Spindle Size/Power Benefits

Can someone summarize for me the benefits of larger spindle HP vs lower and what are some rationale in determining what size makes sense for your use?

More power = potentially faster/bigger bites, and a greater range of tooling.

The 4hp is nice because it’s got a good amount of power, but is also reasonably light. I have done slab flattening with mine and all kinds of other work (including aluminum) and have found it to be just fine.

The larger 8.7 is awesome, but does require 3 phase to get all of the power. When you run it on single phase you’re 6.5 hp. It’s a fair bit heavier too.

How does running the 8.7 hp/6.5 kW spindle on single phase impact its speed range?

It’s just like towing capacity. Depends on what you plan to haul and how often. If you are gonna be surfacing large slabs and using large diameter bits you probably want something beefy. If you plan on using 1/4" bits to cut plywood you can probably be fine with a 3hp. Electrical hook up matters too. Do you have access to 3ph? If not your 9hp spindle is only gonna run 6hp on 220 single phase.

My Avid 4896 is older now with only a 2hp spindle.

“The 4hp is nice because it’s got a good amount of power, but is also reasonably light.”

Does the mass of the 8.7 hp spindle impact precision at certain feed rates? That is to say, might the larger spindle suffer more at speed from significant changes in cut direction compared to the smaller spindles? If so, to a degree that, with some designs, the power-speed advantage is negated by the need to slow down?

Tangential, what is the speed range and optimal speed for best power of the 8.7 hp spindle when ran on single phase?

It can… but we tested and tuned the motors to work with the different weights of the machine.

There’s a big overlap where the 4hp and the 8.7 are in their “ideal” zone. If you’re almost never going to do slab flattening the 4hp is great. If you want to flatten some slabs, but don’t care about doing a few extra passes the 4hp is still an excellent choice.

Conversely If you’re doing a lot of heavy cutting (including slab flattening) and you want to get the max speed out of your machine the 8.7 is an excellent choice. The 8.7 can also do fine detail carving too, it just might be overkill (budget wise) if that’s ALL you’re going to do. The 8.7 also has ER 32 collets which let you use tools that are larger than 1/2 in shank diameter.

One unique of the 8.7 is the ability to get a lot of power WAY down low in the RPM range (1000 RPM) so that can be helpful for cutting metal.

Most (good) spindles have a nearly a flat power curve: https://www.avidcnc.com/dl/cad.pdf/MOTM%20QN-1F%206.518%2024%20ER32DX%20BT%20220380V%2029L0596100F%20performance.pdf

1 Like

THIS is my only regurt when purchasing my PRO 4896. I went back and forth between the 4HP and the 8.7HP. It was clear I didn’t really need the additional power, but I do wish I had the lower RPM range. If you are doing drilling operations then the 1000 RPM would be perfect. Now, instead of just drilling my holes, I just spot them and drill by hand or I use the pecking operation in Fusion 360.

Nevertheless, if I could do it all again or swap them out without taking a loss I totally would. I can’t bring myself to eat the cost to upgrade now since I’m just a weekend warrior. Your mileage may vary…

Are you drilling in wood or metal?