Desktop CNC options

[Al_The_Man]

Thing is....
By the time the servos have to correct (because they are closed loop)
your part is probably already ruined.

This is the main difference with servo's, they are, or should be, always under control via the PID loop, which does not exist on a stepper.
A servo does not correct when it is too late as this means that control has been lost.
Normally as soon as the acceptable excess following error is detected due to what ever reason such as excess friction or collision, the control motion is, or should be terminated.
I agree the cheap way for anyone to get into CNC is the stepper route, but most that I have heard that have moved into servo's would reluctantly move back.
Al.

[wizard]

While it obviously can't deal with very large parts, there are many good reasons to get a desktop mill. Many people are working on projects, like jewelry or model railroading, that require small parts, which can certainly be done on these mills. Others simply don't have the space (or strong-enough floors) for a huge machine.

You are correct if you ignore all the options between a Sherline and a Bridgeport. In between though there are lots of options. In any event this is why I stressed the idea that an individual think real hard about intended usage. It is very easy to end up kicking yourself in the behind for buying too small of a machine. Of course the opposite can be an issue if space is extremely limited.

The thing with Mills is the area taking up by the machine doesn't not impact you like buying a lathe or some other tools would. Yeah they can get heavy as you increase in size but there is a huge gulf between requiring riggers and a Sherline.

While retrofitting a big old cast-iron mill can be an interesting adventure, not everybody's equipped for that, and even if that's the ultimate goal, having a small machine can make the process of producing mounting plates, etc a lot easier.

This is very true but the poster Indicated that he was well positioned with access to tools.

While the small Chinese mills need a lot of work before they can be used in CNC mode, and usually have slow spindles with plastic gears, the American-made machines like Taig and Sherline are easy to convert, with motor mounts, controllers and stepper motors supplied by the manufacturers. Their belt-drive spindles go up to 10,000 RPM, which make them effective tools for cutting aluminum.

This is a very important consideration but one has to realize that adding a high speed spindle is always an option and has been common practice in industry. On the other hand a Sherline is handicapped in reverse with its high speed spindle if work in steels is desired.

But if you want a Sherline, I'd suggest the 5400 model over the 2000 for CNC use. The 2000 has a lot of tilts and adjustments which are handy for making odd-angled holes and slots, but those also make it less rigid and harder to tram, and those tilts aren't very useful in CNC mode.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

More good points. I have nothing against Sherline, my only concern comes from previous experience buying to small. It is well worth the time to think hard about the wisdom of any specific tool.

[inthebay]

Thank you all for your extremely well thought out ideas, let me explain my situation a little bit further.

I do have a large area currently, big enough that I could easily fit a TM1 or VF1 with no problems, alas, I do not have enough cash for one of those beautiful machines.

For my uses, I will be mostly making small bicycle components, derailleur parts, stems, linkage bits. etc.

I have one more year (my third) at my technical school where I will be getting a second diploma to add to my Manufacturing one. Here this gives me year round access to our CNC mills and Lathes.

My idea being that I can have a small machine like the Sherline and modify it to my uses. I am thinking the 2000 model, then buying some 80/20 aluminum extrusion, tapping it, and removing the x-y axis swivel, and just retaining the tilting Z axis. This will stiffen the entire machine. Most of my work (95%+) will be with milling 6061-T6 aluminum, at small depths. If I was to need to cut steel I could always revert the pulley on the machine back to it's 2800RPM max one.

The nice thing is, I'm planning on moving out to a small home, and having a little desktop machine like a tiag or a sherline would be beautiful for fitting in a garage shop or the like.

[wizard]

At least it narrows down what you intend to do with the machines.

Thank you all for your extremely well thought out ideas, let me explain my situation a little bit further.

Hey we can only try. Sometimes we mis completely.

I do have a large area currently, big enough that I could easily fit a TM1 or VF1 with no problems, alas, I do not have enough cash for one of those beautiful machines.

Real life sucks! However do realize that getting close to such capabilities! for your needs, isn't totally impossible.

For my uses, I will be mostly making small bicycle components, derailleur parts, stems, linkage bits. etc.

Believe it or not this helps a lot because we no have an idea about your interests. I do have a couple of thoughts here. One is that some of these parts might require a lathe. The second item is that some bicycle parts actuall are rather big, so if you intend to make sprockets and so forth you really need to make sure your machine has the XY movements to cover the parts.

I have one more year (my third) at my technical school where I will be getting a second diploma to add to my Manufacturing one. Here this gives me year round access to our CNC mills and Lathes.

I see that as a golden opportunity, one that many on this forum would envy as you basically are not constrained to pre canned conversion kits. It also gives you the option of going DIY instead of buying the machine tool itself.

My idea being that I can have a small machine like the Sherline and modify it to my uses. I am thinking the 2000 model, then buying some 80/20 aluminum extrusion, tapping it, and removing the x-y axis swivel, and just retaining the tilting Z axis. This will stiffen the entire machine. Most of my work (95%+) will be with milling 6061-T6 aluminum, at small depths. If I was to need to cut steel I could always revert the pulley on the machine back to it's 2800RPM max one.

honestly I'd think long and hard about going this route. If you don't think the Sherline will be stiff enough for your needs it probably won't be. Trying to retro fit a machine that in its basic form doesn't meet your needs is a bad idea in my book.

Looking at your items of interest leads me to believe most of the parts could be carved out of flat Aluminum stock. This is where a gantry type machine could be of advantage for you. Such a machine will not take up much more room than a Sherline but could be optimized for stiffness. Made out of steel it will be heavy but you still can keep the unit manageable through good design and an eye towards optimizing for the goods you expect to make.

