Using guide rail to joint an edge?

[vkumar]

I was removing a rough edge on a board 8 foot long  using 2 connected guide rails and  TS 75 saw.

The guide rails were a 1080 and a 1900.  I used the recommended procedure of bringing the rails close together but not touching, putting  a straight edge against  one of the edges, and then snugging the connector screws.

I then ripped 2 boards.  When I but the 2 edges against each other I can see that they are not quite perfect.  There is a 1/16 th gap in the middle. 

Is this the best I can get out of the guide rails?  Or is something wrong with my procedure?

Any help would be appreciated.

Vijay

 

[greg mann]

There are several things you can do to mitigate this. First, are you sure stresses were not relieved as you ripped the boards? Let's assume this is not the case. Use the longest acceptable straightedge you have when joining the rails. I would want, at the very least, 4 feet of straightedege to assure good alignment, longer would be better. Whatever misalignment you have gets doubled when you flip the boards face to face, so your 1/16 represents 1/32 misalignment in the rails. Also, you can start by aligning the rails on the work so that the largest portion possible is covered by the longest rail. This will minimize the amount affected by any misalignment of the shorter rail added to get enough length.

Another technique is to cut one edge and then but the second board up to the fresh cut and clamp the board in that spot. Then recut on the rail as though you were ripping one board. Any variations will be parallel to each other as represented by the kerf. This is very easy to do. Even if the edges are right off the tree it only represents one extra cut.

 

[Page]

Here is Bob's procedure on edge jointing with plung saw.
Edge Jointing

 

[nickao]

What kind of wood?

If it is just framing lumber for instance you could have easily cut it stick straight and the boards bow during and after the cut because of the internal stresses of the wood, as the previous poster mentioned. Many times I have had to cut construction boards slightly bowed to get then to match up.

Using furniture grade lumber(clear)  kiln dried to 6-8% is about the only way to eliminate the wood stresses from the equation and I have still seen lengths that long slightly curve after cutting. If the wood has a moisture content of 12%, which is not bad, it can easily still bow. Even if you are doing everything right the wood may still change a little after a long length is ripped.

Test your cutting technique on plywood and you will know if it is your procedure or the wood. The ply is not effected by moisture at all unless it is literally wet with water.

Nickao

 

[woodshopdemos]

Here is Bob's procedure on edge jointing with plung saw.
Edge Jointing

Yes, Bob Marino did rip long boards with edges good enough to glue up without further jointing but a long guide rail was used. From the sounds of things, you have a gap where the two rails joined.
  Was Bob lucky when this happened? No. I have done it dozens of times since. Don't have to edge joint any more.

 

[vkumar]

What kind of wood?

If it is just framing lumber for instance you could have easily cut it stick straight and the boards bow during and after the cut because of the internal stresses of the wood, as the previous poster mentioned. Many times I have had to cut construction boards slightly bowed to get then to match up.

Using furniture grade lumber(clear)  kiln dried to 6-8% is about the only way to eliminate the wood stresses from the equation and I have still seen lengths that long slightly curve after cutting. If the wood has a moisture content of 12%, which is not bad, it can easily still bow. Even if you are doing everything right the wood may still change a little after a long length is ripped.

Test your cutting technique on plywood and you will know if it is your procedure or the wood. The ply is not effected by moisture at all unless it is literally wet with water.

Nickao

The wood is red oak, quite dry. 4/4 and 8/4 stock.  I was removing just a scant 1/8 to 1/4 inch of f the edge to get  a straight edge.  I'll have to try this on plywood.  Bob's method of cutting through 2 thicknesses of stock probably compensates for the error on each good enough for edge gluing , but does not guarantee a straight edge (I think).

After a clean one bad edge I need to rip the stock to width, so that is why I am concerned about the straightness.

Some more investigation to be done on my part I think. Keep the ideas coming.

Vijay

 

[nickao]

You should be able to get great results with that wood.

 

[JayStPeter]

You should be able to get great results with that wood.

Agreed, done it a number of times.  Even with 2 55" rails attached I've been able to joint 6' pieces of Maple/Cherry/Walnut for glueup.  I use the top of my tablesaw to align the rails.  I just stand them on edge while screwing them together.  Take your rails and put them against something reasonably straight and see where the problem is.

