Offsetting in a Four Jaw [Archive]

Anorak Bob

24th June 2011, 12:47 AM

Before I go on, the trick and the tailstock are rip offs. The offset setup was featured on the cover of a Nexus Special Interest publication and the tailstock is a Hercus copy.

The centre point is offset from the bar's centreline by about 3mm.

I made the tailstock centre from 4140. A useless idea. It's too soft.:doh: On the other hand, the use of two centres and a DTI works perfectly.

Might prove handy for someone out there.

BT

azzrock

24th June 2011, 01:48 AM

that tail stock looks great to say the least. and i was happy to see you using a dead center to measure off set. i wasn't shore if it was a good method or not. know ive seen you do i know
it must be.

RayG

24th June 2011, 03:25 PM

I made the tailstock centre from 4140. A useless idea. It's too soft.:doh:
BT

Hi Bob,

Nice tip, did you harden the 4140?

Regards
Ray

Anorak Bob

24th June 2011, 03:40 PM

I haven't Ray. It would be a perfect job for the little oven I have, shame it's in bits.
I imagine I would cook the point if I attempted flame hardening.

Bob.

Stustoys

24th June 2011, 03:52 PM

BT,
If you heat the thickest part and let the heat run up to the tip, things should happen a little slower.

I havent used any 4140. Could you quench just the tip in water and let the rest air cool so you dont need to temper?

Stuart

RayG

24th June 2011, 04:03 PM

Hi Bob,

What Stuart suggested would work, the "as quenched" hardness of 4140 is 56 Rc.

But then again, it would be an ideal job for your oven when it's back together.

Regards
Ray

Anorak Bob

24th June 2011, 04:03 PM

Heat treatment is something I admit to knowing nothing about Stuart. My only hope would be that I could fix it if I stuff it up. Hopefully, someone versed in the art will comment.

Bob.

Edit... Ray answered while I was typing. I think it was RC who said you heat it to dull red and quench but that was in oil. What's the deal with water and the temperature of the steel prior to immersion?

Stustoys

24th June 2011, 04:32 PM

BT,
I also have a limited understanding of hardening. I think the answer to your question is, water will give you a harder finish but it is more likely to crack. (which would be unlikely in your case I believe). How much harder? No idea.

Stuart

Anorak Bob

24th June 2011, 05:14 PM

Dave J

24th June 2011, 05:19 PM

Stustoys

24th June 2011, 05:21 PM

BT,
You dont want to temper if you can get away with it, thats why I was saying to only quench the tip. But Ray should know more.

Stuart

Vernonv

24th June 2011, 05:57 PM

After a bit of digging I found RC's comment in the thread about boring bars.

Cover part with soap.. Heat to dark red with LPG burner ... dunk in oil... polish and temper..

rough but it seems to work..I asked RC this question in the boring bar thread, but never got an answer ... so I'll ask again here ... does anyone know the purpose of the soap?

azzrock

24th June 2011, 05:58 PM

which part of the tail stock do you want to harden? just the center?

Stustoys

24th June 2011, 06:05 PM

Vernonv,
I can only guess thats its to try and keep some oxygen away to keep scale down.
Stuart

Dave J

24th June 2011, 06:10 PM

I asked RC this question in the boring bar thread, but never got an answer ... so I'll ask again here ... does anyone know the purpose of the soap?

I also saw your question and was wondering what the answer was.

Dave

Stustoys

24th June 2011, 06:28 PM

I guess I should add that soap can be used as a temp indicator for annealing Aluminium, but I dont think thats any use(as a temp indicator) on hardening steel. There are special anti scale paints and powders or you can wrap the work in wire, all these make it harder to know what temp the work is at though.

Stuart

RayG

24th June 2011, 06:31 PM

Hi BT,

Here is the data on 4140, I just want to re-inforce the fact that it's oil quenched, quenching in water would be a no-no..

http://www.backsaw.net/pics/HT/4140.jpg

I should add, that my expertise in heat treatment is limited to finding the right page in the book, :)
after I get the furnace up and running, maybe I can add a little experience, as to what the soap does, I suspect it's to keep scale formation down?

Regards
Ray

azzrock

24th June 2011, 06:33 PM

Hi Bob,
As you say an old one but a good one and will help a lot of members here out setting up a 4 jaw.:2tsup:
I have a spring/pump centre similar to the one below I use for the same thing.
Shop Made Pump Center (http://homemetalshopclub.org/projects/pmpcntr/pmpcntr.html)
I keeps constant pressure on the tip when bringing it in from off centre.

Dave

hi.dave. thats what i was talking about. there is lots of diff ones out there but i was tough to use a dead center. and have been ever since . it made me think was i tough the right way?

Stustoys

24th June 2011, 07:28 PM

I just want to re-inforce the fact that it's oil quenched, quenching in water would be a no-no..

