Table Tilt Lock, Mark V Model 510/520

[dusty]

My table tilt lock has been getting progressively less effective. So much so that I employ other means to secure the table,

I have inspected and cleaned the trunnions and the locking pads. The parts all look fine but the tilt lock performance has not been improved.

Has anyone had and resolved this problem. I consider it a serious safety issue if left unresolved.

[DLB]

I think I've read some old threads on this, but I don't think there was resolution. The thinking at that time was that one trunnion or the other was not contributing, IIRC. Some ideas:

Thread condition of the rod and specialized nut is important. Any possibility that the threads are bottoming out? Test with a thicker washer under the nut? Clean threads with tap and die.

Do you use the $20 bill trick? Or other means of setting some clearance when you mount a table to the trunnion? Could result in too much clearance and/or a slight angular error. Test by loosening the table mounting bolts for either the front or back trunnion and locking the tilt with the table slightly loose.

Testing the locks with the table removed should tell you if there is a problem is in one trunnion or both, narrowing down the scope.

I would also test with a longer tilt lock handle. As we get older we simply don't deliver as much torque to things like this as we once did. There is plenty of exposed nut under there to reach in with a 9/16" open end wrench.

- David

[DLB]

One more thing is that wear on the tie bar will eventually result in an ineffective lock. I'm going to use a disc brake analogy. The tie bar is soft metal (aluminum alloy) compared to the trunnion and acts like an inner brake pad. Except that unlike a disc brake pad and unlike the outer lock, the tie bar does not move to adjust for pad wear. Wear will eventually compromise the inner locking surface to the point that the trunnion is no longer being squeezed between two surfaces as intended, and lock effectiveness will be greatly reduced.

I have a disassembled tie bar and will try to get some pix of this later. What I don't have though is original dimensions or an effective way to measure the wear.

- David

[dusty]

I hate to take the table off of the trunnions to do this but I might have to. I have been doing a little test on the duration of "Main Table Alignment" and removing the table would terminate that prematurely. I may not live long enough to start over. It has been eleven months since I performed an alignment on the table. I do an alignment verification every couple weeks using a couple different methods ("scientific" and "down and dirty").

[DLB]

I found the other thread I was thinking of, evidently there are others: viewtopic.php?f=10&t=15439 Since this thread had a ton of detail I will skip the new pics, they won't add anything new. My attempt at a summary, as the other thread is 10 pages:

The OP, Dusty, reported tilt lock issues. Some other users had or have similar problems, most do not. The problem was found to be a gap, shown here, between the rear trunnion and the tie bar while the trunnion was locked:

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It is my understanding that there was no such gap on the front side. Where the gap came from, or when it was introduced, was not determined. Dusty reassembled, realigned, and everything seemed good. The gap was eliminated and the tilt lock worked as intended. It is my current opinion, not directly supported in that earlier thread, that for this gap to exist it must have been present when the table was bolted to the trunnions. My thinking is that the trunnion must be jammed on its axle somehow by the combination of vertical and horizontal forces applied by the lock wedge, rather than slipping horizontally into its intended position. Once locked to the table in the wrong position, the trunnion will be held in that wrong position by the table.

- David

[dusty]

I had forgotten that other thread so I went back over it about three times trying to relate then with the problem I have now. The discussion about the gaps that exist between the table bar and the trunnions is very significant. On the bench (without a table attached) those gaps differ. Obvious I guess because with the table attached the trunnions are a fixed distance apart (14 13/16" by my measurement). On my setup in the shop the distance is 14 1/2" (with the table tilt lock applied). If being bolted to the table contributes to this, it may mean that how the trunnions are positioned when the table alignment is done and the trunnion bolts secured leads to the slippage. Why? Because if the trunnions are held too far apart when the tilt lock is applied the face of the trunnions are prevented from contacting the table bar. Only the soft metal brakes shoes apply friction to the trunnion.

[dusty]

Nope. That theory is a pipe dream. I separated the trunnions with a piece of wood 14 1/2" long and the tilt lock captures the trunnions perfectly. I interpret this to mean that the way I bolt the trunnions to the table is not the root cause of my slippage.

[algale]

Yeah, that was a good read. I stand by all I said in that previous thread.

In summary, when a table alignment is performed following the standard operating procedures, the bolts from the table to the trunnions are loosey goosey when the table lock is applied. This ensures the trunnions are in contact with the aluminum lock wedges of the table lock AND that the back of the trunnions are push/pulled into contact with the machined bosses on the tie bar. I believe BOTH the aluminum lock wedges AND the bosses on the tie bar contribute to the overall stability of the locking mechanism.

The purpose of Nick's dollar bill trick was to induce a few thousands of an inch gap between the trunnions and the bosses on the tie bar to permit easier tilting after alignment. This shouldn't create a locking problem because the gap is so small and in operation, the application of the tilt lock will in IMO overcome the few thousandths gap and push/pull the trunnions into contact with the tier bar.

If, however, you are using some nonstandard alignment procedure, I could imagine one accidentally inducing a larger gap between the trunnions and the tie bar that would be too large for the table lock mechanism to overcome.

[dusty]

I agree with almost everything you said. However, I do not buy into the theory that tilt lock is achieved by anything other than friction between the two aluminum blocks and the trunnions.

The dollar bill trick only ensures that there is some spave between those bosses and the trunnion.

To confirm: tilt the table to vertical, lock the tilt lock and attempt tp insert the dollar bill (or piece of paper) between the boss and the trunion (showing that locking action does not involve the bosses on either end of the table bar.

If I pull the 14.5" spacer out and tighten down on the tilt lock, the wedges are forces inward and capture the trunnion. Yes it is locked and the trunnions are in hard contact with the table bar but the trunnions are also not separated as they would be if bolted to the table.

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[DLB]

I agree with all that algale said. But I would add that I think it is possible, or at least plausible, to accidently induce a larger gap when following one of the 'standard' alignment procedures. I can feel on mine that if I use the tilt lock to pull the trunnions into proper position they have some tendency to bind on the 'axle.' If they bind during assembly, installation of the table is going to lock in that incorrect setup.

... On the bench (without a table attached) those gaps differ. Obvious I guess because with the table attached the trunnions are a fixed distance apart (14 13/16" by my measurement). On my setup in the shop the distance is 14 1/2" (with the table tilt lock applied)...

I don't understand this, especially the 14 13/16" part. I measured two, one on the bench without a table measured slightly under 14-1/2", ~14-15/32". The other, with a table, measured very slightly over 14-1/2". These are both with the tilt lock applied. IMO, the difference would have something to do with manufacturing variation and/or wear, not the presence or absence of a table. Please explain the 14-13/16" measurement, I think this could be the key.

- David