I'm new to machining doors. I have to machine butt hinges into the edges of doors. The hinge leaf will protrude through the veneered face of one side. How do I keep the veneer from blowing out at the one end of the hinge? We have an Onsrud CNC, with a flow through spoilboard. I have made pods to hold the door in place. I have beveled bits to create beveled edges. Because of how the beveled bits were made (larger diameter at the bottom of the bit), the hinge protrusion must be on the exposed side of the door when it's on the table.
We are primarily a cabinet shop, with occasional runs of around 50 doors. How do I keep the veneer from blowing out, short of stopping the program, manually clamping a backer board to the top of the door or scoring the hinge points?
Assuming your machine is capable, use two bits. One LH rotation, and one RH rotation. Have each bit enter at the correct point so they spin into the good section of material.
Looking at your standard 'U' shaped hinge cutout (opening upwards through a veneered face)… Use a standard rh cutter (we use a 12mm single flute RT cutter for consistent size), start your cut 2 or 3 mm above the LH side of hinge cutout, machine down into the door at hinge depth at a 45 degree angle, cutting across the LH hinge edge by about 0.5mm in both X and Z (cutting on the LH side of the cut, back cutting). Continue down into the door till you are around 5mm (cutter not past its centre point) in, then cut along the x-axis towards the RH edge of the hinge, continuing the backcut (avoids break out) until the edge of the cutter overcuts full hinge length by about 0.25mm. You should get a chip-free top edge using this method. Now use a standard hinge relief program making 'U' shaped cuts starting at top left of the pass at the mid point of the hinge, work outwards to clear the hinge.
I have applied this in doors with vertical and horizontal grained veneers with no problems. When cutting laminate face doors, the 45 degree initial angle needs to be knocked back to about 30 degrees.
Note you will get a slight overcut with this method. This is hidden under the hinge knuckle, however, and has never caused us a problem.