Tips on jointing

[Dan Voight]

I have two wonderful two piece red spruce tops that I attempting to join at the time and I think I need to be pointed in the right direction. I am using a brand new Delta 6" variable speed jointer. I thought that would do the trick.

Here is what I've been trying:

I get the inside surface of both pieces flat by running them across the jointer.

Then I plained the outside with my Wagner safe-T plainer down close to my final arching height.

Then I clamp the two halfs together by thier inside surfaces and run them across the jointer.

I thought that sould do it but something is not right. Anthing would help.

Dan

[austin]

Dan,
Well for one, I would use a hand plane instead of a powered jointer. I can't seem to get a perfect joint with anything but a hand plane, and a #7 at that.

Two, clamping the two halves together is probably distorting them slightly and thereby giving you an inaccurate joint.

I used to do my joints in tandem, planing one and then matching it to the other against a light to see if there are gaps. Now, I match it to a straight edge up against the light. When both halves match the straight edge (i.e. no light through the gap) THEN, and only then do I put them together to check the fit. 9 out of ten times they are perfect at that point.

Also, when I joint, I run the wood over the plane which is held upside down in the vise. This works better for me than clamping the piece of wood and running the plane over the edge. This way I ensure that the wood is not being distorted by the pressure of the vise.

If I am having problems with a particular piece of wood, I will clamp a piece of wood next to the vise to run the workpiece against to help maintain squareness of the joint.

Take very light cuts with an extremely sharp blade. I have a Hock blade and capiron in my #7 plane that work very well.

[sunburst]

I joint my plates with a #7 plane too, but I used to use a jointer. It can be done, but the jointer needs to be very well set up with freshly sharpened and honed knives. Those are things you can't expect from a new jointer "right out of the box".
Also, a jointer is not an automatic tool. You have to learn to use it. Get some scrap wood and practice. And, unless you already know how to sharpen and how to set up a jointer, learn and practice those skills first, and then you'll be ready to learn to use the jointer to make light-tight joints.

A search here should bring up several old threads on jointing plates with lots of good information and pictures.

I don't think it is a good idea to plane the thickness down until after the joint is glued. The more wood you have to work with the less accurate you need to be during the process of gluing the halves together. Using a rubbed joint, as I do, I like to be able to get those halves together and positioned fast, so a little extra wood lets me do that without worrying about perfect alignment.

To joint wedge shaped pieces on the jointer I mill the inside surfaces flat, like you said, then run that flat face against the jointer fence (checked for square). That gives a 90 degree corner on each piece, and a flat surface after gluing. Or, at least close enough to flat to mill it flat easily. That's one of the reasons for leaving the pieces thick until later.

[billhay4]

Clamping the two inside surfaces together before you joint the glueing edge is the problem. You need to use the jointed face as a reference face for jointing the edges.
Make sure the fence is square to the bed. Use the jointed face against the fence and joint the edges separately. This will give you close to a 90 degree angle.
Place the pieces together to see if the join is clean and tight. If you have a clean join, glue it up. Be careful with the join line.
Bill

[Antlurz]

When setting up a new/strange jointer, DON'T assume it is ready to go. You need to take a good straight edge and check carefully to ensure both halves of the table are perfectly parallel. Check to see that any gap up close to the blades and further away are identical. Failing to eliminate that can cause no end of problems, and any misalignment will ensure a major headache.

Ron

[Rick Turner]

We get tops in the ball park on a well tuned jointer, and then go to 100 grit self stick sandpaper that comes on a roll. We stick that down either to a piece of ground granite or use the very flat table on our pin router. We go for a very good glue joint which then goes together very easily.

Yeah, I know all the stuff about sanded glue surfaces vs. planed, but this works and it works great on about 25 sets of guitar backs and tops a month. For purely acoustic instruments I'll use hot hide glue; for production instruments my guys use LMI white glue. We spring tape the joints unless we're fighting the wood a bit, and we just don't have glue joint problems or failures. Clamping pressure requirements are much less for hot hide glue, by the way, as the stuff shrinks and pulls the joint together as it dries. Some violin makers don't even clamp the seams but rather do a rubbed joint.

[Antlurz]

`Well, Rick, since you have told that dark secret about sanding the joints, I guess I can admit to doing the same thing. While I'll not claim any sort of production quantities, I've yet to have a problem, regardless of whether it's a musical instrument or a piece of furniture...

YMMV

Ron

[markishandsome]

The only thing that surprises me is the 100 grit. Last joint I sanded i took to 220. Is that overkill?

[sunburst]

Sanded gluing surfaces are part of life. How else can one easily install tonebars, head blocks, fingerboard extenders, etc.?
I usually go to 120 grit, but sometimes I'll "overkill" them to 220 or finer.

I glue my mando top and back center joints with a rubbed joint, straight from the #7 plane. I start with the jointer to get a preliminary straight line, like Rick and co., but being a one-man operation, I don't have any trouble keeping my #7 plane razor sharp and well set up. It usually only takes a few strokes to get a light tight joint that feels like it has a vacuum in it. My jointer is only capable of that when it has just been set up with honed knives and if I don't achieve a good joint on the first few passes, it may be too late, especially with hard maple.

[John Bertotti]

I also have a #7 jointer plane and love it. I use it on it's side and run the wood across it.


Added that sunburst is the one that turned me onto clamping it on its side.

