# How often do HSS end mills need sharpening? SOLVED



## TomWS (Dec 19, 2021)

I'm sure this question been asked before, but I couldn't find it using search.  So, I'm a beginner at metal milling and I was working on a project today and about midway through the project it seemed as if the cutting was struggling a bit more than it was in the beginning. It wasn't extreme, but did seem that it wasn't cutting as easily as earlier. This made me wonder how I know when it's time to get my end mill sharpened.

The specifics are:
Milling a recess in a block of 6061 aluminum,  End Mill is a 3/4" 4 flute HSS end mill that I bought from LMS (my Mill is a mini 3990).  They're coated with some kind of gold coating.  Spindle RPM a little over 1000.

I have added power feed to the X axis and it's probably around 9-10 IPM.  It doesn't have speed control.  Most of the cuts were using power feed.  I initially started cutting 0.020" deep per pass but that seemed too slow so I increased the depth to about 0.040" per pass.   I used Tap Magic Aluminum as brush on lubricant.  Most passes were about 6.5" long, 0.312" wide per pass.  Overall I cut about 0.375" deep and about an inch wide.  All passes were conventional cut, with a climb cut retrace back to the start.

Not sure what more you need...


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## benmychree (Dec 19, 2021)

It is not how often sharpening is necessary, but it is a matter of how dull the end mill is and how that is effecting the cut, if you can see a bright spot on the cutting edge, it is time.  It is strange that there is no speed control on the power feed, 9-10 inches per minute seems to be pretty fast.


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## TomWS (Dec 19, 2021)

benmychree said:


> It is strange that there is no speed control on the power feed, 9-10 inches per minute seems to be pretty fast.


Well, I had a speed control on it but it was intermittent so I hooked it up directly to the DC power source.  Still 9-10 is below the recommended Speeds and Feeds from LMS site.  They recommend 15IPM for 4 flute 3/4 inch EM.

I'm not sure I know what you mean when you say 'bright spot' on the cutting edge.  Can you explain?


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## Aukai (Dec 19, 2021)

Are you using cutting fluid? I have read that aluminum does not like coated cutters, and may get weldment?


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## TomWS (Dec 19, 2021)

Aukai said:


> Are you using cutting fluid? I have read that aluminum does not like coated cutters, and may get weldment?


I am using Tap Magic Aluminum.  There is no sign of metal sticking to the cutter and chips look curly.


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## benmychree (Dec 19, 2021)

TomWS said:


> Well, I had a speed control on it but it was intermittent so I hooked it up directly to the DC power source.  Still 9-10 is below the recommended Speeds and Feeds from LMS site.  They recommend 15IPM for 4 flute 3/4 inch EM.
> 
> I'm not sure I know what you mean when you say 'bright spot' on the cutting edge.  Can you explain?


I guess that would be more obvious on uncoated cutters, it would indicate wear of the cutting edge.


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## TomWS (Dec 20, 2021)

I looked at the end mill and, other than the very tip of one of the flutes, there doesn't seem to be any obvious wear.

Here is what I'm trying to machine.  Overall size is 170mm x 38mm and the area that I'm milling is shown in blue.  The total depth I'm milling is 10mm and is 21.61mm wide.

What I've been doing is taking 8mm wide slices about 1mm deep with each pass.  I'm now thinking that I should use the edge of the end mill to go almost the full depth with each pass but only 1mm thin cuts.  This will spread the heat along the length of the mill rather than just the tip.   Is 10mm long x 1mm deep edge cut too aggressive for my mini Mill?


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## TomWS (Dec 20, 2021)

Here is what I get with a 9.8mm height, 0.330mm cut.  I don't think I should cut any deeper, it seems to be 'lugging' with this much depth...


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## rabler (Dec 20, 2021)

My admittedly moronic approach to this question is to keep a new end mill on hand.  If the new end mill cuts better, the old one needs help.

Then I get to ask what I did to dull the old end mill.  That's where the thinking and learning begins.


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## TomWS (Dec 20, 2021)

rabler said:


> If the new end mill cuts better, the old one needs help.


