Collet Wall section - sanity check

[Barbter]

Gents - sanity check please....
Old customer resurrecting a project I first suggested for them in 2017. It appears, one cannot rush things....
Lots of different length and detail parts, all made from the one extrusion.
I was looking to spark a special made long nose collet in the concept shape attached, but fear the wall section will be too thin (7.3mm) in 2x areas.
That is (obviously) only thin at 2 sections - left of centreline and mirrored right of centreline - and is "thick" radially everywhere else.
They are a commercial punch it and crunch it company - so saying something like "run collet pressure at 100 psi maximum" on the planning, will not mean it is ran at that.....
What do you reckon?
Cheers!

 

[Imachine909]

It would make me nervous sending one to a costumer where pressure is unregulated. In saying that what kind of volume will they be cycling?

Years ago I had a similar collet with four "thin areas" on them of .175" each and they ran basically uncontrolled on pressure. I had two of them for the same job one broke out at 220,000 cycles and the other at 270,000.

This was just my experience. Not sure if it's any value to you.

 

[Barbter]

Many thanks - so your .175" = 4.5mm which is much less of a section to what I have here.
Was yours the same (ish) size collet (3")?
Qty = cycles = There's 15 or 16 part numbers made from this extrusion - but some numbers are ordered once every blue moon. Some probably obsolete now.
Currently (last few years) there's 4x main numbers running - with annual qty's of 6000 tops total for all parts.
So I'll be long in the ground before we get to your cycles!

 

[Imachine909]

80mm rings a bell. If it was not 80mm it was around 3" yes.

With those low volumes I would not hesitate personally.

 

[Barbter]

Okay many thanks - that's some good piece of mind.

 

[Oldwrench]

If the collet is heat treated steel and it's supported in a taper I wouldn't worry about it at all. Committed worse sins than that with 5C collets.

 

[SeymourDumore]

Like Wrench said, the taper should take care of the stress issue.
If you're still worried about it, make a .05mm protrusion at the bottom to act like a "workstop", so you
know that the bottom corners will never be engaging the part.

 

[Barbter]

If the collet is heat treated steel and it's supported in a taper I wouldn't worry about it at all. Committed worse sins than that with 5C collets.

Yes very true - but what worried me is potential drawtube pressure and also as you can see by the pic - component has a lot of stick out.

I'll do as Seymour suggests - the component seating/location floor, will be radiused to removes stress

 

[Oldwrench]

If it were a continuous bar passing thru the collet, the stickout wouldn't matter (exc ept for deflection) since it would be cantilevered. If you are really worried about heavy cutting pressure ripping it out of the collet, perhaps the part would be amenable to passing thru shaped chuck jaws? It'd be an interrupted cutoff but that's doable. I didn't notice whether you ID'd the workpiece material—if it's extruded aluminum no sweat, if its a profile cold-drawn from 4140 then I share your misgivings.
Low DOC, charge accordingly...

 

[Barbter]

It's 6000 series ally extrusion. 1x part number solid, the other hollow.
Job is currently made using milled out soft jaws to the form shown - but this plan is to remove the need of removing the collet system, putting up the chuck, then removing the chuck to do every other job in the place.
If it was my factory i'd have had no worries about jumping with this - but as it's not, hence my request for a sanity check!

 

[Oldwrench]

Well, I for one think your collet design will work just fine, with no concern about draw tube tension, but I can't vouch for the other thing. Hell, I can't even vouch for my own.

 

[Barbter]

Bumping this....to make from solid, what material would be a good choice, and what heat treatment would be preferred?
I'm thinking through hardening rather than case and it doesn't have to be rock hard - I'd expect tough would do?
....and thinking turn it with a base/spigot on it, heat treat, clamp on the base/spigot, spark the centre to shape/size, wire the slots and wire (cut) off the base?

 

[Oldwrench]

Collets are mostly made from 1075, but an alloy steel is probably better if you're DIY. Definitely through harden, you want the increased tensile strength all the way through the section, and remember it's a spring...

 

[Mud]

How about 4140HT and nitriding?

 

[Oldwrench]

You can reliably quench and temper 4140/42/45 to Rc52 which translates to a tensile strength of around 275000 PSI. JMO, but I don't think pretreated material is nearly strong/hard enough for the repeated clamping load on a collet. Make a hanging fixture for heat treating so it is held vertically for heating quenching and tempering. Be aware that if you leave material to be severed later the part might go twang (it's OK if it spreads but not if it closes up).

 

[Barbter]

Yes....the twang factor (closing) is an exceptionally good point!
I'll have to look at the specs - I found DIN 6343 to also be a material used...
Absolute hardness i don't think is a requirement - tough is more important as this isn't going to see mega cycles.
I was wondering about an already heat treated billet - something like 17/4 - as availability is good and the finished shape is easily turned hard(ish) and sparking/wire won't be an issue.
But the twang factor.....