Question about collets

[kd0afk]

I am reading the latest issue of "The Home Shop Machinist" and in the article about collets it shows a 5c collet chuck. The caption reads;"A system used on the 9" South Bend lathe to allow the use of 5C collets. It works when you can't do better."
What does "..when you can't do better" mean? Is 5C not the best choice for a collet system? I don't understand.

 

[portlandron]

It's no so much about the collets but about how they are being held. When collets are being held in a collet holder that is inside the spindle of the lathe they are running as true as the spindle and collet holder allows. For all practical purposes the only deflection would be from the spindle bearings.

When you mount them outside the spindle, in a chuck, you have more overhang which can equal more deflection. There is also the addition of chuck alignment or run out.

 

[rodw]

It's no so much about the collets but about how they are being held. When collets are being held in a collet holder that is inside the spindle of the lathe they are running as true as the spindle and collet holder allows. For all practical purposes the only deflection would be from the spindle bearings.

When you mount them outside the spindle, in a chuck, you have more overhang which can equal more deflection. There is also the addition of chuck alignment or run out.

So does this mean that my 5C holder that fits in the spindle taper and passes right through the spindle is a better option than fitting a collet chuck? I wondered how accurate it might be and if it could be tightened up crooked.

I have only played with it but I will say that I like the 5C collets and the collet block I got for the mill. I still use ER32 for mill tool holding.

 

[Sshire]

Another consideration about collet adapter vs collet chuck. The carriage travel toward the head is limited. I'm using a Bison Set-Tru 5C collet chuck and the carriage travels under it giving about 6" more travel toward the head. I may not be understanding how the adapters are used, but in a parting cut, where the tool is at 90 degrees to the spindle,the carriage can't move close enough to the head to part off close to the collet nose. Am I missing something here?

 

[canadianhorsepower]

Am I missing something here?

Stan,
depending witch set up you are using yes you'll run out
of space. Picture one is a common practice cheap but work and you will run out of space. Second picture more money, but you get what you pay for

http://www.mmsonline.com/articles/when-to-use-a-collet-chuck
this is a good article on the subject

 

[rhankey]

Another consideration about collet adapter vs collet chuck. The carriage travel toward the head is limited. I'm using a Bison Set-Tru 5C collet chuck and the carriage travels under it giving about 6" more travel toward the head. I may not be understanding how the adapters are used, but in a parting cut, where the tool is at 90 degrees to the spindle,the carriage can't move close enough to the head to part off close to the collet nose. Am I missing something here?

I think that potential issue varies depending on the lathe you are using. For example, on my Hardinge HLV, in which the 5C collets mount within the spindle nose, I still have no problem parting off right next to the collet nose.

 

[rodw]

I have the spindle adapter in the drawing Luc has posted. You need a minimum 38mm spindle to use these so they are not for small lathes.







From the earlier post, I was not sure if this was likely to be more accurate than a collet chuck. Any comments?

Am I missing something here?

On my lathe there is a pressed metal guard attached to the saddle above the leadscrew which also works as a stop to limit forward travel as it contacts the headstock behind the spindle plate. Removing this guard lets the tooling travel last the spindle plate. I made a mental note that I would need to remove this guard if I was turning say a chuck adapter plate bolted directly to the spindle but even with this guard in place, there is plenty of travel to use the collet adapter right up to the collet. Maybe yours has a similar guard?

 

[canadianhorsepower]

You need a minimum 38mm spindle to use these so they are not for small lathes.

This company sell some 4inch one
http://www.ecolletchucks.com/BISON/BISON-4INCH-5C-MANUAL-COLLET-CHUCK.htm

 

[rodw]

This company sell some 4inch one
http://www.ecolletchucks.com/BISON/BISON-4INCH-5C-MANUAL-COLLET-CHUCK.htm

That is for a chuck. I was referring to the spindle adapter. Also on that page, there is a collet stop on the bottom right. I can highly recommend them. I have one I got from Little Machine Shop for about $10 or so. It lets you do one setup for multiple parts. It worked well for me in a collet block in my mill.

 

[canadianhorsepower]

[quoteI was referring to the spindle adapter][/quote]

oops:hDe: Rodw sorry I didn't pay attention

 

[kd0afk]

Metal lathe accessories has a 5c collet chuck foundry kit so when you make it there is little or no run out. My lathe is 4.5' so the loss is ok. I would go with a 3c system but I really need the capacity to turn larger stock.

 

[platelayer]

I am reading the latest issue of "The Home Shop Machinist" and in the article about collets it shows a 5c collet chuck. The caption reads;"A system used on the 9" South Bend lathe to allow the use of 5C collets. It works when you can't do better."
What does "..when you can't do better" mean? Is 5C not the best choice for a collet system? I don't understand.

