Issue with Hole size

We are currently having an issue related to hole sizes, for our picket panels. The commercial tolerance for the OD of the picket ( 1/2 inch round pipe) is +15000 and - 30000.

We have experinced that when we change the hole size by even 2000 the pickets dont fit well , either too tight or loose. Is there a way to determine an optimum hole size for a material with such wide tolerances. Should we use some statistical tool to determine the mean of a sample of the pickets and use that as our hole size???

Would appreciate your thoughts on thsi issue.

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I think that what you'll find happening is that the output of any one machine will tend to be fairly consistent, but if you start buying from a different manufacturer (or if the manufacturer does some maintenance) then all bets are off. If you need that sort of tolerance then expecting something with a 10x published variation probably isn't going to work in the long run.

Having said that -- yes, you could measure one of every ten pipes as they come in the door, and try to set your hole size. If I were to take this approach I'd make sure to measure each one and calculate a little histogram to get an idea of the spread and to look for a double hump that would indicate two lots or a running change in the manufacturer's process. If the spread's not too bad then go with the hole size that'll lead to the fewest rejects; you should be able to do this with your favorite spreadsheet program.

I'd also consider whether I could buy or make an easy-to-use tool to size the pipes -- I guess I'll call it an outside reamer for lack of a better term. That way if I got a load of pipe that was all over the map, or if I got tired of measuring I could just size the ends when I cut the pipe.

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Tim Wescott

I'm a little confused. Do you mean .+.015, -.030" ?

I guess that depends on what you're doing. There's not much you can do about the tolerance used by a commercial supplier. If it was my product, I would look at these 3 options.

1) If your "product" is short run stuff, go to the hardware store and measure the material till you find the size you want. 2) Turn the OD of the pipe to fit your hole 3) Drill your hole loose and use a setscrew or weld to tighten the pipe in place.
Reply to
Dave Lyon

"Sai" wrote in news:1130341395.791321.208880

You have a few choices, all of them involving additional cost to the process, I will leave it to you to determine which is the most cost effective method:

  1. Use statistical tools to sort and segregate the commercial pipe by OD, and batch run, adjusting hole ID by batch - not really a very good method , as this leads to easily mis-matched material to hole size.
  2. Buy pipe that is of tighter tolerance - material costs are going to be more up front.
  3. Machine a skim cut on the end of the pipe that fits in the hole so that you know exactly what the size is going to be every time - this will require a machine and operator, but you control the process in-house.
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