- Joined
- Dec 20, 2012
- Messages
- 9,422
I'd like to add onto the already excellent comments from @wrmiller , @brino and @higgite.
An ER chuck is useful when turning stuff that is of a common size (like 3/4" OD round rod, etc). If you have more than a few to turn then a collet will hold the pieces accurately and allow you to switch to a new piece quickly. Nominal stock can vary in size but is usually slightly smaller than the stated size; an ER chuck can compress about 0.039" and still hold the work so they're useful. Note that for an initial turning, the work will not be any more accurate than if you held it in a 3 jaw chuck.
An ER chuck really becomes useful when you have already turned a work piece and need to remount it for further work. If you re-mount the work in a 3 jaw chuck, it will have significant run out unless you have an Adjust-tru type chuck like Bill mentioned. An Adjust-Tru chuck allows you to get the work piece concentric with the spindle by adjusting the chuck mount itself, which is really, really nice to have. With enough patience, an Adjust-tru chuck can be made to run with almost zero run out. Lacking one of these chucks, an ER collet chuck will allow an already turned piece to run with minimal run out. The amount of run out will depend on the run out of your chuck/collet/nut system. My ER chuck will mount a piece with 0.0001" actual run out so its pretty accurate. Not all chucks will do this but most will be close enough for most purposes.
ER chucks are also able to grab a threaded work piece without doing much, if any, damage to the threads. Don't underestimate the value of this. They also grab without damaging the surface being held like a jawed chuck can and this is especially valuable when the part being grabbed is a bearing surface or if the material is soft.
ER chucks also have no jaws that can take meat off of your hand. I use gravers and files up close to the chuck at times and a rotating jaw can easily rip off a knuckle if I lose my concentration. In these cases, I use an ER chuck for safety more than anything else.
ER chucks allow you to hold short parts of at least 3/4" length. If the work is shorter than that, the collet may not close down accurately and that can affect your concentricity. As Tom said, you can also hold pieces that are larger than your spindle bore and bury it as far as the chuck body allows. This is handy at times.
The bottom line is that an ER chuck is useful and desirable. It is NOT necessary on the lathe; you can easily get along with a good 3 jaw and 4 jaw independent chuck. Over time, you will find that your 3 jaw chuck is the most often used chuck but when you need to quickly chuck a piece with a fair amount of accuracy and don't wish to fuss with indicating it in with your 4 jaw, the ER is a good option.
I should also mention here that accuracy with any ER chuck is very much dependent on good collets and a good ER nut. Do not expect to have optimal performance if you use cheap Chinese collets and nut. Buy good collets and a good nut, then torque the nut to specs (about 130 lb/ft).
An ER chuck is useful when turning stuff that is of a common size (like 3/4" OD round rod, etc). If you have more than a few to turn then a collet will hold the pieces accurately and allow you to switch to a new piece quickly. Nominal stock can vary in size but is usually slightly smaller than the stated size; an ER chuck can compress about 0.039" and still hold the work so they're useful. Note that for an initial turning, the work will not be any more accurate than if you held it in a 3 jaw chuck.
An ER chuck really becomes useful when you have already turned a work piece and need to remount it for further work. If you re-mount the work in a 3 jaw chuck, it will have significant run out unless you have an Adjust-tru type chuck like Bill mentioned. An Adjust-Tru chuck allows you to get the work piece concentric with the spindle by adjusting the chuck mount itself, which is really, really nice to have. With enough patience, an Adjust-tru chuck can be made to run with almost zero run out. Lacking one of these chucks, an ER collet chuck will allow an already turned piece to run with minimal run out. The amount of run out will depend on the run out of your chuck/collet/nut system. My ER chuck will mount a piece with 0.0001" actual run out so its pretty accurate. Not all chucks will do this but most will be close enough for most purposes.
ER chucks are also able to grab a threaded work piece without doing much, if any, damage to the threads. Don't underestimate the value of this. They also grab without damaging the surface being held like a jawed chuck can and this is especially valuable when the part being grabbed is a bearing surface or if the material is soft.
ER chucks also have no jaws that can take meat off of your hand. I use gravers and files up close to the chuck at times and a rotating jaw can easily rip off a knuckle if I lose my concentration. In these cases, I use an ER chuck for safety more than anything else.
ER chucks allow you to hold short parts of at least 3/4" length. If the work is shorter than that, the collet may not close down accurately and that can affect your concentricity. As Tom said, you can also hold pieces that are larger than your spindle bore and bury it as far as the chuck body allows. This is handy at times.
The bottom line is that an ER chuck is useful and desirable. It is NOT necessary on the lathe; you can easily get along with a good 3 jaw and 4 jaw independent chuck. Over time, you will find that your 3 jaw chuck is the most often used chuck but when you need to quickly chuck a piece with a fair amount of accuracy and don't wish to fuss with indicating it in with your 4 jaw, the ER is a good option.
I should also mention here that accuracy with any ER chuck is very much dependent on good collets and a good ER nut. Do not expect to have optimal performance if you use cheap Chinese collets and nut. Buy good collets and a good nut, then torque the nut to specs (about 130 lb/ft).
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