The problem with collet chucks is that because we are adding an extra piece onto the lathe we are also adding to the tolerance stack, and it is quite lightly such devices will exhibit more runout than the bore of the lathe spindle which have been specifically manufactured to locate collets in the lathe. Beyond that of course with any sort of chuck, overhang of the bearings is increased, and therefore the likelyhood of deflection, however it depends of course on the magnitude of the cutting forces as most of us would simply take lighter cuts to mitigate that problem. We use collets in general as a quick way of gripping work reasonably accurately, but how accurate will depend on the original manufacture of the lathe spindle and the collets themselves. The best lathes (Schaublin/Hardinge for example) when new with new collets may exhibit very little runout at all, indeed I have seen some Schaublin lathes where only the merest flicker of the DTI was apparent. I suppose at the end of the day it depends what the requirements are, and there are other ways of achieving similar levels of accuracy such as using "griptru chucks" or soft jaws that can be machined out to suit a particular job. - It's really horse for courses!

 

[platelayer]

Metal lathe accessories has a 5c collet chuck foundry kit so when you make it there is little or no run out. My lathe is 4.5' so the loss is ok. I would go with a 3c system but I really need the capacity to turn larger stock.

The other thing to bear in mind is that collets do not have the gripping force of a chuck, and therefore you may be better using soft jaws bored out to suit the job if you need the accuracy.

 

[Tin Falcon]

Why not go with a 3C system and buy a couple of pot chucks.

Tools for cheap Mass. USA has them for about $30 each.

available in 2 or three inch so you can bore them to whatever size you need.
Tin

 

[kd0afk]

Why not go with a 3C system and buy a couple of pot chucks.

Tools for cheap Mass. USA has them for about $30 each.

available in 2 or three inch so you can bore them to whatever size you need.
Tin

This is an option I have thought about. I forgot about the pot chuck. Tools 4 cheap has a 3c system for just a little more than the kit from MLA so I might just do that.
I was under the impression that a collet grips better than a chuck because of the gripping surface area but I guess I was wrong.

 

[Tin Falcon]

I was under the impression that a collet grips better than a chuck because of the gripping surface area but I guess I was wrong.

Regular 3 jaw scroll chucks grip at three points
independent 4 jaws grip at four points. an improvement would be a 6 jaw set true chuck. these are nice but relatively expensive.

A regular 3 jaw chuck with soft jaws is an improvement also as they can be machined true for a job and they grip segments of circle rather than points.

A pot chuck is also machined to size for the job or can be machined in steps.
the pot chuck like collects grip most of the entire circumference of a round part . All but the relief slots. When you machine a pot chuck place spacers in the slots tighten the chuck then machine to size . when you remove the spacers the slots will contract as the chuck is tightened and grip the part.

you are not wrong the pot chuck is more of a collet than a standard 3 jaw scroll chuck in the way iT works.
Tin

 

[kd0afk]

The other thing to bear in mind is that collets do not have the gripping force of a chuck, and therefore you may be better using soft jaws bored out to suit the job if you need the accuracy.

Where do get your information from?

 

[platelayer]

Where do get your information from?

Well apart from being a professional engineer, it 's from experience in the workshop and in the workshop and conversations with my peers. If you doubt it think of the mechanical advantage a chuck has over a collet!? Initially there is the gearing, and then the scroll which allows the user to impart significant pressure on the workpiece. It all depends on the requirement. Collets are for quick accuracy within prescribed limits of manufacture.

 

[stevehuckss396]

The other thing to bear in mind is that collets do not have the gripping force of a chuck

Amen brother. The only time I use a collet is to hold a part without messing up the surface of the part i'm holding. I also like to use them when making valves so the stem and heads are concentric after rotating the part. Chucks are for the heavy cuts.

 

[platelayer]

Regular 3 jaw scroll chucks grip at three points
independent 4 jaws grip at four points. an improvement would be a 6 jaw set true chuck. these are nice but relatively expensive.

A regular 3 jaw chuck with soft jaws is an improvement also as they can be machined true for a job and they grip segments of circle rather than points.

A pot chuck is also machined to size for the job or can be machined in steps.
the pot chuck like collects grip most of the entire circumference of a round part . All but the relief slots. When you machine a pot chuck place spacers in the slots tighten the chuck then machine to size . when you remove the spacers the slots will contract as the chuck is tightened and grip the part.

you are not wrong the pot chuck is more of a collet than a standard 3 jaw scroll chuck in the way iT works.
Tin

The other thing worth pointing out is that collets are less likely to damage the workpiece because they grip more lightly over a greater surface area. Circumferential grip is only achieved when the size of the workpiece closely matches that of the collet. Being from the UK I've not come across the term pot chuck. - Perhaps we don't have them here, but is there a picture available on the site.