[Newbie] Hss Vs Solid Carbide End Mills, Lessons Learned, Questions.

[jwest7788]

So, My recent haul of used machine tools and bits has given me lots more to learn with.

While working yesterday on making some t-slot nuts, I was switching through different end mills trying to find what worked best for the particular job.

Essentially, one issue I noted was that the HSS end mills (new) I used really had some bad chatter taking 0.020 depth of cut, 1/3 the cutter doing the work (1/2" 4 flute end mill) in some off the shelf cold rolled square bar.
--> Using cheap "cutting oil" from Princess auto.

I noticed that it seemed to be re-cutting chips pretty badly, which I assume was the issue.
It seemed to me that the cutting oil was not allowing the chips to leave the cutter, and thus re-cutting the chips, causing the whole process to go slow, sound and feel bad, and in general not be pleasant.
Note: By the end of the cut, the part was still cool to the touch, and I could see the cutting oil was muddy with micro-chips.

This bring me to the first set of questions:

No matter the bit material or cutting fluid, I should expect the chips to "eject" from the work area, correct?
--> I was getting a shoddy muck of cutting fluid, micro chips, and some small chips, but all in the work area.

What viscosity should cutting oil be for this application? (I think the cheap **** I have may be intended for another purpose, it's pretty viscous.) 10w30 thick, but appears to be dedicated cutting oil.

Should cutting fluid be constantly applied, or should I just put a light coat on the work piece before I begin?
--> Seems like my brush may have been helping to keep the chips on the cutter?

Can you mill with HSS bits without cutting oil? Or will I quickly destroy the bit?

I'm still learning the whole speeds and feeds thing, but what are the signs that I am working at too high an RPM?
--> I am unsure if the noises my mini mill are normal, or alarming, so I fear I am either over working, or under working the machine's capabilities. I suspect under working the machine, due to the lack of chip ejection, but on that same note, the machine is making some noises I am not yet comfortable with.




Carbide end mill was used as well. Same process as above, but without cutting fluid.
Chips were flying, turning light brown, all was good. Cut twice as much material at three times the rate.

Obviously, am much happier with the carbide end mill and would love this capability from all of my HSS tools too.

So what were the differences between the carbide, and HSS tests:

Both 1/2" end mills
Both 4 flutes
(Same or better depth of cut)
Carbide vs HSS
No cutting fluid




I have so many HSS tools, I need to figure this out, but I am tempted to just switch to using carbide all the time based on yesterday's results. Need to learn! Help!

 

[T Bredehoft]

I just stopped cutting on some 41L40, a leaded tough steel. I was using TiN coated (gold) HHS, lots of vibration, slow feed and depth of cut, (5/16 cutter, .062 deep) too slow. I called my source for steel (Speedy Metals) they said I could use 200 SFM withTiN coated HSS, That works out at about 2200 rpm, faster than I want to work. I found that I had one 5/16 carbide 4 flute that was fairly sharp, I could take 1/8 depth of cut at 1300 rpm. A lot more satisfying. Because of the LedLoy, I was cutting dry. I got a slot almost 3/4 square hogged out, too hot to touch, too hot to cut to exact size without being concerned with shrinkage, I'm going to finish the cut with HSS, for good finish, it's a new cutter. But Yes, use carbide when you can.

I guess this doesn't answer your exact question, differing steels for one point.

Since I don't have mist capability, I often put a drop or two of Tap Magic along the tool path. If you haven't tapped using Tap Magic, you're in for a great surprise. Whatever the cost, it's the best.

 

[Ulma Doctor]

generally speaking you will turn a HSS tool slower than you would the same size tool in carbide.
some machinists never use coolant on all but the most difficult of materials.
a slower tool speed with a high feed rate is usually better than a high tool speed and slow feed.
that's when you'll get chips that get cut multiple times.
small milling machines aren't always rigid enough to get full feed capabilities ,
so you may need to experiment with your mill to come up with the best solution for your set up.

most materials you'll ever work with can be cut by HSS tooling.

i do like carbide endmills and use them for when HSS may not do the job as efficiently in harder/abrasive materials

 

[brino]

My recent haul of used machine tools and bits has given me lots more to learn with.

Experience is a great teacher. Personally I find I learn more from that than from anything.

To help reduce chatter:
-have you checked that your dovetail slides are adjusted and lubricated properly
-if your feeding in the longitudinal direction can you lock the transverse feed slides (or visa-verse)
-is the vertical feed locked? (perhaps the endmill cutting edge spiral is pulling the vertical feed down)
-are you conventional milling or climb milling? (typically applied to horizontal mills, however, even an endmill can pull the work piece into the cutter when there is backlash)
-are you using power feed or hand-feed? if hand feed try to keep it constant.
-is the work deep enough in the vise?

