Could I get an idea on what different sized mills can hog?

[shild]

Some of you guys here have said the biggest thing holding me back if I want to machine faster is the rigidity of my mill (which is an X-3). But how much faster can I hog with a bigger mill? How much better would an RF-31 clone do? Or an RF-45 clone? A Bridgeport? K & T mill? Gorton? What is the proper way to measure to compare these mills? I can do a little better with what I've got if I drill 4 holes in my desk to bolt it down can't I?

[BClemens]

here's your first 2¢... Any bench sized mill should be bolted to a solid cabinet or stand - if for no other reason than safety. Stay away from round column mills for a couple of reasons: rigidity and the ability to raise Z without having to re-zero your work. The ability to efficiently 'hog' is related to the size of the machine, a reasonably precision and set-up machine will hog better than one of the cheaper, poorly made imports. Anyhow, you 'hog' faster or slower depending on what your machine can handle. If you purchase a used machine, you may find that it is either worn badly or improperly set up and even a new cheaper machine can suffer the same problems and not 'hog' well enough. Chatter is the biggest problem with poor machinery. If you look for a used machine, go for as large a machine as you feel you can deal with. Heavy is a good thing when working with machine tools....

That is a tough question with many aspects to take into consideration....it is totally the capability of the machine no matter the size. Smaller. lighter machine - 'hog' slower. An important thing to keep in mind is to keep the milling cutter as short as possible and also held as close to the spindle as possible - use a collet when a heavy cut is attempted. Remember the basic rule: chatter is the result of too slow a feed or cutter speed too fast - climb milling on a loose machine is certain death to your work or cutter no matter what the feed or spindle speed may be.
BC

[Dave_C]

Shild,

There are some standards that you can draw from. It would also be a good practice to find a speed and feed calculator on the web and run some examples. Some of these will let you enter depth of cut as well as chip load and then give you the HP required for the cut. Some of these are more detailed than others but most or free to use.

Some basics rules: Depth of cut is generally never over twice the diameter of the end mill! However this changes as you take wider and wider cuts so don't expect to take a 90% step over at the max depth. Example: At the max depth of cut the step over might just be 20%!

So really, no one can tell you what your machine can or can't do. Start with mild passes and work up until you see the results start to change. Is the machine laboring, it is chattering, it is doing something you don't like, then back off the cut width or the depth of cut until you like the way it cuts.

Just because a machine comes with a 2 HP motor does not mean everything else on the machine is ready for a real 2 HP material removal cut.

I have a 1.5 HP CNC mill with a spindle load meter on it. With a .375" 3 flute carbide cutter taking a 90% step over at .250" deep, I'm still only runing at 40% spindle load. But it makes real pretty cuts and I don't feel the need to make it hog any faster. (Chips are nice, even and consistant)

Dave C.

[rkcarguy]

That's a bit of a loaded question, there are parameters to follow for different mills. Machine rigidity, tightness, material being, cut, and size will dictate what kind of cut can be taken. I've worked on a very large horizontal mill and dialed in .200" in stainless with a 4" carbide insert face mill and let it rip, and used a few of these little hobby mills that wouldn't slot 1/8" aluminum with a 1/4" end mill without "complaining" about it.
As far as climb vs. conventional cutting, I've always conventional cut my heavy cuts and then run some tension on the table lock and climb cut the last ~.010" to get a really nice finish if needed.

[shild]

here's your first 2¢... Any bench sized mill should be bolted to a solid cabinet or stand - if for no other reason than safety. Stay away from round column mills for a couple of reasons: rigidity and the ability to raise Z without having to re-zero your work. The ability to efficiently 'hog' is related to the size of the machine, a reasonably precision and set-up machine will hog better than one of the cheaper, poorly made imports. Anyhow, you 'hog' faster or slower depending on what your machine can handle. If you purchase a used machine, you may find that it is either worn badly or improperly set up and even a new cheaper machine can suffer the same problems and not 'hog' well enough. Chatter is the biggest problem with poor machinery. If you look for a used machine, go for as large a machine as you feel you can deal with. Heavy is a good thing when working with machine tools....

That is a tough question with many aspects to take into consideration....it is totally the capability of the machine no matter the size. Smaller. lighter machine - 'hog' slower. An important thing to keep in mind is to keep the milling cutter as short as possible and also held as close to the spindle as possible - use a collet when a heavy cut is attempted. Remember the basic rule: chatter is the result of too slow a feed or cutter speed too fast - climb milling on a loose machine is certain death to your work or cutter no matter what the feed or spindle speed may be.
BC

Alright, guess I'll have to put holes in my desk. Maybe it will be more rigid to have a few sheets of plywood between the mill and table? When possible, I've always choked up the endmill right where the shank ends and cutting edges begin. But now that you've mentioned it's importance, what if I choke it up even farther? So some of the cutting edges of a 1/2" endmill is inside the 1/2" collet? Or maybe it's a bad idea because the cutting edges can mark up inside of collet? What if you have a 7/16" endmill with a 1/2" shank in a 1/2" collet? Can I choke that up beyond where the shank ends so I can drop the head a bit lower?

