Thread: Measurements and allowing for planing/ thicknessing

It would depend on where and how you source your timber. Traditionally, you would source straight seasoned timber off the saw and surface 1 face, 1 edge with the jointer and finish to required size with the thicky, maybe ripping to width (or slightly over) if it is worthwhile. Timber sold this way is generally sized as nominal mill saw settings, and there will be some shrinkage in seasoning, and further loss in surfacing. For good straight flat timber, the general allowance tended to be 1/4 in in the old money, i.e. a board sold as 6x1 in seasoned could be about 1/8in undersize at purchase, and you might recover a max 3/4x 53/4 finished board. The worse the original board is for bends, bows, twists and cups, the more you will waste and your recovery will be less.

If you are buying DAR (dressed all round) stock, in theory, if you can get perfect stock in the size you want, it should not need machining, but that would be extremely rare these days. Allowing for corrections is something you need to factor when buying as you see the material, rather than something you can make a general allowance for. Basically finalise the design and prepare a detailed parts list to take shopping, and select timber to match parts list requirements, rather than buy a lot of timber and hope to get what you need out of it. If possible, once you decide you want a particular piece, write on it in chalk as an indicator of what it was for. When you get it home, stack it in the shop flat and stickered for a couple of weeks to acclimatise to conditions in the shop, then cut individual components oversize and machine to about 2mm over on all surfaces, and sticker again for another couple of weeks. It should then be safe to machine to final size and expect material to hold size and flatness etc for the build.
To my mind, there is little point in buying DAR at nominal sizes close to your requirements, then chasing things trying to machine out imperfections once you get the material home, as everything will be randomly undersized and a nightmare to work with. Our American friends suggest allowing at least 20% wastage beyond required minimum sizing for a project to allow selection of appropriate material for each component, and machining, working around defects etc.

Hope this helps you, and sure others will have different ideas.

Malb, you're a legend.

Malb has said it all.

"When you get it home, stack it in the shop flat and stickered for a couple of weeks"

Just one question...by stickered, you mean an actual sticker to mark out date etc, or is this a term for something else I should know but don't?

A sticker is just a small piece of wood between each piece to add airflow around the timber

Just an additional comment here ... that probably doesnt need to said, but just in case.

Try to machine all components that are supposed to be the same thickness in one batch. That way, you are not trying to reset the thicknesser to find your final measurement again.

While not mandatory, it will reduce the time required to finish any joints that need to be made flush (e.g. a table top).

Also, if you're ripping long boards, make sure to leave plenty extra width to allow for the timber to bow as the internal stresses are released.
The amount you need to allow varies from timber to timber (thicker stuff tends to move more as well) and there's no way to tell which way it will move when cut, but I have personally witnessed straight boards develop 20mm of bow as they go through the rip saw.

Great information above, well done.

Just as a side note, from my sawmilling background, the longer the length, the less recovery you will generally get. It is difficult to mill and dry a perfectly flat and straight set of 3.5m to 5.4m boards for a large table than a set of 1.8m boards for a eight seater square table. I have sometimes supplied 5.4m redgum boards for large custom jobs, and they are like hens teeth in the rack to find straight and flat. So if you are planning/quoting a job that requires multiple long lengths, allow a little more. You will often be charged a premium for the longer, rarer lengths also. Different species will also dry straighter than others, i.e. black heart sassy can have a spiral grain and dry with a slight twist no matter how much weight you have on the rack and care is taken, yet most blackwood is nearly bulletproof and will come off the rack like gun barrels.

Some species that are prone to collapse during drying, such as myrtle and redgum, may need a little extra planing down to remove every last depression, yet this can be overlooked a little on the bottom side of the table.

Good luck with the project

Cheers

James

To your point, Glenn:

I tried this other day on another project. I had two boards for a glue up, and I planed them, then took them to the thicknesser. I got one planer to my liking, then fed the other through. Big mistake...it was too much for one cut (I thought it was only a light pass, so wrong) and got a few chunks taken out of the end of the board. Would I be better off feeding them through in one go, then lowering the cutter, feeding them all through again etc until I find the correct final thickness? I hope I'm making sense here...

Find the thickest one, set your thicknesser to take a doable pass then feed them all through, change setting (0.5mm, 2mm, whatever your machine can handle), rinse and repeat until you get to where you need to be.

