Way tube tie bar - How tight?

[edma194]

The way tube tie bar gets locked to the headrest (left base casting) with a lever arm lock assembly. The lock shaft has a special large beveled head that the lever pulls in against the way tube tie bar. The tie bar deforms when it is tightly secured to the headrest. The lock shaft is a screw that shortens the effective length of the shaft so the tie bar can be held very tight, and the tie bar will bend significantly if it is.

So is there some standard way to adjust the lock shaft? How tight should the tie bar be when locked? How much deformation is tolerable?

[jsburger]

My first question is... Has anyone heard of a tie bar being broken from being over tightened? What is that mechanism trying to prevent? The way tubes can't lower any more and they can't raise on their own. The only thing they can do is move slightly laterally. So how tight does it need to be? Just enough to prevent lateral movement. IMO slight pressure on the "pony tail" is enough. Why would more be needed to make the tie bar deflect?

[edma194]

It has to prevent side to side movement or the way tubes, and upward movement also. There is no rigid part keeping the tie bar down, it's the pressure of the lock shaft against the tie bar holding it. And it has to do that while using the machine as often might be, with an unbalanced block mounted for turning, dropping heavy pieces of wood down on the table, knots causing kick back while sawing, and don't forget raising the casters that causes a loud bang on a concrete floor. On top of that the headrest leaves two small ledges for the tie bar to sit on and they are at different heights to allow the magic screw to raise or lower the back end of the tie bar up or down. The tie bar has to be tight enough to resist any pressure from the way tubes to resist that adjustment.

Slight pressure is not very specific, there's a point where it's tight enough to resist the forces that can shake the way tube assembly. And the tie bar does deform at that point, just a little, but it can be tightened and much more with much more deformation. Certainly there's no need to tighten it more than necessary, but what is necessary is not clear. If there's no word from up high, I think 'slight pressure' could easily end up being insufficient in somebody's perception of what that means. The tie bar can be deformed a lot with out breaking,

[edflorence]

Slight pressure is not very specific, there's a point where it's tight enough to resist the forces that can shake the way tube assembly. And the tie bar does deform at that point, just a little, but it can be tightened and much more with much more deformation. Certainly there's no need to tighten it more than necessary, but what is necessary is not clear. If there's no word from up high, I think 'slight pressure' could easily end up being insufficient

The "word from up high", at least per a 1987 Mark V manual is: "To check the headrest lock, grasp the way tubes near the way tube tie bar and pull up. If there is "give" in the lock, unlock the handle and turn the shaft clockwise with a screwdriver. If the lock is difficult to operate, the shaft is too tight. To loosen, unlock the handle and turn the shaft counterclockwise."

The way I have always interpreted these instructions with their use of somewhat vague terms like "give" and "difficult to operate" is as follows: the way tubes should not move at all when grasped and pulled up. The lifting force, if sufficient, will move the entire end of the machine but the way tubes will not move. To me, this is the "no give" condition. At the same time, the locking lever should be easy to move into and out of the lock position. If you were to exert enough force to bend the tie bar you would definitely find the lock lever "difficult to operate." The two conditions work together and once both these conditions are met you should be good to go.

[jsburger]

That description tells me it should not be so tight to deform the tie bar. That is what I meant in my previous post. We have been using the MK5/V for almost 70 years with no problems vis-a-vis the tie bar. So why why question it now? All of the what ifs don't seem to be born out in users experience.

[edma194]

I didn't think this was any kind of controversial subject. I have never owned a new Shopsmith, all of mine are used, and on the 4 machines I have assembled the tie bars are all tighter than the minimum necessary. I don't know why and I have no idea how they would have been set at the factory. One was bending the tie bar a lot when closed so I started looking at all of them. Using the method Ed from Idaho described above I found that the lock shaft could be loosened quite a bit and I was still able to lift the machine by the way tubes and rock it side to side without any movement. Looking at the indent in the tie bar where it meets the tapered head of the lo1ck shaft it looks like it was designed to have tie bar bent a lot before the lock shaft head and tie bar fully mate. That doesn't seem to be necessary to hold the way tube assembly tight. Maybe that was to allow the tie bar to be tightened further if it permanently deformed from being locked over time. Or maybe that was to account for variances manufacturing or assembly. Or maybe there's nothing more to know. If your way tubes are locking down tight you have no reason to change the lock shaft, but if you did I think you'd be surprised how little pressure is needed to start deforming the tie bar.

And why now? It's round-about, but I dug out my broken greenie tie bar to see if it had changed over time and the replacement I used for the table modifications on my drill press would be a problem. That made me wonder if it broke as a result of overtightening so I looked at all the machines and found no consistency in how they were adjusted.

[dusty]

Do the tie bars retain a bend when the lock mechanism is released (lock handle up)? If so, how much?

I tighten mine only enough so that I can not lift the way tubes.




















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