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 Q. Our tumbling media are 7/8 x 7/8 inch at 45-degree cut triangles in a medium cutting composition. Our parts are steel cylinders made by cutting lengths of three- and four-inch diameter CRS tubing. There is no lodging problem and we are able to tuse the media until it finally goes to drain. We were recently offered a large volume of used media in a similar composition, but it is a short cylinder shape that is angle cut from each side. The size is about 5/8 inch. The quantity offered will last us nearly a year. I have some concern about using this media. Will it debur as well as my angle cut triangles? Will it have shorter life since it is smaller? Can I mix these two media? Should I have any other concerns? T.L.

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A. This media should be a good buy and serve you well. Good used media has the same performance potential, per pound, as new media of the same size, shape and composition. The shape you are describing goes by various names including: Tri Cyl, V-cut cylinder and WEB™ (a trademark for Markee).

As to your specific question, given exactly the same compound and machine-with identical settings, deburring is a function of media size, composition and shape. The two shapes involved here are both quite effective for the cut-off burr you are removing. Assuming that the compositions are similar and that the bulk densities of the media are the same, it then boils down to the size of the media being the main factor. You have a full range of sizes, from 7/8 inch down to what goes out the drain. This gives you a good finish but the speed of deburring is accelerated by the large sizes in the mix. When you start with a smaller size you will lose some deburring speed. My suggestion is to make media additions with equal quantities of the new triangles and the used media.

Does smaller last as long as larger media? In the case of using media down to drain size, the rate of use is determined by what is going out the drain and it won’t be noticeably different. If you were removing undersized media at say 3/8-inch size, then the smaller media would not last as long. There are some differences that can be argued but you should not experience a measurable difference in the quantity you will use over time.

Some other concerns need to be addressed. Some used media can be very dirty on the surface. It may have oils, heavy metals and other considered hazardous waste products that will get into your system and perhaps down your sanitary drains. Check this out and know what you maybe faced with in advance. Another concern is media dust. Some brands of media seem prone to leaving a chalky residue on parts. Those media require more rinsing of the parts.