Jointer Table Saw Jig Question

[JaGuR]

Hi guys and gals,

Newish to wood working and am about to receive my first decent table saw and have been watching a lot of YouTube vids in regards to a table saw jointer jig.

My question is, why can't i just use a straight edge on the table saw fence and run my timber through the ts with high points on the straight edge and the blade set to take the bow out on the outside ?

So basically just making the fence longer the the price of timber i am trying to straighten ?

What am i missing ?

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[Alkahestic]

When you use the TS fence as a reference, your cut edge will be parallel to your fence referencing edge. That means that unless your reference edge is already jointed and therefore flat and straight, your cut edge is just going to go from a random wavy edge to a copied wavy edge. Remember that the whole blade isn't cutting your workpiece, it's just edge closest to the front of the TS.

When you use a jointer jig, you'll note that the workpiece does not touch the table saw anywhere except at the cutting point. The jig provides the reference and since your jig is sliding along the mitre slot (which is hopefully straight and your blade is parallel to it) the workpiece will have the cut edge to be parallel with the mitre slot. Then you can use the jointed edge as a reference against your normal fence to get a board that is of the same width throughout.

[elanjacobs]

My question is, why can't i just use a straight edge on the table saw fence and run my timber through the ts with high points on the straight edge and the blade set to take the bow out on the outside ?

So basically just making the fence longer the the price of timber i am trying to straighten ?

Technically you can, but your fence would have to be long enough to have the high points in contact for the entire cut, which is not very practical as that requires a fence over twice as long as the piece you're cutting

[orraloon]

Extending the fence will also make it more prone to flex. The usual way is to use a strait board as a jig and attach the bent board to it. When you get the first edge strait then run that along the fence and get the other side strait.
How to Cut a Straight Edge on Crooked Boards - YouTube (https://www.youtube.com/watch?v=-693rYQITM0)
Regards
John

[malb]

As Elan has said, its a matter of length and practicality, jig can be a little longer than material (room for clamping each end to grip material) to get a straight edge on part, versus having to extend the fence to more than double the length of the material if you wanted to go that way. Then the secondary factors come into play, how rigid is the fence, does the outfeed end move away from the blade with the added leverage etc. Many fairly low grade to mid level saws have low quality fence systems that are locked at one end only and prone to movement at the other end in their natural state, then you add a lot of extra length and leverage, and it can move a lot more.

[havabeer69]

Dont worry mate, if your buying a table saw soon enough you will be buying:
a jointer, then a thicknesser then a sander then all these odd measuring and clamping tools, a pocket hole jig, an upgraded fence and DRO for your table saw, 2 different dust collectors because the first one wasnt quite right.....

Its a disease, and this is wood workers anonymous :U a safe space