Cross-cut sled

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On Sun, 23 May 2004 01:11:44 GMT, B a r r y

I could send you some pics of mine. got a couple of good features going there....
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On Sat, 22 May 2004 18:50:40 -0700, snipped-for-privacy@thanks.com wrote:

Thanks!
Send 'em to nospam @ snet dot net.
Barry
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On Sun, 23 May 2004 10:28:31 GMT, B a r r y

Barry- I made up a little PDF about my table saw sled. it's posted to ABPW. you're free to use it as is on your website, or if you would prefer I'll send you individual pictures.     bridger
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On Fri, 28 May 2004 02:25:06 -0700, snipped-for-privacy@thanks.com wrote:

Looks like a very functional setup. I liked the through-holes for the clamps.
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On Sat, 29 May 2004 02:02:36 GMT, Mark & Juanita

thanks. I don't clamp everything I cut on it, but when you need to you really need to....
I use that sled for the majority of crosscuts in my shop.
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On Fri, 28 May 2004 19:53:09 -0700, snipped-for-privacy@thanks.com wrote:

I'm going to put this up soon.
My home DSL line is a test / development line, usually unrestricted at 6-8 megs. Unfortunately, tests of the latest stuff aren't going so well, so I'm stuck at 21.6 via dial up. 8^(
As soon as the DSL line is dependable, I'll add your ideas.
Thanks again! Barry
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snipped-for-privacy@hadenough.com says...

Can you repost those pics? can't seem to find them
thanks,
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Can you please repost that PDF. It doesn't seem to be there anymore
Thanks,
snipped-for-privacy@thanks.com says...

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"Mark & Juanita" wrote in message

I'd venture that most of my crosscuts on a sled are less than the width of the blade and wouldn't even engage a splitter. There are exceptions of course, like when crosscutting panels, but generally those are done on stable materials that are not likely to close up on the blade, and anything laying on the table of the sled is basically stationary from the surface to surface friction since it is the sled that's moving, not the material.
IME with a sled, much of the hazard to precision can to come from pulling the cut piece back though the blade after the cut is made. On critical pieces, I don't even attempt to pull the sled back to the starting position until the blade stops on each individual cut ... too many times just the slight kiss of the blade on the drawback (either from the inevitable slop in the runners, or slight movement of the part) is enough to lose the precision of the sled.
...and, if you're like me, don't forget to put the splitter back on when you take the sled off.
--
www.e-woodshop.net
Last update: 5/15/04
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I built a sled 30 years ago and still use the same sled today. I recently replaced my table saw and was surprised to find that the sled fit my new saw. The two slots and the blade align perfectly.

I don't quite understand your logic here. If you put two pieces together the error is additive. An error of 0.0015" across 5" will cause a joint to be 0.003" out of square across 5".
Dick
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In rec.woodworking

I think you're misunderstanding what he is saying. If he cut a board 12" wide, the error would be that much larger than it was at 5". And if he cut a 24" board, it would be even larger. See?
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wrote:

