Octa-Gone Wrong!

Even though my blog has remained in a near-dormant state for a good week now, I have spent the past few weekends casually working on a fruit bowl with an octagonal design and theme. It’s frustrating enough having such little time to work on things like this but, when things just don’t go quite as well as you had hoped they would, it makes you feel like giving up, doesn’t it?

It may looks as though I have made good progress on this bowl in the photo above. Look a little closer though and you’ll see that I, quite literally, can’t quite get it together on this one…

I’ve double-checked and carefully rest my saw blade three times now and yet, for some reason, these compound mitres aren’t coming out at a perfect 22..5°… Or, perhaps they are and there’s another obstacle preventing two of these joints from pulling up neatly once they’re wrapped up in the ratchet straps. It’s not always the same components, either. There’s a discrepancy somewhere but, I’m just not sure of where or how to find it.

To cut these mitres on such small components (‘segments’, only 105mm at their longest), I came up with a simple work-holding jig in the form of a sled designed to fit in to the only (left-hand) slot on my Elektra Beckum PK200 table saw. I do feel that the jig is quite reliable and, with the stop block in place, I’m confident in saying that each of the eight segments I’ve cut is identical, thanks to this… Meaning that they’re each now a good 2mm under-size, as I’ve re-cut these joints twice now and, they still won’t all pull together neatly.

This is the first time where I’ve attempted to assemble any shape with more than four-sides. I’m sure that the addition of the ‘slant’ or slope to the bowl’s outer edges only helps to complicate matters. Perhaps I should instead attempt to build a simple 90° octagon with vertical guides, if only to affirm my confidence in my jig-making abilities on this project.

If the “other” angle is out (erm, the “taper“…?!), could it be responsible for these joints not going together correctly, even if the ends are all mitred at a precise 22.5°? Or, perhaps I should invest in a Bevel Box…!

I have already begun documenting this one in video format. If I can find a way around this inconvenience then, I would like to finish the finish the short series off.

Thanks for reading.

8 thoughts on “Octa-Gone Wrong!

  1. don’t know, looks like you did the right thing, are there joints between the parts, maybe with the strap it’s just difficult to get it all in place. I am not convinced that it’s wrong.

  2. If you can’t close them up, turn them into a feature!

    Run beading down the insides – bit of a feature.
    Down the outsides – run the unit through the saw again, partial depth directly into the seam. You can then stick a spline in vertically, in a contrasting colour. Sand it flush, and people will wonder how the hell you got it so perfect!

    1. Thanks, Stu, that’s actually a great suggestion, if it comes to it! Usually, I’m the first to think of ways to ‘hide’ my mistakes… 😳


      I’ll try Bongo’s tape trick first though, just in case (can’t believe I didn’t remember that one myself). It may not be clear in these photos I’ve shown so far but, there’s already a fair amount of walnut detailing used to contrast with the ash. That’s my only concern against putting more in. Unless, perhaps, I use something slightly ‘warmer’, like American cherry…

  3. Tricky business. I take it dry, and that it is cut and assembled in the same day? I have found in the past with similar projects that almost imperceptible warp can easily add up to cause problems with the joints. Just leaving the slats on the workbench for a few day, so that only one side is exposed to the drying atmosphere, can be enough- though I am sure you knew that already, just a thought…

    One trick to make assembly and alignment slightly easier, which is probably more useful when you have more slats (but could work here too), is to lay them all side by side on a flat surface, and use some tape to stick them together. Then you can sort of roll up the shape and it keeps the outside of the joints tightly together and aligned. Is hard to put in words – like the third and fourth photo here: http://www.floweringelbow.co.uk/2011/woodwork/making-an-atabaque-capoeira-drum-%E2%80%93-part-2-steam-bending/

    I also like Stuart’s suggestion if you get fed up with it 😉

    1. Wow. Olly have you been in our workshop? For the past few days, we have been doing something similar. Using a certain Festool Plunge Saw…. All will be revealed soon. 😀

      1. Hi Tom,

        It’s purely a coincidence! 😀 This has been on my mind for the last seven-months. I look forward to seeing what you guys are working on. 🙂

  4. A brief update, guys – I tried the masking tape idea earlier today but, sadly, I’ve still got the same problem; gaps between any two of the joints while all others look perfect. 😦

    I may not try gluing the bowl up in two halves and then hand-planing the final edges to fit perfectly… Or, it will be Stu’s spline suggestion.

  5. Nice little project, having a look after you subscribed to my blog. I can probably help you out a bit here.
    Firstly you need to make the structure rigid when working on it, I suggest you make a template for the base (or the top) to sit in. MDF with some plates cut and then glued to fit each face of the bowl should work. This means you can sit the structure firmly before you clamp, and when you clamp it will not move at the bottom. It needs to be just tight enough to hold it in the right place.
    Straps are not actually very good clamps for an angle face, what I have done in the past and used for one of my tables is a face plate in mdf cut to match each face of the bowl but slight less wide. On the plate face you glue an mdf or wood block, then to clamp firmly you can put the strap around the bowl but above the blocks and when it tightens the blocks stop it from moving down.
    Its a really tricky thing to do especially with this many faces but it will work when you’ve practiced a few times.

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