Countersunk bolts are bolts that are recessed with their heads flush to the surface. This is done for several reasons, the most common being to gain clearance or for aerodynamics. You have probably seen countersunk fasteners in wood decking or the runners on drawers. The steps are basically the same no matter what material you are assembling.
Whether it's for a HID mounting bracket or for an end-plate, at some point you will probably need to countersink/spotface a fastener. Using these steps, you can produce clean professional results. No matter how tempting it is, do not partially drill a hole with a larger bit to countersink a bolt head. When purchasing a bit you need to know two numbers. The diameter of the fasteners you are working with and how many degrees the bolt head is. Make sure you purchase the correct taper.
A microstop cage is not needed but it makes production faster and the results cleaner. Start by drilling the correct sized hole in your stock. Now comes the countersinking. If you are using a microstop pre-set the depth so that when tightened the bolt head is flush with the stock. The countersink bit will cut the correct taper and debur the stock for you.
Oil will help prevent any chatter. If you still experience low speed chatter, reface the hole at a higher speed. If you have a high speed chatter, reface at a lower speed. If the above methods do not work you may need to try a different countersink. If correctly installed the head of the bolt will sit completely flush. If it does not, you need to reset your stop and reface the hole. If it is recessed, you set the stop too deep.
In this guide I used Hi-Lok titanium bolts which have no grip on their heads. They are tightened from the bottom with a hex socket and wrench as shown below. These bolts produce a very smooth unique finish. In addition to looks, they also offer the weight savings of titanium. When used correctly on brakes, rims, or other rotating assemblies, the pounds saved translate into horsepower.
This is just a basic guide to help you understand what countersinking is. It does not cover issues such as safety wire, or how to properly torque your bolts.
For the more complete guide with images see:
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