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Forum topic by MarkwithaK posted 09-29-2013 07:13 PM 2698 views 2 times favorited 23 replies Add to Favorites Watch
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MarkwithaK

370 posts in 1868 days


09-29-2013 07:13 PM

The other day I built a new crosscut sled. I watched the video by William Ng and used his equation to square up the fence.

A-B/4/ Length of cut X distance of fence.

After plugging in my numbers I get:

1.093 – 1.089 = .004/4 =.001

At this point I’m thrilled.

My issue stems from when i plug that number into the rest of the equation it tells me that I need to move the fence up .0026.

Being at .001 is great…I wouldn’t even gripe too much at .002 but having to move almost .003 starts to concern me.

Am I correct in that the .001 is how far I am off square as it sits and .0026 the amount I would have to move based on a the full length of my fence?

-- If at first you don't succeed then maybe skydiving isn't for you.


23 replies so far

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Jeff82780

184 posts in 1685 days


#1 posted 09-29-2013 07:25 PM

its been a while since I saw William ng’s video, but I don’t ever remember plugging a number back in, I believe you are off .001 and you need to use a .001 feeler gauge and move it that distance. Anything up to .0003 is extremely good and I would leave alone. You may end up making things worse if you keep fiddling with it. Good Luck!

-Jeff

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RPhillips

524 posts in 527 days


#2 posted 09-29-2013 07:52 PM

I don’t recall it saying how far to move the fence, as this would pend on the distance between the axis that the fence would move on, which would have to be calculated into the equation as well.

I’ll be building one soon following William Ng video as well.

-- Rob - Indianapolis IN - Learning... one mistake at a time...

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MarkwithaK

370 posts in 1868 days


#3 posted 09-29-2013 08:09 PM

Sorry, the equation is to calculate the error ratio which according to Ng is the distance to move the fence. In my case that would be 26” from the pivot point (far right side of the fence).

About 7 or 8 minutes into the video.

5 Cuts ti a Perfect Cross-Cut Sled

-- If at first you don't succeed then maybe skydiving isn't for you.

View BJODay's profile

BJODay

393 posts in 633 days


#4 posted 09-29-2013 10:48 PM

Mark,

A piece of paper is typically 0.004” thick. Don’t beat yourself up over such a small discrepancy.

BJ

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MrRon

2874 posts in 1934 days


#5 posted 10-02-2013 07:34 PM

The fence distance can be anything you want. If you make the fence length a distance measured from the pivot point to say 24” to the left of the pivot, that is where you measure your deviation at. If 30”, then that is where you measure the deviation. Just make a mark any distance you want from the pivot and that is your reference point where you measure your deviation. The further away you get from the pivot, the greater will be the deviation.

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MrRon

2874 posts in 1934 days


#6 posted 10-03-2013 10:41 PM

What is your length of cut? You have to divide .001” by length of cut and then multiply that by 26”.

View rg33's profile

rg33

51 posts in 692 days


#7 posted 10-04-2013 12:41 AM

the setup for this as I recall is you cut four sides (rotating 90 degreees each time) then you cut a strip of the fourth end (the side you first cut). Measure the difference in widths and that is how far out of square you are on the ENTIRE PERIMETER OF BOARD you just cut. So if you had a 20” by 20” piece this would be the error in 80”. I dont know how big the piece you were cutting was but if your total error was .004” then forget about any more adjustments. to give you an example I was cutting a piece roughly 20X20 and I ended up with .018” difference in width on the strip I cut that means that I am only out of square .0045” per 20” or less than .003” per foot which is more than fine for 99.999% of any woodworking anyone will ever do. The woodwhisperer has a good point on accuracy here:
http://www.thewoodwhisperer.com/articles/how-much-error-is-too-much/

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waho6o9

5092 posts in 1267 days


#8 posted 10-04-2013 01:33 AM

Maybe measure your diagonals.

If they’re the same you’ll be fine. Leave the .001 stuff
for the machinists.

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bowedcurly

486 posts in 419 days


#9 posted 10-04-2013 02:09 AM

.0003 hell that’s to bearing fit, there is nothing on a table saw that’s even near that, just sayin

-- Staining killed the wood<<<<<>>>>>Dyeing gave it life

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Rick M.

4149 posts in 1070 days


#10 posted 10-04-2013 04:02 AM

Been a long time since I’ve watched that video but if memory serves it was the most convoluted way to square a fence I’ve ever seen.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

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jmartel

2326 posts in 840 days


#11 posted 10-04-2013 02:37 PM

bowedcurly, wouldn’t you say that the arbor bearing in the table saw has a bearing fit?

-- End grain is like a belly button. Yes, I know you have one. No, I don't want to see it.

View oldnovice's profile

oldnovice

3798 posts in 2058 days


#12 posted 10-04-2013 08:56 PM

I use 1/4” tempered Pegboard mounted to the runners and mount the fence using the holes in the Pegboard. I have used this technique on a number of sleds and found less than .002” error.

I have two steel rails that have both 1/4” through holes (at the far ends) and threaded holes between them. I drive dowels through the Pegboard into the rails (typically a very tight fit) and then counter sink the holes that align with my rails threaded holes. The fence must be carefully constructed since that determines true 90°. I drill 1/4” dowel holes and 1/4” threaded holes (with inserts) to align the fence to the Pegboard and use the same methodology when mounting the fence as I used for the rails.

The reasoning for using peg board is that the holes are very accurate and I can also make a 45° sled by using the appropriate holes in the peg board.

My PC is in for motherboard repair otherwise I could post the entire process!

-- "I never met a board I didn't like!"

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Rick M.

4149 posts in 1070 days


#13 posted 10-05-2013 04:05 AM

The pegboard idea is very interesting. I look forward to your motherboard returning so you can post pics.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

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exelectrician

1665 posts in 1118 days


#14 posted 10-05-2013 04:47 AM

Buy a good quality sliding chopsaw and ditch the sled, forever.

-- Love thy neighbour as thyself

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comboprof

277 posts in 425 days


#15 posted 10-15-2013 01:20 PM

It seems you have not told us what the length of the cut was, i.e the distance between where you measured A and B. But your calculations suggest this was 10”. Also you give 26 as the distance from the pivot to where on the fence you plan to make the adjustment. If so you are correct and need to adjust by .0026. By why are you concerned. It is what it is. The error could have simply been introduce by you when you set the original sled rear fence. Because it is so easy to make the adjustment I would do it. On the other hand as they say here it may not make any noticeable difference in your projects anyway.

In my opinion William Ng method is brilliant, accurate and easy to use. It is not convoluted at all.
The crux of his method is that it finds a way to use the digital caliper to accurately measure the error.

-- -- Cheers, Don K. (Michgan's Kewenaw peninsula)

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