Router Plane

Monday, September 10, 2018

Large Segmented Bowl - #7 Final Turning & Finishing


After quite a bit of time spent removing very little material I got the shape to 95% done.  Most of the time went into refining the shape and making very sure all the curves were smooth as you move along the outer face with no flat or high spots.  It’s what’s called a “faired” curving surface.  Fairly easy to see or feel one that isn’t but it can be hard to cut one when turning.  To make sure I was there I took the piece off the lathe and stood it upright.  Here is what that looks like and I am happy with the result.  I can now do the final 5% of the turning then finish sand to 320 grit both inside and out.

Next is to part off or cut the bowl from the particle board mounting blank.  I start by using a parting tool that is a little over 3/16” thick, really I think it’s actually 5mm.  I go as far in as I comfortably can then quit.  Here the parting is in progress.

From there on I lock the spindle then use a hand saw to cut down toward center.  When I get close the piece wobbles a bit and at that point a little twist and it pops off.  Here it what the bottom of the bowl looks like at that point.  The piece of MDF I had put in long ago in post 3 is now visible and will be used to center the tail stock in a bit.

I could mount the bowl back in the lathe and turn the particle board remnants off but I hate to turn particle board.  It’s hard and dulls the tools.  So, I turned to a pneumatic tool, a die grinder with a carbide burr.  It spins at about 20,000 RPM’s and makes quick work of the removal.

Mounting the bowl back on the lathe is next.  No screwed-on face plate here as the top rim is finished and there is no place to screw into.  Two methods come to mind.  First, is a vacuum chuck that uses a vacuum pump and some air tight fittings to hold the piece in place.  Unfortunately, I do not have one.  What I did use is a large set of quarter circle aluminum plates that attach to my scroll chuck and have rubber knobs screwed into them.  They can hold onto a piece from the outside or the inside.  Here due to the curved outer surface I will put them inside the bowl then open the chuck expanding the plates and holding the bowl in place.  However, I do not want to put too much outward force on the bowl because I could split it apart and that would not be a good thing!  Here is the plate and the bowl mounted on it.  The tailstock has been run up and set in the little piece of MDF I talked about earlier perfectly centering the piece.

To rough out the bottom I decided to turn the bowl at the very low speed of 49 RPM’s and use the die grinder to get a flat albeit fairly rough bottom.  It’s pretty simple to do, I set the tool rest parallel to what I want my finished angle to be, clamped a guide board to its back and run the grinder back and forth.

From there I can do the final turning of including the last inch of the outside, smooth the bottom and turn the center recess smooth then do the final sanding.  Here you can see one of the glue blobs from when I glued the bottom ring together.  Because I had put a finish on the center insert before assembling the ring the glue just popped right off with no problem.

To get from the rough stair stepped blank to a finished form requires a fair amount of material removal.  When I was doing the inside, I cleaned the shop up at the end of each day.  When I did the outside, I did not.  The result is a big pile of shavings that would make some really, really good tinder for starting a fire.

With the turning completed I just had to remove the MDF center block that was held on with double face tape and do some finish sanding.  Also, as I was turning the bottom I decided to add a little rim and recess. 

Here is the bowl sanded and all ready to be finished.

As I said before I debated on the finish going back a forth between my favorite finish, matte sprayed lacquer and Danish Oil Finish.  I finally decided to use Danish Oil Finish as it will give me a nice low-luster finish bringing out the grain of the cherry and walnut.  It does take longer than lacquer where I can do two or three coats a day the Danish Oil Finish will probably take me the better part of a week to do.  That’s because I want to put at least three coats on.  I will put one on the inside plus about a third of the outside and wait overnight for it to dry then the next day do the rest of the outside and wait overnight for it to dry, then repeat.  I probably could push it a bit and put one coat on in the morning and one late in the afternoon but it’s late summer here in the desert and the afternoon’s get hot.  Besides, I am not up against a deadline so I can take my time.  The photos below show how I set the bowl for the inside (left) and outside (right) application process.

The bowl ended up being about 18 ½” in diameter and right at 12” tall.  That’s a little smaller diameter that I had initially intended but the final shape was determined by what looked right.  To give you an idea of what it looks like here is the bowl with a 2-liter bottle of soda next to it.

After a week of applying the three coats of finish and letting it set to cure for a couple of days here is what the completed bowl looks like.

I enjoyed making the piece but right now am not sure where it will end up.  It’s too big to go most anywhere so I will have to give it some thought.  I had thought I would run into more problems than I did due to the size so that was a good surprise.  The one thing that was a little surprising was when I got the top and bottom halves glued together how heavy the whole assembly was.  However, after turning it to final size and thinning the walls down it is not heavy at all.

My lathe has a second set of mounting holes on the legs that are offset from the main bed.  Doing some measuring I find that if I really wanted to I could remount one of the bed extensions to the alternate mounting holes and turn a piece almost 38” in diameter.  That would be a whopper and probably so heavy I probably would need a hoist just to move the blank.  Remember that just because you can does not mean you should.  On the other hand, it’s like a mountain that just has to be climbed.


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