Well, my Craftsman hollow chisel mortiser is on its way to its new owner now, thanks to the NCWoodworker Intrastate Transportation Authority™. I figured I would post a few "pointers" on the use of the HCM, in case anyone was interested - especially the new owner. 
These are just some tips that I have found through trial-and-error (mostly error) and reading various articles on the subject. Hopefully some will find this useful - I know I didn't know a lot of these things when I first got this machine.
If anyone has any more pointers to add, please feel free!
These are just some tips that I have found through trial-and-error (mostly error) and reading various articles on the subject. Hopefully some will find this useful - I know I didn't know a lot of these things when I first got this machine.
- Securing the machine
This tool is fairly sturdy, but it will tip if you're cranking down on the handle. I always clamp the back of the tool base down to the workbench.
- Setting the chisel & bit
Insert the chisel and bit together and then tighten the chisel first. Just let the bit rest on the table for now. Set the chisel so it has about 1/16" gap at the top, and tighten the set screw - don't worry about squaring it to the fence at this point.
Once the chisel is in place, raise the bit up as far as it will go into the chuck, and tighten the chuck. The wide part at the end of the bit will stop it even with the mouth of the chisel. Once the bit is secured, now loosen the set screw and raise the chisel all the way up so there is no longer any gap at the top. This will provide proper chip clearance between the chisel & bit.
With some types of wood this spacing may need to be adjusted up or down (by moving the bit, not the chisel) if chip clearance becomes a problem.
- Securing the fence
The design of the fence on this particular machine allows for some vertical play. This presents a problem because the hold-down is attached to the fence, and the workpiece can be lifted up off the table - not good. Problem is fixed with a couple of small C-clamps attached to each end of the fence.
I always check to make sure the chisel is square to the fence at this point, and then I try to make sure that the fence stays straight while I'm tightening those C-clamps.
- Securing the workpiece
Obviously the hold-down will keep the piece down on the table, but a quick-grip clamp will keep the piece from drifting away from the fence. It will also prevent lateral movement which can be frustrating when it occurs. Always work the side that is closest to the fence, then flip the piece end-for-end and work from the other side. This way your mortise will always be centered.
- Don't measure!
IMHO this is the key to joyful mortising. Whenever you can, use a stop block and a spacer block to keep the mortises perfectly uniform for all the parts of your project. The exact size of the spacer block is not really critical, as long as it's close to your layout lines. That mortise doesn't care if it's 2" long or 2-1/8" long. All you want to do is make sure it's centered (see above) and uniform in all the pieces that need to be uniform. That will really make fitting the tenons a lot less of a headache. And speaking of layout lines, another advantage of using stop blocks is that you only need to mark up the first piece (assuming you did a good job milling all your stock to the same dimensions).
With some planning ahead, you can often batch process most of your mortises without repositioning the stop block. When it's time to flip the stock end-for-end, use your existing partial mortise to set the stop block on the other end.
If the mortise is too far away from the end of the stock, you may not be able to set a stop block on the fence like in the above pic. In that case I use a longer accessory table with a glued on stop block, and I just slide the table into position and clamp it down to the base.
- Cutting the mortises
I don't have a pic of this, but I usually cut the first corner against the stop block, then add the spacer to cut the other corner. Then I take the spacer out and skip spaces in between the two cuts (not a continuous cut). If you try to cut a mortise right along the edge of your previous cut, the bit will deflect and you will curse. Just come back and clean out the little bridges left behind to finish the mortise. Hopefully that makes sense.... :eusa_thin
- Dust collection
Yea right... good luck! ;-)
If anyone has any more pointers to add, please feel free!
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