Starting a big log for large dia hollow-form

[John Tisdale]

Almost 25-years ago I got mesmerized on Moulthrop's work and redirected without looking back. If you check out Ed's, Philip's, and Chris' work, you'll note that all are "big" - they have "presence". I think all will agree that a 5" diameter and a 20-" diameter, with the same design, out of the same log, and with the same finish, are very different: one is cute and the other commands attention. The problem is, big turnings come from big (and heavy) logs, take a big lathe and can hurt real bad if you screw-up.

• All logs start between centers with 1.5" four-prong spur and live-center. After determining the axis, I drill a shallow 1.5" hole, with a forstner, about 1/4' deep for the drive, and a shallow 9/16" forstner hole for the live-center, assuming Oneway live-center. Keep both shallow - you may have to adjust the axis
• Raise up with your chain-hoist - a one-ton from Harbor Frt costs around $60 - a barn-door track and car from Grainger are about $40 - I ran out of neighbors willing to help mount a 200-lb+++ log a long time ago. Adjusting the axis becomes no big deal and reversing on the lathe is easy
• Snug it up and go. The live-center end will be the tenon for faceplate
• Turn the outside to final design - no returning to fix it later
• Cut the tenon same dia as your faceplate - my faceplates are 6" Oneway. Make the tenon surface "aero-space flat" or a teeny bit concave. Next step is to precision drill: I use #14 SS oval-head sheet metal, 1.25" for inside holes, 1" for outside holes (tips ground off). I found marking with "hinge-drills" to be invaluable when drilling 18-holes. Then drill holes with 11/64" bit with a depth stop set to the screw extension. The #14 screws and hole count assume the 6" Oneway faceplate
• Mount on the head-stock and secure with live-center for final rounding/balancing. Then remove tail-stock and start hollowing. You shouldn't need a steady-rest - with screws properly hand-torqued, it ain't going anywhere.
• After hollowing to maybe 1" thick (to allow for warpage) you're ready to dry. Boiling in a large pot for about 2-hours minimizes cracking and speeds final drying - allow 8-mos to a year for drying

After reading the above I have to wonder: Is there anybody out there stupid enough to do all this? Am I that stupid to do all that? Jury is out.

 

[Alan Weinberg]

I own a Moulthrop piece from all three generations—who is Chris? Did you mean Matt?

You say the exterior cannot be refined after turning it around on the tenon/faceplate. Why?

Last, why use such short screws in the faceplate? Longer makes more sense, no? Do you use the faceplate instead of just a tenon?

 

[Randy Anderson]

I've got a 150lb+ piece of walnut out back that I'm getting ready to hoist up onto my new "big boy" lathe as you call it. I wouldn't call it stupid - it's doing things many won't. As the principal at my kids school used to say all the time - strive to do hard things others won't do.

I'll be doing a session/demo at the local woodworking shop this coming Saturday on the unique steps for deep hollowing. Maybe there will be one in the audience that's willing to take a shot at it.

 

[John Tisdale]

Did mean Matt - guess I'm getting old

I've found that taking the wet log to final shape makes the envisioned shape more attainable when re-rounding after the inevitable warpage. Especially with walnut, assuming the end-grain runs from 3 to 9 and the side grain is noon to 6, the difference in thickness can be almost an inch on a 20" piece. Just re-rounding to the original shape can leave you with potential thin spots - changing the design can be a problem. I love walnut root-ball and that stuff is really whacky .

Regarding the screw length, I've gotten very comfortable with six long screws, 1.25". in the six center holes and 1" (tips ground) in the twelve outer screws. Reason is: no way do I want a 6" base on one of my hollow- even the ones >20" dia.
When the piece is rounded, shaped, and sanded to maybe 220 and, to my thinking, perfect, I then remove the outer screws on the faceplate and "dive under" - the side is curved to intersect the bottom annular ring and the tenon is 3.5". At that time the piece is removed from the lathe, removed from the faceplate, and a 1/2" galvanized floor flange / 10" nipple is attached to the tenon for the finishing process.
I go through the barrier/sealer applications until the piece is perfect. Then it goes on the Kelton mandrel for tenon removal / concave bottom cutting. Then, when the sealer is sanded to 220 and perfect, do I put it on the "umbrella fixture" and shoot a very high-end auto clearcoat. A couple of day later I knock off the orange peel with paper-backed 800. hand-sand to 3000 and then buff with wool and foam buffs.
After that, to the gallery it goes.