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Table Tubes vs Trunnion Pivot Point

dusty

I am putting this in the Maintenance Section even though it has nothing to do with maintenance. It also does not have anything to do with wood working.

I had been working on some design changes for my outfeed table when I made the following observation:

The two table tubes (514344, Table Bar and Tube, #163) are offset approximately 5/8" from the pivot points of the Main Table Trunnions.

I am hoping that someone can explain to me why this might have been done.

JPG

Without going out and looking, I believe it is so that when the table is parallel to the posts, there is room for the stop screws etc.

reible

Hi,

I can't tell you why 5/8" but it has to be some distance away. Without measuring I could have not told you the distance but I know it is not in the plane of the pivots.

BTW when adding a table to the back of the shopsmith you want to use the center line of the pivot points to locate the center line pivot point of the outboard table. If not you introduce "flutter" as it tips. Like wise the shopsmith support table when used on a 520 has the pivot point mis-located (this might have been fixed?).

This post shows the issue.

https://forum.shopsmith.com/viewtopic.php?p=13271&postcount=17

Ed

robinson46176

Maybe to keep the blade centered in the slot as the table is slanted?

There is a difference between the pivot pin and the top of the table.

.

dusty

reible wroteHi,

I can't tell you why 5/8" but it has to be some distance away. Without measuring I could have not told you the distance but I know it is not in the plane of the pivots.

BTW when adding a table to the back of the shopsmith you want to use the center line of the pivot points to locate the center line pivot point of the outboard table. If not you introduce "flutter" as it tips. Like wise the shopsmith support table when used on a 520 has the pivot point mis-located (this might have been fixed?).

This post shows the issue.

https://forum.shopsmith.com/viewtopic.php?p=13271&postcount=17

Ed

I must admit that I saw this post way back when. It didn't register with me then because I did not understand its significance. In fact, I still don't but now I realize that if I did understand I would not be bothered by the flutter I have on my outfeed table.

I would sure appreciate one of your typical tutorials on this subject so that I can quit scratching my head.

fjimp

dusty wrote

I would sure appreciate one of your typical tutorials on this subject so that I can quit scratching my head.

Hey at least you Can scratch your head. I was told yesterday I have six more weeks before I am allowed that much movement in my right arm. Jim

dusty

fjimp wroteHey at least you Can scratch your head. I was told yesterday I have six more weeks before I am allowed that much movement in my right arm. Jim

Thanks Jim for the reminder that I have many more things to be thankful for than to complain about.

I hope you are doing well in your recovery. Whatever - don't screw it up by getting too active too soon. I've been there - you don't want to go there.

hjlssfor1

Dusty, as someone who hopes to make an outfeed table in the not-far-distant future, I hope you will keep the list informed of your design modifications and end result of your current efforts. Your insights always are very informative, useful, and appreciated.

Hank

reible

dusty wroteI must admit that I saw this post way back when. It didn't register with me then because I did not understand its significance. In fact, I still don't but now I realize that if I did understand I would not be bothered by the flutter I have on my outfeed table.

I would sure appreciate one of your typical tutorials on this subject so that I can quit scratching my head.

I'll see if I can work it in to my list of "todo's".

In order for the main table and the out feed table to stay on a plane they both have to rotate about a single center line or axes. The closer this gets the better the design gets.

Ed

JPG

Not sure this will 'explain' anything, but, the geometry has changed from model 10 through the 510 etc.

First me earlier comment re tilt was incorrect as we shall see.*

Using the pivot as a reference, the following tube and blade slot offsets were roughly eye balled.

.............Model 10.........Mark VII..........500...........510 + = away from headstock

slot..........-5/8"...............-1 1/2..............0..............0

post..........1/4..................0*................3/4.............5/8

Except for the M VII the post is always 'out' from the pivot. (the M VII tilts +- 90 degrees to 'vertical' both directions)

The post is always out from the slot. The M VII is further away probably due to the 0 post/pivot offset and its greater tilt range. Blade/slot adjustment for tilt is larger on the 10 and the M VII.

Perhaps as Farmer has stated above, the post offset minimizes the blade adjustment when tilting. It also reduces the tie bar/post 'offset'(blade clearance).

I think there are tradeoffs here and any design is compromising something.

Tain't simple Magee!

dusty

reible wroteHi,

I can't tell you why 5/8" but it has to be some distance away. Without measuring I could have not told you the distance but I know it is not in the plane of the pivots.

BTW when adding a table to the back of the shopsmith you want to use the center line of the pivot points to locate the center line pivot point of the outboard table. If not you introduce "flutter" as it tips. Like wise the shopsmith support table when used on a 520 has the pivot point mis-located (this might have been fixed?).

This post shows the issue.

https://forum.shopsmith.com/viewtopic.php?p=13271&postcount=17

Ed

Yeah, that is for sure. I can attest to that now.

When I built my outfeed table (all previous versions), I used the vertical support tubes for the reference. Whenever I tilt the tables I experience the moving trailing edge of the outfeed table.

My problem now is that I don't believe it will be worth the effort to relocate the lower tie point. Especially since I am able to adjust the diagonal support bar to compensate.

I still do not understand the dynamics of what is happening. I am hoping that you can provide a tutorial to accomplish that. I see it and I believe it but I don't understand it.

I also would like to understand why Shopsmith did this. There has to be a reason. It would have been so easy to locate the trunnions so that they were centered on the support tubes.

dusty

robinson46176 wrote
Maybe to keep the blade centered in the slot as the table is slanted?

There is a difference between the pivot pin and the top of the table.

.

I am missing your point. The tables actual pivot point is in line with the blade if the quill is fully withdrawn. When the table tilts, no matter where the pivot line, the blades relative location is going to change.

Trunnion Offset 006 Custom.JPG

Oops, the image doesn't show the blade. Trust me, it is in line with the table pivot. The attached image only shows how the Table Tie Bar's design creates the offset (between the pivot point and the centerline of the table tubes) that I am dealing with.

Ed in Tampa

dusty wroteI still do not understand the dynamics of what is happening. I am hoping that you can provide a tutorial to accomplish that. I see it and I believe it but I don't understand it.

I missed something again what is happening. I know you said the support tubes are 5/8 offset the piviot, so what? (not being a wise guy I just don't know what the problem is)

Please explain it to me. Thanks

charlese

Glad you said that, Ed! I have been wondering why there was a concern? And what is it that matters?:confused: :confused:

JPG

To avoid confusion I will refer to the worktable supports as posts and the outfeed table support as a tube(telescoping).

Having the pivot in line with the blade minimizes the blade tilt adjustment. The blade offset deviation due to table tilt is proportional to the radius from the pivot to the blade. If the slot is offset from the pivot, that radius is greater. Such is the case with the 10 and M VII.

Back to your original question - post offset. The trunion is attached to those posts. The truinion base provides the pivot points. The trunion needs a cross bar to connect the two posts and pivots. The cross bar introduces multiple interference possibilities. The bar cannot be in line with the pivot since the blade occupies that space. The bar must be far enough away to provide clearance for the arbor and blade guard. The bar must not interfere with the trunion segments. The bar must be further away to allow for the tilting table, but this is a catch 22. Too far and the tilt angle range is restricted.

Tis conjecture at this point, but I think the offset is to provide greater stability by virtue of the decreased 'arm' needed for a given bar/blade separation. The arm dimension is divided into two branches in opposite directions. Thus a 'T' shape rather than an 'L' shape.

The M VII due to it's greater tilt range needs more bar to blade clearance, so the blade is offset further from the pivot which needs to be aligned with the blade assuming under table symmetry.

As for the 10, I think lessons were learned from it. Also the blade was smaller and this stuff was less significant(sorta;)).

IIRC Dusty, the support tube drops down from a point on your outfeed extension and attaches to a 'tube pivot' at the bottom end of the table support post and is pivoted at both ends to allow for blade height variations. I assume you initially aligned that upper attachment point(with another pivot) with the posts(makes sense!!!....but. . .). Moving that point to align with the worktable pivot(vertically as well as horizontally) is crucial I think, but is only half way there. The bottom end of the telescoping tube is still at the table post location. Methinks the pivot for the telescoping tube needs to be offset to align vertically with the worktable pivots(maybe*).

However, your original placement of the outfeed table attachment point guaranteed no side to side movement only IF the attachment point was also the same dimension below the table top as the main table pivot is from its top and in line with the worktable pivots. Methinks it was originally aligned with the posts and the height not considered(conjecture). i.e. the three pivots must share a common axis. That leaves that pesky 5/8" bottom offset*. I believe it must be accommodated at the bottom of the post. An additional offset away from the post towards the 'rear' will not affect this.

The kickers are: The upper end of the tube must does not move relative to the bottom end of the post when either tilting or adjusting the worktable height.

* Get that and I think the position of the lower end of the tube becomes moot.

