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Benefits of Hydraulic Power in machine tools


Mar 13, 2023
Hello, I am new to abrasive machining and trying to learn as much as I can. At the company I work for, every grinding machine we own operates using hydraulic power. Why is it that hydraulic power is used in the abrasive industry, and not on other machine tools such as lathes, mills, etc..
What benefits does hydraulic power provide that makes them effective for grinding operations? How does this affect the machining process?

Well I am not an authority on hydraulics, that being said hydros are used in Bullard VTLs, Warner Swasey & Gishlot lathes and some gear shapers. I would say more bang for your buck. 1 electric motor, hydro over electric provides more power and affords rapid changing of direction with minimal ancillary components. My thoughts; but I am not smartest tool in the shed. So maybe some other folks can learn us more better.
hydraulics have dampening qualities. They are harder to positionally control and speed change control, slow rapids without oversizing pumps, weight.... Granted servo over hydraulic is changing some of that, still a large dollar bill difference - can go with Linears at the same cost.
We had a couple smaller Cincinnati vertical mills that were 100% hydraulic. Fantastic machines but if you weren’t careful you could snap a 2” endmill like it was nothing.

The big Hydrotel was hydraulic too. The stylist on that machine was so accurate it would pick up .002”. I wrote “Front of Die” on a wood model for the operator with paint marker. That 50yr old mill actually machined the paint maker letters in to the die. I never would’ve believed it if I didn’t see it myself.
This almost sounds like a homework assignment, but here's a few thoughts:

1) Power density - hydraulics can put a lot of force in a small area, so making it easy to fit motion devices like cylinders to control axis displacement.

2) Relatively simple to control basic movement - hydraulic valves and adjustable stops are cheap (ish) and precise enough for gross movement (usually not infeeds without fancier controls).

3) More robust under dusty/gritty conditions. As hydraulics already require seals to keep fluid in, they also help keep dust out. While still needing additional sealing for best life, they're easier to protect than precision devices like ballscrews and bearings.

4) One hydraulic pump can power multiple axis, while electric controls typically require a motor per axis.

And many more reasons. Do a little web searching for a more complete review.
Some metalworking shapers and especially planers used hydraulics instead of the traditional scotch yoke or mechanically driven rack and pinion respectively. More linear forward stroke in the case of shapers and a faster return stroke with the tool spending more time engaged with the work and less time doing nothing. Also easier to stop and reverse direction of a big multi-ton planer table with hydraulics. The downside obviously being that hydraulics are noisy, expensive and require rebuilding every time a seal fails which can be a major PITA.

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Back in the 1960s and early 70s, IBM hard drives operated with hydraulic systems. The read/write heads were positioned with a 100psi pump and a series of different sized spool valves activated by solenoids to control the speed of the heads from track to track. There were 200 tracks on the magnetic surface that were 1/100 of an inch apart.

The high speed printers - 600 or 1000 lines per minute - used hydraulics to control the paper movements again with solenoid operated valves. Both systems required very precise mechanical valve adjustment and even more precise electronic timing of the solenoid drive circuitry.

Hydraulics make a very easy way to do traverse. Speed of traverse is easy to adjust on the go. Accurate stroke reverse position is not so important. Some dedicated production machines also used hydraulics for both rapid and feed.
Hydraulics make a very easy way to do traverse. Speed of traverse is easy to adjust on the go. Accurate stroke reverse position is not so important. Some dedicated production machines also used hydraulics for both rapid and feed.

Yes, and with that said hydraulic systems in surface grinding allow for the same fluid to be used for way lubrication. Removing circulating grit is a high-priority in grinding.

Case in point: the TOS hydraulic surface grinder I’m resting my boots on as I type this has a total-loss hyd system whereby the hyd oil is mixed with way oil (like 3:1) and the 50 L in the base runs the table traverse and lubricates the works. About a tablespoon/hr of spent oil is ejected out the side into a waste oil tank.
Remember that hydraulics started in the 20's and there wasn't any suitable electrics that were comparable, for multi axis vari/speed drive. One power supply and plumbing to servos and cylinders with speed control and power. I believe Sunstrand was one of the earlier hydraulic pioneer builders. So there has been a long time maturing before electric servos and computers came about and still hydraulics are being used but less and less as electric drive becomes cheaper and more versatile. Many hydraulic hard parts(pumps motors and cylinders) go for many years before replacement, but they all eventually leak. Hoses first then seals.
Also, when hydraulics were first starting to be used they were able to deliver smooth motion at higher speeds. Gear trains and screws didn't have that ability. Once hydraulics became established, new methods have to provide a significant advantage to dislodge the proven, reliable technology.
Hydraulics may be old tech but sound. Once you get into the high tech game, electronics designed to fail, more parts to go wrong. I have been using the same three kinechek speed controls for 10 years and they have yet to leak any fluid.
My favourite machine hydraulics are the kind that dont worry about leaks,as all leaks drain back to the main tank......this is how all the Landis Type C grinders work.......in fact the valve mechanism runs 'out in the open ' as it were ,draining direct into the tank underneath...........Contrast this to grinders that leak pools of oil onto the floor ,and have enclosed oil tanks outside the machine.