Could anyone offer me their opinion on the best material to make a precision grinding vise. I thought I would make them out of either 01 or, A2 but, everyone (including some manuals) say different. One manual I have says 4340 or ATL-33 - case hardened. I dont know about the availability of these steels however. I could make it from 1018 and have it case hardened but, I dont want to spend alot of time making these vises and not have them be "right". I would rather spend $100 on some good steel. I have heard arguments from everyone - some saying 01 or A2 are too brittle. I am kind of interested in case hardening ATL-33 but in my 16 years of machining I have never worked with or, even heard of this material.....
Patrick

Like most engineering questions this one doesn't have a single "one size fits all" answer.

Size, design, loads, degree of precision and other factors define the sheaf of suitable materials. Imo, anyone who says "X must be done using Y" is just a cookie cutter thinker, not an engineer.

The only real answer is to figure the requirements of the application and then select material for physical properties and financial viability. (imo again, of course)


Tiger

Not sure how i'd do it, probably like you, start with research. here's the stuff that strikes me off the bat...

I often use casehardening rather than tool steel and I usually send stuff out for case hardening and have been impressed. I can get a 50 thou depth and to Rockwell 65 and because the inside is ductile, don't need to have it tempered.

I'm wondering what the advantage is in using chrome moly? If its being case hardened, what's the point? its not a tool that you need a stronger steel for and do the heat treatable properties matter if you're case hardening - not saying it wouldn't be good, just doesn't leap out at me why

As well as harde I'd want it stable, this is a problem when you are heat treating - ie cycling between freezer and oven dozens of times to get rid of the stresses etc. I wonder if case vs tool is more or less stable. I'd want to know that the hardening isn't going to crack it. maybe air hardening tools steel, case hardening is very good in this regard.

Cost and machinability. I'd rather cut free cutting mild steel and its cheaper, but agree with you for a serious project getting the right material is more important than saving a few bucks

do you have a heat treat place that you use? if you get a good one, those guys can be pretty informative

Patrick,

Since a grinding vise is intended for light duty with no shock loads, but exposed to abrasives. A relatively hard surface is all that I'd expect to support the precision long term.

As far as case hardeing. 8617/8620 would be reasonably priced compared to the 4000 series moly steels.

Sure you CAN make quenching steels brittle, but that is where a controlled HT process pays off. Attention to details in the process should still get these materials into a usable range for the application. Right on the Starret packages it shows the critical temp and then the drawing temps over time to get it below the brittle stage. There may be better steel for obtaining specific tensiles and yields for red line engineering, but would that really apply here?

If you had an oven. I would prefer D2, S7 or other air hardening materials to avoid the shock of quenching. Even with these they still recommend a draw after HT.

I don't know if eBay could save you time and money to get a ready made grinding vise. Although gaining the experience in this kind of over all project can be worth something in itself.

DC

D.C.
I have decided on 8620 RD steel. Apparently it can be hardened to RC 20-40 and THEN case hardened. This way I can have a VERY tough and ductile core and a VERY hard shell. I sent for a quote on the price.
I am a toolroom/prototype machinist who does mostly CNC milling work. I use my grinding vise on the mill CONSTANTLY. Unfortunately the other day our dedicated grinding person was PRESSED to get a difficult job done and I volunteered my grinding vise which was turned into a permanent fixture. My company offered to buy me another vise but, I was never really happy with it anyway. You see it was one of those cheap (8 years ago it was $90) imports. When I got it it was out of square and bowed .0015. So I thought "no big deal I will just grind it". Yeah right!! It was made out of such crappy steel that it kept warping on me. I ended up lapping the bottom and never could get it square any better than .0003. I like the Hermann Schmidtt vise but, am not going to pay $670.00 for one. Besides there are a few "add on's" that I would like to incorporate into my vise. Anyway, my company said that if I make 2 vises (one for me one for them) they will buy the stock and pay for heat treat. Also I may be able to have our finish man take care of the grinding.
I want the vise a little longer than the Schmidtt vise and want to make interchangable jaws that "lock" into place. Alot of times I make aluminum soft jaws to hold irregular shaped parts on the NC mill.....
Patrick

Sounds like our professions are very similar in some respects.

