Trying to cut boards to equal length - Woodworking Talk - Woodworkers Forum

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post #1 of 34 Old 01-30-2012, 12:55 PM Thread Starter
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Trying to cut boards to equal length

Hello, I am rather new to woodworking, and I am building a large dobsonian telescope mount. The mirror box needs to be four panels of 1/2" Appleply or similar hardwood. the dimensions of each need to be near exact at 17 and 3/4" by 15 3/4". I cut all the pieces from a board on my table saw ,pushing each one tight against the fence, but somehow, each of the boards is something like 1/8" different from the others. Now I am thinking about how I can make them equal to each other, without taking too much wood from any of them. Any suggestions appreciated. I was thinking about running them all through the table saw at the same time, and on the left side of the table, clamping a 2x4 piece of wood, sort of as a left sided fence, and squeeze all the boards together so there is no change for error.
in general, how does one get exacting cuts, with larger boards? I found information on smaller pieces of wood, but not larger. thanks!
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post #2 of 34 Old 01-30-2012, 01:29 PM
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Use only your saw fence set at the dimension, cut all the pieces for the same measurement, individually at that saw set up. When ready for the next size, set the fence and cut each piece one at a time. IOW, each size hasn't changed from one to the other (for the same dimension).

Don't try to cut pieces that are ganged up...like on top of each other.







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post #3 of 34 Old 01-30-2012, 01:58 PM Thread Starter
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ok, but on the second setup, how do I make sure they are all the same size? It seems like your just telling me to plop down the boards (which are different lengths, and cut the against the fence? yeah, and? How do I make sure they all end up same size?
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post #4 of 34 Old 01-30-2012, 02:13 PM
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theoretically if the fence doesn't move and you don't change anything other than the board to be cut, each one should be the same.

Anther option would be to use a table saw sled and use a stop block on one end and cut the other end off.
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post #5 of 34 Old 01-30-2012, 02:17 PM Thread Starter
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I notice that the boards can move around a little during the cuts though, maybe undulating a little against the fence.
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post #6 of 34 Old 01-30-2012, 02:43 PM
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Quote:
Originally Posted by chironik@yahoo.com View Post
I notice that the boards can move around a little during the cuts though, maybe undulating a little against the fence.
What kind of fence are you using? If you set the fence and use the miter gauge in the slot on the same side of the blade as the fence to provide support behind the board, then there shouldn't be any moving.

If that is outside the ability of your tablesaw, you can try a jobsite route that works for 2x4 gang-cutting - stack all the pieces, clamp together, clamp a square down as a guide and cut them all at once with a circular saw.

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post #7 of 34 Old 01-30-2012, 02:51 PM
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I take it you are crosscutting? If so are you only using a miter gauge without any thing else to guide the cross cut?

1st make sure your blade and miter slot are aligned perfectly and miter gauge set at 90ļ, then the rip fence to the blade.

If you are not using any attachment (fence) to your miter gauge that effectively widens the gauge so your piece of wood is stabler, then add either a piece of wood that is perfect flat and parallel as per the image below.


You can even add a jig to size the cut perfectly to the wood fence. The pic above shows using the left miter slot, most use the right, depending on where the most support on your table saw is you can either.

Last edited by yocalif; 01-30-2012 at 02:54 PM.
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post #8 of 34 Old 01-30-2012, 03:15 PM Thread Starter
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I do not have a miter gauge, this is an older craftman table, with a new blade, and I have this little portable miter handheld guage, and I like the idea of making a simple jig as above, I just need to re-read the instrutions.
I also have a miter saw with laser guide. Problem is of course that miter saw is really a chop saw and only gets one pass. Was thinking how much I like that laser. Could I use the miter saw for a couple of passes on each piece, by that I mean, I would make my first chop, re-set the wood, once or twice, so it would take a few times on each wood piece, but that laser makes me confident about where the blade will go.
thanks!
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post #9 of 34 Old 01-30-2012, 03:32 PM
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One thing you have to watch with the laser on your miter saw is that the laser is true. The line can look right but if you put you blade down it can really be off. As with any tool make sure your laser is true. Trust me I learned the hard way.
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post #10 of 34 Old 01-30-2012, 03:35 PM
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If you're ripping using the fence and getting different widths every time, it's either operator error or a bad fence. I also have an older craftsmen, and I have to measure BOTH sides of the blade (front and back) because the fence sucks.

