Today I needed to make a fairly precise mounting bracket....and my buddy with a machine shop was away on vacation. I had to get the bracket done today....so I imported the .dxf file of the drawing into my PlasmaCam software. The part needed a bunch of 1/4-20 tapped holes in 1/4" steel plate, as well as 4 countersunk holes for 1/4" bolts.
I resized all of the holes that needed tapping to about .187", as the proper drill size for tapping 1/4-20 is no. 7, or .201". After plasma cutting the part using the PlasmaCam machine and a Hypertherm Powermax45....I went to the drill press and ran the #7 drill through all of the holes (I used a high quality cobalt drill bit as the air plasma cut holes have a nitride hardening on the edge....if it was an oxygen cut, there would be very little hardening). The four clearance holes were countersunk for flathead socket screws. Here are a few pictures....The tolerances for the part are pretty tight...about .005", more than adequate for the job! Amazing what you can do with the wrong machine when you put your mind to it!
By the way....this bracket is to hold two different z axis slide assemblies for a cnc machine that will be equipped with a Hypertherm HPR260xd plasma and a new 1.5 kW Fiber Plate Laser. Plasma and Laser on the same machine.....this will be the demo machine in the Hypertherm booth at the upcoming Fabtech show in Atlanta.....should be a great demonstration showing how plasma and laser can work together on one machine. The plasma can cut from gauge to 1.5" thickness, the new Hypertherm laser can cut from gauge to 1/2". Kind of ironic that the little Powermax45 air plasma is cutting out parts for these high end industrial machines!