Ridgid TP1300 height adj. slipping

[NWOhioJim]

I have a Ridgid thickness planer TP1300 which works very good for what I need it for.  The height adjustment is slipping as I feed in boards.  I've looked at it and cleaned it up, but still seems to slip.  Is there a part in there that is worn that needs replacement?  I also need to change the knives.  Maybe dull knives could be causing the problem.  Thanks in advance for your help.  PS, where is a place to get good knives?  I know in the past there have been suggestions post here, but I can't remember the details. 

Jim

[R Clark]

My Delta benchtop will slip out of adjustment when the knives are sufficiently dull.  The resistance from the dull blades overcomes the friction fit of the clamping mechanism on the lock bars and will force the cutterhead upward.

[Gary G™]

It’s your dull knives.

[WoodTinker]

I have a Ridgid thickness planer TP1300 which works very good for what I need it for.  The height adjustment is slipping as I feed in boards.  I've looked at it and cleaned it up, but still seems to slip.  Is there a part in there that is worn that needs replacement?  I also need to change the knives.  Maybe dull knives could be causing the problem.  Thanks in advance for your help.  PS, where is a place to get good knives?  I know in the past there have been suggestions post here, but I can't remember the details. 

Jim

Would recommend Holbren for the knives.