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PostPosted: 17 Oct 2013, 08:08 
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Prompted by a Thread question by woodfarmer regarding cutting segments for bowls I jumped in with some images.

I've taken the liberty of cribbing some of the material from that thread to start this W.I.P. off.

Now like all workshop projects there are no hard and fast rules of "how to do" and the following is just a rough run through of how I set about my simple segmented boxes and bowls, others will use different cutting and turning methods, indeed far more accurate and intricate segment preparation and turning skills than I will ever attempt or have the patience to master.

Hopefully the following will prompt someone new to turning to have a go, if nothing else it saves a great deal of expense on wood stock and reduces the waste wood creation considerably.

For my stuff I use a basic Chop Saw, just need to make sure everything is set up square in the vertical plane and that angles are set accurately in the horizontal.

The most important of needs is to prepare your stock for even thickness & square so that it can be cut accurately by just flipping 180deg.

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PostPosted: 17 Oct 2013, 12:13 
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I personally do not use abrasives when producing segments and rely totally on accuracy of cutting, I found that trying to abrade a segment is fraught with multiple chances of creating inaccuracies and a fine abraded finish is not conducive to best mechanical key for adhesive.

The Chop saw is a basic Rexon CMS.
Attachment:
DSCN4152 (Large).JPG
DSCN4152 (Large).JPG [ 68.15 KiB | Viewed 2434 times ]

Simple and robust is often best, only want would be similar with regenerative braking to speed things up.

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PostPosted: 17 Oct 2013, 16:57 
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There is an old run-through of a lidded segmented box on my web site.
Not the way I assemble them now but it's how I started.

Decide what nominal size you want to end up with, if you construct the way I do using up scrap wood then the available diameter of the material for the base and top rim are relevant.

I use my Calculator for anything new & I have printouts for most often used, saw stops etc. are marked up with regular options.
Image <<<< Link
Tip:-- Don't be too critical on stock width, if you have spare then allow extra thickness in your early attempts to give yourself some error padding.

Sort out some scrap:-
Attachment:
DSCN4153 (Large).JPG
DSCN4153 (Large).JPG [ 117.33 KiB | Viewed 2388 times ]

Run it through the saw:-
Attachment:
DSCN4156 (Large).JPG
DSCN4156 (Large).JPG [ 104.49 KiB | Viewed 2388 times ]

Put it through the thicknesser to get it reasonable square and constant thickness:-
Attachment:
DSCN4157 (Large).JPG
DSCN4157 (Large).JPG [ 75.69 KiB | Viewed 2388 times ]

Decide if you want contrast bands and do likewise and chop them off at the thickness you want:-
Attachment:
DSCN4158 (Large).JPG
DSCN4158 (Large).JPG [ 97.03 KiB | Viewed 2388 times ]

Note: The use of a support media for stock that reaches over the cut path, saw plastic inserts are rarely level or rigid enough for small segment support.
Attachment:
DSCN4159 (Large).JPG
DSCN4159 (Large).JPG [ 94.55 KiB | Viewed 2388 times ]

Adjust Chop Saw stop to segment length (allow for contrast width if used):-
Suggest you run a scrap length through to check your sizes.
Then just keep chopping away by turning the wood stock through 180 deg. until you have enough segments and a couple of spares if you have enough wood length:-
Attachment:
DSCN4160 (Large).JPG
DSCN4160 (Large).JPG [ 98.58 KiB | Viewed 2388 times ]

The above sequence took 13 mins total according to the image EXIF files.

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PostPosted: 17 Oct 2013, 17:28 
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Note:-- If you want repeatability and minimum amount of aggravation and disappointments then it is essential to set up the saw correctly.
DO NOT rely on any existing graduations or stops without checking.
I use an Engineers Set Square off a dummy piece of flat stock laid across the base to set the blade vertical and check that the vertical traverses is spot on.
For the Horizontal angles I cut stock and check it against a digital angle finder on a reference surface, you can get away with a few tenths of degree in cutting errors but you need to start as true as possible.
If you look carefully at the front right hand side of my saw (in previous image) you will see a knurled knob, this is in fact a location dowel inserted in a hole I drilled through the frame and rotating table when I had the table clamped correctly so that I can come back to the setting. (The table clamp and associated notches do not return close enough for segment work without trial and error checking)

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PostPosted: 18 Oct 2013, 17:05 
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Having collected your batch of segments and associated contrast fillets, if using them, it is wise to do a test clamp just to prove that nothing has gone astray, saves a lot of frustration and wasted glue just for the sake of a few extra minutes.
Attachment:
DSCN4161L.JPG
DSCN4161L.JPG [ 119.68 KiB | Viewed 2293 times ]


Note my assembly aids:-
I use a hand drill set to screw driver mode fitted with a nut driver and use the ratchet torque limiter as a vibration aid to help agitate and seat the glued segments.
A small persuader also helps ensure any segments that slip out of line or ride up off the base plain are returned to position.

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PostPosted: 18 Oct 2013, 17:19 
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Glue up the segments, rubbing the individual joints as you go to ensure even and good spread of adhesive.
Attachment:
DSCN4163L.JPG
DSCN4163L.JPG [ 122.82 KiB | Viewed 2293 times ]

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PostPosted: 18 Oct 2013, 17:21 
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First one glued and clamped:-
Attachment:
DSCN4164L.JPG
DSCN4164L.JPG [ 124.22 KiB | Viewed 2274 times ]


And the second one assembled and both ready to be put on one side for glue to cure.
Attachment:
DSCN4165L.JPG
DSCN4165L.JPG [ 129.74 KiB | Viewed 2274 times ]


I use Cascamite adhesive, mainly because it does not have joint creep as PVA can with wood/humidity movements.