Get that done and the post/pivot offset becomes a mere curiosity rather than a 'problem'.:)

I think that will eliminate the stuff you are trying to get rid of(stuttering, tube readjustment when tilting). With the outfeed table tube attachment/pivot in line with the trunion pivots, the position of the upper end of the tube will only move when table height is changed, but will be the same amount as the main table. The tube bottom end moves with the post bottom which also moves the same amount as the worktable.

Ed in Tampa

JPG40504 wroteTo avoid confusion I will refer to the worktable supports as posts and the outfeed table support as a tube(telescoping).

Having the pivot in line with the blade minimizes the blade tilt adjustment. The blade offset deviation due to table tilt is proportional to the radius from the pivot to the blade. If the slot is offset from the pivot, that radius is greater. Such is the case with the 10 and M VII.

Back to your original question - post offset. The trunion is attached to those posts. The truinion base provides the pivot points. The trunion needs a cross bar to connect the two posts and pivots. The cross bar introduces multiple interference possibilities. The bar cannot be in line with the pivot since the blade occupies that space. The bar must be far enough away to provide clearance for the arbor and blade guard. The bar must not interfere with the trunion segments. The bar must be further away to allow for the tilting table, but this is a catch 22. Too far and the tilt angle range is restricted.

Tis conjecture at this point, but I think the offset is to provide greater stability by virtue of the decreased 'arm' needed for a given bar/blade separation. The arm dimension is divided into two branches in opposite directions. Thus a 'T' shape rather than an 'L' shape.

The M VII due to it's greater tilt range needs more bar to blade clearance, so the blade is offset further from the pivot which needs to be aligned with the blade assuming under table symmetry.

As for the 10, I think lessons were learned from it. Also the blade was smaller and this stuff was less significant(sorta]also[/B] the same dimension below the table top as the main table pivot is from its top and in line with the worktable pivots. Methinks it was originally aligned with the posts and the height not considered(conjecture). i.e. the three pivots must share a common axis. That leaves that pesky 5/8" bottom offset*. I believe it must be accommodated at the bottom of the post. An additional offset away from the post towards the 'rear' will not affect this.

The kickers are: The upper end of the tube must does not move relative to the bottom end of the post when either tilting or adjusting the worktable height.

* Get that and I think the position of the lower end of the tube becomes moot.

Get that done and the post/pivot offset becomes a mere curiosity rather than a 'problem'.:)

I think that will eliminate the stuff you are trying to get rid of(stuttering, tube readjustment when tilting). With the outfeed table tube attachment/pivot in line with the trunion pivots, the position of the upper end of the tube will only move when table height is changed, but will be the same amount as the main table. The tube bottom end moves with the post bottom which also moves the same amount as the worktable.

Oh that makes it all perfectly clear. HuH?????????????????:eek: :eek: This is going to keep me up at nights.

I know Dusty is working on an outfeed table and I understand that the main table piviot is offset. And apparently when you tilt the table the outfeed stutters (what ever that means). I didn't even know it could talk let alone stutter :eek: :D

dusty

I am terribly sorry that you and Charlese are so bored with all of this, Ed.

I would like to think that it is helpful in some way but if it is not I can do nothing about that.

When my emails and PMs stop coming, I'll quite posting this kind of nonsense.

JPG

Ed in Tampa wroteOh that makes it all perfectly clear. HuH?????????????????:eek: :eek: This is going to keep me up at nights.

I know Dusty is working on an outfeed table and I understand that the main table piviot is offset. And apparently when you tilt the table the outfeed stutters (what ever that means). I didn't even know it could talk let alone stutter :eek: :D

Understanding all that requires understanding 'the problem with the 5/8" offset, so HuH?????????? in your case(confusion previously self declared) is not surprising.;)

Bottom line is getting the three pivots on a common axis. I could have simply said that but understanding is in the details. Yes there is also some 'other' stuff answering other posts in there towards the top.

Dusty: if this has confused you, PM me.

dusty

JPG40504 wroteUnderstanding all that requires understanding 'the problem with the 5/8" offset, so HuH?????????? in your case(confusion previously self declared) is not surprising.]

No, I am not confused by what you have posted. I appreciate your feedback. I don't always understand without prodding the gray matter but I am not adverse to doing that.

Shopsmith offset those posts from the table pivot point for a reason. I am just trying to understand why they did that. I am convinced that this design is near perfect and when something doesn't seem logical, it tweaks my inquisitive mind (keeps the gray matter pliable).

Ed in Tampa

What is out feed table stutter?