lathe, hard jaws crafting :)

[deadlykitten]

hello everybody :)

i must grip o42, and my hard jaws grip at least o82, so they are too big ..

i send some soft jaws to heat-treatment ... now i just wonder what geometry to cut ?

this image is only for cross section .... i think 30 or 40 degrees open is a good start :) kindly !

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[deadlykitten]

i found this ones as stock ... i have never used such jaws ...

from " o42 material " i must deliver " o40 part" ... i wonder if they grip firm and i hope that part's exterior won't be stung ... hmm

[deadlykitten]

hi, does someone has ideas about angle, height ? i think i will use a thread knife ... kindly !

[deadlykitten]

tadaa finished ... grip is powerfull enough, at 2mpa material crust is shatered ...

there is not only a pressure sound, but also a pierced sound ... they bite

i just increased presure to 3mpa, and tomorow i will start roughing

...

1st i thought to make same hardened jaws at a diameter close to material, but after i saw jaws from post #2 i wished to try them ... what i don't like is that they are for a large domain, like 40..80, or 20..45, and if a domain is wide, than it won't fit a particular diameter like a custom one ... also, they were ~400euros ...too much for what they do ...

[deadlykitten]

if anyone interesed, here is " how to "

image 1)

- choose a primar angle; 60 is a bit too much, but i went whit it because i did start from a previous machined jaw
- for normal jaws, without biting effect, 20 .. 30 is enough - they focus for 3 contact points / lines, 1 for each jaw
- for bite effect, there should be 6 contact points / lines, 2 for each jaw ... for this to be effective, this lines should be a little distanced, so a greater angle is required

-0.15 is the distance between jaw and material at medium section ... this value, for OD, should be positive, so to ensure that byte effect will occur near edges and not near center

image2)

- this groove has the same effect as the 0.15 ... it eliminates contact in center, thus more to edges

- teeth surface should be square / rectangle, with dimensions arround here [ ~1.7 ... 2 .. 2.5 ]
- byte effect is pronunced among longer edge; if teeth is slim, than byte effect is powerfull, and this slim direction should be oriented among cilinder/material section, and not among cilinder/material length, because byte must oppose cutting force, that tends to push material into chuck


one last thing : as you know, hard jaws, without biting effect, new or crafted, may not grip cilindric, even on a material with it's diameter close to their, so a taper may be required ... biting effect does not require such an inspection

[normal jaws] : they land on material, and full opposite force appears at 1st contact, so jaws start to slide and search their position among material
[byte jaws] : full opossite force does not appear at 1st contact, but after pierce phenomen, so in between, jaws continue their movement, until one teeth got deep enough to create full opposite force ... in that moment, it can not slide, so it act;s as a rotation point ... this is way some manufacturers deliver hard jaws with their teeth smaller, but not enough to pierce as a grip jaw ...they will leave a mark, but will not require taper

[deadlykitten]

time to share a kitty trick for OD ...

does anyone has a simple solution for ID ? kindly !

[deadlykitten]

hello, the part described in previous post allows repeatable&precise jaws positioning before machining them to a specific diameter

common jaw boring rings can not deliver such precision, except this ones, shared here in last post : http://www.cnczone.com/forums/okuma/...ing-rings.html

however, those can not deliver repetability for example you can not hit same position after a month

repetability is not required for soft jaws, while for hard ones is a must, because jaws must be clamped, after heat treatment, at same position as the one before heat treatment, so to finish them on a specific depth among diameter

thus, repetability is corelated with the depth required for finish machining

... heat treatment for all volume with ~same structure > a common jaw boring ring may be used
... heat treatment for hard superficial surface layer, and softer core > precise (re)positioning is required; "hard jaws" are delivered with such heat treatment

why 2 craft hard jaws ? to increase stability at high cuting specs, thus to achieve a better grip at same hydra presure otherwise, material will be pushed by knife

such jaws should not only grip, but bite

[deadlykitten]

img 1a : the sleeve inside a kitagawa 10" chuck; i have increased it's dimensions, by 0.7 on radius, because chips may get into the chuck while machining, because the original sleeve was 2 small; a 0.2 metalic spy ( Fuhlerlehren.jpg ) may get between the original sleeve and the chuck, so it was a welcome door for small chips

after clamping the jaws, during machining chips may get inside the chuck between my "custom" ring and the chuck, thus i needed to seal this setup

in img 1b is the idea behind this, like to take the frontal of the sleeve and put it in front of my ring; only technical condition is the perpendicularity as shown; final control, after clamping, is with a dial gauge, as shown in same image; i crafted the part with <0.01 on the dial gauge, but, after clamping, this value became 0.06; this is because the forces from the chuck are not perpendicular on S axis however, at 0.06 chips won't get inside as easy as before

in images 2a,b,c is the final ring just a part required to finish hard jaws ...

... sealing the chuck during machining is an issue
... common setups do not seal the chuck as it should
... there is no point to grease a chuck that is not sealed
... i don't grease chucks ... i keep them clean and i inspect them periodically; there is enough coolant going inside of them > i will be back with this some parts still crafting as long as surfaces that are in contact look ok, and slide, checked by hand is ok, there is no need to grease / prevention

[deadlykitten]

hello i would like to share some dealers for jaws, with a wide offer :
... beta
...... BETA - Modern clamping systems
... bisson
...... http://www.myjawfinder.com
... schunk
...... https://gb.schunk.com/gb_en/clamping...he/chuck-jaws/
...... https://gb.schunk.com/gb_en/clamping...uickfinder/#//

when crafting hard jaws, i buy soft ones + machine + heat treatment :
... olc45 : carbonitriding
... MnCr : cementation ( hope translations are ok )
...... some vendors deliver soft jaws without Carbon; is good to ask for material type

another option is to craft the jaws on my own, but if a vendor can provide apropiate jaws at a reasonable price, than i preffer buying, so to reduce machining time

i shared this because my main suplier is out of the bussines, and this is the best i could find in the last days kiiiiiindlllllllllllllllyyyyyyyyy

ps : there is also Kitagawa, with a basic offer, that may be just fine for most cases : Jaw Finder | Kitagawa

