Is 1/2" roughing endmill too big for my PM25MV?

[Wonderclam]

I need to get me a roughing endmill for my Precision Matthews P25MV.

What size do I get? If 1/2" too big? I hear that 3/8" regular endmill is too big for my machine, but what about a 3/8" roughing endmill?

Also, as a general rule, do I mill using roughing endmills and just use regular endmills when close to finishing the final form? Like when I'm close to the point of doing the finishing pass?

 

[pontiac428]

The size of your end mill depends more on feed rate, RPM, and depth of cut than it does size. Ultimately, rigidity and power limitations will stop you from taking CNC style hogging cuts out of alloy steel, but it won't stop you from going slow and easy and letting the tool do the work.

You are right about the idea behind roughers. Roughers can remove more metal using less power. Regular mills will leave a better finish. When and how you switch tools is up to you, but you'll develop a feel for it with just a little practice.

 

[Wonderclam]

So with smaller diameter endmills, It's possible to feed faster, have higher RPM and larger depth of cuts?

 

[mmcmdl]

So with smaller diameter endmills, It's possible to feed faster, have higher RPM and larger depth of cuts?

Smaller end mills snap easier than large . Go with the biggest your machine can handle .

 

[ChrisAttebery]

As a general rule I use a 3/8" end mill unless I need more DOC.

 

[mikey]

I use a 3/8 roughing end mill on my little Sherline mill. It will take a full diameter depth of cut in aluminum, less in steel. Your mill should easily take 3/8" or 1/2" rouging end mills but 3/8" would work well for you. A roughing end mill will typically cut 20% faster in both speed and feed and will last far longer than a finishing end mill will.

For slotting and pocket work, use a coarse pitch. For profiling on the edges, use a fine pitch. For aluminum, look for a 3-flute hi-helix rougher. Best brand I use is Niagara Cutter, although there are many others.

Do most of your end mill work with a roughing end mill and save your finishing end mills to clean up the marks left by the rougher. This will greatly extend the life of your finishing end mills.

 

[macardoso]

G0704 CNC guy here...

With smaller tooling you will find the spindle speed to be your limiting factor. And with large tooling, the machine's rigidity.

I have found through lots of trial and error that in aluminum my machine runs best with a 3/8" endmill, but is fine with a 1/4" (less productive) or 1/2" (have to baby the cutter). In mild steel it seems to work best with 1/4", but is fine with 3/16" to 3/8". I have run tools from 1/64" to 3/4" well enough, but I cannot use these tools anywhere near their potential.

Roughing endmills are great. When you are using them on a manual machine, it feels like cutting velvet vs the vibrations that normally come from endmills. Helps with HP requirements and material removal too.

EDIT: FYI, a G0704 is very close in rigidity and HP to your PM25V

 

[T Bredehoft]

I have a 3/4" three flute inserted carbine mill for my PM25. Yesterday I was cutting steel the full width of the cutter, about 020 deep at 8 inches per minute 750 RPM. Faster wanted to thump/chatter, same feed rate, that's as fast as my home made feed goes. Like cutting butter, chips all over the place.

 

[mikey]

Tom, my Sherline inserted carbide fly cutter is 1-1/8" OD and is essentially a single flute face mill. It will easily take 0.020" cuts in steel and way more in aluminum. Leaves a beautiful finish, too. I use it on my Sherline mill and my RF-31. It is one of my most used tools because I use it to square work pieces and also use it for stock reduction. For some things, a face mill is the right tool.

 

[bakrch]

As a general rule I use a 3/8" end mill unless I need more DOC.

G0704 CNC guy here...

With smaller tooling you will find the spindle speed to be your limiting factor. And with large tooling, the machine's rigidity.

I have found through lots of trial and error that in aluminum my machine runs best with a 3/8" endmill, but is fine with a 1/4" (less productive) or 1/2" (have to baby the cutter). In mild steel it seems to work best with 1/4", but is fine with 3/16" to 3/8". I have run tools from 1/64" to 3/4" well enough, but I cannot use these tools anywhere near their potential.

Roughing endmills are great. When you are using them on a manual machine, it feels like cutting velvet vs the vibrations that normally come from endmills. Helps with HP requirements and material removal too.

EDIT: FYI, a G0704 is very close in rigidity and HP to your PM25V

Just going to add +1 to both of these posts. I've tried many end mills and settled on 3/8" for general purposes. If I need more than 1.5" of flute length that is when the 1/2" end mill will come in. 1/2" works perfectly fine, but if you don't have a reason to use it you're just wasting money.

Another scenario I would use 1/2" is if I were in a production mindset (as much as I can be on a machine like this) and want to use the end mill for dual purpose for facing. 1/2" amounts to fewer passes.

The only drawback to the roughing end mills is the swarf, not as easy to clean up. I generally avoid using them for this reason, but they sure do cut nice when you need them to.