12".
cut
The error in "squareness" is based upon a defect in the angle of the cut relative to the side of the board that is supposed to be perpendicular to the cut in order for it to be "square" (as in a right triangle). As I am getting this, when we take the side of the board parallel to the rail of the table and the one that the blade engages is taken as the reference line from which the kerf is supposed to be absolutely perpendicular in order for the cut to be "square," then the error on the other side of the board (the one on the rail side) is such that the deviation from perpendicularity is only 0.0015" over a board 5" wide?
Side A of board ____________________________Vertex A | | | | ____________________________| Vertex B Side B of board
When sawn on a perfectly aligned machine (one that can exist only in the imagination) then Vertex A = Vertex B = 90 degrees iff Side A is parallel to Side B (not demonstrated by the original poster) and the right side of the board is "square".
But if the alignment is not "perfect", then the angles of Vertices A and B would not be 90 degrees and the end would not be square. So, is the gentleman saying that the deviation from perfect square across a 5" distance between *lines* A and B is 0.0015"? If that is the case, then we have:
Side A of Board ____________________________ Vertex A /| / | / | / | _________________________ /__| *Vertex B Side B of Board C D
Highly exaggerated, of course but *Vertex B (also Point D) would be the perfectly aligned position. However, due to the error, C becomes the Vertex B and the distance from C to D is 0.0015". Is that what you understand this to be?
Since the distance A to D is 5" and the distance C to D is 0.0015", we can find the angle CAD from:
Tan CAD = 0.0015/5 = 0.0003 and angle CAD = Around 2 seconds of arc!
WOW!!!! I doubt that this degree of error would ever be worried about by any woodworker - if that is what the original poster meant by error over 5". Hell, I'd bet a damn good roofing square is off by at least that much. You've got to be a good distance away from Vertex A before such a small error would be noticed. Consider D to be 5 miles away from Vertex A. Then C would be out of place by 0.0015 miles and that comes out to be a misplacement of only 7.92 feet!
So, I ask again, how was this error measured? It seems to me that just tightening a tape measure could compress wood by that much at the application point... then you've got the error of the tape measure and the error of your eye and the error of the changing water content of the board and some other errors thrown in. I'd say it's close enough for government work ... IN THE OLD SENSE!!!
Oh, yeah. Note that in the second ASCII Art attempt, the misalignment could have been rotated the other way but the 2 seconds of arc would be the same since the ideal vertex would form the midpoint of the base of an isosceles triangle.
Agkistrodon
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OK up to your last number. The tan of 0.0015/5 =0.0003 = 62 arc seconds. Still a very small number. It is fairly reasonable to measure this . Take a 4" long board and cut it in the middle. Now flip one piece over and put the two cut edges together. The angle error is doubled. If you push one piece against a straight edge the other piece will deviate from the straight edge by 2 X 0.0015/5 X 24" or 0.014". This is still a small number but it is within reach to measure that amount.
Dick
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wrote:

can
Yep. I misread the table. I need one of those fancy calculator things.
Agkistrodon
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fOn Sat, 22 May 2004 23:40:16 GMT, "Agki Strodon"

yep, what both Bruce and AgkiS said. That is exactly what I was describing.
As further clarification, My only concern was with side B of the board, a piece that had been jointed flat only moments before performing these tests.
... snip

What I meant. ... snip

As I responded in another post, I used a machinist square and feeler gauge. Actually, the error is slightly under 0.0015, but my feeler gauge set doesn't have anything smaller. I'm certainly hoping this is sufficiently good such that only slight planing or sanding will be required for any boxes built using the Leigh jig.

BTW, the error was in the other direction, but, as you say, the effect is the same, I just had to apply the mallet in the opposite direction :-)

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Thank you all for your comments and insight on sled making!
-- Karl B
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And for my .02 worth:
http://www-personal.umich.edu/~mrwizard/wkshps/shpnotes/index.html
Dale
K. B. wrote:

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"How" and "What" are you using to make these measurements on wood and of course "why" ???
Mark & Juanita wrote:

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wrote:

How: Machinist's square and feeler gauge
Why: Take four pieces that are out of square by 1/32" (or even 1/64" -- normal high-precision wood measurements), assemble into a frame. How well-crafted will that frame appear? Just because it doesn't make sense to measure some things to better than 1/32 or 1/64 (or even 1/16) -- there are other times when getting something cut square (or mitered at 45 degrees) to high precision is essential. Another example, take 4 pieces of wood and dovetail all ends to assemble into a box. If all sides of the box are out of square by 1/32, how well will those dovetails fit?

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I grant you that careful measurements are required for any woodworking but when I hear folks talking about somthing that's .0005 out of square, that's getting a little silly.
I own a LOT of measuring devices and I believe I only have one ruler that even shows 1/32" marks, which I can barely see, little less make a correct mark to.
I do have a Incra ruler my wife bought me several years ago that has 1/64" and I can say without a shadow of doubt, I can NOT measure anything using that ruler.
I do all the normal joinery including a few dovetails and as a general rule, most of the joints are tight and quite fine.
I have seen these silly "measurement" things for several years here on the rec and I think it really must make people crazy cause they can't measure and cut a board at some of these "extreme" tolerances.
I go to GREAT lengths to "not measure" if at all possible.
I use story sticks and templates if at all possible.
Mark & Juanita wrote:

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