ALLOWANCE TO FINISH
Between the end-user, machine shop, and/or service center, when discussing round steel shafts, there are issues with “allowance to finish”, and even with the method of grinding that will be utilized to produce the finished polished shafts. If subsequent bar finishing or grinding will be done, always let your vendor know what method of grinding will be utilized; are you centerless grinding or grinding on centers. Remember this: “When the bar doesn’t clean up, who’s wallet comes out?”
Each method will have a unique set of requirements; we will discuss those in a future note. In a perfect world there would be one semi-finished condition for all rounds. Call it Hot Rolled, Drawn, Peeled, Rough or Fine Turned. All sizes would have a standard “stock allowance for clean-up”, no matter the mill of origin, or size of bar. All lengths would also have the same perfect straightness.
Regrettably, that is just not the case. At any given time, a service center may have stock from a half dozen various bar mills. Each one has their own description of what constitutes a “Hot Rolled” finish allowance. Some mills will only give a “peeled” or rough turned finish. Another may have hot rolled, or even forged to size with allowance, not machined.
If you are selling steel, how do you come up with a textbook answer that explains which size will make the finished size? When your customer asks what size they should order to make a given part; assume they are asking: “What is the price of a car?” As a seller, can you control the machining or grinding process? Can you insure the capabilities of the operator, or even potential “movement” of the steel? Obviously, you cannot. To even attempt to help the customer, you need much more information. Qualify, qualify, qualify.
Whether you are buying or selling, make sure both parties understand each other’s needs and abilities… When the bar does not “clean-up”, who’s wallet comes out?
-Howard Thomas, August 6th 2018