Advice on planing/preparing endgrain for jointing

[Col]

I'm a novice and this is my first serious woodworking project so looking for some advice please

I am planning to build an octagonal coffee table
The top will be cut from a piece of oak staved kitchen worktop (40mm thick) but I don't want endgrain along the edges.
Therefore I will cut 8 isosceles(?) triangular segments - with the oak staves parallel to the short side and glue along the long sides (which will have endgrain at a slight angle to the edge surface).

Plan to cut the segments with a plunge saw (with guides). (Not planning on investing in a table saw). Hope the marking out will be accurate and ideally this might give a surface suitable for jointing but probably not :-(

Therefore I would then need to make this endgrained edge perfect for gluing - these edges will be about 450mm long. Options:

(1) Low angled jack plane (don't have one and I reckon that my 'by hand' skills won't be good enough any time soon)
(2) Use a planer (multiple passes, taking minimal material off per pass). With the angled grain direction I would pass the thick end of the wedge over first (and wouldn't be concerned about damage at the 'point' end since I would plan to have a small octagon set in the middle so would be cutting the points off anyway). Are there extra safety precautions with endgrain on a planer?
(3) Disc sander - not high on my wishlist to get one and I'm not convinced that I would be able to get a perfect 450mm long edge on a 'shorter' sander.
(4) other suggestions?

Appreciate any comments on the options and other ideas from your experiences ...

Thanks, Col

 

[AndyT]

I wouldn't want to put anyone off, but there's a reason why you don't find many octagonal tables made up from eight identical triangles of composite wood. It would be seriously difficult to make it accurately! It could be feasible using the sort of machinery that was used to make the worktops - but you don't have that. A table of triangles could be made using veneer on top of flat boards - where it is possible to cut the triangles in pairs so that they fit properly - but that's not what you have asked about.

If I were you I would put this one aside for a while and get some experience and practice on more basic designs which have evolved to be sound as furniture and practical to build with minimal tools. An 'ordinary' table could be made with just a saw, chisel, plane, ruler and bench, even if it did have an octagonal top.

Also, what's so wrong with end grain? It will at least show that you have used solid timber. If planed and sanded properly it can take a finish to match the rest of the edges of the top.

 

[Racers]

Hi, Col

Wow that would be difficult, all the errors will add up so by the last piece it will be miles off.
Even veneered tops usually have an inlay in the middle to hide where the points don't line up.

Pete

 

[Phil Pascoe]

Here's an exercise for you - get a bit of scrap 2" or 3" x 1" , two or three feet will do, and try to make a miniature square frame. See if you can get the corners with no gaps, then you'll realise how difficult it is.

 

[Sheffield Tony]

I was thinking that this might not be so bad to do if you joined the segments in pairs into 4 90 degree segments, then into two half-octagons, then into one finished octagon, but then I had a second thought - won't the joins be likely to open up as the wood moves ? If it shrinks, it will shrink more across the grain than along it, making the 8 pieces > 45 degrees, so splitting apart in the middle. If it swells, it will part around the edge.

Probably not only difficult to achieve, but not very stable either !

 

[moz]

I was thinking that this might not be so bad to do if you joined the segments in pairs into 4 90 degree segments, then into two half-octagons, then into one finished octagon, but then I had a second thought - won't the joins be likely to open up as the wood moves ? If it shrinks, it will shrink more across the grain than along it, making the 8 pieces > 45 degrees, so splitting apart in the middle. If it swells, it will part around the edge.

Probably not only difficult to achieve, but not very stable either !

I completely agree. I have seen one example of this and it did fail catastrophically. In the orientation you describe, it would be even worse since your joints would be mainly end grain. There are only two ways of doing this. Firstly, join conventionally to produce the required width then cut into an ocatgaon shape. Secondly, by veneering.

John

 

[Sgian Dubh]

I completely agree. I have seen one example of this and it did fail catastrophically. John

Here's an example. The four segments in the two pieces made up a square only about 300 mm long on each edge. As can be seen the change in MC resulted in the joints opening up. Whether the joint opened up at the centre or towards the outer corner depended on if the wood dried further after assembly (opened at the centre), or got wetter (opened at the outer corner). These bits were made up to demonstrate the likely failure of such a construction. Slainte.

 

[Col]

Andy - thanks for that - I had a feeling it wasn't going to be easy :-(

I have made some simple pieces and was looking to make something we really wanted!

...

Also, what's so wrong with end grain? It will at least show that you have used solid timber. If planed and sanded properly it can take a finish to match the rest of the edges of the top.

The endgrain was really a secondary concern - the table would be sitting on 50mm wide staved flooring and it would look better if the staves on the table didn't run in one direction.

Col

 

[Col]

Pete,

Hi, Col

Wow that would be difficult, all the errors will add up so by the last piece it will be miles off.
Even veneered tops usually have an inlay in the middle to hide where the points don't line up.

Pete

I was thinking of constructing two pieces each of 4 triangles, then replaning the final edge of each to remove errors before gluing (and having an octagonal insert in the middle to avoid point problems).

Thanks for your thoughts ...

Col

 

[Col]

Phil,

Here's an exercise for you - get a bit of scrap 2" or 3" x 1" , two or three feet will do, and try to make a miniature square frame. See if you can get the corners with no gaps, then you'll realise how difficult it is.

I had actually tried out my octagon with 6" by 1" pine (using a mitre saw) and it lined up with no gaps so I was quite encouraged - rather unfortunately judging by the responses here!

thx, Col

 

[Col]

Sheffield Tony, Moz, Sgian Dubh,

I think you all have highlighed the real flaws of the design - failure along the join caused by differing expansion/contraction.

Do you think this could be overcome by fitting two worktop joiner bolts (or equivalent) along each join (bearing in mind there will be a central octagon so I should have enough width at the narrow end of each truncated triangle)? Or is it really just a non-starter?

Thanks, Col

 

[Phil Pascoe]

1/ no
2/ yes
think when you last saw a table top made that way........................that's why it's not done - a lot of people have already discovered that it doesn't work very well.

 

[moz]

Sheffield Tony, Moz, Sgian Dubh,

I think you all have highlighed the real flaws of the design - failure along the join caused by differing expansion/contraction.

Do you think this could be overcome by fitting two worktop joiner bolts (or equivalent) along each join (bearing in mind there will be a central octagon so I should have enough width at the narrow end of each truncated triangle)? Or is it really just a non-starter?

Thanks, Col

What you can't get away from is that the shape of each triangle is constantly changing and this cannot be resisted however it is joined.

John

 

[Racers]

Hi, Col

Have a look at this frame made from beach, its not one of mine I might add.

That's what can happen even if you get it to look right at the beginning, veneering would be the best way.

Pete

 

[Col]

Many thanks to everyone who's responded - I guess I'm now convinced that I shouldn't even attempt to start this design :-(


Thx again, Col