How Large a piece can be held in a chuck?

[Trevor Mills]

Would a 19” diameter by about 26” deep chunk of green wood be OK if the outside was shaped using a face plate, and then chucked to turn the inside, the way we do smaller bowls? (stronghold chuck with 4” jaws) - or should the thing be on a faceplate for the whole procedure?
I haven’t done pieces this large before so looking for some advice.

[Thomas Canfield]

I don't think I would even attempt to turn something 19" diameter and 26" deep on a faceplate. I have a 6" Oneway faceplate and have some issues with smaller pieces than that using 1/4" d x 2" lag screws (1-1/2" thread in wood). Think that a steady rest is definitely in order. I did turn a 33" Dia x 2-1/2" platter weighing about 50 pounds on a 4" stronghold after rounding it up using the 6" faceplate and initial weight of 70 pounds, all without tail stock support. Have you considered the weight hanging on the headstock - would guess over 250 pounds depending on wood and moisture.

[Chris A Lawrence]

I would start with an appropriate size face plate and all the screw holes filled using tail stock support to shape the outside. If you have an appropriate size chuck to handle that size piece you can use it with a steady rest. I wouldn't hollow anything over 15 inches deep without a steady rest. I just got done hollowing a piece that started out as a 18" diameter x 13" deep chunk of green wood and it weighed a ton. I had to dig deep to hold it up while i threaded the faceplate on the spindle. Once i shaped the outside i reversed it on my nova titan 2 chuck with 5 inch jaws using a dovetail recess and hollowed it out without a steady rest.

[Trevor Mills]

Hopefully I’ve attached images.
I roughed out the 19” diameter block of green cedar using an 8” faceplate with the tailstock engaged. No problem.
I shaped it and I didn't measure but now it’s probably about 17-18” x maybe 22-24 “ deep. Now that it’s reversed and attached in the chuck I’m getting a bit of wobble and wondering if I should rethink the whole process.

[Richard Coers]

Just curious. Do you always work with the tool rest sitting down that far? Can't say I've ever run my tool rest bottomed out on my Oneway 2436 since I got it in 1998.

[Trevor Mills]

No, it’s always raised when turning.

[Dick Strauss]

I apologize for going through basics in my message but don't know your level of experience. I applaud your moxie but am concerned for your safety based on your comments.

For bowl turning, 3x the jaw minimum diameter (fully closed) is a good rule of thumb to use for novice Turner's (max 5x for very experienced and precise turners that have extremely good tool control using a bowl going). For maximum holding power the jaws should be very close to all the way closed with a properly shaped tenon to match the jaw profile along with a flat shoulder to ride on top of the jaws.

Once you get beyond a normal bowl shape (1/2 diameter in height) all bets are off. You start putting more and more torque on the piece as the distance increases from the center of the check. This means you have to take lighter cuts to equate to the same force. If you are using scrapers including flat topped carbide tools, you are using higher forces to separate the wood fibers making the force at a distance (torque) worse.

In your case , I would use a faceplate for almost everything, especially when I assume there will be hollowing. You should leave the bottom near the faceplate a very large diameter for the hollowing process and plan to shape it last! This means you have to plan your shape to include 3-4 extra inches to allow for waste where the faceplate screws enter the wood at the base (depending on the length of screws) and your design. Also faceplate screws should be driven at an angle, not straight in if possible (this gives the screws a lot more holding power!). The base should be flat on the perimeter and slightly concave toward the center. The only thing that you can't do on the faceplate is finish shaping the very center of the bottom of the foot.

Also, as Chris mentioned, you should be using a steady rest on the upper shoulder area to help dampen vibration.

In addition, you better have an extremely heavy hollowing rig or a long heavy curved toolrest to work at that depth without a lot of vibration.

Might I suggest you get in contact with a mentor that has experience with something this size...?

