Noob - End Mill Confusion

[Simon Wells]

I have been doing some research about end mill selection on various places, but I am still confused as to the correct size and type mills to get for our mold tool application.

We have just purchased a Syil X4 STD mill with ER40/R8 collet set and now looking for the correct end mills.

We will be machining 6061 Aluminium blocks and 316 Steel 3mm plate.

Initially we will be machining dry, whilst we wait for the forgotten coolant kit, but will be running that later.

If someone is able to advise on how to select the correct mill, I can provide a before and after drawing to show exactly what we want to achieve.

Thanks very much in advance.

Simon

[cjjonesarmory]

Is the question in regards to cutter material type, number of flutes, etc?

I have good luck using cobalt end mills. The cheaper imported HSS cutters tend to dull pretty quickly. Carbide end mills seem to chip way too easily and are expensive to replace when this happens.

I normally use 1/2" dia cutters, just because it fits the majority of my needs. The diameter you choose is really dependent on the application. Some will say that you need 2 flute mills for aluminum, but I have been doing quite well with 4 flute end mills in 6061 aluminum. I honestly do not notice a huge amount of difference with the various coatings. If you are going to be running without coolant, plain HSS or cobalt without a coating is fine, but you can also consider using TIN coated or TIALN.

For smaller dia cutters, using a 2 flute versus 4 flute becomes more critical to reduce the possibility of clogging the flutes which will result in broken end mills and/or material being fused to the cutter.

Stub mills are better if you don't need the additional length.

Best advice is just to buy several different types and experiment. There are no absolutes, each application is different so what works for one may not work for another.

If this was not the answer you were looking for, leave some more detail and I'll try to do a better job of answering.

[Simon Wells]

@cjjonesarmory Any advice is welcomed to be honest.

I have read that several factors affect swarf removal, including the depth and angle of the flutes, the size and shape of the chips, the flow of coolant, and the surrounding material. Also, do I need to consider traditional milling or climb milling? Climb milling would seem the better choice to remove chips and lengthen life of the mill and I believe it would be ok to do it on the Syil.

For the rough cuts I could use a larger (1/2" 10 to 12mm) 4 flute, then for smaller detail use a 2 to 5mm with 2 flutes. I dont think I will be looking for rough mills as I would still like a reasonable finish to the surface of the block.
If I have understand correctly, the smaller the diameter, the less flutes to have as the aluminium could clog the flutes, which would be more likely when no coolant is used or a non-coated mill.

So from what I have seen so far, traditional end mills are what I should be looking for, size dependant on smallest features and how fast we need the rough to be removed.

Now we do have to cut out some apertures through the steel plate (3mm thick). We need to consider the mill diameter, as we have to have some radius in the corners of these typically rectangular cut outs, but I dont know if we need a plunge mil for that kind of thickness.

Hope that all makes sense.

Thanks.

Simon

[HuFlungDung]

For aluminum machining, I'd recommend YG endmills, the 3 flute variety with high helix. These also have a polished flute for better chip evacuation. They are typically uncoated and will last for a long time. I would not plunge cut with these tools, they like gentle ramp entries.

That said, a wee bit of lube is a minimum requirement for machining aluminum, because you can clog up any endmill when it gets hot, and the aluminum starts to stick to it. A Trico Microdrop system works decently well, much better than nothing. It might result in some smoke generation if you are pushing hard. The small air blast that works with the Trico system also does a decent job of moving the chips out of the cutting zone.

For 316 stainless, I don't have much experience with heavy hogouts, but it can be machined dry with more standard endmill configurations. The high helix endmills for aluminum, while they would cut stainless for a few moments, you'd probably lose the corners of the tips pretty quick, because they are delicate. The correct coating on the endmill is mandatory for stainless cutting, as it needs to be resistant to chip welding.

When you get your coolant system on the machine, flood coolant and HSS or cobalt bearing HSS endmills, in very sharp condition, can do a good job of heavy material removal. Built up edge is less harmful to HSS tooling, so a sharp edge can be maintained for quite a while without degradation like a crumbling of the edge of carbide. But HSS must positively be flood cooled to last very long. The heat transfer rate of stainless is very slow, and so the heat in the cut zone is exaggerated beyond what one typically expects when machining steels.

