Need Advice about Table Alignment

[dusty]

Using a hole size of 0.375 and a screw size of 0.369, and 'guessing' the trunion hole spacing is 4", the hole/screw slop allows about 1/10" movement at 18" from the trunion which amounts to less than 0.4 degree range. That is less than the amount allowed by the 3/8\1/2 front trunion screw/hole.

No question that increasing that 0.006 slop to 0.131 will greatly increase the range. That may be too much. Perhaps 7/16 is a better choice for the rear trunion holes.

Consider there is other 'slop' that will affect blade to table alignment(trunion mounting tubes\holes\clamp and headstock lock and quill runout.

Considering all that, the use of dial gauges is likely folly.

Question remsains, was Nick correct or Gail/Gale?

Why guess. Measure it and you will find it to be 3 1/2".

[reible]

Hi,

It may not be oblivious but when one starts to talk about more then one hole the whole game changes. One hole one bolt and the close fit/loose fit and you can do the simple math.

However, we can look at this several ways but to keep it simple lets say we two holes one in each part.

You have two parts and the parts must fit together, this means that the location of the two parts have to be within a tolerance. We will call that a location. It is from a reference point to a location at a x and y location. Of course once the hole is placed it is where it is, and it is unlikely to be right at the exact location we think it is on every single part we drill. So we say we know the hole has to be at this location or within a certain tolerance of that location to be usable.

The second part is done like wise, in this case lets make it a drilled hole that is threaded. It like wise will be within a tolerance of where it we think it will be and every part will fall somewhere with in that tolerance in order for it to usable.

When we take the parts and put them together using lets say a cap screw that screw will be located by the tapped location. And yes even the cap screw will have some differences between parts but for practical purposes we will give it a nominal dimension and use that. The hole in the one part now provides some movement due to the hole size and the fastener size.

Pretty simple right? It is but when we add a second location things start getting fuzzy. The hole location on the part we started with may or may not be right where we thought it was and the same will be true of the second hole. It could be say x+1 units or y+1 units different then the first hole. So it could be closer, or farther away or even at some chance the same distance away.

The second tapped hole is like wise at some location, with in tolerance of the first hole. Once drilled a tapped with a fastener in place it is fix. The two fasteners could closer or farther apart then the perfect location but need to be with in some tolerance.

We are now going to put the two parts together, the two fasteners are located where they are and are fixed. The part with the holes will need to fit and now is were it starts getting tricky. When the parts are made they have to be designed to fit even if the hole are towards the minimum distance or towards the maximum condition. Same for the fasteners, and that part. Not surprising one is called maximum material condition and the other minimum material condition.

So now when you put the parts together you will have different fits. In some cases the amount of movement might be none, or in other cases the same as a one hole case. In most cases one will expect that it is neither the best or worst case and you will have less then the maximum movement between them.

Now if you want to have adjustment like say the case of a shopsmith trunion and table you have to have the holes large enough to accommodate the tolerances and to accommodate the movement needed to do the alignment. If designed correctly you want all tables to fit all trunions so long as they are made correctly and meet tolerances.

If we picked one table and one trunion and put them together we might find that a 3/8" hole will work because the locations allow it. Take the same table and change to another trunion whose tolerance is still held but say at a maximum condition, now what happens? It may not fit with enough room for adjustment! Take another table and it may work, another table or trunion and well who knows how many work and how many don't.

If the design was done to use 1/2" holes then you can be reasonable sure the parts will fit together and will allow for adjustment. Change the hole and without doing the redesign of the tolerances who knows.

It is actually a bit more complex because there are other factors coming into play but unless we had actual shopsmith drawings there is no way of us knowing how all of this should work together. Other factor might be is the fastener perpendicular to the surface, just imagine for a moment that it is at some angle, even a part of a degree off and imagine the hole it fits in is also off by a fraction of a degree in the opposite direction, this will change the fit of the fastener in the hole..... And, who said the hole is actually round?

OK now back to being retired.

Ed

[admin]

At the request of a forum member, I asked Jim McCann about the issue of trunnion hole size.

At initial release the rear trunnion holes were 3/8". Our pre-release testing uncovered no problems with alignment.

After reports from customers of alignment or binding problems, we re-evaluated and went to 1/2" holes.

If the older trunnion with smaller holes is causing problems, please contact customer service for a free replacement.

[algale]

At the request of a forum member, I asked Jim McCann about the issue of trunnion hole size.

At initial release the rear trunnion holes were 3/8". Our pre-release testing uncovered no problems with alignment.

After reports from customers of alignment or binding problems, we re-evaluated and went to 1/2" holes.

If the older trunnion with smaller holes is causing problems, please contact customer service for a free replacement.

Hooray for admin and Shopsmith!

[dusty]

Shopsmith has taken this same position before. That has been reported in threads referenced by this one. What is good to know is that Shopsmith has stood firm in their commitment to support the Mark V. I witnessed that same commitment when Shopsmith offered assistance to correct a Main Table that I had which was less than perfectly flat. Even more impressive to me was that they did so without recalling the Main Table (based on my reports only).

[JPG]

So I can expect to 'discover' 3/8" rear trunion mounting holes on my 'early' 510. I cannot say I 'noticed' when I had it apart.

Neither have I attempted aligning it (yet).

[dusty]

I sure hope Joe got the Main Table aligned.

[joe_cool]

I sure hope Joe got the Main Table aligned.

Hey Dusty, I have it roughly aligned. I'm out of town this week at the Beach, Enjoying my 1 week i go away during the year. I'll get back to my Shopsmith next week to do a Proper alignment

I'll let you know how it goes when i get back