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Segment accuracy

How to achieve it

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Ray H31/12/2009 20:34:09
33 forum posts
I have from time to time produced wooden porthole liners varying in diameter from 12" to 16" (inside). The first, made from single blocks of sapelle, was glued end to end and turned carefully. The rest have been made from layers of segments (once I realised my initial mistake!).
The ends of the segments of each layer are glued and then clamped using a band clamp. Once dry each layer is clamped to the previous layer(s) as an entity.
No matter what saw I use - mitre, table or hand -  I cannot seem to get the segments to join without gaps which, luckily, tend to largely get hidden when the item is turned and the waste cut off. I make a trial set and test them for fit and then adjust the angle of cut (slightly) to correct the error. Sometimes this has no effect and sometimes it has the complete oppoisite effect, moving the gap from the inner to the outer edge.
I'm about to embark on a number of 15" diameter porthole liners for a friend which I currently estimate will require a total of 360 segments - twelve segments per layer, three layers per liner, ten liners. And this will be followed by a further series of a similar number of, but significantly smaller liners.
What is the trick to getting the angles cut precisely so that the butt joints are exactly that and don't have great big gaps either at the outer or inner corner? Is my error in holding the wood to be cut against the fence/mitre block rather than clamping the wood to the fence/mitre block?
What little hair I have left is rapidly dwindling further.
Happy New Year to you all.
Sparky31/12/2009 21:15:40
7631 forum posts
22 photos
Hi Ray
We must be twins as I have the same problems when I tried.....and like you, managed to get around the gaps during the turning.

You'll need to speak to our Dennis Wake (segmented album) , he has made some beautiful fragmented work and has it off to a tee.
Rest assured, when he sees this he will give his help as he has done with others
Mike Jordan01/01/2010 09:36:31
166 forum posts
17 photos
Hi Ray
Ive made a huge number of porthole liners and, like you , I kept altering the method to make life easier and get a good fit between segments. My liners had only six segments in each circle or layer, the more you have the better the chances of turning it up without tearout at the joints. Most methods of cutting the butt joints seem to have a margin of error. I found it better to use an angled shooting board to trim all ends before gluing up.
I then glued up two half circles and allowed the glue to cure before "fitting" the last two joints in the circle. his also allowed the inside curve to be cut on the band saw before gluing up the two halves. you can then laminate as many layers as you need.
You can also save time by making thicker layers and gluing them together to make a double thickness liner and cutting it in two or more after the glue has set. Only feasible if you have a safe method of cutting through a thing that size.  As you must already have discovered these are a time consuming job that involves a suprising amount of materials and lots of repetative work. To hang on to whats left of my sanity, I now point customers to a nice chap with a 30,000 pound CNC machine that makes them in minutes.
If you get a reputation for making a good job of them. you will have boating customers all over the country!

Edited By Mike Jordan on 01/01/2010 09:37:53

Ray H01/01/2010 10:11:18
33 forum posts
Many thanks for the responses so far.
Previous attempts have used less segments. I opted for layers of twelve segments in an attempt to save material. The boat is being fitted out and there should be a large number of offcuts that can be used.
I like the idea of glueing up half layers and cutting them on the bandsaw as that would enable me to be even more economical on timber and have a lot less waste to clear away.
I made a couple of 12" ones for my own boat out of solid pieces of Ash. They do look better than segmented ones but have moved quite a bit, something the segmented ones don't seem to suffer from.
Delete01/01/2010 13:57:50
575 forum posts
The only time I have made a Port Liner I also found it a bit of a problem . The Ports were not round but had rounded corners  and straight sides Top and bottom were Parallel one side was vertical with the remaining side at an angle.  I ended up making a jig and then laminated the corners using Veneer offcuts. The corners then had to be finished with a rebate and one edge rounded over.  Needless to say it took one hell of a time. I vowed I would never "do that again".
I think the idea of two halves is good. I assume that any small discrepancy is lost when the four final surfaces are trued up. I like it  I am now realy cheesed off because I didnt think of it.
But lets face it thats what this Forum is all about. Not getting cheesed off but helping one another with good ideas. Pit some of my ideas are not so good.
dennis wake02/01/2010 00:53:57
2044 forum posts
1451 photos
1 articles
hi Ray
    i have just seen this and as Marc sayes i have don lots of segmented work bur this is only open segmented work .i have a remedy for you thow if you are making them in segments as you say then produse half rings with 6 of your segments. make your self a cuting sled for your table saw so that you can secure the half rings on to it as that the ring is just over hanging the edje and true the half ring up with the saw.if you are not grasping exactly what i am on about go to this link>>here< then go to his my projects then segmenting then scrole down to the bottom of the pag and you will see exactly what i mean.i hope this is of help to you .

