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So How Accurate is Acceptable on My CrossCut Sled?

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Forum topic by Dwain posted 09-09-2017 06:55 AM 2355 views 0 times favorited 14 replies Add to Favorites Watch
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Dwain

478 posts in 3695 days


09-09-2017 06:55 AM

Topic tags/keywords: cross cut sled table saw accuracy

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.

-- When you earnestly believe you can compensate for a lack of skill by doubling your efforts, there is no end to what you CAN'T do


14 replies so far

View gmc's profile

gmc

47 posts in 1993 days


#1 posted 09-09-2017 11:50 AM

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.

-- Gary, Central Illinois

View Bill White's profile

Bill White

4805 posts in 3797 days


#2 posted 09-09-2017 01:15 PM

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

-- bill@magraphics.us

View Rich's profile

Rich

1979 posts in 426 days


#3 posted 09-09-2017 02:04 PM

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.

-- No matter how much you push the envelope, it'll still be stationery.

View rwe2156's profile

rwe2156

2714 posts in 1317 days


#4 posted 09-09-2017 02:18 PM

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.

-- Everything is a prototype thats why its one of a kind!!

View Dwain's profile

Dwain

478 posts in 3695 days


#5 posted 09-09-2017 02:34 PM

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!

-- When you earnestly believe you can compensate for a lack of skill by doubling your efforts, there is no end to what you CAN'T do

View waho6o9's profile

waho6o9

8027 posts in 2413 days


#6 posted 09-09-2017 02:35 PM

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!

View splintergroup's profile

splintergroup

1699 posts in 1059 days


#7 posted 09-09-2017 02:51 PM

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!

View Aj2's profile

Aj2

1175 posts in 1634 days


#8 posted 09-09-2017 03:15 PM

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

then you might need a adjustment.:) :)

-- Aj

View ArtMann's profile

ArtMann

686 posts in 652 days


#9 posted 09-09-2017 03:57 PM

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?

View woodbutcherbynight's profile

woodbutcherbynight

3644 posts in 2245 days


#10 posted 09-10-2017 01:09 AM

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…................

-- Live to tell the stories, they sound better that way.

View Dwain's profile

Dwain

478 posts in 3695 days


#11 posted 09-10-2017 03:39 AM

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!

-- When you earnestly believe you can compensate for a lack of skill by doubling your efforts, there is no end to what you CAN'T do

View Dwain's profile

Dwain

478 posts in 3695 days


#12 posted 09-10-2017 03:40 AM

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!

-- When you earnestly believe you can compensate for a lack of skill by doubling your efforts, there is no end to what you CAN'T do

View Rich's profile

Rich

1979 posts in 426 days


#13 posted 09-10-2017 03:54 AM

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.

-- No matter how much you push the envelope, it'll still be stationery.

View Dwain's profile

Dwain

478 posts in 3695 days


#14 posted 09-10-2017 01:42 PM

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

-- When you earnestly believe you can compensate for a lack of skill by doubling your efforts, there is no end to what you CAN'T do

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