Machining services, especially CNC costs can inflate if you are not aware of some of the following concepts in machining. If at all possible when designing an interior pocket section of the part you need to have machined; stay away from using sharp corners by allowing for the radii of the end mill to be used. If it is absolutely necessary to have this sharp corner, there are ways of achieving this but it will increase the cost of the part. A couple of processes can suffice which are broaching and a process called “cut-away”.

Cut away is a process of cutting out the corner areas in the pocket a little deeper allowing the mating part to retain its sharp 90 degree angles while not interfering with alignment. Cutting deep pockets in to the material requires a little finesse and more time as you want to step down the end mill in small increments and run a very slow feed rate and low RPM’s. It will be necessary to use the technique of broaching if you require a pocket with sharp interior corners. It’s also probable that the company providing your machining services will use a large diameter end mill to rough and finish the pocket and use the broach technique for the corners, this will achieve the desired results but increase the time needed to machine these parts.

The reason the machinist will not use a smaller radii end mill is to prevent breakage and to eliminate chatter on the material resulting in a poor finish of the part. An additional aspect of savings when you are designing a new part is to think about how the material will be held when the machining process begins. If a part requires more than a simple vise to be secured, meaning if the part requires a custom fixture as a result of the complexity, then the costs involved will naturally be increased. If the part has parallel edges you can generally asses that a common machining vise can be used which will keep the costs as low as possible. Parts that do not require multiple steps will also reduce costs and the machinists at Hi-Tech Mechanics are masters at figuring out how to machine a part in the least amount of steps. If you are machining a part from a flat sheet quick fixtures can result from existing areas in the part that will be cut out of the final part.

Using an area known to be cut out in the final part, the machinist will use this area with a thru hole to bolt the material down to the platen while cutting away the outer dimensions and can generally clamp the material down to the platen when cutting away the interior thus saving time building a fixture. When designing your part, take this into consideration and add this as a note to your drawing. Your machinist will normally see these opportunities when assessing your drawing but it is a good idea for you to be aware of them also. Also 10 to 20 parts will cost you less than 2 parts because of the off set in the set up of the machine and the creation of the program among other related fees.