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Milling Fail, and my Nuub mistake… Help with - Speeds, feeds and how this VN12 should sound?
- Thread starter John TV
- Start date
- Joined
- Sep 25, 2014
- Messages
- 1,111
The off balance was not really noticeable. The lathe is a light pattern 15" swing, commercial class machine. The speed was probably about 180 rpm. I don't pay a lot of attention to the rpm, I mostly run what feels "about right". I had to play around with the speeds and feeds to get a decent finish. Some of them worked out with a beautiful, fine phonograph finish, the first couple were good, just not as pretty.
For interrupted cuts, if I make everything really short and as stiff as possible - then it is not a big deal. Just cut away, it works fine. I don't think there was a problem with damaging inserts - perhaps I used 2 edges.
I was careful in how much I took off. These are the holders for my smaller lathe, so I just skimmed enough so that when the holder sits right down on the nose of the compound, then the tool is right on center - and I removed the height adjuster. For the primary cutting tools, they are not likely to ever be removed from that holder. Of course other holders are still set up to use the height adjuster.
I encourage you to really consider using the lathe for flat work. It is a great machine for other than just round stuff. I have good mill options, I used the lathe to skim the holders by choice.
Let us know how you make out on the next one you cut. David
- Joined
- Apr 30, 2015
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- 11,327
Try Brian Gruschow to resharpen your cutters: (he does horizontal cutters too)
www.endmill-sharpening.com
mark
www.endmill-sharpening.com
mark
- Joined
- Sep 3, 2011
- Messages
- 478
Were you climb milling or conventional milling? The No. 12 doesn't have an anti-backlash mechanism, so you can't climb mill with one in horizontal mode.
I was conventional milling, I did not, however, lower the knee to "come back" to starting position tho...maybe that was an additional mistake. I really think the material was just too hard for the cutter i was using.,.., That said, will try again soon with a different cutter in aluminum and mild steel. I'm still wondering about depth of cut too. I've read that rubbing is the killer of many sharp edges. How deep should one start, and doesn't the width of the cutter come into play here too? I keep hearing 1 to 2 thou. per tooth but is that true with a 3/8 wide cutter and a 3 inch cutter? I don't think I have the horsepower to take that big a cut ( have not caluclated that out but 3 inches wide it just seems like too much)? But I am still smiling and climbing that steep learning curve too. thanks for your thoughts.
Here is a link to a YouTube that is showing a horizontal mill taking roughing cuts of 200 thou and finish cuts of 100thou I think in aluminum. I wish they had gone over steel a bit more but those depths seem huge to me. Again, I have no real point of reference but the power to cut that deep that wide and the load per tooth must be huge. This original film was made in late 70s if I remember.
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- Sep 3, 2011
- Messages
- 478
John,
I don't have any hands-on experience with slab milling cutters, to take this with a grain of salt: Cutter diameter and material SFM (surface feet per minute) determine the cutter RPM. Feed is determined by the RPM and the number of teeth on the cutter. Each tooth/flute needs a minimum amount of "bite" in order to cut. If you don't feed the cutter enough, I imagine that the tooth will smear the corner over and create a ramp that forces the cutter and stock apart, resulting in the cutter rubbing rather than cutting.
The maximum depth of cut is a function of the horsepower of the machine. Even a 1 HP horizontal mill can take an amazingly deep cut. I don't think that the cutter width enters into it, because the "teeth" on a slab mill are helical and cutting is only taking place at one place on the flute. As the cutter rotates, the cut moves from one side to the other. They still need a big enough bite to work.
Now, if you're only using part of a slab mill, you may need to increase the feed. The helix is designed to finish one cut as the next flute is coming into contact with the stock. If you only use half of the cutter, the previous flute will finish and there will be a period of time where the tool is unloaded, before the next flute slams into the stock. (At least, that's how I picture it.) If that's correct, that might produce the hammering sound that you're having.
Another possibility is that you have your gibs are too loose and the machine is able to move about as the cut proceeds. A common mistake is to tighten up the gibs just enough to take the slack out while keeping that silky smooth feel when turning the handles. The gibs should actually have a bit of drag. Adjust them by using a test indicator between each axis and the column, starting with the knee. If you can get the indicator to move by pushing side-to-side or up and down against the axis, then the gib for that axis needs to be tightened.
You should definitely practice using a block of aluminum or mild steel of known alloy until you get the feel for the depth of cut and gain some confidence. Your ear will tell you when the machine is starting to lug down and it's time to back off on the depth.
FWIW, one of my reference books (Design and Use of Cutting Tools, by St. Clair) has a table that lists feed per tooth of 0.012" for soft steel and 0.010" for aluminum (roughing cuts, HSS cutters). Machinery's Handbook (25th ed) lists feed per tooth of 0.004 to 0.007" for HSS cutters in mild steel. So your feed rate of 0.001" per tooth is probably too low.