[shild]

Shild,

There are some standards that you can draw from. It would also be a good practice to find a speed and feed calculator on the web and run some examples. Some of these will let you enter depth of cut as well as chip load and then give you the HP required for the cut. Some of these are more detailed than others but most or free to use.

Some basics rules: Depth of cut is generally never over twice the diameter of the end mill! However this changes as you take wider and wider cuts so don't expect to take a 90% step over at the max depth. Example: At the max depth of cut the step over might just be 20%!

So really, no one can tell you what your machine can or can't do. Start with mild passes and work up until you see the results start to change. Is the machine laboring, it is chattering, it is doing something you don't like, then back off the cut width or the depth of cut until you like the way it cuts.

Just because a machine comes with a 2 HP motor does not mean everything else on the machine is ready for a real 2 HP material removal cut.

I have a 1.5 HP CNC mill with a spindle load meter on it. With a .375" 3 flute carbide cutter taking a 90% step over at .250" deep, I'm still only runing at 40% spindle load. But it makes real pretty cuts and I don't feel the need to make it hog any faster. (Chips are nice, even and consistant)

Dave C.

Yeah, on my machine, sometimes you can here the gears chatter against each other. I believe it's more likely to chatter if I use a 2 flute endmill that's not very engaged in the cut. Also my machine has a sheet metal cowl that really begins to rattle when I do a heavy cut, mostly because of column twisting. I've seen someone put a heavier motor on the same mill I have but I"m not sucessfully using all the stock motors power yet.

[shild]

That's a bit of a loaded question, there are parameters to follow for different mills. Machine rigidity, tightness, material being, cut, and size will dictate what kind of cut can be taken. I've worked on a very large horizontal mill and dialed in .200" in stainless with a 4" carbide insert face mill and let it rip, and used a few of these little hobby mills that wouldn't slot 1/8" aluminum with a 1/4" end mill without "complaining" about it.
As far as climb vs. conventional cutting, I've always conventional cut my heavy cuts and then run some tension on the table lock and climb cut the last ~.010" to get a really nice finish if needed.

Yeah, I often put tension on the table locks too. Especially on the ones I move less often. Guess that's going to wear out the leadscrew, dovetails and gibs faster, but maybe more numerous lighter cuts without table lock tension would put just as much wear on it?

[Fender]

If you are trying to remove metal quickly, consider using a “roughing” end mill. I used to have a Clausing 8520 benchtop vertical mill, and was astounded how deeply I could cut using the side of a 1/2” roughing end mill. The roughing mills break up the chips into particles, as opposed to the slivers one gets from a standard end mill. As I recall, I took a cut about 0.100 deep across a 1” face. This would not have been possible using a standard two- or four-flute end mill on this vertical milling machine.

[tornitore45]

First you should have enough feel to "Listen" to what the machine is telling. If you generate too much heat either the RPM is too high or the cutter is dull. If the machine groans you are feeding too fast.
Second the faster metal removal tool is a drill bit drilling into a pre-drilled hole that clear the web.
Once the part is Swiss Cheesed a sharp carbide end mill of diameter adequate to the part and the mill rigidity will quickly finish the job.

[BClemens]

Alright, guess I'll have to put holes in my desk. Maybe it will be more rigid to have a few sheets of plywood between the mill and table? When possible, I've always choked up the endmill right where the shank ends and cutting edges begin. But now that you've mentioned it's importance, what if I choke it up even farther? So some of the cutting edges of a 1/2" endmill is inside the 1/2" collet? Or maybe it's a bad idea because the cutting edges can mark up inside of collet? What if you have a 7/16" endmill with a 1/2" shank in a 1/2" collet? Can I choke that up beyond where the shank ends so I can drop the head a bit lower?
[/quote]

It doesn't do much good to chuck or insert a milling cutter in a collet beyond the shank. Actually the shank is softer than the cutting portion so is less brittle - less likely to snap - they will, but will take a bending moment far better than the hardened and sharpened cutting portion. You have the idea anyhow - don't leave a lot of cutter 'hanging out'. Choke up on it but not beyond the shank.

Yes, stack some plywood on your desk and bolt it all down - then bolt your mill to that. If the desk base is stable, that should work fine. But you're going to enjoy a floor model knee mill far better...
BC

[Dick_Morris]

First off, make sure you are getting the most out of the mill you have -

Make sure your setup is rigid.

Tighten the locks on the axes that aren't moving, set the lock to a slight drag on the moving axis.

Use sharp cutters. Don't be cheap and try and use a worn out cutter for "one more job."

Use coolant where appropriate. It will increase the life of the cutter. If you can flood the cut it will also help clear chips. A slight breath of compressed air will also help remove chips and give a limited amount of cooling.

My experience is that carbide cutters are sharper out of the box than HSS (at least they are better at cutting me when I handle them). They last longer and allow for a higher speed, which allows for faster feed and quicker removal of material. The downside is they are more brittle and more prone to chipping or breaking if the machine isn't rigid.

My first mill was an Atlas horizontal mill with a Rusnok vertical head. It was cute and I did a lot of work on it. Then I upgraded to a Bridgeport clone with a 9" x 49" table. I'd much rather use the bigger mill.

[SteveR]

What Fender said. If you haven't used a roughing end mill, do this first. A high benefit/cost ratio.

SteveR