I plane the area, so there is a perfect flat where the jaws will make contact. I see your point opening them to the max gives the best purchase.

I'll experiment with it, Thanks for suggesting it.

Re: Screw chuck

Jorge Castañeda

Thank you John,

Looks like nice gadget to try.

Thanks for bringing it to my attention

Re: Screw chuck

robert

I have used the screw chuck and the same happened with me. I now use the Elio Drive 2.5", and it works the best.It holds great and no spin out.

Re: Screw chuck

Dale Bonertz

The drive centers that John and Robert have shown are very nice but are more for one shot on the exterior form. If you cannot adapt to coring smallest to largest (some people just freak out and can't seem to save the largest blank) then those drive centers are harder to re-center unless you pre-drill a hole for them to slide into. Even with the pre-drilled hole they are harder to center the core because the core won't have the centering hole from the tail center. If all else fails and you continue to core largest to smallest then a 3" face plate and using the tail stock has as much and maybe more holding capacity than a screw chuck. A three inch face plate would only get in the way if you are using the oneway or bowl saver units for coring. If you are using the McNaughton then the face plate won't get in the way and you can remove it on the last core and not have screw holes hindering saving a fourth blank.