[Chris A Lawrence]

What chuck are you using to me it looks like a g3. If it is i would caution turning something that big and heavy with it that chuck is pretty lite weight for something like that. You will always get a little wobble when you flip a piece. You can even get a little wobble if you take something off the chuck and put it back on. All Dick Strauss's points are spot on and to add because of the depth when the walls of that get thinner they will flex when spinning. You should look into buying or making a steady rest to help support the end or you may cut through in spots if you go thin.

[Reed Gray]

Part of it depends on how big your chuck and chuck jaws are. With a piece like the one in Trevor's pictures, that could be done with the big Vicmarc chuck, and probably with some others. The problem isn't the diameter, it is how far off the headstock you are hanging, which is a leverage thing... That is what a steady rest is for, though, there isn't very much room for a steady rest under that piece. The chuck will drive the rotation fine, but even bolted to a face plate, that piece would wobble.

robo hippy

[Brice Rogers]

"bit of wobble" - - with a piece that large, it has moisture in it, unless it has been laying around for about 20 years.

I've found when turning something with a fair amount of moisture in it that I can get it perfectly round, then come back to it an hour later and it is no longer round. Reason? It is drying and shrinking differently in the radial and axial directions. When I take a break, I usually "bag" the piece after a spritz of water.

[Mick Fagan]

As a person who sort of does a fair amount of green wood turning, some of which is similar sized to the above pictures, please be aware that green wood certainly attacks some screws.

I had one occasion where I left a face plate on over about three days on a really green piece of wood; cut down earlier the day I attached the face plate. I used appropriately sized screws to hold everything together, roughed it out to a smooth shape, made a tenon, reversed it onto a big Vicmarc chuck and appropriate jaws, then removed the face plate.

I discovered that two of the screws twisted off as I was undoing them, leaving what was in the timber, in the timber. A couple of others were decidedly unhealthy, but came out, the rest were alright. Talking about this to a long time wood turner one day, he smiled and showed me some coated exterior screws that were able to withstand the sometimes aggressive liquids inside some trees for a much longer period than what I had used.

These days with green wood, I use exterior screws designed for treated pine (or similar) as a bit of insurance. Plus, I no longer leave a face plate on longer than necessary, unless I forget about it.

Mick.

[John K Jordan]

...Talking about this to a long time wood turner one day, he smiled and showed me some coated exterior screws that were able to withstand the sometimes aggressive liquids inside some trees for a much longer period than what I had used.

These days with green wood, I use exterior screws designed for treated pine (or similar) as a bit of insurance.

What kind of exterior screws? Do you mean what is sold as deck screws at Home Depot, etc?

[Chris A Lawrence]

I always use stainless steel screws for green wood. I get a few uses out of them before the heads get stripped and i cant get a Philips bit to turn them anymore.

[Mick Fagan]

"Originally posted by John K Jordan" What kind of exterior screws? Do you mean what is sold as deck screws at Home Depot, etc?


John, I used what is virtually a generic term in Australia, for external use construction of treated pine timbers. Decking screws are usually different as decking is in this country usually hardwood, sometimes really hard hardwood. Stainless steel is often used for these and in the case of our own decking, required pre-drilling to prevent any timber cracking and to allow the stainless steel hob nails used, to work correctly.

I did a small bit of research on the matter, eventually contacting a major supplier for advice. Their advice was to use treated pine screws as for my intended purpose they would suffice, they directed me to their appropriate web page for more information. Scroll down past the first text and pictures to the bottom of the page text, where some clearer information is available.

https://www.allfasteners.com.au/products/screws/treated-pine-screws

Eventually I was able to find some good gripping screws for green wood, compared to normal screws. I have found that green wood can at times be quite flexible, with fibres moving a bit over time and with the forces used by turning making the screws sometimes come slightly loose. This can be seen with the attachment where there is a standard 80mm wood screw alongside a 76mm long treated pine screw. The treated pine screws that I eventually found and use, have a greater holding capacity in very wet wood.

As for the type of driving head, my preference in descending order is Square drive, Pozidriv and lastly, Phillips drive.

Mick.


