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[Garry Reid]

I have recently purchased an early edition LS12 that had an old but functioning blade. I cut a few rocks and the blade got duller, stalling the motor. I decided to try the sharpening method demonstrated on Highland Park's videos. I probably did not contact the blade at a perfect perpendicular angle and maybe used too much force as well. I think I disturbed a diamond insert and started to get saw marks on my slabs. I should also mention that I found the feed rod was bent and the threads on the feed rod end screws were worn. So, I replaced the feed rod, replaced the feed rod end screws and nuts, made sure it was running horizontally, made sure the blade was running true and installed a new blade. They slabs are much better but there is still some faint marks on the slabs from the new blade. I am not sure what to suspect at this point.

[Slabbercabber]

Make sure the carriage runs parallel to the blade.  I like to put a dial indicator in the carriage and run it by the blade.  With care, a pencil will do.

[Garry Reid]

This will be more of a test than the static measurements I have done trying to make sure the blade is parallel to the carriage rods. I don't have a dial gauge but it's definitely on my list to purchase today. Thank you.

[peruano]

Saw marks come from unequal pressure on the blade with multiple possible causal factors. 
For me the primary one is surging.  Worn feed threads, loose carriage flop, dull blade causing the feed to be sporadic, alignment, and probably a host of other factors. Blade alignment by itself should not create marks unless if affects the feed of the work. If the feed dog (*or connection between the feed road and the vice sled is not secure or the threads not exactly fitted there will be the potential for surging and saw marks.  Keep playing and it will be cured. 

[Garry Reid]

I have had concerns that the carriage might have too much play because of it's age. At this stage, I have ordered a dial gauge and holder from Amazon and in a holding pattern for now because I don't want to risk cupping the new blade and adding another element to the problem. While my saw is idle I am going to drain ad clean the saw and oil. I'll have a good look at the connection onto the feed rod. In have just replaced the feed rod and end nuts, screws and feel good about how I have that set up but the carriage is a bit of  a question mark. There is a turn-and-a-half of free play when advancing the vice in or out when changing direction and the thumb screw (single on this early version) that locks the vice in position must be mushroomed because it is not removeable. I have to see if I can somehow cut the end off so I don't damage the threads.
I don't know if upgrading the whole carriage is a possibility with this vintage but I would do it if I can. For now though, I'll really have a good look at the carriage set up.
Thank you very much for sharing your knowledge.
Garry

[irockhound]

Common problem also is having one of your arbor bearings going bad.  When the cut starts and the blade cuts semi true but as you get deeper in the cut and the pressure increases on the bearing and the slop of the bearing then causes the creation of the grooves as the blade now has changed it's alignment.  Oh and I also have had this happen just recently and why I found out was the blade came to a stop on my ls-12 and the belt started slipping since it was an old belt.  put on a new belt and then the bad arbor bearing brought the saw to a slow stop almost like it was finishing a cut.  Didn't make a sound just stopped,  thankfully I was in the garage and when I walked over to the saw I noticed the pull chain was still slack so shut down the motor and drive.  Put one hand on the arbor pulley and the other on the nut on the other end of the arbor and try pulling while pushing on the other side.  Any movement and the bearing is gone.

[Garry Reid]

I am pretty sure the arbour bearings are good but I'll definitely check for any play while I have it apart. Thanks for the heads-up!

[irockhound]

Funny thing was after the first stop and the bad belt I put in a dressing stick and made some cuts and it was fine on the first rock I cut after that maybe a 3" x 3" and then the next rocks even smaller triggered the stop with the newly dressed blade with the new belt.

[Garry Reid]

I want to thank you guys for the advice you gave me on my old Lortone slab saw. BTW I said it was an LS12 saw but Lortone says it predates the LS12 and they have not sold parts for them for 15 to 20 years. It has a 12 inch blade, lift off lid and a rectangular window.
Unlike an LS12 I am familiar with, with this saw I can remove everything in the box in one go because it is mounted to perimeter angle iron. So, I did that, checked everything I had not already replaced, made some corrections to a couple of non-associated issues with the carriage and reassembled. I had to wait for the dial gauge I ordered from Amazon but when I got it and set the blade up I found it was out a significant amount.
After filtering the oil I found I didn't have enough oil, so then had to wait for new oil to arrive. Long story short, the saw is now cutting as it should. No saw marks on the slabs and the cycling noise that I had is gone.
In the mean time I am now more knowledgeable about my saw and have checked the the feed components and carriage setup and know this saw is an oldy but a goodie. Thanks again very much for pointing me in the right directions.

[peruano]

Congratulations. Part of the fun is keeping the equipment running and understanding how it works. Now back to the rocks (the main program).