As a time indicator:-- from the shot of the test clamping to complete glue-up including adhesive measuring/mixing was according to the EXIF data 27min.

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PostPosted: 18 Oct 2013, 19:09 
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Great post, Many Thanks.

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PostPosted: 18 Oct 2013, 22:14 
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Thanks, this has been really useful. I have turned segmented bowls before, a long time ago, but the blanks were pre-made. I hope to get most of the timber for the segments from short (2-3 feet long logs) mostly oak, some ash, acacia and the odd fruit wood. All will be rescued from my firewood pile :)

I notice that your original diagram showed 8 segments but the workpiece shows 12. I am assuming that it is easier to make bigger bowls by using the greater number of segments. I appreciate that length of segments and any contrasting (or not) straight pieces also affects the size.

Is there any general rule relating size to number of segments?

regards

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PostPosted: 18 Oct 2013, 22:44 
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woodfarmer wrote:
....I notice that your original diagram showed 8 segments but the workpiece shows 12. I am assuming that it is easier to make bigger bowls by using the greater number of segments. ...
Is there any general rule relating size to number of segments?


Obviously the smaller the number of segments the thicker the stock needs to be and more wood will have to be turned off.

It's a matter of personal preference, I just find that 12 looks better proportioned to me for my small boxes.
I used 24 segments for this bigger Bowl:-
Image

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PostPosted: 19 Oct 2013, 12:32 
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Next comes the preparation of the glued segments and the top and bottom pieces for final glue up.

The first image is a bit gratuitous to this process but it shows how I consolidate time use when machines are in use and prepare stock volume when time permits.
Attachment:
DSCN4166L.JPG
DSCN4166L.JPG [ 132.19 KiB | Viewed 2162 times ]


The glued segment sections and rough blanks selected for tops and bottoms.
Attachment:
DSCN4167L.JPG
DSCN4167L.JPG [ 103.24 KiB | Viewed 2162 times ]

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PostPosted: 19 Oct 2013, 12:56 
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First task in preparation for final glue-up.

Mount segment ring for clean -up.
Attachment:
DSCN4168L.JPG
DSCN4168L.JPG [ 125.56 KiB | Viewed 2157 times ]


Warning:- Always clamp in compression, finding out that a glue joint is not sound or wood structure weak whilst cutting when mounted in expansion is not a procedure to be encouraged.

Note:- Cascamite recommends caution when components are to be machined and allow 48 hrs or so before subjecting to heavy cutting loads, I have never had a joint fail with items cured overnight at domestic room temperature but like many of my other tasks I tend to do glue ups in batches and rough assemblies are more often than not lying around for days,weeks, or months even. So if you are gluing up in an unheated shed be cautious.

I do a lot of my roughing out turning by using tools in a boring mode, much the same as if using a pattern makers or metal lathe.
Attachment:
DSCN4169L.JPG
DSCN4169L.JPG [ 125.31 KiB | Viewed 2157 times ]
Attachment:
DSCN4170L.JPG
DSCN4170L.JPG [ 86.39 KiB | Viewed 2157 times ]


If you don't have a carbide tipped tool then a stiff sharp 1/2" scraper can be used in the same mode.

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PostPosted: 19 Oct 2013, 13:10 
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With a sharp flat scraper finish off the mating surface:-
Attachment:
DSCN4171L.JPG
DSCN4171L.JPG [ 118.48 KiB | Viewed 2155 times ]


Check for flatness across the diameter with a steel rule, if you have it near you will get a squeak if the rule is presented as the lathe slows down, you'll know when you get a perfect one the squeak is unmistakable.
Attachment:
DSCN4172L.JPG
DSCN4172L.JPG [ 121.98 KiB | Viewed 2155 times ]


Turn the piece around and complete the other side:-
Attachment:
DSCN4173L.JPG
DSCN4173L.JPG [ 114.45 KiB | Viewed 2155 times ]
Attachment:
DSCN4174L.JPG
DSCN4174L.JPG [ 110.19 KiB | Viewed 2155 times ]


Do likewise for any other segments whilst you have the chuck mounted:-
Attachment:
DSCN4175L.JPG
DSCN4175L.JPG [ 114.56 KiB | Viewed 2155 times ]

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PostPosted: 19 Oct 2013, 13:23 
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Now to sort the tops and bottoms out whilst we still have these jaws/chuck mounted.

Take a base piece and mount:-
Attachment:
DSCN4176L.JPG
DSCN4176L.JPG [ 103.23 KiB | Viewed 2152 times ]

Roughly true up the face and edge as far as possible.
Mark out for and cut a recess mounting socket to suit your jaws. (I always use my simple gauges)
Attachment:
DSCN4177L.JPG
DSCN4177L.JPG [ 100.39 KiB | Viewed 2152 times ]

Attachment:
DSCN4178L.JPG
DSCN4178L.JPG [ 97.65 KiB | Viewed 2152 times ]

And do the same for any other bases you have ready.
Attachment:
DSCN4179L.JPG
DSCN4179L.JPG [ 112.42 KiB | Viewed 2152 times ]

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PostPosted: 19 Oct 2013, 13:34 
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Mount the top piece and rough true, mark the basic joint dimensions from the segment ring:-
Attachment:
DSCN4180L.JPG
DSCN4180L.JPG [ 107.63 KiB | Viewed 2150 times ]


True up the mating surface much the same as you do the segments, note the undercut central area, more on that later:-
Attachment:
DSCN4181L.JPG
DSCN4181L.JPG [ 107.13 KiB | Viewed 2150 times ]

And repeat for any other tops:-
Attachment:
DSCN4182L.JPG
DSCN4182L.JPG [ 114.43 KiB | Viewed 2150 times ]

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