The nice thing is, I'm planning on moving out to a small home, and having a little desktop machine like a tiag or a sherline would be beautiful for fitting in a garage shop or the like.

Well yes and no. All machine tools are nice to have. The thing is desktop mills in and of them selves don't take up a lot of square footage compared to the way a lathe or some other machines do. A lot of a mills capability (size) ends up going vertically. So the idea that you got to go Sherline to fit seems a bit bogus. I'd rather that you put emphasis on other factors here such as the ease to add ball screws, retro fit linear slides and the lack of need to improve the platform for stiffness.

One factor you may be looking at is weight, which is a real factor in home machines. I cant dismiss the issue but can say this, to light of a machine can be a very real problem in desktop CNC machines. Look at your installation sort of like a refrigerator something that you and maybe a couple of friends move in place once and that fridge tends to stay there forever. Ideally a machine tool should be thought of in the same way it gets moved into position, set up and aligned in that position for an extended time.

One thing you need to remember is that CNC machines require containment as the likely hood is very high that you will want to run coolant of some sort. Even if you don't run coolant chips still get everywhere. This issue has to be considered in any mill installation regardless of size if semi un attended operation is expected.

[Steve Seebold]

Thank you all for your extremely well thought out ideas, let me explain my situation a little bit further.

I do have a large area currently, big enough that I could easily fit a TM1 or VF1 with no problems, alas, I do not have enough cash for one of those beautiful machines.

For my uses, I will be mostly making small bicycle components, derailleur parts, stems, linkage bits. etc.

I have one more year (my third) at my technical school where I will be getting a second diploma to add to my Manufacturing one. Here this gives me year round access to our CNC mills and Lathes.

My idea being that I can have a small machine like the Sherline and modify it to my uses. I am thinking the 2000 model, then buying some 80/20 aluminum extrusion, tapping it, and removing the x-y axis swivel, and just retaining the tilting Z axis. This will stiffen the entire machine. Most of my work (95%+) will be with milling 6061-T6 aluminum, at small depths. If I was to need to cut steel I could always revert the pulley on the machine back to it's 2800RPM max one.

The nice thing is, I'm planning on moving out to a small home, and having a little desktop machine like a tiag or a sherline would be beautiful for fitting in a garage shop or the like.

If you're going to be making bicycle parts, why don't you look at the Tormach PCNC's? You can get in to a PCNC770 for less than about $16,000.00 for a brand new machine, nicely tooled.

[inthebay]

You can get in to a PCNC770 for less than about $16,000.00 for a brand new machine, nicely tooled.

Mostly because I'm a starving student graduating this year from my manufacturing program, hoping to make 22-28$ an hour this summer. I simply don't have that much money. I'm looking under $4k

[TechGuy5002]

Mostly because I'm a starving student graduating this year from my manufacturing program, hoping to make 22-28$ an hour this summer. I simply don't have that much money. I'm looking under $4k

Your best bet would probably be a manual machine conversion. Since you have access to a machine shop you could use it to machine all of the parts for your conversion. The biggest issue is probably the weight of the machine and moving it around. You should be able to pick up a used machine probably in the $2K to 3K range and you probably need to invest new screws for X and Y axises to remove backlash and improve accuracy. That probably will cost around $500 to $1K. and another $400 to $600 on motors and electronics and few hundred for odd bits. However, typically tooling costs will be significant, since you need clamps, vises, end mills, etc, but these can be purchased over time.

The biggest challenge to CNC conversions is access to machine tools to do the machining of the parts, which you already have. Its difficult to machine parts on a mill that taken part for the conversion. Of course having a working mill might also provide the means for extra income if you are able to freelance mill work.

I think you'll be disappointed in a small Desktop mill and I think you'll end up painting yourself into a corner. Taigs and other small hobby mills are really geared for modelers. At some point you going to want to machine a part that the taig mill can't do and you have to upgrade later and you will be out a few thousand $$$ for the Taig and the tooling that is only usable on the Taig.

Also don't forget the costs associated with CAD/CAM software.

[mactec54]

inthebay

If you want to use a servos, so you can have a closed loop, Then that is what you should get, they are far better & even easier to set up than steppers are, The machine you have chosen is a little wimpy, but if you are doing light work & light cuts it will be fine

Here are the ac servos you should be looking at, if you want a very easy set up

DMM Technology Corp.

[wizard]

Take a look at the Little Machine Shop online store, the have an entire CNC machine for about $4500 and have a couple of Tormach models starting at about $7000. This gives you a range of machines available retail at slightly more than your budget. I've actually seen the Little Machine shop machine run at Cabin Fever, yes it is a small machine but it also is reasonably capable. Frankly it is the smallest machine I might even suggest for bicycle parts.

On the other hand I tend to agree with some of the suggestions about DIY here. If you want something at least partly transportable a conversion of some Chinese iron is highly reccomended. I'd suggest looking at the benchtop machines thread here on CNCZone. Contrary to some opinions you can get real work done on these benchtop CNC machines. That is not to say that they can replace a full sized mill, just that with in limits the converted mills are capable of doing real CNC machining in a respectable way.

More importantly if you don't own a shop or home, calling in riggers every time you move to a different place is expensive. A small mill will be far easier to deal with until you get established. Mind you when I say small mill I'm talking some that may be several hindered pounds but still manageable by two people and a few tool.