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Choosing a micro lathe

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11 hours ago, measuretwice said:

A classic that should be on everyone's bookshelf, at least everyone interested in making things, is "The Amateurs Lathe" by Sparey

Thank you for the recommendation, ordered this morning arriving tomorrow. Looking forward to a good read. 

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4 hours ago, Squiffything said:

I think this is something I will need to invest in otherwise it becomes an unusable item. Added to the list together with a rotary table.

There's truth to that.  You often see people holding an end mill in a drill chuck (gasp) or three jaw.  It can work, but is problematic in that the tool can slip which if excessive can even damage the chuck.   These chucks get no bite in endmills which are hardened end to end.  They're intended for work or drills (the end of which is not hardened) where they get enough of a bite so they can hold.   You really should have a collect chuck or end mill holder for end mills

I've a collet chuck for a U3, very simple affair - basically a screw on ER chuck.  Probably wouldn't take much to have a batch made and sell on the fleabay

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19 minutes ago, measuretwice said:

They're intended for work or drills (the end of which is not hardened) where they get enough of a bite so they can hold. 

Is there a way to see if something is hardened? And if only partially? I've got (cheap) coated drill bits, who knows what they did to them? As simple they appears, there is an universe of complexity associated with drill bits. 

Quote

I've a collet chuck for a U3, very simple affair - basically a screw on ER chuck.  Probably wouldn't take much to have a batch made and sell on the fleabay

Exactly my thinking, because this specific MF14x1 chuck currently isn't available anywhere. I want to make my prototype first and then the batch. 

Another guy insist that faceplate + chuck like arceurotrade sells is the way to go because the faceplate is finished on your lathe. But I don't see how a single piece chuck can be worse if manufactured correctly.

In the meanwhile I have no choice but keep the endmill in the three jaws. Well that isn't long since Taig milling attachment arrived just yesterday.

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On ‎6‎/‎10‎/‎2019 at 6:05 AM, vinn3 said:

     thread pitches;  S.A.E. or MM ?   vin

   buying attachments for a lathe -  be careful.    an example;   the head stock (what you screw the chucks onto,) on an U S lathe  is 1/2 x 20 thread.  tooling made for a metric head stock WILL NOT FIT !  vin

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33 minutes ago, jdm said:

Is there a way to see if something is hardened? And if only partially? I've got (cheap) coated drill bits, who knows what they did to them?

The shank on a drill shouldn't be hardened - you might have noticed if you've ever had a one catch and pull a burr up on the shank, these are easily filed off because its not hardened.  You can tell if something is hardened by running the corner of a file over it....skips and its hardened. starts to cut its not.

 

Edited by measuretwice

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On 6/11/2019 at 3:25 PM, measuretwice said:

You really should have a collect chuck or end mill holder for end millsI've a collet chuck for a U3, very simple affair - basically a screw on ER chuck.

I've researched. I think ER collet aren't right to hold an endmill:

  • Force is angular to center line of tool holder
  • Less gripping area results in lesser accuracy

https://www.bilz.com/products/cnc-tool-holders/super-collet-chuck/

At least a 3-jaws chuck grabs the entire shank. A mill collect (MT2 with drawbar) look like below. Not cheap, even the Chinese one. And can't be used direct on the C0/U3 which has no taper. Maybe would be good devise something that can use holding slot on the shank.

HTB1oLinLXXXXXXMXXXXq6xXFXXX7.jpg

Below the C0 with TAIG milling attachment. The device footprint is exactly the same size of the cross-slide, and its existing holes are just a bit off the T-slot. The slide has a sink where the compound pivots, the attachment could be milled to accept a bushing to made it rotate precisely.

P6150782.thumb.JPG.9ecec6f313edde09f6b5f18cec382ea0.JPGP6150783.thumb.JPG.266c4f374b93f61103252bf50ec95a9a.JPG

 

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4 hours ago, jdm said:

I've researched. I think ER collet aren't right to hold an endmill:

If not end mills, what are they are for?  ER's are primarily a tool holding system (vs workholding).  That super collet might have advantages over ER, (or could be hyperbole)  but take a look at a tool changer on a typical cnc - I would say ER's are the most common way to hold end mills. 

Whether one is a bit better than another imo doesn't matter - anyone is 500x better than no collet for hardened tool holding.  While ER's have the advantage of being able to hold a wider range of sizes, if I had a choice, I'd prefer a spit collet or ER.  Nevertheless, availability, cost, small form factor and that its such a simple thing to mount on an existing spindle make them an easy and practical choice.  

As for length, so long as you grip enough so its solid, it doesn't matter that much - grip is a function of the coefficient of friction and force applied, it doesn't depend on surface area.  As I said, point loaded chucks like a three jaw or drill jaw are intended for, and really only effective with soft material where they can get a bite so they don't slip under load.  I suppose in engineering terms bite means the point load imparts a slight elastic (or often with work plastic) deformation of the surface under the jaws so the jaws don't slip.  that doesn't happen with the higher tensile strength of a hardened piece.

Will a 3 jaw work with an end mill?  Yes you can get away with it to a point with extremely light use but it will be the first thing to fail and when it does you risk damaging the chuck jaws.  Its something you do if you have to, but its not the best or right way.

Finally, even if you have a soft shank, a collet is still a superior holder from the standpoint of runout.  A three jaw will have runout so that the endmill often would cut on one tooth; machining takes longer, there's a high chance of breaking an endmill and a poorer finish are the results.

If someone really want to improve the Unimat, a new spindle hardened and ground that accepted 8mm or even 10mm collets would take that machine to a new level.  iirc, such a factory spindle was available; too bad they weren't more widely picked up as overall they are a neat little platform

Edited by measuretwice

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