Gotta say I’m disappointed with the Leigh D4.
I am very interested whether others have seen the phenomena I am experiencing or if this is me having done something wrong.
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The jig is way too flimsy. Additionally it’s got issues with squareness that it shouldn’t have were it engineered correctly ( for the List price they want that is).
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The L brackets that hold the Finger Guide assembly are made of the same silly crummy weak Zink alloy as are the fingers.
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I have seen that particular casting alloy before on fairly cheap handles and other low stress applications. Leigh changed the Zink ratio and calls it a “proprietary alloy” (WOOO HOO) which, is the same as a cook adding more salt to an existing dish he saw in a book and then claiming to have created the dish. Leigh uses this alloy for the following reasons:
<!--[if !supportLists]-->1.)<!--[endif]-->It’s cheap and easy
<!--[if !supportLists]-->2.)<!--[endif]-->The Technology is simple and lends itself to zero or few secondary operations as it doesn’t shrink when cooling in the mold and can be cast with fine surface finishes.
<!--[if !supportLists]--><!--[endif]-->3.)The alloy has a tendency to be somewhat self lubricating.
<!--[if !supportLists]-->4.)<!--[endif]-->Did I mention cheap and easy
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The problem with the L bracket and its receiver is simple: It’s not robust and it does not hold a square. It isn’t intend to hold a square. Leigh leaves that issue to the consumer to retrofit to the jig. The L bracket relies on strength and square from a consumer supplied support board. However, I have found that this is a dicey issue as when I clamp the support board in after or before lowering the finger guides down, the support board is kicked out of square by the clamp bar and holds the fingers slightly out of square with the board being cut.
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I also observed that if the board to be cut is placed in the jig with a lousy few ounces of force it too will lift the guide finger assembly and cause it to lie out of square.
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This is a problem because the router must follow the finger guides along two planes. There is the horizontal plane where the guide bushing in the router contacts the finger guides but, there is also the plane of the Z axis which should be dead flat and square to the work piece and not have any ramp or slope or the cutter will describe an out of square angle on the workpiece.
The result is that when I rout the Pins, the bottom of the cut out is out of square in a way that places a noticeable gap on the outside of the joint when assembled. I can sort of kind of compensate for this by doing the following:
<!--[if !supportLists]-->1.)<!--[endif]-->Do not apply clamping pressure to the support board letting it float free.
<!--[if !supportLists]-->2.)<!--[endif]-->Be ever so gentle when inserting the work piece into the jig for fear of deflecting he finger guides.
<!--[if !supportLists]-->3.)<!--[endif]-->Be ever so ginger with the router not allowing the weight of the router to bear fully in the finger guides.
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These problems would not manifest had Leigh invoked a more robust design ethos.
The finger guide assembly really ought to be heavier and the L brackets should be heavy steel and or cast and ought to raise and lower in some form of snug bearing ( bronze bushings would do nicely) instead of the stupid sloppy rectangular slot Leigh uses.
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and that the learning curve can be steep - though I never found this to be true. 
