Expected Service Life for a CNC Spindle

How long should a CNC spindle last before it needs replacing? That depends on many operating conditions, including tool sharpness, type of cooling system, and ramping parameters. August 24, 2008

I wanted to know if having to rebuild a spindle after two years is normal. I realize there are a lot of variables that go into a spindle needing to be rebuilt and I will try to name a few of them.

We have an Onsrud Panel pro with 12HP motor. We mostly cut 4x8 sheets of plywood and occasionally some hardwood (we make kitchen cabinets). We average probably 5-6 hours of actual running time a day, five days a week. We have had our machine since October of 2005.

Is it reasonable that our spindle would need to be replaced in this time frame? I won't go into the trouble shooting methods we have tried, as the nature of my question is just to know if it is reasonable that a spindle would need rebuilt in a little over two years.

Forum Responses
(CNC Forum)
From contributor F:
What kind of spindle is it - HSD, Columbo, etc?

From contributor M:
Here is a good question for you. Do you plunge into your cuts? Or do you ramp in? The reason behind it is that plunging is extremely hard on the bearings. Spindle motors are designed to withstand lateral pressure, not vertical pressure. Thus one of the big reasons most spindles need to be rebuilt.

From contributor F:

Does that mean you should not drill holes with a router spindle?

From contributor B:
It looks like they are ignoring your real question. To put it plain and simple your spindle should last several years even if you are plunging with it. There are several things that can make a spindle wear out prematurely. But under normal conditions two years is too short of a life span. A friend of mine just sent out his spindle because the bearings went bad but his is eight years old and he cuts mostly Corian which can be hard on spindles.

From contributor K:
Unless you are really stressing out the spindle in some way that is not obvious, and fairly unusual, a 12 HP spindle should last at least twice and more likely three or four times that long cutting normal sheet goods. Many last even longer with care and good cutting methods. That being said, what is the rest of the story? What kind of tooling are you using, etc? Most insert tooling is harder of the spindle than solid body. There are a million reasons things can go wrong, very occasionally even a manufacturing defect, but more often than not by far it is due to methods.

From contributor F:
Typical life expectancy for grease lubricated spindles below 24,000 RPM max speed is approx. 6,000 hours. Many go longer and some fail long before. It seems like the three most common culprits contributing to early failure are out of balance tooling, inadequate dust collection and spindle crashes especially if the spindle is off at the time. Also, the spindles that use an air venturi to provide cooling always seem to run too hot and burn up bearings as a result.

From the original questioner:
I believe my spindle is a Colombo spindle. We do ramp in for our production runs (cabinet vision). We also occasionally use a straight plunge on a part that is programmed by itself. We don't use insert tooling on any production runs and I don't believe we have any insert tools for our CNC machine period. Most of the time we are cutting plywood with a 1/2" or 3/8" 2 flute cutter.

We use Vortex Tools, and below are the item numbers
# 1555 1/2" 1 1/2 D.C.
#1565 1/2" - 2 1/8" D.C.
#3435 1/2" Up/Down Cut
#1350 1/2"- Down Cut
#1385 3/4" shank 1/2" cut 3 1/2" Cutting length
#3135 1/2" Compression
#3189 1/2 Compression with 1/4" upcut
#3435 Chip Breaker-

Contributor M you were right, the nature of my question was if two years is an unreasonable amount of time, even in the worst case scenario.

From contributor J:
"Do you plunge into your cuts? Or do you ramp in?" By ramp I presume that you mean plunge at an angle instead of perpendicular to the surface? I don't understand how ramping the plunge cut makes any difference. The same amount of vertical force is applied in either case, isn't it?

From contributor J:
How is this spindle cooled? Is it liquid cooled with heat exchanger, self contained electric fan or does it has a air venturi blowing air into an opening at the front of the spindle? If it has an air venturi you must supply a large amount of compressed air to have any chance of properly cooling the spindle. Also check to see if you have a model RA, RB or RC spindle. Some of these spindles only have a 30% duty cycle rating. Also the RPM you operate the spindle at determines the heat built up in the spindle itself. 12-14,000 RPM usually generates max heat.

