Hello, everyone. A while ago I bought on eBay a set of many ER11 collets that are of metric nomenclature. There have been times when I need to use a specific drill bit that has me fitting it into a collet tightly. Is there anything wrong with this?. Of imperial nomenclature, I only own a 1/8" and a 1/4" collet. Would getting a whole set help me with fitting non-regular tools?. Is the metric one I have (17 pieces, 1mm-7mm) fine?. Thanks.
The ER collets have a range they can hold. I believe the ER-11 have 0.5mm range, with the designated size being the top end, so a 5mm collet will reliably hold from 4.5 to 5.0mm diameter. Most sets, like the 17 piece set you refer to, cover the entire range, so it doesn’t matter if the set is metric or imperial. For example, for a bit with a 2.2mm shank, you would select the 2.5mm collet.
You generally do not want to force a tool in. It should slide in and out easily when the collet is fully released.
For drilling using these collets, I usually use oversize shank bits and the same size for all bits of a range. 1/8" nominal is a common shank size in the US (full range of sizes from 0.25mm (0.010") to 3mm (0.119") is available with this shank), as are a variety of standard metric shank sizes. These go by a number of names, such as
micro drills' andcircuit board drill’, some suppliers call them `quick change’ (not to be confused with hex shank bits for a handheld drill motor). These bits tend to run quite true, give well sized holes, and hold up well, though they generally cost more than standard bits. DO NOT use this type of bit in anything other than a collet on a well aligned machine (mill or drill press). They are very brittle and will snap if there is any significant side force due to runout or misalignment.
About the largest drill I have used in the Nomad is 1.5mm (in softer material). Larger than that, I either mill the hole or pilot for drilling to size on a larger machine. In aluminum, 1.0mm diameter might be pushing it, due to the low torque, depending on the drilling strategy and chip clearing (short pecks, proper feed rate, and good chip clearing help a lot)