Shopmade router jack

[Bob Hammond]

Hi, my plunge router is mounted upside down in an old cabinet. When setting the bit projection, it is tiresome to fight the springs and twiddle the fine adjustment knob. So I made this jack that operates on the principle of folding wedges. It resembles a machinists planer gauge. It is placed between the router and the shelf below it, and it is very smooth and precise. As illustrated by the orange tape strip in the picture, about ~4" of horizontal travel raises the top surface (which bears against the router) 0.500". If additional height is needed, I just slip a block beneath it.

To make it:

1. Joint one edge of a 12" x 3" x 3/4" stock, and cut a wedge from hard maple (about 1:8 taper here). Joint the sawn inclined edge.

2. Cut a sawkerf down the centerline of the inclined edge 3/8+" deep to fit a 1/8" x 3/4" x 6" aluminum strip.

3. Then cut the wedge in half to make two matching 6" wedges. and glue the aluminum strip fin into the lower wedge. This will keep the wedges in register.

4. Glue & screw the 3/4 x 3/4" maple bar on the end of the lower wedge, and then drill & tap it for the 1/4-20 eye screw. You may wish to use a metal threaded insert instead of tapping the threads directly in the wood.

5. Wax the screw and the loadbearing surfaces of the wedges.

6. Make a scale if desired (It's not so difficult; should I write about how to do that?), but usually I use a ruler or height gauge on the router bit.

7. If turning the eye screw by hand is too slow for you, you can replace it with a hex-head bolt and then use a drill-driver to speedily adjust it.

This same mechanism can be used to make a precise adjuster for router and saw fences, etc. The taper can be altered to suit, but I'd keep it from 1:4 to 1:8. Also, make a single gauge from only one of the wedges that is cut from the rectangular stock, since there is often a slight taper on a rectangular piece of stock unless it's been carefully jointed and plane.

[Bob Hammond]

It occurs to me that my router, a Bosch 14xx series, has a flat top that the upper wedge bears against and moves smoothly across, and that the vents on the router top are not obstructed. For you, it may be necessary modify the jack by placing a rub block on the top of your router. If that is so, I suggest the following modifications:

1. Cut another 1/8" slot on the top surface of the upper wedge and glue in an aluminum strip.

2. For the router top, cut a small block with a matching 1/8 slot, and then fit it so that vents are not obstructed. I would use double-stick tape (woodturner's or carpet tape) to attach it to the router, so that it can be easily removed if necessary.

[Darrel Friesen]

That's cool Bob. Reminds me of the D'Aquisto style archtop bridges that use a similar sliding wedge design.

[Bob Francis]

Sweet! I was overcomplicating something like this and knew it. Thanks Bob!

[Steve Senseney]

I like it!

[Bob Hammond]

Steve,

If I remember correctly, some long time ago, you posted a template for the even spacing of six strings across a nut or bridge.

That is the same graphical method that I had in mind to make a scale for this jack, because it's not so easy to cut and joint a perfect 1:8 taper on the wedges with common woodworking tools. I had in mind to increase the number of divisions from six to ten, so that decimal math can be used. (or maybe eighth divisions) The same method can be used to make a 1/10 vernier for the scale. Would you describe how to do that?

There is another consideration about making a scale for this jack mechanism, and that is about changes in humidity. Right now my place is extremely dry, but next summer the humidity will be high, and so the dimensions of the wedges will change. That's why I measure the adjustments by the router-bit projection, rather than using a fixed scale on the jack. But if the shop environment is controlled, then a fixed scale could be very convenient, especially for other applications such as fence adjuster.

[Bob Matthews]

That's an excellent idea Bob, thanks. I have been fighting with my router and table for too long now and shall be making one over the holidays.

[David King]

You could even calibrate the turns to .001" using a 1/4"-20tpi screw and 1:5 or a 1:10 slope

[Steve Senseney]

I have thought about the venier scale.

It would be simple to lay out a scale with marks, with labels 1-10. Print this at full scale, then print at 110% scale. You would then have the 2 scales needed for vernier calibration.

Picking out the correct total length for the correct rise would require knowing the angle, and using math that I have avoided for the last 40 years!!

I like your design, but I never trust any derived measurement. I would test with scrap and measure twice!!

[Bob Hammond]

A computer generated scale would be very nice and neat, but it's not difficult to make one with paper and ruler (and it might be faster). I'll see if I can make one up and post pictures with explanations. In the meantime, here's a nice link that explains vernier scales with animated figures, for those who might not be familiar with them in this age of digital measurement devices:

http://whistleralley.com/surveying/vernier/

Hmm, maybe I should make a jack from a plastic, e.g. HDPE, so that it wouldn't be susceptible to warpage.

Also, there is another thing that I've noticed about using this jack. It is plenty strong enough to distort the surface of the router table so that the surface around the bit is higher than at the edges of the table, and so the table must be sturdily braced.

Which brings to mind, that a small jack might be useful inside an instrument for brace and crack repairs, or gluing of bridges. Just be careful!

[Mario Proulx]

This thread's title is a bit misleading, methinks. When I first saw "router jack", I thought it was something to raise or lower a router that is fixed into a router table. After looking at the image, I had no clue what it was, but now I understand that it's a device for setting the router bit height/depth?

[JC Whitney]

Nope, if I understand correctly it is indeed a jack. Slip this gizmo between the bottom of the router and the cabinet below, release the router's lock, and turn the screw... up/down she goes! Just like my trusty old scissor jack.

[Bob Hammond]

I've seen the same thing done to jack up a porch roof so that a support column could be replaced. In this case, it's working against the weight of the router's body and the pressure of the plunge return springs.

[Mario Proulx]

Ah ha! I see.....

I don't have a plunge router, so all of mine are adjusted by either turning a collar, or the router motor itself.

Doesn't the screw get bound-up as it rises, or did you build-in some "slop" to allow for it?

[David King]

Mario, that's a good point and I'd think one of those barrel-shaped nuts used to hold together Ikea furniture would work. Ideally I'd want a screw from a turnbuckle with LH and RH threads to eliminate the backlash. I'll bet you could get two with the pivoting nuts from a wooden hand screw clamp. See: http://www.rockler.com/product.cfm?page=18917

Cheaper yet would be a miniature machinist's jack of which I have several but never thought to apply here. http://www.grizzly.com/products/Machinist-s-Jack/G9700

[Bob Hammond]

Mario,

Yes, the cheap eye-screw shown here can get sticky and sloppy, especially on the downward slope when the pressure load is falling. The way around that problem is somewhat like tuning a string to pitch. First slack off a bit on the screw and give it a tweak (tap it and maybe run the router for 30s or so to rattle & relieve any residual friction from other parts), and then tighten up to the desired setting. Now after using it for a week or so, I think that adding a threaded female insert should be done, and if I wanted to make it smoother, I'd adjust a threading die to hand-cut a screw that fits the insert's threads closely.

This afternoon I made a vernier scale for it, but I've decided that in this application that too much error will accumulates in other parts of the setup -- for example, I could set the jack exactly to a 'perfect'' expanded dimension, but the unpredictable distortion of the table-top or other parts would negate that setting. I think that it's better to stick a piece of tape on the jack and pencil a reference mark for adjustments, and then make adjusts by directly measuring the router-bit projection. After all, that's what's important, not what a scale on the jack might read.

David, I think your suggestions are excellent. I've used handscrews and their parts for other purposes. The Grizzly jack will work, but the beauty of this wedge method is that it's cheap to make to a particular size that is appropriate (remember the fence applications?), and easy to see because the visual process of adjustment is linear instead of angular, and it gives fine control.

[Dick (DT) Trottier]

Hi Bob,

4. Glue & screw the 3/4 x 3/4" maple bar on the end of the lower wedge, and then drill & tap it for the 1/4-20 eye screw. You may wish to use a metal threaded insert instead of tapping the threads directly in the wood.

If you change the design slightly such that the screw is parallel to the wedge your jack will make smoother adjustments. Drill and tap for the screw at the wedge angle rather that square and add a small counterbore in the wedge to capture the screw tip. As it is, the end of the screw is constantly changing it's contact point on the upper wedge as you adjust the height.

Good luck and best wishes for 2013...

[Bob Hammond]

Dick, that's a good suggestion, so long as the screw has clearance to extend below the bottom surface of the lower wedge. An alternative would be to place an acorn nut (with a hemispherical surface) on the screw, to make a single point of contact that could slide easily.