[cjjonesarmory]

I have read that several factors affect swarf removal, including the depth and angle of the flutes, the size and shape of the chips, the flow of coolant, and the surrounding material.

That is true, but unless you are in a high production setting I think you'd be better off starting with a generic 2 or 4 flute. Most of the end mills specialized for aluminum are two flute. The just don't seem to do the best job for my applications, but some find them useful.

Also, do I need to consider traditional milling or climb milling? Climb milling would seem the better choice to remove chips and lengthen life of the mill and I believe it would be ok to do it on the Syil.

Most milling is done as climb milling in my case because I have a very large machine and my cuts are relatively small. Technically large cuts are supposed to be done with conventional milling with finishing cuts being done with climb milling. With conventional milling the cutter is being pushed back away from the stock by the combination of rotating direction and feed direction. With climb milling the cutter is "climbing" the stock. In some cases with very powerful mills this climbing action can pull the cutter too quickly through the stock and break things. It's very obvious when I use a large cutter on my own machine that the cutter will almost overcome the friction in the leadscrews and table and nearly pull itself through the stock when using climb milling for heavy cuts. The finish you obtain with climb milling for a finishing cut will be much better than the finish obtained using conventional milling for a finishing pass.

For the rough cuts I could use a larger (1/2" 10 to 12mm) 4 flute, then for smaller detail use a 2 to 5mm with 2 flutes. I dont think I will be looking for rough mills as I would still like a reasonable finish to the surface of the block.
If I have understand correctly, the smaller the diameter, the less flutes to have as the aluminium could clog the flutes, which would be more likely when no coolant is used or a non-coated mill.

I think you are right on track with that paragraph. It would be difficult to find anything except for 2 or 3 flute end mills in smaller diameters than about 1/8" anyway.

So from what I have seen so far, traditional end mills are what I should be looking for, size dependant on smallest features and how fast we need the rough to be removed.

Sounds right.

Now we do have to cut out some apertures through the steel plate (3mm thick). We need to consider the mill diameter, as we have to have some radius in the corners of these typically rectangular cut outs, but I dont know if we need a plunge mil for that kind of thickness.

I'm not positive what you mean by "plunge mill". There are "mill drills" that are essentially end mills with a 45 degree point, but most of them are carbide and will chip easily. There are also "slot drills" which is really just another name for a 2 flute centercutting end mill. 3mm is almost 1/8" thick and you should have no problem feeding horizontally once you penetrate the plate.

I suppose this brings up one more point to be aware of. End mills with greater than 2 flutes may or may not be "centercutting". If you want to be able to feed the end mill downwards (and not sideways) through the stock, you need to make sure it is of the "centercutting" variety. Centercutting end mills have 2 cutting edges that meet in the center of the end of the cutter. This will allow you to "plunge cut". Non-centercutting end mills do not have cutting edges that meet in the middle and you can not plunge them straight through the material.

There's so much more to what I have stated above, but I tried to give you the basics. Hopefully it will give you a start. If you have any more specific questions, feel free to ask.

[cjjonesarmory]

That said, a wee bit of lube is a minimum requirement for machining aluminum, because you can clog up any endmill when it gets hot, and the aluminum starts to stick to it. A Trico Microdrop system works decently well, much better than nothing. It might result in some smoke generation if you are pushing hard. The small air blast that works with the Trico system also does a decent job of moving the chips out of the cutting zone.

WD-40 works well for aluminum too in a pinch, but it's rather smoky. I use Rustlick WS-5050 for just about everything that requires coolant. Don't use coolant on cast iron by the way...

I have cut aluminum for short periods without coolant, but you have to dial down the cutter SFM to around 100. You can look up the term SFM if you aren't familiar with it, it's not the same as RPM. Light cuts are essential, but eventually you'll toast the cutter. Since it looks like you are planning to use coolant eventually, you can start off and practice with WD-40 which is available at most hardware stores.

[Simon Wells]

Many thanks for spending time in responding, it is appreciated and comments are taken on board.

Yes, plunge mills I think they are also referred to as slot drills, IE they allow vertical plunging/drilling as opposed to the X/Y machining.

I think there is also a little difference in terminology for mills from UK/US, too many plunge, shank, centered etc.

You have been a great help confirming my thoughts.

