Is this usable in model machining?

[almega]

I bought a box lot of metal at auction and incuded in with a bunch of aluminum and some 1018 CF was this stainless steel. Some of it is 304L and the rest is 316L. The square blocks are 2" square and the round stock is 1-3/8" diameter. I have read good and bad about it and I am not sure I should use it or can effectively machine the stuff. Any comments or suggestions from the forum?

 

[Cogsy]

A quick google suggests those two grades are problematic to machine - even professionals who commonly machine 304 don't like the 304L variant. Having said that, you don't have much to lose by taking a test cut and seeing for yourself.

 

[DJP]

With carbide tipped cutters I have had no problem machining stainless steel. It welds beautifully with low hydrogen rods. When drilling with HSS bits keep the speed slow and apply constant pressure. If the drill bit slips it will generate heat and a hard spot in the metal. Cutting fluids help a lot and I like Chromatap because I have enough for lifetime.

SS stands up to the weather so for marine fittings it is perfect.

 

[Jennifer Edwards]

I love machining stainless steel. I have never had a problem getting a nice finish with any grade.

My trick is to use carbide tooling, plenty of coolant, and take nice deep cuts. I find that really small cuts do not provide the best finish.

 

[vederstein]

The "L" variants of stainless are slightly changed to make them more weldable. One job ago the machine shop worked with a bunch of 316L for creating a certain type of measuring instrument. They machined it (because they had to) but all tooling was carbide with high speeds and low feeds. To this day, I don't know how they managed to thread the stuff without constantly breaking taps.

My experience with stainless is an unhappy one. Although I'm an mechanical engineer, this hobby has me become the defacto machinist at my current employment. I sometimes have to modify parts at me current workplace. If those parts are stainless (usually 304), I always use carbide tools. And because stainless work hardens, drilling in particular can be difficult.

...Ved.

 

[Entropy455]

If you don't need to weld it (ever), get yourself some 303 stainless. It's got sulfur in it, which makes it machine like butter. More specifically, the sulfur keeps the stainless from work-hardening during machining - like 304/304L and 316/316L are so well known for doing. The 303 retains all the strength and corrosion resistance as 304/304L and 316/316L, but again, easy to machine. You can take light cuts with 303.

Unfortunately, 303 will crack if welded. . . .

 

[almega]

What does the "L" designation signify that is the difference between 304 & 304L and 316 & 316L?

 

[Cogsy]

The 'L' designation is low carbon variant for better weld-ability, but this seems to make them even more problematic to machine (from what I understand).

 

[comstock-friend]

As Cogsy says, the 'L' low carbon version minimizes (controls) carbide precipitation after welding for better corrosion resistance, although not much in the literature about the effect on machinability (here is an example: http://www.ssina.com/download_a_file/machining.pdf ). 304/304L and 316/316L are about universally hated for machining (see Practical Machinist forums). Their go to is 303, but you don't have that.

But that's the material you have and it is useful for certain applications, so let Google be your friend for tooling, feeds, speeds, etc. for when you need to use it.

 

[almega]

After all I have read and considering the limitations of my equipment, it may end up as paper weights or counter weights to my front porch Christmas decorations. Thanks all.

 

[Entropy455]

You can machine 304/304L & 316/316L with small and light-duty equipment. You simply must know the limitations of the tooling and the stainless itself. As others have already stated - take heavier cuts (0.010" min per pass, or 0.020" is even better). If you try to skim-cut 0.002", you will quickly discover why people hate stainless.

When drilling holes, drill it fast, and drill it in one continuous plunge. If you try to stop and start the drill mid-hole, it's over. The metal will work-harden like something fierce, and you'll start snapping drill bits.

Again, purchase some 303. It's not that expensive, and it's a pleasure to machine in comparison.

That being said - don't give up on machining 304/304L & 316/316L - until you at least try it.

 

[Wizard69]

Please don’t give up before trying. Stainless can be extremely useful in the right situation. It isnt much different than trying to machine other alloys like 4340 that can work harden in a flash. So some general machining suggestions:

1. Cut your feet per minute by half vs what you would for mild steel. Frankly I do this by feel a lot of times, I don’t suggest this in most cases. At work anyways I only work on a small range of materials.

2. Keep you feed rates somewhat aggressive. The absolute worse thing you can have happen is to have the tool rub, once that happens you have trouble. What is even worse is that once people create hard spots they tend to try to correct by decreasing feed instead of increasing feed.

3. Coolant /lube is a good idea for managing thermals but you can’t count on it to prevent work hardening. Work hardening is directly related to low feeds / rubbing.

4. Carbide isn’t the panacea that many think it is. I’ve had work hardening in 4340 with new carbide. Again it is all about feed rate. An example here; when facing that slug of 4340 I got some significance can’t work hardening that created the most radical noise. Simply increasing feed rate solved the problem. The first pass with the increased feed rate still had issues through the work hardened areas basically cutting out the hard stuff. The second pass resulted in a nice finish. Now stainless and 4340 machine differently but the work hardening is very similar.

In case you are wondering my theory here is that the cutting action in these materials hardens the material with each pass of the cutting edge. The high feed rates are designed to make sure the cutting edge gets under that hard surface. By high feed rates I mean fast enough to get under that work hardened surface. This will vary some with materials

On low power machines you have options to deal with limited power and rigidity. For example step drill instead of trying to force a large cutter through. At larger sizes boring operations may be a better use of available power. For turning operations use positive rake tools.

After all I have read and considering the limitations of my equipment, it may end up as paper weights or counter weights to my front porch Christmas decorations. Thanks all.

Well if you really don’t want to make use of this windfall, you could send the materials my way

 

[Jennifer Edwards]

I have to agree with what you are saying. I have found that SS, especially the 400 and 500 series of alloys, produce a better finish with aggressive feeds and depth of cut.

For best results I take as deep a cut as I can, slow down my revs, increase the feed, and use plenty of coolant if you have that available.

Taking too light a finish cut can cause problems, it is better to try and have your last pass be a medium depth cut.

 

[Glorfindel]

Machinery hand book is your friend.