-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
35 vs 72 piece Collet set?
- Thread starter LVLAaron
- Start date
- Joined
- Dec 27, 2014
- Messages
- 4,087
Since the Original Inquirer (OI) has completed his accumulation of over 100 collets, I'll chip in with my experience. Fourteen years after retirement, I bought a PM 25 mill and went back to playing with metal. Currently have a 10-30 PM Lathe, and bought an ER40 Zero Set collet chuck from one of the vendors and went on about my playing, ordering a collet as the need occurred. I've got about 20 now, fractional, and haven't needed a new one for several years. McMaster Carr delivers next day, and i have no need for any faster shipment, I did retire to relax, not work to a schedule.
[Asside] Typing on a Computer in Holland, the normally spelled English words get red underlined if they differ from the spelling of Dutch words. Makes for intersting proofreading.
[Asside] Typing on a Computer in Holland, the normally spelled English words get red underlined if they differ from the spelling of Dutch words. Makes for intersting proofreading.
- Joined
- Jan 31, 2016
- Messages
- 12,794
I use a Bison 4 jaw scroll chuck with a set-true plate quite often . That and a Bison 3 jaw ST pretty much covers the gamet of stock sold .
- Joined
- Feb 20, 2019
- Messages
- 352
First time you knock a digit off on a 4-jaw or 3-jaw, you'll understand the attractiveness of a smooth chuck if you need to work close.
- Joined
- Feb 1, 2015
- Messages
- 9,948
There seems to be some misconception as to how a 5C collet functions. Firstly, the grip range of all my collets are about 1.2" long. Secondly, to function properly, a 5C collet grips the work along its entire length of the cylindrical bore.
The drawing below shows a 5C collet in a collet chuck. The collet' features include a cylindrical work holding region, A, formed by three split fingers and a flexure region, B. When a work piece that is smaller than the nominal diameter is inserted and the collet tightened, the collet fingers will bend in region A to grip the work. The collet first bends in a simple arc at point F, shown exaggerated for purposes of illustration, causing the collet fingers to grip the work at C, and pulling the fingers away from contact with the chuck at E with point D providing the contact with the chuck.
At this point, the clamping of the work is unstable as it is only a ring of contact and the work can pivot around that point. This can easily be demonstrated by mounting an undersized bar in a collet, using only enough clamping force to grip the work. If you apply force to the far end of the bar, the bar will deflect and will take a new position, as can be verified with a dial indicator.
Further tightening draws the collet deeper into the chuck, forcing the collet flexure region to take a "S" shaped curve with bends at F and G until the collet makes contact with the work along the entire surface A and point B is again in contact with the chuck.
It is often recommended that undersized work should be limited to .003" less than the nominal diameter. This is because forming the "S" curve introduces considerable stress to the collet fingers which increases dramatically as the work diameter departs further from the nominal diameter. There is another reason as well and that is when the work diameter is less than the nominal diameter of the collet, the collet fingers only make contact with the work along three lines, shown as points F in the end view. This is why "emergency" collets are used when the number of pieces justifies the additional machining. The collet is bored to exactly match the work, insuring contact around with the full work surface.
A 5C collets ability to grip undersized work is limited by the width of the slits between the fingers and by the ability to tighten the collet in the chuck. The smallest diameter that can be gripped by a 5C collet is slightly less than the nominal diameter less the slit width, in theory. In practice, the force required to properly close the collet on the diameter may be more than can be applied by the collet closure mechanism. The slits on my collets are between 019" for the 1/16" collet and .055" for the larger collets. A collet set by 1/16th's would not be able to cover all possible diameters. A set by 32nd's would be able to close on any diameter within its range. A set by 64th's would create less stress on the collets in the case where the work diameter was slightly oversize for a nominal collet, requiring to go to the next larger size but may not be warranted for the occasional user.
