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5th Jun 2019, 11:57 AM #16Most Valued Member
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stray how are the 2 pistons hydraulically connected?
When the brass fitting is screwed in what size/shape/diameter/length is the hole beyond the castellation?
For me more pics of the system are needed as there are too many pieces of the puzzle missing.
shed
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5th Jun 2019, 05:11 PM #17Most Valued Member
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Brazed up hole suggests an oil gallery may have been drilled then plugged/capped permanently?
I usually poke compressed air in each hole and see where it escapes to help work out connections.
Steve
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6th Jun 2019, 10:22 PM #18Golden Member
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Apols.. I haven't been able to get back to shed to take more pics. Will do.
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8th Jun 2019, 06:20 PM #19Golden Member
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Back to the shed. Some more photos.
I did some experimenting with it today. Back to iso68 hydraulic. When working, that should be fine - so I'm aiming to make it work nicely with that.
The two cylinders are connected via a port. The slotted screw seems to plug it. The valve screws in from below. some more pics:
IMG_20190608_075239.jpgIMG_20190608_162701.jpgIMG_20190608_164835.jpg
One thing I didn't notice first time around is the small hole in the little cylinder - I am assuming this is a bleed. I'll get there in a moment.
I put a suitable ball bearing in base of the brass thingo and and reassembled. That let *no* oil back out and so, despite looking like it might get the ram lifting, would not permit raising the ram manually and letting it back down. It was pretty rock solid. On lifting the ram the ball can, of course, get sucked out, so, I suspect that is what the cross drilled hole is for - to hold some small retaining pin or something to keep the bearing from going rogue.
Back to that bleed hole. Hmmm .. evidently, it did not bleed anything. It is not clogged. In the pic above I have inserted a small wire in it to show how far out the piston has to be for that hole to be exposed to oil. When all fitted back into machine, even with that piston at it's most extended, and using all available adjustment, that hole will still be covered by the piston and thus, will not bleed. In other words, in operation, the piston cannot come out far enough to expose the oil to the bleed hole. Hmmmmm .....
So, I thought I had it there for a moment, the ball bearing thing with retainer pin seems it might be correct ... but the bleed hole thing still leaves an oily conundrum.
All comments welcome.
Greg.
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8th Jun 2019, 07:28 PM #20Most Valued Member
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Stray if there is a bit of space at the end of the brass fitting then maybe consider this.....
If it had a lightly spring loaded disc (or a wafer) that sat on the end of the brass fitting then oil would freely pass in one direction and when the flow is reversed the flow would be restricted by the the disc sitting flat on the brass fitting and yet still let the oil slowly flow through the slots to gently lower the blade into the cut.
cheers, shed
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10th Jun 2019, 09:35 AM #21Golden Member
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Hi Shed, thanks. A contraption like that has passed my mind. I had a pretty frustrating day on this yesterday - testing stuff. I do wish a Hercus hacksaw owner would chime in here with a pic or three!!
I thought I'd just make up a new test 'plug' from aluminium and just leave a small hole in it - no bearings or whatever. No joy - but I also realised that I might be battling some air ingress. Even when testing again with ISO 140 oil some air may leaking past the vertical piston into the cylinder below. air = not working hydraulics.
They say working on old machines teaches you patience. This is an example of that. I've had that thing in and out maybe 20 times with different oils and ways of sealing etc. Before I go mad with 'not getting anything achieved' syndrome I'll working on some other worn-out-as-hell aspect of this old machine and stew on this for a few days.
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10th Jun 2019, 11:32 AM #22Most Valued Member
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IF you have some distance beyond the brass fitting, when screwed in, then a loose fitting ball bearing that will sit on the top of the brass fitting would probably do the job.
It needs to be loose to allow the fluid to pass by to the piston, but large enough to sit comfortably on the brass fittng.
The ball would be operated by gravity and oil flow.
The slots in the end of the brass fitting are there to bypass oil at a metered rate, this amount of leak would be factored into and accounted for by the amount of flow from the pump and still have enough flow and pressure to lift the blade.
So basically it is a system based on percentages, x amount of oil goes one way and y amount goes the other way
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10th Jun 2019, 12:38 PM #23Golden Member
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Hi Shed, thanks - I tried the ball-bearing-resting-on-top thing. When the ram is lifted the sudden influx of oil dislodges it and the bearing then just roams around the innards. With nothing to secure the bearing there it'll not do the trick. If the ball finds its way back to the 'valve' area it rests beside it, not on top of it - as the valve if off center and not a the the lowest point of that cylinder. I could go for a very large bearing, but the off-center thing would still mean it wouldn't find its way back on top.
It all seems simple but it ain't easy to figure! Everything on this machine is like the simplest thing ever so somehow I think this mechanism is likely something very simple too. Just for the life of me can't figure it out! Mind, there is a small spring in the water pump so that is 'fancy' - so it is not beyond possibility that there could be a spring involved here as well.
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10th Jun 2019, 07:05 PM #24Most Valued Member
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Just be aware that you're only looking for a very small amount of leakage during the cut.
The pump and cylinder almost becomes a closed circuit, the only time oil gets sucked up is when you physically lift the arm.
Piston goes in, cylinder goes up, piston retracts and the cylinder goes down
My PH has a valve to adjust the leak down, but it's pretty much closed in operation, just not nipped up hard. Probably takes about 5mins to drop 100mm at a guess.
If you just lean on the arm it's not really noticeable that it's dropping - just feels solid.
Have you tried the ball bearing in the bottom, raising the arm and just letting it sit for a bit and see what happens?
Steve
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11th Jun 2019, 07:27 PM #25Golden Member
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Steve, I might try that thank. I'll need to bodge up something to keep the darn bearing from going rogue, but I'll try that and see what happens.
With dropping at that rate you'd best not lift it too far above the workpiece I guess or you'll sit about waiting for it to lower before you can start cutting!
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11th Jun 2019, 08:16 PM #26Most Valued Member
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Absolutely!
Definitely arrange that it doesn't have some form of variable rate control, since cutting a 20mm piece of stock is going to require a different rate than a 100mm piece.
Steve
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11th Jun 2019, 09:35 PM #27Most Valued Member
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At a guess i would say that the hercus is meant to have the full weight on the blade on the cutting stroke and the lift is only on the reverse stroke.
My power hacksaw has a sliding weight on the top to adjust for more cutting pressure.
Actually the lift pump on my power hacksaw has not worked for about 20 years, yeah yeah i know, slack eh !
And for larger stock i often hang a length of hollow bar on the lift handle to more put pressure on the cut
and speed things up a bit.
One day i might fix the lift but it is a loooooong way down the list and i don't think that it makes that much
difference to blade life, not for the amount that i cut these days anyway.
cheers, shed
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11th Jun 2019, 10:20 PM #28
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12th Jun 2019, 06:50 PM #29Golden Member
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Interesting Shed: "I don't think that it makes that much difference to blade life". I would have thought the rubbing on the backstroke would kill the blade. There you go.
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12th Jun 2019, 08:24 PM #30Most Valued Member
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It does not do that much cutting these days, maybe 1 or 2 a week and the blade is probably 5 or 7 yrs old?
If the lift was working it would clear the cuttings more efficiently and cut quicker and negate the need for
the extra weight of hollow bar speed cutting attachment
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