Faceplate Dogs

Last month I roughly sawed and filed my cast aluminium blobs into blocks. The resulting blocks were too large to fit into my 3 jaw chuck so I hoped to mount them on the face
plate. There are many ways of bolting or clamping items to a faceplate but I wanted the full surface to be available for machining and most techniques mount over the top of the item. Tubal Cain came to the rescue with his book Workholding in the Lathe which describes faceplate dogs. These simple devices allow the work to be clamped laterally using screws. The book had some example devices and I drew up a variation as show below.

Materials

  • Mild steel 20mm A/F hex bar, alternatively square bar 9+ mm
  • M5 nuts and washers (to fit slots in faceplate)
  • M5 bolts

Build Instructions
Here’s my instructions for making these items based on the size of my lathe and the number of slots in the faceplate.

  1. Cut the hex bar into 3 of 20mm lengths using a hacksaw
  2. Machine the ends flat to make it easier to clamp for drilling
  3. Mark out location of hole in the centre of the bar, 4mm from one end. Centre punch location
  4. Drill 4.5mm hole all the way through
  5. Counter bore 5mm hole part way through, this is not necessary if your bolts have thread for their entire length or if you are using smaller bars
  6. Tap hole with M5 tap
  7. Turn down bar to be 5mm for a length of 12mm (opposite end to hole)
    Position of the tool for the first cut Results of the first cut
    If you try to turn a small amount from the hex bar it will chatter badly and may be wrenched out of the chuck, if however you make your first cut large enough so that it can complete a circle in the metal this will not occur, your first cut should look like the photo above, just clearing the flat sides of the hexagon.
  8. Cut the M5 thread along length leaving just less than thickness of faceplate.

Using the faceplate dogs
Faceplate Dog
The completed faceplate dogs are loosely bolted onto the faceplate. The work is put in position and the bolts tighted. The faceplate dog’s screws are then tightened to lock the work in place. Make sure there is clearance above the lathe bed for the work and screws. You may want to manually turn the faceplate to ensure nothing catches. For large pieces of work you should check that there is enough movement in the cross slide to machine the work. You may need to adjust the cutting tool so that it can traverse both to the centre and edge of the work.

An example bar held with the dogs and the results of machining the face. This piece is about the maximum that can be machined on this lathe.

Example with a large bar

Mounting a small bar.

Improvements?
The screws used can damage the metal being machined if it is soft like the aluminium I used. The problem could be solved by either filing or maching the end of the screw. This could be combined with a brass cap for the end of the screw.

Other techniques
Mounting work on the faceplate is not the only technique for machining a flat face on a piece of work. If I had a milling machine then I could use that. I could also mount the metal in a vice or plate attached to the cross slide and then use a fly cutter attached in a chuck. for very large work the face could be machined in sections which is not an option when mounted on faceplate as the work has to turn. See Tubal Cain’s other book Milling Operations in the Lathe (Workshop Practice) for details.

Lathe dogs
You should not mistake Faceplate dogs for Lathe dogs also known as Lathe Carriers, Driver plates or Catch plates, these devices clamp around a piece of work that is being held between centres and cause it to be turned round. The dog is often driven from a peg on a faceplate or as in the example below the dog has a bent leg in it that fit through one of the slots in the faceplate.

Lathe Dog or Lathe Carrier

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