[braddo]

I have been doing quite a bit of reading, and have downloaded several calculators and such and I am still completely in the dark about this question.

I have a 1/8" 2 flute end mill and would like to cut small depth passes (like .005") using a small flex shaft driven handpiece as a spindle in a lightweight CNC.

I am getting answers literally all over the map, from definitely go as fast (RPM) as you can go i.e. 30k RPM and don't "baby it" i.e. high feedrate, to definitely use 8000 RPM, 50 -250 IPM feedrates. I cannot find chipload for these little tiny bits and seemingly cannot use the calculators - the complex ones like gwizard ask what type of mill I have (?) chipload, SFM and other parameters I don't have. Others don't seem to compute anything but just ask for all of the numbers I thought the calc was going to calc.

Originally, since so many folks raved about them, I got some single flute carbide cutters from Onsrud - Dropped a hundred or so on a few, but they just immediately plunge straight in and the single flute seems to be far too aggressive for my lightweight setup. The two flutes look "close" in that I'm getting channels, but with occasional pulling to the side and not as clean as I would like. But don't know which way to go, slower, faster - I've done some "matrixes" slower faster but none seem like they're in the ballpark.

Thanks!

[acannell]

I have been doing quite a bit of reading, and have downloaded several calculators and such and I am still completely in the dark about this question.

I have a 1/8" 2 flute end mill and would like to cut small depth passes (like .005") using a small flex shaft driven handpiece as a spindle in a lightweight CNC.

I am getting answers literally all over the map, from definitely go as fast (RPM) as you can go i.e. 30k RPM and don't "baby it" i.e. high feedrate, to definitely use 8000 RPM, 50 -250 IPM feedrates. I cannot find chipload for these little tiny bits and seemingly cannot use the calculators - the complex ones like gwizard ask what type of mill I have (?) chipload, SFM and other parameters I don't have. Others don't seem to compute anything but just ask for all of the numbers I thought the calc was going to calc.

Originally, since so many folks raved about them, I got some single flute carbide cutters from Onsrud - Dropped a hundred or so on a few, but they just immediately plunge straight in and the single flute seems to be far too aggressive for my lightweight setup. The two flutes look "close" in that I'm getting channels, but with occasional pulling to the side and not as clean as I would like. But don't know which way to go, slower, faster - I've done some "matrixes" slower faster but none seem like they're in the ballpark.

Thanks!

so what happens when you cut a 0.005" deep slot with a 1/8" two flute end mill?

[braddo]

Well, the bit does cut but appears to sort of push the aluminum around, small chips do get generated, but a bunch also seems to gum up around the sides of the slot. This is cutting at 25000 RPM, either dry or with WD40 as a lubricant. The line it cuts will be straight for a bit, say an inch or so, then, as it gets deeper (the piece isn't perfectly flat) it will start to swim around and the line becomes wavy. If I make multiple passes in that slot it will continue to cut, but will follow the originally formed wavy line. Pretty sure at this point that the rig isn't stiff enough for what I'm attempting. Over the past couple of weeks I've stiffened it up quite a bit, and also gotten a stiffer motor (1/2 HP Grizzly flex shaft). Am just about to try out these improvements, but now cannot go over 10k RPM.

[acannell]

Well, the bit does cut but appears to sort of push the aluminum around, small chips do get generated, but a bunch also seems to gum up around the sides of the slot. This is cutting at 25000 RPM, either dry or with WD40 as a lubricant. The line it cuts will be straight for a bit, say an inch or so, then, as it gets deeper (the piece isn't perfectly flat) it will start to swim around and the line becomes wavy. If I make multiple passes in that slot it will continue to cut, but will follow the originally formed wavy line. Pretty sure at this point that the rig isn't stiff enough for what I'm attempting. Over the past couple of weeks I've stiffened it up quite a bit, and also gotten a stiffer motor (1/2 HP Grizzly flex shaft). Am just about to try out these improvements, but now cannot go over 10k RPM.

you can generate alot of heat at 25000 rpm. combine that with alot of runout because of a spindle meant for construction work, and your 1/8" end mill can get the crap kicked out of it really fast from heat and end up just rubbing as it loses its cutting edge.

whats bugging me about this is that isnt what you are trying to do a common task for diy CNC routers? and if so hasnt someone already figured this out? so maybe there is a solution to your woes

[Routerfiend]

Hi Braddo
Cutting anything requires feeds & speeds to be just so. Depending on what you are trying to achieve will also have a bearing on you F&S . If you are after .005" deep cut using a twin flute end mill then I would suggest fast multi passes but use some light lube ( 3 in 1 Professional Spray ) if you don`t have a spray mister set up. On mine I would run at 18500 rpm @ 200 ipm . Every machine is different and settings will vary . The biggest problem with ally cutting is clogging ( Especially with multi toothed cutters ) A single toothed cutter would be more appropriate for thin alliuminium sheet . I would suggest keep the rpm high and adjust the feed rate until you get the desired effect.

