Small CNC mill choices

[zondar]

Dear Hobby Machinists Folks,

I am a beginner at metal working who is moving towards building a small CNC mill.

I have a Sherline long-bed lathe and some accessories. Although I had specific tasks lined up for it, I mostly purchased it as a "toy" to learn on. It's a nice little machine that is fun and perfect for educational use. Of course it's very small, but I can think of ample fun projects for which it will be fine. Also, I use it in a spare bedroom dedicated to hobbies, where it's very quiet and so easy to take out or put on a shelf.

Now I'm interested in a traditional-style CNC mill (not those router types). Again, I do have some specific tasks for it, but again, a big part of the build is for the fun and learning that goes along with it. But having decided that, I wonder if I should stick with the small, quiet, light approach, or go bigger? That is, my default plan is to get a Sherline mill, but then I thought that something like the PM-718VT looks mighty tempting too!

The Sherline is my most likely choice, as I'm half way there already with parts and accessories. I'd be going with the 5400 12" machine with extended column. This is the rigid column version (hehe, "rigid" compared to a tilting one anyway), with standard lead screws in "CNC ready" form. I don't see ball-screws being cost-effective on this mill.

I prefer to stick with open-source software, for which the main choices include LinuxCNC and GRBL. At the moment, I think I'm going with GRBL. The reason is that a dedicated linux box would not needed, and any computer, including linux and Macs, can talk to it. A limitation of GRBL is that it's currently 3-axis only, and I do have a rotary table. However, hobby-level operations requiring a rotary table usually only need one or at most two other axis movements anyway.

I'm experienced with electronics, and have looked at options for motor control, etc. I think a straight-forward open-loop stepper-motor system is an appropriate fit to a Sherline. With about 400 oz-in of torque, if one of these starts to miss steps, then the little Sherline is almost certainly being pushed too hard. GRBL only needs an inexpensive Arduino and a USB connection to any computer. Other than that, an E-Stop and limit switches, connectors, etc., are needed. The cost of all that can be surprisingly low, and so a cool little 3-axis CNC mill can come in around $2k including some accessories. I do wonder if it would be too messy for an bedroom-type hobby room, though.

But then the thought of something like the PM-718VT, which apparently has factory ball-screw kits available, seems tempting. Ah, but with a stand, DRO, the higher-tier ball-screws, shipping and tax, it comes in over $7k without any accessories. I'd also need to invest in more expensive servo motors rather than steppers, more expensive drivers, bigger power supplies, and so on. I'd likely go with LinuxCNC or similar rather than GRBL for the extra features. With a minimum of tooling, it could easily creep (or leap) up to $10k. I'd have 400 lbs to move around, and I'd have to put it in a dark, unconditioned garage space. And if I did all that, why not go with a PM-833 or better anyway?

Curses on life's compromises!

What do you all think?

 

[Aaron_W]

I don't CNC but I do pay a little bit of attention. Eventually I will probably end up adding a small CNC mill.


If you want ready to go rather than a DIY project you have Sherline which you have already mentioned. I have a manual 5400 mill, it is a very nice (very small) mill.

Taig is a competitor that offers similar machines and also made in USA. Their machines are slightly bigger, and often a little cheaper but basically in the same general class.

Taig tools

Carter Tools is a re-seller that has a lot of good information. Taig's company website leaves a bit to be desired.

Carter Tools

Both companies offer CNC ready and complete CNC kits, although I don't think Taig goes as far as Sherline in offering a computer / software package.

As far as ball screws they are supposed to offer a lot of improvement, but are rather expensive and from what I understand you are committed to CNC with them, no using the mill as a manual mill without replacing the lead screws with conventional ones.


Step up from there would be something like Tormach, a little bit bigger and a lot more money. Starts around $7000 with a working envelope not a whole lot bigger than a Taig or Sherline. They make larger machines but then you are looking at more like $15,000+. I think these are really marketed towards hardcore hobbyists and light commercial use.

Tormach



From there you have the DIY approach, converting a larger mill to CNC, or buying a used industrial CNC, although there is probably something else out there in the same market as Tormach. Anything bigger than Sherline, Taig and I'm really out of my area. There are members here who actually know the CNC stuff.

 

[Firebrick43]

Dear Hobby Machinists Folks,

I am a beginner at metal working who is moving towards building a small CNC mill.

