Micro Mill Maintenance Guide

Proper maintenance and care will assure that your MicroMill system will work at peak performance for many years of operation. Following the simple maintenance procedures below is all it takes to keep your machine in good running condition.

Lubricating the Ways and Lead Screws

The steel ways and lead screws of the machine should be well lubricated at All Times to provide smooth, free movement. Standard Automotive Transmission fluid is readily available and is an excellent lubricant for this purpose. Using a standard oil can, apply generous amounts to the steel Sliding Ways and Lead Screws before and after machining operations.

Backlash Measurement

The backlash of each axis can be measured by mounting a Dial Indicator to a secure base with the contact point against the moving member.
The following procedure will determine the backlash for the X-axis:

1. Set the JOG INCREMENT to 0.100 inches.
2. Jog the X-axis in the negative direction 0.100 inches.
3. Position the dial indicator against the table enough to deflect the needle approximately 0.050 to 0.100 inches.
4. Zero out the indicator.
5. Jog the X-axis in the positive direction 0.100 inches.
6. Note the difference of the dial indicator from Zero.
7. This difference is then the backlash of the X-axis.
8. Enter this backlash directly as a value in inches using the backlash compensation option.

Typically the backlash is between 0.0015 to 0.003 inches, but can be as high as 0.005 inches or more due to machine wear. If the backlash is this high it can be adjusted as described in the next section.

Adjusting the Lead Screw Nuts

If your machine is running on a continuous basis and has accumulated many thousands of inches of travel on each axis throughout the years the Lead Screw Nuts may begin to show wear. This is evident if the backlash or play is larger than you think it should be. The backlash of a new system is typically from 0.0015 to 0.003 inches. If the backlash is larger than this the Nut may need to be tightened down a little. The split bronze nut assembly is used on the X and Y axes of the machine.

The outer two hex screws tighten or pull down the nut while the center hex screw loosens or pushes it open. This push-pull arrangement has to be adjusted very precisely. If the Nut is too tight it will cause much friction and will be very difficult to move the axis. If it is too loose the axis will turn very freely, but the backlash will be too large for precise axis positioning.

The adjustment of these hex screws is very, very sensitive to the slightest turn. They should be adjusted no more than 1/30 of a turn at a time and tightened by only the force you can produce with your thumb and forefinger on the small end of the L-shaped hex wrench.

Tightening Procedure:
1. Loosen (CCW turn) the center hex screw slightly (1/30 turn or less).
2. Tighten (CW turn) down the outer two hex screws an equal amount.
3. Re-Insert the Lead Screw and test for tightness or freedom of movement and Backlash.
4. Repeat 1 to 3 until desired performance level is obtained.

Loosening Procedure:
1. Loosen the outer two hex screws slightly (1/30 turn or less).
2. Tighten down center hex screw an equal amount.
3. Re-Insert Lead Screw and test movement freedom and backlash.
4. Repeat 1 to 3 until desired performance level is obtained.

Note: This can be a very tedious process and can really throw the whole Lead Screw/Nut system out of calibration (much to tight or too loose) if not done in the proper fashion. If you are not very experienced with ‘the feel’ a properly adjusted machine should have it is recommended that you do not attempt this procedure.

Adjusting the Brass Gibs

If you are not very experienced with "the feel"' a properly adjusted machine should have, it is recommended that you do not attempt this procedure.

Box Way Assembly Gib
The brass gibs may also need adjustment over time. The brass gib of the Z-axis Box Way Assembly is adjusted with hex screws on the top and bottom of the assembly. The top screw tightens the gib on the steel way while the bottom one loosens it.

Saddle Gib
The brass gib on the saddle or Y-axis is adjusted with the two hex screws shown to the right. The longer middle hex screw is used to lock the saddle in place, which would generally NEVER be done on a CNC machine. This would only be done on the Manual MicroMill.

Adjusting the Head Stock

The HeadStock is removed or re-positioned on the dovetail by loosening up the two hex screws shown above.

It is very important NOT to over-tighten these two screws when setting it back in place. Only a small amount of tension is required to securely fasten the dovetail.

Tighten it with only the amount of force you can provide by holding the short end of a standard L-shaped hex wrench between your thumb and forefinger as shown in the picture above. If the tension is too tight the spindle will not turn freely and may become damaged by overheating. This will also prevent it from running at the top (high-speed, low-torque) spindle speed.

Note: If you have accidentally over-tightened the spindle dovetail you may have "crunched down" the bearing race assembly. This would be evident if it does not start on the top spindle speed. If this is the case you will have to "loosen up" the bearings again by setting it at the 2nd top spindle speed and letting it continuously run overnight for a period of 12 hours or more. The bearings should loosen up after this and it should be able to start on the top spindle speed. If not, the spindle bearing race may be permanently damaged and will have to be replaced.

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Published 3/20/2017 2:56:42 PM
Copyright 2016 Dennis Bohlke