I have a set of JessEm roller guides on my SawStop table saw and my router table.

I am considering adding a third roller unit to the table saw JessEm track. I have one in front of the blade just a few inches back from the front of the fence. The second is in line with the blade.

I see stock drifting away from the fence near the back of the fence occasionally. I’ve checked the fence and it is parallel to both the saw blade and the saw’s two slots. The cut measures perfect even if I see the stock drifting away from the fence well behind the blade.

I would add the third roller guide about two thirds down the fence well behind the blade.

Any safety concerns? Bad idea?

Try this first (assuming I understand the meaning of "inline" correctly):

Move the first roller closer to the throat plate (about a couple inches from the front teeth of the blade) and the second roller closer to fence behind the riving knife or just behind the back teeth of the blade if the stock is short rather than in line with the blade.

I keep both rollers within an inch to a few inches from the fence depending on the width of the workpiece, but never inline with the blade. (The back roller must not be positioned past the blade on the offcut side which can cause kickbacks.)

Also when feeding the stock, the feeding force should be angled towards the work's far corner torching the fence (as if the rollers were not used).

In the end, I wouldn't worry about the drifting IF the cut quality is not affected in any way. I think one roller is about $160 to $180 Cdn (can't remember the exact cost).

I see stock drifting away from the fence near the back of the fence occasionally. I’ve checked the fence and it is parallel to both the saw blade and the saw’s two slots. The cut measures perfect even if I see the stock drifting away from the fence well behind the blade.

Maybe check your riving knife adjustment?

I have the JessEm guides and just had this exact issue. For me, the issue was my riving knife. I was using a thin kerf blade and my riving knife was out of alignment on the left side of the blade. The right side was OK as I was not getting any binding. The left side was gently pulling the stock away from the fence.

My post on FB:

As I understand it you should be switching to a thinner riving knife when changing to a thin kerf blade. Unless the saw is under powered I don't see a benefit for a thin kerf blade, but there are negatives like poorer cuts due to vibrations etc. All my table saw blades are 1/8" thick, which makes switching blades very easy.

Trent Davis has a pretty thorough article on using thin kerf blades with the stock 2.3mm riving knife. A thinner riving knife isn't required with a thin kerf blade.

I have a PCS 1.75HP and the thin kerf blade I used had a kerf width of .093 (the minimum for the 2.3 riving knife) but a body thickness of .062 which was thinner than the tolerances on the riving knife for body thickness (.071-0.83). Trying to compensate for the thinner body, I incorrectly shimmed the left side of the blade .010, pushing the kerf out of alignment with the riving knife. As material was fed past the blade, the riving knife pushed the material to the left, away from the fence. It was easy to discover once I knew what to look for.

I use a stabilizer when making cuts with my thin kerf blade to help with vibration and in most of the material I use -- 12, 15, 18mm Baltic Birch -- I haven't noticed any decrease in cut quality, but someone else's experience might be different. What I have noticed is less resistance when feeding material into the thin kerf blade.

Even if @Birdhunter is not using a thin kerf blade, the first thing I would check on his saw would be the blade's alignment with the left side of his riving knife. A third JessEm wheel shouldn't be necessary if the saw is properly aligned.

My rollers seem to have held up despite the severe changes in temperature and humidity between seasons. If they show issues in use, I'll try the cleaning trick for the Microjig grripper, and "refresh" them with alcohol.

The tires on my two units had gotten loose and gummy. I was told that the tires are the most ordered replacement parts.

BH,

Do you know if they'll deteriorate over time even if not used? If not, I better order a couple as spares.

Some rubber parts are known to decay or crack after a long period of time in storage.

...The tires had become tired and floppy.

Jeez, that seems to be happening more and more to me the older I get! 

Mike A.

The tires on my router table unit were so bad that I wasn’t seeing any push toward the fence. The tires on the table saw unit were not as bad so I don’t think the tires were the problem. My guess is the wood (quarter sawn oak) was moving. Also, I moved the aft roller further back about 4”. That seems to have helped.