Table Tubes vs Trunnion Pivot Point

dusty · Post by **dusty** » Fri Feb 08, 2013 2:48 pm

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 · Post by **JPG** » Fri Feb 08, 2013 3:06 pm

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 · Post by **reible** » Fri Feb 08, 2013 3:35 pm

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.

http://www.shopsmith.net/forums/showpos ... stcount=17

Ed

robinson46176 · Post by **robinson46176** » Fri Feb 08, 2013 3:44 pm

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 · Post by **dusty** » Fri Feb 08, 2013 5:26 pm

reible wrote: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.

http://www.shopsmith.net/forums/showpost.htm?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 · Post by **fjimp** » Fri Feb 08, 2013 5:43 pm

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 · Post by **dusty** » Fri Feb 08, 2013 5:52 pm

fjimp wrote: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

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 · Post by **hjlssfor1** » Fri Feb 08, 2013 10:55 pm

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 · Post by **reible** » Sat Feb 09, 2013 12:13 am

dusty wrote: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.

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 · Post by **JPG** » Sat Feb 09, 2013 12:39 am

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!