Opinions seen to vary on that.
A test piece could be in order.

Stuart

Grahame Collins

24th June 2011, 07:40 PM

I seem to remember reading somewhere that the soap coating prevents oxidising.

Grahame

RayG

24th June 2011, 09:10 PM

Opinions seen to vary on that.
A test piece could be in order.

Stuart

Hi Stuart,

A diversity of opinions is always good. I'll scan the relevant details on heat treating AS4140 and post it later, might throw some light on the topic.

Meantime, I came across the following...

A is for air quench like A2 A6 etc.
W is water quench like W1 and so on
O is for oil quench like O1, O6

D... like D2, doesn't fit the above neat scheme, so what does "D" stand for?, the suggestion is that most toolmakers think it stands for DOG, because of it's working properties..:rolleyes:

Regards
Ray

Dave J

24th June 2011, 09:18 PM

hi.dave. thats what i was talking about. there is lots of diff ones out there but i was tough to use a dead center. and have been ever since . it made me think was i tough the right way?

Hi,
In the end they all do the same job, so they are all right :2tsup:
I used to use a dead centre, but since making the spring centre I find it to be easier to use because it will keep constant pressure on the job when bringing it into the centre, and if you are using parallels/ packers to jack the job out off the chuck face, the spring will help hold them while adjusting.

Dave

Grahame Collins

25th June 2011, 11:08 AM

I have just done some googling on the steel supplier sites and found the following on 4140.

C& P as follows

Atlas Speciality Metals
Hardening
Components should be heated slowly to
850 to 860°C, held until uniform, then
quenched vigorously in oil (or polymer
with an equivalent quench rate to
between 80 to 110°C). Polymer
quenchants have similar cooling
capacities to oil, while having the
advantage of a being less likely to ignite.

Interlloy
Hardening - Heat to 840 oC - 875 oC, hold until temperature is uniform throughout the section, soak for 10 - 15 minutes per 25 mm section, and quench in oil, water, or polymer as required.
*Temper immediately while still hand warm

Bohler Uddeholm
Harden 830-860oC Oil quench

I suspect the Interlloy site migh be in error as the rest of them say oil quench. Its a relatively easy error to make if the person typing in the info cut and pastes the same text quite a few times and is not aware of the fact that the 4140 is oil quenched .

The other information that I have seen seems to indicate that 4140 cracks in water as it quenches too rapidly.

Grahame

RayG

25th June 2011, 02:45 PM

Thanks for posting that Graeme, I agree, the Interlloy data looks like a typo.

The main differences between water, oil, air quenching are the cooling rates, the water quench is of course 10% brine, and cools the most rapidly, oil is next and cools a little more slowly, and air the slowest. A complex shaped part with stress points would be more likely to crack if incorrectly quenched.

The point I want to make is that the rate of cooling is evidently critical to the process, especially as far warping and distortion. For example flat parts need to go into the quench vertically and be agitated, just the few milliseconds difference between cooling rates on either side of a flat plate can cause warping.

Regarding the soap....
I ordered some of this stuff last week from Rosemill PBC Anti-Scaling Compound (http://www.rosemill.com/category_s/47.htm) it's a powder coating that stops scale and decarburization. I think it might be an alternative in some circumstances to the stainless steel foil. Got some of that ordered as well. So we will see how it goes.

Regards
Ray

Stustoys

25th June 2011, 04:41 PM

. A complex shaped part with stress points would be more likely to crack if incorrectly quenched.

Yes, But I wouldn't call a dead center point a complex shape.
I wish I had bought the 200 odd kgs of 4140 on ebay a few months back now :(. I'll be going to Bohler Uddeholm some day soon, I'll see if they have any off cuts I can have a play with. What's funny is Machinery's Handbook says (page 415) "These steel are usually considered as oil quenching steels, although some large parts made of (4140) maybe quenched in water under properly controlled conditions". Yet this guy has made small screws out of it and water hardened. http://www.ctmuzzleloaders.com/ctml_experiments/mantonlock/mantonlock3.html (wlmailhtml:{39BAE3B7-E875-4F82-BDF9-3DD0A594E2BB}mid://00000495/!x-usc:http://www.ctmuzzleloaders.com/ctml_experiments/mantonlock/mantonlock3.html)
This guy has some interesting things to say as well http://www.dfoggknives.com/waterhardening.htm (wlmailhtml:{39BAE3B7-E875-4F82-BDF9-3DD0A594E2BB}mid://00000495/!x-usc:http://www.dfoggknives.com/waterhardening.htm)

I read some where that when they used to hand quench files(maybe they still do for all I know), they would straighten the file by the way they laid them into the quench bath. I guess the first 1000 were the tricky ones lol

Don't you just need to purge your furnace with argon? then you won't need paint :D

Stuart

Pete F

25th June 2011, 05:09 PM

Ray where did you get the information that water quenching 4140 is a "no no"?

