feed and speed theory and practice.

[ihavenofish]

so, i bought a (sieg kx1/novakon nm070 mini mill. and and just starting to get it going. have some toooling ariving this week, but bought some offcut metal scraps and have been playing with it today.

this is my first mill of any kind, so i have zero practical experience, but ive been planning this for like 10 years and have built up a ton of theoretical knowledge.. most off the internet, but some from my father and friends father who are both machinists.

when i first got the machine, i ran a 1/4" 3 flute end mill through some mystery aluminium at 100ipm and 5000rpm. this was an accident as i misread the feed calculator i was using. the math works out to .007fpt on that cut. people on here screamed when i did it.. "ur doin it wrong!". they claimed i should have done the cut at mo more than 10 or 15 ipm. manufactures guidelines for side cutting on this particular M42 end mill are .002fpt.

thing is... it worked just fine with just a spray of solvent as coolant. i discussed with someone knowledgable here that it was really the tool thats the limiter here, and that it might wear out quick abusing it like that. he also said id get a better finish going slower. fair argument and sure enough slowing to 25ipm and taking deeper cuts yeilded both a better finish, more accurate cut due to less deflection, and in fact higher metal removal rates.

a fine lesson learned i say.

so today, i bought a fly cutter. i put in a piece of 1018 steel, set the carbide cutter to a 2.75" diameter and based on not my calculator, but rather a tormach demonstration *in aluminium* proceeded to trim off about .01" off the bar at 10 inches a minute and what i think was around 1000rpm.

i say "i think" because my spindle control isnt working corectly. any speed thats not full (5k) kinda jitters and doesnt do what the control claims.

so the cut was.. kinda bad. it cut well enough, but left a pretty bad finish behind. i bumped the speed to a theoretical 2000rpm and got a heck of alot better, bordering on downright nice.

now, heres where theory meets practice again. 2000rpm with the fly cutter in steel is 1440 surface feet per minute. this is way beyond the recomendations ive heard from anyone around here.

after a few runs i got annoyed with my jumpy spindle and just put it on full speed. 5000rpm at 2.75" is 3600 sfpm. ran it throught the steel at the same 10ipm. sparks! after the lights show, i saw all the little pigtail chips were black and the workpiece... perfect. not even warm, better finish than the last run and the cutter seemed to ba fine as well. i should note theres been no coolant of any kind in this test.

i used to have a chart that showed machining "zones" for metals. for example zone 1 for titanium says 200-250sfpm is where you need to be. then, at 1100sfpm a second zone kicks in up to 1300sfpm. every metal had 2 or even 3 zones where machining characteristics were ideal. aluminium even had a zone saying 12000sfpm was ok. ive since lost this chart and know it was likely tied to one manufactureres specific tools, but what happened today made me remember all about the concept. it also dawns on me why most literature keeps to the low zones - or doesnt even mentions there is more than one optimum speed... simply because manual mills and older cnc's cant usually hit them.

so, now i ask the crowd of people with far more practical knowledge than me... is this right? can i mill steel at 3600sfpm without ill effects?

or am i an idiot whos wearing out tools?

also, anyone alse done any crazy things way outside machining "conventional wisdom" that worked well?

[John Welden]

also, anyone alse done any crazy things way outside machining "conventional wisdom" that worked well?

Sounds like you're doing what you need to do to get the results you want. If you're not blowing through tons of expensive cutters or damaging your machine, than the speed and feed chart doesn't really matter.

There are tons of variables when machining. Sometimes you've just got to play around until you figure out what works on your machine.

That fly cutter you're using may be a bit large for your mini mill. It probably doesn't have enough power at low RPM's to run your cutter at the proper speed. Jacking it up to 5k to get some HP and then running a high feed rate in theory works, but it's not exactly what I'd consider to be good practice.

I'd recommend taking mini cuts on your mini mill. Smalll cutters and small cuts. Treating that thing like a real machine is going to beat the crap out of it. I'd always like to hear it buzzing along nicely. The machine will be a lot happier if you treat it like what it is.

