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How square is square?

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Blog entry by nobuckle posted 1361 days ago 1440 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

Gene Howe

5499 posts in 2052 days


#1 posted 1361 days ago

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

DonH

483 posts in 1441 days


#2 posted 1361 days ago

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

GaryL

1074 posts in 1454 days


#3 posted 1361 days ago

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

Bill729

238 posts in 1705 days


#4 posted 1361 days ago

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

Bill

View TopamaxSurvivor's profile

TopamaxSurvivor

14720 posts in 2299 days


#5 posted 1360 days ago

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 ;-))

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

View sras's profile

sras

3813 posts in 1753 days


#6 posted 1360 days ago

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

Robsshop

809 posts in 1598 days


#7 posted 1360 days ago

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 repurposed wood shop treasure ! ;-)

View davidroberts's profile

davidroberts

1002 posts in 2109 days


#8 posted 1360 days ago

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.

-- God is great, wood is good. Let us thank Him for wood......and old hand tools.

View Roger's profile

Roger

14311 posts in 1428 days


#9 posted 1360 days ago

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. Kentuk55@bellsouth.net

View Roger's profile

Roger

14311 posts in 1428 days


#10 posted 1360 days ago

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. Kentuk55@bellsouth.net

View nobuckle's profile

nobuckle

1120 posts in 1385 days


#11 posted 1360 days ago

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

TopamaxSurvivor

14720 posts in 2299 days


#12 posted 1360 days ago

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

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

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