Backlash Eliminator Question

[MikeH]

I saw an advertisement for a WMW Heckert FU450X1800 mill that is for sale. It is way too big for my home shop.
But what got my curiosity peaked is it was listed as having an automatic hydraulic backlash eliminator.
How does that work?
Is this a hydraulically moved machine instead of lead screws?

[old mart]

At a wild guess, there is an oil pump keeping the pairs of leadscrews apart taking up the backlash and lubricating them at the same time. Hopefully someone has one of these machines and will explain. Is this the one? https://www.machinetools.com/en/for-...rizontal-mills

[EVguru]

The Elliot Sturdimill at work had a manual backlash eliminator. There was a knob on the apron that adjusted the two halves of the leadscrew nut.

[Doozer]

When I worked for Michelin, in the shop we had a Heckert mill.
I don't remember the backlash thingy, but it was a very stout mill.

--Doozer

[Rich Carlstedt]

There are two methods for backlash elimination that I know of:

For lead-screws the nut is split in half ( Like two nuts on the same shaft ) but one nut has fine threads on its OD and that nut by slightly rotating adjusts the span and eliminates any backlash , so basically thrust loads switch between nuts. The rotation can be by spring (ala Cincinnati ) or hydraulic force. Adjustment is critical and the manuals always say it needs to be done by a professional !)

For gears, There is a method that splits the gear along the face, say the gear is 1/2 "wide, well it will have a 3/8" wide gear and a 1/8" wide gear.
The wide gear is the working gear (keyed to 3/4" shaft) but is 1/2" wide hub and a boss of 1"OD and and the slim gear rotates on this OD. Now they cut pockets in both gears and place a spring (s) between the two gear. Engaging this gear means compressing the spring slightly and the thin gear keeps the main drive gear in contact with the mating gears in the assembly. You only need this on every other gear in the string for the assembly. Sometimes this is called "silencing" or low noise gears. There is no backlash BUT...It works for one direction primarily. When reversed , the spring side becomes the driver and there may be spring compression moments based on load

Rich

[MikeH]

At a wild guess, there is an oil pump keeping the pairs of leadscrews apart taking up the backlash and lubricating them at the same time. Hopefully someone has one of these machines and will explain. Is this the one? https://www.machinetools.com/en/for-...rizontal-mills

That thing is huge!!
It is this one, https://rover.ebay.com/rover/0/0/0?m...2F362302220500
I thought this one looked big.

[MikeH]

There are two methods for backlash elimination that I know of:

For lead-screws the nut is split in half ( Like two nuts on the same shaft ) but one nut has fine threads on its OD and that nut by slightly rotating adjusts the span and eliminates any backlash , so basically thrust loads switch between nuts. The rotation can be by spring (ala Cincinnati ) or hydraulic force. Adjustment is critical and the manuals always say it needs to be done by a professional !)

For gears, There is a method that splits the gear along the face, say the gear is 1/2 "wide, well it will have a 3/8" wide gear and a 1/8" wide gear.
The wide gear is the working gear (keyed to 3/4" shaft) but is 1/2" wide hub and a boss of 1"OD and and the slim gear rotates on this OD. Now they cut pockets in both gears and place a spring (s) between the two gear. Engaging this gear means compressing the spring slightly and the thin gear keeps the main drive gear in contact with the mating gears in the assembly. You only need this on every other gear in the string for the assembly. Sometimes this is called "silencing" or low noise gears. There is no backlash BUT...It works for one direction primarily. When reversed , the spring side becomes the driver and there may be spring compression moments based on load

Rich

I saw the gearing system you described, once. I always wondered why they did that. Thanks.
I can see that it would allow endless rotation.
The only other gear based system i have seen has a rotation limit. That is the use of a clock spring at the end of the gear chain, like in dial indicators.

[Paul Alciatore]

The modern ball screw adds a third way to accomplish this. PRECISION!

[J Tiers]

The modern ball screw adds a third way to accomplish this. PRECISION!

And even with them, there may be two nuts loaded against each other like the leadscrew system.

[darryl]

Well I've often wondered about using hydraulic actuators instead of lead screws. Using a DRO would allow the feedback needed to control the valve. Very fast positional error correction can take place with a properly designed control valve, and I don't think there's any problem with the torque levels that can be developed. Operating speed might be an issue in some applications, but I've never seen the need to move a table or cross slide so quickly that a hydraulic system couldn't keep up.

Seems like there would be some ideal aspects to it.

[MikeH]

Well I've often wondered about using hydraulic actuators instead of lead screws. Using a DRO would allow the feedback needed to control the valve. Very fast positional error correction can take place with a properly designed control valve, and I don't think there's any problem with the torque levels that can be developed. Operating speed might be an issue in some applications, but I've never seen the need to move a table or cross slide so quickly that a hydraulic system couldn't keep up.

Seems like there would be some ideal aspects to it.

The machine shop I worked in, during the early ‘80s bought a used large CNC lathe the worked that way. Sorry, I don’t remember the brand. Sadly, the mover disconnected of the control wires without labeling anything. They had a string of technicians in trying to fix it. It still was not usable when i left. The shop owner is who explained to me how it worked, and had tested it before buying it.

[3 Phase Lightbulb]

Well I've often wondered about using hydraulic actuators instead of lead screws. Using a DRO would allow the feedback needed to control the valve. Very fast positional error correction can take place with a properly designed control valve, and I don't think there's any problem with the torque levels that can be developed. Operating speed might be an issue in some applications, but I've never seen the need to move a table or cross slide so quickly that a hydraulic system couldn't keep up.

Seems like there would be some ideal aspects to it.

I was thinking the same thing, but I wonder how long typical hydro seals would last.

[darryl]

When I think about this I think of shock absorbers on vehicles- they are subject to continuous pounding and relatively high speeds. The shocks on my Land Cruiser are original and have almost a half million miles on them. They have taken a lot of pounding and still work. It doesn't seem like there should be a seal problem in any properly designed hydraulic system.

[Rich Carlstedt]

Almost CNC was TRU TRACE attachments

http://www.machineco.com/Milling_Machine_Bridgeport_Tru-Trace_stkC1638.htm

Using the valve to control the mill or lathe is very viable. I mean you could put a miniature servo or stepper on the stylus to control the mill.
Here is the reason it's not done
Too much maintenance ! and too big a footprint

Look up the old Cinncinatti HYDROTELS, the fore runner of CNC's
Rich

[Noitoen]

Hydraulic actuators are rigged just like servo motors. The closed loop controller connects with some proportional solonoids and the digital scale. It acts just like a motor