LOL!  Yeah, I guess that's pretty foolproof!  Thanks!
I would like to get a sense if my speed and feed is reasonable for this task.  Given that the LM3990 does not have a speed setting on the speed knob (other than 2500 max which is pretty useless) I have a feeling my 1000 RPM was closer to 1500.  Unfortunately my POS handheld tachometer is equally useless.


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## rabler (Dec 20, 2021)

Consider trying a roughing endmill.


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## TomWS (Dec 20, 2021)

@rabler Yeah, on your advice, just ordered one, sigh...
FWIW, I did try another mill.  I moved to my 11/16"  (working my way down the box of mills) and it does cut a lot cleaner.  Still have to go slow though so I'll wait until the roughing mill comes in.
Thanks for your help.

Guess I toasted the 3/4".  Do I toss it or can it be resharpened?


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## davek181 (Dec 20, 2021)

Feeds and speeds, the great mysteries of machining.  I am no expert here, barely even a novice.  If you have a chart, by all means use it as a guideline, but also watch the chips and pay attention to the machine.  You will get more noise and vibration if you are exceeding your machine capabilities.  I leave the chip brush on the top of the head and if it really starts dancing around I am getting close to excessive.  I also watch the chips, on a cut like you are doing they will come off looking like straight slivers.  You dont want big chunks, rather just slivers.  Yours look pretty good by my experience, which is minimal as I stated earlier.  Also on aluminum the 2 flute cutter will often work better because the teeth will need a little more time to clear as opposed to harder metals.

Another thing I use, especially on steel is you want the chips to come off in fair little chunks but not dust, as then the feed is slow.  I gauge steel by cutting fast and deep enough to start the lube smoking, but the chips should not be coming off blue.

Like anything else, the more you use it the better you get.  Keep learning and don't spin the tool too fast and burn up the cutting edge.  I have learned to default to slower and speed up as needed.  

Just my .02 as another novice machinist in larvae stage, as it were.


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## Mitch Alsup (Dec 20, 2021)

As someone fairly new to machining, but one who has never dulled an end mill (yet--but getting close) I have chipped the corners of carbide end mills.......



TomWS said:


> The specifics are:
> Milling a recess in a block of 6061 aluminum, End Mill is a 3/4" 4 flute HSS end mill that I bought from LMS (my Mill is a mini 3990).  They're coated with some kind of gold coating.  Spindle RPM a little over 1000.



My G0730 mill (1000 pounds 1.5 HP) would chatter if I were to spin a 3/4" EM at 1000 RPMs, for ½" and above EMs I tend to stay in the 250-400 RMP range.
I also lube aluminum with WD-40 (with no disrespect to tap magic) lube mild steel with heavy cutting fluid, and I tend to move the table (manually) 4-5 Inches per minute for best finishes.

{I am also using 35 YO knives in my kitchen that are as sharp today as when I bought them.}

The speeds-and-feeds people will probably indicate that you are properly loading the flutes of the end mill.


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## markba633csi (Dec 21, 2021)

Many cheap-o endmills out there- good USA endmills cost more but last far longer.  Buying on Ebay can save money, sometimes you find an estate sale lot of cutters in new or nearly new condition for a bargain price.  In my experience, a lightly used US endmill can outlast a new import one
-Mark
Good US brands:  Morse, Putnam, Union, Cleveland
PS I would cut your speed down a bit- 3/4" endmill is pushing it on a mini-mill


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## GrayTech (Dec 21, 2021)

¾" is typically max endmill diameter for a smaller mill. Speed and feed charts are aimed at rigid industrial size machines, compensate accordingly. Slower feeds and/or increased speeds.


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## rabler (Dec 21, 2021)

The ends can be resharpened if you have the right equipment.  Generally not worth sending it out for resharpening unless you're getting into really big endmils.   Resharpening the spiral flutes is more difficult.  But most people just throw it in a bucket of old HSS pieces to keep for possible later re-use as some shop-made tool, or just toss it out.

I'm running a 3HP 2000lb mill, and tend to max out at 1/2" end mills for most work.  If I need to face off something or get a wide consistent finish, I use a face mill (or fly cutter).  Those big end mills don't justify themselves in smaller machines.  The import sets of gold colored HSS endmills are generally not the highest quality.


