how is knurling specified? is it surface roughness, i.e. peak to trough? is there any specification for angle of the knurled pyramids or the pattern? can it be easily done on a flat surface on aluminium alloy? thanks.
Dear hob:
As to specifications: URL:
David A. Smith
Hi Hob:
For most machine shops you're going to get what you get. It depends on what knurling tool(s) they have on hand. There are straight knurls and right- and left-hand diagonal knurls and diamond knurls. They can be specified in "teeth per inch" (circular pitch) or sometimes in "diametral pitch" (of the tool), like a gear. There may even be metric ones too. Diametral pitch knurls supposedly track better as the work piece rotates, as long as the blank diameter is a proper fractional multiple. For a knurl of DP = 64 or
128, for example, the blank diameter should be a multiple of 1/64th inch. Most of the knurls I have seen are the circular pitch kind (teeth per inch).The upshot is that unless you're really picky about what the knurl looks like, just find out what your machine shop has for tooling and see what you like. Most knurling sets have interchangeable wheels and often you have a choice of coarse, medium and fine, and perhaps straight, diagonal or diamond.
Don Kansas City
look at machinery's handbook
Unfortunately, this is one of those subjects where the Machinery's Handbook isn't really connected with reality. Mine (23rd ed.) goes into a five-page grand soliloquy about "standard" diametral pitch knurling tools of 64, 96,
128 and 160 DP, which apparently adhere to an ANSI standard from 1984. The problem is that these are not the knurls everyone is using and one would be hard pressed to even find them in a tooling catalog. This is another one of those things that young engineers specify and where machinists get a good laugh. Besides, a knurled surface is usually specified merely for use as a gripping surface for the human hand. It's not rocket science.There are a number of these pitfalls for the uninitiated in the M.H. Just because something is listed in there doesn't mean that it is always practical in the real world. There are charts showing the proper uses of exotic carbon and alloy steels that are simply not available to an average manufacturer. There are charts of "standard" counterbore sizes for socket head screws, but if a machinist has an earlier version of standard counterboring tools, he's not going to run out and buy a new set.
The M.H. is an extremely useful and indispensable reference source for thousands of things--I've almost worn mine out--but it is necessary to use it in conjunction with tooling and material catalogs, to see what is really available, and to consult with machinists, operators and maintenance personnel to determine what is practical and possible.
Don Kansas City
Don--no disagreement with your general point, but I will point out that I said "look at" not "follow slavishly".
thanks for all the advice. the only unanswered point is - 'can it be done on a flat surface?'. my thoughts are that it can't as the standard knurling process involves forcing the knurling tool radially on the rotating surface. this can't be done on a flat surface! i guess the options are to painstakingly mill the surface or to produce a die of some sort. any thoughts?
yes, it can be done to a flat surface.
again--look at machinery's handbook, and then, as Don said, talk to a skilled machinist
Dear hob:
Knurling's purpose is to increase the coefficient of static friction (essentially). What is your intended purpose on this flat surface?
You could roll on the "roughness", like a rolling pin. You could use a shotgun. (Sandblast can to a very rough job.) You could EDM the pattern in.
David A. Smith
Yeah, you can roll a knurl on a surface ("flat" or "face" knurling). If you're going to do a lot of it, it really should be done with a special rolling machine. But for "now and then" applications it is routinely done in a vertical mill (Bridgeport). They chuck the knurling tool into the mill spindle, press it down against the workpiece and then crank the bed back and forth, while the tool remains stationary. The knurling wheel is set a little deeper with each stroke until you get the desired pattern. I believe you can use the same wheels as for rotary knurling, but you might need a special tool holder that can be chucked into the quill.
Don Kansas City
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