JET JBM-5 Mortiser
by Mark Mandell

With 100s of square spindals staring at me from the plans for the Mission Garden Room, it was obviously time for a power mortiser. So, off to the Toystore to comparison shop the offerings.

[The PM-719, a very nice "production-shop level" unit, was immediately ruled out; I simply don't have $600+ to shell out on this type of tool.]

With no in-person availability to look over the Grizzly and Woodteck offerings, choices got narrowed rather quickly to the Delta and the new JET JBM-5 unit. Point-for-point the only real difference seemed to be the paint color, the riser block Delta option (why not just build in more height, anyway?), and JET's inclusion of 3 chisel/bit sets for a total price $40 less than the Delta.

While mindful of a previous Pond string concerning screaming chisels, I bit on the included chisel deal (and the 40 bucks); I can always replace the Taiwan bits with good Euro's or even British Clico's (highly recommended by my sharpening guy) if the need arises, and I like white bettern bluish-gray anyway.

Since the tool is essentially a drill press that cuts square holes, there's not much to assembly; took all of about 20 minutes and there it was.

The column groove guide set screws took a little figgeting (open-end + allen wrench duo) to get to the point where the motion up & down the column was smooth, but still solid.

Chucked up the 1/2 chisel set, put a piece of red oak under the clamp, and proceeded to cut a 1/2" x 2" mortise with little trouble [and no squeeling]. The chisel did, however, require more down-force than I expected. The slot was also a bit rough-edged because I had neglected to parallel/square the sides of the bit with the wood, the fence, and direction of feed. Resetting the chisel's orientation a touch (cake via front-mounted set screw) yielded immediate improvement. I tried four different kinds of wood, hard and soft, and found that varying the amount of bit protruding below the chisel's points made a difference the amount of applied leverage required. Can't extend too much bit, however, or you wind up having to reset the bit and go in again to clean up the lower portion of the mortise, and possibly snap the bit due to excessive flex.

During the test cuts, I noticed that the handle [16" long from the pinion shaft] had an excessive amount of freeplay, almost 1 to 1 1/2" at the end. Contacted JET for possible defect, and they had me take the unit to a local distributor/repair guy for checkout. He could't tell me much since he had never even seen the tool (newly added to JET's line), and didn't have the specs. I left it with him and proceeded to do my own research [back to the Toystore plus 3 other places who carry the tool] only to find that all of them [JET & Delta] have about the same amount of slop in the lever handles. Gave the repair-guy a week to play with it with no results, so took it back home.

Problem appears to be in the handle's springloaded hub casting and the pinion shaft which mesh together with a set of teeth so that the handle can be repositioned for maximum depth of cut while maintaining good leverage. However, even a small amount of play in those teeth results in a lot of handle lash when you get 16" out from the center of rotation. While I judge the floppy handle to be a design defect, it does not effect the quality of the cuts made, only the operator's sense of control. If, however, I had that kind of slop in a new drill press, it'd be boxed and outtahere, freight-collect, in a heartbeat.

The fence is merely adaquate and the hold-down fork functions to allow the chisel to be removed from the wood after the cut is made. Neither, however, are particularly solid or stable. No, I'm not complaining that I didn't get a Powermatic for the price of a JET. It does, however, appear that I'll be doing some modifications to make the tool more precise and predictable.

Lastly a note on screaming chisels. The machines cut with a heavy-threaded brace-type bit running at 1750 rpm inside the square chisel, and the two "meet" at the end of the chisel where the bit is ground to match the inside cup shape of the chisel. When I ran test cuts in pieces of fir and cherry, I found that that surface began to loaded with resin and the bit started to get noisier. Keeping the bit slightly lower than the chisel opened the gap between chisel and bit and reduced the noise. I also improved things by honing the bit's mating surface with a hard arkansas slip.

All-in-all, I got what I paid for, and the machine will do what I bought it for. It is not, however, one of those tools that will give you that tactile "gee-wiz" feedback of a job well done.

Perhaps the manufacturers can come up with a modification to cure the handle play problem. Be even nicer if they sent out a freebe retro-fit cure package.