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## TomWS (Dec 21, 2021)

GrayTech said:


> ¾" is typically max endmill diameter for a smaller mill. Speed and feed charts are aimed at rigid industrial size machines, compensate accordingly. Slower feeds and/or increased speeds.


I guess I assumed that, if I used LMS's Speeds and Feeds tables, they would already compensate for that, but, well, I guess that's how ya learn things!

I've ordered a roughing mill, it's coming in tomorrow.  I'll report back on how I made out with it.
In the mean time, I want to thank y'all for helping.  I'm just that little bit closer to perfection now


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## Winegrower (Dec 21, 2021)

End mills can be sharpened.   I bought a Darex E80 or such to do this…turns out there is a learning curve on this and to date I’ve messed up more cutters than I’ve saved.   This machine does both the flutes and the tips, but note that sharpening the flutes decreases the diameter of the end mill a bit, and you need to remeasure if that’s important to the current cut.


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## TomWS (Dec 21, 2021)

Winegrower said:


> ...note that sharpening the flutes decreases the diameter of the end mill a bit, and you need to remeasure if that’s important to the current cut.


Indeed.  I have some experience with CNC routing and woodworking and have come to understand that you shouldn't rely on the stated size of a tool.  It will get you close, but measure the cuts (not the size of the tool) if you want exact.


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## Alcap (Dec 22, 2021)

I’ve been saving my dull end mills , hope to build a sharpener jig like the ones Harold Hall made . http://www.homews.co.uk/page121.html.  Most of mine get just the very tips that get dull , very seldom am I taking deeper then .030” on steel on a 1/2” cutting full width .


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## brino (Dec 22, 2021)

@TomWS 

Hi Tom. I see that you are calling this "Solved", but I thought I'd chime in anyway.

When I first saw your thread title my first response was that the question was along the same lines as "How long is a piece of rope?"... a question that cannot really be answered......

My second thought was just, "When they are dull.".... but observing that change in function only comes with experience.
You have received some great responses above.

However, I just ran your numbers and 1000 RPM is about twice the RPM I'd use.

For a HSS cutter in Aluminum I'd want to run about 100-110 sfpm. (as a hobby guy with sloppy machines and no production deadlines)
For a 3/4" cutter that means between 400-600 RPM.

There are a number of online calculators for this.
I thought LMS had one, but I cannot currently find it.....

From: http://www.carbidedepot.com/formulas-turning.htm



From: https://www.kennametal.com/us/en/resources/engineering-calculators/miscellaneous/speed-and-feed.html



-brino


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## TomWS (Dec 22, 2021)

Alcap said:


> I’ve been saving my dull end mills , hope to build a sharpener jig like the ones Harold Hall made . http://www.homews.co.uk/page121.html.  Most of mine get just the very tips that get dull , very seldom am I taking deeper then .030” on steel on a 1/2” cutting full width .


Thanks for the link to the sharpening jig.  I think, at this point in my 'career', I'll take his first suggestion:
"Most home workshop users will consider sharpening end mills a non starter due to    the complications of sharpening its edges. This is understandable and whilst I have provided designs for doing this *I consider it is only worthwhile if the milling machine is made considerable use* of. " (Emphasis mine)


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## TomWS (Dec 22, 2021)

brino said:


> For a HSS cutter in Aluminum I'd want to run about 100-110 sfpm. (as a hobby guy with sloppy machines and no production deadlines)


THAT is what I need!  DATA!  Thanks!
LMS calculator uses 200 sfpm.  Link is: https://littlemachineshop.com/mobile/speeds_feeds.php
I'll change their number in their calculator.  Do you have any other SFPM values for a hack like me?  Mild steel, Brass, SS?

Or... maybe it's as simple as taking the 'standard' recommendation and cutting it in half???


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## brino (Dec 22, 2021)

TomWS said:


> Do you have any other SFPM values for a hack like me? Mild steel, Brass, SS?



Sure, here's what I use.......

