Worn out bits

[Kenny_BTFP]

I'm putting my ShopBot Alpha through the ringer right now. I'm cutting aluminum bar and have been running into some issues. The bar stock is 1/2" and 5/8" thick, and im cutting holes into it and trimming the edges to size. I have my feed rates and tool choices down, and am getting great cuts out of them. But there a few things im having trouble with. 1) Keeping my bits cool, and 2) how quickly they wear out. My cut file has several different cuts in it that require different tools, so each cutter is getting a break. However, each cutting tool is running for 30-40min straight before that part of the cut file is done and ready to move onto the next. I'm noticing that my bits aren't lasting much longer than a day in some cases, two days in others. I'm wondering if there are any suggestions to help prolong the life of the bit. I am using a cold air gun with two outlets on the bit/ material. and I have set the material size larger than the actual material so that before each new cut the bit has some time to cool down a little. An example is: im using a 65-025 bit (single O-flute Upcut) to trim down the edges of one piece and later cut small holes into another. This bit lasts me about 2, sometimes 3 days before its done, but each cut it runs is going through 5/8" of aluminum and taking 40 min each time.

Someone suggested programing in steps between each new cut to have the bit dip into a cup of lubricant or water to cool it down, but due to the amount of time it takes to cut each thing im not sure that will help, plus im using the cold air gun. I am under a time crunch to complete these cut outs and assemble the pieces.

[bleeth]

For aluminum that heavy you may be better off with a different end mill. There is a whole lot of information needed to give anything like an accurate response to your question. Feeds, speeds, depth of cut per pass, what does "2, sometimes 3 days" really mean in terms of actual hours cutting material with the bit? Are you ramping in? What's your plunge speed? What type of aluminum?
Answer all of the above to the best of your ability and some of the aluminum experts (maybe even the guy from Jersey) can get you dialed in.
Remember that a Bot is not a mill and heavy regular use on aluminum of that type is not what it is built for.

[blackhawk]

Kenny - Have you tried any TIN or TICN coated cutters? I have seen these coatings more than double the life of the cutter in certain situations.

It is messy, but you can use a coolant mist to help cool the bits. MSC or McMater sells these units. A popular brand is Kool-Mist.

[Kenny_BTFP]

The aluminum is 6061. My feed rates are .1 in/sec. My plunge rates are between .05 and .1 in/sec (depending on the size of the bit and the cut its doing. Im ramping all of my bits (which since i added the ramps has prolonged the life and made the cuts nicer.) On my line cuts im using a zig zag ramp and i have it ramping the entire length of the cut with the depth per pass set to .18in so that the bit is never cutting more than .09in at any one time. On the holes im cutting im using a spiral ramp and the bit is spiraling all the way to the bottom. The smaller bits are set to a .05 feed and .05 ramp for the holes. Again this has already proven helpful. I started using a two flute end mill (onsrud 40-103/ 40-133) but noticed that caused rough edges. I have since moved to the O-flute up cuts which have drastically increased the smoothness of the cut. For the holes i am using bits that are around half the diameter of the hole being cut so that there is plenty of space for chip removal plus there is not material left in the center of the hole. The hole cuts cause most of the issue of heat. where as the line cuts tend to stay fairly cool (room temp). 1 day of cutting is 18 hours. which is more work on the machine than it is on the bits. Each bit runs for about 40 min before it is swapped to a different bit for a new cut and then isnt used again for about 3-4 hours. In all each bit does about 1:30-2:30 hours in cutting a day. My O-flutes are lasting the longest, so far i have a 1/4" o-flute that has gone for 3 days and is still cutting nice.

[garyb]

Kenny, due to what you have described so far I would recommend you move to the Onsrud production tools, you will find them in the Milling tool catalog.
I would recommend the AMC700756 for uncoated and AMC700757 for the ZRN coated tools.
these are a 2 flute 1/4 dia 1/4 shank 3/4"LOC 2"oal with 0.015 corner radius
you can also take them square or with a 0.03, 0.060 or 0.090 corner radius
these are a production tool design for aerospace and before you panic the uncoated tool is $31.05 the coated is $36.55
Gary