jointing boards advice

[wallace]

I was preparing some boards on the planer ready for gluing together and ran into a problem. When the pieces were butted together their was a very small gap in the centre of the board, so no good for gluing. Is this human error or machine error. Thanks Mark

 

[Sgian Dubh]

It's hard to say, and it may be that there isn't an error at all because it could be due to stress release in the wood as the board is worked. It may be useful to check the set up of your planer to ensure the tables are coplanar and the knives are set correctly, but I'd only check that if almost every board you flatten shows the concavity at the centre. Your technique may also be faulty, but without seeing what you do it's unfair to speculate.

However, you seem to be inadvertently creating a sprung joint, which is actually exactly how plain edge joints should be prepared, although the spring should be very slight. If your inadvertent spring is too great then some corrective work is required. The guidelines in the following link at my website may offer you some useful tips on edge jointing issues and techniques. Slainte.
http://www.richardjonesfurniture.com/Ar ... e-ups.html

 

[custard]

Wallace, it all depends what you mean by a "very small gap".

The manufacturer's recommended set up for my planer is that a 2m long board be hollow (or "sprung") by between 0.2mm and 0.5mm. It's fairly easy on this machine to dial in whatever degree of springing you want, I normally stick to about 0.3mm on a 2m edge as I find this glues up beautifully with virtually invisible glue lines.

To put this in a practical context, if you were edge jointing two boards that were 1m long you'd see a 0.3mm gap in the middle, with a strong light behind this is a pretty obvious gap, even though it can normally be closed up with hand pressure alone, and disappears completely when clamping with even glue squeeze right along the joint. You could try measuring your gap with a feeler gauge to see how it compares.

 

[wallace]

Thanks a lot, so I have done it correctly without knowing. That makes a change for my work

 

[RogerS]

Mmmmm..sprung joints..two boards ...so far so good. But what do you do when there are three...or more.....boards.....

 

[wallace]

Don't confuse me

 

[Sgian Dubh]

Mmmmm..sprung joints..two boards ...so far so good. But what do you do when there are three...or more.....boards.....

Simple. Three boards = two sprung joints: four boards = three sprung joints, etc. Woodworkers have been doing it for decades, if not centuries, and I've certainly been doing it for at least four decades.

I assume you're jokingly trying to play Devil's Advocate, not unless you really don't understand the technique. I assume you've read the information at the link in my first response to this thread? There's an explanation in that link about the sprung joint and how, and why, it works. Slainte.

 

[RogerS]

Devil's advocate...kind of. This topic came up in conversation with a well-respected woodworker who was positing exactly that question.

 

[custard]

Mmmmm..sprung joints..two boards ...so far so good. But what do you do when there are three...or more.....boards.....

Interesting question. I assume you mean as the amount of hollow is additive with each additional board do you reach a point where you have an "hour glass top" or something similar. In theory yes, in practise though it's more important that the ratio between board width at the middle versus board width at the ends remains constant with two sprung boards or two hundred sprung boards. In fact I'm just finishing a new bench top with seven or eight 65mm thick sprung maple boards and there's been no problems from "excessive springing"!

 

[Sgian Dubh]

Devil's advocate...kind of. This topic came up in conversation with a well-respected woodworker who was positing exactly that question.

I'm struggling to understand what kind of the question your well-respected woodworker may have raised. Sprung edge joints are such a standard feature of making wide solid wood panels that I'm surprised he or she isn't fully conversant with the practicalities of executing it and the technical reasons for its inclusion in the job. Perhaps he or she too was playing Devil's Advocate?

I suppose, much as custard picked up, people may wonder about the potential for an hour-glass shape developing, particularly in a very wide panel. In reality, the spring should very slight so if an easily visible "hour-glassing" develops then my conclusion would be that the spring was executed incorrectly, i.e., too much concavity on the edge of each board requiring far too much clamping pressure to close the gap. This sort of poorly executed sprung joint is likely to lead to failure of the panel at a joint or somewhere in the long grain because of the amount of stress built in to the structure.

In any case, it's typical to make up a panel that's a little too wide so that after the glue up there's enough meat to straighten one edge with a plane or surface planer followed by making the opposite edge parallel-- that takes care of any hollows, bumps, convexity, etc, on an edge just the same as straightening the edge of any board or plank. That is the routine if the long grain edges of the panel are meant to be parallel, which is not always the case of course because cabinet and table tops may end up shaped one way or another on all the edges. Slainte.

 

[Charlie Woody]

Well I have managed to do the reverse of what Wallace did ...... small gaps at the ends of the boards i.e. meets in the middle but not the ends

I suspect that this is my technique rather than the machine - a Hammer A3 31 - which has self setting blades and the tables are factory set.

What I thought I had been doing was putting small amount of pressure downward on the infeed table until past the cutter then on the out feed table whilst also applying pressure against the fence.

Was that correct procedure?

I have been looking on You Tube to find something to show me the correct way to do this but no luck finding anything so far. So any help appreciated guys!

 

[Sgian Dubh]

It sounds like your technique is basically right with regard to where and when during progress of the board over the machine you apply pressure. If you are applying decent downward pressure at the beginning of the cut on the infeed table until 200 mm or so of the board is on the outfeed table whereupon you smoothly transfer your hands over the crown guard one at a time that should be okay. It's possible that you're transferring too early and applying pressure on the outfeed side causing the piece to rock on a pivot point, but it's difficult to diagnose from afar. You may also be putting the convex edge or face down instead of the concave one which can cause you difficulties if your experience is limited. And it's not always the case that there's a simple choice to make between concave and convex because the edge or face is wavy or multi-bowed so you have to carefully select exactly where you apply pressure to prevent rocking the piece as it moves across the cutters.

There is the slight possibility that your infeed and outfeed table aren't parallel, i.e., the outer ends of one or both tables dip up or down and that can cause problems along the lines you've described. Checking this can be difficult without appropriate equipment and knowing what to look for, so I think in the first instance you'd be best to ensure your technique is good so that you can eliminate that as a regular cause of the problem. Slainte.

 

[custard]

Hello Charlie, I use a Felder which is often similar in layout to Hammer machines. On the Felder there is a dedicated control for adjusting the degree of concavity when edge jointing, basically it adjusts the height of the outfeed table relative to the cutter block. It's under the outfeed table and is highlighted by the red arrow in the photo. Each full clockwise turn of this knob raises the outfeed table by 0.1mm. It's such a convenient and reliable adjustment that I'll often tailor the cut for individual tasks, selecting greater or lesser degrees of "spring".

Check to see if your machine has something similar.

 

[Charlie Woody]

Hello Charlie, I use a Felder which is often similar in layout to Hammer machines. On the Felder there is a dedicated control for adjusting the degree of concavity when edge jointing, basically it adjusts the height of the outfeed table relative to the cutter block. It's under the outfeed table and is highlighted by the red arrow in the photo. Each full clockwise turn of this knob raises the outfeed table by 0.1mm. It's such a convenient and reliable adjustment that I'll often tailor the cut for individual tasks, selecting greater or lesser degrees of "spring".

Check to see if your machine has something similar.

Custard
I don't see anything similar on my machine. Thanks for the suggestion. I just need to practice my technique some more I think!

 

[Jacob]

I was preparing some boards on the planer ready for gluing together and ran into a problem. When the pieces were butted together their was a very small gap in the centre of the board, so no good for gluing. Is this human error or machine error. Thanks Mark

Human error of course. You can't blame the machine (or the wood) for not knowing what you are trying to achieve.
I would expect to finish board edges with a finely set long plane, treating each joint individually, not relying on machine perfection.