SAE drill size to ER collet size

[DavidR8]

On my mill I use an ER32 collet chuck with 11 collets. A recent project revealed that I am missing collet sizes to hold some SAE drill sizes.
To figure out what I collets I was missing I made this chart showing the SAE drill size up to 1/2" and their corresponding ER collet size.
Hope this is useful to others.

 

[mikey]

Be careful when clamping down with the ER collets you use for tool holding. Eventually they will lose their accuracy if taken beyond their nominal size too often. The correct tool to hold drills is a drill chuck.

 

[DavidR8]

Be careful when clamping down with the ER collets you use for tool holding. Eventually they will lose their accuracy if taken beyond their nominal size too often. The correct tool to hold drills is a drill chuck.

Thanks Mikey, duly noted. I did notice that for some drill sizes they were at the extreme ends of the clamping range.

 

[benmychree]

Be careful when clamping down with the ER collets you use for tool holding. Eventually they will lose their accuracy if taken beyond their nominal size too often. The correct tool to hold drills is a drill chuck.

I quite agree; the drill chuck is the proper tool.

 

[DavidR8]

@mikey @benmychree
The situation I'm trying to avoid by using drill bits in ER collets is having to swap out the collet chuck for a drill chuck.
But that doesn't sound like a good approach.

 

[mikey]

Thanks Mikey, duly noted. I did notice that for some drill sizes they were at the extreme ends of the clamping range.

It is good to know that ER collets have a range that was intended to accommodate variations in tool shank sizing. While they do have a 0.040" range, they were not intended to be used to clamp that full range. They are most accurate, and are able to maintain that accuracy, when used with tools very close to the nominal size of the collet.

 

[martik777]

I use ER25 with a full set of metric collets to handle any drill size up to ~ 16mm, collets are a bit cheaper than ER32 and visibility is better due to smaller chuck diameter. I also bought separate 3/8 and 1/4 collets as they fit better than the closest metric size.

 

[mikey]

@mikey @benmychree
The situation I'm trying to avoid by using drill bits in ER collets is having to swap out the collet chuck for a drill chuck.
But that doesn't sound like a good approach.

If you're using good collets, and I hope you are, they are too expensive to be used to hold drills that are not nominal in size. Why risk their accuracy? The drills they hold are not precision tools and will not drill much more accurately because they are held accurately. There ARE precision drills that are certified as to their precision but most hobby guys don't use those. For most commonly used jobber and screw machine drills, a good keyless drill chuck is more than accurate enough.

As for the hassle, you might look into the TTS system from Tormach. It takes seconds to change out an ER chuck for a drill chuck. Loosen the drawbar a 1/2 turn, tap it and catch the tool as it falls out. Drop a new one in and tighten the drawbar. We're talking maybe less than 5-8 seconds for a tool change. And the system is accurate enough for our RF mills.

I know you know all of this, Dave. I'm saying this for some new guy who doesn't.

 

[mickri]

My ER32 metric collets sit face up in their holder. When I need a collet I just keep sticking the drill/end mill/whatever in the collets until I find the one that fits. I use the 10mm and 13mm collets the most. They have their own collet nuts. I only use the ER32 collets on the mill/drill. Too much trouble to switch between the collet chuck and the drill chuck. I have to get a stool to stand on. Loosen the drawbar. Wack it with something to get the chuck to break free. Switch the chucks and tighten up the drawbar. I stopped using the ER32 collets to hold drills on the lathe tailstock after I got a drill chuck for the tailstock. I still use the ER32 collets for work holding on the lathe with the collet chuck that I made for the spindle. No gaps in coverage with metric collets.

 

[DavidR8]

Thanks @mikey and @mickri.
I did have a few TTS holders that I bought used.
I think that I will do some more research on the system.
The holders are frighteningly expensive for us North of the 49th folks.
Is there a reasonable facsimile?