From contributor H:

Have you contacted Onsrud? Is this unusual or can this be expected sometimes? I would be very interested in their responce. Another thought - it seems to me that small shops get the short end on warranty. Most of us run our machines less than 1000 hours a year where the big boys can run 6,000. How many hours on your machine?

From contributor M:
I used a 9 HP Columbo on a Multicam for many years without incident, Cabinetvision, Alphacam, ramps and very similar Onsrud tooling. Vortex is very good tooling too and should give you the same spindle life. From what you say you are pretty standard in methods, and that you really have a good argument for being shortchanged on the life span of the spindle. Also, Contributor H is right on. I bet you don't hit 1,000 hours run time per year real run time, and even if you hit 2,000 hours (congratulations on a great business if you do), which is roughly the time an employee works on a 40 hour week, 50 weeks a year with two weeks off. You should expect a lot more from a spindle.

From contributor B:
The number one thing that can cause a spindle to burn out so quickly is heat. Dull tools or wet wood (too high of moisture content) can transfer heat to the spindle and burn out the bearings. I use a very small Temp gun to read the tool when it comes out of the work. If it does not cool quickly then it is getting dull and needs replacement and should never get over 350 degrees Fahrenheit. So my question is, are you burning up your tooling as well?

From the original questioner:
Thanks everyone for you tips and comments. The situation is still not resolved but we are still working on it. Contributor M, I agree that we probably don't hit 2,000 hours a year on the router. It is hard to tell, especially because we don't have an hour counter on our machine.

Contributor B, I asked our CNC operator how he determines if a tool needs to be changed. For our Plywood, we run a 1/2" compression bit, 18,000 RPM's and like 750 inches per minute. He said when the tool starts to make a slight burn as it goes around a corner that is their trigger to change tools.

For the 1/2" down cut which we use for cutting hardwood, he checks it with his fingernail to see if it is sharp before each new job. Also of note, he is able to touch the tool and tool holder with his hand after a tool change, (on the 1/2" compression bit).

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
Here are some common causes for spindle failure.

(1) High Radial Load - The failure that occurs when the machine feed rate is too fast for the material being cut or when high feeds are pushing a tool with chipped or very dull cutting edges. This is determined by the failure of the first of the front bearing pair.

(2) High Axial Load - The failure that occurs when the spindle suffers a high axial impact, such as plunging into the material rather than ramping in, or crashing into the work table. This failure is determined by the failure of the second of the front bearing pair.

(3) Unbalanced Tooling - Failures occur when the tooling used is not properly balanced or exceeds the recommended advised tool dimensions or weight limitations. This failure symptom is observed in the damage to the rear bearing pair.

(4) Actuation While Running - The failure that occurs when the piston of the pneumatic actuator contacts the drawbar while the spindle is still rotating. This can be caused by operator or programming errors. The failure or adjustment of the proximity sensors to read the position of the drawbar or the sensor or relay that senses shaft motion can also cause it. Another possible cause is contamination of the pneumatic actuator or the exhaust muffler of the actuator. This failure is determined by the witness marks on the end faces of the actuator piston rod and the drawbar nut.

(5) Shorted Winding - This failure normally occurs when the spindle is not receiving the proper input power. In most cases, it is a result of the parameters of the frequency inverter not corresponding properly to the electrical characteristics of the spindle. This is normally determined by conferring with the customer.

(6) Tool Sticking in Taper - This is normally due to the transfer of heat caused by an oversized tool. It can also be caused by an improper ejection stroke of the drawbar due to contamination in the actuator or broken springs in the drawbar assembly. This is normally determined by the examination of the drawbar.

(7) Tool slipping in taper - This is normally due to the transfer of heat from long heavy cuts, resulting in a thermally expanded or contracted tool taper. It can also be caused by an improper ejection stroke of the drawbar due to contamination within the pneumatic actuator or broken springs in the drawbar assembly. This is normally determined by the examination of the drawbar.

(8) Other - Spindle fails due to unusual circumstances such as shipping damage, electric fan failure, electronic box malfunction, etc.

Crash - this is normally caused by operator or programming errors. This failure occurs when the spindle is driven into the worktable or surrounding components on robot applications. This is determined by the physical damage of the shaft taper and spindle body.