For HSS cutters:
steel, cast iron: 80 sfpm
aluminum: 110 sfpm
brass: 110 sfpm
copper: 80 sfpm

A few notes:
You will see wildly different recommendations in any text dedicated to professionals where the equipment is new and tight, and time is money.
I treat these as "starting points" and adjust up/down to suit the task, material, equipment, etc.
In practice, I like only having two starting points to remember; it's easier on my little brain....
These assume some cutting fluids, but they don't have to be esoteric, expensive, hard to find fluids; here's two that I can find at my local hardware store:
I use pipe threading oil for cutting steel
https://www.homehardware.ca/en/1-litre-pipe-cutting-oil/p/1142041
For aluminum I like the clear, odorless lamp oil
https://www.homehardware.ca/en/710ml-clear-paraffin-lamp-oil/p/4360517?page=search-results page

I don't use much carbide tooling, but cutting speeds there can often be increased by 50%.

-brino


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## mikey (Dec 23, 2021)

Tom, you've gotten a lot of great input but I wanted to chime in on a few points.

The 3990 is a mini-mill so not a lot of power or mass. While you can put a 3/4" end mill in it, that is way big for a machine of this size. You have to remember that you need enough power and rigidity to cut effectively with a cutter of that size and you just don't have it. I suspect that a max end mill diameter for your machine would be close to 3/8".
The cuts you're making are profiling cuts. Speeds and feeds differ for profiling cuts vs slotting cuts, just as they differ for roughing and finishing end mills. What greatly impacts on your speeds and feeds are how much of the diameter of the end mill is involved in the cut (called the radial depth of cut) AND how much of the length of the end mill involved (the Axial depth of cut). With each profiling cut you make, BOTH of these depths of cut have to be considered as they determine what your speed will be to enable the end mill to make the cut. The greater each one is, the slower the spindle speed must be.
The feed is very much dependent on the diameter of the end mill and how many flutes it has. The more flutes, the faster the feed. Keep in mind that calculators and charts and tables assume you are using an industrial machine with the rigidity and power to push an end mill through the material at these feed rates. Just to be clear, a 3990 does not fall into this category and hence, the feed rates do NOT apply to your machine.
The concepts of "chip load" and "metal removal rates", in general, do not apply to a manual mill and certainly not to a mini-mill so forget that.
With regard to when a HSS end mill needs to be sharpened, it is a plain and simple fact that us hobby guys typically cut with the end of an end mill and this is especially true when we are first starting out. Sort of makes sense, too, because isn't that how an "end" mill is supposed to cut, on the "end"? The reality is that the quickest way to dull an end mill is to take baby cuts with the end at improper speeds and feeds. Better to use a reasonable axial and radial depth of cut at the proper speeds instead of using the end or taking baby cuts; that will reduce wear more than anything else. Roughing with a finishing end mill in this fashion is also common to hobby guys and will dull the end mill even faster. If you look at a brand new quality end mill, you will see little tiny hooks at the tips of each flute; when those hooks are gone or when the tips of the flutes are not sharp, the end mill is done and needs to be resharpened or replaced. Far and away, improper speeds dulls end mills more than anything else.
Okay, so what to do about all of this? I'm no expert but I've been using a Sherline mill for close to 40 years and sort of have an idea of how to do it, at least on that machine (and my bigger mill).

