jimthej wrote:Any jig or extension that fits over the top of the fence or can be made to fit over the fence can be attached to a top T-slot with a T-slot bolt and Through Thumb nut, or locked on with one of the expandable plastic bars that come under the feather boards.
Just acquired the Nick Engler book on Jigs, Fixtures and Shop Furniture He describes a 4 foot one that has triangular braces on the back side of the overhang. I think I will adapt his design for my recently upgraded 520.
Jim
{After reading my posting it sounded to negative so this is a major rewrite as of this edit]
I have some concerns over the use of the top of the fence to attach jigs or fences that need to be dead on at the face of the rip fence. First is that making a joint 90 deg. from the top to the side might be harder to get right then if you just went to being parallel to the fence. The height would have to be such that the vertical surface would not touch the table when it is attached at the top... if it did touch you might start getting a twisting motion and not be at 90 deg to the table. The attachment point would either have to be adjustable or within the slop of the t-nut system as it is very importain that the vertical surface be touching the fence at every point. If you leave a gap the pressures during use could deflect until it got to the real fence... something that you don't want happening.
If you are talking attaching a hold down or feather boards this top attachment is fine but if you are using it as a true surface to work off of.... why not use the one that is the real one? Attaching to the front of the fence is a very positive way of doing things. The fence has provision for front mounting the same as most saw rip fences and this has been done this way for a lot of years now. I just don't see any advantage to using the top???
I know I should be more open minded about ideas like this. I just find it hard to understand, so if someone can explain why I would want to change my thinking go ahead teach an old dog a new trick.
OK well maybe I like a few "new" things that I haven't tried yet. Like the two parts (clamps) that where posted earlier... mostly because I see them working like I think they should, ie clamping in the right direction and to the right surfaces.
Ed