Makita 118" Rails for Makita Plunge Saw Issues

[tim walker]

I bought this track about a year ago and have just recently gotten around to having a need to use it to square up a couple of sheets of 3/4" (18MM) ply. I use a TSO GRS-16PE guide rail square which I have confirmed as a perfect 90 deg. I also have a large Woodpeckers square which I have also confirmed to be spot on 90. I have pulled my hair out attempting to square up a 84" x 46" sheet of ply. I have use both squares and on the long cuts I cannot achieve a straight cut. I decided to take the back edge of the rail and lay against a freshly cut long edge and low and behold there is about an 1/8" gap (not measured) indicating the edge of the rail is not flat and I truly believe that has been what is causing me to not be able to get square.

Has anyone else had an issue with long rails, especially Makita? And how do I prove to Makita that it is not perfectly flat? Some pics attached. 465736465737 These are taken from a fresh long cut using same rail, approximately 84" long.

Thanks all

[Gustav Gabor]

I believe you're trying to say the issue you have with your Makita guide rail is that it's not accurately straight, not necessarily it's flatness.

Not too long ago, I bought a Makita 118" rail, and found it wasn't straight. at least not enough for me.
Within an hour of buying it, and testing it, I took it back to the place I bought it from for a full refund.

Seems it's a hit and miss as to whether the Makita, or ANY guide rail one receives/buys is actually straight.

I'm guessing Makita will say it's "within tolerance" .....

[Rick Potter]

Do you clamp it down? If not, try that first.

[Rich Engelhardt]

If you want or need better accuracy, pony up for the more expensive Festool tracks.
I had both until I sold my Festool saw & there is a noticeable difference between the two.

[Jim Becker]

One other important thing about this...even a minor deviation in straightness is magnified a lot more on a long track than it is on a shorter one. But a 1/8" deviation is "yuge", IMHO.

[Jim Dwight]

If your track is truly 1/8th off over it's length that seems to be too much to me too. But I think you are asking how to test. If you have granite countertops, I would lay it on edge on them and measure for gaps. I would trust that straightness more than a plywood edge. But I have checked many sheets of plywood and I typically find them as square as I can measure. I have a 18 inch square of plywood, CNC cut, that I put a fence on to make it kind of a giant speed square. That is what I would use. I don't trust my carpenters square. But it is only 18 inches. But it the plywood looks square with the tools I have, I consider it good enough and just clean up the edge.

I do not think there is a square for a track that will reliably give you a 48 inch square. I have definitely not used them all, I just don't think I would want to carry it around if it was rigid enough to do this.

So in my opinion, the key question is whether your long track is straight. I've never actually checked my long DeWalt - which is a little shorter than yours. But I've used it a lot and not had any issues. When I prepared the edges of the 10 foot boards for my dining room table top with my track saw, using my 103 and 59 inch tracks joined, I found it is about 3/16 wider in the middle than it is at the ends. Probably the joint in the tracks but could indicate my long track is not perfectly straight. Doesn't bother me. That difference also accumulated over 6 boards. I think that's 10 cuts.

If you do not have a stone countertop I'd probably use the factory edge of a sheet of plywood. I think they're pretty straight. It won't be as long as your track but should give you a pretty good idea.

[John Gornall]

It's the actual cut being straight that counts. Lay the rail on a sheet of plywood. Clamp it so it won't move. Using the Makita scoring feature cut a shallow kerf the length of the plywood. Pull a string line from the kerf at one end to the kerf at the other end. Straight? Mine is.

[Gustav Gabor]

This is how I check for straightness on straight edges and guide rails.

https://live.staticflickr.com/65535/51541637842_b99bb5ee87_z.jpg (https://flic.kr/p/2mwynfj)

I generally use Webber/Starrett gage blocks as the 3 blocks, and can check for discrepancies as small as .0001", which of course is a bit nuts for woodworking.
Ideally, in order to get the most accurate results, the outside blocks will be placed as close to the ends of the rail as possible.
This method will note any deviation from dead straight, however will not necessarily find any oddball curves in the rail or straight edge if the curvature isn't uniform.

[Eric Schmid]

I would start simple to minimize variables. It does appear that your track has a bow along the edges, but…what happens when you make two cuts and mate them together?

I’m not talking about square, because this adds another variable. Just two “straight” rips down the length to start. Label and flip one of them and mate the two freshly cut edges together.

If the cut side of your rail is convex, the edges of the cut pieces should be further apart at the ends. If the cut side is concave, the gap will be in the middle. If the rail is bent in a specific point, you should be able to see that as well.

Once you know if your rail can cut straight, then you can deal with square.

[Bill Dufour]

You are using the edge you cut as a reference to determine straightness. that is nuts. At least use a factory edge or a taught wire. A plumb bob wire should be as straight as you need for wood working.
Bill D.

[Jamie Buxton]

Here’s a way to test the rail’s straightness without relying on any external tool - whose straightness might be a question.

Use the rail and saw to rip a sheet of plywood from end to end. You can even rip corner to corner to get a longer rip. Remove the saw and rail. Fold the two pieces of plywood together. Do not flip one end-to-end. Just fold them together. Align the cut edges. If the cut is bowed, you’ll see it.

[tim walker]

So placed the edge along a very wide piece of granite in the kitchen. My 4 ft machinist straight edge indicates it is perfectly flat over the 4 ft and sliding it down it indicates next 4 ft is flat also. There is still a measure 0.02" gap on the same end as the first pics I sent. The 0.02" is measured with feeler gauges.465814465815

[Rich Engelhardt]

What about the cutting edge of the track?

[Dave Sabo]

So placed the edge along a very wide piece of granite in the kitchen. My 4 ft machinist straight edge indicates it is perfectly flat over the 4 ft and sliding it down it indicates next 4 ft is flat also. There is still a measure 0.02" gap on the same end as the first pics I sent. The 0.02" is measured with feeler gauges.465814465815



DO NOT ASSUME that your granite counter top is flat !

That rail may be garbage anyway, but most people assume their pretty stone tops are perfectly flat. And that is almost always not the case.

[tim walker]

I have a 48" machined straight edge that is sup[posed to be within 0.001" tolerance over the 48". I slid it along the countertop in 2 ft increments and it indicated flat. About the best I can do tpo assume flat. It showed the same gap on the granite as it did along the freshly cut piece of ply at the same location. Regardless, this track is causing me to not be able to exact diagonal measurements indicting something is out of square somewhere.

[David Buchhauser]

I think that a 1/8" bow in the edge of your guide rail would (or should) be very apparent by just sighting down the edge with your eye. You could also position your guide rail so that the edge faces up and clamp it in a vise using soft jaws or blocks of wood to prevent scratching the guide rail. Then pull a string tight from one end to the other. If the edge of the guide rail is bowed, this simple test will certainly show it.
David

[Dave Sabo]

Like I said , your rail may be garbage anyway.

Does your “accurate” straight edge show a dip in the rail or counter top in the same spots on both the counter and rail ?

What does the straightedge show on the inner spine at the same spot as the pictured dip ? That’s the one that the saw actually registers on.

Are there other dips or bows along the rail ?

That end of the rail should be hanging off of an 8’ sheet by at least 8”-12” anyway - effectively taking the curvy end out of the equation.

Don’t use the TSO square for the first long cut.

As mentioned , clamping is a good practice.