That's kind of an open ended question. Have you done any research or trials on your own?
Ok I am sure some of you have had enough experience with the machine so enlighten me on the ballpark figures for RPM/Feed/DOC
HSS and carbide
Aluminim, 1018, stainless 304
- profiling, pocketing, roughing
That's kind of an open ended question. Have you done any research or trials on your own?
Research yes, trials no since I dont hav the machine. The problem is that due to the nature of "mini" mills their feeds, sppeds and DOCs are quite different from what the big guys would absorb. So I was hoping to take on someone else's experience with small devices and what they concluded to be most suitable parameters.
Actually let me piggy back on Zaebis' question...
Syil america has posted a UT video of the S3 taking 0.0375 in2 off Aluminum 6061-T6 (hardness 90) at 26 ipm. I presume he was using a regular chinese end mill (1/2" 2 flute). No RPM was mentioned. That is just under 1 cubic inch of material per minute.
The SGS demo video I linked to in the other thread is probably using a machine costing $100K and is taking 0.1 in2 on Aluminum 2024 (hardness 120) at 500 ipm and 12,000 RPM. That is 50 cubic inches of tougher material per minute, but presumably with a better end mill. Both are roughing.
That is a 50:1 difference! (for roughing, never mind capabilities)... still on one side you have a better tool, and on the other side you have a softer material.
It would be cool to see an "all things equal" comparison.
BTW, back to Zaebis question... did anyone publish a record of successful RPMs/IPMs/Steps/Tooling/Coolant/Materials for the S3... if not may be someone with a bit experience could start a thread. I think that would be cool, like a place we could refer to for a starting point -- would that make sense?
There's no shortage of recommendations on speeds & feeds for various materials on the web or in books. Machinery's Handbook is almost a requisite for any half-way serious home shop machinist and it has several pages on the subject. That gives you a starting point and experience will soon teach what works well for your mill and cutters.
It might also be useful to know how much HP is required for a given set of conditions as that will give you the upper bound on speeds, feeds, WOC, and DOC.
ME Consultant Standard or Pro are utilities that can do much of these calculations for you:
Allowable tool speeds shouldn't change much from large to small machine, but feedrates will of course be lower with a mini mill. RPM=(3.82*sfm)/tool diameter
For 1018, I'd drill at 65 sfm with HSS and 200 with carbide
Milling at more like 100 sfm for HSS and 300 with carbide because it is not constantly rubbing like a drill. Flood coolant is assumed. Coolant with some real oil is better.
For 304, I'd drill at 25-30 sfm with HSS (cobalt is much better)
Milling at 50sfm and 150 with carbide (coated cobalt and carbide are much better)
Example of formula: drilling 1/4" hole in 304 SS, 30 sfm
3.82*30/.25 = 450 rpm.
Feedrates: On my 40 taper CNC, I would mill in feed per tooth at .5% diameter for slotting. I use variable helix endmills allowing full slotting at one diameter depth. Sound will tell you a lot. Short holders, short tools.
I looked at the datasheet for one of my end mills and the parameters it gives are not really applicable to a benchmill like the SX3.
If we pick the SGS 34800 which is a 1/2" 3 Flute end mill. The data sheet http://www.sgstool.com/catalogs/PDFs...s/sf_scarb.pdf says that if I'm cutting Aluminum they "recommend" 1600-2000 sfm. They say rpm = sfm * 3.82 / tool diameter (same you did), which gives us 12200-15200 rpm. The feed rate (feed per tooth x number of teeth x rpm) ends up being 220-273 IPM. Then they have the extended reach that is even more aggressive.
If we bring down the RPM to 3500, the feed rate becomes 63 IPM for an axial depth of 1.5x the diameter and a radial width of 0.5 the diameter.
In the ZCarbAP datasheet for a 1/2" cutter slotting a low carbon steel at 100% Rw they recommend 3360-4090 RPM and 32-39 IPM
All of these are way out of the range of a bench top mill. I mean you can program 3360 rpm and 32 IPM, but if we try to take a 1/2" wide and 1/2" deep slot on steel with that I suspect we will not have much success.
