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Can't remove bow in long timbers with planer (Read 6094 times)
big_all
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Re: Can't remove bow in long timbers with planer
Reply #9 - Jan 16th, 2013, 1:24pm
 
other points to to note about bowed timber

if you have your timbers to size and you are building a frame with infill like a door or cabinet you can often push the bow out against the other rail or components
or if its still a bit out place it on the hinge side and use a third hinge

you may off course have to give extra support to the "frame" during construction and gluing to stop it setting out off shape

but remember the thicker the timber behind the bow the less likely you are to even it out

i have cut a plank off 8x2" for 2 3x2 door rails first cut dead strait second cut bit off a curve last bit 1 3/4" like a banana Grin
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« Last Edit: Jan 16th, 2013, 1:32pm by big_all »  

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Re: Can't remove bow in long timbers with planer
Reply #8 - Jan 15th, 2013, 10:07pm
 
And it could just be the wood.  Some wood is just like that. Internal stresses..released a bit by planing...then they come back again.

And at that length I would definitely have some support on the outfeed.
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woodsmith
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Re: Can't remove bow in long timbers with planer
Reply #7 - Jan 14th, 2013, 5:53pm
 
The longer the length of board the harder it is to get it flat; as a rough rule of thumb the maximum length I work on being able to flatten is a board that is twice the length of the planer beds. If your timber is greater than that ratio you could rig up some temporary table extensions to help.

As for you not being able to get a board flat I would suggest you get a piece of flat softwood, make sure it is really flat to start with then take a 1mm pass over the planer and check if it is now unflat. If it is then you have a problem and you could check if the tables are coplanar with each other by taking off all the cut on the infeed table and seeing if the two tables are flat by using a long straight edge. If they are then I would try resetting the height of the blades in respect to the outfeed table. It can be quite critical and I would try setting the cutters very slightly either side of your current setting and see if that helps.
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big_all
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Re: Can't remove bow in long timbers with planer
Reply #6 - Jan 14th, 2013, 11:15am
 
yes both ends need to be level
if the back end is climbing up as you plane the front end will be planed wrong as will the back end as the front drops off the table

44mm is a standard stock size is it a special wood
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Mannyroad
Re: Can't remove bow in long timbers with planer
Reply #5 - Jan 14th, 2013, 9:08am
 
Hi Woodsmith/ Big_all,

Thanks for your posts.

I see you point about not pressing down too much initially as this will remove the bow and make the cutter take the same from the entire board length, thus not removing any bow.

The boards were cut and thicknessed to 47mm for me, allowing me 3mm for final planing down to 44mm.  They've been laid flat in my garage (they're for new doors to the garage) for several months now so should be in stable condition (stress following planing excepted).

The main bow is to the edges of the timbers.  I reckon there is about a 4mm bow over the 8 foot length of the timber, so by your reckoning Woodsmith, which makes perfect sense, I would lose about 10mm overall, which is fine.  I will have another go with the concave stile edges using no downward pressure and see how it goes, not too hopeful though because I can't help but feel that the short length of the tables allows the long timbers to arc over the tables/cutter, if you see what I mean.

The face of the stiles is bowed maybe 2-3mm and I suspect the shear weight of the pitch pine is taking the bow out as it goes over the cutter, so not sure how to sort this.

One thing I don't understand is that when I plane the edge of the 7" and 9" rails (4 foot in length), I can't seem to get a flat reference surface when tested with my stainless straight edge.  It seems to be very slightly concave after passing over the jointer as though it's taking slightly more from the middle of the rail than the ends.  My knives have been painstakingly set to the correct height above the outfeed table (so as to move a piece of wood approx. 2-3mm when rotating the cutter) so I know its not that causing this. I wondered if it might possibly be the tables not being coplanar as this is a planer/thicknesser I bought from a joiner who seemed genuine and said it was working perfectly (he'd just bought a bigger more commercial one). I'm not suggesting they are out of parallel, I just can't figure out why I can't get a FLAT surface/edge.

I here a lot about making sure the tables are coplanar but don't know where the adjusters are for aligning the infeed to the outfeed table if they prove to be out of parallel.  Anyone know where the adjusting goes on for a Kity 636 as I don't have a manual?  It's the older version, not the more modern looking 2636(?) one that is available these days (who's manual doesn't seem to tell you how to adjust the tables anyhow).

Cheers guys.

Thanks guys
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woodsmith
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Re: Can't remove bow in long timbers with planer
Reply #4 - Jan 13th, 2013, 7:32pm
 
You did better than me with your editing then, I previewed my first post then managed to delete it before saving it.
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big_all
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Re: Can't remove bow in long timbers with planer
Reply #3 - Jan 13th, 2013, 7:09pm
 
you posted whilst i was editing keith so you can have the glory for the planing bit  Grin Grin
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woodsmith
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Re: Can't remove bow in long timbers with planer
Reply #2 - Jan 13th, 2013, 6:59pm
 
Are the boards going to be thick enough when you plane them flat? You need to measure the amount of bow on the concave side, double it then add 2mm, subtract that from the existing thickness and that will give the the maximum thickness you can get out of this board.

As for planing, it sounds like you are pressing down too much initially. With a bowed board you need to feed it over the cutter block with as little downward pressure as possible, so that it just removes material at the two ends. Once you have taken most of the bow out you can then feed it across the cutter with downward pressure initially on the infeed side but transfer your weight to the out feed side as soon as there is enough timber beyond the cutter to do so safely.

I hope that helps.

Keith
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Re: Can't remove bow in long timbers with planer
Reply #1 - Jan 13th, 2013, 6:47pm
 
you need to select your timber carefully straitest bits for the rails or longest components
cut the timber 100mm longer than the components and plane the shorter lengths this will reduce the problem by around 80 to 90% if you half the length

you plane with the bow up so the front and back are reduced until the
bottom is flat
hold firmly gently push down as little as you can and maintain control

it should go  zz------------------zz
thenzzzz-------------zzzz
then zzzzzz----------zzzzzz
then zzzzzzzz----zzzzzzzz
then zzzzzzzzzzzzzzzzzzzz
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« Last Edit: Jan 13th, 2013, 7:04pm by big_all »  

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Mannyroad
Can't remove bow in long timbers with planer
Jan 13th, 2013, 3:42pm
 
Hi all,

I'm new to this forum so please bear with me.  I'm a reasonably competant DIYer but am struggling to remove bows in some 8 foot long 5" x 2" pitch pine timbers that I'm using for door stiles.  The timbers are bowed in both planes and I've read that I should use the planer to remove the bow (concave face downwards) and once flat use the thicknesser to remove the hump so to speak on the opposite side.

Problem is, I've put the timbers over the planer (Kity 636) a number of times (with 0.5mm cut) but can't seem to see any change in the bow, despite being careful to ensure the timber is held down firm to the outfeed table.  Seems that I could probably keep planing till there's no wood left and it wouldn't remove the bow.  By the way, I've only just bought the planer thicknesser and am still getting used to it.

What am I doing wrong please?

Cheers, Barry
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