Thursday, 20 December 2012

Milling Cutters

If the impending Zombie apocalypse happens today this post is a little pointless :p but i came across a great website that supplies all sorts of milling cutters, even the exotic ones like tiny woodruff cutters.

As i need a cutter to cut my drive bolt for the printers extruder, i would really like to learn how to cut my own cutters, i have played a little and have come to the conclusion that i need to either make some sort of grinding tool with an indexing head/chuck.

I have nice shiny new dividing head that my mate built for me, so i am half way there. but as i am sure i have mentioned before that i am an impatient unit i was looking on the web at whats available. I came across and searching through their online catalog i found this cutter

Double angle woodruff cutter this tiny little cutter is the ideal profile for my hyeena bolt, 66108 is the one i think will do me. the measurements are all imperial so i will convert to metric so my brain can make sense of it.

D1                                        = 1/8th inch             = 3.175mm
Neck diameter                     = 1/16th inch            = 1.5875mm
(D1-Neck)/2 Shoulder size  = 1/32th inch           = 0.79375mm 
L2 Shoulder width               = 0.17in                   = 0.42mm
Shank Diam                         = 1/8th                      = 3.175mm
A angle of cut                      = 30'                         = 30'

looks like this guy is a little bit small to make my life easy. if i want to cut the teeth in one pass i need a cutter thats at least 3.5mm diameter, if use the next size up cutter 3/16 its 4.7625mm in diam. this cutter would be able to cut an entire tooth in one motion.  without needing to move along the shaft/gear/bolt. this larger cutter 66112 has a shoulder width of 0.5842mm at its widest. i had drawn my bolt to have a 1mm wide gap between the peaks of each tooth. so i will use the dividing head to turn the job while the cutter has made its initial groove. this will give me the option of cutting wider grooves as well as narrower grooves without having to buy two tools they are only $35ea.

so the more i think about whats required to make my own cutters i see that there is some really complex maths involved while this in it self is not too troubling it makes me think that the device that is required to cut cutters is rather complex. to cut the flutes on a straight cutter you need A,B,X,Y,Z this seems not too imposing until you add the word precision into the equation. if i want to be able to use cheap off the shelf grind wheels and stones i will have to be able to some how know what the diameter of the wheel or stone will be, if i can find a good diamond wheel i will be set as their diameter doesn't vary a great deal when compared to a carbide disc or stone. so i will need a way to touch the wheel to sense its cutting edge. this wont be too hard if use a micro switch.

thinking about the software side of things i would need to break it down into a series of passes.

1. Profile
      This will grind the side profile of the cutter, ie ball nose, woodruff, slot cutter etc.
2. Pluting
       This will grind the flutes into the cutter.

To grind the profile the cutting disc will be perpendicular to the rotating axis, that is if the tool steel blank is held along the X axis left to right. the cutter would rotate in the A axis and the grinding wheel will rotate in the Y axis at the same height as the center of the toolsteel. the grind stone would move in and out towards the rotating center of the toolsteel according to the profile required asnthe toolsteel rotates.

To grind the flutes the cutting disc/grind wheel will need to be pivoted in the B axis to the angle of the flute to be cut and offset to set the depth of cut, as the toolsteel is rotated the grinding disc will need to move along the X axis at the correct rate to make the screw/helix shape.

I theory this all sounds simple enough, write some gcode that makes the profile of the blank then write gcode that cuts the helix of the flutes. when it comes to practice it will be a different story, will post some screen grabs and explanations of how it will work soon.

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