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.

Large Segmented Bowl - #6 Gluing the Halves Together & Turning the Outside

Gluing the two halves together follows the same process as adding layers.  I need to align the offset between the mating rings then clamp it all together.  The one difference is the centering alignment is more critical here as I want that interior joint to align as close to perfectly as I can get it.

Once the glue cured I removed the clamps and the small face place from the top stack.  Then it is time to mount the whole stack on the lathe.  That’s easier said than done as the blank is fairly heavy and pretty awkward.  Once mounted I put a live center with a flat plate end in the tailstock and ran it up against the MDF disk.  The live center applying pressure against the MDF disk will help kill the vibration while I am doing the turning.  The flat plate is because as much as I tried the top stack was not exactly aligned with the bottom stack.  It was probably less than 1/32” off but the existing center point of the MDF disk did not exactly line up with a pointed live center.  Here is a photo of what the tailstock looks like. 

To get a feel for how the full blank turns I started out at a slow speed, like 50 RPM’s and gradually increased the speed up to about 350 RPM’s.  That may not sound like a lot but remember the blank is about 19” in diameter so that outer edge is whizzing by at over 1,700 feet per minute.  Surprisingly the blank ran very smooth and I had no problem in truing the outside of the upper stack to match the bottom stack.

With that initial work done I started bringing the rim and the top 3 layers into shape.  After a little turning I took the MDF disk off and did a check with a pair of calipers to see how the wall thickness was progressing.  Having just started the outside shaping I had plenty of room and so far, no surprises.  Here the left photo shows the whole bowl and the right one is a closer look at the initial shaping.  Note the sacrificial ring is still attached although there is only about ¼” material left holding it to the top ring of the bowl.

As I turn the bowl to its final shape the process is to cut away some material, take off the MDF disk, measure the wall thickness, mark the outside with reference marks showing areas still too thick, put the MDF disk back on, run the tailstock up against the MDF disk then turn away more of the wood and repeat.  Not really hard but just a little tedious and time-consuming.  Below is where I am not quite half way done working on the outside. 

There are two things to keep in mind while doing the final turning.  One is keeping an eye on maintaining an even wall thickness which I do with calipers.  The other is making sure the outer surface is not only smooth but that the curved surface is just that a continuous curve with no flat spots, hills or valleys.  That is a lot harder than it sounds as there are no templates, no jigs to hold the cutting tools and no line to cut to.  It is all done freehand by eye.  That said I do use a couple of aids – one is my fingertips.  Lightly running your fingers from top to bottom will let you know a lot about surface irregularities even when you can’t see them.  Another method is to take something like a credit card or some sort of straight edge and hold it along the top to bottom axis then rock it back and forth, it should rock smoothly.  If there is an inconsistency in the curve the rocking motion will not be smooth.  Here I am using a card scraper to check. 

When I find a spot that is just a hair off and needs help I turn the lathe to its lowest speed, in my case 49 RPM’s and shave the high spot off or if it is a low spot work both sides until I get a smooth transition.  I use the card scraper because it is flexible and I can put a little curve in it which helps even things out.

With the outside of the top half of the bowl finish turned I am now close enough to the bottom of the bowl I do not need to keep the MDF disk attached to the top to kill the vibration while I am turning.  As such I can part off the sacrificial top ring.  Here in the left photo you can see where I have very carefully started the cut.  I continued cutting until I could start to see some gaps then quit and just pulled the ring off.  The right photo shows the thin sliver, barely 1/32” thick, that was all that was left holding the ring on. 

Getting ready to turn the leftover ridge off and down flush with the bowl surface it occurred to me that a little raised lip at the edge might help define the rim.  A little delicate work and I had the transition both inside and outside nearly done.  Here is a closeup of the lip and the entire rim.  I think I will keep it. 

Once I had the top done I went back and started working my way down the last half or so of the bowl.  It’s the same process as the top half except I don’t have to mess with taking the MDF disk on and off so it goes faster.  Here I have the shape roughed out but the walls are still about an eighth of an inch or so too thick.  From here I keep turning and measuring to get the wall thickness and the shape right until I get to about the last three bottom layers. 

Next up – Final Turning & Finishing

Large Segmented Bowl - #5 Adding Rings & Fitting the Halves

To start working down from the top I need to build a base similar to what had been done for the bottom layers.  I keep a lot of odds and ends from various projects hoping to be able to use them elsewhere and this just happened to be an occasion where I could.  When I made the Snare Drum I built a multilayer base and could now re-purpose two of those layers to act as my base. 

