Difficulty adjusting thickness setting on planer

[Blake]

I have an older non-pro planer. It had not been used for several years. I recently used it a few times with good results, but recently I wanted to adjust the thickness down to 1/2" and found that despite complete cleaning and lubrication of screws raising and lowering the work platform (don't know the proper term) and the pivot points at their respective tops and bottoms I cannot get the unit to raise higher than about 11/16". The mechanism raises and lowers smoothly up to about 3/4", starts to have resistance and essentially binds up completely at about 11/16". I'm very hesitant to force it further. While investigating the problem I realized that the table will also not go down to within about an inch of the LOWEST travel of the support screws. Again, in the middle area of its travel it adjusts smoothly, with essentially no resistance. I have inspected for any evidence of binding against the inside of the machine shell. Everything is well lubricated. I don't get it! Help!

[Blake]

Additionally, to all appearance, the "table" appears to be level and true. I lined it up with the side ribs within the shell at about half height and it runs parallel to those ribs.

[BuckeyeDennis]

When you turn the thickness-adjustment crank, are all four of the table mounting posts (i.e. jack screws) turning? I'm wondering if one of the drive sprockets might instead be spinning on its post (although they're supposed to have roll pins installed that prevent that).

[JPG]

Brush out the crud from the jack screw threads at the travel extremes.

[Blake]

Thanks both of you BUT: Dennis - All four posts are turning and it operates very smoothly except at extremes. JPG - The threads are pristine at both the top and bottom extremes. Its baffling me.