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A few times I have purchased hole saw kits, there is one center piece and bunch of different sized saws every time I have tried to use one them by the second or third hole they are coming apart... It gets very frustrating. Now I just buy one that is together and the size I need.

It seems like having one center bit and several interchangeable hole sizes would be a great idea. But I never get it to work in practice. Is there a secret to how to make them stay together, when you swap out pieces?

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    I haven't experienced this with my set. Maybe has to do with the quality of the thread to tighten it? – Pascal Belloncle Mar 21 '15 at 0:18
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    Which variety of hole saw are you using? If it's the one with thin flexible blades that fit into slots in the arbor, try switching to one with cup-style blades. – keshlam Mar 21 '15 at 0:25
  • Judging by the photo, yes, that's your problem; "adjustable " hole saws are finicky beasts. – keshlam Mar 21 '15 at 0:26
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    I have never had that problem, either. Do they come apart while drilling, when you take the saw out of the hole, or when exactly? – Christopher Creutzig Mar 21 '15 at 12:11
  • They come loose with usage, and each time come apart sooner, after a few holes they will not stay together for one hole. This is the type I used but it has been some years ago Current design may have improved, the versions I have used did not have the drive pins as shown in Cathodes answer. – James Jenkins Mar 21 '15 at 22:32
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I have not seen the type of adjustable hole saw you describe, perhaps it's a regional thing (I'm on the west coast USA), but the type I'm familiar with have a spring loaded collar with "drive pins" that mate with holes in the bottom of the saw bit itself.

I would buy mandrel like this:

hole saw mandrel

And a hole bit of the appropriate size which threads onto the collar screw:

hole saw bit

After the bit is threaded on, the collar is snapped forward and the drive pins engage two of the four holes in the bit's base and prevent it from moving.

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