Cutting Stainless

[tuxlab]

I have taken a few cnc classes at the local community colleges but I am not a machinist. I am thinking of doing a demo day to kick off a project based hackerspace and I want to make some simple bottle openers to give away.

I will cut the opener from 1/8" x 1/2" x 4" stainless steel stock, 303 or 304 or 316. . . whatever is the cheapest I can find.

I have drawn the part and am now looking at endmills. I am looking at maritool and I noticed they classify the non-aluminum endmills as finishers and roughers. The roughers are quite a bit more than the finishers.

The questions I have are,

1. Is there any advantage to using roughers and is there a good rule of thumb on when to use roughers vs finishers? Because I notice for aluminum some of the 3 flute endmills can remove more material faster than traditional corn cob roughers.

2. Is leaving just .05" of "margin" too ambitious, should I shrink the design a little to accommodate for variations in the stock material?

Thanks,

tux

[Perfect Circle]

This should get you going in the right direction...sorry I do not have that much time today to go into full detail about all the do's and dont's of machining stainless...Good Luck!

http://www.stanford.edu/group/prl/do...pdf/millss.pdf

[ToyMaker94566]

303 is the most forgiving of the three, I would go with that if given the choice. A hog/roughing endmill is not necessary in this case because your material is only an 1/8 thick. Just get yourself a stub length Carbide 4 flute endmill and you should be able to crank out a couple hundred with good repeatability. I'm just wondering how you plan on holding the part while you machine all 360 deg of surface? You're gonna need some fixturing with that design.

[Matt@RFR]

I agree with using 303 if at all possible. It won't give you that super shiny finish like 304 or 316, but you'll be done with the parts a lot faster and you'll put the endmill you used back in the drawer for another day. I also agree on using a stub flute endmill with 4 flutes and a corner radius. Looks like a 1/4" endmill will fit?

STUB LENGTH, CORNER RADIUS, VARIABLE FLUTE END MILL FOR STEEL

With that endmill in 303, I'd take the outside profile in one pass at full depth (plus corner radius) at 7640 RPM and 55 IPM. Coolant works well at that speed.

Same for the pocket but ramp in at 5350 RPM and 21 IPM with a 4º ramp angle.

As far as fixturing, you don't mention quantity, but if it's around 100 or less, or you'll never make the parts again, I think I'd just clamp them in a vice on parallels, drill the holes, cut the pocket, then bolt to a little fixture using a top cap of aluminum. Use an island that is slightly undersized, but the same shape as the pocket in the part for location. Piece of cake.

[tuxlab]

For fixturing I am thinking of a three step process. The inside of the bottle opener are pocked from both side to ~1/3 of the total thickness

Op 1 - Face mill, pocket and drill the two holes
Op 2 - Face mill, pocket
Op 3 - clamp down part using the two hole and profile the outside contour.

I ended up with 304 because it's quite a bit cheaper than 303 and I am also thinking about adding an extra pass to chamfer the edges.

If I want to engrave on the part, what type of endmill should I use?

thanks,

[ToyMaker94566]

Personally, I would have made them 3/8 thick and much smaller. Small enough to fit on a key chain. Then you can use 1/2 x 3/4 x 3" stock in two steps.

Op1: hold in a vise about 1/8 deep, deck it, profile and chamfer complete.

Op2 or next vice: flip over holding part in a pocket, deck it and chamfer edges... Done!

You may have saved a couple of bucks on metal but you're gonna burn thru tooling now; 304 is not your friend.

[tuxlab]

I didn't know 304s are that hard on the tools. . . . ouch. . . lesson learned.

Going with 3/8" thick will definitely save some time. . . ouch . . another lesson learned.

btw, what's the minimum thickness needed to hold a part securely in a vise pocket for steel and aluminum?

[jvangelder]

Originally Posted by Matt@RFR With that endmill in 303, I'd take the outside profile in one pass at full depth (plus corner radius) at 7640 RPM and 55 IPM. Coolant works well at that speed. Same for the pocket but ramp in at 5350 RPM and 21 IPM with a 4º ramp angle.

Just out of curiosity, are these numbers you use or ones out of a calculator? Ive run about 4k lbs of 304 SS in the last 2 months and my sfm is less than half what your reccomending. My numbers started at mfg reccomendations and are tweaked for tool life. Is there really that much of a difference between 303 and 304?

-Jacob

[gizmo_454]

Minimum thick to hold something securely in a vise is all relative. If you are going to grab a 2" mill and hog on something, you'd better be holding on to something substantial! If you have a 1/4" or 1/8" mill, you sure won't have to hold anywhere near as much. I have gotten away with holding about 0.060" of the bottom before with a similar application to what you are doing. That's not to say that is the least you can hold on to. That was just all I was willing to try. I really don't like the idea of things flying through the window!

Good luck!

Mike

[Matt@RFR]

Originally Posted by jvangelder Just out of curiosity, are these numbers you use or ones out of a calculator? Ive run about 4k lbs of 304 SS in the last 2 months and my sfm is less than half what your reccomending. My numbers started at mfg reccomendations and are tweaked for tool life. Is there really that much of a difference between 303 and 304?

Yes and yes.

[Jhil66-3]

Originally Posted by jvangelder Just out of curiosity, are these numbers you use or ones out of a calculator? Ive run about 4k lbs of 304 SS in the last 2 months and my sfm is less than half what your reccomending. My numbers started at mfg reccomendations and are tweaked for tool life. Is there really that much of a difference between 303 and 304? -Jacob

Yes 303 and 304 are night and day. Sfm between the two Is very different

[Machineit]

For machinability on a scale of 0 to 100, 304 is rated at about a 42. Regular 303 is about 73, and 303 Se is rated in the mid 80s. Like all have said, it's night and day. 303 is slightly more expensive, but well worth it in the end to save tools and time.

Type 303 Austenitic Stainless Steel: Excellent machining characteristics. Free machining version of Types 302 and 304 is used for parts requiring extensive machining. Sulpher added to make it 303.

Type 303 Se: Basically same as 303 Obtains free-machining characteristics by the addition of selenium rather than sulfur. Selenium produces better surface finish Selenium improves formability and weldability.

I use 303 whenever possible.

Mike