Always rough with a rougher when possible; it will save your finishing end mills. You can go about 20% faster and cut about 20% deeper with a rougher compared to a comparably sized finishing end mill. When profiling, use a fine pitch rougher; when slotting, use a coarse pitch rougher. This has to do with chip clearance. My little Sherline can push a 3/8" coarse pitch rougher in a full 3/8" deep slot in 6061 without even slowing down.
Use finishing end mills after the rougher to refine the finish and bring the cut to final size. When profiling, 4 flutes or more work well. When slotting, 2-3 flutes work better for chip clearance. You have to go slower when slotting and you go faster when profiling; more flutes allow for faster feeds; fewer flutes require slower feeds.
Limit the diameter of your end mills to sizes your machine can handle. There are exceptions to this but the majority of the time I limit my Sherline to 3/8" max, although I've gone up to 1/2" on it at times. I limit the end mill size because I know that if I get my speeds and feeds right, the mill can handle the cuts I ask of it. If I go bigger, it cannot, and it cannot because I just don't have the power, rigidity or speed necessary to handle a big end mill.
When cutting aluminum, high helix end mills work better. For slotting, go with 3-flutes. When profiling, 4 flutes or more work better.
Use HSS for most materials. Use cobalt when machining higher carbon stuff or stainless. Use carbide when you need to go deeper, taller or smaller; carbide is stiffer and will be more accurate in deeper slots or features. Carbide is also better when the edge requires a great deal of accuracy because the end mill is less likely to deflect.
Finally, learn how axial and radial depths of cut are used to determine speeds. This is critical for you. Just because a table or calculator spits out some number, that has to be tempered by the fact that you're using a mini-mill and not a Lagun or Bridgeport.
I am attaching a data sheet from Niagara Cutter for 6061-T6. It will give you an idea of the concepts of axial and radial depths of cut and how your choices affect speeds and feeds. Look it over; it should be self-explanatory but I can guide you if you need it. Also remember that these recommendations are for full-sized mills but if you limit your end mill size to 3/8" or so, the recommendations in this sheet can very likely be used with your mill without modification.

I've thrown a lot at you but I do hope this helps.


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## TomWS (Dec 23, 2021)

mikey said:


> I am attaching a data sheet from Niagara Cutter for 6061-T6.


Thank you very much for the advice and the data sheet.  I'm a bit confused by the data sheet, however.  The way I read it:
1. Axial Depth should not exceed 1.5x diameter.  My Axial depth is slightly less that 3/8" so I'm ok there even if I use a 3/8" diameter bit.
2. Radial Depth Ratio determines the SFPM value.  So, if I'm using a 3/8" (10mm) diameter bit at, say, 12.5% stepover (Dia/8) I should use SFPM value of 600. 

That doesn't jive with any of the numbers I was seeing.   LMS calculator uses 200, others recommend 110, etc.   What am I missing?


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## mikey (Dec 23, 2021)

Yeah, speeds for aluminum with smaller end mills will easily max out your speed so max out your speed and focus on feed. Personally, I prefer to feed manually with these smaller end mills so I can feel what the cutter is doing and this takes a bit of time to get right. When a cutter is working right, you will feel a slight resistance to the feed. As you feed in, you will feel the cutter contact and then you'll feel the resistance to the feed increase. You want to feed just enough to keep a slight positive contact with the material as it cuts. Harder to describe than to do but it is important because this works for ALL cutters for ALL manual feeds, either on the mill or lathe. You are looking for a slight resistance to the feed, and then you have to maintain it throughout the entire cut. Get it right and the tool will cut efficiently and accurately; push it and the tool will deflect.

The other thing I meant to mention is that using cheap end mills is false economy. Cheap end mills do not cut well, they do not last and they make learning to use an end mill much harder. I highly recommend you buy a good high helix 3 flute roughing and finishing end mill from a good maker when working with aluminum. I much prefer Niagara Cutter end mills over all others; they work, they last and they are accurate. My current Niagara 3/8" high helix coarse pitch rougher for aluminum has to be over 10 years old now and is still going strong. My Brubaker high helix finishing end mill is well over 5 years old and still cuts like new. My point is that it pays to buy good end mills appropriate for the material you have and then learn to use them properly. 

Good makes include Niagara Cutter, Brubaker, Melin, Regal Beloit, OSG, Putnam, Titex. There are others. Note that Shars, Harbor Freight and LMS are not on this list. 

*Always buy new end mills*, even on ebay. Do not buy used end mills unless you can sharpen end mills properly, including the hook at the tips. 

Limit the size of your end mills to sizes your mill can handle. Again, 3/8" to maybe 1/2" would be the max. Quite often, you can save money by buying off sized end mills. The vast majority of the time you can use a slightly smaller end mill and just cut a slot to size by moving your X-Y coordinates. For profiling, the exact size of the end mill doesn't matter.

