Saturday, September 15, 2007

Trim Router Offset Base v0.1 (Part 1)

As you'll find in my posts, I'm a huge fan of cheap tools that work. Harbor Freight (aka: Horrible Freight) is one of my favorite tool stores.

One of their gems, IMHO, is the 1/4" Trim Router. It goes on sale for $15 frequently, making it an amazing buy. I like its size better than full sized routers. It just fits my hand nicely, plus it can be used one-handed when necessary.

As cool as this little workhorse is, it's missing one thing: An offset base. While I might be able to force a commercial unit to fit, it would be huge compared to the router, expensive, and it wouldn't work as a table base. I'm building a benchmount router table, and I want to use the offset base as the platform to hang this router from.

After a few design ideas, I ended up with a 5" circle for the router mount, a 1 1/4" circle for the knob end with a 7 1/2" reach between the centers of the two circles. The total length is just over 10", ideal for a small trim router. Plus it's small enough that .220 thick acrylic will be rigid enough for table use.

I added "pin holes" to mount locator pins, centering pins, or when used in a table, pivot pins. One pin hole is off-center at the big end of the 5" circle. The rest are staggered 1/2" apart starting 1 1/2" from the collet center and ending at the knob mount that's 1 1/2" from the small end.

Those pinholes will allow the base's use as a circle jig too, with 1/2" precision.

Construction of this version 0.1 is rough. I suck with a jigsaw. Especially this Skil 5amp model I just got a couple months ago. I can't get the hang of using the scroll knob on top, and so my curves aren't as smooth as they could be. Version 1.0 will be made with this base, allowing smooth and correct circles.

After drawing the plan, I made a template using a piece of hardboard. This material is sturdy, dimensionally stable (won't expand or shrink due to humidity), and cheap.

I made my own compass to draw the circles (I've since purchased a "real" compass). I then used my table saw (with a Harbor Freight 8" 40t carbide cutoff blade) to hit the straights and trim close to the circles.

I then used that Skil jigsaw to make the circle cuts. I ended up cutting a bit smaller than I had designed, but that worked out ok.

Making your own compass is easy. Just take a scrap of wood and drill two holes, the distance between them being the same as the radius (distance from the center of a circle to the edge) of the circle you are trying to draw. Stick a screw or nail through one hole and into the workpiece, and the other hole gets your pencil or pen.

Once you've cut out your template, the edges will probably be rather rough. That's OK. Hardboard is easy to sand smooth. I used a piece of 220 grit paper and just held it in my hand to sand the edges. Keep smoothing the edges until they're VERY flat and smooth with no ridges, ripples, or bumps.

Any imperfections WILL be transferred to the acrylic by the router!

Once the template is ready, use double-sided tape to stick it to your acrylic. Note that most acrylic you buy will have a protective thin plastic sheet on both sides. LEAVE THIS ON. It keeps the acrylic from being scratched and damaged. It also makes removing the tape easier when you're done with the template.

Apply a little pressure for at least 30 minutes to make sure the tape isn't going to slip. I set a thick book on top of the template/acrylic sandwich to let the tape set.

Clamp the sandwich to the workbench. Using the Harbor Freight 1/4" trim router with a 1/2" laminate trimming bit (and matching bearing) I duplicated the template in the acrylic.

When aligning the bit, make it so the bit ends and the bearing begins both within the thickness of the template. This ensures that your router is cutting through the entire depth of the acrylic, but still allows the bearing to ride on the template to guide the cut.

The cut made in acrylic by a router is nice and smooth. I debated flaming the edges of the acrylic to smooth it up, but the cut was already nice, so I didn't need to do anything else. I may decide to flame the edges on the final version though.

This is the end of Part 1. Part 2 will include putting
the pin holes in, cutting the bit opening, and
mounting the base to the router.

No comments: