Machinable Stainless for Car Trim

[ACHiPo]

I need to make a few brackets to support a luggage rack for a sports car and am looking for a material recommendation. These parts are typically chrome plated, but I'm thinking that stainless would be a better choice due to the cost of plating a small number of parts.

For machinability 416 seems to be a good choice. It has lower corrosion resistance than martensitic stainless alloys, but I think it should be adequate given this car will rarely if ever be exposed to rain or moisture.

Are there other alloys I should consider?

What recommendations do you have for machining success? I'm thinking heavy cuts and sharp HSS tools?

 

[Robert LaLonde]

416L has a little better machinability than 416.

I would note if you want to push corrosion resistance there is a 316L also. Its not as nice to machine as 416L, but it is more machinable than regular 316.

Both like heavier cuts on rigid powerful machines.

An alternative might be anodized aluminum. I'd have to look up its ability to be anodized well, but 7075 is stronger than some steels. Anodizing and color anodizing can be done in a home shop if you really want to. I would also comment that if not abused and scratched up the natural oxidization on 7075 that has been nicely machined is quite pleasing to look at. 7075 is a dream to machine, but for practical purposes is not weldable. (There are some esoteric methods, but not in most shops.)

Another alternative is powder coating. Its not as difficult as some folks would have you believe. I powder coat small items with a heat gun, loose powder, and a toaster oven.

 

[benmychree]

The most machinable stainless that I have machined is 303, call it "screw machine stainless" it is not a lot less machinable than cold rolled steel, you just have to run a bit lower cutting speed; it does not work harden.

 

[Robert LaLonde]

The most machinable stainless that I have machined is 303, call it "screw machine stainless" it is not a lot less machinable than cold rolled steel, you just have to run a bit lower cutting speed; it does not work harden.

It doesn't work harden "as readily." If you take rubbing cuts, and don't cut through the hardened layer it can work harden. Generally though as long as you're always "cutting" when engaged any work hardening is very minor. Almost negligible.

 

[benmychree]

I have machined probably thousands of pounds of 303, and have never had the least problem with work hardening.

 

[Robert LaLonde]

I have machined probably thousands of pounds of 303, and have never had the least problem with work hardening, but maybe that is just me???

Saying 303 doesn't work harden as an absolute statement of 100% pure indisputable fact is like saying the same about the non-weldability of 7075 aluminum. It is not an absolute. Its just a majority.

 

[benmychree]

"They" also say that 303 is not recommended for welding; nearly all of our shop products over 45 years were made of 303; we never had a weld crack or failure of anything we sold to the winemaking trade, those products were our main source of income, we never had a single claim for damages resulting from the use of any of our products. We bought a lot of sanitary fittings to be welded on to tube, etc; in later years, when thy began to be imported from "offshore" suppliers, they too were obviously 303 instead of 304, one little cut taken on them showed that, still no problems; could I admit that there "may" be some tendency to work harden in some tiny measure? Perhaps, but not to my eye or experience; tiny finish cuts can be taken with out any work hardening effect, and allowing the tool to dwell in one spot has never caused a problem in that area fro me.

 

[ACHiPo]

Both like heavier cuts on rigid powerful machines.

I'm not sure how deep a cut I can take on my Logan, but hopefully deep enough. I should be fine with my mill.

I have machined probably thousands of pounds of 303, and have never had the least problem with work hardening, but maybe that is just me???

I like the idea of 303.

 

[projectnut]

The food company I worked for made the majority of it's own processing and packaging machinery. This machinery was subjected to nightly wash downs with caustic chemicals and 140* degree water. By in large the majority of the equipment was built from 316 stainless. Once you get used to machining it you don't think twice. The only problem we had were weldments. 316 doesn't hold dimensionally as well as we liked. In some cases we would leave the parts slightly oversized and machine to tolerance after the welding was completed. Some of the better welders could get just enough heat into the weld to minimize warping and eliminate the need for a final machining.

In our case the USDA required continuous welds between mating surfaces to eliminate places for bacteria to hide. It took some serious skill to continuously weld a 6' section elegantly enough to make the USDA inspector happy, while on the other hand keeping it water tight and yet leaving enough material that the seam could be finish machined if necessary. In many cases I would swear it looked like the welding had been done by a jeweler. Very Impressive.

 

[Robert LaLonde]

This is an ag community here. A couple different local fab shops are busy year around with various ag and ag products processing equipment. 304 seems to be the stainless of choice for most things with a little 316 thrown in here and there just to make things interesting. Atleast that's what my favorite local metal vendor stocks the most of. I found out about 316L because the accidentally gave me some by mistake when I ordered 416L.