We’re pleased to offer this guest posting from Kitagawa Europe on the importance of proper chuck maintenance for CNC lathes.
It is important to undertake regular maintenance on your CNC equipment to ensure maximum levels of performance and uptime. Of all your equipment, it is your power chucks that require the most attention and the majority of machine shops will grease them on a regular basis. Unfortunately, not every machinist understands the basics of chuck lubrication.
Below we ask (and answer) the four salient questions surrounding chuck greasing, so that you can keep your operation working to the highest possible standards.
Why is greasing the chuck important?
The vast majority of chuck manufacturers will use a wedge design. As a result, the power transfer through the chuck is achieved via an angled wedge arrangement – a transfer of axial forces to radial jaw forces.
Wedge style chucks are so popular because they offer several advantages, including the fact they are heavy duty, compact and transfer forces efficiently. There is however one disadvantage to wedge style chucks; the fact that there are greater contact surface areas between the wedge, master jaws and chuck body.
It is essential for the internal contact areas to maintain a coefficient of friction, if the wedge-style chuck is to remain safe and efficient. If the coefficient of friction is too high, the efficiency of force transfer can fall. So, whilst the hydraulic pressure may remain the same, the chuck loses gripping force; resulting in an unsafe situation.
By regularly greasing the power chuck, you can maintain the integrity of the chuck’s efficiency and operating characteristics.
How often should a chuck be greased?
To say that a chuck should be greased ‘regularly’ is a far too vague phrase to use. All power chucks should be greased at least once for every eight hours they are in operation. However, if you have high rpm requirements, short cycle times or use a particularly aggressive coolant; your chuck is likely to need greasing more often – sometimes as frequently as every four hours. By keeping a close eye on efficiency between lubrications and shortening the time where required, you should be able to find the perfect greasing schedule.
What lubrication should be used?
No matter how smooth metal surfaces may appear, they all have microscopic peaks and valleys. These can allow areas of the surface to break through the lubricating film; creating metal-on metal contact. Not ideal when you consider that wedge-style chucks can have as much as eight tons of friction being applied to the wedge, master jaws and body.
In order to avoid this metal-on-metal contact, it is advisable to use a denum-disulfide-based (moly) lubricant with 20 – 25% moly. This type of lubricant is superior to the lithium and mineral-based greases which are commonly found on the market. Moly serves to provide a barrier between the surfaces, protecting them even under heavy loads. So don’t let anyone tell you that it is okay to use any old grease – if you want to keep your chuck working properly and extend its lifespan, use the proper lubricant.
Anything else to consider?
In addition to applying moly-based grease, there is some other maintenance that should be carried out. Every six months you should dissemble your chuck to inspect it. Be sure to refer to the manufacturer’s manual before you begin taking the chuck apart. Once you have the chuck in pieces, clean out any debris that has gathered in the guideways. Your final check should be to see if there is any burnishing or galling.
Guest post is provided courtesy of Kitagawa Europe.
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Bob is responsible for the development and implementation of the popular G-Wizard CNC Software. Bob is also the founder of CNCCookbook, the largest CNC-related blog on the Internet.