Hi,
If you have an option, always get the Taiwan rather than the Chinese machine from PM. I have both a PM940M VS CNC Chinese Mill and a Taiwan PM1440GT Lathe and the Taiwan product is far superior. It is largely about the initial design, but even more importantly the manufacturing QC. Bigger is not always better.
From your photos it appears that you have 100Amp 220V service for the shed, but it would help to know the wire gauge and the insulation type to know what the feed wire capacity is. They appear to be Aluminum wires that "feed" into the 4 slot 100 Amp Mains breaker. If the wires are oversized for this breaker and the one back at the house then you could conceptually just increase the breaker capacity as these limit the total current available. You should check the breaker back out the house to see if it is also rated at 100Amp. The wires maybe able to carry more than 100Amps. TBD. It is not possible to see the writing on the wires in the photo. So there are two of these large wires providing the incoming power to the over sized 100 Amp mains breaker located across the top of the box. There is a third large wire that connect to the Ground/Neutral of the box and I cannot say for sure, but it appears that there it a ground rod connected to the ground at the box. Which is as it should be. Anyway, you have 220V arriving at the shed and it appears to be wired up correctly. If the "feed" wires are oversized than you could increase the load size of this mains breaker or just purchase a new breaker box. The last time I purchased breaker boxes (sub panel) I purchased long GE boxes which came with a bunch of breakers and accepted 1/2 width breakers so that one can get a lot of them into the box. This box was a 200Amp Mains box with 200Amp service breaker switches. However, I only ran 150Amp 220 volt wire to it. This is safe as I had breakers at the mains box to provide the over all current limit. The other twist to this was that even though I ran wire capable of 150Amp, I used a 125Amp breaker at the mains panel. I did this because the 125Amp breaker only took up two slots. A 150Amp breaker would have taken up 4 slots, much as your current 100Amp sub panel mains switch does.
Any of the breakers which are functioning as pairs (doubles) are providing 220V service. It appears that on the top left hand side of your box you have six breaker slots taken up by 20, 40, and 50Amp double breakers which provide 220V service to some appliances. According to the box labels these are 20 Amp (Electric Heat), 40 Amp (Air Compressor and Door Pump motor), 50 Amp (Welder outlets). Most of the rest of the breakers are for 20 Amp outlets. There is also one labeled Furnace which I assume is for the fan etc. for your gas furnace and a water pump. You have an Eaton (Cuttler Hammer) box. I do not know the model of this box, but many of the Eaton boxes will allow you to put two (half physical width) breakers in the slot where there is currently only one full size breaker. Hence you should have plenty of room in the box for more circuits.
So, I assume your electric heating is using the top left hand pair of slots. 20Amp. This seems like a pretty reasonable heater. This is not a heater which will keep one comfortable in this size of non-insulated shed but may prevent freezing. Clearly you need to get the furnace fixed to be comfortable. As others have said, you seem to have plenty of power capacity. You do not run all of these appliances at the same time so probably never come close to needing more than 100Amp at 220 volts. The welder is the big hitter and you have to ask not only would you be running two or more of these appliances at the same time, but would you have too do so. If not then what is the concern. Even if you have to run your grain dryers you could shut them off for a little bit while you were using the welders or other large current devices.
Anyway, sum up the amperage of all of your breakers. I think you will find that their is the equivalent of 20+40+50+20*(13/2) = 110+130=240Amps at 220volts. Far more than the 100 amp 220volt main breaker. This is normal. Add up the total of the appliances that you would be using simultaneously to see what you absolutely have to have.
Also be aware that a induction motor requires more current to start than it does to run. This is especially true if the motor is under load during start up, such as with a compressor where the tank is already partially pressurized. I once had a 1 HP compressor which would start up just find on a 15Amp breaker service, but it would not cycle with the tank largely full without tripping the breaker. I eventually ran a 20 Amp service.
My recommendation is to simply replace some of your single pole 110V 1 inch wide breakers with 1/2 inch width units and install a couple of double pole 1/2 size breakers to provide 220 service where you need it. So that you can see what I am talking about here are a couple of links to GE breakers. I did not immediately find the equivalent Cutler Hammer (Eaton) units.
Pair of 1 inch coupled breakers to provide 20 Amp 220 service. Similar to what you have for your heater circuit.
GE Double Pole Bolt-On Breaker is compact and thermal-magnetic devices designed for residential and commercial applications.
www.homedepot.com
Pair of 1/2 inch couple breakers to provide 20Amp 220 service. This unit could replace the unit above and yield a full breaker slot.
GE - 20 AMP 1 in. Double Pole Circuit Breaker - Lifetime warranty when used with Powermark Gold Load Center. Copper stabs. Every breaker exceeds UL, NEMA, ANSI, CSA requirements. Box type terminals. 65oc/75oc
www.homedepot.com
Single 1/2 inch breaker to provide 20Amp 110 service. Two of these units could replace two of your current 1" wide breakers freeing up a slot.
The GE 20 Amp 1/2 In. Single Pole Circuit Breaker is tin plated for corrosion resistance, and to make the connection reliable and permanent. It includes a heat resistant thermoset case and cover that adds stability and structural integrity.
www.homedepot.com
Either of the Mills you are looking at appear to run off of 110 volts 20 amp circuits. However, the 728 has 1HP motor and variable speed while the 727 says it is a 1.5HP Motor and its speed is varied via gear settings.
The Lathe you are considering, PM1228VF-LB, power requirement is stated to be "Voltage / Phase/ Amps 120 Volts, 11 Amps". It is China made. Which lathe you really want to get largely depends upon what kind of work you are going to be doing.
Anyway, it appears to me that you current electrical service can be easily upgrade to run even larger machines than these! Will you ever be running both mill, lathe, and welder at the same time?
PS. Before you go out an purchase breakers of any kind you have to make sure that they are physically compatible with the box that you have. You cannot just swap one brand or style for another. While they pretty much all work the same way inside, the physical packages are sometimes quite different and will not physically interchange. The best way to tell is to physically see if a breaker will install into your box.
Good luck.
Dave L.
