"Jack Lai" wrote in message
...
Is there such thing as an over and under size reamer set for metric sizes,
if so where can I buy one, if not what do people do to get over and under
sized hole quickly?

Hello Jack,

Yes, such sets are available. I have one from Twenty-First Century
Manufacturing (often known by their trademark: "21CM"); it is Set No. 160
and contains under-sized, nominal, and over-sized reamers for 3mm, 4mm, 5mm,
6mm, 8mm, 10mm, & 12mm. Interestingly, the reamers are sized by their
Imperial equivalents, so the set contains:

3mm (0.1181"), 3mm Under (0.1171"), 3mm Over (0.1191")
4mm (0.1575"), 4mm Under (0.1565"), 4mm Over (0.1585")
5mm (0.1968"), 5mm Under (0.1958"), 5mm Over (0.1978")
6mm (0.2362"), 6mm Under (0.2352"), 6mm Over (0.2372")
8mm (0.3150"), 8mm Under (0.3140"), 8mm Over (0.3160")
10mm (0.3937"), 10mm Under (0.3927"), 10mm Over (0.3947")
12mm (0.4724"), 12mm Under (0.4714"), 12mm Over (0.4734")

As you can see, each "under" reamer is 0.001" (0.0254mm) smaller, and each
"over" reamer is 0.001" (0.0254mm) larger, than the nominal size. This
doesn't consistently follow ANSI standards for metric clearance or
interference fits, but generally falls into the tolerance range for a "Close
Running" clearance fit (over) or a "Medium Drive" interference fit (under).

As for suppliers, I know that KBC Tools (http://www.kbctools.com/) sells the
21CM line of products. If they don't carry this set, they can probably get
it.

But even if you can't (or don't want) to buy metric over/under reamers,
there is a lesson to be learned from the above: you don't necessarily have
to buy specific metric over/under reamers; instead you can buy Imperial
equivalents. If you go through the table of ANSI Preferred Metric Fits in
Machinery's Handbook, you can select the fit you need, look up the metric
size, divide that size by 25.4, and then order the closest matching Imperial
reamer. As long as the Imperial reamer falls into the tolerance range of
that metric fit, you'll be fine.

- Michael