POTD- PROJECT OF THE DAY: What Did You Make In Your Shop Today?

[Inferno]

First-order rate reactions are always limited by temperature if all reactants are available in excess. Whether degreasing, performing electrolytic derusting, or eating away an iron-based tool with alum, temperature will make the difference between a slow reaction and an aggressive reaction. Same goes for injuries from chemicals. Always consider temperature when using the chemical cookbook. The solubility of alum doubles in the interval between 50C and 80C, for example. That's why you ended up with gemstones when the solution cooled! Also consider that alum eats chromium the same way it eats iron, so this process will work with 300 series stainless, but not 400 series.

Is that why the spoon I was using shows no sign that it was in the Alum mix?

 

[pontiac428]

Is that why the spoon I was using shows no sign that it was in the Alum mix?

Indeed! Flatware and most kitchen stainless is 300 series for corrosion resistance and passivity. It's formable and weldable, but if you need high dimensional strength, you gotta add chrome and moly to the mix. When you sandwich each iron atom between two nickels in the matrix, it's a lot tougher to access those irons, especially with a bulky molecule like potassium-aluminum disulfate dodecahydrate.

 

[dkemppai]

Indeed! Flatware and most kitchen stainless is 300 series for corrosion resistance and passivity. It's formable and weldable, but if you need high dimensional strength, you gotta add chrome and moly to the mix. When you sandwich each iron atom between two nickels in the matrix, it's a lot tougher to access those irons, especially with a bulky molecule like potassium-aluminum disulfate dodecahydrate.

I always thought that most 300 series stainless corrosion resistant due to the chrome content. In 304 for example, there's more chrome than nickel.
You seem to be more on top of your metallurgy/chemistry than I am... (Most of my playing with stainless comes from martensitic (400 series) steels.)

I've also wondered how high nickel alloys like Invar 36 rate for corrosion resistance compared to 300 series? Invar is obviously made for the 'invariant' properties, but I always sort of guessed that corrosion resistance would 'come a long for the ride'. But as it lacks chrome, does it also lack formation of that passivization layer?

 

[dkemppai]

Dogs are fun. Unfortunately, had to put my buddy down a little while ago. These are photos from the last good ride we took in Mid February. This was her absolute favorite chair, ever! Period! No questions asked! Winter or summer, if this thing was out of the garage, she was on it. In the end she couldn't jump up any more, so had to be lifted up, with bad hips and arthritis. But even then it was still her favorite place to be.

They're all one of a kind. She was a special one of a kind!


Decided to actually try to finish a started project. Picked up that arbor press a little bit ago, and ordered a chunk of rack with the right pitch pre-milled into it. Turned out to be almost the same cost as a 1018 blank from mcmaster, but having teeth already milled was a no-brainier. The problem was it was 1.5" sq, and the needed rack is 1.25" square.

After a half a day of messing around in the shop, milled it flat and ground it to about 0.0015" under the nominal groove width. The original was about 25 thou undersized, so this one will be a lot tighter. I'm going to make new gibs from bronze, but they may not even be needed with the new rack fitting so tight. The slot milled in the housing is really nice in clean, looks ground almost. The cover, not so much. I'll probably dust that one flat in the mill and/or surface grinder before fitting the gib.




Sadly, one little 1/4" carbide end mill gave it's life in the processing of saving this old arbor press. You did good little end mill, you did good!

This was a previously used carbide, and it ran a lot of chips out at 9K RPM. Didn't really feel like hogging it all out with a bigger (=more expensive) end mill, so let this little thing chew on it in the CNC. It took a little more than 2.5lbs of steel off. Pretty good life, for the cheapest carbide Enco sold.



And, finally my wife's nemesis, Ebay struck again. Been looking for something like this for a long time now. Finally spotted one that looked good enough to jump on. Other than a few very minor 'tool box' marks (and a light scotch brite of the R-8, it's very clean. No signs of crashing, etc. Been having a hard time justifying one, and didn't dare go the import Chinese route. This used one looked like a good compromise. I think the modern criterion equivalent is about $600 new. I'm WAAAAAY too cheap for that to happen!

 

[pontiac428]

In 300 series alloys, the chromium is beset on all sides by nickel. Metals form crystalline structures and allotropes with their alloying components, that is the basis of metallurgy. 400 series has a much lower proportion of nickel, leaving chrome vulnerable. Without nickel to buffer it, chromium will get a hard-coat oxide on contact with air like aluminum does.

