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I’ve made a scarf joint sled for my tablesaw. I checked and double checked to make sure that the sled fence and the blade are parallel and the sled and blade or perpendicular to the top of the saw. So why isn’t my line not straight. See photo

I used a 40 tooth combination blade to cut it. could it be from deflection of the blade

The red line is the edge of the scarf joint

Thanks

Could you put the sled and the workpiece on the saw, with the saw off, and take a picture of the setup that you ran? That might help someone diagnose the problem. And if it is not clear from the photo, let us know what brand/model of table saw and what brand/model of any other thing used during the cut, like if a miter gauge is part of the sled.

Initial thoughts are that your stock was not vertical.

I have used a taper jig and some clamps and run the taper jig along the table saw fence and would get pretty much what you have in the picture.

I switched to using a wide blade in the band saw and didn’t see that issue anymore but there was more to clean up on the two faces of the joint.

I chalked it up to my table saw sucked and the blade was deflecting when trying to saw into such a wide piece.




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I thought of that but it was a test piece of MDF. Because of the sled design, you can't clamp past where the blade cuts, so maybe it was not flat against the fence. I am thinking of redesigning it but I want to correct any mistakes I made with this one.

Any sled designs you like

Thanks

The table saw is a Ridge with a Granite 40"x 27" dead flat top.

The sled is attached to a piece of hardwood that rides in the miter gauge slot. The tolerance is very tight. It does not rock left to right.

Thanks for your help

What blade did you end up using?

I ended up using the bandsaw and a 3/4" blade that I use for resaw. It did require a lot more cleaning of the faces of the joint though, but not too bad. My table saw is a cheapo Bosch jobsite saw, so not well suited for cutting through that thick of stock.

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Steve,
Here's one way to test the accuracy of your sled. Clamp a test piece to your scarf jig just as you would a neck blank. Use a machinist square to make sure your test piece is square to the table and the blade is square to the table. Place the machinist square against the neck blank and apply the same downward pressure to the sled as if you were getting ready to make the cut. Check to see if there is any movement in the sled causing the blank to go out of square. Over the years I've had a few sleds that seemed tight and square only to get a little wobble when applying cutting pressure. Even a small variance will cause the cut to wander. One other thing to check is the 90 degree stop on your table saw. Unplug the saw and check to see if there is any side to side movement in the blade. Also, I take several passes to cut a scarf joint, checking after each pass to make sure the angle is correct.

Steve

A No. 4 hand plane would make quick work of correcting the angle, although, I'm sure that you want to dial in your jig...

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Steve Sollod (pronounced sorta like "Solid")
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forget the sled chances are your blade or work isn't square to the table. If the blade can cut through this on a sled do this

A clamp the work where you want it cut. Lower the blade and mount the work then raise the blade through the work. It will be the most accurate way
if you have a cheap blade that may be as good as you get. Use a good blade.

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You could try tilting the blade slightly - but that set-up looks backwards to me. A minor kick back might pull the clamps into the blade. Maybe I'm being a worry wort.

I'm working through this exact challenge with my neck scarf miter sled - similar situation in that I've checked my sled for square, as well as my blade. This is on a 12", 5hp Grizzly with a full 1/8 Kerf Freud LU84M012 12-Inch 60 Tooth ATB blade. Should be a pretty low amount of deflection with that much steel and carbide.

Mine is cutting more subtly out of square, and is quick to clean up with a few passes with a hand plane, but it would be great to solve.

I'll try double checking for square when the stock is clamped and with pressure put on the sled.

When you are trying to cut wood that is standing on edge on a table saw, even the tiniest imperfections will send the angle off a lot at either the top or the bottom (which will be side to side on the neck). I think it is easier to just make the cut on the bandsaw, freehand to a pencil line, and clean it up with a blockplane after that.

My sled is a little different, but has cut many necks with minimal cleanup. It’s made using stabilized subfloor (very heavy and stiff), but most importantly the fence is secured to the base with 90° full-height gussets that eliminate any flex. Even with a very sharp blade, there is tremendous torque from the blade attempting to twist the whole thing.



