Jig to centre rings

All my early segmented bowls have had the rings centred by eye and this has worked reasonably well. However I've not been happy with doing it this way for some time. Therefore I've now made a jig which makes the process much quicker and more to the point much more accurate. The jig consists of a base board made from melamine covered chip board. This has concentric circles marked on it and spaced  " apart. There is also a piece of perspex again marked with a similar set of concentric circles. The two were then clamped together, with the marked rings lined up, then 3 holes were drilled in the corners to take dowels. The dowels were then glued in the base board.  My jig allows for rings up to 10" diameter as this is the maximum I can turn with my lathe.

The process of using this jig is very simple. First the largest ring is fixed to the base board with double sided tape, making sure to centre it with the appropriate marked circle. Next the perspex is located on the dowels and slid down to leave enough space between it and the ring attached to the base board for gluing in the next ring. The next ring is glued and placed on the top of the ring already on the base board. The perspex is now pushed down to this ring and the circles marked on the perspex are used to centre this ring on the one below. Pressure is applied by hand for a short while and then the stack (complete with jig) is placed in a press and suitable pressure applied. With the glue I use I leave each ring about 15 to 20 minutes before repeating the gluing process with each ring until the stack is complete

Below are two pictures showing this jig in use. The one on the left shows the forth ring being added to the stack. The image to the right shows the stack, complete with jig, in the press



Depending on how strong your double sided tape is you might want to cover the base board with something transparent to prevent the tape from removing the melamine layer! In the pictures above you'll see I have a layer of celluloid covering the rings on my base board.


Making a cutting sled

Below is a brief description of how I make the cutting sleds which are vital for accurately cutting the segments which form the rings. Note I use a band saw to cut my rings although I know many other segmenters use a table saw to do this, hence if you intend using a table saw you'll need to suitably amend the woodwork so that the sled functions on your saw



When wanting to make a segmented object
one has first to work out the design. The simplest
 way is just to use squared paper, or one can use
a spreadsheet finally one can use one of the many
CAD drawing programs on the market.
Once the number of segments has been
fixed for your project you'll need a
suitable cutting sled to accurately cut the
angles. Here we see a framing square used
to obtain the correct angle. The long side
being set to 20" and the short side to N,
where N= 20 * Tan (180/n) and
n is the number of segments.
Here we transfer the angle to a
 bevel gauge.




This shows the underside of the new sled.
There is a hardwood strip, machined to fit
 the guide on my bandsaw, together with a
softwood strip which acts as an addition
guide and helps when setting the cutting
angle. Please ignore the centre grove as this
piece of ply has been recycled from
another life.
This is the top of the sled and shows a
piece of temporary scrap cut on the same
line that the band cuts. The bevel gauge
then sets the "first guess" of the cutting arm,
 which is then clamped to the sled.
Here a stop block, together with
some strips of cardboard are fixed
behind the cutting arm. At this
point the piece of temporary
scrap can be removed.



We now cut enough segments to form a quarter
circle.
Once cut they are loose fitted together and put
inside a carpenters square. Ideally we want
NO GAPS between either the segments or
the square, i.e. as shown at the top in the
next picture .
Sadly most of the time you'll get
something like the bottom two of
the  above. This is where the stop
block and the cardboard packing
 come in.


The above shows which way the cutting arm
must move depending on if you have "inner"
or "outer" gaps. So by adjusting the amount
of cardboard packing, usually replacing some
cardboard with pieces of paper, you keep
cutting segments until you get a "perfect"
 fit in the square. Once at this point you then
cut a full ring of segments and cross your
fingers that you have NO gaps. You'll  be
 very lucky to get this first time so will have to
 continue with arm adjustments until you do get
a perfect ring.
Here I show my completed sled, not I've
found it a good idea to have some sort of
clamp to hold the wood whilst cutting as
the slightest movement will affect the fit
of the segments. This one includes a crude
clamp which can be used to securely hold
the wood which is being cut.
When I first started segmented turning
I attempted to make a variable cutting
sled. But I found this didn't work very well
and hence I now have various sleds with
each one firmly fixed so that each cuts for rings
containing a given number of segments.
Making a thickness sander to fit on my lathe

As my main interest is segmented turning I really needed something to assist in flattening the rings before glueing up the stacks. What I made is loosely based on the one described here.

Shop made
                                            thickness sander with dust
                                            hood removed
View from
                                            the other end of thickness
                                            sander
Dust hood before
                                            fitting over sander drum
This shows my first sanding drum which was made from some old block board I had lying around. Although it did allow me to sand some rings I wasn't entirely happy with the results and have since have made a replacement using birch ply this appears to be giving better results. Currently I'm using 60 grit paper but will probably switch to using 120 shortly.
The sanding drum has at the chuck end a glued on face plate ring and for the tail stock there is a large washer which locates in the live centre and thus avoids wear in the drum centre each time it is used.
Most important with such an attachment is dust extraction. Here you can see the hood I've made which fits over the drum and is plumbed into my extractor. It works fairly well and most dust gets sucked away. Note it is upside down in this photo.
Shop made thickness
                                            sander with dust hood
                                            fitted.
Vew from headstock of
                                            thickness sander.

The platform which holds the rings  for sanding is made from two sheets of old melamine which I had lying around reinforced with old to stop them flexing. The two are hinged on the far side of the lathe. When in use the bottom one is securely bolted to the lathe bed. I have a sliding holder for the rings which has runners which secure it to the top melamine panel and hence stop it lifting.
I have a simple screw between the two melamine sheets at the opposite end to the hinge which allows for the space between the sliding work holder and the bottom of the sanding drum to be varied from about 3/8" to just over 1.5". I found very early on with using something like this that the rings to be sanded need to be fixed to the sliding work holder (I use double sided tape) otherwise the rings bounce about under the sanding drum and you get rings which are anything but flat!


Making a jig for sanding my cut segments on my belt sander

To try and improve the accuracy of my segmented rings I've decided to make sanding jigs, each one being appropriate to the number of segments in a complete ring,  to fit on my belt sander. Below you can see the parts of this jig and how I fit it on my sander. There are two main parts to each jig:-

  1. The base board (photo 1 below) with a fixed arm set very accurately at the appropriate angle to the belt so that each cut face of a segment can be sanded. The process of setting the angle of the fixed arm is exactly the same as that described above for my cutting sleds.
  2. The push stick (photo 2 below) with the ends sanded to the appropriate angle for its associated base board.

Here you can see the base board of my 45 jig clamped to the table of my belt sander. Also note that  the belt set is in a vertical position. The block at the outer end of the fixed arm acts a stop block when sanding each cut face of a segment.
Here you can see my 45 push stick. The end which contacts the segments is sanded to 45. Whilst at the other end I have a stop block with two fold down arms attached. This stop block is attached to the push stick via a routed slot which allows me to position the stop for segments with various lengths. The drop down arms are cut from old CDs or DVDs and allow me to sand the thicknesses of a CD from each cut face of a segment. The stop block is initially positioned so that a segment is held tightly against the stationary sanding belt and with  both arms folded down. The stop block is then locked to the push stick. Here a guide has been also clamped to the base board. It is spaced so that there is a snug fit for the push stick to slide between the fixed arm and this guide.
The sanding process involves clearly marking the cut faces of each segment with a  1 or 2 . One of the "CD" arms is then raised as shown above. Each segment is then sanded with its 1 face against the sanding belt, as one of the arms has been raised then just the tickness of a CD is sanded from the 1 face. The second CD arm is raised and each segment is sanded with its 2 face against the belt.

Once this has been done for each segment we have sanded a maximum of the one CD thickness from each cut face.

If the fixed arm has been positioned acurately then all the segments should fit together in a perfect ring with no gaps.

 
A jig to insert flower shaped pattern into a bowl base

Below are photos of the jigs I made to insert a flower shaped pattern in to the base of a flower shaped bowl I made for my clubs February open competition.





Here I show the two parts of the jig which allowed me to accurately place the Forstner bit drilled holes. The two dowels align the two parts together and also to the base below. On the left side of the jig is one mahogany plug.
Here the two parts are separated. The way I used this jig was first to centre it on my intended base and drill the two dowel holes on the pillar drill so the jigs and base were correctly aligned. I then removed the jig which had just the central hole and fixed the other part of the jig to the base with the dowels. I then used the Forstner bit to drill alternate holes. The jig was then removed whilst I glued in place the first 3 plugs. I next replaced the jig and drilled the other 3 alternate holes. Again the jig was removed whilst the next three plugs were glued in place. Lastly the other part of the jig was dowelled in place whilst the central hole was drilled. This done the jig was finally removed and the central plug glued in place and the base was ready for building into the bowel. This simple jig allows repeatable pattern in the work piece. By changing the order of hole drilling & colours of wood you can produced a variety of patterns!
This is the jig that I made to locate my router over my lathe so I could accurately make dowels which fitted in holes drilled with my  Forstner bits. First I glued together stack of wood of desired colours and mounted them between centres and then roughly turned them round with a gouge. Next I mounted the above jig on the lathe and fixed the roughly turned stack of plugs between centres inside the jig.  Here you can see my router seated on the jig, with the router guide sitting in the slot on the top. To get the plugs down to the required diameter I ran the lathe as slow speed and the router (fitted with end cutter) at high speed. The router was then moved a long the central slot. The fine adjuster on the router was used to slowly bring the cutter down until the stack of plugs was the required diameter. Once the required diameter had been obtained the stack was removed from the lathe and appropriate lengths of plug cut from the stack.