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Getting perfectly flat without a jointer
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Getting perfectly flat without a jointer
Hello — I am trying to joint a Tele-style mahogany neck blank. I have a Metabo planer in good condition, but no jointer. I secured the c. 40 mm thick blank to a flat plywood sled and shimmed it well. It’s hot-glued in place, and absolutely no rocking from any corner or edge. But as I plane it down, I still have about 1 mm difference from one end of the blank to the other when I put a straightedge on the surface (see photo, with backlighting).
I have accounted for plenty of space beyond the snipe lines at either end, so snipe should not be a factor in the area under the straightedge.
Any thoughts on how to flatten it without a jointer at this stage? I can set it down on a long sheet of sandpaper and slide it back and forth on doubled up MDF, which should help (though I worry a bit about applying uneven pressure).
Any other thoughts, or insight into why this is not flattening perfectly on the planer? Thanks!
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16 Replies
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That is a really tall order for a planer probably. If a power jointer isn’t in the cards, with some work, a jointer plane can actually be used to great effect on a project like this. There is some learning to do though.
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Maybe I just need to bite the bullet and get up this learning curve then. Thanks Ian.
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This is a fun tool.
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I do the sled thing with my thickness sander and it works well generally.
How deep a cut are you taking? I would try taking tiny cuts so that you can see that fall off slowly disappear.
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Thanks Paul — I take a quarter turn on the handle as recommended in the machines’s manual. I might try it again with an even smaller turn between cuts and see if that narrows the gap. Thanks!
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Yeah you want to take cuts that are barely anything. Mark the surface up with pencil cross hatches and take the tiniest cut possible. You should see the planer catch in some places and not others. As you slowly come down it should take more and more and then your complete pass should be flat.
The other thing could be that the wood is got some wild grain thing and you’re releasing tension in the board. In that case I consider the wood suspect for a neck if it moves a lot as you’re milling it.
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The other thing is that it could be flat, but curved. Meaning that if you clamped it against something flat, it would be flat, but it’s naturally taking a curved shape.
Again that might not be suitable for a neck blank. But for me after I mill the neck (including the back, on CNC) I clamp the fingerboard and the neck together against a flat surface and that tends to make things flat.
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Thanks for the additional replies Paul. I did go back and try it with extremely light passes (barely turning the handle) but still the same outcome. I’m beginning to doubt the sled so will make one from doubled up laminated plywood (glued together clamped on a granite kitchen counter) and see if that does it.
As for the wood, it looks pretty uniform — and in fact is the first board I find that is flat sawn, with perfectly vertical grain. Will report back. Thanks!
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I think I know what’s happening.
You need to take the end of the board as it’s coming out of the planet and apply some upward pressure on it when it gets to the end.
Planers aren’t really meant to do this job, obviously. It’s a jointers job.
I think what’s happening is that at the end of the cut the planer is pushing upwards on the sled at the end of your cut. The sled is probably longer than your stock. There is nothing to stop the planer from digging in on the way out.
It’s good practice with a planer to put some upwards pressure on the beginning and end of a cut. I think maybe more so in this situation.
Could be, anyway.
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You’re right that the sled is quite a bit longer than the blank. I don’t know if what you’re describing is meant to deal with snipe (I left more than enough space at each end to allow snipe and just trim it off). But I’ve seen this advice and will try it as well.
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I could be wrong but snipe I think is more like tear out that happens at the end of the board but a little different from what you’re describing.
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Depending on budget, a 16-32 thickness sander is an invaluable tool (I have the supermax and it’s great). A planer is pretty rough on most guitar woods. I do this sort of thing on my thickness sander.
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I feel this is a big missing element in my workshop (for guitar making at least). But where I live all tools, and especially machines, are a good 2x the price in the US or UK. So I have to think long and hard about what to prioritize. After reading your comment, I actually looked up making one and am thinking of putting this DIY drum sander on my project list https://youtu.be/eeiszkNAZbQ?si=kfPsd0ioe-1CCVXa. Looks reasonably simple and very adjustable.
For context, I’m not a professional luthier — I build for myself, but do care about making the highest quality instrument possible. Thanks for the follow ups.
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That could work but it would make an insane amount of dust, you definitely want a cover on it and dust collection.
And for doing guitar tops and thinning stuff no way a drill will be enough power. You want a monster motor. Mine blows my fuse all the time. To sand 15″ of wood at one time takes a lot of power.
But in principle it could work. I would look for other designs.
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Good advice, as usual. I actually went back and tried to re-level the planer’s infeed and outfeed foldable ledges — very hard to do perfectly because they are fundamentally at slightly different planes. But I made a few cuts and it seems better already. Will try to fine tune it and see if I end up with something good.
I also wonder if I’m not obsessing too much (especially after the recent adjustments, which leave average variations at about 1/10 of a mm at different points. After all, once I glue the fretboard and sand it flat, that should end up being a flat reference surface, which will be followed by further levelling at the fret tops. Still, I’d like to tend to perfection throughout.
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This is a little late but I think your first problem is the base. There is no such thing as flat plywood nowadays. There used to be quality plywood that was really flat back in the day but I would say your plywood base is probably curved. You would need to make a box beam that is flat and stiff to run your neck blank on, even if you use that sander you’re thinking about. But then, the pieces to make a box beam need to be straight and flat as well! You should also use some winding sticks to see if it’s twisted.
Cheers, Dan
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