I have wondered about this for some years now

[reible]

If you were to loosen the 4 fasteners that mount the table how much movement is allowed.

In this case this is a 520 table and has a piece of MDF on it and clamped in place. I placed a sheet of paper under the quill and mounted a short ball point pen in the drill chuck. The table is away from the tubes so it is free to move as much as it can.

I have not check to see if it has all 4 holes the same size but I expect it does since it is a newer table.

dot making.jpg (239.06 KiB) Viewed 1960 times

I only taped my first attempt and when reviewing it I was apparent that the pen was flexing quite a bit. I did five more tries altering the parameters and while this is only a makes shift test with some faults I was a bit surprised by the results.

With this sample size of one table and how it is set up I would guess that results could vary.

So has anyone else ever tried this? Results?

So how big do you think the dot is going to turn out to be?

Anyway here is the video so you can see the problem I was having.

https://youtu.be/qDalzueC23M

Ed

[Ed in Tampa]

What I think would be more interesting is to set the table to one extreme or another and then tighten the four bolts recording any movement.

Another interesting test would be to set the table to correct alignment then tighten the four bolts.

Lastly it would be interesting to set the table to perfect alignment tighten the bolts and then loosen the table and adjust the table to the dot then check to see parallelism to blade.

[reible]

Again this is not an exact measurement and only relates to what I have tested.

So did you put down your best guess?

Still have a moment before the big reveal.............

Last chance...........

dot size.jpg (119.97 KiB) Viewed 1901 times

Ed

[algale]

Interesting.

Do your trunions have four 1/2 inch bolt holes or do you have the trunions with the two undersized 3/8" inch bolt holes, as described in this old post by Nick:

Also check the mounting bolt holes in the trunnions. All four bolt holes should be the same size. If two holes are 3/8" dia and the other two are 1/2" dia, you may have a bad run that got past us many years back. When the table is tightened down, the improperly machined trunnions pull the table out of true. Send us the trunnions; we'll check them; and if necessary, replace them.

The reason I ask is that, as a thought experiment, if all the bolt holes in the trunions are of equal dimension, I would expect the diameter of that dot (the amount of play) should be equal to 1/2 the difference between the diameter of the trunion bolt holes and the bolts themselves. Like I said, I think the bolt holes in the trunions are supposed to be 1/2" but I don't recall what the bolt diameter is.

[reible]

I do plan to check the bolt holes but have not done so yet. This is a newer table so I do expect the holes to all be the same size. On the one table I had with the wrong hole size was an older table and I think that the situation was fixed long before this table was purchased.

You are correct in that if you had one bolt and one hole the maximum would be the difference between the size of the hole and the diameter of the bolt. Add a second bolt and hole and things change because of tolerances, those being the locations of the hole and tapped hole in the table. Add a third and fourth bolt and holes in to the mix and add the placement of the two brackets and the world is not so simple any more.

I will try to get to checking the hole size today but I have some other things going on before I can get to it.

Ed

[DLB]

Is this not a math question?

The trunnion holes are 1/2" and the trunnion bolts are 3/8". Based on that, I would say that the table can be moved 1/16" in all directions; thus the maximum travel from one extreme to the other is 1/8".

Yes, there might be some vary slight deviations brought about by component tolerances but is that really going to be significant.

I agree. Deviation up or down from that value could have multiple causes, but that's the nominal.

I'm scratching my head about the earlier Nick post. I've seen a couple of Marks with undersized holes and IIRC it is one specific hole on one specific trunnion.(?) And I always believed it to be deliberate, kind of acting as a hinge point for aligning the table. Sometimes unsuccessful, but deliberate. With two undersized holes the table would be essentially un-adjustable.

- David

[dusty]

I was in the process of editing my previous post and deleted it accidently. Thankfully it has been quoted and remains.

I jumped at a conclusion and was right ONLY if the movement is left/right or up/down. If there is any rotational movement the numbers change because of the geometry of the hole placement.

[algale]

I still think the movement would be 1/16th in any any/all directions, not just due north, due south, due east, due west.

[DLB]

I was in the process of editing my previous post and deleted it accidently. Thankfully it has been quoted and remains.

I jumped at a conclusion and was right ONLY if the movement is left/right or up/down. If there is any rotational movement the numbers change because of the geometry of the hole placement.

Unfortunately your drawing was not present when I quoted your post. Perhaps you can add that back in?

I'm not understanding your last point. Your conclusion seems correct for movement at any angle, and therefore for rotational movement. What am I missing? (Alan be me to the punch here, but we seem to be in agreement.)

The bolts themselves are going to have some extra give when not tightened down, depending on how loose it was, because they can be slightly angled. The table system has some well-documented inherent instability when vertical or horizontal force is applied. So if we are trying to explain a difference between Ed's results and a theoretical 1/8" I'd say those variables that could make it smaller than predicted are trumped by those that would make it larger. In a sample size of one. And Ed's measurement system might have slightly more error band than the calipers themselves.

- David

[dusty]

I still think the movement would be 1/16th in any any/all directions, not just due north, due south, due east, due west.

I think the dynamic that is not being taken into consideration is what happens at all four (five) locations when something moves.

PS I just realized that Ed is talking about movement about the center of the axis of rotation which is different that distance about the trunnion holes.
That would increase his dot by the radius of his pen.