I cannot say if the 8620 will dance around on you during grind. I think I would be a little suspicious if finish grinding after case hardening for that reason. Keeping the grind depth minimal could make all the difference. I think I would be inclinde to let a course stone spark out rather than use a finer stone that could build up heat, but I am not an old experienced grinder hand by any means.

I just had some quotes on a couple 14" rounds @ 2" thick. The 8620 was almost half the cost($465) of 4140 at around $800 each IIRC. I still went with the 4140 for a thru-hardening die that gets reground during its useful life. The case hardening did not help much other than retaining some of the ductility.

The original die casing had a bronze insert for hydroforming stainless, but the wear rates were horrible(blanchard ground 4 times per 12hr run). The 4140 will be solid without the insert, so in effect is somewhat experimental. I'm keeping the HT down around 55 so it should take the fatigue cycles and give a decent wear rate. My hope is that the up time production will help offset the extra cost of the 4140 material verses the constant maintenance issue of regrinds. Besides the reduced machining and not adding the bronze insert. The up front cost may be higher, but the payoff can be greater if we can resolve any other issues that may rear their ugly head unforeseen.

If you so choose. I am sure there are plenty here that might enjoy your documentation in a project like this. Post it up! :cheers:

DC

D.C.
I used to work in a small shop that made dies for swaging stainless. I think you will find that 06 (GRAPHMO) will provide exellent wear resistance for your application. It is basically 01 with graphite running through it. The graphite provides lubrication. Also it cuts much easier than 01 but, can be hardened to the same RC. However, if the bronze inserts you are talking about are AMCO bronze - I dont think ANY other material will be longer lasting.......Patrick

Well you have first hand experience witht he stability of heat treated steels. This will be an issue for your self built unit also. I would talk to hour heat treat people and see what they advise.

Personally I'm fond of Stainless when it comes to tools exposed to water based fluids. While not a true stainless, the A2 you where thinking about will have some rust resistance after heat treat. Probably not a big deal for a tool used everyday, but something to consider when it gets squireled away.

All that aside, I still think that you need to talk to your heat treat people and seek their advice for a stable material and treatment process. Like it or not stress in your materials will cause movement.

Thanks
Dave

Take this as half statement, half question, cuz you guys are pro’s and I’m not.

With heat treating tool steels, a good part of not cracking has to do with design, not whether the heat treat is done properly. I thought a case process had a lot more design latitude, ie sharp corners, thin sections than tool steel would allow

why on this application would you care how tough the core was if case hardening gives you 60 Rockwell to 50 thou – what physical property of a hardened steel core matters here?

One Of what do mean by being suspicious of grinding a case hardened piece – what is the concern? I would have thought that if the core is ductile it would mean less stress - I mean the quench produces stress risers right whether its case or tool steel right?

I was under the impression that any steel after quenching could move around without seasoning, that there was no silver bullet because the act of quenching locks into the crystalline structure stresses, are you saying there steels that you are stable after hardening? I know my tool and die maker friends season their best tooling before finish grinding to try to work out these stresses.

Take this as half statement, half question, cuz you guys are pro’s and I’m not.

Pro is a relative term for metaligists. I'm more of a hacker that has had some exposure to the different processes I have needed to do over the last 30 years. My limited experiences do not qualify me as a pro. I am still learning as I go. :rolleyes:

With heat treating tool steels, a good part of not cracking has to do with design, not whether the heat treat is done properly. I thought a case process had a lot more design latitude, ie sharp corners, thin sections than tool steel would allow

There is a hand in hand relationship here and either portion of the project can screw up the end result. The unexpected still happens for no obvious reason.

why on this application would you care how tough the core was if case hardening gives you 60 Rockwell to 50 thou – what physical property of a hardened steel core matters here?

I look at this as part of spring with a wider capability to handle cycled stresses. This application could make the difference in returning to its original shape as the material yield strength goes up, but won't snap like glass below the surface.

One Of what do mean by being suspicious of grinding a case hardened piece – what is the concern? I would have thought that if the core is ductile it would mean less stress - I mean the quench produces stress risers right whether its case or tool steel right?

My suspicions are based on the case no longer being equally supportive of the internal and/or applied stresses if an excessive amount is removed from one side verses another. That does not make it fact, just suspicion?

I was under the impression that any steel after quenching could move around without seasoning, that there was no silver bullet because the act of quenching locks into the crystalline structure stresses, are you saying there steels that you are stable after hardening? I know my tool and die maker friends season their best tooling before finish grinding to try to work out these stresses.