408665

[Brice Rogers]

If I hold something "green" in my chuck for more than a day, I can expect that the mortise/tenon may turn black. Sometimes, when I remember, I'll put stretch wrap between the chuck and workpiece. I suppose that I could also use tape.

[Chris A Lawrence]

Everything i have read says not to use countersink screws with faceplates and to only use pan head type screws. Have you had any problems with heads breaking?

[Mick Fagan]

Everything i have read says not to use countersink screws with faceplates and to only use pan head type screws. Have you had any problems with heads breaking?


I take your point and have used this work action when working in railway line systems around 45 years ago. Also, when fabricating steel, I've used rivets, nothing countersunk with them.

However, the face plate that came with my Revo Laguna 24-36 lathe that I bought last year, came with countersunk holes; suggesting that countersunk bolts or screws were the go.

The Vicmarc face plate rings that I have, are all countersunk and I have had some pretty big pieces of timber hanging off of them.

Another thing to remember is that of the various chucks I have seen and used, all of them had countersunk retaining holes for their respective bolts to hold the chuck jaws in.

Attached are my Vicmarc chuck face plate rings and the OEM face plate that came with my lathe; which I have never used.

To specifically answer your question; no.

Mick.



409257 409258

[Jamie Hunt]

These allfastener pine screws are ruspert coated, which is basically a fancy (but excellent) galv like coating over carbon steel. The research I have seen here shows that stainless screws have the best longevity for CuAz and ACQ timber treatment, and ideally 316/A4 not 30, see:

Stainless Screws in Copper treated Timber (https://www.anzor.com.au/blog/stainless-steel-fasteners-with-treated-timber)

And a range of stainless decking screws (https://www.anzor.com.au/blog/what-stainless-steel-screws-are-best-for-decking)


"Originally posted by John K Jordan" What kind of exterior screws? Do you mean what is sold as deck screws at Home Depot, etc?


John, I used what is virtually a generic term in Australia, for external use construction of treated pine timbers. Decking screws are usually different as decking is in this country usually hardwood, sometimes really hard hardwood. Stainless steel is often used for these and in the case of our own decking, required pre-drilling to prevent any timber cracking and to allow the stainless steel hob nails used, to work correctly.

I did a small bit of research on the matter, eventually contacting a major supplier for advice. Their advice was to use treated pine screws as for my intended purpose they would suffice, they directed me to their appropriate web page for more information. Scroll down past the first text and pictures to the bottom of the page text, where some clearer information is available.

https://www.allfasteners.com.au/products/screws/treated-pine-screws

Eventually I was able to find some good gripping screws for green wood, compared to normal screws. I have found that green wood can at times be quite flexible, with fibres moving a bit over time and with the forces used by turning making the screws sometimes come slightly loose. This can be seen with the attachment where there is a standard 80mm wood screw alongside a 76mm long treated pine screw. The treated pine screws that I eventually found and use, have a greater holding capacity in very wet wood.

As for the type of driving head, my preference in descending order is Square drive, Pozidriv and lastly, Phillips drive.

Mick.


408665

[Brian Deakin]

(https://www.accu.co.uk/en/p/126-what-is-the-difference-between-phillips-and-pozi-screw-heads)Phillips screw heads are designed so that the screwdriver will cam-out (slip) if too much torque (power) is applied. The reason is that this prevents the risk of the screw head being twisted off by a power tool. This can be helpful, because if the head breaks off, a screw is very difficult to move.
The Phiilps design is often criticized for its tendency to cam out (https://en.wikipedia.org/wiki/Cam_out) at lower torque levels than other "cross head" designs. There has long been a popular belief that this was a deliberate feature of the design, to assemble aluminium aircraft without overtightening the fasteners Extensive evidence is lacking for this specific narrative, and the feature is not mentioned in the original patents. However, a 1949 refinement to the original design described in US Patent #2,474,994 describes this feature.

Pozidriv screws, on the other hand, are designed specifically so that the screwdriver head does not cam-out.

https://www.accu.co.uk/en/p/126-what-is-the-difference-between-phillips-and-pozi-screw-heads