Riving knife alignment problems

[reubenjames]

I've never been satisfied with how my riving knife lines up with the saw blade. I went so far as to purchase a second upper saw guard unit at one point because I was convinced something had to be wrong with the one I had. It's not an offset problem that can be solved with the screw on the lower saw guard and it's not an issue with using the wrong arbor for the table system or a third party blade (I use a Shopsmith blade). The knife isn't parallel to the blade, it's at an angle. I think the problem really lies in how the collar of the lower guard fits on the quill housing. There is a lot of slop and I feel like I can fiddle around and get it dialed in pretty close some days, but there's no easily repeatable method for replicating that alignment. I can pull the collar so it's right up against the lip at the top of the quill, or at the bottom, but the truest position I can find is somewhere in between, which makes it hard to replicate without a lot of trial and error. Using an improperly aligned knife can be worse than no knife, I've found. And any safety equipment that isn't reasonably convenient runs the risk of not being used--that is not something I am comfortable with. The blade is on and off a lot to change operations; I need a repeatable way to easily align the knife.

Is there a process I'm missing, or a physical piece, or could my lower guard be compromised and in need of replacement? Please let me know what questions or pictures you need from me to help me troubleshoot this. Thanks in advance!

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[BuckeyeDennis]

I used to have exactly the same problem, and I kept trying to solve it by pressing the guard mount against the quill ring just so, as I was tightening the clamp screw. But what I eventually discovered was that back of the riving knife was rubbing/binding against the back of the slot in the table insert, and this prevented it from positioning repeatably left-to-right.

When I discovered the interference problem, the first thing I did was to relieve the table-insert slot a little. But then I learned that the root cause was that I had the blade guard tilted rearward just a fuzz. So now I always set it up tilted forward just a fuzz, which eliminates the interference.

With the interference gone, I don't have to futz with the guard mounting. Just stick it on, tighten the clamp screw, and let it draw itself into alignment. Once I set the riving-knife adjustment for that process, it repeats just fine.

[reubenjames]

This seemed plausible, as I know I have had issues with the back of the riving knife hitting the table insert before. So today I went in and removed the table from the equation entirely--just tried to get the lower saw guard, blade, and upper saw guard mounted and aligned. Prior to tightening the red knob on the lower saw guard which holds the riving knife in place, the knife runs parallel to the blade (or at least very close). They may not line up, but that can be fixed with the screw on the left (from the operator's perspective) of the lower guard assembly. I wasn't so much interested in lining that up today as in determining if the riving knife remained parallel with the blade: it did not. Tightening the red knob pulls the knife out of parallel. Tightening the set screw of the lower saw guard around the quill collar seems to pull things further out of parallel. Thus, after tightening, if you are sighting down from the top of the Shopsmith, you can see the end of the riving knife is to the *left* of the blade, it crosses over the blade, and as you move down the knife it ends up on the *right* side of the blade. Only having one point of pressure (the red knob) seems like it could cause some issues with securing the knife, even though the metal plate "sandwich" runs down along the knife which slots into those two protruding pins. I wouldn't expect it to pull that much out of alignment. Tightening the collar set screw seems to exacerbate an already skewed situation.

I'm going to study the exploded view of the lower saw guard tonight to see if I can identify any missing or damaged pieces on mine that might be contributing to this problem--the saw guard was part of a used Shopsmith purchase and it has some pretty gnarly bites taken out of the plastic, so it was definitely damaged or possibly mistreated at some point. Outside of rolling the dice on a replacement lower saw guard and hoping that corrects it, I'm at a loss. I can't adjust the position of the blade to match the knife, matching the knife to the blade is the only option.

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[BuckeyeDennis]

Yep, it sounds like something is wrong with your hardware. I just reviewed the alignment manual. It explains the offset-adjustment screw you mentioned, but there’s no adjustment for riving-knife left/right tilt angle.

I also bought my 520 used, and I have a dim recollection of having to straighten the lower part of the riving knife. Tough stuff, as I recall ... it was like trying to straighten spring steel.

