I've had to write this out more times than I would like to have, so I figured I'd write it down here so it can answer other people questions and you guys can add to it.
It's a pretty common question for people who either just starting, or moving to a new machine (generally up in size, capabilities and capacity) to ask the advantage and disadvantage questions and what to look for.
I'll highlight what I either know from experience or research, take it with a grain of salt.
Mini mills -
Craftex CX600, CX601, CX605, CX611, CX612
https://www.busybeetools.com/categories/metalworking/milling-1/
King Canada KC-20VS-2, KC-15VS
https://www.kingcanada.com/en/products/metalworking/milling-drilling-machines/
Grizzly G8689, G0781, G0758, G0704, G0758Z, G0463, G0619, probably more of these machine codes
https://www.grizzly.com/search?q=(categoryid:480)
I may have some machines (especially in the grizzly set) that shouldn't be considered a "mini-mill" in the way I am thinking. Generally, these type of machines have a price tag under $3000 new, and a direct drive from spindle to motor. They will probably be R8 or MT2 taper spindles, and probably up to 1hp spindle motors (DC brushless, generally speaking). They would be suited to small work, typically in non-ferrous and plastics, but are capable of work in materials such as mild steel (and probably stainless if you're determined and patient).
What I personally would consider advantages to these machines:
- They are small and light (which also will be a disadvantage in some ways), making them easily movable and a small footprint for basement shops and limited budgets.
- Dovetailed ways for the Z, and should allow for head tilting (sometimes all the way around) either by pivoting of the Z axis head mount, or in some instances by rotation of the entire column.
The disadvantages I see are:
- Very limited travels and capacities of tooling (even a drill chuck and bit combo can make these almost unusable)
- Very small quill travels, this is made up for somewhat by the ability to move the head in a somewhat accurate manner with reliability due to the dovetailed ways constraining the Z axis.
- Not rigid at all, light cuts will have to be taken to A) not stall the motor and B) not have massive chatter. For many this is within reason as its just a side hobby and time is less of a concern. Making prototypes with these machines is possible if the materials and operations are kept inside machine constrains.
- Due to cost, they are likely to be low on the accuracy side. I would expect that they may cut a slot, but the tolerance of that slot would be sloppy. This can be corrected but with significant time investment.
Bench mills
Round column style mill/drill (RF-25, RF-30, RF-31 style, many distributor codes).
These machines CAN be productive if the expectations of material removal rate (e.g. time spent machining vs material removed) are kept within reason. They have reasonable mass to them for a hobbyist but would not be reasonable for any sort of machine shop (you'll likely never see one in a machine shop). They are a good upgrade VS cost from a mini-mill as they have larger travels and more HP to the spindle, but likely would not be acceptable as a long term solution unless only light machining is to be done. In my opinion these are more appropriately a glorified drill press with X/Y table. They will likely chatter due to lack of rigidity and have no constraints for head movement.
Advantages:
- Relatively inexpensive (especially 2nd hand) and many available.
- Much larger work envelope than mini-mills
- Work well for drilling applications
Disadvantages:
- Head does not rotate.
- Not rigid enough for moderate milling
- Head adjustments have nothing constraining head orientation, meaning that the head can (and will) rotate when moving it up and down if the quill stroke is not enough travel.
- These machines will always be belt driven which eventually gets irritating changing speeds (I'll cover VFD's later)
Dovetail style bench mills (gear head)
RF-45, PM-45, etc.
This style of bench mill is (as far as I know) the last step of machine that can be put on a bench before entering the mini-knee mill size of machine. They are more expensive than all others before but are generally much better quality, much heavier, have greater travels in all directions and have the added benefit of gearheads for spindle speed. They can come in essentially all spindle varieties (R8, MT, BT30) and are likely the best candidate for CNC conversion in a bench style machine. They are capable of most all machining operations (as always, within reason) and if the time is spent to bring them into a higher accuracy range can do incredible work (Stefan Gotteswinter is a good example of this). My opinion is this would be the top tier for most hobbyists as they are small enough they can be disassembled and moved into a basement, and are worth investing time into making them more accurate.