I buy my new steel from Edcon, and this is a handy little sheet they have that summarises some metals, certainly all the ones I typically see anyway.

http://www.edconsteel.com.au/pdfs/information/steel_identification.pdf

Pete

RayG

25th June 2011, 06:01 PM

Ray where did you get the information that water quenching 4140 is a "no no"?

Pete

"Heat Treatment, Selection, and Application of Tool Steels" by William E Bryson

AISI 4140 is listed as an oil quenched steel, I imagine that must mean something. He devotes a chapter to each steel with do's and don'ts..

It's all about cooling rates and crystal structure... but don't ask me, I'm on the learning curve with heat treatment. Maybe, when the furnace is up and running, in the next week or so, I can answer a bit more from practical experience.

Regards
Ray

Elaborating... when you quench in brine, the salt plays a part in the process forming a protective layer... if you get uneven cooling the austenite fails to transform into martensite and the retained austenite causes spots of poorly hardened material..

RayG

25th June 2011, 06:20 PM

Hi Stuart,

That sword maker you linked to has some interesting comments...

Quoting..
To say " steel x cannot be hardened in water" is untrue and unproven. To use temps and techniques based on oil hardening in a water quench is also doomed to fail. I don't profess to be an expert in anything, or particularly great at anything either. I know little about metallurgy and as I get older I don't WANT to know any more. I simply try and try again, and test in practical ways.

Another Quote... about sharp corners
Sloppy grinds, lines, shapes, and burred edges will cause at least warpage and at most cracking. You cannot quench something in a fast quench like water with grinder burrs and really sharp corners all over the place and expect it to survive the shock. Knock off the edges, make sure everything is even and smooth, make sure ridgelines are straight and consistent. What comes out of the quench is directly connected to what went in.

I guess if it's about cooling rates and some black magic... Interesting point he makes about the time between quenching and tempering, Bryson says the exact same thing, you must IMMEDIATELY temper when the temperature reaches 52-65C

Regards
Ray

PS Belated apologies to BT for the continuing hijack... take me to Cuba...

Pete F

25th June 2011, 08:09 PM

AISI 4140 is listed as an oil quenched steel, I imagine that must mean something.

Indeed.

Grahame, I highly doubt this is a "typo". My understanding of the steel making process is that it's more like a chef cooking in a kitchen as a manufacturing process. Each batch of steel is ever so slightly different from each other, and presumably one manufacturer's steel is similarly different from another's, albeit falling under the somewhat broader specification of the material they're making, in this case 4140. It could well be that the steel being sold by Interlloy is capable of withstanding water quenching, whereas the same grade sold by another manufacturer is not simply by virtue of the slightly different alloys they use.

Pete

RayG

25th June 2011, 10:37 PM

I suspect that this particular rabbit hole goes deeper than I care to dig, but here goes....

Start with this 76 page excellent discussion on quenching, the CCT (Continuous Cooling Transformation) diagrams are the critical thing here...

http://www.houghtonintl.com/images/Hougton%20on%20quenching.pdf

The CCT diagrams show what cooling rate (quenching velocity) is required to avoid undesirable pearlite and bainite crystal formation, rather than the desirable martensite crystals..

Note the effect of alloying in the position of the austenite/pearlite boundary is to move the boundary (nose) to the right of the CCT diagram.

Now, read the following...

Heat Treatment: Principles and ... - Google Books (http://books.google.com/books?id=A2QG3UssqKUC&lpg=PA233&ots=Gluk9pnKmw&dq=asymmetric%20cross-section%20martensite%20warp&pg=PA233#v=onepage&q&f=false)

The point being made here is that differential conversion of austenite to martensite between the inside and outside of the part can result in cracking, hence the desirability of slower quenching (within the limits of the CCT diagram) and conversion to martensite more uniformly across the whole part...

My conclusion is that (fast) water quenching is more likely to crack than (slower relatively speaking) oil quenching.

One thing I've picked up is that Polymer Quenching looks pretty good...Might see if I can find out who sells the PAG (PolyAlkylene Glycol) stuff..

Regards
Ray

Stustoys

25th June 2011, 10:51 PM

What I don't like about what the sword maker says is the part on dropping the temperature 100F, as if any old temp will do.(he may well be right I havent tried it)

There is a bit of black art to it. Thats why people use test pieces and some of us even have hardness testers:). As I understand it, its section changes and sharp corners that give the most problems, thats why I included the guy that hardened bolts, but who know that temps he used.
Water quench with no temper is a WAG that may or may not work. being a pretty simple shape of small cross section and not heating right through all may help(they may all make things worse, as I've said I havent used 4140 for this sort of thing), but if it does work it should give the center the hardest surface possible(with 4140, without bringing case hardening powders into it)

Stuart

p.s. I haven't read you last post Ray

Pete F

25th June 2011, 11:23 PM

My conclusion is that (fast) water quenching is more likely to crack than (slower relatively speaking) oil quenching.

