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Building the Avid Pro: Part 2 - Spindles and Steppers and Drivers, Oh My!

I have made good progress on cleaning out my space and started assembly of the frame, rails, gantry and such. But first lets talk about the various active components.

For the spindle, I had read a number of positive reviews of G-Penny so I chose their square frame, ER25 version with ceramic bearings. Ceramic bearings will have a longer life span than steel ones. The square frame should not need a spindle mount like the round ones do. I picked a 220VAC model. The 110VAC models are cheaper but I do not trust a 110VAC spindle to actually develop 2.2KW. That would require 20A at 110VAC which is an uncommon circuit in North America. Besides, GPenny doesn't seem to sell one which reflects well on them. Too many vendors these days focus on price and not on whether it is right for the customer. I also got the Huanyang 220v 2.2 kW VFD to drive it. Huanyang is a well known Chinese brand and has a lot of users so if I need help there are plenty of people to ask. Fortunately, I have a 220VAC circuit in my shop. I got the ER25 collet because that supports larger router bit shanks than the more common ER20. Mounting it on the Z Axis took some drilling. Learn about that here.

I decided to go with NEMA 34 stepper motors. It was a hard decision for me and I wavered between that and NEMA 23. While I can get more power with the NEMA 34, they generally have higher inductance which limits your top speed at a give voltage level. Generally, to get faster "rapids", you have to go to higher voltage. But, NEMA 34s generally have more torque. The one I chose (KL34295-43-8B) has 3.3 mH of inductance so not that low but the price was reasonable. And, they have 960 oz-in/6.8 N-m of holding torque - pretty beefy. They pull 6.1A.

Choosing the NEMA 34 pushed me to a higher voltage. Originally, I was planning on 48 VDC but decided to go with 60VDC to partially compensate for the higher inductance and because, well, I can! I picked an unregulated 1200 kW - 20A at 60VDC - power supply. It's a beast. In addition, I added a couple of small 12V power supplies for the motion controller breakout board I will be using. More on this in a later blog.

With the above choices, I moved on to the stepper drivers. I needed ones that could handle 6A and 60VDC. I wound up choosing the DM860T from Steppersonline. I'm not 100% sure this the best choice so I will run them a little under 6A. Hopefully it will work out ok. If it doesn't you will certainly hear about it!

Some of you will be asking why I didn't go with servo motors. There are many clear benefits and I did consider it but the cost is a fair amount higher even when you consider that you don't need the drivers. Maybe I will switch some day, who knows.

That's it for now, stay tuned for the next installment, assembling the Pro4848.


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