Crosscut Sled--What did I do wrong?

[Daniel Grieves]

Having read so much about how useful a good crosscut sled was, I finally built myself one this weekend. I followed the basic instructions described here:

base is 3/4 inch birch plywood. The front & back are 2x4 common lumber. The runners are birch plywood slices, carefully taped to fill the slot and minimize wiggle. The table seems to slide smoothly and easily over the blade but when I went to make a few cuts with it (3/4" cherry, not a problem for my saw usually) the blade bound and wanted to kick the whole thing back at me.

What was my mistake? Thanks in advance, Dan Grieves

[Leon]

I recommend a harder material for the runners. Oak, Maple, Steel. I am guessing your runners are flexing and causing your sled to not go in a straight parallel line to the blade. It will work better also if you mount the runners into a dado so that there will be no flexing.

[Ba r r y]

If it's not the flex that Leon suggests, maybe the runners aren't square to the blade slot?

This would move the slot from side to side as the sled travels along. With the saw shut off can the sled move smoothly over the blade for the full travel?

I lay the runners in the slots with glue on them, lay the panel on, place some weights, and add screws after the glue sets. The blade slot dosen't get cut until after the face(s) are added, then the rear face is squared to the slot and glued. The saw itself is the perfect jig for aligning the runners.

Dadoing would add a whole bunch of extra work, in my opinion. Since I usually make sleds and jigs when the need arises, I tend to simplify them as much as possible. My smaller sleds don't even have a front fence.

I've used ash, red & white oak, birch, and maple for runners. All worked fine.

Barry

[Dave Balderstone]

Or maybe the blade isn't square to the miter slots...

[Leon]

I hope it is not.. :~) Maybe parallel is what we are looking for here.

[Ba r r y]

RIGHT! I'm sure both of us mean parallel.

If the blade were square to the runners or slots, I'm sure we'd get all kinds of neat problems.

At least _I_ always know what I mean.

Barry

[Andy Dingley]

Not from me - they're dangerous bloody things. A UK HSE inspector will usually throw a wobbly if he sees one too (they're having a downer on "emerging blade" cuts these days).

Throw it away now and build a crosscut _BOX_. This is similar, but it has a top too. The sides are tall enough to keep your fingers away from the blade and there's a wide strip (often transparent) across the top, covering the blade from the top direction. This also helps to stiffen the box, avoiding the sort of flex and binding in the baseplate that you're getting.

You can also (if you make a box) use a baseplate of thin Masonite, rather than thick plywood. If this should choose to bind, the force is minimal and it's unlikely to lift or throw.

There should be closed-ended tunnels at the ends of the slot too, so that the whole blade can be "swallowed" without protruding. Make the ends of them thick enough to survive running into the blade from time to time.

[Larry Jaques]

On Mon, 8 Nov 2004 15:59:16 -0800, "Daniel Grieves" calmly ranted:

IF your sled runs fine with the blade up + no wood, and there is no slop in the runners, and the blade is new or very sharp: Most probably, you didn't hold the wood firmly against the back fence or didn't hold it down, perpendicular to the blade. Either will cause binding.

[Dave Balderstone]

Oops. Yeah, parallel, that's it...

;-)

[Mark Jerde]

To help hold the wood in place I put down strips of "Skid Guard Safety Tape" on the back and bottom of my sled. You could also glue strips of sandpaper but I already had the self-adhesive strips. It made all the difference for keeping the piece being cut in place.

-- Mark

[Fletis Humplebacker]

Did you check the speed of feeding and proper blade for crosscutting?

[bridger]

one thing to check is that your 2x4 front (the one the wood rides against) is straight. if it's concave you could get that kind of binding.

it really should be made of stable dry material. I gave up making them out of 2x. these days I make them out of baltic birch ply...

[Bob]

I thought a picture would help. Here is a fancified version of what you are talking about.

[Mark Jerde]

Is that a MuleCab fence? (I'm thinking of getting one.)

-- Mark

[J T]

Tue, Nov 9, 2004, 12:13am (EST+5) [e-mail] (Leon) says: I recommend a harder material for the runners. Oak, Maple, Steel. I am guessing your runners are flexing and causing your sled to not go in a straight parallel line to the blade.

I glued my plywood strip runners like that, and no flex there. My sled works fine, no problems. I'm thinking his blade might not be parallel with the slots.

JOAT Viet Nam, divorce, cancer. Been there, done that. Now, where the Hell are my T-shirts?

[Mark & Juanita]

... and if the problem is that his runners are flexing, the only thing he is going to accomplish by that is adding mass to that which will be thrown back at him.

So, how do you actually get something *into* this totally safe box? and how do you hold anything steady with all these safety devices hanging about the thing? I personally use a clamp to hold the piece I'm cutting, thus accomplishing two things: 1) it makes sure the piece does not slip while being cut and 2) it keeps my fingers safely away from the blade.

I've found that a simple block wood attached at the back center of the sled accomplishes the same thing without the complexity of a "tunnel"

[Guess who]

with one either side for safer "handling".

[George]

All kinds of dancing around this one, but this answer is incorrect in one important aspect.

Blade parallel to the miter slot is the first problem. This can cause the blade to bind, even though it's going to produce a square cut. Are you lifting splinters from your plywood? one of the sure signs of non-parallel on a tablesaw or heel on a radial.

If you have your runner(s) tight, make sure they're tight all the way through the cut, though it makes no difference in the world if they are tight in the miter slot. *What makes a difference is that it references one or the other side consistently.* This means straight, and I mean straight as in no light when you set it on your reference. Some sled builders recommend deliberately undersized runners on either side, pinching the sled by riding the inside of the slots or out. Keeps binding to a minimum by providing a bit of dust clearance.

[Bob]

Sorry, I don't know, Mark. The link belongs to someone else. I just happened to see it an thought it was useful to post here.

Bob

[Daniel Grieves]

Ok, first of all...Thanks to everyone who took the time to respond. Here's what I can gather from your various responses:

1) Make sure my saw blade is parallel to the mitre guage slots. Is there a more accurate way to do this than just building a simple T-square type thing that I would ride in the slot and make sure it touches the saw blade equally at all points?

2) Double-check that there's no play in my runners. Will do.

3) If 1 & 2 don't eliminate the problem, I will replace the 2x4 with something more stable to prevent the sled from flexing.

4) If 3 doesn't work, add a top to provide even more stability. I'm guessing it would have to be something pretty hefty (but clear) to be workable.

5) I guess I'm a little confused on 1 point. I thought the design of the sled was to hold the stock against the front but Larry made it sound like the wood runs against the back edge. Which is correct? (When building my sled, I only checked the front board for perpendicularity to blade.)

Thanks again, Dan