|Forum topic by runswithscissors||posted 10-30-2014 04:13 AM||1586 views||3 times favorited||3 replies|
10-30-2014 04:13 AM
This project shows how I addressed several of the concerns that people (including myself) have had with benchtop mortisers. Among these are the inadequacy of the typical holdown, the slowness of shifting the stock laterally by hand for each cut, and the narrowness of the table that becomes problematic with long pieces, such as the stiles for a door.
I started with an 8”X4” piece of aluminum rectangular tubing with 1/4” walls. As I recall, this cost about $25 to $30 for a 24” length from my local metal supplier. I split this tubing on my TS, cutting at opposite corners, to yield two aluminum angles, each with 4” and 8” legs. The idea was to nest one inside the other, connecting them with small bolts through sawed-out slots. This allowed the inner one to slide laterally.
The bottom EL attached to the mortiser’s fence, using HDPE spacers of about 1/2” thickness, both to raise the table and to provide a slick, easy-moving in-and-out adjustment. The Delta has a rack and pinion set up that simplifies this. Notice that I had to put extensions on the clamping knobs to make it easier to adjust them by reaching over the top.
Raising the table base allowed me to attach a gear rack to the front edge of the inner/top aluminum angle. Though I attached this by drilling and tapping holes for 8-32 flat head machine screws, I might have instead spot welded a small angle iron to it and bolted that under the base. This would be a little simpler, as the holes wouldn’t need to be tapped.
I bought the gear rack and pinion from Applied Industrial Technologies, who happen to have a retail outlet in Bellingham. The cost of this was about $45 for a 2 foot piece. The gear rack didn’t need to be that long (1 foot would have been ample), but they only sell it in 2 foot lengths. Almost any gear rack would work, and I would have cannibalized one off some other machine, but nothing was available.
The inner, sliding aluminum angle is attached by small hex head machine screws through slots that can be seen in the photos. These slots are in both the back and the bottom of the base. They allow about 4 1/2” lateral movement. By carefully tightening the screws, the movement is free, yet not sloppy. The screws are backed by washers, which smooth out the movement. The holes are of course tapped. I upset the threads on the bolts to hold them in the desired adjustment. I sprayed Dri Lube on the aluminum to ease the sliding.
The first hold down I tried I cobbled together out of aluminum bits and the screw from a clamp. The mount for this can be seen in some of the photos, in between the Bessey clamps. To give it a better grip, I attached self-adhesive non skid material to the back of the table. This worked, but it was somewhat slow to clamp and unclamp, and the screw had to be run down very tightly to avoid lifting the wood during the withdrawal of the mortising chisel. So I decided to try the Bessey self adjusting hold downs, and these work extremely well. The self adjustment range is fairly generous, and the tension is easily adjusted. Though there are two of these, when mortising the end of a stile, a single hold down has enough strength to resist lifting. They also are very quick to lock or unlock. I mounted them on 2 inch square tubing (1/4” wall) to raise them high enough for the stock I was mortising (about 2 3/4” high). For narrower stock, I find it easy enough to slip in a spacer to raise the wood high enough for the clamps to engage. At some point I may try to devise a way to adjust the height of the clamps to handle a wider range of material widths (or heights) without fussing.
The non-skid material on the back is no longer necessary, so I will probably remove it, but I hesitate because I fear removing the adhesive could be a PITA.
The X movement is done with the knob seen in the lower left of some of the photos. This is mounted in a homemade bracket, and attaches to the pinion or spur gear with lock nuts. The size is about right, giving me sufficient fine control while permitting rapid adjustment.
Using this set up is a two handed affair, with the left hand controlling the lateral movement while the right hand plunges and withdraws the chisel. The video (if I am able to make it work) shows how I can cut a mortise in a rapid plunge, withdraw, move with a left handed twist, and repeat, almost a quickly as you can say it. I find it helpful to spray Dri-Lube on the chisel from time to time.
After this was finished, I used it to to cut 36 mortises in the stiles for 6 louvered closet doors. It worked extremely well, and made the whole job go fast. I also used it to cut little 1/2”X1/4” mortises to receive stub tenons on the louvre slats. To do this, I twisted the mortising chisel to the angle I wanted, ran a row of 1/4” square shallow mortises, then shifted the table back (Y axis) to allow the slots to be elongated. Altogether there were about 550 of these little 1/4” X 1/2” angled mortises.
Is there any protocol that says which movement—lateral or fore and aft—is the X and which is the Y?
-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened