er collet holding

[winger]

How far does the stock need to be inside an er collet not to damage the collet and still hold. We don't have a 5c set up for the small lathe at work.
I have a er32 camlock holder I made but the parts are only about .2 long. (.8 dia) I think I could get by with light cuts facing but some of them have a counter bore on the part off side.


Dave

 

[ps123]

You can put a short piece of same diameter stock in the back of the collet to keep it from crushing.

 

[Gordon Heaton]

You can put a short piece of same diameter stock in the back of the collet to keep it from crushing.

You can, but its mighty inconvenient!

 

[Gordon Heaton]

How far does the stock need to be inside an er collet not to damage the collet and still hold. . ?

The only safe measure is all the way to the back edge of the collet.

 

[Mtndew]

the parts are only about .2 long. (.8 dia)

.800 diameter and only .200 long? You would distort the collet relatively quickly. If you're just lightly clamping, you might be able to make it last a while though.
Mari-Tool sells them for only $21 each so it could be worth it to buy 2 or 3 to get thru the job.

 

[johnmontrose]

The only safe measure is all the way to the back edge of the collet.

If I may, could I slightly disagree with that? My minor objection is possibly more directed to slightly wishy-washy use of words than anything else.

The collet body of each item in a specific ER series is the same length. However, the gripping length of each collet within that series is not the same. Smaller collets have a gripping length that is less than the overall body length.

See page 254 of this: http://rsward.se/wp-content/uploads/2013/07/REGOFIX.pdf

I have never considered this, but I wonder if the gripping length of a 6mm ER16 collet is different to that of a 6mm ER40 collet.

 

[Gordon Heaton]

. . .Smaller collets have a gripping length that is less than the overall body length. . .

That's true as far as it goes. My understanding is that little significant grip is produced beyond that point, but the rear end of the collet can still be damaged by compression if tightened without supporting material. I'm not an ER expert, though. From page 18 of the document you linked to:
"Insert tool to the full length of the collet for best results if possible. However never insert the tool less than 2/3 of the collet bore length. Improper tool insertion can permanently deform the collet and will result in poor runout."

Emphasis added. The above seems to support the idea that 'safe' is all the way through the collet.

 

[AlfaGTA]

You made the holder...Make an emergency ER to accept your job. Bore with a step just for the grip length shoulder to locate the end of the work.
leave the ID small where the work is not to keep the collet stiff so it won't distort when tightened.

Cheers Ross

 

[winger]

the 2/3 min hold makes sense. Making a collet sounds doable.
Thanks
Dave

 

[JohnnyF1v3]

How far does the stock need to be inside an er collet not to damage the collet and still hold. We don't have a 5c set up for the small lathe at work.
I have a er32 camlock holder I made but the parts are only about .2 long. (.8 dia) I think I could get by with light cuts facing but some of them have a counter bore on the part off side.


Dave

I'm a Swiss machinist with considerable experience with ER collets.ER 7 through Er 25 specifically. Not to sound snooty as a Swiss guy, but our guide bushings require +/- .0015" tolerance for stock, so special attention to size of tooling and materials is always considered in the Swiss field. I will say that you can tell the experience of a companies staff by the damage or lack there of of both ER and machine collects. The amount of pressure when only using less then 66% of the the collet diameters length will cause an angle embedded in the collet. Also, the difference in collet diameter to tool size can permanently deform an ER collet if used incorrectly. That being said, if you want the best E.R collet I'd highly recommend rego fix. They take some abuse and hold the best concentricity.

 

[Limy Sami]

How far does the stock need to be inside an er collet not to damage the collet and still hold. We don't have a 5c set up for the small lathe at work.
I have a er32 camlock holder I made but the parts are only about .2 long. (.8 dia) I think I could get by with light cuts facing but some of them have a counter bore on the part off side.


Dave

Bore a pocket in a set of soft jaws and be done with it. .

 

[Bill D]

For a nut the standard is given that 1.5x to 2x diameter is maximum needed. So for a one inch collet 1.5-2 inches of engagement.
Now the friction fit of a smooth rod is less then a thread connection so I would double that depth of engagement as a first guess. Of course the force is not axial but radial.
Bill D