Since the large face plate is in use and I am not going to take it off until the turning is done I used my smaller faceplate.  In the photo below starting at the top of the clamped stack you can see the smaller black 3” diameter black face plate just peeking out behind one of the clamps.  It has been screwed to an MDF layer which in turn is screwed but not glued to a segmented pine ring.  The MDF and Pine ring are not glued together so I can take the MDF piece off and check the joint between the top and bottom sections.  I will take a photo when I get there so if it does not make sense now it should then.  The top ring of the bowl (on the bottom of the stack) is centered on the Pine ring then glued in place which is what is going on in this photo.  Note the top ring like the bottom ring is made up of only cherry segments.  That’s a design choice to act as a visual cap on the bowl, or at least that is what it is supposed to do.

 

The photos below show, just like before the rings being added and the interior face being worked into final shape is stages.

After adding one more ring, the fourth and last one I spent quite a bit of time going back and forth between the two halves measuring and refining the joint where the top and bottom will be mated.  Not only do I need to match the inside diameter I need to make sure the curve flows across the joint.  That curve whose radius changes as is goes across the two rings to be mated has to look and feel continuous.  When I got to a point where things looked like they might match up I took the stack off the lathe, unscrewed the MDF disk from the Pine ring and set it next to the bottom half.  This photo shows how removing the MDF disk allows access to the inside which will enable me to check how well the two halves come together.

Setting the top section on the bottom and aligning them gives a rough idea of the bowl profile.

With the top in place I could see how close I got to matching the two halves.  It was really pretty close, better than I had hoped for a first attempt. 

Once I had checked out the joint and made some marks to indicate what additional shaping needed to be done I pulled the top off and screwed the MDF disk back on.  Below is just before aligning the top and screwing it back in place.  The green mark on the Pine ring and the MDF is my reference mark so things go back together the way them came apart.  There is also a blue one on the opposite side. 

You would think that using the reference marks then screwing the MDF disk back in the exact location where it came off would automatically center everything allowing me to go right back to turning.  That’s what I thought too, but was wrong.  There is just a little bit of wiggle room even using eight screws and putting the disk back in the same place.  To correct I just snugged two screws down then mounted the stack back on the lathe.  With that done the tool rest is set so it just touched the edge of the 4th ring.  Then as I spun the stack I could see what adjustments needed to be made to center the stack.  It took a little time but ended up just fine. 

I worked to match the exterior diameter of the bottom ring of the top stack to the top ring of the bottom stack which is pretty easy.  It just requires a light touch with the tools and frequent stops to measure so as not overshoot.  The inside diameter also needs to match up and the aforementioned curve has to flow across the joint.  It is sort of like a real marriage.  When it’s good it’s very good and when it’s bad it’s a disaster. 

A couple of fittings which required going through the steps of taking the MDF disk on and off got me very, very close.  The inside of top stack has just a tiny lip overhanging the bottom.  I think I will leave it that way and do the final work after the two stacks are glued together.  Below is a photo that shows how the two stacks match up with the red arrow pointing at the joint.  This is the photo I was referring to when I was talking about gluing the 1st ring on in the second paragraph.

At this point I am almost ready to glue the two halves together.  To help minimize any problems with glue removal I am going to put two coats of finish on the inside before gluing the two halves together.  With the finish on it will be much easier to do any cleanup afterwards.   However, this means that I have to have the inside completely done and sanded.  I start with 120 grit sand paper and work my way up through 320 grit.  Here is what the halves look like ready to finish.

I debated on the finish for a while but finally decided to use Danish Oil Finish.  It should give me a nice low-luster finish bringing out the grain of the cherry and walnut.  Below is the top stack showing the first wet coat of the oil on half of the piece.  I will put two coats on then glue the halves together.

Next up – Gluing the Halves Together & Turning the Outside

Large Segmented Bowl - #4 Rings & More Rings

With the second layer glued in place and the clamps removed it’s back to the lath to turn the corners off and make the layer round.  The left photo below is before I started turning and the one on the right is after I have turned the blank round.

I centered the 2-ring bowl blank on the next layer, marked the centering circle and the orientation lines as before.  Here if you look close in the center you can see one of the orientation lines marked with an “A”.  With the blank still in place I clamped the alignment blocks where they go. 

