hlron,

  For my situation, the solution seems to be to sand the end of the thumbscrew... sanding the ends of the blade didn't help me.

 

Spence

try washing the oil off the blades??/

 

just out of curiousity are  you by chance using flat or spiral blades? if spiral try using plyers to untwist the bottom part of the blade other wise what the others have suggested should cure the problem

I've had my Dewalt since they first came out about 15 years and I had a similar problem. Tightening the lower blade too tight will cause the blade halder to stretch and requires replacement. I even made a wooden wrench to add torque which made matters worse.

 

The solution I found was to drill a hole into a piece of 1/4 thick plexiglas about 2 inches wide and 4 inches long. The hole needs to be drilled with a drill press so it is at 90 degrees to the plexiglas. The hole diameter is slighly smaller than the threads on the lower thumb screw. Use the lower thumb screw to tap threads into the plexiglas.

 

Now screw the lower thumb screw into the plexiglas until the tip just protrudes past the plexiglas.Color the metal tip with a black sharpie pen.Move the jig back and forth over a flat abrasive surface until the metal is flat and the ink removed. Now it will hold a blade with light finger tight pressure for several months.

 

Doug Turner

I also had this problem with my Dewalt saw witch I have for 10 years what I did was taken the lower thumb screw and reversed it with the top thumb screw and so far it has worked out fine go luck

It does happen to me once in a while.  Usually it is when I am pushing too much on an old blade that has dulled.  It's the wanting to stretch out the life of the blade instead of changing it. 

When I first change the blade I check it a few time to make sure it still is tight.  I find that the blade will slip out of the bottom holder slightly.  I reposition it and keep cutting.

Make sure it is well into the bottom holder.

 

Someone asked if you were using flat or spiral blades? If you have the problem with spiral blades, they will clamp on edge & after tightning the tensioner, it's just a matter of time & it will pop loose. It turns flat & slips out. That's just spiral blades that I'm talking about. If you have problems with the flat, then you should make sure the left set-screw is even or protruding out of the hole. If it is inside, the you bend the blade & or, it doesn't tighten the blade. Just some thoughts here & hope you can solve the problem. I have the 788 & no problems so far. Good Luck.     Larry

Larry again. I forgot to mention, if the blade doesn't go down far enough, maybe the set screw is protruding out to far. Does it clamp the blade at all or just won't clamp the blade?   Larry

Thank you everyone but I have tried all this before nothing is working. Im using flat end blades. The distance betweenthe top & bottom holder is to far apart and its only catching the tip so thats why I losing the blade. I  need to know how to adjust the lower arm up. any help please.  Linda

Linda, I'm not sure if this will help, but, go to Tool Talk(in left collum) then click on DeWalt 788 adjustment . There are several responses to adjusting the distance between top & bottom holders. They were having the same problem way back then. I have not looked at my saw to see where the adjustment is made, but, I'm sure it can be.   Good Luck          Larry

Thats were i was this morning, reading on it , tool talk, left side, and i beilve i clicked on pdf format and it broke it down into a manual with exploded  drawing, but i think you have a bad saw with a too short a arm and im afraid the saw will have to go back or get a correct replacement arm.

After experiencing the same problem, more so with the top holder though, I took a tri angular minifile and lightly roughed in two scores on the thumbscrew. I have not had a problem since.

 

Mike