Even 1/32 inch will make a big difference from board to board, so you have to make sure that thing is dead on. Don't trust the tape on the fence... Use a tape measure. And along those lines -- use the same tape measure for the entire project.

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post #11 of 34 Old 01-30-2012, 06:10 PM
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Chironic, I presume you work with a table saw, and your fence is by now well set and stable. I was dealing with the problem like yours many times, and -- again other than fence -- what is greatly important, is that you provide a strong holding pressure on the side of a piece that goes into the blade. Two things:

(1) use a good feather-board, with the front feather coming close to the blade (and preferably, the full contact length of the feather-board long enough -- close to the length of your piece);

(2) you need a strong holding pressure on your piece as it comes out behind the blade. Of course, you can use another feather-board, but in my experience the best is a good, well-springing splitter. On most of the saws, a splitter is essentially, a part of protector assembly, but I use my own splitters (have made a set of them, using a mild steel, with the thickness slightly smaller than a blade kerf); make sure that the right side of the splitter is flash with the right plane of the blade).

This way, your piece is guided not by the fence alone (which in no way provides good precision), but also by your "left handlers", so that it rides in a well defined channeling structure, and doesn't not depend on operator's errors like unsteady hand, etc. But with all these holding things -- be CAREFUL: use a good pusher that not only pushes your piece, but also hold it down at a sufficient length; try to not put your hand on the piece...

Good luck.

Last edited by AlWood; 01-30-2012 at 06:17 PM.
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post #12 of 34 Old 01-30-2012, 11:42 PM Thread Starter
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"pulling da trigger"

so, what I have done, and I guess it's kind of "ganging up"
is I have leveled out/squared the stack to cut the height of my mirror box
for my dobsonian telescope

http://www.obsessiontelescopes.com/p...ions/index.php

so I have four 1/2" boards. all I have is my table saw 10" blade (rip blade w fewer teeth). But it was late by the time I got set up, and as I decided to save the setup for tomorrow. please look at the pictures and tell me im not crazy.
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post #13 of 34 Old 01-31-2012, 12:01 AM Thread Starter
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I see the pic I tried to post didn't make it into the thread.
I took my four boards, roughly 16 x 18", leveled/squared em at the bottom; wood screwed em twice, measured the table saw, and saved the setup for tommorow to push all the wood thru in one fell swoop. I have my fence and a little push stick I made. It seems like a lot of stock to put through at once, bu then again, shouldn't a medium sized table saw accommodate 2" of hardwood?
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post #14 of 34 Old 01-31-2012, 12:24 AM
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I'd like to help here, but I'm a bit confused. By equal length and your cuts being 1/8th off, are you trying to cut the width or the length? Both fence and miters have been mentioned here and they just don't mix.

If you're trying to cut equal width, use only the fence. Make sure your stock has a true edge by placing it on a true flat surface and a light source behind it. If you see light sneaking out from under the board, your edge is not true. Now you need a jointer or add another true edge on top of the opposite side to use while creating a true edge. I know some folks understand what I'm saying here, so if you don't understand, ask.
Once you have a "true" edge, make sure your fence is square and recut using the true edge against the fence

If you're trying to cut equal length boards, using a miter, using a fence could be very dangerous to you. you cut off boards could bind and be ejected at a very rapid speed (kick-back). Best case scenario, your cut off snag a bit causing them to be of unequal length and not get ejected. The solution to cutting equal length pieces using a fence and a miter is for you to clamp a piece of wood to your fence BEFORE the blade. That way you can butt the clamped wood and cut without the snag. Again, I know some folks already on this forum know what I'm talking about... so ask.

Good luck and welcome to the world of woodworking. It's another great hobby like astronomy.

