Large Platter/Wall Hanging -work in progress
A goal when I purchased my Powermatic 3520B in '07 was to turn a large platter at least once. About 4 years back I got some slabs of Ash that I stored vertical in garage with ends sealed to air dry. The largest was 3-1/2"T x 20" W x 60+" long with trimmed sides off bandsaw mill. I had some additional material about 3"T x 20" W with waney edges. I cut the thinner slab and trimmed down to 7-1/2" W. I made a sled arrangement to level both sides of the 20" W piece with router to clear up warp in drying, and then ran it through a friends wide belt sander to get real flat surface for faceplate 4 mountings and edges trued on jointer to get true square faces of now 2-7/8"T slab. The smaller slab sections (20# each) were flattened on friends 8" jointer and edges joined and run through a planer to have uniform 2-1/2" T each side to help balance.
I had taken a day workshop with East Texas Woodturners club in '07 with Frank Penta doing his 3 axis base 9" platter and made some adjustments to use Stronghold #4 jaw chuck for this 33" platter. I made 3 different test pieces out of pine on offset dimension and settled on 1". I am using a 6" Oneway faceplate with 12 - 1/4"x1" lag screws and have a Don Pencil center finder with 5/16" pin. I found the center of the 20" wide section and layed out the center and 3 offset centers. I made a guide drilling a 5/16" hole with drill press in 2"T board to establish true holes. The faceplate was positioned using center and a location screw was set to hold faceplate to mark the 12 holes for 1/4" screws. A total of 56 holes were eventually drilled. Attachment 382996
Biscuits were added in the waste area of the slabs and the section glued up with a flat top side. Hate to admit that the first glueup was hurried and bad joints. Then had to rig up to rip the slab to remove glue joint and do it again. Second time was successful. Attachment 382994
Then to bandsaw. I set up 3 way stands with roller balls to allow rotation of slab which weighed about 75 pounds going to the saw. A friend helped carry the slab and it cut easily rotating by hand. 28 pounds of slab were trimmed off at bandsaw. I wrote the thickness at center on both sides for reference and plan to be able to check wall thickness from those reference points.Attachment 382999Attachment 382998
Mounting the faceplate in the "0" center and mounting on lathe with friends help, with NO TAILSTOCK live center for security, the speed was slowly raised from 0 to 190 rpm (33 x 190=6270) with no vibration. It was a little clunky getting the back leveled off with the 1/4" difference in slab thickness, but not that bad. The back was then worked down out to edges slowly and the edge and front face trued up to get a good balance ready to go to the offset centers. The speed was increased a little up to about 250 rpm as progress was made. It was easy to bog down the motor if the cut size got to big cutting at the larger diameter for sure. The base was flattened and concentric areas for chuck and first reduced area done. I left the tenon 3/8" high to get a good grip doing the face and hollowing. I will plan to leave a tenon on inside to be able to work down the base tenon and then use the base recess to chuck and turn off the inside tenon later. (Working without a tailstock does make one think through the processes and there is no going back.)Attachment 382997
I was able to block up with wedges under the piece for support to remove from lathe by myself and piece now weighs about 45 pounds with 5# of faceplate. Then came shifting to offset centers and turning the overlapping circles at the offset centers. The 33" D piece is now spinning like a out of round 35"D piece but lathe is stable for sure at the 190 rpm. The care in drilling the face plate mounting screw holes paid off and it is easy to change centers precisely.
The base has gone through all 4 centers but needs detail work of texturing done. I am making some cardboard templates to help determine the shape of the platter face putting a bowl shape in the 20" W section and planning on something out in the glued section rim that can be dyed or otherwise help hide the glue joint and grain change.
I have mounted the piece in all 4 centers and so far no real problems encountered.Work in progress and will report more in weeks to come.
