Thread: Need help with slight but consistent concavity off the jointer

(a) will give a convex shape
(b) will give a concave shape

Check the blade height above the outfeed table too. Are you getting any snipe?

Cheers
Michael

Originally Posted by MarkInBoatshed

The jointer is fairly well tuned (by me), cutters sharp and aligned with outfeed table, tables shimmed to be coplanar, etc but clearly one of these things is not set quite right.

Oh
I thought the outfeed table should be above the infeed, to match the bit you plane off.

If the knives are not above the infeed, they won't touch the timber.

There's an article in one of the recent wood working magazines about setting up a jointer. Check your library.

In another, there's an article about how one fellow has his tables at a very slight angle to the knives, so he can joint edges before glues up a lamination and make the edges every so slightly concave, so a clamp in the middle pretty much clamps the whole thing. He uses a clamp at each end too. That one might be in Popular Woodworking.

Originally Posted by Johncs

Oh
I thought the outfeed table should be above the infeed, to match the bit you plane off.

If the knives are not above the infeed, they won't touch the timber.

Yes, but that is controlled by the height adjustment. The blades are set to be very slightly above the outfeed table so a blade grabs a straight batten of wood off the outfeed table and drags it no more than 2-3mm (done by hand of course)


Cheers
Michael

Michael,

Not getting snipe, and cutter height is correct, so I will recheck the tables. It looks like that's where the problem lies.

Many thanks for your help.

Mark

Originally Posted by mic-d

Yes, but that is controlled by the height adjustment. The blades are set to be very slightly above the outfeed table so a blade grabs a straight batten of wood off the outfeed table and drags it no more than 2-3mm (done by hand of course)


Cheers
Michael

I've read that before, but I don't really understand it. However, it's not an issue for me atm, and when it is I will review sites such as these:
http://www.google.com.au/search?ie=U...tune+a+jointer
http://www.taunton.com/finewoodworki...F.aspx?id=2643
and see whether thewoodwhisperer has thoughts on the matter.

Originally Posted by MarkInBoatshed

With 2400mm boards across my jointer I am getting consistent concavity, about 1 to 1.5mm at the deepest point, approx in the middle. Answers to the theory questions will be greatly appreciated.

Thanks and regards,
Mark

Just a wild guess but have seen it many times before and guilty of it myself until I noticed what I was doing.

When feeding at first there is a tendency to push the boards onto the outfeed table. As the board gets to the middle, the natural process is to push down on the centre of the board as it moves over the knives. Which can account for the increase of depth of cut then pressure is transfered to the outfeed table and the remainder of the stock is pulled over the infeed to tail out.

For a test try feeding onto the outboards table for about the lenght of the table transfer your effort to then pulling the rest of the board over the knives from the out board side see if that eliminates the problem.


Cheers


Steve

Thanks Michael & Steve,<o></o>

Steve, I am following your advice and only putting pressure on the board on the outfeed table when the board is well along the table.<o></o>

I re-shimmed my tables and ensured they are coplanar. I believe they already were but now I had definitely eliminated that variable, and I still had a slight concavity (1mm in a 2400mm board).<o></o>

Michael, you answered my question about misaligned tables and suggested I look at the height of the cutter blades. You mentioned the test which I also used, which is that the knives, when revolved under a straightedge or flat-edged board, should move it along by about 3-4mm.<o></o>

Now that I was focused on the height of the knives, I remembered an article on the website NewWoodworker.Com.LLC, a site which has provided me with a lot of good advice. The article: Hands Off Jointer Outfeed Tables!
http://www.newwoodworker.com/jntrouttables.html<o></o>
had been taken by me literally.

Then I saw this comment:
http://www.woodweb.com/knowledge_bas...t_Problem.html<o></o>
From personal experience, I will guess that the knives are close to flush with the outfeed table, but not quite. The best way I have found to tell when the setting is correct is to take two boards at least six or seven inches wide by at least four or five feet long and joint one narrow edge of each. Then hold them together and sight the joint with a light source. If there is a gap in the center and they touch at the ends, then raise the outfeed table a smidgen (just a little!). Lower the outfeed by the same little bit if the boards touch each other in the center and the ends have a gap. Seeing is believing.<o></o>

Well, these guys were talking about the same thing, using a different method.

<meta http-equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><link rel="File-List" href="file:///C:%5CDOCUME%7E1%5CMARKFE%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml"><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <wompatibility> <wreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <wseAsianBreakRules/> <wontGrowAutofit/> </wompatibility> <wrowserLevel>MicrosoftInternetExplorer4</wrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:72.0pt 90.0pt 72.0pt 90.0pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]-->NewWoodworker.Com.LLC was saying: set your knives up perfectly and you will not need to make any further adjustments, stop fiddling with the outfeed table; it is a gross adjustment which will get you further from the mark. He has a companion article which explains cutter setup, <style>ons */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} h1 {mso-margin-top-alt:auto; margin-right:0cm; mso-margin-bottom-alt:auto; margin-0cm; mso-pagination:widow-orphan; mso-outline-level:1; font-size:24.0pt; font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:72.0pt 90.0pt 72.0pt 90.0pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]-->Setting Straight Jointer Knives<o></o>
http://www.newwoodworker.com/setjntknives.html<o></o>

What they are both saying is that the knives must be perfectly even with the outfeed table, not above by enough to move a straightedge 3mm, and not below.<o></o>

In the absence of an ability to set jointer knives within, say, 0.002” of the outfeed table, adjusting the table, by minute amounts, will get you there. I have tried it and solved my problem.<o></o>

However, I would prefer to set the knives perfectly in the first place. I would follow the advice in the Setting Straight Jointer Knives article except for the fact that I am next week installing a Byrd Shelix cutterhead, which means I have no alternative but to adjust the outfeed table (theoretically, once).<o></o>

If anyone is interested in knowing how the Shelix cutterhead performs, let me know and I’ll report back.<o></o>

Thanks again and best regards,<o></o>
Mark<o></o>

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Thanks Mark, that's excellent, excellent information. Next time I set my knives I'll do that. Thanks for the link, posting it and not letting me (us) go on following by rote what I've been told.

Cheers
Michael