Alignment of miter rail on jigs

[Michael Merrill]

OK, I was just beginning to build a box joint jig and as I used my crosscut sled notice that is wasn't perfectly square. So I decided to tune the sled first so my next pieces for jig started square.

The sled has two runners but what is the best way to get these as accurate as possible, I'm going for dead on why not right. The problem is that no matter how you start to attach I think you'll need to tune the rails by trail cuts and just changing the rail slightly. If youve got pilot holes drilled you reall can't reposition the rail.

I was thinking to use a screw slot router bit and just make two of the holes slightly oval to allow maybe 1/32 movement or so. I figure with this I can tune the sled with just two screws mounting the rails and allow the others to be standard holes to lock the rails into position.

What are people's thoughts on this approach? Better ideas? I would really like to get the sled dead on so I can depend on it's squareness.

[frank shic]

get a sliding table attachment if you have the room.

[Charles Wiggins]

OK, I was just beginning to build a box joint jig and as I used my crosscut sled notice that is wasn't perfectly square. So I decided to tune the sled first so my next pieces for jig started square.

The sled has two runners but what is the best way to get these as accurate as possible, I'm going for dead on why not right. The problem is that no matter how you start to attach I think you'll need to tune the rails by trail cuts and just changing the rail slightly. If youve got pilot holes drilled you reall can't reposition the rail.

I was thinking to use a screw slot router bit and just make two of the holes slightly oval to allow maybe 1/32 movement or so. I figure with this I can tune the sled with just two screws mounting the rails and allow the others to be standard holes to lock the rails into position.

What are people's thoughts on this approach? Better ideas? I would really like to get the sled dead on so I can depend on it's squareness.

Michael,

Not quite sure about a tune-up, but if I were to do a build from scratch, I would start with a general saw tuneup to be sure that everything with the saw was square and true.

Next, I would size my guide rails to the slots and pre-drill & countersink the screw holes in the rails, being sure to have screw-holes near each end of the rails. I'd slide the rails back just far enough to have clear access to the first screw-hole in each rail from underneath.

Then I would then place the sled bed on top of the table saw and align it to the desired position and position the ends of the rails, then shoot the first screw in each rail. Then I would slide the whole assembly forward so the the first screw-hole in the opposite end of the rails is exposed from underneath and shoot those two screws, then I'd pull it forward to barely expose the next set of holes and shoot those two screws.

THEN, I'd go back to the first side the do the second row of screws there... then back and forth until all of my screws were through the rails and into the sled.

I've also seen instructions where they advised shimming the rails proud of the table and using super glue to fasten the rails to the bed, then once the glue is dry flipping the whole assembly and shooting the screws.

Anyway, once the rails are positioned, put the sled on the saw and clamps it down do you can start the saw and raise the blade through the bed and slide the bed to cut a line across the middle of the bed. But don't cut all the way across. Lower the blade and place a sized wood shim in the saw kerf to use as a guide for your square. Place the square against the shim and use that to square up your front and back fences. This should give you a perfectly square crosscut jig.

[glenn bradley]

This may give you some ideas. I use the fence as a known parallel to the blade and let it square my sled-bed. I then use couble stick tape to attach the runners before driving in screws.

http://www.sawmillcreek.org/showthread.php?t=50581

[Michael Merrill]

Most of the things mentioned here is how I first created my sled and it it "pretty good". I did pre drill my rails, used double stick tape to set the rails, I guess the issue I'm trying to correct is that I found it hard to get the sled dead on in that manner.

I figured now that the sled is constructed it could be "tuned" just like we tune our saws to zero in on that perfect setting. But now with all the rail holes set it's difficult to tweek them ever so slightly to get that perfect setting. Maybe the problem is that you all have had better luck with the initial attachment and that your saws and fences were already better tuned than my initial starting position.

Maybe I'll review how my fense and saw alignment is as well. I guess I'll need a micrometer tool to get started.

[Thom Sturgill]

When I built mine I did as you said and roughly set the rear fence using only two screws, one into an elongated hole. I then crosscut an 8" board that I had jointed and after sawing checked the board by putting the cut ends side-by-side and checking for error. Then adjust and cut again and repeat until perfect. THEN add additional screws to fix the fence position.

[Michael Merrill]

Well spent some time today and found the saw to be in decent order as far as tune so I did concentrate on the sled. I ended up recutting my rail as the original allowed for more slop than I liked. I change to UHMW runners and recut new ones with better fit. After quite a bit of fussing to attach just right I think I have made a significant improvement, a test of a 16X12 piece produced a good square corner.

So maybe the runner slop and slight misalign was all I was fighting.

Now on to the box joint jig!

[glenn bradley]

Maybe the problem is that you all have had better luck with the initial attachment and that your saws and fences were already better tuned than my initial starting position.

The rails are of secondary consideration. As long as they ride well and have a good fit with no slop, that is the end of their role in adjustment. Simply adjust your rear fence for a true 90* to the path of travel using the 5 cut method and all will be well. After considerable weather change I have had to re-adjust mine a bit but only once so far. I took just a couple minutes.