There's no doubt about that Ray. My understanding is that, in a nutshell, the faster the material is cooled the greater the hardness that will be achieved. However balancing that is the greater the propensity to cracking. Therefore only use the quenching media required to achieve the required hardness, basically in the order air, oil, water, brine. I have no idea where the polymers fit in here, I've never had anything to do with them.

Unrelated, but I'd hoped to do some case hardening tonight actually, but need to tap the parts first. However my M12 tap is basically crap and I don't expect to be able to get a new one before Monday when I'm off again :doh:

RayG

25th June 2011, 11:28 PM

What I don't like about what the sword maker says is the part on dropping the temperature 100F, as if any old temp will do.(he may well be right I havent tried it)

Hi Stuart, that's an interesting point, the austenizing temperature for 4140 is 855C (1575F) and you have to hold above that temperature for the soak time, (5 minutes per inch of thickness) Reducing the temperature (which is what he says for water quenching) below the critical temperature won't work. (I don't think he said what alloy he was using, but he does mention 4140 in the list) It's not going to harden properly if heated to less than that critical temperature... ?? But then again, that might be what's needed for swords, maybe the edges get hotter, hard edges and soft center..

Regards
Ray

Stustoys

25th June 2011, 11:33 PM

I suspect that this particular rabbit hole goes deeper than I care to dig, but here goes....
Indeed it does

The point being made here is that differential conversion of austenite to martensite between the inside and outside of the part can result in cracking, hence the desirability of slower quenching (within the limits of the CCT diagram) and conversion to martensite more uniformly across the whole part...
But in this case the part wont be heated right through or all heated all over or all quenched. So you just might get away with it..... you just might not to.

My conclusion is that (fast) water quenching is more likely to crack than (slower relatively speaking) oil quenching.
Yes, but also the hardest surface.

One thing I havent seen on my quick flick through of your links is anything on the effect of quench bath temp on hardness.

Stuart

RayG

25th June 2011, 11:35 PM

My understanding is that, in a nutshell, the faster the material is cooled the greater the hardness that will be achieved.

That's what I thought too, until I read the Houghton documentation, faster cooling (beyond the boundary on the CCT curve) won't make it harder, just increases the risk that the outside will convert to the harder material before the middle, and hence "ping" the crack appears.

It follows that the CCT curve will differ between different alloys, so some are suited to faster quenching (water) and some can be quenched more slowly, even, air quenched like A2.

Regards
Ray

pipeclay

26th June 2011, 12:18 AM

This is a long way from techniques or tips for setting offset on a 4 jaw chuck.

RayG

26th June 2011, 01:32 AM

This is a long way from techniques or tips for setting offset on a 4 jaw chuck.

You noticed...:D

Perhaps, a new thread on heat treating 4140, might be in order.

Regards
Ray

Anorak Bob

26th June 2011, 01:46 AM

A worthwhile thing Ray,

Save me trying to remember which thread this invaluable information is hidden in.

Bob.

azzrock

26th June 2011, 07:14 AM

so in general would you heat treat the centre before or after you have finished machining it.. and i'm not quite shore why the point is off set. i think if you only have to have two axis's in the job. then
just use tail stock with a sharp dead centre to quite your set up of the offset point.
i hope that makes sense.
in a way if the the dial may not be necessary.
the dial indicator would be needed if the amount of off set needed to be matched with another part.

Pete F

27th June 2011, 11:53 AM

Unfortunately to answer the previous question on the alternative thread simply wouldn't make sense, so although OT I'll post here and hopefully that will close this part of the loop.

Regarding water quenching 4140, I spoke to Interlloy and in a nutshell this is what I was told. As I suspected, their website was not a typo, and 4140 CAN be water quenched ... sometimes. It will depend on the size and shape of the component in question as to whether water is a suitable medium.

As to why Interlloy suggest it as possible, while other suppliers and sources do not, remains a mystery. However it was confirmed that the basic chemical composition for the grade of steel will fall within the specification parameters for that grade, however the precise composition could be obtained from the test certificate available on request. I'd suggest that would be only made available to larger customers and if a hobbyist were to ask for one having bought a 300 mm bar end, I'm sure they would receive the "appropriate" response :wink: It could well be that the precise composition of Interlloy's 4140 makes it less likely to crack than another supplier's composition. On the other hand it could simply be more an attitude of "suck it and see".

I think the bottom line is the grade is borderline as to whether water quenching cools too fast, however it will depend entirely on the size and shape of the part. Not a lot of comfort if a complex one-off has been completed, and I guess the answer is to oil quench and if that isn't hard enough then water quench and hope for the best!

Pete

old_fella

27th June 2011, 03:34 PM