Your Opinion on Max RPM

[Tinyfxds]

So we just had a spindle melt down on Friday and right away everyone blames the program department.  It seems a few of the operators believe that max rpm should never be utilized except for short bursts.  A short burst would be a few minutes at max RPM we were told.  Now, we don't usually make a habit of maxing out the rpm's on the machine but if we have to we will.  In this case the machine was running for about 3 hours at max when the spindle went.  I don't feel that this is an excessive amount of time for a machine to run maxed out.  The place I used to work would run their spindles at max for 8-12 hours during very long finishing programs on large cavities. 

 

To put things into perspective, this machine was never used very often as it didn't have coolant plumbed in it.  This machine was primarily used for cutting fiberglass, wood, nylon....etc.  We just added coolant to the machine last week and are cutting different steels and alloys in it.  My feeling is that, not running this machine for long periods of time and then asking it too perform long run finishing at high rpm, has more to do with the spindle melting down than anything.  Oh by the way, the machine is like ten years old and this is the first time the spindle went out.

[Guest]

This issue really varies from machine to machine.......some spindles have a max spindle and they can run there period, others have a max speed that is only meant to be run in bursts.

 

Place I used to work the Fadals have 10k RPM spindles but we would only run that at 9k RPM's.  Why, run at 10k regularly, we would burn out the spindle.

[Guest MTB Technical Services]

You can safely ignore the operators.

Saw this happen many times with KOMO routers.
 

All machines will have multiple Spindle Charts in their manuals for Horsepower, Torque etc.

These charts will include a duty cycle that will answer this question for a specific machine.

These charts will also include the rating interval used.

That's why you can't trust the Haas horsepower rating as it's only a 5 minute rating when quality machines use a 30 minute rating.

You should find a max RPM chart or at least guidelines for your machine in the manual.

 

A general rule of thumb for medium to higher end machines is that If the machine has a spindle chiller unit (radiator), you can safely run Max RPM

if the spindle load is below 50%, for an entire shift and then some.

 

Most lower end machines don't have the quality in the bearings to allow max RPM at higher loads for indefinite periods.

When you add the lack of a spindle chiller to the equation, you can cause premature failure.

Cutting dry only compounds the problem because simply running coolant through the spindle does wisk away some heat.

 

In your case, cutting fiberglass is a major clue to the failure.

Unless the machine was designed like a graphite cutting machine, glass shavings/powder will enter the spindle jacket and destroy the bearings prematurely.

That's why you NEVER use a high end machine for abrasive composties unless it was specifically desgined for it.

In addition to the spindle damage you'll also have damage to the linear guides and ball screws.

 

In your specific case, the spindle damage was likely causd far earlier and only reached failure because of the recent high heat.

In short, MAX RPM did not cause your failure, fiberglass penetration of the spindle jacket did by damaging the spindle bearings.

[Tinyfxds]

 

In your specific case, the spindle damage was likely causd far earlier and only reached failure because of the recent high heat.

In short, MAX RPM did not cause your failure, fiberglass penetration of the spindle jacket did by damaging the spindle bearings.

 

I guess I never looked at it that way.  That machine cut a lot of FR4 and G10 garolite

[jeff]

I run my Okumas at max rpm (15k) all the time. Sometimes for 30 minutes at a time or more.

And one of the mills is 8 years old, still going strong.

[Newbeeee™]

You may need coolant to run as it may go around the spindle cartridge which acts as a secondary cooler, as well as the spindle chiller???

You also have to remember that most shop floor don't want things to run too fast as their overtime might disappear.

Where my mate is at the moment they have sh!tty old 6krpm Bridgeports running on some good monthly repeat work (Ally). And they have turned off their MAM for 3 months as it is out of work. The foreman won't let jobs be swapped over because of OT and 'what's the boys going to do if the work gets transferred onto the MAM'...

 

Our Chevalier's (10k rpm belt drive) run max when we can and they last on average 2x years before seizing.

A rebuild inc fitting is just over £3k.

Our Feeler (15k direct drive) has lasted a year with no issues to date :fingers crossed - knock on wood:

Our Robodrills run 10k all day everyday and we've had one for 4 years and one for nearly 3. Had to put one spindle in one because of a BANG...

 

At an old place we had POS Hitachi's (vs50's and vs40) with 12k rpm in-built motors. Well sometimes they seized within a day of running back in.

They were atrocious and on average would last 6 to 8 months.

The sales guy (archetypical one at that ) used to say - 'they're not supposed to run flat out, you wouldn't get in your car and drive it all the time flat out would you'. And these were £250k machines and the funny thing was the owners used to agree with him!

[gcode]

You have to be careful running Haas VMC's flat out especially if you're not using coolant.

The spindle is surrounded by a water jacket that the coolant flows through.

If you don't run coolant.. the coolant in the jacket can heat up and the spindle won't cool properly

I always hooked a hose up and routed it back to the coolant tank so I could run coolant

through the spindle when dry machining

[The_kid]

yeah the manufacture everything to do with it and weather or not it has a spindle chilling unit or it uses a a cooling jacket.  as others have stated refer to the charts.  The main cause for failure that I have seen is when the Dublin coupling goes out for thru spindle coolant and the coolant gets into the top/rear bearings it washes the grease out and just cooks everything. I have also seen it wash the grease outta the Bellevue washers causing rust then eventual fracture and failure.  or the labyrinth seal on the front gets clogged and can no longer purge anything that gets into it.   I have rebuilt easily about a dozen spindles and its pretty cool to see the different designs.  

 

Most of the time a local repair guy can repair these fairly quick and inexpensively.  

[Guest]

High end machines generally speaking will run at MAX RPM indefinitely unless otherwise specified.

 

One exception I know of is RoboDrill 24k spindles. They'll run indefinitely at 19k. At 24k I want to say 30min. Duration is what seems to be popping in my mind at the moment.

[Bob W.]

Haas spindles are cheap (~$4k) so I would run mine at the limit and they would need to be replaced every two years.  The additional work I got done would more than pay for it so I considered them a consumable.  If one is running at the max chip load that cutters can take, backing down 10% will reduce the throughput by 10%.  If a machine is generating $20k per month, which is realistic for a Haas, that drop in throughput would be costing $2k per month.  Run it hard and replace it when it goes bad.  Compared to the extra $48k you will make in the two years $4k is pocket change.  Nice thing about Makino spindles is they are designed for it so I run at the limit and don't worry about it.  I run the Makinos like I ran the Haas, it costs a lot more to slow down than it does to service the machines.