Preferred milling axis and selecting end mill diameter

C

Clunker1

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Beginning to use a newly acquired manual mill (Gorton 8). First project is t-nuts. As a newbie, I have a couple of questions. First, what is the preferred milling direction. Is it best to mill on y axis (perpendicular to vise jaws) or on x axis (parallel to vise jaws)? Second, how do you decide what diameter end mill to use?
Thanks
 
Some operations require Y direction travel, but mostly X is used. You can use any endmill you like from say, 1/4" up to 1/2" and beyond.
Larger endmills tend to get expensive quickly. When surfacing a larger area you can use a flycutter instead of mowing back and forth with an endmill. Personally I use 3/8" sizes fairly often, both 2 flute and 4 flute. I even have some 3s. 2 flute cutters clear chips better, 4s give better finish.
When cutting slots you usually don't cut to size in one operation as it tends to leave a very rough finish from chips being pulled back into the
cutting area/zone. In those cases use a cutter a bit smaller than the desired slot width and do several passes.
Aluminum can often be cut dry, but for steel you should use some type of cutting fluid.
-M
ps Gortons are good machines, I wouldn't mind having one if I had the space for it
 
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For the tool size, I like to use the largest that will fit. They are more durable and less likely to deflect. For t-nuts, there is no real size constraint, so whatever you have should work fine. I only use smaller end mills when I'm in a pocket or slot and need the smaller size to fit.

Direction doesn't really matter. The forces are the same. It usually has more to do with workholding than anything else. Try to hold as much of the work as you can. For t-nuts, I like to use X as my vise is mounted with the jaws parallel to X and it lets me hold the long side of a bar. I generally try to limit the length to about the jaw length to ensure there isn't an end flopping around on the side. My mill also only had power feed on X until recently, so that played into it. It's nice to be able to let the machine feed.

Keep in mind that unless your material is provided with a spec for parallelism, you might well be holding a lot less material than you think. It doesn't take a lot to make it so that you have only a few points actually held by the jaws. It's usually a good idea to square the stock up so that you know everything will be held tightly for deeper cuts.

Remember to use conventional milling directions for deeper cuts. I try to keep climb milling to a few thous for finishing cuts.
 
You'll hear a lot about speeds and feeds, but a term that I only started hearing/learning about recently is MRR (material removal rate). Basically, how fast can you chew up metal, given YOUR machine and setup. For instance, say you swapped the 1Hp motor for a 3Hp? Your MRR goes up, unless the whole machine starts flexing. That is a real thing, and is why I now have a BP clone instead of an RF-45 clone.

So, I learned about MRR. I have a 1-1/2" endmill that I got on auction for $5, then had to spend $40 on a holder for. I would use it to cut a T-nut, but I'd still take only a .25" wide/ .25" deep cut, 'cause that is what my setup with that cutter will handle. If I swapped out for a sharp carbide tool, I might be able to double that. The point here is that the size of the endmill doesn't necessarily matter, unless your doing a slot cut.

How do you learn the MRR of your machine? Broken endmills and a notebook. I purposely set out to get an idea of the limits of the machine, and had a few regrinds that I was willing to sacrifice on the alter of education. Keep increase the cut till things get wonky, usually resulting in a broken endmill. Listen to the machine and the sound of the cut. It will tell you what you can get away with once you understand its language. And, write down your results.
 
You'll often get a little advance warning from the machine before an endmill snaps- vibrations and noise will increase. The machine will let you
know thru the handles that it's not a happy camper.
 
markba633csi said:
You'll often get a little advance warning from the machine before an endmill snaps- vibrations and noise will increase. The machine will let you
know thru the handles that it's not a happy camper.
Click to expand...

That's a downside of power feed and CNC. Things go bang and you don't get warning from the wheels, because you aren't touching them! :)

And it's not always going too fast. Sometimes, too slow, sometimes not enough cutting fluid, etc.. Just remember that tooling is consumable and you learn as you go. And it's easier to say than to do, I still swear at it when I break something. :)
 
For my machine "too slow" is a loud screeching noise. Essentially chatter. I get the same (chatter) if I try to cut too much "surface area".

Say I need to remove a 1/2"x1/2" channel. My MRR is that 1/4"x1/4" cut, but 1/2"x1/8" is the same volume. That rectangle cut with the tall side being vertical has more surface area, especially on the side cut, and will result in more chatter. I could also use a 1/2" diameter endmill, and take 1/8" at a time, but that single cut is going to be both my rough and finish cut. Hard to get a good finish while hogging material.

I had a bunch of 1/2" through slots to cut in 3/4" steel. I started with drilling a row of 7/16 holes for each one. Just to clear material. Then I went back and forth with a 3/8" endmill taking .300 per pass. Finished up with a single pass of the 1/2" endmill.
 
I'm not familiar with your mill, but I wanted to add that although it might be much more efficient to use a larger end mill from a material removal rate point of view I find it easier and more forgiving to start with medium size end mills. Medium size for me is 8mm to 10mm (0.3in to 0.4in). Using an end mill like that is more forgiving when your material comes loose rather than when using a 1 in end mill.

Yes, your end mill might snap, but, not much else will likely happen. I had a 16mm endmill "discover" my head tilt bolts were not tight enough during milling on a bench top mill. I've been happily using 8mm (0.3in) end mills on the same machine for weeks. So my point is that cutting forces are usually less with smaller end mills.

This brings me to second thing. Carbide vs hss. I prefer carbide end mills in 8mm- 10mm size. Why? Not just because faster MRR, but due to faster SFM (rotation). If you feed a hss tool and a carbide tool running at proper rotation speed at the same feed speed the carbide tool will have far lower load per tooth and consequently less cutting forces than the hss tool. This places less demand on work holding etc.

As to breakage potential.. I had my share of hss end mills snap too, and I had carbide cutters only loose a tooth or two so they remained usable after a mishap. I think a beginner will do good getting both.
 
ttabbal said:
That's a downside of power feed and CNC. Things go bang and you don't get warning from the wheels, because you aren't touching them! :)
Click to expand...
Full autos rely on the load meter . They sense the tool getting dull and automatically swap it out . I went out to the Makino plant in Ohio back in the eighties , 5 people and a dog running the huge plant . ( the dog was there to guard the machines so the humans didn't fart with them )
 
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