Thread: Advice on some Jointing techniques please

What brand / model and new or secound hand

Hi Ray, new Hammer A3 31 with spiral head, total table length 1400mm. It has an infeed extension of 400mm (so total infeed of about 1150mm, and I have a roller stand for outfeed.

Website.

Your logic is pretty much spot on. Breaking down long bits to minimise loss and using a table saw for initial straightening on really bent stock is the way to go (it can be done without the saw but takes longer). Always joint with the cup/bow down (up? I never know which way to call it) so you have 2 contact points on the table and shift your downwards pressure from the infeed side to the outfeed side as you go. Too much pressure can artificially straighten the timber so be mindful of that as well.
Contrary to popular belief, you only lose the height of the bow, not double; kinda hard to explain without drawing it, but that's the way it is. So your 4x2 with a 1 inch bow will end up as 3x2, not 2x2. Also, halving the length of the board cuts the height of the bow to a quarter, not a half: 20mm bow in 1000mm goes down to 5mm in 500mm. Again, not what you might think, but I did the math and it works.
I think that covers most of jointing 101, good luck and keep your fingers out of the way

Just a few of my thoughts.....
In general it is better to remove equal amounts off edges and faces to get down to a DAR size, one reason being that the distribution of moisture within the wood relative to the edges/faces is maintained, thus flat boards are a first choice, this also means less machining and handling is involved to get to the final size.
If a bowed/bent/twisted board is machined there will be areas where more/less material is removed/not removed thus giving rise to an uneven distribution of MC relative to the new face/edge and potential for further drying movement issues, then also throw in any internal stress movement issues as these uneven amounts of timber are removed.

If non flat boards are to be machined I'd suggest cutting to length required plus green then dress but also only skip dress and then set aside for a period to allow equillibrium, if further movement is noticed maybe another skip dress/settle and then final dressing, but if still further movement is noticed I'd seriously consider not using the piece, it may be suitable for use somewhere where it is restained from movement but not in a door frame for e.g.

As far as which way to cut your 4x2, it's a how long is a piece of string thing, depends on what you want out of the piece of wood, if I was looking at your bit of wood I am always going to ask myself can I get to the final size with the minimum of processing, if this was the only bit of wood and we had to use it I'd cut to overlength, remove (rip) the majority of the concave/convex curve off keeping in mind whether I wanted a 2x2 or a 2x3, I'd use my BS but TS is fine, skip dress and allow some settle time and keep an eye on it over a number of weeks. It is also quite feasable to joint a face as a first operation then proceed to the TS to rip the curve/s off, this gives a flat surface and makes the TS operation safer and easier.

If I had a knob or a curve towards the end of a board that was close to length but I didn't want to cut closer to final length I will make enough part passes to remove just the worst of the curve/knob, sometimes this might mean placing the lead part of the board on the outfeed (bow up,knob/curve down) and lowering the infeed until the cutter head starts to make contact, I then take a cut or (I might say halve the total difference and make 2 cuts), depth of infeed can be as much as 5 to 10mm in these cases, depends on how much curve there is, then take a normal 1, 2 or 3mm cut for the full length, a lot of the time there is no material left for maching on the opposite side of where the knob/curve was but sometimes I might need to get 5 or 10mm of length depending on what is revealed after final machining, if nothing else it is cut off along with any snipe.


Hope this helps somewhat.



Pete

Thanks Elan and Pete, all good to know.

Originally Posted by elanjacobs

Contrary to popular belief, you only lose the height of the bow, not double....

Just thinking that through just now (with the aid of coffee and a fag) and you are quite right. I even think I can explain it without a diagram!

If the bow is 20mm (assuming the same each side) then when I cut off 20mm from the concave side I haven't cut any width from the middle of the board, just two long skinny triangles from the ends. Then when I flip it I will only be cutting off an arc going from ~0 to 20 to ~0mm off the length off the board on the convex side, so only a 20mm reduction overall. So where I'm cutting off 20mm on one side I'm taking 0mm off the other, 15mm & 5mm, 10mm & 10mm etc. Piece 'o cake! (3 edits later, I think that's right )

And you can be sure that I will treat the machine with the greatest of respect. I've already had my "warning" from a table saw. A small nick to the thumb a couple of years ago that gave me the worst ever hit of adrenalin. I felt physically sick for 24 hours - beats me what adrenalin junkies see in it!

Brett, have a look at this

How to set and use a Surface Planer (Jointer) - Part 1 - YouTube

Milling Four Square - Face Jointing - YouTube

Thanks Chris, I'll have a look at that.