mini lathe lever collet closer?

[InspirationTool]

Anyone know of a lever actuated collet closer for the mini lathe or a similarly sized lathe with a lever collet closer? I don't have room for a Hardinge, but I do lots of small parts, and would like to do them faster.

Thanks!

-Jeff

[RotarySMP]

Hi Jeff,

I have just completed an ER-32 collet chuck for mine - not what you are looking for. To make a lever collet chuck that doesn't have a huge spindle nose overhang, you would need to use small collets like 3c.

If you can find an Morse #3 to 3C collet adapter, it should be easy enough to make up the lever closing adaptor.

I believe you can get something like this for the Myford hoby lathes, which also have a MT#3 spindle. http://www.lathes.co.uk/myford/page3.html

[RotarySMP]

Here are a couple of pictures of the ER-32 chuck I made.

[RotarySMP]

Did you see that Little Machine shop has a 3C collet closer for $99? You'd just need to make a up a lever attachment.

[InspirationTool]

I did see that.

But I'm not sure how to go about making the closer... I know it will have to have bearings in it. I'm open to suggestions.

Thanks for the links on the Myford lathes!

-Jeff

[RotarySMP]

Hi Jeff,

I looks like you could do this with about 8 major machined parts. You would have to probably experiment with the springs to get the right pull (I would start with valve springs from the wreckers.

Here is a quick sketch of top looking down. You need to make the bearing outer race holder a sort of gymbol with the handle forming a yoke around it.

I have drawn it with a fixed attachment on the Pulley cover, although this is a zinc muck metal, and might need to be remade in something stronger.

It's getting late here. If you want me to draw this up in 3d, I'll do it this weekend.

[InspirationTool]

Hi Mark!

It looks like the spring is what holds the collet closed. Correct?

In the hardinge models I've seen you push to open and push to close. It stays either way.

I think your way would be easier to build.

No need for a 3D model, I got the idea.

Thanks!

-Jeff

[InspirationTool]

(Great drawing by the way.)

I was looking at it, and you could eliminate the bearing if you detached the lever from the bolt. After all, if you are only pushing on it, like that lever actuated draw bar for the Sherline, then it doesn't need to be connected.

Lemme go find a picture of that...

-Jeff

[Geof]

My interpretation of the picture Mark posted is that the spring closes the collet and the lever is pulled to open it.

If I am wrong in this intepretation the following does not apply.

I think you might find it difficult to find a single spring strong enough to close the collet. You do not mention what size you intend to use but the force needed for most collets is in the many hundreds of pounds. I have recently completed a 5C collet closer for a Haas TL1 which needed 1800 lbs; this is the optimum force given on the Hardinge website.

Coupled with the need for a high force which is probably not possible with a single spring is the fact that to open it you have to apply an over-force because you are compressing the spring even further. On my closer I allowed for up to 2500 lbs opening force.

An additional complication is that if you have a small taper collet such as Morse Taper it is self locking so you have to overcome not only the spring force but apply a significant excess to break the lock on the taper.

And finally if you do get the collet open with the lever it only stays open as long as you are pulling on the lever so it gets a bit tricky loading parts. You need to incorporate some type of over-center mechanism in the lever so you pull it past a mid-point and it relaxes back slightly and stops.

The commercially available collet closers I have seen for small lathes do not use springs they have a toggle arrangement operated by a hand lever; I have done a crude drawing showing the principle. It shows a cross section, both the wedge driven forward by the lever and the part that is attached to the collet are rings which encircle the spindle and a draw tube which is what connects to the collet. The wedge ring has a flange that fingers from the lever bear against and often the flange is hardened and the fingers are bronze so the collet can be opened or closed with the spindle turning.

On a do it yourself basis I think it is easier to make a closer using multiple springs with an air cylinder to open it. Have a look at my thread "TL1 Conversion to Tube Processing Machine" in the Haas forum. I can also post more pictures there if you want to see more detail.

[RotarySMP]

Good post Geof,

You idea has the makings of a very ellegant solution. Your toggle opens the collet as it moves up the ramp. How do you close it? Maybe replacing the ramp with a cam slot?

I was wondering what the closing force on a 3C needs to be. Could you post the link to this 5C closing force? Do they also list forces for smaller collets?

I got the idea with the spring from the Automatic tool changer for the mini mill, but then again, with a ATC you only need enough force to hold two tapers tightly together, whereas here you need enough force to close the taper and provide sufficient clamping force.

For the sort of parts you can hold with 3C (up to 1/2" diameter) I am not so sure that you couldn't make my idea work. Maybe not with valve springs, but with a stack of Bellville washers.

Jeff you are right, the handle could be disconnected ommiting the bearing. I would think it would all get a little wobbly though.

You need something like ebay 190121671299 or here is a partial one in the states. 120131086073. These Weiler turret lathes are now dirt cheap here in Europe. Even fully loaded with accesories, they rarely fetch over €1000. Weiler is the Mercedes of German Lathes (well one of them - there are lots of excellent german tool companies)

[Geof]

Originally Posted by RotarySMP Good post Geof, You idea has the makings of a very ellegant solution. Your toggle opens the collet as it moves up the ramp. How do you close it? Maybe replacing the ramp with a cam slot?...

The toggle moving up the ramp and pulling the collar back closes the collet. Moving the ramp away allows the toggle to return for the collet to open. 5C collets are not self-locking which is partly why they need a substantial closing force.

I didn't keep the link I found. Just Google '5C collet closing force' I think that is what is used. I can't recall what others I noticed I was only worried about the 5C.

Your belleville washer idea will work but you still have the problem of opening it against the springs and holding it there.

[RotarySMP]

I googled "3C collet closing force" and the top hit was this thread - Google's webbots are pretty fast.

You could hold it open with a piece of rope looped over the handle attached to the lathe bed