Dunham collet closer care and maintenance

When the Dunham collet closer is taken care of, it runs very well. There are a number of issues with the use that should be attended to regularly.

Dunham Care and Maintenance

  • Use as low a pressure as will get the job done. The bearings in the closer take the load of the pressure. As you turn the pressure up, the bearings are worked harder. If you are doing 1/4" diameter work, don't have the pressure at 80psi.
  • Make sure the lubricator for the collet closer is working!!!! If the closer is run for even a short time without lubrication, the bearings will fail. It may take a few weeks for the failure to occur, but it will. No amount of over lubrication will help after the bearings fail. If you find that you do not have to put oil in the lubricator reservoir, then it is not working!
  • Short cycle times can cause closer failures. If the cycle time is very short, under 7 seconds, it can cuase the closer not to get lubrication. The lubricator is driven by the air purge line. When the air is flowing, the oil is pulled into the closer. The standard configuration for when the air flow is on, is when the spindle is on. On the short cycle runs, the air is not on enough to get the oil into the closer. If you have this problem, contact the factory and we will send you documentation on how to have the air flow on all the time.
  • Add Slick-50 or STP oil treatment to your lubrication reservoir. We have found the addition of these oil supplements do help!!! It is not an exact science for us. We have had reported to us that mixing the STP 50% with the standard oil works well. Also Slick-50 in varying amounts also does well. We don't know how much is the correct amount, but we do know that the temperature of the closer is significantly reduced.
  • Check the run out! If the closer is running out, even a little, the bearings and seals will quickly degenerate. Before the machines are shipped from the factory great care is taken to make sure the collet closer is aligned correctly. After they have been run in the realignment process must be done again. The alignment is not difficult to do, an indicator with magnetic base is suggested.
  • Bar pressure to high or to low. If the bar feed pressure is to high, the bar can be forced out of the collet. Pressure being to high or low will cause part length variations!
If the collet closer is not running within .001" you will need to adjust it. One item in particular are the locking screws on the adapter. The screws work against brass pads that sit on the threads of the spindle. By tightening the locking screws, you can adjust the runout on the back end. See Item 2 below. Whenever the collet closer is removed, this process must be repeated!
Make sure the set screws into the draw tube are tightened evenly. See item 3 below.
Collet closer not stroking or can not turn the knurled ring on the back end:

This can come from the draw tube moving in the knurled ring on the end. If the set screws (item 3) work loose, the tube can move. If the tube moves forward, the stroke of the unit is effected. The tube should be close to flush on the back end. See above photo.

Another reason the draw tube might not move is if the allignment key (Item 1) is either stuck in, or it has backed out all together.

Stuck in - If the key is broken it can stay in the spline in the draw tube, take it out and inspect.

If the key backs out, the draw tube can rotate during the cycling of the machine. The collet will then either un thread or thread so tight that it can not move.

Or the O ring is swelled and needs service