Hi folks.
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A quick question on tear out of box joints.
The box joints I’m cutting are as wide as the dado cutter will go and about 26mm deep in reclaimed pine on the end grain.
I’ve tried everything I can think of to reduce the amount of tear out; scoring a line, tape, keeping the board tight to the jig (these boards are big) but some of the tear out is horrendous.
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Any suggestions gratefully accepted.
Glynn.
Replies
This might not be feasible for you since you say these are big. But I usually clamp (handscrew type work well for this) the opposing sides together and cut them together. That ensures both sides are identical as well as providing a backer board for the leading piece. If I'm cutting something that wants to tearout easily, I've sometimes clamped another shorter backer piece to take care of the backside of the trailing board.
If you build it he will come.
Doulas
If you see the attached pic you might see my dilemma.
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Glynn
I cant really see the tearout in the pic but I've done the 2-fer cutting on some almost that big. I'm not sure if you're planning on re-making, cutting shorter and re-doing, or what. But I'd definitely do it that way if I were doing it. Just line up the board edges and end, plus another scrap piece and throw some clamps on them and cut them at once. The scrap piece just needs to be tall enough to get a clamp across all 3 pieces plus the jig fence without tipping the work by clamping it to the fence, or over the fence if you dont clamp to that as well. You'll end up with a backer on both pieces that way, and it should be darn near impossible to get tearout. I've cut a number of 1/2" and 3/4" baltic birch ply ones that way which tends to get some pretty bad tearout if you dont have backers behind the work. Your fence is tall enough that I'd probably clamp to that as well for a bit extra stability. Bit of a pain repositioning the clamps for every cut, but you're also cutting 2 for each setup. My preferred clamps for this is the longer handscrew type. You can get them really tight so nothing shifts without worrying about clamp screw divots plus if you position them in a convenient spot, they sort of become jig handles as well.
Doug
If you build it he will come.
Edited 6/7/2008 10:47 am ET by douglas2cats
Douglas.
Why don't the attachments always load?
2nd time lucky.
Of course that’s it simple a LARGE backer piece.
I spent about 3 months putting this jig together so I don’t really want to change the way I do it. Besides it used to take me far too long to get the boards to that condition.
See attached for how the wood started out.
Cheers
Glynn
I've got a smaller version of your jig and have the same problem with pine and cedar. What helps me is to back the work with a 1/8 piece of hardboard. After each set, I just rip off the fingers on the hardboard and start fresh.
Joe
Knuts
Yep See Attached
Glynn
Do you have another board behind the workpiece to support the fingers during the cut? If not, use one. Any tear out will be confined to the sacrificial backer board.
-Steve
Glynn,
The "secret" to clean finger joints cut with a power tool is to use a backing piece to support all the edges where the blade (saw or router) breaks through. That backing piece should be made of a hard, dense-grained wood like beech or rock-maple, with the end grain facing the blade.
Put an end-grain piece behind the work piece when the first cut is made, so that the cut also creates the finger shape in the backing board end grain. The end grain of beech, for example, is very fine and tough. It will prevent any breakout on the workpiece, as long as the backing piece is kept registered to the blade and the work piece is held firmly to it (no gap between workpiece and backer).
I make lots of finger-jointed drawers and boxes using a router table with a cross cut sled, in the same way as you are using your dado. There is never any breakout at all when the cross cut fence has end-grain beech as the backer to the work piece.
Of course, you also need a sharp, true-running blade.
Lataxe
"End grain" - never seen that suggested before, but seems inspired. Likely could fabricate a relatively narrow width, glue to larger sheet stock, and go to the races. Must be something to drinking all that tea across the pond there . . .
Don,
I confess that the end grain backer board is a Lee Valley concept, included in their router table sliding carriage in the form of a block captured in a dedicated hole using pronged nuts that slide in the carriage T-track. The block is a cube of beech around 1.5" all round, with the end grain presented as the area the cutter will break through to.
Although a block lasts a good while, it can be quickly replaced if the cutter-shaped hole begins to get a sloppy edge; or if different sized cutters are used.
Lataxe
Glynn,
I’m cutting are as wide as the dado cutter will go
Couple of questions:
Do you get the same results when cutting smaller box joints? Do you experience tearout with just a sawblade cutting? Does a backer board solve the problem? (Sorry 3 questions :-) )
I'm curious to know if you're either pushing the limits of the dado head and/or there is a lot of runout with the TS arbor.
Regards,
Let us know
Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
Kiddervilleacres
Tear out with this wood is a bit of a nightmare.
I will try using a LARGE backer but I already have some replacable Ply in place that is acting as a backer already. The problem seems to be holding the work tight up to the backer and the rest of the Jig. I’ve not done a whole lot of testing on other woods to see the out come. As I seem to be stuck making large boxes for every one.
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See attached
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Glynn
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Glynn,
I'm curious as to how things work for you with backers boards and like your approach of screwing a replacement. One would need to make sure the leading edge remains dead flush with the fence though.
I have a new Freud box joint set and want to begin using it. It allows for ¼" & 3/8" box joints so would like to make a jig to accomodate both widths. This might get to be a little tricky though as to proper spacing.
That's a mighty handsome box you made and if that stack of wood is representative of your materials, then let me be the first to congratulate you on your stock preparation. The one on the right looks a bit ominous to me with them nails peeking out!
:-)
Regards,
Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
KiddervilleAcres
Well thank you for the complement but really I’ve still got a long, long way to go with these before I’m going to be happy with them.