[djr76]

You are just gonna prematurely wear the inserts out. Not all tools are the same as in inserts, grades, geometries ect. The best thing to do is consult the manufacturer of the tool or the technical support were you bought the tool. They will have the best starting points for your working conditions.

I know there is some new cam algorithms that have pushed solid carbide endmills way beyond their known optimal operating parameters maintaining a constant Total Engagement Angle but those are generated and not hand written and probably out of your realm.

For this being your first machine and you are a beginner, you shouldn't be pushing your machine tool and the costly cutting tools beyond their capacity. You will just end up getting pissed at yourself when you break the machine, tool, part, or yourself. Gotta learn how to crawl before you can run my friend. Ive been a professional machinist for 13 years on expensive 20+ hp machines and still dont know everything there is to know.

[ihavenofish]

i think i agree about the use of smaller cutters. i reduced the fly cutter to 1.75" and its gor a 100 times better finish, due i think entirely to it causing less flex in both the cutter and machine. its also more balanced so it makes less noise.

ran int an issue though now. my cheap $12 fly cutter body wont hold the cutter tool. after a few passes it works itself loose and shifts a half a mm or so. does drilling the tool so the set screws have something to register on sound reasonable? im not prepared to by anything fancier just yet.

anyhow, my 1" steel block is now a 3/4" steel block, haha. thats enough goofing around for today.

thanks for the thoughts.

[Geof]

Originally Posted by ihavenofish ....so, now i ask the crowd of people with far more practical knowledge than me... is this right? can i mill steel at 3600sfpm without ill effects? or am i an idiot whos wearing out tools? also, anyone alse done any crazy things way outside machining "conventional wisdom" that worked well?

Are you an idiot wearing out tools? No, not if you are learning from it.

I notice you seem to have been given somewhat contradictory advice and I am probably not going to change that.

Your 5000 rpm 3600 sfm experience was a bit extreme (actually a lot extreme ) but you discovered an interesting effect and that is the work stays cool the cutter stays cool but the chips come off glowing. Onbig machines with CAM programming this phenomenon is put to use to have very fast metal removal rates but as djr76 points out a bit difficult to do by hand. Not totally impossible, I have simulated this approach with hand programming; have a look at this thread; http://www.cnczone.com/forums/showthread.php?t=73902

However you should scale back a little bit. Those very fast metal removal rates are applicable when time is more costly than tool bits; the tools do die faster measured in time but they remove more metal during the time they are working. Also when you are screaming along like that you need to give the tool a respite to cool off which is why these high speeds are used in combination with the trochoidal toolpathing and air blast.

Don't get intimidated by the people who scream youre doing it wrong, read what they write and store it all in your memory along with your own experience.

Post any questions you have and you will get plenty of replies.

[John Welden]

Originally Posted by ihavenofish i think i agree about the use of smaller cutters. i reduced the fly cutter to 1.75" and its gor a 100 times better finish, due i think entirely to it causing less flex in both the cutter and machine. its also more balanced so it makes less noise.

If you insist on using a big fly cutter, you may want to consider a multi flute shell mill. It will be balanced and the extra cutters will be better than the clubbing your single lip is doing.

ran int an issue though now. my cheap $12 fly cutter body wont hold the cutter tool. after a few passes it works itself loose and shifts a half a mm or so. does drilling the tool so the set screws have something to register on sound reasonable? im not prepared to by anything fancier just yet.

This tells me you're doing something very wrong. Without being there its hard to tell what's happening so please allow me to give some general advice. From now on, any time your mill is cutting, it should sound like a fine machine, just buzzing along with minimal vibration. Run small cutters, like 1/8 or maybe 1/4 inch at the biggest. Take little tiny fine cuts that don't slow the motor down. You need to treat it like its a sewing machine.

