Advice for a large bowl

[Olaf Vogel]

After playing around for the last few months on bigger and bigger pieces, I might have met my match. A friend excitedly dropped of a big chunk of maple: 30" dia, about 20" long and about 200 lbs. Possibly against better judgement, I'd love to try and use this all in once piece, turn it into one big bowl.

Given the dimensions, it would have to be mounted length-wise and hollowed out as end grain. I think I've figured out how to a get big faceplate bolted on there and squared up. Mounting it on the spindle will be either a hoist and tackle or a couple of big buddies.

Assuming I get this hollowed out succesfully (still a big assumption), my biggest unknown is how to dry this without it cracking. My track record in this regard hasn't been great. This log is very fresh, wet and no cracks at all.

I'm considering roughing it in, leaving the walls about 1.5 to 2" thick, then coating it (I have some Anchor Seal, also could use wax) then letting it sit around for as long as it take. But given the diameter of this thing, I'm really concerned about the pulp wood drying, shrinking and cracking.

Any suggestions are very welcome.

I'm not at all sure I can make this work out, but I've got an excess of wood at the moment, so might as well give it a try before this dries out and cracks anyway.

Thanks
Olaf

[Reed Gray]

Well, a few things here.

One, if you are going to mount it end grain wise, then bolts into end grain don't hold very well as that is the direction that wood tends to split into rather than going through the grain where it holds a LOT better.

Leaving it 2 inches thick, and 20 plus inch diameter would be minimal in accounting for wood movement so that when it dried, it might be too far out of round to get a round bowl out of what you have left. If you turn end grain, your chances of splitting are increased because of the pith still being in the log.

My preference, especially on bigger pieces is to turn to final thickness, about 1/2 inch in your case, and slow dry it. I make sure to round over the rims, and I stretch some plastic stretch film around the rim of the bowl. In the case of a bowl that size, I would use 12 inch or wider wrap (saran wrap would work), and be sure to stretch it out. You may want to dry in bags as it is warmer where you are. In a cool basement at least, out of sun and air.

robo hippy

[Wayne Hendrix]

You refer to it as a log. Does it still have the pith? If so mounting the whole thing end grain and turning a big bowl will leave pith and it will be very difficult if not impossible to prevent cracks.

[Wally Dickerman]

From a safety point of view, what you are planning to do could be very dangerous. I know nothing about how much experience you've had in turning, except what you said in your post. Unless you've had enough experience and have the right equipment to safely and comfortably handle such a large job I urge you to think again about what you plan to do. You could get several smaller blanks from a log as large as that.

Please don't think that I'm putting you and your turning experience down in any way, I'm just concerned about anyone taking on a job such as you are planning.

[Prashun Patel]

I am NO PRO, but why not cut it into 2 halves. You'd get two still massive ~20" x ~15"deep bowls, and will have an easier time with the drying.

If you DO go the end-grain route, I'm really interested to see pix of how you mount this and what kind of bolts you'll use.

[Olaf Vogel]

Wayne,
Yes, the pith would still be in there - thats my biggest concern. I'm not sure if its possible to dry out such a piece so it doesn't crack.
Is it realistic to even try? or just go the easy route and create two smaller bowls as suggested? (I love a good technical challenge)

Reed,
Most of the pieces I've done, I finish turned them thin. Then let them dry and distort as they want. However, when dealing with the pith in the middle, its been difficult and not always successful. I do cover the pieces with plastic wrap while working on them, but not after. Would it still dry with warp on?

A couple I've stored (and admittedly forgotten about) just got moldy that way. (although it was fun finishing a big chunk of apple that way. It smelled like fermented cider. I kept wanting to run into the house and grab a beer... :)

Wally,
I agree with your safety concerns, especially with recent posts (that made me run out and get a face shield). I don't take safety lightly. I've been woodworking and turning since I was a kid and just got back into it seriously as a way of relaxing at the end of a tough day. And have been really enjoying it!

For whatever reason, I've always in fascinated with turning large bowls and hollow forms. After starting with several 80 - 100 lbs chunks on my little Delta (and having it bounce all over the shop), I decided something bigger and safer was the answer. When I found an ad for a old pattern lathe, I bought it. According to the owner and his pics, this lathe has done much larger and heavier items in its lifetime. Arguably, he was a pro and I'm not. I spent the winter restoring it and while it won't win beauty contests, it runs extremely well.

I figured that no matter how big / heavy the lathe, there will always be a piece that's too big. In this case the edge is 15" from center. If its 20 lbs off center, even at 100 rpm, thats a lot of force to deal with.
(3 years of university physics and I can't remember how to calculate this.... I'm feeling old now). This lathe is about 2000 lbs, but I wouldn't trust it with that load at normal cutting speed either.

The plan is to rough it in very slow - like 2 rpm, driving it with a gear motor, not the main one. I've got a 1/2" router mounted to the cross slide so I can pass it across the face until its round and (hopefully) fairly balanced. By then it should be quite a bit lighter too.

It piece will be bolted on with a 12" faceplate and the tail stock in place. In the past, I've flushed off one face with the router, used construction adhesive to glue on a 12" circle of birch ply, then put a ton of #14 wood screws through the ply. Then the screws from the faceplate go through everything. Short fat ones into the ply, longer ones through and into the maple. Haven't had that combo come loose yet, even for very long unsupported hollow forms. Since this one has a big face and not much length, I think it will hold well.

After that, I hope to get the steady rest on it and go up to normal speeds for regular cutting.

Well...thats the plan anyway.

[David E Keller]

Sounds exciting, Olaf. That's too big a piece for me to be comfortable turning, but I would be interested in watching something like that... From a safe distance away. If you decide to do it, I hope you'll take some photos along the way. Be safe.