# So How Accurate is Acceptable on My CrossCut Sled?



## Dwain

So I recently put together a large crosscut sled (30" x 36") for my table saw. I made a smaller one (24" x 18") and find it indispensable for small work. I thought a large one would be a great addition.

So I was trying to square it up tonight using the William Ng version of the five cut method. After my fourth run, I got down to .0048. My small cross cut sled is down around .0025 and I find no reason to change it. So I guess I'm looking for advice via multiple choice options. Is it:

1) Very good, no reason to get any better

2) OK

3) Good enough to get by

4) Not good enough.

I appreciate your feedback. Thanks in advance.


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## gmc

Unless you build stuff 50' or longer I wouldn't lose sleep over it. .01 is better than they could do 50 years ago. Look what they built. Good Job on sleds.


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## BillWhite

Stay with what ya got. You can get that much run out with a saw blade. I would not sweat it at all.
Bill


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## RichT

Is the 0.0048 the error over the length of the fence? Assuming your pivot distance is maybe 34", that's a really good number. If it's 0.0048 per inch however, that's pretty high considering that you'll be using it for wide stock. Over the width of a 28" board you'd be off 0.13 inches. I'm also assuming it's 36" wide by 30" deep, so switch the numbers around if that's backwards.

Edit: I posted about this one I built a few months ago. I like to put them together incrementally, working off of available guides on the saw. I used the fence to align the base to the runners. Then, I used a carpenter's square that I know is dead-on and pinched the short leg between the fence and the side of the sled base, and used the long leg to align the fence. Got lucky and it was very accurate first try.


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## rwe2156

1/64" over 12" is accurate enough for ww'ing.

Once you start talking .00_ you're into machining tolerances.

I've watched Ng and Spagnolo IMO its a bit anal.


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## Dwain

Rich,

Thanks for the note. That number is over the entire pivot distance, not per inch. Thanks for your note and the link. It's great stuff!


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## waho6o9

Cut a big square of ply and measure the diagonals, if they're the same you're good to go.

Me thinks you have NASA quality sleds, good job!


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## splintergroup

That's plenty good!
Id' make a crosscut using the sled, maybe an 8" wide piece. Place a trusted square across the cut and see if it lies flush. full contact? you're set to go!


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## Unknowncraftsman

I also think it's good. 
Unless your builds look like this









then you might need a adjustment.


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## ArtMann

I'll bet that if you repeated the test in the exact same way, you would get an answer that is different by 0.0048" or more. You are going past the accuracy that you can reasonably hope to accomplish with that procedure. By the way, how did you get a reading that goes down to the 1/10,000 of an inch?


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## woodbutcherbynight

Wood can expand and contract at greater amounts than that. My 2 cents worth is that it is sufficient
for woodworking. Now if we are talking spaceships and such no keep working on it…................


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## Dwain

Art,

Thanks for your note. I just realized when reviewing your question that I may have made a mistake. Here, you can check my math. It is entirely possible that I did something wrong. Heck, it's probably very likely! Anyway,

Measurement of front end of cutoff: .434

Measurement of back end of cutoff: .44

Difference: -.006

-.006 divided by 4: -.0015

-.0015 divided by the length of the cut off (9.875): -1.5189

-1.5189 multiplied by the distance between the pivot point and the end of the fence (31.5"): * -.00478*

I realize that the .0048 is a negative, not a positive number. I'm not sure if I would do anything with this either, provided my math is correct. Please let me know if I am doing something wrong.

Thanks for all your advice!


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## Dwain

AJ2,

If I could make furniture like that, I wouldn't worry about a cross cut sled either! I'd just be happy to make such cool pieces!


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## RichT

Your math is correct. The negative number only means that the fence is forward of square and if you were to try to adjust it, you would move it 5 thousandths back. That's the sort of accuracy you're looking for in the first place though, so I'd leave it alone.


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## Dwain

Thanks Rich! Glad to hear I don't need to touch it again!


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## flyguy245

Dwain and Rich I have a question for both of you. I am new to Lumberjocks although I have visited the site many times. I have recently built my first cross cut sled. I have a saw stop jobsite saw. I have a small work space. I am having trouble getting my fence square. I followed William NG's video. I have gotten my fence to within .001 and then add the rest of the screws to lock down the fence and then when I run my next piece it is out by .010 or more. I go back through the process and re-adjust and think I am ok just to have the same problem. There have been several times that I followed his directions and adjusted the amount it says only to be out the other direction that much or more. I've rebuilt my sled a couple of times now. Not sure if I am making the mistake or if it is the runners or the miter slots. Anyway I am super frustrated at this point and need a solution as a project that I am working on will require the sled to finish it up.


