The Armour Archive

Greetings all,

I have a question about Surface Feet per Minute calculations for cutting different types of metal.

I found this chart which lists the correct SFPM for drilling and end milling different types of metal. But what I’d like to find is a chart just like this one, but listing SFPM for cutting or slotting, not drilling or milling. Or is cutting similar enough to milling to use the milling numbers?

Specifically, I’d like to rig a jeweler’s saw to cut chainmail links using these jeweler’s blades and arbor. I know they’ll burn up if the SFPM calculations are wrong for what I’m cutting, so that’s why I need the chart.

Thanks!
Deacon

PS: Another question - is this even a good idea? Is this dangerous or ill-advised in any way?

What material are you cutting? I can give you the recommended sfpm from Machinery's Handbook. What size slitting saw are you going to use? The formula (which I think you have) is : (sfpm X 12) / (Pi X Diameter) Of the cutting tool in inches.

Gargoyle,

I'm not really sure what material I'll be cutting just yet...probably a few different types.

From that chart I found, the ones that I'll be most interested in are:
Aluminum
Brass & Bronze
Cast & Malleable Iron
Soft Steel to 40 Rc
Medium Hard Steel 40 to 50 Rc
Hard Steel 50 Rc and up
Titanium Alloys

It just depends on what I can scrounge at this point. I'm sure that what I can find will be covered by that list.

Blade size I'm looking at will probably be 1.5 inches, but I might change that if the sfpm needed and the rpm of my drill press make it unworkable.

Thanks!
Deacon

Some of these things are just better done by feel than great calculations. You are dealing with small diameter objects and simple machinery. Don't try to make life more difficult than necessary. Steels and other tough materials require slower cutting speeds, finer tooth blades, and slower feed rates. Non-ferous (aluminum, brass, copper) require somewhat higher cutting speeds, fewer teeth, and can be fed a little faster. Let your "armourers" touch be your guide. If you shoot the whole rig off the drill press, your pushing it too hard. A little cutting oil (not 3 in 1 or motor oil) wouldn't hurt either. Let me know if you have other questions.

Heh...that's my problem, I don't really have an armorer's touch yet. I was hoping math could be a substitute

Yeah you're probably right - I should just slap this thing together and see what happens...the blades are only a few bucks a piece anyways. Thanks for the rule-of-thumb about speed and feed rate. I'll take it to heart when I fire this thing up.

Thanks,
Deacon

Aluminum will be the fastest at 800 (for 6061) copper alloys are next at 150-250 depending on hardness. Malleable Iron is 165 (though I'm not sure how easily you will wind it without breaking it.) Mild steel (1018) is about 55sfpm. 40-50Rc is 30-40 sfpm (Let me know how you wind it, 50Rc is spring steel ) Anything over 50Rc needs carbide according to the book I used, Machining Data Handbook, Metcut Research Associates. Titanium is 20-35 depending on hardness. Let us know how it works out. I've thought about doing that too.

Are you using a drill press or a vertical milling machine? Feed rates are pretty difficult to control unless you have a machine with an automated table or spindle feed.

If you have a generic drill press, you may have difficulty slowing it down to an acceptable spindle speed. A metal working drill press should be capable of spindle speeds under 250 RPM and hopefully slower. A typical problem is guys have a woodworking based drill press which has few and high spindle speeds. Ok for drilling small diameter holes in metals but too fast for larger 3/8 to 1/2" leading to burned up drill bits and chatter. Slitting saws will suffer the same demise.

Be cool, go slow and the material will "talk" back to you. If it feels like work, you're probably not set up right. If it cuts well with little effort, you're ok.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR><font face="Verdana, Arial" size="2">Originally posted by gargoyle:
(Let me know how you wind it, 50Rc is spring steel ) </font><HR></BLOCKQUOTE>

I'm not gonna wind it! I'm going to travel to every junkyard in Ohio, snag a bunch of springs from old Fords and knit Godzilla a coif

Seriously - thanks for the numbers. They help a lot. And you learn something new every day...50rc=spring steel. Sheesh.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR><font face="Verdana, Arial" size="2">Originally posted by robertcorbett1:
If you have a generic drill press, you may have difficulty slowing it down to an acceptable spindle speed. A metal working drill press should be capable of spindle speeds under 250 RPM and hopefully slower.</font><HR></BLOCKQUOTE>

Yup - it'll be a drill press, and I haven't bought it yet. I'm looking around and finding that's the case...most presses don't want to go below about 550rpm - that'll smoke the blades pretty quick I'd imagine.

I'm also considering building something "custom"...snag a 1/2 hp motor from somewhere and belt it to reduce the rpm. Dunno yet.

Thanks,
Deacon

"Rc" is a reference to hardness, based on the Rockwell "C" scale. The higher the number, the harder the steel. The cutting tools you will use (slitting saws) are probably rated in excess of 60 Rc. Don't be confused by the "Rc" number as a designation of alloy or carbon content.

You possibly, through Grainger Industrial Supplies (or the like) find cluster pulleys that would replace and re-gear the drill press you buy. Otherwise, search the local papers for machine shop sales/metal working tool sales or guys cleaning out their garage.

A true "barbaric" but totally functional option is a Dremel with abrasive cut off discs (very thin). You'll use alot and it will be labor intensive but it may get you going more rapidly.

Good luck!