Replies

1. 
   [email protected] | Jan 07, 2009 06:34am | #1

   To give you a consistent face to use against a fence. 

   The round base can be slightly offset from the true center of the bit.  If you have the flat face, you can put the flat edge against the fence, and know that it has a consistent offset to the center of the motor.

1. 
   knuts | Jan 07, 2009 04:39pm | #2

   I know from use that there's more friction with the flat against a fence. And if the flat moves just slightly away from flush, the bit will swing greatly off track. But if a point on the round base is used as a reference, then less friction and the reference is more forgiving. In fact, I add a round base to my routers that have the flats.

   You may be correct in that, is what the designers had in mind and other WWrs have offered the same reasoning. However, it has the opposite effect on my use.

   This jig is the main reason I like a round base. The 2 fences are squeezed against a sample of the piece that will fit into the resultant dado regardless of it's thickness. I like to run the router down & back without having to rotate the router, cord & vac hose. BTW, this pic shows the setup for a rabbet, but dado or sliding DT the is same.

   View Image

   Edited 1/7/2009 10:40 am ET by knuts

1. 
   [email protected] | Jan 07, 2009 06:50pm | #3

   I have a similar jig for dadoes and rabbets.  I use a fixed base mounted on a router table insert plate with it.  The edges are about 1/32nd off center from the bit.  This tiny offset lets me rough cut on one edge, and then climb cut the final cut using the closer side. 

   In that application, even if it lifted slightly away from the fence I'm still ok because I am removing waste up to the guide, and can clean things up on the second pass. 

   Where the issue become a concern is doing things like cutting a dado with "plywood" bit where the single cut is removing the full width, so a little wobble leaves a gap in the final assembly. 

   I keep a roll of waxed paper in the shop to rub down tools, and guides with.  It leaves just a tiny amount of wax on the surface, and smoothes things up tremendously.  

1. 
   knuts | Jan 07, 2009 08:42pm | #4

   I've got no use for plywood bits. I'm sure you've noticed todays plywood thickness can't be trusted. I've had variations on the same sheet!

   Nevertheless, I cannot think of a good reason for the chord or flat spot! Hopefully, someone has 'the' answer so I can obsess on something else!

1. 
   Cincinnati | Jan 08, 2009 03:41am | #5

   Only thing I can think of is to average out any "imperfections" in the fence. A slight ding will not telegraph on the flat but will on the point of the circumference.Greg

   <!---->•••••••

   Exo 35:30-35<!---->

2. 
   RickL | Jan 09, 2009 05:35pm | #6

   You have the answer. I've never owned a tool that I didn't modify in some  way to suit my needs better. Make your own round base...

2. 
   PADDYDAHAT | Jan 09, 2009 09:17pm | #7

   k, take a look at Pat Warner's site, aka routerman, he makes very superior clear bases I think for every router known to mankind. I have several an they are great and not too pricey. Paddy