For the user not wanting to purchase a set by 32nd's, there is a suitable workaround. A shim made from a beverage can will increase the diameter of a piece of stock by about .008" and some roofing flashing by .020". Cut a length slightly less than the circumference of the work and roll around the work. Insert the work and position the end of the shim next to one of the collet slits. Tighten and you're good to go.
Edit: deleted redundant drawing.
The drawing below shows a 5C collet in a collet chuck. The collet' features include a cylindrical work holding region, A, formed by three split fingers and a flexure region, B. When a work piece that is smaller than the nominal diameter is inserted and the collet tightened, the collet fingers will bend in region A to grip the work. The collet first bends in a simple arc at point F, shown exaggerated for purposes of illustration, causing the collet fingers to grip the work at C, and pulling the fingers away from contact with the chuck at E with point D providing the contact with the chuck.
At this point, the clamping of the work is unstable as it is only a ring of contact and the work can pivot around that point. This can easily be demonstrated by mounting an undersized bar in a collet, using only enough clamping force to grip the work. If you apply force to the far end of the bar, the bar will deflect and will take a new position, as can be verified with a dial indicator.
Further tightening draws the collet deeper into the chuck, forcing the collet flexure region to take a "S" shaped curve with bends at F and G until the collet makes contact with the work along the entire surface A and point B is again in contact with the chuck.
It is often recommended that undersized work should be limited to .003" less than the nominal diameter. This is because forming the "S" curve introduces considerable stress to the collet fingers which increases dramatically as the work diameter departs further from the nominal diameter. There is another reason as well and that is when the work diameter is less than the nominal diameter of the collet, the collet fingers only make contact with the work along three lines, shown as points F in the end view. This is why "emergency" collets are used when the number of pieces justifies the additional machining. The collet is bored to exactly match the work, insuring contact around with the full work surface.
A 5C collets ability to grip undersized work is limited by the width of the slits between the fingers and by the ability to tighten the collet in the chuck. The smallest diameter that can be gripped by a 5C collet is slightly less than the nominal diameter less the slit width, in theory. In practice, the force required to properly close the collet on the diameter may be more than can be applied by the collet closure mechanism. The slits on my collets are between 019" for the 1/16" collet and .055" for the larger collets. A collet set by 1/16th's would not be able to cover all possible diameters. A set by 32nd's would be able to close on any diameter within its range. A set by 64th's would create less stress on the collets in the case where the work diameter was slightly oversize for a nominal collet, requiring to go to the next larger size but may not be warranted for the occasional user.
For the user not wanting to purchase a set by 32nd's, there is a suitable workaround. A shim made from a beverage can will increase the diameter of a piece of stock by about .008" and some roofing flashing by .020". Cut a length slightly less than the circumference of the work and roll around the work. Insert the work and position the end of the shim next to one of the collet slits. Tighten and you're good to go.
Edit: deleted redundant drawing.
Last edited:
- Joined
- Dec 26, 2015
- Messages
- 2,139
/\/\/\ . Exactly as I understand the functioning and use of 5C collets as well, and why I prefer ER40. 
- Joined
- Jan 31, 2016
- Messages
- 12,794
Not that I never use the 5Cs in the lathe or any other fixtures , but you will spring them and ruin the collet if you go way undersize on your part . That's what E collets are for . 
- Joined
- Mar 26, 2018
- Messages
- 8,645
Thanks for taking this one.
I find sacrificial 5C collets to be a valuable tool. Holding a thin part in a 5 C emergency collet that has been cut to depth and diameter is a very handy tool to have in your arsenal. I’m not aware of an ER platform that has this option.
Are there emergency ER collets?
- Joined
- Mar 26, 2018
- Messages
- 8,645
Says here you in Ohio?
Just watched a Seinfeld episode where George and Jerry are sitting in a coffee shop with a globe and an Atlas. Holland is not on either.
Jerry said, maybe Holland sunk like Atlantis.
So, what’s the real story?