I have been thinking about adding a flood-coolant system forever.......the biggest holdup is what fluid to use. I cannot guarantee that my shop is above freezing in the winter so I am too worried about water-based coolant/lubricant in the machine reservoirs to do it. Therefore, most often I use a pump bottle of WD40. Occasionally when I'm having a tough time cutting something I use small amounts of a water-based coolant applied with a brush:
http://www.busybeetools.com/product...res.html?page_context=search&faceted_search=0

To see if the "recutting" or non-evacuation of chips is the issue you could try setting up a test with a lube spray, or even compressed air to see if chip removal solves it. If you do not have a compressor, you could try a can of computer dusting air......

I don't have my speeds and feeds chart in front of me, but really it comes down to surface feet per minute.
You don't say what rpm your running your 1/2" end mills at, but you should be able to find some good online references....

Not sure what milling machine you have, but there was a post here recently about some interesting mods to help with machine rigidity by adding diagonal bracing from the bench to the vertical mill head.

-brino

 

[joshua43214]

Sounds to me like you might be being too nice to the work and going too slowly. Going slow only means a better finish if you are still going fast enough to cut properly.
Wikipedia has a nice page for calculating Feeds and Speeds.
Assuming the SFM for the metal is 100fpm. Dunno what it actually is for cold rolled, would need to check a book, but this is near the bottom for mild steels. Lower number = tougher metal.
For your 1/2" mill
RPM ~ SFM*12/(pi*diameter) = 100*12/(3.14*.5)
RPM ~ 764

Feed rate is then simply
FR = RPM*Teeth*ChipLoad
you can estimate chip load with .0001" per 1/64" of tool diameter. In this case ChipLoad = .0032
FR = 764*4*.0032
FR = 9.8fpm

So you should start with about 765RPM and a feed rate of about 10fpm.
If you are hand cranking, just look at chip color. The chips should cool to a lovely blue color. You do not really need lube, but cold rolled kinda sucks to work with. You are going to have trouble getting a really nice finish.
Try not to cut less than .002" when figuring out feed rate. The tool is actually being cooled by the work and the chip should carry the heat away.
If stuff starts to vibrate and chatter, something is loose. Stop the mill and figure out what needs to be tightened up, if everything is tight make sure the quill is locked, has no meaningful runout and the tool is running true. Fully enveloped cuts will also produce a lot more drama on a small mill.

 

[jwest7788]

-have you checked that your dovetail slides are adjusted and lubricated properly

Yes!

-if your feeding in the longitudinal direction can you lock the transverse feed slides (or visa-verse)

Yep, am locking the non moving axis.

-is the vertical feed locked? (perhaps the endmill cutting edge spiral is pulling the vertical feed down)

Yep, Locked. And cutting very stright, perfect cuts. Some parts are dragging leaving spiral marks on the work, maybe the lack of rigidity is more of an issue that I thought initially?

-are you conventional milling or climb milling? (typically applied to horizontal mills, however, even an endmill can pull the work piece into the cutter when there is backlash)

Conventional, there is too much backlash, climb milling bites, jumps, sparks, and ruins both my end mill and work piece.

-are you using power feed or hand-feed? if hand feed try to keep it constant.

Hand feed, as constant as I can. Am experimenting with speeds trying to find a good fit though, but constant once comfortable.

-is the work deep enough in the vise?

Could be deeper. Will try that tonight.

To see if the "recutting" or non-evacuation of chips is the issue you could try setting up a test with a lube spray, or even compressed air to see if chip removal solves it. If you do not have a compressor, you could try a can of computer dusting air......

Will try tonight, good thought.

I'm using a mini mill, so I know rigidity will be an issue at times. Wonder if bracing is a possibility for this little guy..

Sounds to me like you might be being too nice to the work and going too slowly.

This is a very real possibility. If I push it too hard with a mini mill, am I liable to wreck the mill itself, or the end mill? (or both)
--> This is possible in that I am not confident how hard it "beyond the limit of this mill"

Will try the above, and pushing it a little harder tonight.

 

[joshua43214]

Face Shield + Welding Jacket = force it til it breaks

Breaking an end mill is not as scary as it sounds at these speeds, nothing like loosing a router bit turning over 20k.
If you want real scary, break a grinding wheel. That will make you pucker...

 

[jwest7788]

Face Shield + Welding Jacket = force it til it breaks

Breaking an end mill is not as scary as it sounds at these speeds, nothing like loosing a router bit turning over 20k.
If you want real scary, break a grinding wheel. That will make you pucker...

I'm actually more worries about breaking the milling machine than the end mill. It's just a little mini mill, so I'm not confident the end mill will go first. Anyone confirm?

 

[sgisler]

Had a mini mill for several years before I found my Ez Trak. Broke many an end millworst it ever did to the mill was knock it out of tram. Have at it!


Stan,
Sent from my iPhone using Tapatalk

 

[markknx]

Try about 600rpm. and feed to feel if it fails to give chips feed a bit harder. At .020 go deeper or feed faster. I had a mini and the sweet spot for 1/2" endmill is small so play with speed and feed. remember two things mentioned above, this is a mini so the speed an feed rates have to be adjusted, Make sure you are tight.
If you are cutting to light you will get more of a sandy type Swarf, this is because you are not removing enough material to make a chip. (bad for the cutter) If the rpms are to high a hss bit will dull quick. What speeds did you use?