Trying to figure out the feed and speed limits on my mill

[arrinick]

Hello all,

I have a good machining background, and am not brand new to cnc, but I have a few parts that I want to make that take forever, and I am trying to speed up the process.

Here is the machine I am running-

Sherline 2000 mill with A2Z x and y upgrades, including Kerk 4tpi zero backlash lead screws

Sherline drivers and steppers 135oz

I am running a 3/8 carbide 3 flute endmill with a 1 3/4 LOC, the part is 1.5" deep.

Running 3000 rpms, with doc at .020 and 20 ipm feed, the machine howls like a banshee, and the finish is poor. At doc .010 and the same rpms and feed, it rips right along, but it takes forever to make the part (well maybe not forever, but about 2 hours). Most of the feed and speed info I can find doesn't take into account the size of the machine. I am not missing steps. it is just a matter of getting a decent finish , and cutting most efficiently.

Any help or info would be greatly appreciated, thanks for your time,

Nick Gardner

[HimyKabibble]

Depth of cut and feedrate are both variables that MUST be tuned on a machine-by-machine basis, and when pushed to hard, surface finish is the first thing to degrade. A Sherline is NOT a very rigid machine, and a 3/8" endmill is probably at the top end of its capabilities, so what you're finding is not at all surprising.

Regards,
Ray L.

[arrinick]

Thanks for the input. Does anyone here have any experience with the A2Z monster mill? I wonder how much better off I would be with the z colum upgrade.....

Nick Gardner

[Greg Maxwell]

I have the A2Z column upgrade, the bad news is I have not tried cutting with a 3/8 endmill yet, just smaller 1/8"> diameter endmills. I am very confident that I now have a stronger machine. It feels alot more rigid than the previous headstock assembly.

[arrinick]

Thanks Greg. Well here is another question, I am using a 3/8 carbide endmilll because I am trying to minimize deflection. Would I be better off with a 1/4 inch end mill taking a lighter cut at a faster feed rate? I am having a hard time getting my head wrapped around whats a good feed rate since I get no feedback from turning wheels when in cnc mode. My main source of advice is an old school machinist who worked on bridgeports for years and he has no experience with small machines like mine.

Thanks again everyone for the help.

Nick

[HimyKabibble]

Originally Posted by arrinick Thanks Greg. Well here is another question, I am using a 3/8 carbide endmilll because I am trying to minimize deflection. Would I be better off with a 1/4 inch end mill taking a lighter cut at a faster feed rate? I am having a hard time getting my head wrapped around whats a good feed rate since I get no feedback from turning wheels when in cnc mode. My main source of advice is an old school machinist who worked on bridgeports for years and he has no experience with small machines like mine. Thanks again everyone for the help. Nick

The "feedback" comes from watching and listening to the machine. The first indication you're pushing too hard will be degraded surface finish. After that, you'll get into the spindle motor laboring, or even stalling, or the machine shaking/vibrating. Sset your desired DOC, start with a slow feedrate, and keep increasing feedrate until you see surface finish start to degrade, then back off a little. It's no different from a larger machine in this respect, except your limits will be much lower.

Regards,
Ray L.

[arrinick]

Thanks Ray, that makes sense.

Nick

[Greg Maxwell]

I might suggest looking at the length of the tool as well. 3/8 endmill may be longer than 1/4". The ideal scenario would be a short 1/4". If you can minimize the stick out from the headstock you should be able to increase the feed, doc or speed. I noticed with a long 3/8" endmill (approx 4" stick out) I could literally see and feel the deflection of the headstock by grabbing the endmill, with gloves on of course, and prying back and forth. With the new A2Z column upgrade I am happy to report I don't fell that anymore.

[arrinick]

I have to use an endmill with a LOC of 1.5" or more because that's how deep the part is. I am trying to keep it as short as possible though. I made new drive pullys for my motor to get me up to 5k RPMs, but that didn't seem to help much with surface finish, so I went back to the stock pullys. I susupect that as others have said, I have just run up against the limits of the machine. I guess I'll just bite the bullet and buy the z axis upgrade.

Cheers,

Nick

[HimyKabibble]

Originally Posted by arrinick I have to use an endmill with a LOC of 1.5" or more because that's how deep the part is. I am trying to keep it as short as possible though. I made new drive pullys for my motor to get me up to 5k RPMs, but that didn't seem to help much with surface finish, so I went back to the stock pullys. I susupect that as others have said, I have just run up against the limits of the machine. I guess I'll just bite the bullet and buy the z axis upgrade. Cheers, Nick

Side-milling 1.5" DOC takes a VERY tight, rigid machine to get a really first-rate finish.... I would think that well beyond the abilities of all but the biggest "benchtop" machines.

Regards,
Ray L.

[arrinick]

Hi,

The machine is fully capable of making the part with a decent finish, it's just a matter of how fast. Keep in mind that basically, the only thing that is sherline is the z colum and the spindle. I did a lot of research and the sherline spindle seems to be very good. I have found $5k plus machines that use the sherline spindle. Here is a pic of one of the finished parts. It's a handle for a motion picture camera.

Nick