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post #15 of 34 Old 01-31-2012, 01:06 AM Thread Starter
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Thanks bernie,
So, what I am trying to do here, and if there is a way for me to post pics on the thread from my hardrive, please let me know -- my boards now are all about 18" by 16". so when you ask if I am cutting to width or length, are you asking because of the way the wood grains are oriented?
please picture this, which is my current set-up, and ready for cut tomorrow: four 1/2" pieces of Appleply hardwood, wood screwed together with two 2 " bolts; a craftsman 10 " table saw, blade straight up w. no bevel, a standard rip fence, and a small push stick I made. The table has not miter gauge. I have used my large angle carpenters angle to measure the exact distance from the edge of the blade, to the fence. Clamped the fence, oriented the wood; and now just need to wait for the right time to turn on the machine, and push the wood in, using my right hand to push the stock against the fence, and my left hand manipulate the push stick, and my heart and mind to see me through. I have no miter gauges, sleds, or other than I have mentioned. Though I might change my mind and tomorrow just bolt and feed to boards at a time, which seems to me a little more sane. The old man I bought the table saw though, he is sort of a wood guru, told me I could do it this way. Just not sure that's all there is to it. that is why I am posting here.
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post #16 of 34 Old 01-31-2012, 01:26 AM Thread Starter
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oh and to answer if I will be cutting to width or length, well, both, in different sessions. The first cut will be to height. most of the stock is at about 17 3/4" height, squared on the bottom, and clamped, then bolted together. So the first feed will be the length, wherein I will be trimming width wise. The width of the boards are at about 15 3/4 "; but again, they all vary by as much as 1/8" or 1/4". I would be essentially trimming width wise so everything is equal width.
Then I will unscrew the stock, and level again, and feed the width, again trimming about 1/8" to each one, all at the same time.

Any better suggestons with common wood cutting equiment?
I also have a good circular saw, a jig saw, miter saw, and a router. but how better to go about making all pieces equivalent then using a table saw?


e way down it's
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post #17 of 34 Old 01-31-2012, 01:01 PM
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If you use your miter saw, measure from the blade to the length that you need and clamp a stop block there, then put your boards on the table and cut them to length. They should all be the same when you finish. MEASURE TWICE, CUT ONCE.
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post #18 of 34 Old 01-31-2012, 01:06 PM
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I just read your conversation and I am wondering how accurate your saw is set up. If your blade isn't exactly parallel to your fence, the board will pinch or pull away from the fence as you push it through. Either will give you a different measurement end to end. To fix, raise the blade all the way, lock your fence a few inches away, then measure from the edge of the blade to the fence at the front of the blade and the back of the blade. This measurement will tell if your fence is parallel to the blade or not. To adjust, there should be some bolts on your fence to loosen the clamping mechanism part and the rail part of the fence. Slightly loosen those bolts so the rail moves at the back end of the table. Move the fence into parallel position and re-tighten the bolts. The next thing you need to check is whether you have true 90 degree corners. Checking that requires an accurate framing square. Most framing squares are not square. Test the square by putting the square in position with one blade against a wide panel and drawing a line along the blade that is on the panel face. Then, flip the blade that was against the edge to the other side of the line and line the blade you drew the line against up to the line you drew. It should match exactly. If not you have a worthless square. Now, back to your panels...you will be chasing your tail until you work with accurate tools. If you had a jointer, you could trim from zero to 1/64th or 1/32nd off the incorrect side and make your panels exact. You could also use a router with a pattern bearing straight bit that will follow a pattern and make exact copies in the piece you attach to the pattern. You could pick your best piece as the pattern and trim the others to fit it with this method. These are some options, but accuracy is only as good as the tool set up.
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post #19 of 34 Old 01-31-2012, 01:19 PM
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Quote:
Originally Posted by chironik@yahoo.com View Post
ok, but on the second setup, how do I make sure they are all the same size? It seems like your just telling me to plop down the boards (which are different lengths, and cut the against the fence? yeah, and? How do I make sure they all end up same size?
If you don't understand a suggestion, it will be explained. If you set the fence one time and cut each piece against it, each piece will be the same (as per the fence setting). Is that clear enough?






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post #20 of 34 Old 01-31-2012, 02:10 PM Thread Starter
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Yes your post is clear, thanks. what I did not do the first time is use both hands to feed, and I think that is what went wrong.
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