Below is after the bowl blank was removed.  This makes it a little easier to see the centering circle, where blocks are and how the bowl blank will drop in place.  Next is to add glue, drop the bowl blank in place, rotate it back and forth to spread the glue then make sure the orientation lines are in alignment, put the clamps on and finally check to make sure the layers are still in proper alignment.

The photo below shows how I have several rings in various stages of completion.  In the back is the rough-cut walnut and cherry strips for ring #7 setting to see if they are stable.  In the front left is a row of cherry and a row of walnut segments for ring #6 ready to glue together tomorrow.  At the left setting on the yellow pyramids with the metal clamp is the ring #5 that I glued together today.  To its right is ring #4 that I flattened today and will glue on tomorrow and finally at the right is the bowl blank with ring #3 that I just got done gluing on.

The next day after taking the clamps off I mounted the bowl blank on the lathe and turned the ring round.  The left photo shows that done.  Now with three rings glued on I can start to do some turning on the bowl’s inside.  On the right the bottom of the bowl is pretty well done and the second ring is roughed out.  There is a lot of refinement yet to be done especially at the transition between the bottom and the 2nd ring.  The top ring just has the inner face rounded and a small radius cut on the inner edge.  Lots left to do here but that will wait until I get more rings on.

I am not going to go through all the steps in making the rings and gluing them on since that has already been covered.  If anything that I have not covered comes up I will go over it but, in the meantime, here is where I added the 4th and 5th rings.

Making progress albeit slowly.  Here on the left is the 6th ring added and set up ready to round the outside edges.  The right image shows the 7th ring in place and the inside shaping in-progress.  The bottom layers are pretty much done while the outer three or four rings are still a work in progress.  The closer I get to the last ring added the less finished the piece is.

This is the 8th ring glued and clamped in place.  It marks the half-way point only 8 more rings to go.  If you look close at the bottom ring you can see the step between it and the layer above is getting smaller.  That is starting to cause me some problems in that I don’t have very much room to clamp the centering alignment blocks on.  It’s only going to get worse as the step continues to get smaller.

The left image has the 8th ring on with the outside rim rounded while the right image shows the 9th ring after rounding the outside rim and doing some interior tuning.  The pile of shavings is the result of interior turning and just sits there sliding along the bowl surface as I turn.

As I talked about when gluing the 8th ring on I was running out of room to clamp the centering alignment blocks on.  Well the left image is the 9th ring with blocks barely attached and the right is the 10th ring.  As you can see there is no way I can clamp the blocks on this ring.  That means that I will use a rub joint to help get an initial “tack” to reduce the piece slipping around as I clamp them up.  A rub joint is where you slide or rub the two surfaces back and forth until the glue becomes tacky and grabs.  It makes it easier to keep things aligned as the piece is clamped.  

Here is the 11th ring.  This ring represents the largest diameter of the bowl.  From here on in the rings will get smaller. 

The left photo is with the 12th ring in place.  It is just a bit smaller than the previous ring and that’s because I am working my way down toward the opening at the top.  Because the interior surface of the bowl is curving back I am having to get into some contortions to do the turning.  All along I have been finishing turning on the inside.  Now the interior surface is about 95% done up through the 8th ring and 90% done through the 11th ring while the 12th ring is about half done.  The right photo shows just how tall the stack has become.  There is right at 12” between the faceplate and the outer face of the 12th ring.  Unfortunately, as I was working on this ring I started getting some vibration and minor chattering while turning.  Changing the RPM’s, using a light touch and sharpening the tools helped but this means that I have gone as far as I want adding rings using this setup.  There are a couple of techniques that I could use to steady the bowl and dampen the vibration but I would still have the awkward turning position.   Then there is the problem of weight, as it sets including the cast iron face plate the blank is pushing 50 pounds.  Holding it up at the lathe in proper alignment with one hand while using the other to start the spindle threading into the face plate is getting pretty close to making my eyes bug out.  To resolve all these problems, I will turn the remaining four layers separately then marry the two halves together.  In retrospect I probably should have made the split between the 11th and 12th rings right at the widest point.

Next up – Adding Rings & Fitting the Halves

Large Segmented Bowl - #3 Face Plate Sandwich, Making/Attaching Layers & Turning

Setting the base ring aside I stated working on the sacrificial sandwich that acts as the transition from the cast iron face plate to the actual bowl.  It is made from two layers, a piece of 5/8” plywood glued to a ¾” piece of particle board.  The plywood layer is screwed to the cast iron face plate which is why I used plywood as it holds screws better than particle board.  One thing I do not want to happen is for the screws to work lose and potentially let go allowing the in-progress bowl to launch itself at me.  I had a bowl break free once and that made for a very bad day.  Here the photo shows the two layers glued and screwed together.  The screws will be removed once the glue sets overnight. 