Simon

That is true, but unless you are in a high production setting I think you'd be better off starting with a generic 2 or 4 flute. Most of the end mills specialized for aluminum are two flute. The just don't seem to do the best job for my applications, but some find them useful.



Most milling is done as climb milling in my case because I have a very large machine and my cuts are relatively small. Technically large cuts are supposed to be done with conventional milling with finishing cuts being done with climb milling. With conventional milling the cutter is being pushed back away from the stock by the combination of rotating direction and feed direction. With climb milling the cutter is "climbing" the stock. In some cases with very powerful mills this climbing action can pull the cutter too quickly through the stock and break things. It's very obvious when I use a large cutter on my own machine that the cutter will almost overcome the friction in the leadscrews and table and nearly pull itself through the stock when using climb milling for heavy cuts. The finish you obtain with climb milling for a finishing cut will be much better than the finish obtained using conventional milling for a finishing pass.



I think you are right on track with that paragraph. It would be difficult to find anything except for 2 or 3 flute end mills in smaller diameters than about 1/8" anyway.



Sounds right.



I'm not positive what you mean by "plunge mill". There are "mill drills" that are essentially end mills with a 45 degree point, but most of them are carbide and will chip easily. There are also "slot drills" which is really just another name for a 2 flute centercutting end mill. 3mm is almost 1/8" thick and you should have no problem feeding horizontally once you penetrate the plate.

I suppose this brings up one more point to be aware of. End mills with greater than 2 flutes may or may not be "centercutting". If you want to be able to feed the end mill downwards (and not sideways) through the stock, you need to make sure it is of the "centercutting" variety. Centercutting end mills have 2 cutting edges that meet in the center of the end of the cutter. This will allow you to "plunge cut". Non-centercutting end mills do not have cutting edges that meet in the middle and you can not plunge them straight through the material.

There's so much more to what I have stated above, but I tried to give you the basics. Hopefully it will give you a start. If you have any more specific questions, feel free to ask.

[Simon Wells]

WD40 = Check
Cast Iron = Wont be using it, so check


Thanks

Since it looks like you are planning to use coolant eventually, you can start off and practice with WD-40 which is available at most hardware stores.

[Simon Wells]

For aluminum machining, I'd recommend YG endmills, the 3 flute variety with high helix.

Thanks for the tips, taken on board.

Simon

[Simon Wells]

For aluminum machining, I'd recommend YG endmills, the 3 flute variety with high helix.

Just checked out their site, but seems its all imperial, we unfortunately need metric, but will contact them just in case.

Simon

EDIT: Scratch that, just found a couple of metrics on there. Note to self, open eyes.

[Simon Wells]

I just found this nice little set of 1 to 10mm, 3 flute centre mills.

Think this might be a nice set to start of with and wont break the bank when I destroy a couple.

There is also this site which contains some useful informations on mills, feeds and data tables, in case its of use to anyone.

Simon

[cjjonesarmory]

There are quite a few books out there on small scale machining. Most are written by folks who have used larger machine tools, but the books are geared towards more hobbyist-sized machines such as the Sherline. The concepts on cutter selection in these books are usually applicable to other machines too.

One book in particular is written by (I think) the president of Sherline. It's called "Tabletop Machining".

http://www.amazon.com/Tabletop-Machining-Joe-Martin/dp/0966543300/ref=sr_1_1?ie=UTF8&s=books&qid=1307720303&sr=8-1]Amazon.com: Tabletop Machining (9780966543308): Joe Martin: Books

Another useful book for beginners is "The Home Machinists Handbook":

http://www.amazon.com/Home-Machinists-Handbook-Doug-Briney/dp/0830615733/ref=sr_1_2?ie=UTF8&s=books&qid=1307720303&sr=8-2]Amazon.com: Home Machinists Handbook (9780830615735): Doug Briney: Books

A good thing for anyone doing anything with machine tools is "Machinery's Handbook", although a lot of the info in this one is extremely technical.

http://www.amazon.com/Machinerys-Handbook-28th-Larger-Print/dp/0831128011/ref=sr_1_2?s=books&ie=UTF8&qid=1307720396&sr=1-2]Amazon.com: Machinery's Handbook 28th Larger Print Edition (Machinery's Handbook) (9780831128012): Erik Oberg, Franklin D Jones, Henry H Ryffel, Christopher J McCauley, Ricardo M Heald: Books

Good luck.