Advantages:
- Heavier machine with more rigid construction allows for heavier cutting
- Gear head spindle speed selection
- Can be taken apart to reasonable chunks to get into basements, etc.
- Good (best of bench size, IMO) candidate for CNC retrofits and many kits available
- Offered in many spindle tapers (R8, MT, BT30)
- Reasonable HP motors generally
- Largest of the table and Z travels
- Head pivots 360 degrees
- Frequently have a Z axis motor to raise and lower the head, and sometimes have a reversing switch on the quill travel indicator for tapping operations.
Disadvantages:
- Still a light machine (generally under 600lbs fully dressed)
- More expensive and less available used generally
Options to improve machines:
Power feeds - These are a must if you intend to do manual machining on a regular basis. They are fairly expensive ($3-500 per axis I believe) and almost never come up used, but they are invaluable for surface finish when fly cutting and getting better tool life as they are consistent (ish) in chipload per revolution.
Digital readout - This is invaluable if you have expectations of making accurate parts consistently. They are not too expensive ($300ish for a Chinese version which are plenty suitable for most people).
VFD for spindle speeds - While this is an option and does work well, there is a moderate cost in doing this type of conversion. You'll need a 3 phase motor and VFD. While you can buy used 3 phase motors online, generaly these are not inverter duty motors, meaning they are not made for this application. While running below the data plate speed (generally 1725 or 3600 rpm) the fan attached to the motor is not creating enough airflow for cooling, which will lead to shortened life of the motor. Longer periods of time spent at lower speeds significantly reduces motor life. Also, unless a high quality motor and drive are used (VERY expensive from a hobbyist perspective) they have very little low end torque. Do not expect to use a Chinese drive and kijiji motor and get 25rpm tapping speeds. It is an advantage to have a machine with gear head or pulley speed selection that can be fine tuned with a VFD as that is a reasonable adjustment to make, but you will not reasonably (or inexpensively) be able to get a motor and VFD combo that will allow 200-3600rpm with good torque at the same time.
I'm sure there are many things that I haven't included in here, I will add to this as I remember them (if you dont use them all the time you forget). If you have one of these machines (or more), please chime in on your experience.
It's a pretty common question for people who either just starting, or moving to a new machine (generally up in size, capabilities and capacity) to ask the advantage and disadvantage questions and what to look for.
I'll highlight what I either know from experience or research, take it with a grain of salt.
Mini mills -
Craftex CX600, CX601, CX605, CX611, CX612
https://www.busybeetools.com/categories/metalworking/milling-1/
King Canada KC-20VS-2, KC-15VS
https://www.kingcanada.com/en/products/metalworking/milling-drilling-machines/
Grizzly G8689, G0781, G0758, G0704, G0758Z, G0463, G0619, probably more of these machine codes
https://www.grizzly.com/search?q=(categoryid:480)
I may have some machines (especially in the grizzly set) that shouldn't be considered a "mini-mill" in the way I am thinking. Generally, these type of machines have a price tag under $3000 new, and a direct drive from spindle to motor. They will probably be R8 or MT2 taper spindles, and probably up to 1hp spindle motors (DC brushless, generally speaking). They would be suited to small work, typically in non-ferrous and plastics, but are capable of work in materials such as mild steel (and probably stainless if you're determined and patient).
What I personally would consider advantages to these machines:
- They are small and light (which also will be a disadvantage in some ways), making them easily movable and a small footprint for basement shops and limited budgets.
- Dovetailed ways for the Z, and should allow for head tilting (sometimes all the way around) either by pivoting of the Z axis head mount, or in some instances by rotation of the entire column.
The disadvantages I see are:
- Very limited travels and capacities of tooling (even a drill chuck and bit combo can make these almost unusable)
- Very small quill travels, this is made up for somewhat by the ability to move the head in a somewhat accurate manner with reliability due to the dovetailed ways constraining the Z axis.
- Not rigid at all, light cuts will have to be taken to A) not stall the motor and B) not have massive chatter. For many this is within reason as its just a side hobby and time is less of a concern. Making prototypes with these machines is possible if the materials and operations are kept inside machine constrains.
