Spindle speed

I believe it's more to do with increasing versatility of the R8 spindle. Also, That system has a locking nut on it, so one just has to hit the brake and take a spanner to the nut instead of reaching way up there on top of the head to get at the drawbar.
 
what do i not understand?

There are other holders (like 4 sided and 6 sided collet holders) that can use these same ER-40 collets.
Whereas there are no 4-sided and 6-sided collet holders for R8
Whereas there are 4-sided and 6-sided holders for 5C collets.

However, that said, and the fact I actually have such an ER-40 holder in R8::
I have come to the conclusion that it is better just to buy R8 collets for the R-8 spindle
for 2 reasons
a) nore nose height to table
b) less tolerance stackup;
cost be damned....
 
I'll take a stab at this. If you have good R8 collets, like Hardinge collets that have a confirmed run out of 0.0002", then you are contending with the fact that R8 collets grab the tool shank with only about a 1/2" of surface area, much like a C5 collet, and the fact that the tool shank must be within about 0.005" of the collet size to be held solidly. Good R8 collets are quite accurate; junk collets are not.

An ER collet system has several advantages. It grabs the tool over a longer surface area so it registers the tool more accurately inside the collet. Due to the geometry of the ER design, it surrounds and clamps the tool shank very solidly. If you have an accurate chuck and use good collets then run out is minimized. Moreover, an ER system dampens vibration better due to the mass of the chuck/collet/nut system. Finally, a good ER system is very accurate over a wider range if the chuck is good, the collets are of good quality and you use a good nut that is torqued properly. Granted, the collet is most accurate when used with a tool shank very close to its stated size but small variations in tool shank size can be easily accommodated.

One of the key reasons that ER collets are a standard in the industry is because rather than change the tool in the chuck, the entire chuck is changed when a tool change is needed. Tools are locked into the chuck and remain there unless it wears. Imagine if you had to completely unscrew a draw bar, change out an R8 collet, change out the tool and then screw in the drawbar again to lock the new tool in. Very cumbersome.

I use the Tormach TTS system and have several ER chucks. It is very fast to swap out one ER chuck for another when multiple tools are needed. I think you can go either way in a hobby shop but for me, the ER system has enough advantages that I prefer it over R8.
 
Just one more thing. ER collets are often used on the lathe for work holding and do an adequate job of it. However, run out on the lathe is not nearly as critical and you can get away with an import collet set. On the mill, accuracy counts and there I recommend you suck it up and buy a decent set of collets. It will cost you but you will recover the cost over time because your tooling will be more accurate and will last longer.

Mikey, a newbie question: I believe I understand that with tool holding the run out is important for accuracy and tool wear reasons but why is accuracy not as critical with work holding?
 
Mikey, a newbie question: I believe I understand that with tool holding the run out is important for accuracy and tool wear reasons but why is accuracy not as critical with work holding?

A fair question, and I'm sure others have their own opinions. There is no reason you cannot use high quality collets on the lathe. The reasons I don't feel the expense is justified are:
  • Most of the stock we use in these collets can vary greatly in size. As you know, the farther away from the stated size of the collet the less accurate the collet becomes. Granted, this is less of an issue with higher quality collets but it occurs with all of them.
  • Most of the time, we do not need to work to tenths level tolerances on the lathe. Not only do we not need to do that but you have to ask yourself if you can work to those tolerances. If you use a good nut, you can get a cheap Chinese collet to run out under a thou easily. In fact, with an ETM nut I can get my cheap collets to run out close to 0.0004" TIR, which is 0.0002" actual run out. How much more accurate do you need to get? Can you cut anywhere close to those tolerances with an inserted carbide tool? Really? I can do it with a well-ground sharp HSS tool but with carbide and the deflection I get from the nose radius, that is a challenge.
Truth be told, when I have a critical dimension to hit, I don't use a collet. I use my 4 jaw chuck and I dial it to zero, and then I cut it with a HSS tool. I actually don't use collet chucks often. I use them when I do not wish to mar a fine surface on a previously turn work piece. I use them if the work piece is threaded and I'm trying to avoid damaging the threads, and I use collet chucks when working up close to the chuck with my hands. Otherwise, I use a jawed chuck.
 
Geerbangr, You mentioned "home on leave" If you are in the military I would like to thank you for your service. Otherwise thanks for being a member here.
Ray
 
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