Thursday, 18 April 2013

Nu-Tool mortiser modification

Some time ago I bought a second-hand mortiser made by Nu-Tool (No I've never heard of them either!) from my brother's father in law along with a whole bunch of tools and a decent lathe for just £30GBP (about $45US). I didn't have a mortiser at the time and found it useful for batching out a number of mortises.
Unfortunately over time the clamping mechanism and the fence have worn and it is a chore to use it.
I had an old machinists drill vice and decided to make some modifications to the machine to make it more serviceable.
Here are a couple of images for the same machine from Kristian Dalziels entry on (I forgot to take pictures before I modified mine!)
The mortiser is 230V 370 W (2.35 Amps) and is
rated for 1/2" mortises which is fine
for most hobby woodworkers

The problem as seen in this picture is that the knobs hit each other
there is also not enough adjustment in the fingers
and also the fingers are cast aluminium and not
strong enough to resist the tool pulling out.
I removed the sacrificial wooden top to reveal a great cast iron base. Also the fingers and fence mechanism have been removed.
Cast iron table with two new M8 holes
Then taking the machinists vice I positioned it so the fixed jaw line was on the centre line of the spindle in the side elevation finally using a sharpie to transfer the shape of the slots in the vice through to the cast iron table surface.
Carefully marking the centre of each slot with a measurement from the front face I drew a line right across so I could drill two holes. Then on the drill press I drilled two 6.8 mm diameter holes right through the cast iron. If you have never drilled cast iron before this is one material that you can drill without lubrication - another is brass - and get a clean hole. Then I tapped the holes out to M8 and cleaned up any fragments.

Then I set to modifying the machinist vice by removing the fixed jaw and clamping it to the centre of the existing aluminium fence that I had removed from the mortiser. Then transferred through the holes in the jaw into the fence, removed the jaw and countersunk the new holes in the fence.
Replacing the jaw, seating the fence in position and inserting longer countersunk screws ensured that the whole assembly was solid.
Machinists vice with original fence now fitted
Then it was a simple matter of bolting the vice into rough position and setting up the mortiser. Marc Spagnuolo has a good video on his Woodwhisperer website (thanks Marc) showing how to set up a mortiser so I won't repeat it here.

Clamping some timber in place


Finished mortiser
After setting up a running a few test cuts I found that the operation is now this:

  • Adjust vice so that the workpiece is parallel to the face of the mortiser chisel and the correct distance in.
  • Clamp vice in place using the two bolts.
  • Adjust depth of cut

Insert workpiece using end stops clamped to the fence if necessary.

  • Tighten vice screw
  • Make mortise
  • Loosen vice
  • Move workpiece slightly
  • Tighten vice
  • Make mortise

Repeat the last few steps as many times as you require to make the full length mortise. I've found that light pressure on the vice is all that is required to hold the workpiece in place and the tool pulls out cleanly.

Possible further improvements

  • Bolt steel guides to the cast iron table to guide the vice and keep it square.
  • Modify the vice screw to be at a slight angle relative to the base to apply downward force as well as a clamping pressure

Summing up

So I have brought a perfectly good tool back from possibly being scrapped by reusing a redundant vice and reusing some components from the original setup.

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