[ihavenofish]

Originally Posted by John Welden If you insist on using a big fly cutter, you may want to consider a multi flute shell mill. It will be balanced and the extra cutters will be better than the clubbing your single lip is doing. This tells me you're doing something very wrong. Without being there its hard to tell what's happening so please allow me to give some general advice. From now on, any time your mill is cutting, it should sound like a fine machine, just buzzing along with minimal vibration. Run small cutters, like 1/8 or maybe 1/4 inch at the biggest. Take little tiny fine cuts that don't slow the motor down. You need to treat it like its a sewing machine.

haha, the machine isnt THAT wussy. very little will slow the motor down, its actually got more than enough torque to swing a 3" fly cutter in steel at low rpms. when the spindle control is fixed i will have alot more use of the lower speeds. the issue is the fly cutter set screws back out and the tool itself isnt a very snug fit in the cutter head so it moves easily with very little force. i think if i get the cutter securely mounted it will work very well - at least at the 1.75" setting. 2.75" has too much flex, which is no fault of the mill, just the tool.

[Geof]

Originally Posted by ihavenofish ...the issue is the fly cutter set screws back out and the tool itself isnt a very snug fit in the cutter head so it moves easily with very little force. i think if i get the cutter securely mounted it will work very well....

Sometimes it is not the setscrews backing out it is that they are made out of low grade chees and the cutting impact distorts them. Replace them with good setscrews and you maye solve part of your problem.

Another modification I have done to simple flycutters is tap holes beside the slot for the tool, close enough that when a button head socket screw is installed the head overlaps the tool. Counterbore the hole slightly slightly so the head bottoms out on the tool not on the body of the flycutter and then the tool is held very securely.

[ihavenofish]

Originally Posted by Geof Sometimes it is not the setscrews backing out it is that they are made out of low grade chees and the cutting impact distorts them. Replace them with good setscrews and you maye solve part of your problem. Another modification I have done to simple flycutters is tap holes beside the slot for the tool, close enough that when a button head socket screw is installed the head overlaps the tool. Counterbore the hole slightly slightly so the head bottoms out on the tool not on the body of the flycutter and then the tool is held very securely.

ooh, i like that idea, i think ill try it tomorrow. thanks.

oh, and i saw your thread on trochoidal milling before. its something i want to try as i move forward with "real work". tis an expensive option for software though. i find it depressing that the software cost more than my machine and all my tooling. im still deciding what to do for cam. im supposed to get some demonstrations for a few companies soon for 2.5d basic setups.

[Geof]

For basic 2.5D you really don't need CAM; I program some very complex shapes by hand. I use a very simple 2D drafting program to obtain tangent points for blended curves. The part shown here: http://www.cnczone.com/forums/attach...4&d=1201759938

was entirely hand coded.

Once you are conversant with hand coding then get into CAM and use it to extend your capabilities rather than relying on it as a crutch to substitute for what you don't know how to do.

[flick]

Originally Posted by ihavenofish aluminium even had a zone saying 12000sfpm was ok. ive since lost this chart ...

I know your interested in milling, not lathework, but I might still have a relevant example from my turning experience.

I regularly turn 7075 at 2800 rpm (the max safe speed for my chuck) at a diameter of 12 inches. That's something like 10,000 sfpm (I did the math in my head, correct me if I'm wrong). Wear is excellent. I can make a bin full of chips with one edge like this. By a bin, I mean like the size of the small dumpsters you find behind restaurants and townhomes.

This doesn't work well with geometries or coatings intended for steel. To avoid the built-up edge and weld/tear cycles that aluminum causes, I have to use an insert specifically made for aluminum.

[John Welden]

Originally Posted by ihavenofish haha, the machine isnt THAT wussy. very little will slow the motor down, its actually got more than enough torque to swing a 3" fly cutter in steel at low rpms. when the spindle control is fixed i will have alot more use of the lower speeds. the issue is the fly cutter set screws back out and the tool itself isnt a very snug fit in the cutter head so it moves easily with very little force. i think if i get the cutter securely mounted it will work very well - at least at the 1.75" setting. 2.75" has too much flex, which is no fault of the mill, just the tool.

It's a tiny little bench top machine, so yes, it is THAT wussy. I'm not trying to trash on your machine, I'm only trying to explain that I feel like you should treat it like a very light machine. A 2.75" fly cutter on a real machine can be pretty harsh in steel.

Your machine will last longer, your tooling will last longer, and your parts will come out better if you back off and go easy on it.