I have a Sherline long-bed lathe and some accessories. Although I had specific tasks lined up for it, I mostly purchased it as a "toy" to learn on. It's a nice little machine that is fun and perfect for educational use. Of course it's very small, but I can think of ample fun projects for which it will be fine. Also, I use it in a spare bedroom dedicated to hobbies, where it's very quiet and so easy to take out or put on a shelf.

Now I'm interested in a traditional-style CNC mill (not those router types). Again, I do have some specific tasks for it, but again, a big part of the build is for the fun and learning that goes along with it. But having decided that, I wonder if I should stick with the small, quiet, light approach, or go bigger? That is, my default plan is to get a Sherline mill, but then I thought that something like the PM-718VT looks mighty tempting too!

The Sherline is my most likely choice, as I'm half way there already with parts and accessories. I'd be going with the 5400 12" machine with extended column. This is the rigid column version (hehe, "rigid" compared to a tilting one anyway), with standard lead screws in "CNC ready" form. I don't see ball-screws being cost-effective on this mill.

I prefer to stick with open-source software, for which the main choices include LinuxCNC and GRBL. At the moment, I think I'm going with GRBL. The reason is that a dedicated linux box would not needed, and any computer, including linux and Macs, can talk to it. A limitation of GRBL is that it's currently 3-axis only, and I do have a rotary table. However, hobby-level operations requiring a rotary table usually only need one or at most two other axis movements anyway.

I'm experienced with electronics, and have looked at options for motor control, etc. I think a straight-forward open-loop stepper-motor system is an appropriate fit to a Sherline. With about 400 oz-in of torque, if one of these starts to miss steps, then the little Sherline is almost certainly being pushed too hard. GRBL only needs an inexpensive Arduino and a USB connection to any computer. Other than that, an E-Stop and limit switches, connectors, etc., are needed. The cost of all that can be surprisingly low, and so a cool little 3-axis CNC mill can come in around $2k including some accessories. I do wonder if it would be too messy for an bedroom-type hobby room, though.

But then the thought of something like the PM-718VT, which apparently has factory ball-screw kits available, seems tempting. Ah, but with a stand, DRO, the higher-tier ball-screws, shipping and tax, it comes in over $7k without any accessories. I'd also need to invest in more expensive servo motors rather than steppers, more expensive drivers, bigger power supplies, and so on. I'd likely go with LinuxCNC or similar rather than GRBL for the extra features. With a minimum of tooling, it could easily creep (or leap) up to $10k. I'd have 400 lbs to move around, and I'd have to put it in a dark, unconditioned garage space. And if I did all that, why not go with a PM-833 or better anyway?

Curses on life's compromises!

What do you all think?

First, 400 oz steppers on a Sherline is unnecessary as are servos on a PM 728vt. I am not really sure why servos have permeated the hobbyist realm in the smaller machines as servo advantages can not be utilized on small non linear way milling machines nor by the step/dir controllers utilized by most of the hobbyist macnhines. Some of the new closed loop steppers are a modest increase in price and try to make position and if they loose steps will at least put the machine into fault mode. But the cheapest servos add at least 500 plus dollars for little gain. If your going to CNC the machine, why the DRO?

Why linuxcnc instead of Acorn?

 

[zondar]

I have a manual 5400 mill, it is a very nice (very small) mill.

Thanks for the info. About your mill: do you find that it's too messy for a typical interior room, or does it belong in a garage or basement? I find that the lathe isn't too bad, but I wonder about a mill, and I'd like to plan ahead on that.

 

[zondar]

First, 400 oz steppers on a Sherline is unnecessary as are servos on a PM 728vt. I am not really sure why servos have permeated the hobbyist realm in the smaller machines as servo advantages can not be utilized on small non linear way milling machines nor by the step/dir controllers utilized by most of the hobbyist macnhines. Some of the new closed loop steppers are a modest increase in price and try to make position and if they loose steps will at least put the machine into fault mode. But the cheapest servos add at least 500 plus dollars for little gain. If your going to CNC the machine, why the DRO?

Why linuxcnc instead of Acorn?

Yes, I know that smaller steppers would be better balanced, but that's what I have on-hand. Really, I was just fantasizing a bit about the PM-728, and if it meant paying $1k extra for servos, I might well do without.

