How square is square?

  • Advertise with us
Blog entry by nobuckle posted 11-28-2010 02:11 AM 1961 reads 3 times favorited 12 comments Add to Favorites Watch

I’m building a crosscut sled and I need to know how square the front fence needs to be to the blade. I was using my carpenter’s square and frankly I just can’t believe that a carpenters square is square enough when it comes to this type of jig. Maybe it’s my toolmaking background that is causing the boggle. I switched to using my machinist square but I’m still not sure if the fence is truly square enough. The fence is currently screwed in place, I haven’t glued it yet. What has been you experience in making crosscut sleds? Thanks for your time.

Doug, Ohio

-- Doug - Make an effort to live by the slogan "We try harder"

12 comments so far

View Gene Howe's profile (online now)

Gene Howe

10545 posts in 3457 days

#1 posted 11-28-2010 02:27 AM

I use a large drafting triangle. It’s accurate, and thin enough to fit between the teeth.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View DonH's profile


495 posts in 2845 days

#2 posted 11-28-2010 02:32 AM

WHat I do when I square up a crosscut sled is put two circular magnets on the back and forward portions of the saw blade. Then I use a good carpenters square by placing one side flush to the magnets and the other to align the fence. This is accurate and straightforward to do.

The real problem is keeping it square as seasons change – so I am now using a pivoting fence that can be realigned at any time.

-- DonH Orleans Ontario

View GaryL's profile


1099 posts in 2859 days

#3 posted 11-28-2010 03:21 AM

Brian…What is the brand and model of the square you are using? This seems to be the key to your method, a very accurate square to gauge off of.

-- Gary; Marysville, MI...Involve your children in your projects as much as possible, the return is priceless.

View Bill729's profile


241 posts in 3110 days

#4 posted 11-28-2010 03:45 AM

Thanks for the lesson! Gonna have to getme one of thodr dial indicators!


View TopamaxSurvivor's profile


18291 posts in 3704 days

#5 posted 11-28-2010 04:58 AM

The fastest and easiest way to find square is to scribe a couple of arcs on the saw cut of the sled. From those arcs, scribe two more intersecting arcs 6 inches from the cut. Draw a line between the first point you used to scribe the first 2 and the intersecting arcs. There you have it as perfectly square as it can be if you use a fine point to scribe and are accurate. No measuring fiddling or fussing ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View sras's profile


4812 posts in 3157 days

#6 posted 11-28-2010 05:17 AM

I checked my sled using test cuts. First I trimmed the end of a piece of plywood close the the capacity of my sled. Then I flipped the piece over such that the cut edge is still along the blade path. Slide the piece over a bit and cut off a piece. Measure the width of the cutoff at each end. The difference between the widths gives you twice the error of your fence. For a little extra accuracy, I stacked up multiple cutoffs to further multiply the error.

-- Steve - Impatience is Expensive

View Robsshop's profile


907 posts in 3003 days

#7 posted 11-28-2010 05:39 AM

Hi there Doug,I have learned over the years of building jigs and sleds that accuracy starts with basics . When I set out to construct a sled I start with making sure the blade is aligned with the miter slots as well as the fence on the TS. I personally cut the sleds base to size first and then attach the miter tracks using the saws fence as a reference. With the base attached and sliding squarely against the fence with no binding or free play. I now raise the blade up through the base and cut a kerf through the middle of the panel,making sure not to cut through the front or rear leaving the base intact at the edges . Now lower the blade and install an 1/8” thick aluminum strip in the kerf ( presuming 1/8” blade ?) giving You a flat straight edge to now reference against. Like Gene I use (2) large plastic drafting squares on both sides of the straight edge ( note: I use double sided tape to hold the squares in place). Confident that the squares are accurately placed I now attach the front miter rail followed by the rearward rail. Then it is time to make the first full cut through the entire sleds panel and if the wood working Gods are smiling down on You, Your sled will be cutting 90’s all day long !! Hope this helps in Your quest for perfection, be safe and good luck !

