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Mark J

A Twisted Form

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For *my eye, I think I'd want to see the far side of the arms flow more into the rim of the bowl rather than turn and meet the bowl in the almost perpendicular manner that the appear to now.  I also think I like the original where the arc of the arms appeared not to rise above the rim of the bowl.

Do these comments come across  clearly?  I'm not sure I'm saying them the best way I could.

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18 hours ago, Mark J said:

So this turns out to be an interesting problem.  And I just gotta stop and say, I hate interesting problems.  I mean if you're gonna have a problem couldn't it be just a boring I've solved this a hundred times problem?  No, it's gotta be "interesting". 

So the stack has developed a rocker bottom.  I don't know if this is because the tips of the stars have had some upward stress in the jig and this is a cumulative result, or if this might be that the glue layer is somehow thicker in the body of the star than the arms, but there is just enough curvature that I can't really get the next star to make good contact along all four arms regardless of the pins.  

Not sure how to address this issue so I'm going to let the glue up sit for a bit while I think. 

I wish I had a thickness planer (but I don't), assuming the top is flat I could just shave off a little from the bottom and return to flat.  I could probably find a club member who could help me.    I could place a thin shim under each arm, but I would probably have to abandon the alignment pins.  Any thoughts?

If its just a small curve on the bottom causing the rocker try taping some sandpaper to your tablesaw bed and rub the piece across it till you have it even and flat again. I have to do that with a bowl bottom occasionally.

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Thanks for the suggestions.  I ran this past some club members at the meeting last night and got some other valuable ideas, as well.  

The degree of curvature is more than I thought, like 1/4".

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I did try the sand paper on the cast iron top idea, but that's going to take quite a while.  By the way I suggest covering the top with craft paper otherwise the cast iron will be scratched by loose grit.  And yes, there's a reason I know.  

Another suggestion was to bring the blank back to Make It Here and use the ShopBot to flatten the bottom.  I wouldn't be able to do that before tomorrow.  

So based on yet other suggestions this is what I'm going to try.  This is just a mock up, I will use a screw chuck, but the vacuum was on the lathe.  

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Sand paper on a board with double sided tape.  The board mounts to a face plate and spindle adapter and is restrained from rotating by the ways.

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Thanks, but unfortunately this project has just gone all to "poop".    :wacko::(

I got the sanding contraption put together last night and was making progress on straightening the bottom when I noticed that the small stars on the bottom were not centered on the axis of rotation, though they seemed to be centered on the large stars above.  Then I realized that the center points of all the stars were gradually shifting toward one side of the stack.   

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In small increments the stars are moving to one side and away form the other.  

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A little bit of shift with each layer, not so noticeable at first and difficult to see when the piece was in clamps.  There is a lot of shift overall, but I could possibly work around that with the bowl itself.  Since the bowl is smaller than the bodies of the stars I do have some leeway.  But the shift in alignment of the stars also dramatically effects the angle of twist of the pillars and there's nothing I can think of in the way of redesign that would fix that -- other than to cut them off, which may happen.  

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I don't see any way to salvage the original form.  The pillars would be grossly dissimilar and I can't think of any way to change that.  I will probably cut the arms off and turn the stack as is just to see how easy or difficult it is to turn and there might be something of a bowl in there somewhere.  But I am not motivated to do that experiment  any time soon.   

All of these problems seem to have their roots in the fact that once glue was applied the wood fibers would swell and the stars no longer fit nicely between the pins.  Unfortunately, I got into a rhythm placing the north arm first then placing the south arm as well as possible so with each layer I was inducing a shift to one side.  For as much time as I spent planning this project I should have seen this coming.  I didn't, so that's on me.  I've spent a bit of time thinking about how to mitigate the wood swelling issue or other methods for for alignment, but I have spent just as much time trying to make myself promise never to do this again.  :D

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Maybe you could use an adhesive that won't swell the wood fibers, like epoxy.  Also, you could drill a hole through your bottom form at the center and insert a 1/4" steel rod, and then drill your layers and use that to align them so they don't move while clamped.  If you did this, you might be able to use contact cement and get an instant bond, allowing you to complete more layers in a day and not have to clamp the assembly for so long.

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I'm hoping you don't give up totally on this one but take the lessons learned and apply them.  I, for one, would still like to see how something like this could be done.

Perhaps you need a different bonding agent, maybe one that's not so reactive to the surface but rather works on top of it.  Maybe you need to shellac your surfaces first to prevent absorption.  Might try a different approach for creating your base as well.  Or you could try gluing up smaller sub assemblies of 5 or so stars and then gluing the sub assemblies together.

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I also hope that you don't give up. I was really excited to see how this turns out. If it goes somewhat south just drive a 16 penny nail in it and say it was influenced by Gary Knox Bennett.

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Oh dang dude! I did something similiar on some damn weird cutting board. Perhaps a zillion pieces. It still sits today in two cardboard boxes waiting for a resurrection. Hope you pull this one off! 

