Table Height Lock not Locking Very Well

mountainbreeze · Post by **mountainbreeze** » Sun May 01, 2011 2:39 pm

I have an old Mark 5 whose table height lock isn't very reliable. Is seems to move down (i.e., blade up) with use. Even if I torque it pretty tight, it seems to move a bit with use. Is this just a matter of replacing a worn part or is there something more serious going on? Any guidance on what to look for?

wa2crk · Post by **wa2crk** » Sun May 01, 2011 3:21 pm

Chack the condition of the wedges that grip the table tubes. The gripping area should have flat surfaces where the wedges contact the tubes. Also check to make sure that both wedges are gripping the same amount. A previous owner may have let them become mis adjusted resulting in a loose grip.
Bill V

JPG · Post by **JPG** » Sun May 01, 2011 3:43 pm

mountainbreeze wrote:I have an old Mark 5 whose table height lock isn't very reliable. Is seems to move down (i.e., blade up) with use. Even if I torque it pretty tight, it seems to move a bit with use. Is this just a matter of replacing a worn part or is there something more serious going on? Any guidance on what to look for?

The pinion gears that raise and lower the table also have a beveled flange that presses against the outer edge of the table mounting tubes when the lock is tightened. The pinion gears must be free to move in the carriage bore and along the square shaft that passes through them. When the table lock 'nut' is tightened it pulls the pinion gears inward against the mounting tubes.

There is supposed to be a thick washer between the nut and the crank hub.(the square shaft must also be free to move within the hub). The far end of the square shaft has a clip that bears against the outer end of the pinion gear when tightened.

The washer must bear against the inner portion of the hub, not the outer sleeve that the handle screws into.

mountainbreeze · Post by **mountainbreeze** » Thu May 05, 2011 11:38 am

Here's a close-up of one of the pinions (they both look about the same). I don't see anything wrong or worn but I'm not sure what they look like when they are new. I've checked that the pinions/square rod/lock nut/etc. are installed properly but I still can't seem to get the table to not move down with use. The tubes with the rack seem to be in good shape too. Any ideas?

[ATTACH]12862[/ATTACH]

BigSky · Post by **BigSky** » Thu May 05, 2011 11:54 am

The rack and pinion have nothing to do with your problem. Problem being that the table height lock does not secure the table at the determined height. The rack and pinion, if bad, would make it difficult to move the table up and down. The table height lock is basically a friction device involving the way tubes and the locking (mating) face of the part pictured. Clean the racks and the tubes of all wax and crud and put it all back together.

Good luck.

JPG · Post by **JPG** » Thu May 05, 2011 4:06 pm

[attach]12863[/attach]

Relevant parts with crank collar removed. Nut presses against washer/hub/pinion gear.

[attach]12864[/attach]

Note collar is shorter than hub .

[attach]12865[/attach]

When clamped, collar is 'loose'(washer is not tight against the collar).

[attach]12866[/attach]

When tightened fully(table tubes removed) the pinion gear extends into tube bore about 3/32".

Way tubes not relevant.

foxtrapper · Post by **foxtrapper** » Fri May 06, 2011 8:17 am

Couple of things to check, a few to ponder, and some notions or thoughts. In no particular order.

1. The whole thing is just a friction lock. It's not the most secure way to hold a table in position.

2. Are you really tightening it?

3. Does the locking bolt back out, letting the table drop, or does the table drop under the tight locking bolt?

4. If the locking bolt is backing off, a lock washer will likely stop it.

5. Old oils and waxes make things slippery. Cleaning and wiping down with a solvent on the contact surfaces would help ensure grip.

6. The threads on the lock bolt are a bit rusty, this creates false torques. Cleaning and lightly lubricating those threads will help increase clamping force.

7. The clamping surfaces are a little pitted. I'd probably clean them up with a wire brush.

8. A tie on the adjusting arm will help secure it in place, helping to keep the table from dropping.

9. You can drill and pin the legs for several set positions, much like our old jackstands were. The table resting on those pins will not drop at all.

10. You can get fancy with that drilling and pinning, rotating around the legs, getting smaller gradiants.

11. Dropping heavy wood onto the table will drive it down. Place it gently.

mountainbreeze · Post by **mountainbreeze** » Sat May 21, 2011 4:57 pm

OK, finally got back to this...

A little history: A while back, I decided that the table was binding way too much when moving it up and down and it was quite difficult to set a specific blade height. When moving the table up and down it felt like it was slowly grinding away metal in the rack & pinion system. So, I got out the paste wax and waxed the tubes that project down fron the table as well as the holes that these tubes go through. Problem solved - I thought - since now the table would move up and down easily. It would even fall to the lowest position on its own if I let go of the handle. It was sometime later that I then discovered the table would not stay at its set height even when tightening the lock quite hard.

So, 'foxtrapper' suggested (item 5 in previous post) that I clean the wax off. I did that. Now I'm back to the table does not move with use but it is difficult to raise/lower and set a specific blade height.

Still looking for a happy medium.

JPG · Post by **JPG** » Sat May 21, 2011 5:19 pm

mountainbreeze wrote:OK, finally got back to this...

A little history: A while back, I decided that the table was binding way too much when moving it up and down and it was quite difficult to set a specific blade height. When moving the table up and down it felt like it was slowly grinding away metal in the rack & pinion system. So, I got out the paste wax and waxed the tubes that project down fron the table as well as the holes that these tubes go through. Problem solved - I thought - since now the table would move up and down easily. It would even fall to the lowest position on its own if I let go of the handle. It was sometime later that I then discovered the table would not stay at its set height even when tightening the lock quite hard.

So, 'foxtrapper' suggested (item 5 in previous post) that I clean the wax off. I did that. Now I'm back to the table does not move with use but it is difficult to raise/lower and set a specific blade height.

Still looking for a happy medium.

Wax the edges towards the pinion gear(rack side) and the side opposite. Leave the front and back unwaxed. I am having trouble accepting that a thin coat of wax would cause it to slip but give this a try. Do let us know the effect if any.