Originally Posted by
mwohlenhaus
I got a piece of 1/8" 6061 t6 to use for the radial mount. There certainly isn't going to be an abundance of thread left after counterboring, but it appears to me that it will be adequate. The 1/8" is about 2.98mm thick so I am thinking I will do diet version as it is quite a bit thicker than original. The other option is to sand the piece down (dont have access to a mill) to thin it out a bit and just go with original design as posted by ffkiwi. I am not sure how to proceed on this yet, as I only have a drill press and hand tools. The counterbore is my biggest challenge at this point with making the bottom 90 degrees for the screw to seat against firmly. any suggestions?
well counterbores only go down to 3mm screw size generally in any case....in your situation the only option I'd suggest is using an endmill or slot drill to open out the screw hole to partial depth for the counter bore effect. Obviously you would need to clamp the radial mount fairly well-and be careful with your alignment. Considering the tooling you have available, I would suggest using the clearance drill for the screw shank to align the backplate mount under the drill, clamp well, then without shifting anything loosen the drill from the chuck and replace it with the milling cutter or slot drill, and cut the counter bore, then repeat the process for each of the remaining two holes.
are you familiar with FC3 cutters? these are combination end mill/slot drill disposable cutters-which are much cheaper than either endmills or slot drills-and available in a range of metric and imperial sizes. One of these in the right size would do the job-the only two alternatives would be a D-bit.....and you dont have the equipment to make one-or one of those 'fishtail' carbide burrs-if you can find one that matches the screw head diameter. Whatever you use for the job-make sure the drill chuck is really tight-drills are not very good being pressed into service for milling as there is no means of axial limiting the cutter movement in the chuck, as there is on a proper mill.
Good luck with it...
ChrisM
'ffkiwi'