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## BroncoBrian

I am going to build my crosscut sled today.

My goal: .0047

Then all the answers above apply to my sled as well!


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## RichT

> I have gotten my fence to within .001 and then add the rest of the screws to lock down the fence and then when I run my next piece it is out by .010 or more.
> 
> - Guy


Be sure to clamp the fence tight to the base in three or four places and pre-drill for the screws. Driving the screws might be shifting the fence. After all, it doesn't take much to knock it out of whack.


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## MrRon

I build large scale models and work to ±.003". Models being small take tolerances very seriously. It either fits or it doesn't. If it doesn't, you make a new one, measure it and make another if necessary. When building furniture, I can tolerate ±1/64". I do metal machining also so I'm pretty anal about precision. In your case, .0048" is quite acceptable.


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## RichT

> I build large scale models and work to ±.003". Models being small take tolerances very seriously. It either fits or it doesn t. If it doesn t, you make a new one, measure it and make another if necessary. When building furniture, I can tolerate ±1/64". I do metal machining also so I m pretty anal about precision. In your case, .0048" is quite acceptable.
> 
> - MrRon


We're talking squareness, so ±1/64" by itself is meaningless. The numbers represent how many inches per inch out of square the sled is, so if you mean you can tolerate ±1/64" per inch, good luck getting anything to join together.


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## Woodmaster1

Unless it is .00001 get rid of it. You can send it to me and I will use for awhile to see how good it works.


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## flyguy245

Rich, Thank you. I have clamped it in several places and pre-drilled my holes but still have issues. I may build another fence at this point. I have it down to .006 over 23 inches which I am not happy with but tired of messing with it.


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## RichT

> Rich, Thank you. I have clamped it in several places and pre-drilled my holes but still have issues. I may build another fence at this point. I have it down to .006 over 23 inches which I am not happy with but tired of messing with it.
> 
> - Guy


No, that's good, Guy. You nailed it. That error calculates to 0.00026 inches per inch, which is excellent. Pretty much anything around 0.001" per inch or better is acceptable, and you're four times better than that.


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## Dwain

> Dwain and Rich I have a question for both of you. I am new to Lumberjocks although I have visited the site many times. I have recently built my first cross cut sled. I have a saw stop jobsite saw. I have a small work space. I am having trouble getting my fence square. I followed William NG s video. I have gotten my fence to within .001 and then add the rest of the screws to lock down the fence and then when I run my next piece it is out by .010 or more. I go back through the process and re-adjust and think I am ok just to have the same problem. There have been several times that I followed his directions and adjusted the amount it says only to be out the other direction that much or more. I ve rebuilt my sled a couple of times now. Not sure if I am making the mistake or if it is the runners or the miter slots. Anyway I am super frustrated at this point and need a solution as a project that I am working on will require the sled to finish it up.
> 
> - Guy


Guy,

I understand your frustration. I first made the sled about six months earlier and, after drilling the seventh screw to hold the fence, still couldn't get it right. I was so frustrated I put it down and forgot about it. What helped me get back at it was to build a smaller crosscut sled. The think was only 18 inches deep by 12 inches wide. I don't know what happened, but I had a great deal of success with that. It wasn't as good as my big sled, but it was good enough and it gave me the confidence to tackle the big sled again. I was surprised about the number I got and that's why I opened this thread. I wanted to confirm my number. Anyway, I still had to re-adjust it four or five times, but I this time, I was much more successful. I snuck up on that number and when I hit it, I was done. I even wrote the number on a sled with a sharpie so I could thank the woodworking gods for their assistance!

Rich made the best points. Clamp everything down well, make sure you use a different hole after every adjustment. You will get there!!!


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## BroncoBrian

I finally finished my first sled. I will add it to my projects just to have it recorded somewhere, plus it is pretty!

I checked this a few times because I did not believe it at first. It was -.003 over 52" on the first attempt.

-.003 / 4 = -.00075

No adjustments, just luck. Not too shabby!


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