Edited By dennis wake on 02/01/2010 00:56:06

Edited By dennis wake on 02/01/2010 01:00:55

Ray H02/01/2010 08:58:52
33 forum posts
Many thanks for that. Looks like I need to do some experimenting.
However, being of a reasonably logical mind, I still can't grasp why it isn't possible to get cuts that will make a complete ring without gaps and overlaps.
I've toyed with the idea of making a sled for the router, rough cutting the segments on the table saw and then trueing up the ends on the router table sled as I suspect there is a little movement in the wood when it initially makes contact with the saw blade and this is what is throwing things out.
Mike Jordan02/01/2010 10:08:21
166 forum posts
17 photos
Hi Ray
I think that you are right about the blade movement while cutting.Also the length of each segment  needs to be spot on, just half a mm can throw the circle out.
When it comes to accurate preparation the old fashioned shooting board has a lot going for it. You can adjust the angle by a fraction of a degree by taking a shaving off the edge that guides the plane. The pic shows my double sided board - 45 & 30 degrees.

Best of luck with the project, if the hair loss becomes too much to bear, I still have the phone number and web address for the nice man with the machine! 
Ray H15/01/2010 10:59:49
33 forum posts
I actually managed to cut the latest layer of segments on the table saw with almost perfect joins between each segment.
I'd previously tried Mike's shooting board idea but had a problem when the plane sides weren't at right angles to the plane's sole!
Things also improved when I adjusted the saw blade having found that it wasn't dead on ninety degrees
I do have one further question.
I've cut the segments on a Kity 619 using the sliding extension bar set to the appropriate angle to the blade, clamping the wood to the bar to stop the wood moving as it passes over the blade. Do others do this when cutting segments or do they effectively leave their mitre gauge set at right angle to the blade and angle the blade?
Sparky15/01/2010 17:31:34
7631 forum posts
22 photos
Hi Ray
I'm sorry I cant help you with that question.
I cut all my segments with a hand mitre saw........with a new 'sharp' blade!

Slow but useful
Ray H15/01/2010 17:37:27
33 forum posts
Thanks for the suggestion Marc.
My problem is that I have around 500 (oak) segments to cut and that's a lot of new blades even at 10-20 per cut!
Sparky15/01/2010 17:52:18
7631 forum posts
22 photos
That would do all those cuts mate.
I had to cut over 900 parts of Oak, still good for another 900
The only reason I had to get a new blade was because it was 5 years old and rusty!
Good luck and cant wait to see the project.
Ray H17/01/2010 13:08:08
33 forum posts
Apologies  for any confusion. I'm aware that some hardwoods aren't kind to tools and had incorrectly assumed that your reference to a new blade meant that I'd need to change the blade quite often. Hence my remark.
Subsequent to my original post I bought a True Angle Adjustable Protractor from Axminster and that helped improve the fit of the mitres although they still weren't as tight as they should be.
Yesterday I went to Axminster and bought a Veritas Metric Bevel Setter. That revealed that the True Angle Adjustable Protractor wasn't as true as it should have been because I compared the two and they were different. Having set the mitre guide to the Veritas setter the mitres are almost perfect. Any deficiencies are probably down to the small size of the segments that I'm trying to cut and minute differences in lengths of the segments.
Sparky17/01/2010 20:00:21
7631 forum posts
22 photos
Hi Ray
No problems mate.
With your new tools there should be no excuses getting everything spot on now
Look forward to seeing the results in your album.

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