I need some tubing for a spacer. The outer diameter the same as a
608 bearing, and the inner diameter no greater than 1/4 inch. As light as possible, hopefully no heavier than aluminum. It would be cut to about 1 inch length.
What is a spacer like that called? I could use some keywords.
Don't know but I suspect you'll have to get something made or make it yourself. Tubing is never exact size, or even perfectly round, and there is often a seam up the inside.
To get tubing without a seam, search for "DOM" or "Drawn Over Mandrel" tubing as it is not welded or cast. It is essentially... well... Drawn over a mandrel or precision extruded.
It's what they use when they need the strongest option as well as there are no hard spots created while welding the seam.
Oh contraire! DOM IS welded! I toured Trent Tube in WI and was amazed at the process. It all starts out as coil stock then it goes through a series of rolls that form it into a tube then it's TiG or laser welded, cut to length then drawn over a mandrel in lengths equal to the length of the mandrel.
FWIW. I had ordered some from McMaster Carr for another purpose, they call aluminum seamless tubing "single-line". Their description is "Formed from a pierced cylinder of material, creating a uniform tube without a weld or seam."
DOM usually is first resistance-welded -- often submerged-arc welded -- and then drawn over a mandrel to flatten the weld and to produce a fairly uniform strength, hardness, and diameter. DOM may be shrunk from its original diameter by extruding it through a die while it's being drawn over the mandrel.
Plain ERW, like EMT and common tubing of various types, may be sort of drawn or rolled over a mandrel to flatten the weld, but it's not fully reformed over a mandrel.
Seamless is pierced from solid bar and drawn over a mandrel. Once upon a time it was the best tubing, but DOM made from flat sheet is so good today that the performance is nearly identical. And DOM made from flat sheet generally has more uniform thickness.
Some German tubing company had a miniature DOM machine at IMTS one year -- either '78 or '80 -- that was about six feet long and produced soda-straw-sized tube from a flat strip of steel. I would love to have one of those toys. It was really fun to watch.
In terms of pricing, ERW is the cheapest and seamless is the most expensive. There also are some other methods used to make tubing today, including a spinning method that produces a friction lap-weld. These came after my time covering materials so I don't know anything about them.
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