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That's what I do, but I clean it up on the edge sander...

I can tell you that if you blade cuts this in one slice you will get a much better and safer to raise the blade through the work. Be sure you are square and clamped. My father was a cabinet maker and we used this trick on all miter cuts.
Try it you might see that it is safer and works better.
sleds have too much movement in them.

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blues creek guitars
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John—

Just to make sure I understand (because I might try this, and I treat my table saw with the right amount of fear and respect):

You are saying that a person could position the workpiece to some sort of fixture that is not a sled (because we are not going to move it past the spinning blade), but rather a stationary fixture that is anchored either in a miter slot or to the fence (probably the fence is better). The workpiece is positioned over the blade with the blade below the table, making sure the workpiece is square and that the blade, once raised, will cut on the line, with the kerf on the preferred side of the line. Then the saw is turned on and the blade is raised through the workpiece. Do I have it right? It sounds like a cool method. And if the workpiece is anchored well, it sounds safe enough. No fingers near the blade. I like it!

I use a chop saw for this. Works great. Clamp the wood in place and it's just like John's method of raising the tablesaw blade except the chop saw blade moves downward instead of upward. Almost no tweaking required. Maybe 2 minutes with a hand plane. The saw (and a dust hood for it) takes up a fair amount of space but it gets a lot of use and it's pretty precise.

+2

I Start with a well prepared neck blank, a quick bit of layout, cut with bandsaw, finish up with a sharp block plane. 10 minutes from layout to glued up and a flawless joint.

Best, M

We do very few scarfed necks, and usually just bandsaw and plane. When we do jig up the cut for the tablesaw (usually scarfing non-instrument stuff, but sometimes a neck for a student), we use the jig pictured and then clean up the gluing surfaces with a hand plane using the method depicted in the drawing.









A few things worth noting:

- As mentioned, having correctly dimensioned and squared stock is important...varying width or thickness will skew the cut or the glue-up, as the headstock portion of the neck is reversed in orientation for glue-up.

- Clamping the leading edge of the stock is important, as it is cut free during the operation while the blade is still in contact. An alternative to this is to skew the jig such that the cutoff is left behind the sled and avoids having a piece of loose cutoff chattering against the blade.

- A short miter gauge track is as bad as a loose one - the sled needs to fully register in the track from before the work arrives at the blade to after the blade fully clears the work. Both hardwood and plastic strips wear over time, as well as flex if not fully fastened, so we use adjustable aluminum tracks that allow slop to be largely eliminated

- Because the track fully registers the jig to the miter slot well before the cut, any remaining slop can be largely eliminated by holding some slight rotational pressure with the handles seen. These handles also keep the user from any temptation to put fingers where they do not belong, and this is further reinforced with the combination blade cover and bridge between what can be two halves of the jig if the cut is not stopped correctly.

- For the best surface off the blade, the cut must be done with a sharp, fresh blade that moves continuously through the work at near constant speed. We stop the cut only after the blade clears the cut, but before the jig is bisected.

- Cumpiano has a good gluing procedure depicted for neck scarf joints, and we use a similar jig. Even with a sharp, full kerf blade (1/8" cut width), we still do not consider the joint to be glue-ready off the saw...cleanup with a sharp handplane provides the best surface, which is just good enough, given the higher scarf angles seen in luthiery.

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Woody

So the boxy construction that the right hand handle is screwed to is just that - a hollow long box where the blade hides after it has cut the neck piece?

Very clever

Ed

Thanks, I will try it

That's great thanks for posting it

Yes - the channel acts both as blade guard and carry-thru between the sides of the jig should the cut be continued all the way through (along with the fence itself).

I wish I could claim some credit here, but the jig is close to 15 years old, judging from the 'use' info on the back. We have a few of these really old jigs that just hang out on the storage wall...definitely adds to the 'luthierishness' of the place. Also acts as an awesome dust collector, judging from the accumulation at last use.

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