Once the glue cures the sandwich is run through the thickness sander to make sure the faces are parallel.  The bottom ring of the bowl will get glued to the particle board layer.  When it comes time to separate or part off the bowl I will be turning through it.  Since the screws only go into the plywood it will be easy for me to not hit one accidently.  Hitting a hardened steel screw with a lathe tool is not a good idea.  Next the sandwich is centered and securely screwed to the face plate with a whole bunch of screws, 15 to be exact.  

This assembly is then mounted on the lathe and each layer is turned to a true circle.  Next an MDF reference block in the center of the bottom ring is attached using double face tape.  I used the ring joints to mark it to give me my center then measured the particle board diameter and drew a couple of concentric circles on the ring face.  One the diameter of the particle board and a second just a sixteenth or so larger.  These will allow me to center the bottom ring on the particle board when gluing the two together.  

A layer of glue is spread on the base layer then the face plate assembly is carefully centered on the pencil rings.  Eight clamps hold things in place, but I have to be careful when tightening them as the glue acts as a lubricant which allows the pieces to slip around and out of alignment.  It just takes some time keeping an eye on things and making small adjustments as the clamps are tightened. 

Once the glue had cured I mounted the assembly on the lathe and was ready to go.  The photo on the left is taken from the lathe headstock side while the right one is from the face where rings will be added and the turning will take place.

Below the left photo is a little closer look before I started turning and the right one is after I have knocked off all the corners and trued up the ring. 

Next up is the second ring.  I am fortunate to have a pretty good stack of thoroughly dried lumber.  Some is rough sawn, some is surfaced on the two wide sides and some also has one edge ripped straight.  Well, sometimes it is straight.  Unfortunately, a fair amount of the lumber I will be using for this project does not have a straight edge to reference off of.  This piece of walnut is a case in point as while it was flat and not warped both long edges were nowhere near straight.  They were way too far out to even think about using the hand plane to clean up.  The solution is to take an 8’ level and use the straight edge to mark a reference line.  I then carefully cut along the line using the band saw getting close to straight and then clean up with my long hand plane.  Last, as shown below is to clamp the level to the rip fence on the saw to give me a long surface for the walnut piece to register against.  Flipping the board over after each pass ended up giving me straight parallel edges to work from. 

To make the second ring and all the subsequent rings except for last one I need 12 cherry pieces and 6 walnut ones all the same size.  The process is the same as what I went through to make the bottom layer with one important difference.  I do not have a cut slot on one edge.  Not having that slot allows me to make more efficient use of my wood as there is not a specific Inner or Outer Face.  In the images below, you can see what I mean.  The top photo shows the cuts required for the bottom layer where each segment has to begin with a new edge so the slot is always on the inside.  The bottom photo is for the second layer whose segments can be cut in a continuous string with no waste.

Once I get the 12 cherry and 6 walnut pieces cut I can clamp them together to do a test fit to check for gaps or any other problems.  In this case everything looks good.  Last is to chalk the sides that face up so I make sure none of them get reversed in the controlled chaos of gluing the ring together 

After letting the glue cure overnight as before I ran the ring through the thickness sander to flatten.  Next is to center the ring on the stack.  That’s done by aligning the joints with the previous layer and very carefully measuring the distance between the edge of the to-be glued layer and the turned edge of the previous layer.  If nothing is in error when that distance is the same all around all the joints should align.  If they don’t then there is a problem somewhere.  Here you can see everything is good.  Last is to draw a pencil line around the first layer on the new layer. 

The glued-up bowl stack is removed and alignment marks are drawn on the new layer.  The marks cross the just made pencil line and are centered on the segments.  I make two arcs using a compass working from each joint.  Any error will show up as a gap between or overlapped lines. 

Glue-up is next.  Note that there are alignment blocks held on by orange bodied F clamps.  They are set on the centering circle and keep the two pieces in place while torqueing the grey BESSY clamps down.  Because the glue acts like a lubricant between the gluing pieces without the blocks they will slide around as the clamps are tightened.  Without them it’s a real pain to try and keep both parts aligned.  Once the glue has taken an initial tack the blocks can be removed and the glue allowed to cure.  Looking close you can see how the joints between layers are offset by half. 

Next up – Rings & More Rings