In these tables provided by the manufacturers the RPMs are high and the feed rate per tooth seem to require more power than we have.
So I'm not sure where to get the SFM and feed rate per tooth for this class of machine (?)
You did mention that "allowable tool speeds shouldn't change much from large to small machine, but feedrates will of course be lower with a mini mill"... Does that mean that in the two examples above we can run everything at 3000 RPM and tweak on the IPM and how much we are taking with each cut based on how much the machine complains? I mean that sounds like a plan, if it works cool
A kind of silly question, what is the difference between "slotting", "peripheral", and "contouring" which are sometimes used in these tables. I guess "slotting" is when you have 3 sides of the tool in contact with the material. Not sure about the other two. There is also "profilling" which I guess is either "peripheral" or "contouring"... Ideas?
Last edited by Ed from NY; 06-15-2009 at 12:19 AM.
You are right on about slotting. I'm not sure about contouring vs peripheral. So, if your machine redlines at a speed below the sfm allowed by your tools, you just run your machine at full speed and adjust your feedrate. The speeds I gave are my own, but basically the same or a little lower than the Machinery's Handbook. I have burned a lot of drills and endmills in stainless, so I go even lower than they say in 304 and 316. The problem with the endmills you are looking at is that they will actually chatter more if you feed them less. If you try to run a 1/2" slot, 1/2" deep but run .0005" feed per tooth instead of .003", you will rub the endmill to death and it will sing. What I would do is find out what size Z carb endmill your machine can handle when fed correctly. Try a 1/4" Z carb at .001" fpt. If it can do that, try a 3/8" at .001, .0015" and .002" How much thrust does your machine have in the X and Y direction? How much horsepower? You should be able to easily remove 1 cubic inch of mild steel per minute for every horsepower. I have approached 2 cubic inches per minute per horsepower with a free cutting facemill on a 40 taper CNC. By the way, the Z carbs run longer dry. It is a hard thing for machinists to gt through their head, me included, but I have proven it to myself and others on here have too.
That is a keen piece of advice... "find out what size Z carb endmill your machine can handle when fed correctly" Thank you!
I looked at the "Machine Shop Practice Vol2" by Moltrecht and found some formulas to calculate power requirements.
Rated at 1.34HP, according to Moltrecht I could get the X3 to do 3000 RPM and 27 IPM on aluminum and slot 1/4" (3 flute cutter 1/2" end mill). On a soft carbon steel do 1500 RPM and 21 IPM and slot 1/8" (4 flute cutter 1/2" end mill) -- that is with 1979 cutter technology.
With a smaller cutter or modern cutter technology things should improve... now I need to rum some trials... as soon as I get it all working.
Moltrecht says never to get at or below 0.001 inches per tooth "except with small end mills and when milling certain very hard materials. At such low feed rates the teeth will tend to runb against the workpiece instead of penetrating to form a chip, resulting in excessive tool wear"... so in the examples above I picked 0.003 and 0.0035 inches per tooth. Which is just like you said.
