Thread: Hercus hacksaw hydraulic lifter - oil and other questions

Hey all,


I posted over on the Hercus area a week ago with no luck - so, posting here.


I am getting an old hacksaw back on its feet and am trying to figure the hydraulic lifter. With 140 weight (gear/differential) oil - the lifter manages to move the vertical piston about 1mm or so. I tried ISO 68 - nothing, ISO 90 - nothing. At least with 140 I see something. Though, 1mm is not even enough to cater for the wear to cause an actual lift!


I figure it should be more than 1mm movement?


The pistons seems pretty snug, but I am guessing there will be some wear - the rest of the machine has a fair bit of wear.


And while I am at it, where should the the hydraulic actuating eccentric be positioned relative to the stroke? I am guessing it cuts on the forward stroke, and just near the end of the forward stroke it should starts its lift?


many thanks,


Greg.

FWIW - my Parkanson power hacksaw cuts on the reverse stroke, and lifts on the forward.
No idea if the Hercus is the same or not.

Steve

G'day Greg
If the pump is delivering pressure (might have to spice in a pressure gauge somewhere), then either the valve controlling things is not working or the piston seals are shot and oil is bypassing. If heavy oil is working then it could well be the piston seals. Given what hydraulics are used to lift, a hacksaw boom should not be difficult.

Michael

Thinking about it some more, 1mm of ram movement might not be so unreasonable, as it only has to be enough for the blade to clear on the return stroke.

Steve

My 1950's Hercus cuts on the out-stroke and lifts on the in-stroke. The lift is not huge, more like just taking the weight off the teeth. I have ISO 68 hydraulic oil in mine, as far as I am aware the pump has never been looked at.

Steve, Michael, Gavin - thank you.

These old things are not complicated - no piston rings and such - just a smooth fit inside of a bore. Well, two actually. There is a hole at the base where oil is sucked in and pushed out so the system is not sealed as such. I'm guessing that is to permit raised and 'soft' lowering of the ram.

The small cylinder has a piston coming from an eccentric on the main shaft. The larger (vertical) cylinder is for the ram lifting. The small cylinder piston has about 1" of travel. That will equate to less movement in the vertical because of the different piston sizes .. and the hole the base. The whole thing sits in a tub or oil.

IMG_20190502_180859~2.jpgIMG_20190502_181033.jpgIMG_20190502_180908.jpgIMG_20190502_181456.jpg

To my mind the hole in the base is enormous - like ISO 68 will just whoosh through it and escape and pretty much put no pressure on the vertical piston.

I figure circa 1mm of movement may be enough to stop return drag on the blade ... but that circa-1mm was not actually overcoming the wear in the piston rod eyelets so it never actually lifts anything, and the force under it may not be enough to lift anything. Dunno.

With ISO 68 I didn't see oil leaking past the pistons, but ... if only a few mm of travel is expected then maybe it doesn't take much.

I think my first experiment will be to make a new brass 'plug with hole' for the base with a much smaller hole. If that doesn't work well enough then I guess I have to look at remaking some pistons with a more snug fit. Or both.

Gavin: if I may ask, what position is the eccentric set at ? - like, from the pulley side of the machine, with the ram at full extension, what 'o'clock' is your eccentric set at?

On my parkanson that brass plug in the bottom has a ball in it so it acts as a one-way check valve.
Have a look inside it and see if there's a witness mark to indicate it used to have a ball.
If it's missing it would explain the behavior you are seeing.

Steve

Oooohhhhhh.... I was wondering if it was somehow supposed to function as a valve!

That just might be it. Nice one!!!

Can any hercusaurus owners confirm?

Originally Posted by StrayAlien

Gavin: if I may ask, what position is the eccentric set at ? - like, from the pulley side of the machine, with the ram at full extension, what 'o'clock' is your eccentric set at?

My eccentric is on the left hand side of the blade, standing at the blade end of the saw.
Looking from the left hand side of the saw (the only way you can easily see my eccentric), with the blade frame fully extended, the eccentric is at the 9 o'clock position if you take the connecting rod cap as being 12 o'clock and the connecting rod shaft as being 6 o'clock.

Does that make sense?

Thanks Gavin, very much appreciated. Looking from the left side of the machine (the side with the pulley attached to the main shaft) does the pulley/shaft rotate clockwise or counter-clockwise?

If clockwise, that suggests that the lift starts to happen before the end of the outwards stroke. Makes sense.

Greg.

EDIT: I just realised I got that wrong. For the 9 oclock position as you describe the rotation must be counter-clockwise?

Originally Posted by StrayAlien

Thanks Gavin, very much appreciated. Looking from the left side of the machine (the side with the pulley attached to the main shaft) does the pulley/shaft rotate clockwise or counter-clockwise?

If clockwise, that suggests that the lift starts to happen before the end of the outwards stroke. Makes sense.

Greg.

EDIT: I just realised I got that wrong. For the 9 oclock position as you describe the rotation must be counter-clockwise?

Correct, the motor drives a pulley anti-clockwise on the RIGHT hand side of the saw (facing from the blade end), that pulley drives a shaft across the back of the saw to a pair of gears on the LEFT hand side of the saw which reverses the direction of rotation and feeds into the saw and pump drive, again in an anti-clockwise rotation.

Thanks Gavin. That setup is way different to mine! Mine is belt drive to a darn big steam engine size pulley. But .. it sounds like the end result is counter clockwise. That is how i have the VFD at the moment )

Some pics of the 'valve'. I figure there is 'something' (or two) missing here. The top of it looks to have held 'something' - a flap of some sort:

IMG_20190604_211843.jpgIMG_20190604_211858.jpgIMG_20190604_211919.jpgIMG_20190604_211948.jpg

I am figuring just a bearing in the base there would not allow anything to flow out at all so the only other way out is past the piston - but the clearance between piston and cylinder (even on this worn old machine) is really not very much. I doubt even ISO 68 will squeeze past the piston to get out. I am guessing this 'valve' was used to get oil in fast but limit oil flow out - so that (I guess) you can raise the ram manually (it sucks in oil), and it goes down gently.

Thoughts welcome.

Greg.

I can't see down to the bottom of the bore or in the hole where that brass fitting comes out of....
but at a guess I would think that either a flat do dar or a ball would seat at the top of the brass gizmo, oil pressure would push it off the seat, then the weight/movement of the saw would be somewhat held/slowed while the oil slowly returns through the slots.

cheers, shed

Ball bearing in the brass plug, and a bit of rod or similar across the top to stop the ball getting sucked up too far and blocking the orifice to the bore.

Can't work out what the slotted screw bit does though, but I'd be picking some form of leakdown valve.

Steve

Shed/Steve - thanks.

It might be experiment time. If a ball is at the base, then something needs to stop it coming out. If the ball is on top something needs to stop it just coming off. I thought the slotted screw might do something important like hold something in - but it is pretty stubby and seems maybe to be just a plug. Weird though - coz you'd think they'd just seal the hole after boring.

Like .. if you look at the first photo here: //metalworkforums.com/f65/t2034...97#post1951597 you can just make out a brazed up hole to the right of the slotted screw. I can't even figure why a hole would be needed there.

I might have to have a play with a few bearings and see what happens.