Kerfmaker gone awry

Hi all.

I was playing around with my new kerfmaker this evening and was having trouble making it work right (the dado cuts came out consistently too small). Now, the function of the tool is nearly idiot-proof, so I suspect that the cheap portable table saw I’m borrowing is the culprit. The guide that comes with the table saw (the one that fits into the grooves on either side of the blade) is extremely loose in the slot. I seriously doubt that the blade has been aligned with the fence, either, but I dont think that’d have much to do with it since I wasn’t using the fence.

Since I’m only borrowing the table saw and can’t make any modifications to it, what can I do to increase the quality of my dado cuts on this saw? I’m trying to make a bookshelf with lap joints and would really really like to have it as close as I can.

Thanks in advance for your help!

-- ~ Dan, North Carolina, http://www.BluewoodCreations.com