- Due to cost, they are likely to be low on the accuracy side. I would expect that they may cut a slot, but the tolerance of that slot would be sloppy. This can be corrected but with significant time investment.
Bench mills
Round column style mill/drill (RF-25, RF-30, RF-31 style, many distributor codes).
These machines CAN be productive if the expectations of material removal rate (e.g. time spent machining vs material removed) are kept within reason. They have reasonable mass to them for a hobbyist but would not be reasonable for any sort of machine shop (you'll likely never see one in a machine shop). They are a good upgrade VS cost from a mini-mill as they have larger travels and more HP to the spindle, but likely would not be acceptable as a long term solution unless only light machining is to be done. In my opinion these are more appropriately a glorified drill press with X/Y table. They will likely chatter due to lack of rigidity and have no constraints for head movement.
Advantages:
- Relatively inexpensive (especially 2nd hand) and many available.
- Much larger work envelope than mini-mills
- Work well for drilling applications
Disadvantages:
- Head does not rotate.
- Not rigid enough for moderate milling
- Head adjustments have nothing constraining head orientation, meaning that the head can (and will) rotate when moving it up and down if the quill stroke is not enough travel.
- These machines will always be belt driven which eventually gets irritating changing speeds (I'll cover VFD's later)
Dovetail style bench mills (gear head)
RF-45, PM-45, etc.
This style of bench mill is (as far as I know) the last step of machine that can be put on a bench before entering the mini-knee mill size of machine. They are more expensive than all others before but are generally much better quality, much heavier, have greater travels in all directions and have the added benefit of gearheads for spindle speed. They can come in essentially all spindle varieties (R8, MT, BT30) and are likely the best candidate for CNC conversion in a bench style machine. They are capable of most all machining operations (as always, within reason) and if the time is spent to bring them into a higher accuracy range can do incredible work (Stefan Gotteswinter is a good example of this). My opinion is this would be the top tier for most hobbyists as they are small enough they can be disassembled and moved into a basement, and are worth investing time into making them more accurate.
Advantages:
- Heavier machine with more rigid construction allows for heavier cutting
- Gear head spindle speed selection
- Can be taken apart to reasonable chunks to get into basements, etc.
- Good (best of bench size, IMO) candidate for CNC retrofits and many kits available
- Offered in many spindle tapers (R8, MT, BT30)
- Reasonable HP motors generally
- Largest of the table and Z travels
- Head pivots 360 degrees
- Frequently have a Z axis motor to raise and lower the head, and sometimes have a reversing switch on the quill travel indicator for tapping operations.
Disadvantages:
- Still a light machine (generally under 600lbs fully dressed)
- More expensive and less available used generally
Options to improve machines:
Power feeds - These are a must if you intend to do manual machining on a regular basis. They are fairly expensive ($3-500 per axis I believe) and almost never come up used, but they are invaluable for surface finish when fly cutting and getting better tool life as they are consistent (ish) in chipload per revolution.
Digital readout - This is invaluable if you have expectations of making accurate parts consistently. They are not too expensive ($300ish for a Chinese version which are plenty suitable for most people).
VFD for spindle speeds - While this is an option and does work well, there is a moderate cost in doing this type of conversion. You'll need a 3 phase motor and VFD. While you can buy used 3 phase motors online, generaly these are not inverter duty motors, meaning they are not made for this application. While running below the data plate speed (generally 1725 or 3600 rpm) the fan attached to the motor is not creating enough airflow for cooling, which will lead to shortened life of the motor. Longer periods of time spent at lower speeds significantly reduces motor life. Also, unless a high quality motor and drive are used (VERY expensive from a hobbyist perspective) they have very little low end torque. Do not expect to use a Chinese drive and kijiji motor and get 25rpm tapping speeds. It is an advantage to have a machine with gear head or pulley speed selection that can be fine tuned with a VFD as that is a reasonable adjustment to make, but you will not reasonably (or inexpensively) be able to get a motor and VFD combo that will allow 200-3600rpm with good torque at the same time.
I'm sure there are many things that I haven't included in here, I will add to this as I remember them (if you dont use them all the time you forget). If you have one of these machines (or more), please chime in on your experience.