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I'll spin the lopsided blank I made and see what happens when I apply the tool, maybe all the glue joints will fail and this was destined to disintegrate anyway, or maybe with all the glue this will be like turning stone.  There could be some kind of bowl in there, but there doesn't have to be.  I’ll give it a whirl. 

I'm not saying no, but I'm not committing to attempting this again,either.  It weren't cheap, the veneer alone cost more than a few bucks, and the time invested just to get to this disappointment... still it would be nice to see and I don't like to accept defeat. 

But just to be academic, for any future attempt something in the process would have to be changed. 

The adhesive.  Ideally this would form a bond with the wood as strong or stronger than the wood itself, but form little or no bond with the acrylic jig (which also serves as a barrier for the plywood cauls).  The ideal glue would cause no swelling of wood fibers and have an open time of 5 to 10 minutes and set up time of 15 to 20 minutes.  And would quickly achieve a sufficient bond to be taken out of clamps promptly (30 or 40 minutes would be nice).  And it would dry clear (or a favorable color) and clean up easily.   A squeeze bottle with no mixing would be nice, too.

Epoxy gets high marks on the wood swelling factor, and some others, but sort of fails on some other key points, particularly the part about not bonding to the jig.  Contact cement is an interesting idea, but I can't recall anyone ever commenting on the bond strength.  How strong is it?  Polyurethane? – Nah.  The Quick and Thick seems like the best choice overall, but any other suggestions?

Sealing with shellac is an interesting idea, but I suspect that would affect the strength of the glue bond.  Has anyone ever tried it?  It’d be a lot of shellac, too.  98 stars, both sides. 

Modifications to the stars is something else I have pondered. 
I could cut the stars just a tad smaller to allow for the swelling.
Rotate the stars 45 degrees on the veneer sheet so that the grain runs down the north arm into the south arm rather than diagonally across the arms.  The veneer would not expand parallel to the grain and this axis could be used for the alignment.  But that would leave the grain running perpendicular to the east and west arms and these would be weak and this would require a lot more veneer.

Modify the jig.
I could do without the pins all together and align freehand.  The first dozen stars would be difficult to work with, but I think the overall alignment would be respectable. 
I could remove the left and right pin from each set of three and just use a single center pin between two tips as a guide to freehand alignment.
Use sets of three pins, but position them at 90 degrees instead of 180.  Leave the grain direction in the star alone (NE to SW).  Now use one set of pins to positon the N arms and a second set to position the W arms.  The grain runs from N to W so this dimension won’t change, but the wood can freely swell to the S and E. 
Invent and build an entirely new jig.  By the way the idea of using a ¼” centering pin to position each sheet for a bowl bland would result in a hole in entire blank and hence the bottom of the bowl.  This could be plugged with a contrasting piece of wood or even a finial, but I would like to avoid that. 

For the first two jig modifications I don’t have to make anything new, just tug out the pins.  But all roads lead to buying and cutting more veneer, so I’d have to go back to Make It Here anyway, and now I’m qualified to use the laser.

Like I said though, I’m being academic.  I have a different project to get done before July, so I wouldn’t even re-consider this one until Aug-Sept. 

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If you used a centering pin, couldn't you glue up most of it, then have the last veneers that would form the bowl bottom glued on without it? It seems like that would give you the benefit without being visible in the end product. I probably missed this somewhere, but why did you go with veneer, as opposed to something like 1/4" thick wood to reduce the layer count? I know it would be a rougher initial form, but it might minimize some of the later issues that came up.

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21 minutes ago, SawDustB said:

If you used a centering pin, couldn't you glue up most of it, then have the last veneers that would form the bowl bottom glued on without it? It seems like that would give you the benefit without being visible in the end product.

That's a thought.  And anybody who can pull that much trigonometry out of his hat should be able to count out which layers to leave whole.  I'm kinda proud of the trigonometry piece and for that matter just being able to draw the dang thing in SketchUp.

24 minutes ago, SawDustB said:

why did you go with veneer, as opposed to something like 1/4" thick wood to reduce the layer count? I know it would be a rougher initial form, but it might minimize some of the later issues that came up

The stair step sides would eventually need to be filed and sanded smooth.  I figured that this would be easier to do for 96 little steps than 24 big ones.  Also from a design point of view a 1/4" thick layer has a visible grain pattern which has to be considered in the final form where the grain pattern on a 1/16" layer is easier to ignore.  

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11 hours ago, Mark J said:

That's a thought.  And anybody who can pull that much trigonometry out of his hat should be able to count out which layers to leave whole.  I'm kinda proud of the trigonometry piece and for that matter just being able to draw the dang thing in SketchUp.

The stair step sides would eventually need to be filed and sanded smooth.  I figured that this would be easier to do for 96 little steps than 24 big ones.  Also from a design point of view a 1/4" thick layer has a visible grain pattern which has to be considered in the final form where the grain pattern on a 1/16" layer is easier to ignore.  

Fair enough. I assumed that the smoothing aspect was the reason. I hadn't really thought about trying to disguise the layers, so that makes sense too.

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