Spindle Load

[ISHY]

Just wondering what spindle load everyone runs on a VMC? I tend to keep mine below 40% but I think that might be a bit conservative even taking into account that I would sacrifice speed for new spindles.

[scadvice]

…load should be based on the duty cycle. So your "in cut" time should be part of defining the acceptable load. Most of the VMC spindle motors will state the load rating. An example is on a CNC lathe the spindle motor may be rated at 7.5 hp 100% duty cycle continuous… and 10 hp 100% for a 30 minute duty cycle.

Most cutter loads vary a lot on the load they pull, so it can be of advantage at times to program metal removal (assuming you’re trying to get the most out of your machine time) loads to balance out the hp needs, allowing the motors time to dissipate heat and still get maximized usage.

But I’m like you… I tend to keep my loads conservative. I like to see less than 60 or 65% loads 80% on the time on a VMC. Less wear and tear on the machine, I believe, no matter what the machine builder says. Most of us machine owners are not using our machines as throwaways in the 5th year. So we sacrifice an hour or so a day of productivity for a longer machine life and hopefully less maintenance cost.

The machine is the best employee you can get. It will do exactly what you tell it over and over. So as long as you treat it right, and tell it right it will never make a mistake, hardly ever is sick, and never comes in with a hangover.

Steve.

[keebler303]

I can't do the math for you but I would think that 1 hour of lost productivity per machine per day, would add up to more cost than a spindle replacement.

A rough calculation:

Figure 250 work days a year, lowball guess of $50 per hour of lost productivity makes for an annual loss of $12,500. Figure two days downtime to replace the spindle at a cost of $50 per hour, $800. That leaves almost $12k in allowance for the spindle, and that's assuming you need to replace it every year!

I guess it depends on the machines you're running but I don't think a spindle rebuild costs $12k for most 'run of the mill' (no pun intended) VMC.

Matt

[RICHARD ZASTROW]

Matt, You may be surprised at the price of spindle bearings. I realize this isn't a fair comparison, but I'm in the process of designing a machine that has a headstock similar to a lathe. (2) pairs of ABEC 7 140 mm id angular contact bearings at the front of the spindle have an OEM price of $10,800.

I'm sure your VMC bearings are less if they're ABEC 7's but ABEC 9's are higher still. Plus you may have more bearings.

Pray for the best. (and me to find less pricey bearings) lol

Dick Z

[Geof]

Originally Posted by keebler303 ....I guess it depends on the machines you're running but I don't think a spindle rebuild costs $12k for most 'run of the mill' (no pun intended) VMC. Matt

I think you are correct with a large cushion; on Haas machines a full spindle replacement is les than $5k.

I also think it is a misconception that running a machine at 100 to 120% load is going to significantly shorten the spindle bearing life.

On smooth cutting where the load is constant the forces acting on the bearings are a small fraction of what they can handle; bearings of the size in spindles have dynamic loads that are measured in the high four or five figures in lbs. Find a bearing catalogue and check some ratings.

Intermittent cutting is a different matter because shock loading can briefly drive the forces well above a bearing's rating so keeping the load down may help but then Matt's economics come into play so in financial terms it may not be worth it.