-- Rob,Gaithersburg,MD,One mans trash is another mans wood shop treasure ! ;-)

View davidroberts's profile


1027 posts in 3514 days

#8 posted 11-28-2010 06:08 AM

I agree with sras above. I spent quite a bit of time squaring up my sled. My sled by the way is big and heavy (3/4” MDF with a thick white oak fence), which helps it to hold square. You can get close using a carpenter’s square, or any square, but you need to do test cuts, usually many test cuts, to get it perfectly square. And perfect is what you want, otherwise, the sled it too much trouble to mess with. I assume the fence you are talking about is at the back of the sled, where you place the board. The fence at the front of the sled does not need to be square, it just keeps the two sled pieces together.

I hold the fence to the sled using six 3/8” bolts. The holes through the sled, except for the most right hole, are slightly enlarged (by wobbling the drill bit). I tighten down the most right bolt and adjust the left one each time I make a test cut. For the test cut, I pass the blade through a piece of board, a 1×4. Then flip one half of the board over and butt it up to the other piece. See if the joint between the two boards is tight and both boards are tight to the fence. If not, adjust the left side slightly either forward or backwards and cut another board and test again. Mark the boards so you don’t get confused which side you flipped. Make your final cut on a 1×6 and look for light using your best square.

It took me about 15 cuts before I was satisfied the cut was perfectly square. You will know when the cut is sqaure because the boards will seem to fall in place with no movement when you butt them together against the fence. A wonderful feeling. Then gently tighten the remaining bolts and be careful not to knock it out of square until you get the bolts tightened down good. My sled is square, I mean dead nuts square, and it stays square.

Sorry this got so long, but it pays to be patient and do it right.

-- Better woodworking through old hand tools.

View Roger's profile


20929 posts in 2832 days

#9 posted 11-28-2010 07:15 AM

1st let me apologize for the second part of my 2-bits being so long, but, you’ll understand why when ya’ll read it…. I hope ! hahaha

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed.

View Roger's profile


20929 posts in 2832 days

#10 posted 11-28-2010 07:15 AM

Here goes:
Yup, what davidroberts said, and everyone else too. Really, as long as your blade is square in your table, you should be able to just raise up your blade like you would without the sled on, and, use a square up against the fence and the blade. BUT, if you really want to go krazy, then…. you can try this: Leave all the screw holes to the right of the blade, just a lil loose, and the holes just a lil oblonged to be able to dial the fence in. Start this sequence of cuts with the fence squared to the blade with just a square…tighten the fence at this point. Now,iIf you take a piece of sheet goods about 16-18” square (fairly square), number each side begining with the side up against the fence as # 1, and go counter-clockwise, with # 2 being the side now against the blade, # 3 the opposite of the fence, and then # 4 being the last side opposite the blade. Then, take a slice, maybe a 1/2” or so off of side #2, then turn the sheet piece clockwise and take about the same amount off of #3, then turn it clockwise again so you can take a slice off of #4. Now, turn the piece clockwise again so you can take off a slice of about an 1/8”..... Now take the 1/8” slice you just cut from side #1, using a caliper, measure the thickness of each end of this slice, (the entry edge and exit edge of the blade) is what I’ll call it. These should be the same, or very very (i mean like within a thousanth or so) if not the exact same. If they don’t match to your likeing, you can loosen the fence and micro adjust it whichever way it needs to move. I did this just because I wanted to try it, and, it really will show you how close to perfect you are.

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed.

View nobuckle's profile


1120 posts in 2789 days

#11 posted 11-28-2010 07:36 AM

Thanks for all the great tips. Right now as it stands the front fence (closest to me) is out about .007” in 14”. If I leave it like this the cut would be out of square by .012” in 24”. My sled isn’t even big enough to hold a 24” piece. I think I can get about a 20” panel in it.

-- Doug - Make an effort to live by the slogan "We try harder"

View TopamaxSurvivor's profile


18291 posts in 3704 days

#12 posted 11-28-2010 08:07 AM

On critical cuts, yoiu could shim it with a piece of paper and be dead on :-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

Have your say...

You must be signed in to post the comments.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics