Over-Arm Router Tips

      General advice on ways to use an over-arm router. November 21, 2006

I am curious what the common uses are for over arm routers. I just can't think of what I would do with one. Why are they so expensive compared to shapers?

Forum Responses
(Cabinetmaking Forum)
From contributor D:
Over arm routers are designed for use with a template. Not that they can't and don't do many other things. With guide pin in the table, its center should reference to the center of overhead router. This will allow you to use a template or pattern, whichever name you prefer, to guide a work piece along that pin, while at the same time plunging the router bit into the work piece. Depending on bit length, material type, and thickness, you can make anywhere from one to three passes to complete your cut. It's an excellent production run tool. Although nowadays, CNC routers can easily outwork and hold tighter tolerances than an over arm router.

Some other things you can do with an over arm router are stopped and through dadoes and rabbets, fluting of flat panels, angled dadoes and rabbets. If the table tilts, you can use it to "joint" straight edges onto stock.

A few things to consider regarding the use of over arm routers, is that they can be very dangerous, as can any other tool. A strong familiarity with basic router usage will go a long way in helping to prevent any unfortunate accidents. With the wide variety of router bits currently available, one style of bit comes to mind that should never be used in an over arm router - the up spiral straight bit. It's great for ejecting chips upwards instead of packing them into the dado you just cut. But they have a tendency, by design, to lift the work piece and pattern up and off of the pin. It is true that depending on the weight of the work piece/pattern versus the diameter and length of the router bit, certain combinations may work out just fine. Edge forming bits that are guided by ball bearings should also be used carefully, since they also tend to want to lift the work piece.

Since your router bit of choice is basically going to be hanging there right in front of you, spinning at maybe 15,000 rpm's, you want to make sure that no part of your clothing or body comes in contact with the bit or arbor. This is a potential career/life ender. When feeding stock, always try to use some type of hold down to keep the work firmly in contact with the table of the over arm router. Try not to use your hands to feed a piece while pushing in a direct line toward the bit. Also try to use the guards to shield as much of the bit as possible from unintended contact. Build your patterns, when possible, with handles to allow you to have your hands in control of the work piece. Another thing to consider is the floor you'll be standing on. Pattern routing with an over arm requires much more than just hand and arm strength. A solid non-slip surface to stand on is important to the safe and successful operation of an over arm.

As far as price comparisons between a shaper and an over arm router goes, hopefully from my answer you'll see how it's a different degree of accuracy that's involved. A shaper is basically a spindle sticking up through a table. An over arm router is a spindle that aligns with a pin opposite the end of the spindle. The castings for an over arm router are more complicated than for most shapers. There's such a broad range of pricing, features and capabilities in both machines.

From contributor S:
In regard to the upcut spiral bits lifting the work off the table: No doubt that is why Onsrud, who invented these bits, also brought out an inverted pin router. In that instance, the chip ejection would draw the chips out and pull the work into the table.

From contributor B:
Over arm routers are great for the small shop. I use one to stop dado and rabbet cabinet sides because of the accuracy they provide. During setup, I plunge with the motor off, then adjust the distance between the bit and table to 1/2". I stockbill the width of cabinet tops and bottoms 1" less than the width of the cabinet and always get perfect accuracy.

Contributor D is right about the danger! I had an employee lose the right side of his right hand trying to use a rag as a cushion. I've been using them for 33 years and never had even a close call, but I work safe and focus like a laser beam. I don't use the pin - I fit the machine with a stout fence.

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