Hi there.
First post on this site for me, so here we go (be gentle).
I’ve set up a dado blade in the table saw to cut box joints for a large wooden chest or 3 or 4 or 5.
After spending no small amount of time getting the spacing right I started cutting the real stuff. 3 of the 4 sets of joints went fine and then on the last set the fingers are progressively moving out of line by about 1/32 each finger and that’s a lot by the time you get to the end of 18 fingers and I don’t know why.
These chests are large and are made of reclaimed redwood which take an age and a half to prep and glue up (I think it has something to do with all the nails, Tar and concrete stuck to them).
The jig uses an up side down c section that is over the top of the fence and the other end is attached to the sliding mitre gauge to try and keep every thing sliding together. It’s held together with MDF reinforced with a backing piece.
And none of it looks like it’s moving out of place to me but with so small a movement needed how can you tell.
It takes far too long to get to this stage just to be clobbered by 1/32 can any body help!
Thanks.
Edited 10/18/2007 3:18 pm ET by Guy Forks
Replies
Obviously, something is out of whack with the jig. If the alignment finger hasn't outright moved out of position, it might now be a bit too narrow. It's hard to say without seeing a photo of the jig.
By the way, neither of the two photos you posted look like redwood.
-Steve
Saschafer
I’ve taken some pics and added them below.
One shows the failing fingers (I’ve had to cut the left hand side of most of the fingers that are pointing upward). The others show the jig.
Your right in these pics the wood just looks like Pine.
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Did you cut the two halves of the joint at different times? It looks as if the position of the alignment finger changed between when you cut one side and when you cut the other side.
-Steve
I cut both sides of the end section then one end of the long section straight after.
The thing is the indexing finger is glued and screwed and the whole jig is prevented from moving from side to side with the sliding mitre scale.Now am I right in thinking the only way this cock-up can happen is if the finger or whole jig has moved?
"Now am I right in thinking the only way this cock-up can happen is if the finger or whole jig has moved?"
There are only two possibilities that I can think of:
1) As you say, the position of the finger has moved with respect to the blade. Is there any side-to-side play in the jig? Does the miter gauge bar fit closely to the slot?
2) The wood itself has changed dimensions after the cut. This could happen if one of the pieces started out considerably wetter than the other.
-Steve
Perhaps I am not understanding this correctly but from the last photo (DSCF0090.JPG) it looks like the depth of cut is changing. Is the arbor moving slowly up or down from vibration during cutting?
Rich
The Professional Termite
Edited 10/19/2007 8:59 am ET by trialnut
Gentlemen
I think I’ve cracked it but I’m not too sure why.
First I changed the C section running over the fence as there was a very small amount of play in a sea-saw way (That answers your question I think Steve). This didn’t seem to do too much as the last test piece was still out though by a smaller amount.
Then as the Jig was running like a bit of a dog so I spayed the whole lot with half a can of PTFE dry lube in a fit of frustration. I knocked out another test piece; was so relived with the results I went and cut one of the main joints on the chest and as pictured below it looks better then the others. It’s spot on (needs cleaning up mind)
I don’t know what moved last time and I’m having kittens in case it happens again.
I don’t think the Arbour is moving (it’s locked in position)and the wood certainly isn’t wet.
The one other thing I did do was to tighten up a washer underneath the sliding mitre scale.
If the only thing that can cause this is a sideward movement then it could have been any one or a combination of the things I’ve listed.
Thanks
Glynn
Picture 94.. I assume you miter is on the left side of the blade?You should make a table on that saw to support (as in level to the saw) to support the end of your miter fence..As I see it in the picture, it WILL tip unless you are very watchful!The picture (92) looks as if the fingers are slanting inward into the fingers more and more (from right to left) as they progress. Am I seeing things?Edited 10/19/2007 10:13 am by WillGeorgeEdited 10/19/2007 10:17 am by WillGeorge
Edited 10/19/2007 10:17 am by WillGeorge
Gents
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Will, you are dead right in that I should be using the sliding table (on the left side of the blade) seeing as it is fitted and I will defiantly try that next time out.
I’ve checked out the fingers and they are pretty straight.
Interesting point. I’ve just finished cutting the joints for 2 whole chests. Now on the 2nd from last set they ended up misaligned (they were out a very small on the set before) but I continued and the last lot come out fine ergo I did something different so if any one has the power of telepatheticness can they let me know what it was.
How does this happen? Could it be something I’m doing with the spacer that you use when you’re starting with a cut in the very corner you know the piece you place between the blade and the indexing pin?
Glynn
I hate to say it but it's the design of the jig. You have so much leverage on your fence you are moving your fence by let's say 1/128 of an inch, this adds up to your 1/32 gap by the end of the board.
Make a new jig but make one like a sled that rides in the miter slots. Then you are moving the entire unit as one. make two backs for the sled with the pin mounted to the front most back. Make a few slots so that you can adjust the pin board side to side and tighten with screws. make sure the pin is exactly the same width as the dado.
If you make the new jig your finger joins will line right up.
If there's some gap just soak it in water and let the wood swell :)
Gotta second this one, it's probably the jig. Using both mitre slots with well-fit runners will not only be more accurate it should also be repeatible.John O'Connell - JKO Handcrafted Woodworking
The more things change ...
We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized. I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.
Petronious Arbiter, 210 BC
Gents
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I could try the sled but the reason I didn’t go with that idea in the first place was the size of the stuff being cut. Its 24in wide 40in tall. That’s a big sled and I didn’t think the slots in the table would give me the stability I was going to need. A sled seems like a good idea for material that’s only 6in high but 3ft seems a different matter. I found that getting something that big to run smoothly and being able to push and pull with only one hand (whilst trying to steady the stuff with the other) is a bit of a party trick (may be that says more about my woodworking abilities which aren’t that great).
The question that still begs an answer is what went wrong when 15 cuts went fine and one didn’t and does this not also indicate that the jig in principle works and what’s to say that I wouldn’t have the same problem with a sled.
Then again what the hell I’ll try it.
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Tanks
Glynn
Interesting point. I’ve just finished cutting the joints for 2 whole chests. Now on the 2nd from last set they ended up misaligned ..COULD be you just got in a 'bit' of a hurry.. Thought you were near finished and got sloppy?
Hello
There are lots of good ideas here. I personally like the idea of making a new jig and using a table sled instead of using the mitre gauge. One question although. Have you checked the Dado blade to see if it has loosened up while cutting. perhaps it has a slight wobble in the blade ?That would cause some extra play an take your measurement off a little per cut.
Good luck!
what you have done so far looks fantastic! keep up the good work. ;-)C.A.G.
There are lots of good ideas here. I personally like the idea of making a new jig and using a table sled instead of using the mitre gauge.Right on.. But then again there is that sawdust that collect between the 'STOP reference' and the end of the 'stick' Anybody mention that?
Read Talma's input again. That is the solution. The one slot ride with the "Rube Goldberg"on the fence is your problem. Make a jig with 2 runners that fit in the table saw slots is the key. Your troubles will be over.
Is it possible that the screws holding the jig onto the miter guide are moving? They should be large to just fit in the miter's screw guide. High screw pressure may not be enough to stop lateral motion with the vibration and pressure the guide sees.
Is the slot cut by the blade in the jig getting bigger? If it is then the jig has to be moving relative to the dado blade.
Are you cutting from the bottom edge to the top edge on every side? (Or visa versa?) I could see racking due to the wood dragging differently depending on if you have more wood to the right or left of the blade. And if you happen to start at the top on one side and the bottom edge on the other side that set would fit differently then a set done with both starting at the top or bottom. If this true flipping one of the sides over should lead to a better or worse fit.
Edward
Gents
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There was a small mount of sea-saw motion along the fence with the first jig but I took just about all you could out with the mark 2.
And on the second attempt I made sure to push the jig in the same spot and hold the work piece the same way each time.
I vaguely remember lightly brushing the end of the fence with the side of my leg but I didn’t think anything of it as the fence was locked down.
I was careful not to hit the jig with the work piece and if I did hit the fence or move it in some way how come the final set of joints marries up with all the rest when the set before were out.
I think I done something different right at the start maybe something to do with the spacer block I don’t know and that’s the trouble.
This jig sucks it’s just far too temperamental for the amount of cuts and accuracy needed. It needs beefing up big time. I need to do away with a lot more variables.
This system works fine for shorter boards with fewer cuts.
Overall discrepancy 4mm divided by the number of cuts which was 13 = an error rate of 0.3mm per cut.
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Has anybody else tried this with these size boards and if so how did you do it.
