Collet Stop

[James1979]

Hello all

looking to make a collet stop for my lathe. Easy enough job but the collets are not internally threaded so all the ideas I have and designs out there won’t work.

Does anyone use a collet stop in similar collets please? What is your method?

 

[Dr.Al]

I doubt this is going to help your exact situation as I don't know what your collet chuck is, but I effectively use a drawbar as a collet stop. I made a custom ER40 collet chuck (photo here: https://www.cgtk.co.uk/metalwork/m250/er40mt45). I use a bit of threaded rod (with the end faced in the lathe) as a drawbar. A nut and massive top-hat washer on the back of the spindle tightens the collet chuck into the taper.

As the threaded rod can be screwed into the collet chuck to any length I want (not just to the depth of the thread in the chuck), I can make it protrude into the body of the collet chuck a reasonable distance and use it as a back stop for consistent positioning. I've also got a simple back stop (https://www.cgtk.co.uk/metalwork/m250/backstop) that I use with the three-jaw chuck, but it doesn't work well with ER collets as the force of tightening the collet nut moves the sliding bar, even if the brass screw is very tight. The threaded rod in the collet chuck doesn't suffer from that problem as the thread is tightened by the rear nut and hence can't move.

I suspect it's not ideal tightening an ER collet onto something that can't move backwards with the collet (the collet is moving down the taper but the workpiece is stopped by the threaded rod backstop), but it hasn't caused me any problems thus far.

 

[Agroshield]

What collet system is it and how is it closed? E.g. 5C with drawtube or 5C in chuck. The answer to this constrains the possible solutions.

Do you want something that fits all your collets (from the smallest in the range to the biggest) and can be moved between them?

The more universal you make it, the bigger the challenge. Less versatility and interchangeability makes the build easier.

Make something like an expanding rawlbolt that grips the inside of the collet (same as Dr Al above, but in the collet rather than the spindle). Then drill through its centre for the stop.

If it is for batch work, buy a spare collet and loctite something inside it, into which the stop will screw.

If your stop rod is, for example, 10mm dia., that won't fit a 6mm collet. Similarly, if you are holding a 17mm dia. part with a 10mm hole in it, the 6mm stop rod won't be much help.

What sort of repeatability do you need? If the collet moves relative to the spindle during the tightening process (i.e. drawbar pulling it in), repeatability is harder to achieve. A lever-operated closer will always pull the collet back to the same place.

 

[James1979]

Thanks for the replies.

my collet system is a draw tube through the headstock on a s&b model L.

I am looking for a collet closer for it at the moment which will help

I would like it to be as versatile as possible but may have to forego that for ease. The system I liked was simply an adapter between the internal collet thread and a piece of round bar which works as a stop by means of a grub screw in the adapter. The round bar was alu so one could turn different ends on it to suit what was being put into the collet.

The problem is my collets do not have an internal thread. A rawlbolt type mechanism may be the thing.

 

[James1979]

 

[Rkweld]

Is that collet not damaged? Or has someone tried to internally thread it? From what I have read, the 5c collets were not threaded internally early on. There are expanding style stops to do the job. If i was to make something I would use the principle of an expanding reamer I think. Or an expanding taper collet like some pin and bush assemblies on volvo dumper steering.

 

[Agroshield]

...the 5c collets were not threaded internally early on. There are expanding style stops to do the job.

I do not think he confirmed they are 5C. I mentioned 5C only as an example of a breed of collet. The S&B page at lathes.co.uk says 5C only in connection with the later (latest?) headstock.

I think the expanding one to which you refer is this: https://www.ebay.co.uk/itm/5C-Unive...ge-Quality-NEW-see-pictures-2-3-/284221676609. There might be more pictures in Gloster's downloadable catalogue if he wants to reverse engineer it.

 

[James1979]

I’m not sure what they are actually. I would need to measure them and work it out. They came with the lathe

They aren’t threaded internally and no one has tried as far as I can tell. Not sure what those marks are but it’s only the one collet.

If I was only using one or two sizes I would just buy extra and epoxy something in. I use about half a dozen sizes in the runs I do.

that link on eBay looks is useful. It’s a pain in the **** they aren’t threaded as that would be job done!

 

[Rkweld]

James1979 is your draw bar hollow?

 

[Rkweld]

Is the lathe a smart and brown?

 

[eLuSiVeMiTe]

I’m not sure what they are actually. I would need to measure them and work it out. They came with the lathe

They aren’t threaded internally and no one has tried as far as I can tell. Not sure what those marks are but it’s only the one collet.

If I was only using one or two sizes I would just buy extra and epoxy something in. I use about half a dozen sizes in the runs I do.

that link on eBay looks is useful. It’s a pain in the **** they aren’t threaded as that would be job done!

Crawford 2804 collets


Drawbars hollow. Could you fit a stop on the draw bar. Would mean setting up each time a collet was swapped though.

 

[Rkweld]

Crawford 2804 collets


Drawbars hollow. Could you fit a stop on the draw bar. Would mean setting up each time a collet was swapped though.

That was where I was going if it was a hollow draw bar. Great minds.. and all that...

 

[Rkweld]

Is the lathe a smart and brown?

If it is a model L like it looks it depends on the headstock it has to which collet.

Later headstocks could take 5c, with the draw bar and not the cap.

Was the 2804 in between?

 

[eLuSiVeMiTe]

If it is a model L like it looks it depends on the headstock it has to which collet.

Later headstocks could take 5c, with the draw bar and not the cap.

Was the 2804 in between?

Definitely 2804. Took the same collets as my model M.

I sold it to James.

But I concur about headstocks being varied on the L.

 

[James1979]

Definitely 2804. Took the same collets as my model M.

I sold it to James.

Yeah you would know what they were I guess thank you for clarifying it.

Problem I have with fitting something up in the draw tube is that some of what I’m doing is overall length 14mm. So I’m thinking along the lines of it having to be in the collet

Also I’m after a closer rather than a tube so I’d rather design and make something once that would fit with both.

 

[eLuSiVeMiTe]

@James1979
If you look on the nose of some of the collets you should be able to spot 2804 stamped on them.

Did you notice the collets with the collet block are threaded metric. Same dims but at some point the threads changed.

 

[eLuSiVeMiTe]

Yeah you would know what they were I guess thank you for clarifying it.

Problem I have with fitting something up in the draw tube is that some of what I’m doing is overall length 14mm. So I’m thinking along the lines of it having to be in the collet

Also I’m after a closer rather than a tube so I’d rather design and make something once that would fit with both.

What about push bike handlebar type Affair up the collet. Wouldn't foul the thread.

Edit.
Expander bolt.

 

[James1979]

I will look. I think the metric collets may have that on them actually thinking about it.

I have not used the metric collets as everything I’ve done so far with collets is imperial. Just playing with them they seem to fit the draw tube thread well. I wonder what thread they are. I’ll measure it.

 

[James1979]

What about push bike handlebar type Affair up the collet. Wouldn't foul the thread.

Edit.
Expander bolt.

Yeah that would work. It’s reasonable easy and cheap to source too.

 

[Agroshield]

Could you fit a stop on the draw bar. Would mean setting up each time a collet was swapped though.

A stop on the drawbar has the same disadvantage that Dr Al identifies above: that if you push the stock onto it, the collet then slides on the stock as it tightens. So at the last squeeze of the drawbar, you are trying to move something in a tight collet. That cannot be good for stock or collet.

On the expanding type, it would not necessarily need to be metal on metal. Something that squeezes an O-ring (possibly a square section one) might do. Think drain stopper in miniature.