Does climb or conventional milling only apply to edges of the work piece?

Do you recommend using 1/4 endmills as the largest endmill I should use for my pm25?


I'm always worried I'll snap thinner endmills like 1/4" ones easier than I would 3/8" or higher.
 
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Pcmaker said:
Do you recommend using 1/4 endmills as the largest endmill I should use for my pm25?
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Depends on the application. Since I do CNC, it is easy to program a 1/4" endmill to cut the radius of a larger endmill. On a manual machine this is much harder. Sometimes it is worthwhile to use the larger tool to do the job correctly.

I was focusing on roughing out material and general cutting for my statements above (based on your comment of slotting). Finish cuts will use higher speeds and slower feeds more focus on finish than the type of chip coming off the tool.

My starting point for this size machine is 1/4" endmills (4F) for steel and 3/8" (3F) for aluminum. Adjust based on experience and needs from there.
 
ThinWoodsman said:
What sort of RPM are we talking? For a half-inch cutter, are you doing 500 RPM or more like 300?
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More like 220 RPMs.

I prefer cutting slow and feeding slow (J-head BP in backgear), but when I do this with conventional milling I end up chipping cutters. Well, chipping the big cutters and breaking the small (1/4 and less) ones when they catch.
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When milling harder stuff (from mild steel and harder), I chipped some good end mills before I realized what was causing the problem.
In my case, I was moving the table at the speed I would end up milling the part--this was chipping the cutter just when the cutter came in contact with the piece being worked. So, I slowly sneak up on the edge until it just scratches the surface, and then "present the tool" to the piece being worked so that I can feel the bending force in the handle being turned, done right you can feel the tool enter and bite into the work, and it is at that point where you can start moving the table at the anticipated speed. I have not lost a tooth or edge since I learned this (1.5 years:: except when I release the tension on the 1" carbide cutter and it fell out of the holder onto the table chipping one corner (grrrrr).)
 
You can run any spindle speed you want for any cutter diameter you want. The thing that matters is the feed rate. Feed rate is easy to dial in if you have a CNC or auto-feed. I'm not sure how you'd do it manually though...for that it has to be based on the looks of the chips coming out (size, color etc). You can literally measure the chips.

Since I hate changing belts (and rarely do) and not having a VFD yet I still have to swap cutters from 1/4" to 1/2" with various flutes I use the following formula to figure out my feed rate:

feed rate=chipload x no. of flutes x RPM

Since 90% of the time my machine is set to 1060 RPM if I'm using a 1/4" 4 flute HSS endmill my feedrate will be:

feed rate = .001 x 4 x 1060 = 4.24 in/min

Chipload varies as well as feed rate calcs depending on side milling or slotting. There are some really good videos on YouTube, I think NYCCNC did a series and it was very well done. I highly recommend it even for manual machines just to get a better understanding of it.
 
The truth is that unless you are doing CNC, you will work off of feel and sound alone. No math.

But... sometimes it is nice to see some real numbers to understand how fast or slow you should be cutting.

Don't let us bog you down with the details!
 
Agreed with @macardoso but don't be scared- the math is super simple. It's just three things you multiply together. This should allow you to be in the ballpark. In my example above 4.24 in/min is roughly 4/60= .06 in/sec you can check if that's what you're roughly feeding by doing one-Mississippi, two-Mississippi, three-Mississippi, four-Mississippi and see if you milled/traveled approx 1/4". Doesn't have to be exact but as long as you're in the ballpark you should be good.

To answer your original question though, in slotting you're doing both climb and conventional so it doesn't matter where you start. This is assuming the slot is the same width as the diameter of the cutter. If you're just enlarging a slot then you're either doing climb or conventional (which is preferred in manual machines, except for the finishing pass). Of course the deeper the slot the more power and rigidity you'll need. Also slotting in alum can be a real pain because alum doesn't evacuate as well so fewer flutes is preferable and better to have aluminum specific endmills since the coating prevents aluminum from welding itself on to the cutter which will eventually break it if you keep feeding. So now you need air/coolant. Oh welcome to machining...we're here to help you (empty your pockets) :D Just kidding...but if you have questions feel free to ask, I don't know a lot but I have experimented and broken enough endmills to offer advice based on my personal experience.
 
stioc said:
Agreed with @macardoso but don't be scared- the math is super simple. It's just three things you multiply together
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Part of the confusion is that chip load is something that you manage with the feed rate (as Mitch mentioned above), so using it to calculate feed rate is a bit circular. I've come across more than a few discussions that provide something like the following:
chip_load = feed_rate / (rpm * num_flutes)
feed_rate = rpm * num_flutes * chip_load
Generally, one knows the number of flutes and the RPM, but that still leaves two variables to solve for. I suppose chip load might buried in Machinery's somewhere (away from shop so cannot check), but what would the general rule of thumb be? DOC * length (.005" cut on a 2" long surface = 0.010)?
 
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