Will a plasma cutter be better for the metal cutting?
I'm doing some budgeting for a CRP4848 or maybe 4896 and I'm looking at cheap(er) Chinese NEMA 34 steppers and 2.2KW spindles.
After doing some reading it seems the 800-1200oz steppers are the way to go and something like the 1600oz are going to be too slow. I want to use a 2.2KW 3hp spindle and would like to be able to mill up to 1/2" aluminum. Maybe even some 1/4" mild steel if that's feasible. I assume it will be a slow process but this is not a production machine. And of course plywood, MDF and hardwoods.
Keeping in mind what I want to do with the CRP4848 or CRP4896 what would you choose: 1600oz, 1232oz or 878oz steppers? And why?
Will a plasma cutter be better for the metal cutting?
Good point. Certainly for certain pieces like an exhaust flange cut from 3/8" mild steel yes. But I'd like to be able to machine aluminum as well just like any hardwood with maybe a little slower feed rates.
Lots of views, hopefully someone can give me some pointers.
I think how you intend to use the machine is what needed to be addressed first. Heavy cuts in harder materials require more holding power to push the cutting tool through the material. Rapid traverse speed is only required to reduce machine time. If you have a ATC to change tools then faster rapids help reduce machine time. If you have a lot of parts on the machine with minor machining operations then fast rates to get to each part helps reduce machine time. If youíre only making one part and its only 12Ē x 12Ē you will never reach the rapid rates at any point in the machining process. If your only cutting soft materials then you donít need big motors, NEMA 23ís will be just fine, however you will need longer ramp up times on the motors to get to speed.
The thing everyone needs to understand is Voltage is like the fuel going into the engine. More fuel means more power. At the same time Amperage is like the compression ratio in what it does with the fuel. Low compression will use the fuel to get up to speed but at a slower rate then it would at a higher compression which makes more power. The holding power of a stepper is determined by the magnetic field it produces. More windings produce more magnetic strength. To make more holding power you need to increase the size of the windings. Thatís why 1600 oz/in has a longer body for more winding space and higher magnetic force then a 960 oz/in. Acceleration speed is based on the Amperage capability of the motor. To get more Amperage you need bigger diameter wires, which mean you need to have a larger diameter housing for the motor. If you want to cut thick Aluminum and some thinner steels you need low end holding power to drive the cutting tool through the material. So there is always a balance and a trade off when choosing which motors to use.
The motors I am using are 1600 oz/in, but the only have a 3.5 Amp capability. So I have high low end holding power but if I want to run very high rapid rates I have to reduce the acceleration and deceleration rates to get there. I have run at 1400 IPM but when I try and accelerate too fast the motors go into hysteria. That is where the motor stops turning and completely misses all step inputs. Ahren at CNC router parts has gone to great lengths to pick a fine balance between motor sizes and outputs and combine them with high quality drivers and power supplies. Granted they are a bit more pricy then others, but it depends on what you want to do with your machine as to whether you chose a different and less costly approach. My best to you.
Thanks for the reply TD, keep those great videos coming!
I'm certain that you are right that the steppers that Ahren sells are top notch, carefully selected and may be the best choice but unfortunately they break my budget so I'm looking for alternatives.
In a nutshell you seem to be saying that stepper motor selection is a compromise between power and speed. With that in mind and the fact I'd like to mill aluminum and machine time is not an issue then the 1600oz steppers might be a good choice.
Are these the steppers you are using:
4 Axis Dual Shaft Nema 34 stepper motor 1600 oz.in CNC | eBay
Ezcnc, for this machine and for what you want to do, I would say that somewhere around 900 oz/in would be the minimum, 1200 would be better, and 1600 is the high end for Nema 34 steppers. There may be some suppliers that manufacture these sizes with higher Amperage ratings, not sure. And yes, these are the motors I purchased. They have a much bigger selection of product on their web site.
Stepper Motor/Stepper Gearmotor/Stepper Motor Driver wholesaler and supplier
I have a friend that actually sells American made products in China that suggested I try them. I looked at the 1232 motors but they were not much less then the 1600 motors, so I went with the 1600. They shipped out of Hong Kong DHL and I had them in 10 days total. Just as a reminder, they have 14mm shaft diameters and you will need to bore out the couplers to use them, and I had to grind off about .030 to .040 from the shaft ends to make them work. I also had to grind the shaft flat farther back for the set screws. All in all I am pleased with the kit, everything worked out of the box's. My best to you.
I've spent some time on longs site and looking at all their steppers on ebay. You are right the cost difference between,1200 and 1600oz is very small. The 1600 is looking like what I want to use but I was hoping to get variety of opinions before I jumped off.
We actually get a lot of things shipped directly from china and hong kong and I'm amazed that shipping is as quick as it is. Shipments from New York/back east to us are almost as slow.
Thanks for the tips on the motors, as I've watched your videos I've taken
notes about those types of things trying to plan ahead and have everything worked out before the build.