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Help me understand table saw jointing jig

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Forum topic by Usma36 posted 03-09-2019 10:57 PM 771 views 0 times favorited 16 replies Add to Favorites Watch
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Usma36

16 posts in 303 days


03-09-2019 10:57 PM

Let me start with this… I am very new to woodworking. I saw a few videos of table saw jointing jigs. I don’t understand how they work. If I build the jig in the picture below and clamp down my piece to be jointed how do I get a straight edge if one side is not already somewhat flat. In this picture he seems to just clamp it on with no thought to how straight the board is in relation to the jig. If I clamp the board on and it’s crooked won’t the jointed edge be crooked? Do I just eyeball the placement of the board and hope for the best? I hope I am explaining this in a way that people understand what it is I’m asking. Thanks for the help.


16 replies so far

View mrg's profile

mrg

860 posts in 3567 days


#1 posted 03-09-2019 11:05 PM

If the board is not parallel you clamp the board to the jig and rip that side straight. Next you Rome the board from the jig and place the side you just cut against the fence. No you rip the other side parallel. Now you have a board with 2 straight sides parallel to one another.

-- mrg

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CaptainKlutz

2062 posts in 2062 days


#2 posted 03-09-2019 11:08 PM

That jig works by establishing a straight line.
That is definition of jointing an edge, it makes a straight reference line down length of board.

You are correct that the board can clamped at most any angle with zero regard for existing edges.
A single straight ‘jointed’ edge does not care about rest of board. Only YOU care about where edge is cut, as this defines the max possible width of board.

Does that help?

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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Usma36

16 posts in 303 days


#3 posted 03-09-2019 11:08 PM

So basically the board edges will be parallel to each other but not necessarily square?

View Jeff's profile

Jeff

512 posts in 3762 days


#4 posted 03-09-2019 11:15 PM

No, the single edge shown being ripped in the photo will be flat. This will be the reference edge from which you can then rip the opposite edge parallel to the first. And it will only be flat along its surface. It may or may not be square (or at a 90° angle) or parallel to any of the other faces of the board. It’s a beginning from which you work the other faces.

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clin

1072 posts in 1563 days


#5 posted 03-09-2019 11:17 PM

In case mrg’s explanation didn’t answer it, here’s another way to look at it.

To rip a straight edge on a board, the side against the fence must already be straight. The problem is your board doesn’t have a straight edge on either side.

The jig is a straight edge you clamp to the board. So now your board effectively has a straight edge (provided by the jig). So now when you make the cut, your board will stay in a straight line ensuring you get a straight cut.

A requirement is the edge of the jig against the fence must be dead straight.

This same type of jig can also be used to make tapered cuts. For example you need a board that is 4” wide at one end and only 3” wide at the other end. Assume one side is already cut. So you need to now cut the other to create the 4” to 3” taper. You clamp the board in at whatever angle it needs to be so your new cut will give you the 4” to 3” taper.

-- Clin

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MrUnix

7533 posts in 2766 days


#6 posted 03-09-2019 11:18 PM

So basically the board edges will be parallel to each other but not necessarily square?
- Usma36

Once you have established the straight parallel sides, you can easily cut it to square.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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clin

1072 posts in 1563 days


#7 posted 03-09-2019 11:19 PM


So basically the board edges will be parallel to each other but not necessarily square?

- Usma36

You are correct the jig doesn’t not guarantee that the edge will be square to the face of the board. Your board must already have a flat face AND your blade angle must be set to 90 degrees.

Of course th jig must also be flat, as wit would be if made from plywood.

-- Clin

View Usma36's profile

Usma36

16 posts in 303 days


#8 posted 03-09-2019 11:37 PM

Thank you. That makes sense. That’s kind of what I was thinking. My next question is can someone point me to how I can square up a board once it’s jointed in the table saw if I only have a table saw and mitre saw?

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CaptainKlutz

2062 posts in 2062 days


#9 posted 03-09-2019 11:57 PM


Thank you. That makes sense. That’s kind of what I was thinking. My next question is can someone point me to how I can square up a board once it’s jointed in the table saw if I only have a table saw and mitre saw?

- Usma36

Do you mean square up face of board, or ends?

Cutting the ends square is easy once you have parallel sides.

Squaring the face of board requires jointer, or hand planes.
Getting the two faces parallel to each other, requires planer or hand planes if you like torture.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View Lazyman's profile

Lazyman

4225 posts in 1955 days


#10 posted 03-10-2019 01:23 AM

Not sure that anyone actually said it so I will say it just in case it wasn’t clear…you only cut the first edge with the jig. Once that edge is straight, you remove it from the jig, put that straight edge against the fence and cut the other edge parallel to it. Once you have one or both edges jointed, you can square up the ends either with your miter saw or the miter gauge on the table saw.

As mentioned above, if the faces of the board are cupped, bowed or twisted, that board is probably not a great choice for this sort of jointing. These problems are not easily corrected with just a table saw or miter saw. It is certainly not an operation for this jig.

Since you said you are new to woodworking, I would also like to make sure that you have studied the safe operation of a table saw. The jig helps mitigate some of the risks but cutting non-straight and non-flat boards can be very dangerous if you don’t know what you are doing. There are plenty of videos and other websites available that explain the dos and don’ts of using a table saw. Please make sure that you understand them before proceeding.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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knotscott

8347 posts in 3943 days


#11 posted 03-10-2019 12:05 PM

Since you’re new to woodworking, I’‘ll point out that there’s a difference between face jointing and edge jointing. Two separate actions that both need to be addressed in order to get a truly flat, straight, square board. Otherwise, any irregularities throughout the length of the face won’t be removed, and can effect how square that jointed edge is.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View Usma36's profile

Usma36

16 posts in 303 days


#12 posted 03-10-2019 12:51 PM

I would like to make sure the edges are square so I can glue several together into a panel I bought the wood at a mill and they planed it.

View hairy's profile

hairy

3004 posts in 4100 days


#13 posted 03-10-2019 01:39 PM

Watch this: https://www.thisoldhouse.com/how-to/build-it-rustic-dining-table-jimmy-diresta

I’ve been doing this with plywood that I rough cut with a circular saw, then finish cut on the table saw. This probably won’t work in all situations, but it does work. Be sure to rough cut oversize.

-- Genghis Khan and his brother Don, couldn't keep on keeping on...

View Lazyman's profile

Lazyman

4225 posts in 1955 days


#14 posted 03-10-2019 02:05 PM

It’s great when a Youtuber says they are going to show you how easy something is to do and then they whip out a $1000+ Festool Domino to make loose tenons for the joinery. Also, his technique for jointing the edges free hand on the table saw is not one a beginner should try. Diresta has 3+ decades of experience with a table saw and without an understanding of what can go wrong and especially why, you should not try his technique yourself. He didn’t explain what to watch out for and how to avoid a kickback. Use the jig. It will actually be easier and more importantly it will be safer.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View knotscott's profile

knotscott

8347 posts in 3943 days


#15 posted 03-10-2019 03:09 PM


I would like to make sure the edges are square so I can glue several together into a panel I bought the wood at a mill and they planed it.

- Usma36

Square edges are heavily dependent on how flat the face is, so you will want to address getting the faces flat too, which is best done prior to the edge jointing step.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

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