Speeds for 1095 steel and a carbide end mill?

[EOsteam]

I'm reducing the widths of some 1095 spring steel leafs from 1" to .875". The leaves are .062" thick. Anyone have any ideas for the proper RPM to set on the machine. The end mill is 0.5" in diameter. I already munched one carbide end mill and those things are expensive! The Little Machine Shop calculator recommends 1150 rpm. I'm going to try some soluble cutting oil sprayed on the cutter tomorrow when it gets here to see if heat is one of the reasons the first cutter died so quickly.

HJ

[GlennW]

Angle of engagement is a factor.

You don't want the cutting edges of the flutes contacting the part at 90 degrees as they will soon chip from hammering.

The cutter should engage the work in a more tangent manner.

[Steggy]

Further to Glenn's advice, in the past when I had to do something like this I set the mill's head at 45 degrees to soften the engagement of each cutting face to the work. Use lots of cutting fluid. The recommended 1150 RPM seems much too high for this sort of work.

[EOsteam]

Is a 30 degree angle enough? Also, is it a dumb idea to clamp several leafs together and mill concurrently?

HJ

[Russ Hanscom]

I think you will get better results when you stack multiple pieces; a longer cutter path makes for smoother cutting and only the last piece will have a big burr.

[SteveHGraham]

Leaf spring steel is really nasty.

Amusing story: when I got my mill, a buddy of mine was in town for a visit. On the way down, he spotted a piece of leaf spring on the shoulder and grabbed it, thinking it would be a funny present for me to turn into my first machining project. Knowing even less about machining than I know now, I put it in the vise, squirted it with oil, and watched the mill glide over it without doing much of anything to it.

How about annealing it? I saw someone on a forum recommending that.

[spro]

That leaf was a grief. Even drilling through them before the newer tools, there was spot softening . I struggled with stuff like that, spinning hardwood dowels to relieve the temper in one spot. I turned some unknown steel to create the same heat for a bolt hole could actually be drilled. Tough stuff for an end mill.

[Russ Hanscom]

A carbide mill has no problem with a leaf spring, properly used, I have turned a few broken leaf springs into wedges, because I need a couple of wedges for setup purposes and a broken spring was handy.

[EOsteam]

Here are the followup results from my original question. As stated 0.062" thick leafs of 1095 spring steel were to be machined from 1" wide to 7/8" wide. The leafs varied from 4.75" to 7.25" in length. There will be 8 sets of springs so all leafs of the same length were grouped together. 4 leafs at a time were machined while held in a Kurt vise. The depth of cut was 0.0625". Any overhang was moved so as be be held between the jaws of the vise when machined.

The first try involved a brand new 1/2" Atrax uncoated carbide end mill with cutting oil very liberally applied via an aerosol can. In the picture below the uncoated carbide end mill is the middle one. There was an incredible amount of heat and after 21" of machining a .25" wide stack of leafs, two of the edges of the end mill chipped. You will note the coked oil on the carbide end mill.

Next, I tried a 1/2" TIN coated HSS end mill from China with cutting oil as well. It wouldn't cut at all. In fact it seemed to rub more than cut. That end mill is the one on the right. The RPM was set at 250. The 1095 killed it almost immediately.

After experiencing little success and seeing the coked oil on both end mills, an Atrax 1/2" AITIN coated carbide end mill was ordered from MSC along with some True Tap Aqua cutting fluid. The True Tap aqua was loaded in a spray bottle and used liberally as the machining progressed. The RPM was set at 850 and the travel of the table was adjusted to keep the chips at a light straw color. The end mill cut all remaining 64 inches of 1095 spring steel and still looks pretty good except for maybe the very tips of the flutes. That end mill is the one on the left. While my results are not scientific, my belief is that the heat was what destroyed the original carbide end mill. The end mill and the workpieces remained very cool to the touch throughout the procedure.

AITIN Coated Carbide End mill on the left, Uncoated carbide in the middle and TIN coated HSS on the right

Finish surfaces of the 1095 spring leafs after the AITIN coated end mill w/ True Tap Aqua as a coolant and lubricant

I'm very likely going to use soluble oil more often as a coolant after seeing the difference in the end mills except when I have a high pressure need for the oil. Also, 1095 machines with thousands of little shards which just can't wait to give you a metal sliver. I had to wear some thick rubber gloves when working and cleaning up. After cleanup the mill table and all relevant surfaces were wiped down with a light coat of Vactra #2.

Lastly, I have no affiliation with either MSC, Atrax or CRC and have received no consideration in any form from any of the companies mentioned. This is just an attempt to show a problem and what was done in order to experience success. It is certainly not scientific. I hope somebody else will benefit from my approach.

Good fortunes!

HJ

[Glenn Brooks]

HJ,

Success!! Good info to know. Thanks for posting. How did you mount the springs? Standing on edge or laying flat on top of each other?

And did you cut with the end of the end mill, or the long edge? iam guessing cutting with the end of the mill would create more heat on the tips in your initial process?

Thanks
Glenn

[EOsteam]

The leafs were held 4 at a time in a set of 3/4" deep "Snap Jaws" in the Kurt vise. They were milled down the long axis of the leafs using the end of the end mill.

If I had another uncoated carbide end mill, it would have been nice to try it with the CRC True Tap Aqua cutting fluid just to see if the AITIN coating on the mill that worked so well had made much difference in the longevity.

HJ