Worm Screw or Face Plate Question

[Pat Harris]

I'm not sure whether to use a Worm /Center Screw of a faceplate on a 19 1/2 inch diameter X 10 inches high glued up laminated purple heart, cherry with birch plywood. It is a heavy piece. I will be turning on my Powermatic and I don't have a large faceplate, but will buy one if group thinks that is what I need to secure the top side of the bowl I will be turning. I have held 19" x 4 1/2" platter with the screw centers but this piece is larger and heavier, Just need to get to get bottom and tenon formed as the pieces is glued up in steps What do you suggest and if faceplate Pat Harris, Lexington..

 

[hockenbery]

My roccomendation is to start it with a worm screw and use the tailstock.
The wood cannot come off of this configuration unless a glue failure occurs.

Shape the outside. I would use a chuck only with #3 jaws. Or #4


You might do a lot of the hollowing with the tailstock in place for a while.
It is a pain to work around the center post but it

A 6" faceplate should work as long as the screws are not going into endgrain.
I can't be certain of the grain orientation from the photo

Have fun
Al

 

[odie]

I'm not sure whether to use a Worm /Center Screw of a faceplate on a 19 1/2 inch diameter X 10 inches high glued up laminated purple heart, cherry with birch plywood. It is a heavy piece. I will be turning on my Powermatic and I don't have a large faceplate, but will buy one if group thinks that is what I need to secure the top side of the bowl I will be turning. I have held 19" x 4 1/2" platter with the screw centers but this piece is larger and heavier, Just need to get to get bottom and tenon formed as the pieces is glued up in steps What do you suggest and if faceplate Pat Harris, Lexington..View attachment 8406

Pat......

If I'm understanding correctly:

A worm screw is probably sufficient, if you are bringing it to round and make the tenon between centers. Once you have a strong grip on the tenon, you'll be removing 80% of the weight by removing most of the interior of the bowl. You may want to consider using a waste block, on order to eliminate the height waste necessitated by using the worm screw into your laminated block......

ko

 

[hockenbery]

Do be careful

The flush glue joints are weak to begin with and it is real easy to get a starved joint In that glue up.
A glue failure or a hidden crack in one of boards could send some heavy chunks flying around.

That piece is a lot riskier to turn than a large solid block of green wood.

Be safe

 

[Bill Boehme]

If you will be turning a bowl, why not start by balancing the piece so that the lathe won't be shaking? You could either add wood to fill in the "void" or cut it to an even thickness.

You have at least three options:

• If you first balance the piece, it could be started between centers.
• If you use a faceplate, it still would be a very good idea to bring up the tailstock. I don't see why a large faceplate is necessary -- I think that a 3½" faceplate would work just fine if you use deep thread screws that go about 1½" or more into the wood. I would still highly recommend balancing the piece first. If the wood is well glued, the faceplate seems like overkill. Do you trust your glue up to be strong enough to hold together?
• A screw chuck (same thing as a one screw faceplate), Oneway Jumbo Screw, Vicmarc Wood Screw, or Nova Woodwormâ„¢ in a chuck should also be just fine, assuming of course that the glue job is adequate. I would not do this without first balancing the piece. Always bring up the tailstock.

 

[Bill Boehme]

If any of that plywood has a phenolic top lamination, glue isn't going to hold very well. The way that the stack is oriented concerns me as it seems to be inviting opportunities for disaster as well as not being a particularly attractive final result because of what appears to be a semi-random arrangement of wood. Some plywood is notorious for having large internal gaps. I think that a layer arrangement would be better in all respects.

 

[Michael Mendelsohn]

I don't trust a worm screw in end grain or plywood. The threads in end grain tend to strip out and plywood tends to split.

I would use a forstner bit to drill a hole in the top of the bowl blank and expand my #2 jaws into the recess. I would also keep the tailstock in place while I did the initial shaping and tenon cutting.

 

[robo hippy]

I generally drill a recess in the top and expand into that (my big Vicmark with 2 5/8 inch wide jaws). However with a glue up like that, I would have second thoughts. For sure, it would drive the piece, but if you really crank down on it, you could have glue joint failure. Maybe snug it up enough to drive it, or a 6 inch face plate. You are going to core that aren't you? I also would be careful turning it, and would not be nearly as aggressive as I am when turning green wood.

robo hippy

 

[Steve Worcester]

For something this size, I would do a faceplate as large as possible, as you are going into endgrain on plywood or hardwood.

 

[John Tisdale]

Use a large faceplate

I'm not smart enough to know the failure thresholds - the species, grain orientation, weight, and anomalies (voids, cracks, and in your situation: glue voids/problems) can stack up to a worse case that can cost a few teeth.

A 6"-faceplate is a good investment. I use a Oneway: it has six-inner and twelve-outer holes for #14. I use 1.25" screws on the inner and 1" with tips ground on the outer - I want minimum penetration so I use all 18 holes. Predrill with a drill-stop on the bit.

As I go from chainsaw to lathe with logs up to 350+ lbs, I'm always between centers except when hollowing. Never had a problem.

What can you "get by with"? The probability of a chuck or worm-screw working is probably high. Is the price of a faceplate worth the added margin?

I would stay below 400-rpm, even when balanced. Also, to my thinking you're less likely to catch an edge if you use slicing cuts with really sharp gouges.

Good luck - send a pic when done.