THE ROUTER USED FOR CUTTING BRASS SHAPES
This is an idea which I wished I had thought of 20 years ago. When cutting internal profiles on clock plates the usual tool is a hand fret saw or the powered kind, but which ever method is used it becomes rather expensive and slow when using fretsaw blades. By using a router and a template the job becomes more of a routine than a chore.
This idea would be excellent for clock clubs who make movements on a regular basis or even schools when making multiple brass parts.
The process is quite relaxing apart from the noise and to see a 1/8” high speed steel cutter going through the brass plate is like watching a knife through butter.
By substituting the carpenter’s router bit for a milling cutter we have the basis for forming brass clock plates however elaborate they may be. The first requirement is to purchase or make a speed control for your router to get the revs down to about 3000 rpm. The second is to make a sub plate to fix to your router. I cannot give sizes etc as there are so many routers on the market- I made mine from ¼ inch Plastic sheet.
Whatever fixings you use, they have to be countersunk to keep the plate flat. Next machine a ½” diameter hole through the Plastic while it is screwed to the base plate, this will ensure that the hole is centred to the router you are using. Use a ½ inch router bit to do this job and if you have a ¾” bit it will make the next operation easy, just reverse the base plate on the router and rout the plastic to a depth of say 1/16 inch. Or machine a small hole into the plastic sheet and finish off on the lathe faceplate.
This recess is for a brass collar and the collar is the secret to the whole operation and must be concentric to the ½” hole previously machined. Machine the collar in one operation to ensure concentricity, drill a 5/16 hole and part off .My router uses ¼ shanks so that is why it is drilled 5/16 to give clearance. I used 2 10BA screws to fix the collar to the base plate. (Note 10ba- 1-7mm diameter)
Install a milling cutter (I use 1/8 dia slot drill) and measure the distance from the edge of the cutter to the outside edge of the collar (about –156 thou) this measurement is to be (DEDUCTED) from all templates made. Next make a template of the part you are making and lay over the brass sheet, I use 3/16 or ¼ plastic sheet.
A few tips might be helpful here. Make a 3mm punch from silver steel (carbon steel or drill rod) and use it to spot through your template onto the brass sheet
I use 3mm countersink bolts to fix the template to the brass sheet, over lay the template onto the brass sheet and lay down over a piece of plywood on the bench. This is for the cutter to run into and will save the worktop from damage.
At last we are ready to cut some metal. I would recommend doing all internal cuts first. Set the cutter so the cutting edge is touching the metal then aim for a further cut of -030”. Start your first cut with the collar touching the template and the rule here is to move the router from left to right, or for internal cuts, clockwise- outside cuts anti clockwise. After the first pass switch off and increase the depth of cut a further -030” etc until the cut is full depth.
Repeat for the outside edges of the plate until it is free of the parent metal.
There’s always a catch somewhere, and so it is with this method. If you just want to machine the internal profiles of the clock you are making, then this method will save a great deal of time as all you have to do is make the template from plastic etc and you can finish the outside edges on the band saw. If you want to carry the project through to the end then you might have to make a few templates. As you will see by drawing out your modified templates, it is impossible to do all curves etc on one template alone, but at the end of the day we are talking about cutting plastic to make our templates and once they are made you have them for life. If your clock plate is really elaborate you can make a half template, and after cutting out one side, flip the template over and do the other half to complete the job. Don’t forget that you can buy smaller milling cutters, but the cost does go up the smaller they are. Don’t forget the ear defenders and glasses. David Creed 2002
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