Problems with hydraulic machine vice

[Veero]

We currently use 2 Homge hydraulic machine vices on our Hurco milling machines. They were a considerable investment some years ago and replacing these now would cost around £800 GBP. The problem we are experiencing is that they do not seem to get up to pressure.

The vice winds in manually on the main screw as it should do and once this reaches tightness it disengages the main screw and engages the secondary screw which winds the piston in to increase the pressure exetered by the jaws. This seems to wind in as it should. However when the secondary screw bottoms out which should be at optimum jaw pressure it is still possible to move the workpiece if struck not overly hard with a mallet.

I have looked at these vices myself and overhauled the entire mechanism on one of them. The slides appear to be in perfect service and parallel condition so no tipping occurs when they are tightened. The latch mechanism between the primary and secondary screws. The piston is in good conidition, fully bled of any air and it does not appear to be leaking any fluid since the main o-ring was replaced.

Does anyone have any further information or ideas about why these may not be making full pressure?

Many thanks
Veero

 

[rorschach]

I would suggest teeing a pressure gauge into the hydraulic line to verify if hydraulic pressure is being lost. once you are sure it is. (from your description that would appear to be the case) I'd diconnect from the HPU and use a hand pump on the vise to isolate the pressure loss. if the loss is not happening in the vise. then you need to look at the HPU. (which is where I have a gut feeling your problem lies.

 

[Veero]

Thanks for the reply. However the piston is fully enclosed in the vice stock itself and does not have any external lines or hoses. Im not sure how we would actually be able to attach a pressure gauge to it.

The chamber is preloaded by a stack of Belleville spring washers, so Im wondering if these have become fatigued over time and are not providing enough initial pressure.

I will reply again with some for of sketch showing how the vice works.

Thanks
Veero

 

[MikeHalloran]

It sure sounds like you didn't get _all_ the air out.

Try to bleed it into a vacuum.



Mike Halloran
Pembroke Pines, FL, USA

 

[eromlignod]

Oh, you meant "vise". What a relief. I pictured one of my hydraulic machines out gambling, smoking and soliciting prostitution from one of the lathes!

Don
Kansas City

 

[rorschach]

Ok, I misunderstood how it worked, I was envisioning a hydraulically actuated vise. After re-reading your post, it snapped how it worked to me. Sorry.

I agree you either have air in it, or a bad valve/seal somewhere in the system. The bellville's COULD be fatigued, but that does not sound like the problem here to me.