The number of flutes impacts on chip clearance and feed rates. In slots, go with 2-3 flutes to clear chips better; for profiling, more flutes produce a better finish and allow you to feed faster. In slots, use a low pressure stream of air to clear chips so the edges of your cutter are not doing a lot of re-cutting; you will be surprised at how much longer your end mills will last. 

Lubricants matter. WD-40 works well for aluminum and is cheap. A mister system works best to lube and blow chips clear but a brush and blow gun works almost as well. For steels, any good cutting fluid will work and air is just as useful.

Give it some time and things will work out. You have a little mill so you have to determine what it takes to use it. Much of the information on the net and the forums does not apply because you just don't have the power, rigidity and mass BUT that doesn't mean you can't do the work; it will just take a bit more time and finesse. I use my Sherline a LOT, even though I have a larger mill that is orders of magnitude bigger; the Sherline is just easier to use, more precise and has variable speed so I can dial in my cuts. You would be surprised at what a tiny Sherline mill can do in the right hands. The same will be true for your LMS 3990 once you figure out how to use it.


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## TomWS (Dec 23, 2021)

Ok, thanks for the additional info, but I'm still stuck on the purpose of the datasheet you sent to me.  If I read it correctly it's recommending SFPM much much higher than anything I've been looking at - how am I supposed to use that data?



mikey said:


> Yeah, speeds for aluminum with smaller end mills will easily max out your speed so max out your speed and focus on feed.


Are you saying set my spindle speed to max and then manually feed the mill into work by feel/sound?  Clearly if I use 600 SFPM in the calculator it is, indeed, going to tell me to set my spindle to max speed, but 600 SFPM doesn't sound right at all.


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## mikey (Dec 23, 2021)

Yes, max your speed and feed by feel. Have you tried it? I've been doing this for decades.


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## Aukai (Dec 23, 2021)

You can only go as fast as YOUR machine will allow.


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## TomWS (Dec 23, 2021)

Aukai said:


> You can only go as fast as YOUR machine will allow.


Yeah, I get that.

What I am totally flummoxed about is that the link @mikey gave me had a SFPM value of 600 for aluminum and that makes no sense to me at all.  It is inconsistent with every other source I've seen and I was looking for an explanation of that. 

However, since this isn't contributing to the general wellbeing I'm going to accept all the help I've gotten and tune my cuts accordingly.  Thanks all.


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## mikey (Dec 23, 2021)

Gotta remember that recommendations are for industrial/CNC machines that can run at those speeds; yours cannot so just go as fast as you can. For harder materials, cutting speeds will be much slower but for aluminum speeds are commonly faster than a hobby machine can achieve. Not a big deal. Just run it and feed by feel and you'll be fine.

You can also use power feed. Feed by feel to get an idea of a decent feed rate and dial in a rate that approximates it.


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## Kevin T (Dec 23, 2021)

The thing that I like about HSS is that a good shape is easy to keep sharp with a set of whetstones. Couple minutes and you're good to go again. I usually use them until I can see some imperfection in the cutting edge and then I sharpen.


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## tq60 (Dec 24, 2021)

We get used end mills from a local dealer, check for sharpness and usually can find suitable for hobby stuff.

Regarding speed, as already posted, material and machine matter as does coolant or lube.

We have some radio rack aluminum, gummy aluminum that sticks to the cutter.

Slow and somewhat heavier or fast and light, both work but need ATF for slippery to keep from sticking.

Steel, slow works best.

Slow rpm and slow movement as too fast of table overpowers the mill.

You get a feel for it with practice.

Sent from my SM-G781V using Tapatalk


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## TomWS (Dec 27, 2021)

rabler said:


> Consider trying a roughing endmill.


I finally got a decent 1/2" Roughing End Mill and it works much better than anything I've tried so far.  It's a 3 flute from HTC Tool Company and seems to be good quality.  We'll see over time.  

I was able profile mill 0.7mm depth of cut, 10mm height, using my 9 IPM power feed without any issues.  Spindle speed was 840 RPM and the mill was barely warm after each pass.  I might have been able to cut deeper but I didn't want to push it.

Thanks again for the advice!


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