[awerby]

10k RPM should be plenty for a 1/8" bit. But as you mentioned, your "lightweight" CNC might not be rigid enough to cut aluminum. Here's a chart that gives the chipload for a .125" cutter: http://www.lakeshorecarbide.com/pdf/...-and-feeds.pdf I doubt you're even approaching that, which could be part of your problem. With your high RPMs and very shallow Depth Of Cut, you're mostly just rubbing the material rather than cutting it. Instead of chips, you're making dust, and likely welding aluminum onto your cutter, which could account for the wavy cut (since it's really not cutting at all). I'd suggest increasing the DOC so the tool's actually biting into the metal instead of just gliding on top, reducing the RPMs to 8000 or so, and trying again. You'll know you're getting close when you see actual chips (which will look like little double-pointed needles) rather than aluminum dust in the cut. Sweep these away with a brush, since re-cutting chips is bad, and keep the lube going. It still may not work too well, but that's probably because you've got a machine that's more suited to foam than metal cutting.

Andrew Werby
www.computersculpture.com

[braddo]

So, the Grizzly motor and now 1/16" two flute end mills are working much better. I'm running the motor flat out, which they claim to be 10k but I'm not sure about that. the smaller bit further reduces cutter speed at a given RPM and I feel like I'm in the ballpark. I still have to work on depth of cut - if I go too deep, the bit pulls into the material too much and I get gouging. Since the stock isn't completely flat, I may have to set my zero above the work a bit and make several "air passes" and work my way through the uneven-ness. I'm certainly not going to run a fly cutter in this thing, nor am I going to wait 365 days to flatten the surface with the 1/16" cutter. Regardless, I think I'm in workable territory now albeit right on the edge. Thanks for the insights folks.

[AussieGecko]

I'm feeling your pain Braddo...I've had my new Quick CNC machine for about 6 months and tried to get some answers off a number of forums about feeds and speeds, but ended up just getting fed up with all of the different answers.....

I mainly do engraving on plastics, aluminium, brass and SS (although SS is still a work in progress).

I couldn't even get the plastic right in the first pace as I was babying it way too much. I'd start off with bout 10KRPM and only 500mm/min feed, this was mainly from all of the (is say miss information) you may find on the net. I now use 24KRPM and 3000mm/min feed with great results. I was always concerned about too much feed, but if your cut depth is only around 0.2mm then feed away...

Aluminium was the same, but the one thing I did realise is that I needed coolant. My engraving bits will use 6KRPM with 600mm/min, but if I don't use coolant then I will always generate heat and the finish will start to become rough. I can use a 0.75mm 2 flute ballnose with the same RPM, but the feed can be increased to around 2000mm/min. Pass depth of around 0.15mm each pass, but i have to use coolant.

And another point, make sure that the aluminium you are using is not too soft. 6061 type is typically the type you are after. If it's too soft then it will gum up no matter what coolant you use.

Coolant I use if Mentholated Spirits...

PM me and I will email you my basic feed and speed calc I have made in excel and also the list of feed and speeds I have used to date.

When you first start you will always have too experiment, not all machine are the same

[braddo]

Thanks Gecko - very interesting that you can go 2000 mm/min, that's quite fast. I did manage to actually "finish" a useful piece late last night, early this morning, because of the shallow depth of cut, modest speeds and path length it actually took about 5 hours to complete. I put finish in quotes because it actually failed about half way through the last profile cutting out the outline. But that's OK because the outside is just cosmetic and I can cut it with the saw and finish with a file. Not sure why that happened as I had cut this outline once before to the end with less good chip clearing (I now have a big shop vac on one side, and it's air outlet on the other side, forcing chips from one side to the other). I guess it just wasn't good enough to get down in the shallow pocket. Here's a pic:

https://plus.google.com/101263857513...ts/Ai7o6EoymAD

[AussieGecko]

The 2000mm/min is for engraving not milling. If I was to mill like you have done, I would use 8-9KRPM with a feed of around 450mm/min and use coolant.