All of the super alloys that are common are nickel dominant. They are all "stainless" and don't change much with heat. Similar to tool steels, but instead of iron and carbon it's non hardenable nickel. The alloying elements Cr and Mo are added to change the properties of the material to suit the use.

When you substitute iron with cobalt and alloy it with tungsten, nickel, chromium, and molybdenum, you get cobalt steel. It's called steel, even though there are no iron atoms in it, because cobalt is surrogate for iron in the structure. The nickel super alloys are like that too, except nickel fully replaces the iron. Iron content in these alloys is very small, from fractions to one or two whole number percentages.

 

[vtcnc]

In 300 series alloys, the chromium is beset on all sides by nickel. Metals form crystalline structures and allotropes with their alloying components, that is the basis of metallurgy. 400 series has a much lower proportion of nickel, leaving chrome vulnerable. Without nickel to buffer it, chromium will get a hard-coat oxide on contact with air like aluminum does.

All of the super alloys that are common are nickel dominant. They are all "stainless" and don't change much with heat. Similar to tool steels, but instead of iron and carbon it's non hardenable nickel. The alloying elements Cr and Mo are added to change the properties of the material to suit the use.

When you substitute iron with cobalt and alloy it with tungsten, nickel, chromium, and molybdenum, you get cobalt steel. It's called steel, even though there are no iron atoms in it, because cobalt is surrogate for iron in the structure. The nickel super alloys are like that too, except nickel fully replaces the iron. Iron content in these alloys is very small, from fractions to one or two whole number percentages.

Once again you add a level of science to the forum that I very much appreciate. Thank you.

To add a little bit more to the stainless information pool....300 series is more corrosion resistant than 400 in its "as-used" state. And I'm saying that from the user perspective not necessarily the engineer's perspective, although engineering explains why. Since 400 develops a chromium oxide layer (its passive layer) to be "as resistant" to 300 series, you have to avoid abusing it. 400 series will develop a passive chromium oxide layer just by letting it lay around, clean, dry and untouched for a couple of days. However, you can speed up the process by passivating the surface after cleaning with a nitric or citric acid and then a hot rinse and dry. The nickel content is really what sets 300 series apart from 400 and can take a lot more abuse for this reason and appear to be more corrosion resistant in abusive conditions. But 400 can be as corrosion resistant with little abuse in the right conditions. This is why cleaning and passivating is so important with 400 series fabrication after cutting, forming, welding, grinding, graining, etc. If you don't do the proper cleaning, occlusions will get trapped or mask the passive layer from properly forming.

Incidentally, because 400 series looks good, performs well at a basic level, and doesn't require surface coatings, its one of the reasons it is so prevalent in kitchen equipment fabrication. Most refrigerators and toasters aren't seeing abuse like something would outside, so 400 series tends to be used for visually aesthetic applications where corrosion resistance and strength are desired. Pound for pound, I've heard that 400 series uses nearly 5x the energy cost to produce than 300 series but because of its prevalence in product design the sheer volume of production makes it often more affordable than 300, whose cost is driven more by nickel ore prices.

 

[MrCrankyface]

To considerably lower the level of the discussion.
I think I might have the only K&T 2hl with a 32k RPM spindle.
(highly temporary setup for a rush-job)

 

[mattthemuppet2]

Well I finally finished that dang countershaft pulley. It's not as good as I had hoped, some of the grooves rough, little bit of runout and the low speed sheave is a little tight, but it's good enough

Very happy to not have to do this again for awhile

Low speed at around 25% motor speed

Middle speed at same setting

High speed at same setting

Onto the next project, a riser block for my 6x26 mill

 

[woodchucker]

Well I finally finished that dang countershaft pulley. It's not as good as I had hoped, some of the grooves rough, little bit of runout and the low speed sheave is a little tight, but it's good enough

Very happy to not have to do this again for awhile
View attachment 445841
Low speed at around 25% motor speed
View attachment 445842
Middle speed at same setting
View attachment 445843
High speed at same setting
View attachment 445844
Onto the next project, a riser block for my 6x26 mill

nice tensioner you built there. can you file the sheave to eliminate the rough and sharp edges. It'll save your belt if you can make it nice and smooth.

 

[mattthemuppet2]

Thanks! I've knocked the edges down with a file, but I'm leaving the flanks of the Vs alone as I don't want to mess around with the angle or groove spacing. The problem was some tearing due to tool dig in, so there's not really material sticking out, it just looks crap