preserving the life of your High Speed Router Spindle

Following on from the previous issue, which was Spindle Safety. Spindles NZ Ltd now covers the important issue of how to preserve the longevity of your spindle.

A high speed spindle is usually at the heart of most CNC machines and is therefore probably the most important piece of mechanical equipment. It is still an electric motor but runs on bearings and has complex tool changing mechanisms. Most spindles are sealed for life (greased) ceramic or steel bearings. They are all of the highest precision P3 or P4 quality. Ceramic bearings are now becoming common in most makes of spindle and the advantage over steel is that they run cooler. This being said we occasionally overhaul spindles with steel bearings that could be up to 10 years old.

Warm up

It is important to warm your spindle before use. The bearings are the first thing to heat up, and everything around the bearing is expanding very quickly from cold. If you add the extra pressure of cutting materials you are adding more heat into the bearing area before the rest of the spindle has had time to heat up. The bearings will grow in size and as they are such a fine tolerance the clearances will get tighter. This is the science but a recommended warm up is:

2 minutes at 6000rpm, 2 minutes at 12,000rpm, 2 minutes at 18,000rpm (then another 2 minutes at 24,000rpm if your spindle runs at this speed)

Allow the spindle to rest, usually a good time to load your work, sort out programs etc. Now your spindle is ready to work.

Collission

If you have a collision with your spindle things may not be that bad. Most factories have extraction, vacuum pumps which can make hearing difficult. At the end of the day or at lunch time spin the spindle by hand. A good spindle makes a hiss, a damaged bearing has a notchy or rumbly noise.

The larger spindles handle worn or damaged bearings better than the smaller ones so if you think the spindle is damaged after a collision, plan it in to your work schedule. The smaller spindles (4kW and under) usually have cheap housings and if left with noisy bearings can easily spin in the housing causing expensive rebushing repairs.

How fast should I run

15,000, 18,000, 24000 ??? Tooling manufacturers will tell you what the tools can run at but spindles are all different. Listen to it. Spindles are fed by High Frequency and even without tooling can have strange harmonics at different speeds. We often test spindles and sometimes a spindle can be ‘sweet as’ at 17,900rpm and then at 18,000rpm sound totally different. If you have manual spindle speed override try it yourself. It will even give you a better finish.

Feed Speeds

Tooling manufacturers will give you the best possible speeds under perfect conditions, these are rarely reached as things like tool wear, work holding, changes in material being cut, all affect the feed speeds. Again listen to the noise the spindle makes, if the sound dips or changes tone it may be the spindle is working too hard. This will increase the heat and over time denature the grease and then failure could well be possible.

Clean the ISO taper

Every so often check the inside of the taper on the spindle. Most spindles mark inside and with some scotchbrite and a bit of care they can be easily cleaned. Some spindle leave marks which look like rust, but it isn’t. Some factories are just prone to moisture. The air cleaning blast which comes down the middle of the spindle MUST BE clean dry air. It should not be lubricated by the CNC and should ideally go through an air dryer. Some spindles we have for repair are from just this issue.

HSK Spindles

Due to their design, HSK spindles actually tighten the grip on the toolholder the faster they spin. The problem is that there are areas which can get an ingress of dust and dirt. Whereas ISO30 toolholders tend to shed the dust and dirt. HSK spindles seat on the face of the spindle and the taper AT THE SAME TIME, so spend time and clean the inside as far as possible with a solvent cleaner and then blown out with an air line

Check the cooling vents

SCM spindles cool their spindles with extraction. This a great idea but this can be an area which is prone to off cuts blocking air flows. We recommend a look up the spindle every week and to clear if necessary. Almost all other spindles have aluminium extrusions with air flutes to direct the air a quick blast with compressed air can help.

Jon Escreet Spindles NZ Ltd www.spindles.co.nz