[algale]

When you tighten the riving knife clamp, you can see the riving knife skew itself relative to the blade? AND you have experienced this problem with two separate lower saw guards??

As Dennis is suggesting, the riving knife may be bent.

The other option seems to be that you have had two bent/warped lower saw guards.

[reubenjames]

Correction: experienced it with two separate *upper* saw guards. I bought the second one because I thought it was, in fact, the knife on my first upper guard that was bent. But since both knives do it, I have a hard time believing they are both twisted in the same exact way. So lower saw guard is the only other culprit I can think of.

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[Ed in Tampa]

Besides the bolt there is a positioning pin. Is it possible your slipping the riving knife down too far and your tightening it down on the positioning pin which would skew the Irving knife in much the manner you say.

[dusty]

Judging from the equipment list in your signature block, I conclude that you have either a 510 or a 520.

From your comments I conclude that your issue is with the riving knife that is part of the upper saw guard and NOT the other style riving knife,.

If these assumptions are correct, I suggest that you remove the riving knife from the upper saw guard and then use it (alone) to analyze your problem.

To help, can you post a picture looking down into the lower saw guard with the riving knife installed. Other than a bent knife I have no suggestions as to what might be causing the issue.

[reible]

Shot a few pictures of my guard that might help to spot the issue with yours.

This is a pretty simple arrangement, the knife just slides in and the two pins align it vertical and the other part screws closed clamping it. But since yours has issues there are a few thing that could be issues.

I would first check to see that the back of the lower guard is reasonably flat with a straight edge. I would not expect it to be perfect up if there is some bow or bend of say over 1/16" that is more then I'd like to see.

Here are the pictures of mine, in the first one you can see the two pins and you can do a visual inspection of the area where the knife will touch, including near the two pins to make sure there is nothing obstructing it from laying flat.

g1.jpg (192.83 KiB) Viewed 17999 times

The AL block should also be inspected to make sure there is nothing that would keep it from laying against the knife. You can also check this with out the knife in place in the lower guard.

g2.jpg (288.03 KiB) Viewed 17999 times

Then put the knife in place and see that it fits flat like shown here:

g3.jpg (215.06 KiB) Viewed 17999 times

Add the cap without the fastener tightened and see that it sits flat as seen here:

g4.jpg (205.5 KiB) Viewed 17999 times

Then put it all together and make sure it is still flat against the parts when tightened. If we got lucky the problem should have surfaced by now and you have fixed it.

g5.jpg (218.15 KiB) Viewed 17999 times

If not then we need to see pictures of yours, perhaps the same sort that I posted.

Ed

[reubenjames]

Thanks for the pics, Ed. Sorry for the delay in replying: work and honey-do lists have been keeping me busy.

I still need to take some pictures, but I do have some progress. I received a brand new lower saw guard from the Mothership today.

That brought me up to:
Two upper guards/riving knives. Both were used. The first one (that I'll call the "old" one) is the one that came with my Shopsmith when I bought it (used). The second one (which I'll call the "new" one because it was newer to me and looked to be in better shape) is the used one I bought off eBay when I thought the knife was the problem.
Two lower guards. The old used one that came with my Shopsmith when I bought it, and the brand new one from the Mothership today.

I mounted the new lower guard on the machine today and the "new" upper guard/ riving knife and I was disappointed that they still did not line up properly at all. Just to be thorough, I dug out and tried the "old" riving knife/upper guard with the new lower guard and...ta-da! Lined up, spot on, with no adjustment needed. I unmounted and remounted both pieces a few times to make sure it wasn't overly finicky and I didn't just get lucky. Came back together every time.

My assumption at this point is that my old lower saw guard AND my "new"(er) upper guard/riving knife are both compromised. Which would suggest a pretty bad streak of luck since I haven't run across *too* many other people having this kind of issue.

I do want to fudge with them all a bit more and document with pictures the behavior, but in the meantime, I'm excited/relieved that I'm back in (safely) working order.

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