 

[woodshopdemos]

[/quote]

...  Bob's method of cutting through 2 thicknesses of stock probably compensates for the error on each good enough for edge gluing , but does not guarantee a straight edge (I think).

[/quote]

I don't know where you got the idea that he cut two boards at once. He didn/t. The perfect edge came from the long guide rail and the TS55 (ATF55 at that time) ability to follow it.

 

[greg mann]

...  Bob's method of cutting through 2 thicknesses of stock probably compensates for the error on each good enough for edge gluing , but does not guarantee a straight edge (I think).

[/quote]

I don't know where you got the idea that he cut two boards at once. He didn/t. The perfect edge came from the long guide rail and the TS55 (ATF55 at that time) ability to follow it.
[/quote]

John,

Not trying to be picky but here is a quote from your article about how Bob did it. I agree that it is not necessary with one rail to do both at one time, and my suggestion above was still another alternative, cut one to get rid of a waney edge, cut the second but leave it as cut with the rail in place, set the first up against it and recut. It is something like cutting both at the same time. There was a reference to cutting through two thicknesses. I don't recommend that as it necessitates flipping one back over and will double any error that might be left. Of course that would be no big deal with a single rail.

Quote from your site:

" He disconnects the vacuum hose from the plunge saw and uses it to vacuum any dust or splinters that would get in the way of the two boards. With the area clean, he brings the loose board over to the one that is screwed down and places the guide rail and clamps so that the saw blade can cut both pieces at one time. This is key ? the kerf of the blade must remove a little from each of the boards. In that the guide rail is exactly aligned with the saw, placing the rail to bi-sect the kerf is easier than it may sound."

 

[nickao]

Wait a second, I saw on Johns sight a technique where he absolutely cut two boards on top of each other at once too.

I have not looked at it in several months, but I am sure that technique was on his sight. If not I must be going crazy.

Nickao

 

[woodshopdemos]

I can't compete with you guys.  You are absolutely correct. But my writing wasn't. To joint the two edges, the first cut was done on one board. This then was screwed down. The second board was placed next to the first and butted tightly against it. He then sets the guide rail to cut a full rip of the second board. The scrap is removed. Then he pushes it slightly until it is touching the first board. The guide rail is placed so that the kerf will get some scrap from both boards.

I will try to correct the procedure and pictures.

 

[nickao]

If I understand correctly that would work fine but it seems to me the boards could not be very far off for this to work? They would have to be fairly straight to boards to begin with. Is that correct?

 

[pmkierst]

Then he pushes it slightly until it is touching the first board. The guide rail is placed so that the kerf will get some scrap from both boards.

Ah, same principle as sawing a miter joint to make it match perfectly. Pretty clever.

1/16" is a pretty big gap, but if you can get it down to 1/32" or so, it should be no trouble to clamp up over that length I think. It is pretty hard to get that long of edge "perfect" (and get it to stay perfect is even harder).

 

[nickao]

Yes, that's what I thought and for that to happen those two boards need to be pretty close to begin with right? If the boards are wavy more than an 1/8" or so out from each other the technique will not work, correct?

I am having a hard time wrapping my head around that as it seems some preliminary steps are missing or I missed them.

Nickao

 

[pmkierst]

Yeah, they would have to be within a kerf, though you could run twice (moving in after the first), though it could be tricky. I think the procedure would demand "regular" jointing first (i.e. as described originally) and then the second pass with both. But I think it is important to remember that over very long joins, you don't need the gap down to 0.005" or anything.

 

[greg mann]

I am quoting myself from a previous post. How is that for arrogance? :

"and my suggestion above was still another alternative, cut one to get rid of a waney edge, cut the second but leave it as cut with the rail in place, set the first up against it and recut"

 

[woodshopdemos]

If I understand correctly that would work fine but it seems to me the boards could not be very far off for this to work? They would have to be fairly straight to boards to begin with. Is that correct?

You are absolutely right. You can get that straight and close by your first rip with the gyude rail. It is almost "jointable" at that point. The follow up just makes it real tight.

 

[nickao]

Got it, basically splitting the kerf between each board.

Thanks guys,

Nick