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I was very lucky to find that wood. That pile is one of 3 I had. All from a flat roof. A guy was burning it, 8” wide 1 ¼ “thick. MADNESS!!!!
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It’s got 3 and 4 inch nails and felt nails on one side and a skim coat of concrete on the other. Needless to say I am now a master of the art of sharpening thicknesser knives.
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As to the jig.
The jig I’ve made up will go to any width (well more then my dado set will go).
And last time I had to set it up from a different cutting width (last week) I had it set up and cutting in bout 10mins. Really good apart from the tear out. I’ve kept a known good test piece and I use it to set the spacing up on the jig it works a treat.
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I took me a long time to get my head around how the jig works
If you want a laugh and have some time take a look at this Knots link
http://forums.taunton.com/fw-knots/messages?msg=38123.1
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It’s only short.
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Glynn.
If you're using a backer board, but still getting tear out, the most likely reason is that the workpiece is not firmly held to the backer. Even a barely perceptible amount of slop can lead to quite a bit of tearout.
-Steve
Saschafer
Quite but how do you stick the board to the jig without sticking it?
Glynn
If you can get a couple of F-clamps through the holes (hand holes?) it should help.
-Steve
Saschafer
Oh how I wish.
Tried that. Took nearly a whole hour to cut all the sides but I just couldn’t get it tight enough against the jig (never can).
Glynn
One of the simplest and cheap ways to reduce the tear out from the dado blade is to apply some tape to the back of the board before cutting. I use the blue painters tape on all kinds of work to back up the cut. If you press it down very very firmly it can reduce or prevent the tearout completely. Then the tape comes off very easily. This works with table saw cuts, router cuts, chop say cuts, handsaw cuts, etc. Also you could scribe a line at the base of the finger joints if you don't mind seeing the baseline, or plane them away after. The more teeth and better the dado chippers will probably also help.
mbaker00
I’ve tried the tape though it gave better results they were still far from acceptable. I do have chippers in 5 I think. I’ve scored a base line but the tear out runs a lot deeper then the score line ever could.
Nice try.
Glynn
Dear all
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I think I will try a large MDF backer board with double sided tape.
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Do you think tape will be the best thing to attach the board to the backer?
Due to the fact this wood has enough holes in it already I don’t really want to screw in on.
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Thinking about this a minuet. What would have to be done to allow me to cut all the joints from the front? As the tear out inside the box isn’t so critical.
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I suppose I would have to cut the panels over size, cut the joints and cut down to the nearest whole joint.
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Guy,
It’s got 3 and 4 inch nails and felt nails on one side and a skim coat of concrete on the other.
I know this can be frustrating. I went back to the beginning of this discussion and a couple of things stood out. One is the above comment from you. I think that no matter how diligent you are cleaning old boards up, you never seem get all of it, or at least that's been my experience. Concrete on one side, old nails driven into the other side through felt (or was it roofing shilgles?). Long and short is there has to have been foreign matter left in the wood?
Another comment is that you said at one point that is is/was very difficult to keep the workpiece clamped tightly to the backer board, or words to that effect. This leads me to suspect that the cutter(s) are dull.
If you use a known sharp single blade, do you experience tearout using a backer board as per above suggestions? If you remove all the chippers and mount just the two cutters and try it, do you get tearout? Also there has been no mention of what TS you are using; i.e. is it powerful enough to spin the dado blade(s) whilst taking the max. cut? What happens if you cut a narrower dado/box joint?
Sorry for all the questions but I don't know of a simpler way to help you narrow down the possibilities to solve your problem. Bottom line is that I suspect dull cutters and/or underpowered TS for the size joints you are attempting to cut.
Also, adding more meat in terms of thicker backer boards I suspect is only going to exacerbate the problem.
Regards,
Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
Edited 6/10/2008 7:34 am ET by KiddervilleAcres
Bob
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As to tear out with single or double blades I’m unsure as I’ve never tried it.
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As to the TS it’s an English (well Chinese) brand SIP 12” with 3000 watts that’s 4.02306 HP. I don’t think there’s a problem with the saw.
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On the Dado set front there could be an improvement. After looking at the set there’s a heavy build up of residue on the teeth and they don’t look as sharp as I think they could.
This is a bit surprising as I didn’t think the amount of work they have done was excessive but this wood is a bit sappy so may be a going over with a diamond card is in order (that’s gonna take all b****y day).
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Do you know does this saw blade wax stuff you can buy really do anything.
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Glynn
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Glynn,
Don't have any experience with blade wax. I use Simple Green here in the states and that works really well. I would think that practically anything that will disolve pitch should work. I use a brass brush to clean all my cutters of buildup.
Pine has a nasty habit of gooking up blades and I'm having a similar issue with some Western Red Cedar, even though it is supposedly very dry. I'm also experiencing tearout no matter which way I plane the boards and am confident that the blades are sharp.
Suspect that because it is so dry the fibres tear out easily as I do not have the problem with birch, cherry or even pine that is not as dry. This makes sense to me as one test for truly sharp chisels/blades is to pare pine endgrain.
I hope that is the problem with your situation as the fix is relatively cheap and easy to remedy.
Regards,Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
Glynn,
Just thought of something else too.
When pitch starts to build up, even a little bit, it causes the blades to labor through the wood and thus generate a lot of heat. The heat bonds the pitch to the teeth even more and also tends to collect more and more as time goes on, and not a long time either.
Just me experience, not necessarily based on fact.
Regards,Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
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