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Glynn
Edited 10/22/2007 4:36 pm ET by Guy Forks
Hey man,Not trying to get you to drop a bunch of cash here, but I'm going to give you a bit of my experience. I had similar problems with cutting box joints with a dado on a table saw. I'd think I'd have everything set up perfectly, then I'd start cutting and end up destroying a lot of good wood.Then I bought a WoodRat. It has solved my problems. It takes some time getting it set up, but it cuts finger joints like a champ. Not to mention dovetails, mortice and tenons, etc. Also, I recently bought a bunch of those Festool Dominoes and a matching router bit, and it works just like the Festool. It does a lot of different things very well. If you are planning on doing a lot of these chests, a 'Rat might be worth looking into. If you have any ?'s about the 'Rat, let me know.JH
I have not done joints the size you are doing but I have seen large done on a sled.
Personally if I were cutting them I would just do it by hand, but that's my personal preferance. I would also do dovetails, but I do like the look of the box joint on the piece.
Anyway a sled that uses both miter slots and is at least 1.5 times the size of the edge you are jointing would work great. The width would ensure 75% of the edge was on the sled at all times. By using runners the length of the slot would pretty much eliminate all side to side movement
You would need to make sure that both ends of the jig were fastened to each other and signifigantly long enough prevent twist. I would make it out of 3/4" mdf for the flatness and strength, and make it about 2' long. Make sure to put in some sort of side to side adjustment.
I think this would work great for you
I had a similar problem. The project called for 1/8 in fingers across a 10 in board. Test cuts on 3 in or so boards were perfect but by the time I got to the end of a 10 in board they were way out of line by as much as a 1/16th i.e. half a pin. I had a spendy miter gage (Incra) and called them to complain, thinking it was slop in the pivot bolt. "Ah! Finger joints" the very helpful tech said. He suggested that the shoulder bolt used as a pivot pin may have been at the low end of the tolerance and he sent me a new one free of charge that was at the high end of tolerance. This made no difference.
I eventually fixed it by making sure I pushed the work through with my hands in the same place every cut. i.e left hand well to the left, thereby taking up slack in the miter gage in the same way every cut. That did the trick. So before you buy a Wood Rat check your technique.
Haven't done these for years but when I did, I found that mating edges need to be cut at the same time to prevent the progressively large error you're talking about. Clamp the boards together with the appropriate offset and bob's your uncle.
Hey guyforks
that o4 picture doesn't look like a finger joint it looks exactly like my drive way????
levity please
Hey peoples
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I think the concrete (pic04) was laid by the same clown that put up the stud wall in my kitchen; it’s level at the floor and 1 ¾ in out at the ceiling.
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O.K so correct me if I’m wrong but I’m getting a vibe that may be I should make up a sled?
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With two runners?
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O.K this I shell tackle at the weekend.
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Mr knuts that jig looks mighty fine. How long are the runners on that jig?
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Cheers
Glynn
Guy
I think you need to build a new jig or what I call a sled. Not to quibble on names the important thing is to have a bed for the boards being cut to travel in a straight line and cut the same path in the end grain of the large boards you are preparing for the front, back and sides of your box.
Rather than tell you how to make it, I think it would be helpful to look at Gary Ragowski's video The complete Mortise and Tenon Joint. He uses a sled that will work very well for you if you adapt this commonly used tool for the table saw. Note the boards on the front and back of the sled. You need these to keep the base together and straight once you have run the tool over the blade(dado knives in your case).
Hope this helps
dan
Mr knuts that jig looks mighty fine. How long are the runners on that jig?
No runners...mounts to your miter gage. Always apply pushing pressure the same way. This plan was in one of the mags website a while back. Sorry, don't remember which. This one allows you to fine tune both the finger & the notch spacing. The actual notch is the cutter width.
Hi Mr Kunts.
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I’m at the point where I would like to try and replicate that box joint jig of yours. Seeing as it looks so fine. Is there any way you could post a few more pics of it so I can get some idea of exactly how it’s laid out? And are you able to adjust the width of the spacing block and the block it’s self.
Any help would be much appreciated.
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I built mine with variable spacing from 1/4 to 1 1/8. I mount it to my miter gage, but you could put miter tracks on it easy enough. And you could certainly make this taller & wider for your chest, though for big pieces I use my Woodrat. In trying to find where I got this plan from, I came across 5-6 jigs of this type (Variable spacing) on the net. You can see more on this particular jig at:
http://www.plansnow.com/boxjoint.html
with better pictures than I could provide too!
Mr Knuts
Cheers I did see the plans now one.
I'll down load that and see what it says.
Thanks G.
The plans for the box joint jig are in Shop Notes Issue 8 Vol 2. Here is one I built a couple of years ago.
I found this jig to be the best I've ever made. It can be used on the table saw or router table. Although now I use my Woodrat most.
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