Fine feed control on the Landis 1R grinder
A few weeks ago I repaired the hydraulics on my 1R and took the opportunity to trace the hydraulic lines and measure the breakaway force on the wheel head carriage. It turns out my advise about wheel head preloading given to the original poster was wrong.
A few important observations:
All hydraulic fluid contains water and oxygen. If you let a grinder sit for a few months the water will separate from the oil in the hydraulics tank and in the spool control valves. It takes very little rust to jam the spool valves. The table and wheel head pistons are not sensitive to this. The rust is not tightly adhering to the valves and wipes off with a rag.
Hydraulic oil has additives which prevent the rust from occurring. The additives are eventually used up and it becomes necessary to change the oil.
The lesson is that a grinder operated with spool valves should not be allowed to sit idle for more than a few months unless it has been flushed and refilled with new oil. The difference between the farm and ranch store $30 for a 5 gallon pail of iso 32 hydraulic oil and the Mobile/Chevron/Shell $60 for a 5 gallon pail of oil is how much and what type of rust and oxidation preventative chemicals have been added. This may be an instance of getting what you paid for.
The fine feed control knob on the wheel head is not designed to be used to advance or retract the feed when the wheel head is in the advanced position. It takes about 60 pounds of force to break the wheel head carriage free from the ways. When the fine feed knob is turned .00001 ", all that happens is that the oil between the worm gears and rack and pinion final drive gets compressed. The carriage does not actually move. It will not move until the fine feed has been turned enough to cause 60 pounds of force to act on the carriage. Once this happens, the carriage will jump forward and refloat on the way oil. It will continue moving
until the force acting on the carriage drops below the force of the fluid friction of the ways. That might be 20 pounds. Once the carriage stops moving the oil film between the carriage and ways will drain out and you will have almost metal to metal contact. The carriage is then stuck again. The way stick-slip friction does not allow for small predictable movement of the carriage.
The best way to avoid this problem is to always retract the wheel head first before setting the fine feed. For a grinder with manual feed that means backing off the main hand wheel one full turn until it hits the travel stop. This corresponds to 0.1" of carriage travel. On the hydraulic infeed machines the feed rack is retracted 1.00" inch The fine feed is then set. Any strains in the feed mechanism will be relieved when the wheel head is advanced back to the forward position.
For a manual machine the process is repeatable provided that the main hand wheel is smoothly rotated to the travel stop. If the motion is stopped part way and then restarted it may not be repeatable. The feed rack is preloaded by the initial 60 pound brake away force and then kept in contact with the pinion by the 20 pounds of fluid friction. If the motion is stopped part way the preload will be lost. The load is applied to the surface of the rack teeth that face forward.
If a external preload cylinder were added to the wheel head carriage the cylinder would need to push the wheel head backward in relation to the base casting.
In my original post I suggested pushing it forward. This is wrong.
The hydraulic feed carriage works differently. When the carriage is retracted, pressure is applied to the sliding rack to force it backward 1.0". The same pressure is applied to the preload cylinder to force the pinion to remain in contact with the rack.
When the carriage is advanced, the way oil injector is triggered which refloats the carriage. The pressure is then released on the preload cylinder and the carriage does a fast forward relying on the motion to maintain a loaded rack and pinion. There is a spool valve assembly in the base casting that prevents oil pressure reaching the hand wheel advance piston until the fast advance has come to a stop. What the machine operator sees is a smooth motion going from a fast feed advance to a regulated slow feed of the hand wheel until it hits the travel stop.
The carriage is stuck to the ways at this point and sinks down a bit. A timer is started to complete a sparkout grind . When complete, the retract lever is automatically reset, the way oil pump injects once more refloating the carriage and then the carriage moves back one inch.
The Landis machines prior to the R series applied pressure to the preload cylinder when the carriage was in the forward position. It appears that design prevented repeatable positioning of the carriage. Landis took out a patent in the 1960's for a .0001" fine feed mechanism that changed the carriage position
by adjusting the pressure in the preload cylinder. Small changes in the preload would cause flexing of the wheel head. The idea behind the preload only during wheel head retraction design is that the preload is now consistent and independent of pressure changes in the hydraulic system. The preload cylinder
is used to prevent the rack and pinion from banging together during the fast advance.
In summary, adding a preload cylinder to a manual Landis 1R is a dumb idea.
Carriage way stick-slip friction is not a problem on modern grinders. The hydrostatic way designs are frictionless.
It is also not a problem on box way milling machines. My box way bed mill with glass scales can repeat position to .0001" The difference is that the milling machine has a way loading of 4 psi with an iso 68 way oil in addition to a preloaded ball screw and glass scale feedback for the servo motors.
The Landis grinder has a way loading of 8 psi with a iso 32 way oil. It was intentionally designed to prevent the carriage from floating on the way oil. I suspect a floating wheel head carriage cannot do a repeatable sparkout grind. It may also cause a poor finish from vibration.
Robert