In the sled cutout file, you should add a plug with a .25 hole in the center. I figure the hole would be cut to the inside of the line, and the plug would be cut on the outside of the line. Insert the plug into the center sled hole, install a .25 bit or dowel into your router, align the router in the center hole, and mark the mounting holes for the router on the sled. Remove the plug when you are done.
This would guarantee that the router is perfectly centered on the sled.
That is a very slick solution! I like it!
This is how my router compass works, good idea.
I suggest another addition to increase the foolproofing of the concentricity of the router and the ring. Make shallow reliefs (2mm?) into the sled where the 3 brackets need to mount. This provides a physical index and should theoretically eliminate mispositioning.
How big a hole does the bit need, anyway?
I have giving some thought on how to center the router on the sled, an easy fix would be to mill out a lip for the router to set down into. I used a caliper to get the diameter of my router base and just modified the sled file that I downloaded.
I haven’t made this part yet, but I think it will work.
The idea was with the plug, it would be universal from one router to the next.
@jwolter the hole size is 1.5 inches. At least that is what I modeled above
This is a good idea, but would be router specific.
Perhaps the sled design can be modified to include tabs on the center portion with a central hole as per the plug. That way the cuts are all made initially without having to cut a plug to fit and hope that there is no problem with alignment between cuts.
Once the router holes are located then the central plug tabs can be cut and the sled is complete.
The plug could initially be cut during the sled cutout process, similar to the two brick holders. No extra effort needed. Cut the sled template, insert the plug, align router base … remove plug.
true, I would just worry that there might be some misalignment between the two parts, or that the plug wouldn’t fit well (too big, too small, etc.). Leaving the plug attached to the sled with tabs ensures that this is not an issue and reduces cutting time. Of course, cutting the tabs later means that you can’t reuse it, so there’s that. Perhaps a combination of both?
Gotcha… didn’t quite understand what you meant inthe earlier post… good idea…
I used tabs as you described, and made a centering jig by temporarily screwing a second sled-sized disc to the underside of the sled with a pair of keying pegs. I used glue and screws to attach the central alignment disc to that jig. When it was dried, I cut the tabs with a chisel to set the jig free. That leaves me with a centering jig I can affix to the sole of my sled.
ooo good idea! With those pegs you wouldn’t even need to do a sled sized under piece, just enough to get outside the central hole with room for a couple of pegs.
This is straight up brilliant!!!
Anyone want to make a project for this in the community garden? I’ll update the instructions to link there instead of pointing to the old file
that depends on the size of the bit you are using
leaving the plug in with tabs is going to be far more reliable.
even the best hole size is going to vary from one router to another (think trim
router to monster 3HP motor)
Ok, it seems the best option is to leave the plug attached with tabs to the sled until after the router base is installed. At which time the plug will then be removed. Whoever decides to build the G-Code that is to be uploaded into Ground Control, I have one last request. When you make the hole in the center for the .25 inch drill bit/dowel that will be chucked into the router, please add at least +04 tolerance to make it a little easier to insert the bit/dowel into the hole, otherwise we may break the tabs holding the plug while aligning the router base.
Thanks everybody for a great discussion.
I just cut this bad boy out tonight. Worked wonderfully even with my dull bit. Much easier to get the router dead center. Also I think with this even if your maslow isn’t 100 percent accurate in one direction (mine was making slightly flat circles)the hole is always in the middle so whatever the case it’ll be more accurate than eyeballing.
nevermind…I just noticed it was in the garden 
Thank you so very much for this piece of genius!
I modelled and printed a PLA plug and used it for my Bosch. Worked a charm, but when I went to bolt the router on I got pretty worried that the base hole on the router looked out of line. Turns out the base hole IS out of line, but the bit is +/- 0.1mm (not inches, mm!) because of your idea.
Cheers!