Originally Posted by malb

It would depend on where and how you source your timber. Traditionally, you would source straight seasoned timber off the saw and surface 1 face, 1 edge with the jointer and finish to required size with the thicky, maybe ripping to width (or slightly over) if it is worthwhile. Timber sold this way is generally sized as nominal mill saw settings, and there will be some shrinkage in seasoning, and further loss in surfacing. For good straight flat timber, the general allowance tended to be 1/4 in in the old money, i.e. a board sold as 6x1 in seasoned could be about 1/8in undersize at purchase, and you might recover a max 3/4x 53/4 finished board. The worse the original board is for bends, bows, twists and cups, the more you will waste and your recovery will be less.

If you are buying DAR (dressed all round) stock, in theory, if you can get perfect stock in the size you want, it should not need machining, but that would be extremely rare these days. Allowing for corrections is something you need to factor when buying as you see the material, rather than something you can make a general allowance for. Basically finalise the design and prepare a detailed parts list to take shopping, and select timber to match parts list requirements, rather than buy a lot of timber and hope to get what you need out of it. If possible, once you decide you want a particular piece, write on it in chalk as an indicator of what it was for. When you get it home, stack it in the shop flat and stickered for a couple of weeks to acclimatise to conditions in the shop, then cut individual components oversize and machine to about 2mm over on all surfaces, and sticker again for another couple of weeks. It should then be safe to machine to final size and expect material to hold size and flatness etc for the build.
To my mind, there is little point in buying DAR at nominal sizes close to your requirements, then chasing things trying to machine out imperfections once you get the material home, as everything will be randomly undersized and a nightmare to work with. Our American friends suggest allowing at least 20% wastage beyond required minimum sizing for a project to allow selection of appropriate material for each component, and machining, working around defects etc.

Hope this helps you, and sure others will have different ideas.

great information

I'll just add ...

now you have your own jointer and thicky, you no longer need to work to exact dimensions.
are far as finished product goes, 4 table aprons each 91.3 x 19.5 will work perfectly as aprons, there's no need to take them to exactly 90 x 19.

the same goes for boards destined for a table top, provided they are all the SAME thickness, the exact thickness is no longer relevant

Originally Posted by zoovegroover

To your point, Glenn:

I tried this other day on another project. I had two boards for a glue up, and I planed them, then took them to the thicknesser. I got one planer to my liking, then fed the other through. Big mistake...it was too much for one cut (I thought it was only a light pass, so wrong) and got a few chunks taken out of the end of the board. Would I be better off feeding them through in one go, then lowering the cutter, feeding them all through again etc until I find the correct final thickness? I hope I'm making sense here...

And to Elans point - thats exactly the process I follow. Once I have a clean set of first faces & edges from the jointer, I lay the boards out and sort in sequence thick to thin. I then set the thicknesser to take a workable pass on the thickest piece (depth of cut will depend on required finish quality, type of timber etc. etc). Trap for young players here ... on longer pieces, remember to check the thickness of both ends - and on long boards the middle. Remember - jointers can actually produce a tapered board which is thinner at one end.

Continue to pass all boards through on each setting - assuming they are thick enough to actually be cut. You will reach a point where all boards are cutting along their full length and width. Continue this process until you reach your final desired thickness. As Ian says - whether its 19mm or 19.5mm is often irrelevant. Its the consistency of thickness that is most often important.

Cheers...

Originally Posted by elanjacobs

Find the thickest one, set your thicknesser to take a doable pass then feed them all through, change setting (0.5mm, 2mm, whatever your machine can handle), rinse and repeat until you get to where you need to be.

Thanks, Elan. Slightly confused on this one, though. Sorry, I'm still new to all this...So, if I take a pass off the thickest one and I'm happy with that, I'm then left to feed thru the rest that are thinner than the one I just passed thru, no? In my mind it seems that I would use the thinnest as that's the one they'll all need to be planed to match. So run thru thinnest, make sure it's fine. Then use that setting to get the others to match. I'm probably way off and thinking of this in a totally illogical way, though. Could you clarify for me a bit? Thanks for your help!

Thanks everyone so far for weigh in, this is incredibly helpful for a new player like me trying to take a big step up.