[Steve Hinde]

Well, I cheat a bit too. I initially square the edges on the 48 inch belt sander with 80 grit, (no tear out in Maple) then on the shooting table with 120 paper. I check for a tight fit, then a light pass with a scraper blade to get the dust and fuzz off. Hide glue with light clamp pressure on a clamping board I made. Works for me on guitar tops and mandolin tops so far. Leave the extra material as John says.If I don't like it, run it through the band saw and do it again. Then I run the plates through the thickness sander to get both sides flat and to arching thickness. One final check of the line. Works for me. My 1.5 cents

[Lab]

I use 220 grit self sticking sand paper. The kind you use when you rent a sander to refinish hardwood floors....good quality and lasts a long time. Its similar to the way Rick Turner does except I glue my sandpaper to the side of a 24" level. I lay the two pieces of wood to be jointed on a table, one on top of the other. The top piece of wood overhangs the bottom piece about a 1/4"...I lay the level on its side, place it against the top piece of wood and move it back and forth until its perfect..I repeat the process for the bottom piece.I have a large window in my shed that I use to check the joint. I just place the two pieces of wood on the glass and check the seam...Repeat until you have the desired fit....A word of caution....Place a strip of sandpaper and both sides of the level...use one side for your spruce tops and the other side for your backs.....Hope this helps...

[buddyellis]

I lay the plate with the flat down on a well-leveled 1x6 ‘shooting board’ on top of my table saw, and clamp it with cauls, and run the jointing plane which has been setup to shave tissue paper on its side (similar to john, but the plane is moving, not the plate). I find on hard maple it’s often easier to ‘pull’ the plane towards me, but YMMV. You really don’t have to worry much about the ‘squareness’ of the edge of the plane to the plate, as long as you are always using the same side of the plane down on both pieces. The complementary angles offset each other, even if the ‘cut angle’ is a bit off.

But, first, you need to get your plane setup to do jointing, and there are a few steps to make it perform as best as it can.

Make sure the blade is very square, NOT slightly 'rounded' (this url shows how NOT to do it) (http://www.hntgordon.com.au/sharpeningsmoothingtryingblade.htm) as you would normally have a plane setup so it doesn't 'dig' at the edges. Setup the 'frog' (that's the part the blade sits on, it has two screws typically through its bottom, so you can adjust the throat depth back and forth, see here (http://jonzimmersantiquetools.com/features/stanley.html)) to where the blade is as close as workable to the front edge of the throat. The closer the blade is to the front of the throat, the less chance you have of tear out on hard woods, and especially really figured woods. Since you aren’t going to be cutting anything but jointing shavings (this is your jointing plane!) you need very little clearance here.

Next, make sure that the bottom of the plane is flat. Use the top of your table saw or electric jointer, spray some contact cement, and stick a whole sheet of 120 grit paper on there, and carefully level the bottom of the plane. Pay special attention to three points: the leading edge of the bottom of the plane, the section of the plane leading up to the throat slot, and the trailing end of the plane. It is 'ok' (though perhaps not optimal) to have a bit of hollow anywhere else but these three points. The lead and tail should be obvious, they help you with the 'flatness' of the joint, and if there is a hollow at either the front end or back end of the plane, then you aren't getting the 'full' useable length of the plane
As for the point before the throat, basically you want the section of the plane that is just leading the blade to be as close as practically possible to the blade, and if there is a hollow here, then the 'effective' distance there is extended to wherever the 'hollow ends' If there is a hollow in front of the throat, you will have a harder time with tear out. The further this distance, the more chatter and tear out you will get. You also want the chip breaker, especially for hardwoods, to be VERY close to the edge of the blade. A short throat, and an extremely close chip breaker make your life much easier in regards to planing figured wood (not that it becomes 'easy', but more manageable with a proper plane setup). If you have money to burn, take it to a machinist and get it ‘leveled’ but but unless the plane is in real bad shape, generally you can work out any hollow spots right there on your tablesaw with some sandpaper.


Lastly get that blade ground square, get the back extremely flat, and the edge honed sharp enough to cut hair off your teeth (or at least able to shave your arm). Blade sharpening is a whole separate exercise.

[sunburst]

Along with all that, I also hone a very slight "back bevel" on the iron of my jointer plane. With that, I have yet to try to plane any figured maple that wouldn't shave off in "tissue paper" slices.

[John Bertotti]

Ok what is the back bevel?

[sunburst]

Ok what is the back bevel?
Lay the iron on a fine sharpening stone on it's honed back, lift the back (non sharpened) edge slightly and hone a small bevel on the back side of the iron. It effectively gives it a steeper cutting angle, and it works better in very hard and very figured wood.

[buddyellis]

Making the plane blade similar to a knife edge which essentially imparts a lower angle to the cutting face. Low angle planes are designed for 'end grain' work which is essentially what you are doing when planing figured wood. You can approximate that by back beveling the 'flat' side of the blade slightly like a knife would be ground, except not that extreme. (correct me if that's not what you're talking about John)

[buddyellis]

Actually, it's the other way around, as John said. Duh.

[John Bertotti]

I was actually curious as to the angle but I got the gist from the description. Thanks sunburst. I tried a low angle plane on a piece of really figured wood and it tore out so bad I wont ever try a low angle plane again. I had that blade so sharp I could literally shave my face with it. The adjustable throat was as small as possible and the cut depth was giving me shavings I could see through except for the tear out.

[Keith Newell]

I also use a large jointer plane, a #8 and clamp it down to a flat table and use shims and a square to get it perfect. I then use a flat board to space the wood off the table and on to the blade and plane everything by hand. I have had perfect joints since then and learned to use thick leather gloves so my hands don't get permanently scared hehe http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif
Keith
Http://www.newellmandolin.com