contouring aluminum with small bit

[corpse]

I'm trying to machine some aluminum -not sure of the grade as I got a bunch of small cut offs from my bro, it's probably 6061 tho (unless I grabbed some 7075, both is common in his shop, with normal large mills).. I'm using a sherline mill, and for my end mills, some carbide bits that around .050-.100.. My feedrate is very slow - I set it too .5 - and after starting the program, I broke a couple end mills right off the bat.. One of them made it a whoppin .100 before it snapped - and I kept sprayin it with wd-40 to keep it lubed..

Now, I'm sure I've made plenty of mistakes, some of which you'll catch in the above message.. So I guess my question(s) is/are, what am I (probably) doing wrong, or how delicately should I be treating this bits? My plunge depth in the program I set to .050. I *assumed* the .5 feedrate was ok, since in manual mode I just hit the X jog key and it milled in a nice tiny little groove - w/o any fluid.

[Ken_Shea]

What RPM is the Sherline capable of?
Any aluminum build up on the cutting edge?

Chips need flushed away more then the cutter may need lubed on very small bits.

Always use the largest end mill possible.

.050 may be a bit on the heavy side for a .050 and .5 IPM is on the low side.

You are not rapiding (is Rapiding a word ) into the part are you and then starting the .5 IPM feed?

[DAB_Design]

Originally Posted by Ken_Shea Chips need flushed away more then the cutter may need lubed on very small bits.

So true

[corpse]

For flushing the chips away, should I not bother machining with these tiny bits until I can get a proper streaming system? Right now I just have hte machine slapped up on the workbench, no enclosure or anything.. I was planning on building one in the future, but it sounds like I should sooner vs later?

I'm not sure what rpm I'm operating at.. I don't have any solid way of checking, other than operating at full speed.. There's a paper template I can place on the pulley to give me an estimate, but I can't remember where that is available - anyone know?

[Rekd]

Depending on the RPM, you should be able to go at least .02" deep at a pass. I have a 10,000 RPM spindle and only do .035-.050" deep passes with a .093" EM. (That's at 9,000 RPM, at 75 IPM)

If you take light enough cuts, (less than .020", you should be able to run the small bits without coolant, especially if you can get Tialin coated ones)

[corpse]

Originally Posted by Ken_Shea What RPM is the Sherline capable of? Any aluminum build up on the cutting edge? .050 may be a bit on the heavy side for a .050 and .5 IPM is on the low side. You are not rapiding (is Rapiding a word ) into the part are you and then starting the .5 IPM feed?

I'm not moving fast into it - I g00 to my starting position, then g01 after that, set the plunge rate to .5, and move down ~ .045. I guess later 2nite I'll rerun the program but set the Z absolute at .030 over the material, so that'll cut .020. I will also kick the feed rate down a bit, maybe try .3

There is no build up on the cutting edge... If there was, would that indicate the bit is too dull to cut, or rpm too low? (Remember, I'm new to machining AND CNC stuff, so I have LOOOTTTS to learn!)

edited for crappy grammar

[Ken_Shea]

Build up can be a result of dull cutter, chips not being removed and or cutter becoming hot from the previous reasons and welding the chips to the cutter, this is especially true for soft ot untempered aluminum. In your case from what you said it does not seem that it had time to get hot.

Normally it is recommend that you set the top of the part to Z0, it will be much less confusing since you know that any -Z value will be cutting into the part. I am unfamiliar with your CAM or Controller but I would think that both the Rapid depth down toward Z0 and then the plunge to say .050 above the part and then selected feed would all be set within the CAM software. I would double check all these settings. You should try as RekD suggested and take a lighter depth of cut. I doubt the Sherline has the kind of RPM that Rekd has so keep the feed slow say 2.5-3.5 IPM for a little trial and error and increase it from there. You can blow the chips out of the way as well with compressed air. Coolant is messy but it can make a big difference.