Forum: Dear Mr. Murphy

Today’s Machining World Archives April 2011 Volume 07 Issue 03

Dear Mr. Murphy,

In your “Shop Doc” in the Jan/Feb issue on “Push Back Trouble Using Collets” I don’t see why would you use the formula 2 π r2 + 2 π r h for the surface area of the collet bore and not just 2 π r h. The area of a cylinder surface (where the pressure is applied) is just 2 π r h and you don’t have to include two surfaces of circle with the diameter of 1”, hence 2 π r h = 2 x π x .5 x 1.25 =3.9269 in².

Mark Dmytrow

Dear Mr. Dmytrow,

You are correct! I made a mistake. I originally used 2 π r h but while proofreading I decided to look up the formula to be sure it was correct and came up with 2 π r2 + 2 π r h. It didn’t seem right, but I found it in three sources, so I changed my original math. Now, with no deadline looming, I realize that 2 π r2 + 2 π r h gives the surface area of the top, bottom and periphery of a cylinder, which of course is not the case in a collet bore where the only surface in contact with the work is the periphery.

I apologize for the oversight.

Dan Murphy


In response to the “Swarf” in the March issue on hiring temps, we too are having difficulty finding qualified people to run our machines, particularly our screw machines. We have been on a temp-to-hire basis for about eight months now. It takes a lot to get on the regular payroll—attendance, skill, quality and efficiency are looked at carefully before we offer a regular position to someone, and this can take up to six months. This is made clear to all people who are interviewed so they can decide if this is where they want to be employed. So far we have found one keeper and have let three people go. This is working better than our old method of getting people on the regular payroll and hoping they work out.

Bruce Renwick
North American Fabrication Co.
Loves Park, Ill.

Two Responses to “Swarf,”

Working Under the Table, March 2011
The last time congress was deciding whether to extend unemployment benefits the line at our front door was 20 people deep. As soon as benefits were extended we had no more applicants. We are back at 2008 employment levels, but our unemployment rate went from 2.3 percent in 2007 to 9.85 percent currently. This is costing my company an additional $75,000 this year. By the way, 2009 was the first year we ever laid-off anyone after 30 years in business.

Jim Harrington
Engineered Material Sales, Inc.
Kalamazoo, Mich.

I agree that some people abuse the system, and there have been people like that for years. I also agree that unemployment benefits should start declining after a set time. But I do not agree with getting rid of unemployment benefits completely. What happens to all the money that has been taken out of our paychecks for years to cover us if we become unemployed? Yes, this money has already been used on others, but why should all the people who have worked for 20-30 years paying in benefits not have the security they’ve been paying for if their job goes belly up? Just because it is sunny today does not mean it cannot rain tomorrow.

Joe Crawford

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