Well, smaller endmills are cheaper to play with, but .003" is very high feed for a 1/8" endmill. Even with a CAT 40 spindle machine I would never feed a 1/8" endmill that hard except maybe with only .005-.010" engagement on the side. The feedrate per tooth that a cutter can handle without snapping from bending stress is proportional to its diameter, as well as the depth of cut you can take with it. I have actually snapped a 1/4" Z carb with only 1/4" depth full slotting at .0015" feed per tooth. It was quite a while ago and I have been monitoring my spindle runout much more closely since then. I looked at pictures of an X3. It appears to be a big bad macine compared to a Taig or Sherline. R8 spindle, right? I would use only collets, not endmill holders. Even on my Bridgeport, that made a huge difference. With any machine, you want the cutting edge as close to the lowest bearing of the spindle as possible. Any distance you have creates bending. Bending is proportional to the third power of the distance between support and loads, all other things being equal. I learned this in Mechanical Engineering and then again very intimately as a machinist. Some never really do. When I see a guy running a CNC with a 1/2" endmill and a holder with a 4" projection length I get really frustrated. Whatever machine he has, he could be cutting easily twice as hard with a 1.38" holder, not to mention having less runout on his cutter, because runout is proportional to length out of the spindle. You can prove this to yourself pretty easily with a vise and anything round that is a few feet long. Broomstick, threaded rod, anything. Clamp it in the vise with only 1 foot hanging out and get a feeling for how much it bends with your weight against it. Then leave 2 feet hanging out and do the same thing. You'll be flexing it 8 times as much. Yes, 2*2*2. That's because your bending moment was doubled, as well as the length over which it was applied. The third multiplier of 2 is hard to explain but it is true. Then leave 3 ft hanging out and you will get 27 times the deflection )3*3*3). I used to buy cutters with longer length of cut because they were only ~10% more money with twice the cutting edge. I wasted a bunch of hours finding out that I want the shortest cutter that will do a job. So when talking of small endmills, this is not less important, it's more important. I think your machine can handle a 1/4" varimill, cutting as much as a 1/4" slot in 1018 steel. I would use a scrap piece and build up to it. Run full speed at 3500 rpm, 1/8" depth, .001" feed per tooth (14 inches per minute). That's only .44 cubic inches per minute. See how it sounds. Listen for how much flex is released when it breaks through the material at the end of the cut. That will give you an idea of how rigid your machine is. If you want to run bigger diameter cutters, I'd run them more shallow with good feedrates ran than full depth and rubbing feedrates, but .003" fpt for a 1/8" is way high. That's a healthy feed for a 1/2" endmill fully engaged in steel. So if you wanted to cut with a 3/8" Z carb, you could try 3500 rpm, 1/4" depth, .0012" per tooth. That's 17 inches per minute and 1.6 cubic inches per minute. That is all I'd try with 1.34 hp and it may stall. Running 1/8" depth and then 3/16" depth first would be a good idea. By the way, the sfm numbers I see them giving for stainless have never given me more than a very brief experience with a tool. 303 stainless is nice. It's sulfurized and makes a nice chip, like 1018 cold rolled. Much different than 304 but with the same corrosion resistance. Let me know how it goes. By the way, I have a source for private label varimills that work quite well at about half the price of Z carbs. Email me if you'd like his email.
Not saying it is right, just here is what I did...
a. Feed rate per tooth = 0.0035 (because I wanted to stay away from 0.001 and most of the recomendations in the book start with 0.003)
b. RPM = 1500 (could have picked a higher RPM with a smaller feed, but then line (i) goes up)
c. Cutters = 4
d. IPM = 21 (calculated: d = a * b * c )
e. Width of cut = 0.5 (slotting)
f. Depth of cut = 0.125 (choice of removing 1/8" of material per pass)
g. Metal removal rate = 1.31 in3/min (calculated: g = d * e * f )
h. Power cte from a carbon steel with 100-120 hardness = 0.66 (from a table, based on material being cut)
i. Feed factor = 1.27 (interpolated from a table, based on the choice on (a))
j. Tool wear = 1.1 (from a table, factor for end mills)
k. Power at cutter = 1.21 hp (calculated: k = g * h * i * j)
m. Efficiency factor = 0.9 (belt driven, from a table)
n. Power at motor = 1.34 hp (calculated: n = k / m)
Thanks for the advice! I'll start with the numbers you suggest and then see if I can build up to the numbers suggested in the book.
a = 0.001
b = 3500
c = 4
d = 14
e = 0.25
f = 0.25
g = 0.875
h = 0.69 (126 hardness)
i = 1.6 (goes up A LOT with smaller (a)'s)
j = 1.1
k = 1.06
m = 0.9
n = 1.18 hp
I do not have any projects now that use steel. My next 2 projects use Nylon, but I ordered some A36 (two one-foot pieces of 1x4) and 1018 (one two-foot piece of 1x4) to run some tests, and to use in projects later. Got it from http://www.metalsdepot.com 1x4 seems to offer the best pricing and fits right in the envelope of the machine.
Last edited by Ed from NY; 06-15-2009 at 12:11 PM.