About DRO's on CNC'd machine: A good DRO will give you information on actual physical position, but a CNC machine's "position" is liable to error, e.g. when those open-loop systems start to miss steps or are bumped.

LinuxCNC simply because I know a little about it and think it would work for me, while I know little or nothing about other competitors. But I'm familiar with Arduinos and would probably start with GRBL anyway for its simplicity.

My main problem with larger machines is that I'd be crossing a threshold: From hobby room to garage. Now, that would be great. I'd get a good bandsaw, drill press, grinder, a properly-big lathe, etc. But all that starts with the first machine that needs to live in the garage, and so that threshold is a precipitous one!

 

[Aaron_W]

Thanks for the info. About your mill: do you find that it's too messy for a typical interior room, or does it belong in a garage or basement? I find that the lathe isn't too bad, but I wonder about a mill, and I'd like to plan ahead on that.

I started out with a Sherline lathe in my hobby room (upstairs bedroom). The mill is quite a bit messier. The lathe puts most of the chips right in front, the mill flings them every where. I probably could have made it work but ended up moving both down to the basement where they have attracted many more machines...

I have carpet in that room and my wife has to pass though my room to get to her sewing room. Hard floors I wouldn't have been as concerned and with CNC you can put it in an enclosure. Pretty hard to use a manual mill closed up in a plastic box.

 

[Firebrick43]

Yes, I know that smaller steppers would be better balanced, but that's what I have on-hand. Really, I was just fantasizing a bit about the PM-728, and if it meant paying $1k extra for servos, I might well do without.

About DRO's on CNC'd machine: A good DRO will give you information on actual physical position, but a CNC machine's "position" is liable to error, e.g. when those open-loop systems start to miss steps or are bumped.

You really don't need servos for a pm-728. They have little to no advantage over a closed loop stepper saving you 700 dollars and another 200 savings from not getting a DRO

I think you are greatly overestimating a dro for seeing lost steps. Even at a slow speed the numbers are going to roll by so fast you couldn't tell that you missed some steps. For less money you can get some closed loop steppers that can actually try to make the steps commanded and if they simply can will fault out and send alarm to your control. You will only see the missed steps in a crash, a broken tool, or in bad dimensions when done or partially completed. Also, if you have properly sized steppers, your machine is aligned/adjusted/lubed, and don't have crazy g code you won't miss steps.

 

[zondar]

OK, I'll take your word about the servos. And I had been wondering about how important a DRO might remain in a CNC context (I wasn't actually planning for both; as I said I was just fantasizing a bit and adding up the potential costs).

I already have most of what I need to CNC a Sherline (except for the mill itself). The exercise of building one would be, to a degree, just for the fun and educational value of doing so and learning how to use CNC. But if I have to put it in the garage anyway due to chips flying everywhere, then I really should consider if a bigger machine is a better idea.

A Taig is slightly more robust and has a ball-screw option at a not-too-terrifying price, but I don't like the swiveling column or the short Z travel. I don't think I'd go that route. The typical Chinese mini-mills, at least at the lower end, aren't appealing to me either.

Looking at that PM-728 again, with the premium ball-screws and no DRO or tooling I'd still be looking at about $6k delivered/taxed, plus at least $1-2k for new tooling and accessories appropriate for it. But that's still a relatively small and light mill in the grand scheme of things, and even so I'd feel obligated to get a "real" lathe to put along-side it, too. A PM-1340GT would probably do, if those ever become available again. ;-)

 

[JimDawson]

For a small CNC mill you really can't beat one of these. This one needed a little love, but only has about 30 hours on it. It just followed me home one day. 4 axis, 6 tool changer, full enclosure. Very high quality, made in Austria. Not much bigger than a Tiag. Needs a controls upgrade that I'll get to one day, currently has a Fanuc emulator controller. These were about $35K new, but I have seen a few on the used market at reasonable prices.

 

[zondar]

Looks very interesting. Unfortunately, when I look at used machines around here, all I find are worn-out piles of rusty iron, catalog shots instead of actual photos, and people who are utterly, fantastically, pathetically delusional about their pricing.

I'm sure there are still good sellers and good products at fair prices to be found used on occasion, at least if one is patient, diligent and quick with cash when something good does come up, but with my level of experience I think I'm best off sticking to new products.