Assuming that you cleaned it of debris and are using the proper blades, there is an interesting note in the manual that may be your problem:[br]
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"If you tighten the screw without the pin on the slider fitting properly in the hole in the blade shank, the pin or the blade shank will be damaged. This may cause the blade to be extracted unexpectedly during operation."
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***"If you tighten the screw without the pin on the slider fitting properly in the hole in the blade shank, the pin or the blade shank will be damaged. This may cause the blade to be extracted unexpectedly during operation."***
At the repair shop I work at I have also experienced some saws with damaged boots/rubber grips that wouldn't hold a blade properly so if there is any damage you may need replacement parts.
Here is a link to the instruction manual. Page 7 details blade replacement.
https://cdn.makitatools.com/apps/cms/doc/prod/JR3/7d497f7e-3f42-4053-95f6-8bcdb23c0eb7_JR3000V_IM.pdf
Assuming that you cleaned it of debris and are using the proper blades, there is an interesting note in the manual that may be your problem:[br]
"If you tighten the screw without the pin on the slider fitting properly in the hole in the blade shank, the pin or the blade shank will be damaged. This may cause the blade to be extracted unexpectedly during operation."
At the repair shop I work at I have also experienced some saws with damaged boots/rubber grips that wouldn't hold a blade properly so if there is any damage you may need replacement parts.