[deadlykitten]

[ how to achieve high tirr & uniform distribution of the clamp pressure for the hard jaws ]

hello everybody jaws from image1 had been on the lathe for a 10 months, delivering thousands of parts

tirr after a long period : 0.07 at 6D; value when new was 0.03..0.04 at 6D

tirr is checked using a caliber part, which has the OD pretty close to jaws ID

now i am machining a part as in image 2 ( o40 x 15D )

i wish to share how to craft such jaws :
... grind the face of the jaws ( after heat treatment ), indicated with the blue arrow, as in image03; this surface must be paralel with the teeth of the jaw ( or with the surface between the teeth );
... put the jaws on the chuck and grind the interior ( use something like the part from post #6, so to achieve high repetability on the clamp position; this is critical )
... now clamp inside the jaws a caliber with the OD pretty similar with the jaw ID, like in image04
... NHERE
... if there is tirr, and it should be, measure the "angle=a1 between OB and a horizontal", thus measure the conicity
... to measure angle=a1, simply use a comparator across the caliber, and do a bit of math
... now measure the "angle=a2 between OA and a vertical"
... remove the caliber, and clamp the chuck on the part from post #6 ( or whatever alternative; clamp repetability is critical ) - show in image 05; part from post #6 is represented with a blue line
... measure the "angle=a3 between AC and a vertical"
... measure the "angle=a4 between CD and a horizontal"
... repeat the grinding process, so to modify a4 with a1*80%; idea is not to input the entire correction
... at this moment, angle a4 should be equal with a4-a1*80%
... now clamp again that caliber; image04
... if you are lucky, previous angle a1 should now be a1*20%, thus less conicity, thus less TIRR
... also previous angle a2 should have modified with a1*80%
... if you compare a2 with a3, you will have a clue about the difference of jaw axis between "grinding position" and "clamping on part" position ( in other words, the difference of jaw tilting )
... at this moment, angle a4 + ( a2-a3 ) should be pretty close to a horizontal, thus uniform distribution of the clamp pressure should be achieved ( carefull to have increased contact towards the frontal, not towards the back )
... if tirr has increased, than something is wrong : machine is old, math is incorrect, etc
... if you are not satisfied with the tirr, GOTO NHERE and repeat until you are satisfied


i have programs that reduces the duration required to find the position where the grinding stone comes in contact with the jaws; i run such programs with the light close, so to see the sparks


i wont share the programs now, because is simply too long since i last used them, and it would take me too much time to understand them and explain them properly


kindly

---

even standard hard jaws, clamping a diameter pretty close to their diameter, may have a lot of tirr and/or uneven distribution of the clamp pressure

this is normal, because each chuck tilts the jaws in a particular way, so same set of jaws on 2 different chucks may perform differently

to achieve high tilt repetability on same chuck, i clean it once/year and i use stuff to seal it, thus to reduce the amount of swarf ( chips ) that goes inside it

[deadlykitten]

[ how to sense the difference between soft & hard jaws ]

hellow there is a signifiant difference in clamping between soft & hard jaws, at same hydraulic pressure.

this difference is being perceived more or less, depending on setup, thus there are setups during which this difference is amplified, making it easier to feel this difference

from time to time i prepare a milling setup, on the lathe, using a heavy fixture; one day, for some reason, there were hard jaws instead of soft jaws : when i clamped the fixture, clamping occured quicker and it felt more rigid; i felt like the cnc was taking the fixture from my hands much more faster .... when using soft jaws, after the jaws are making contact, i can feel that there is a delay during which they compress : a fraction of the hydraulic power is lost within this elastic deformation

[ how to sense the difference between normal hard jaws & serated hard jaws ]

from time to time i prepare a turning setup, during which a material o42 sticks out from the chuck for cca 300mm; when i replaced ' hard jaws ' with ' serated hard jaws ', when i clamped the chuck, and keeping my hand on the material at the far end, it was like a very short strong hit with a baseball bat; the grip feeling was much more intense than when using ' normal hard jaws '

also there is crunch sound when the serations are breaking into the superficial layer of the bar; is not ok to look without protection ( glasses, window ) as tiny metal parts may hit the eye ball learned it the hard way

last time when i have run this setup i have sticked out the material even more : from 300 to 450; i have encountered some problems, but not because of the jaws



so, one key aspect to sense these differences is repetability, thus to have the hand used with a certain set of jaws when clamping a part; this involves series

when crafting single parts, etc, it may be possible to miss this thing, because a set of soft jaws, that are prepared for a specific diameter, may deliver a better sense of grip compared to a set of hard jaws that are not prepared for that specific diameter

---

another aspect is that custom hard jaws are more reliable when machinining many parts & more resistant in case of a colision & less likely to lose grip in case of high specs

when there are milling setups on lathes, chips will stick to almost everything; is good to prevent chip acumulation near the clamping zone / kindly

[deadlykitten]

one more thing, very important : standard hard jaws, from vendors, may not deliver a cilindrical grip, or not even a grip among a line paralel to Z axis : this happens because each chuck tilts it's master jaws in its own way


a normal heat-treat on soft jaws may make wonders; if possible, go for carbonitrurizing or cementing, because a ' normal heat-treat ' is like lemon-beer with candies; go for rough beer with sausages & mustard ...

go hard or go home