Question using 5th Cut Method

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Forum topic by zipmac22 posted 07-02-2017 05:08 PM 1071 views 0 times favorited 3 replies Add to Favorites Watch
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40 posts in 1627 days

07-02-2017 05:08 PM

Hey Y’all,

I’m making a cross-cut sled for my Bosch 4100 tabe saw. I tried to square up the cross-cut sled, but I’m not sure if I’m figuring the math correct using the 5th cut method. I wonder if anyone could look over my numbers and see if I’m on the right path? Here’s the measurements from my fifth cut.

Front: .5395
Back: .3075
5th Cut Length: 9 5/8” or 9.625”
Length from pivot point to end of the fence: 29.5”

I came up with .17776623

I’m still un sure of what I need to do with the (.17776612) to give me the distance I need to move the fence. Do I use a feeler gage closest to (.17776697)? I do know that I need to move the fence back since it’s a positive number.

Thanks for your help!


-- Chris, Central Texas

3 replies so far

View TheFridge's profile


10859 posts in 2260 days

#1 posted 07-02-2017 05:13 PM

William Ng explains it and shows how to do it in his video on making sleds

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Loren's profile


10477 posts in 4422 days

#2 posted 07-02-2017 05:15 PM

I haven’t done it in quite some time but
as I recall you cut a wider piece off for
the 5th cut and the amount of taper is
4-times the amount your sled is out of
square. A 1/64” out-of square might be
hard to spot, but x4 it becomes 1/16”.

You came up with something a bit less
than a tenth of an inch so I think you’d
want to move the fence (or try paper
shims to figure out how much) about
a quarter of that or .178/4

Ng’s method is probably more scientific
than mine. Getting any saw to cut
cabinet panels dead-square is something
of a hassle I’ve found. In most work it
doesn’t matter but I’ve fussed with frameless
cabinetry and in that it’s really important.

View Rich's profile


5617 posts in 1363 days

#3 posted 07-02-2017 08:58 PM

Distance to move fence = (A – B) / 4 / L X D

Where A is front, B is back, L is length of 5th cut and D is distance of pivot.

So, your error is 0.006 inches per inch, and you are correct that the fence should move 0.177”. Since the error is positive, the fence should move back, as you said. You can watch the William Ng video mentioned earlier, but basically, you are going to clamp a blocking board touching the fence, pull the fence back and then push it back to the block with a 0.18” feeler gauge in between and secure it there.

Edit: Obviously, you’ll have to stack multiples to get that. Mine only goes up to 0.03 for a single gauge. You can also probably stack 0.177 exactly, but it doesn’t really matter much at that point.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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