There are far to many variables to have a silver bullet. Reducing the chances is about as good of odds one can expect.

Martensite is transformed from austentite and is more stable for precision tooling. The seasoning process can be induced with large temperature swings over time. The best time to do this transformation is immediately after HT to the critical temp. I can see this as an option for inspection and parts expected to be stable for tight running members.

A grinding vice used on most shop mills that have trouble holding anything better than a half thou may be a bit overkill, but to each his own as the need applies and makes them sleep better at night.

DC

Regardless of the material you use ( steel is steel when it comes to modulus of rigidity), heat treating will ultimately provide you with the wear and toughness properties you want/need.

ANY time you start machining or heating and quenching metal, residual stresses are generated. They will affect you sooner or later.

We deal with carb and hardened 8620 a lot when we make grind billet cams. The stuff, due to the irregular shapes, moves as soon as you touch a grinding wheel to it. We've seen almost 0.005 bend develop in cams when you go from as heat treated to finished grind. Thankfully, the low yield point of the core makes it easy but a pita to straighten. Modulus wise, it is no better or worse than muffler tubing..... However, if you intend to pound on it, the substrate will yield and the surface will crack. Look for a punch/die material if you'r going to pound on the jaws....

We make cams from 8620, CrMo steel and/or various tool steels. The non-8620 stuff requires more sophisticated heat treating but they stay VERY stable once H/T'd, PROVIDING you do it properly.

One VERY critical thing (regardless of steel used) is stress relieving PRIOR to harden and temper. If you simply harden and temper (H/T) the stuff will move around a lot (residual stresses either generated or relieved). If you do hi temp stress relieve followed by harden and draw (usually double) things seem to be a bit more stable - at least that's our experience of late.

My recommendations would be to use a 4140 or 4150 steel for general mechanical construction - relatively cheap and available and either is good for vise construction. First have it annealed and then have it normalized, preferrably in neutral salt bath to avoid decarb BEFORE MACHINING.

Normalizing results in 26-32 Hrc which is pretty tough. Or, you can by PHT (preheat treated) which is Rc 28-32 and machine it as is.

To make it even tougher, hi temp stress relieve after machining at 1200 for 1 hr per inch of material with furnace cool if at all possible. Then harden and double draw subsequently to Hrc 46-48.

The jaws can be made of an appropriate tool steel (O1, O6, whatever) so as to give you whatever properties you need (abrasive wear resistance, siezure resistance, whatever). The key here is to do the 1200 deg stress relieve prior to harden and draw.

Lots of good material (PDF's or .doc's) info on tool and construction steels can be downloaded from Leed Steel and/or Timken.

MOST air harden steels are noted for size and distortion stability because of the quenching medium and the lack of quenching induced distortion. Don't overlook this type of material....

Re: distortion - steel changes size during heat treat (most grow, 8620 shrinks in carb and harden) and size chage varies from steel to steel and temper to temper. YOu need to compensate for this on size/lenght critical applications. Talk to a metallurgist or your heat treater for specific recommendations.

Finally, FIND A GOOD HEAT TREATER. Ask around. Generally guys who do vacuum or salt bath heat treating are a bit more in tune with the latest procedures than a local blacksmith. Some guys do specialize. We called around for nearly 2 weeks before we found a guy who was even willing to do try cams made from tool steel.

HINT: try to find guys who heat treat long broaches. They tend to be a bit keener on keeping parts straight for what should be obvious reasons considering what they specialize in....

Here is an IGES file of the vise that I want to make. It is not quite complete as I have to make the tightening assembly and also some jaws. However could some of you look at it and possibly critique' it. Perhaps some of you could offer opinions also.
I got a quote on A2 steel. For both the main body and jaw it would only be $90 for A2. My Father in law is going to get me some 8620 for free so I am going to stick with that for now. If ,after heat treatment, I find that the 8620 flexes too much under load I will remake the vise out of the stronger A2.
I forgot to mention that I do quite a bit of jig boring also and my tolerances are typically + - .0002 or, even closer. That is why I am being such a stickler on the accuracy of the vise.....
Patrick

Well something having "cast" would help.....Mehanite Castings....followed closely by "aluminum castings"......geesch.....can we get a grip....