Quick question for anyone with a shop press.

[Flynth]

If you have a shop press with a spring return single acting hydraulic cylinder (preferably 20 ton an over) could you please let me know if the cylinder ram at near full extension has some side to side play, and if yes, is it causing you any issues with using the press?

I've recently built a press and I used a Chinese 50 ton cylinder and pump set. Unfortunately (perhaps on purpose?) the cylinder has been built with fairly loose connection between the piston and the rod and 10 thou radial clearance (20 thou diameter difference) between the rod and the hole in the bottom closing cap. The result is almost a quarter inch of side to side movement of the near fully extended ram.

There are various ways I can try to fix tgat, but first I'm trying to establish if this is indeed a problem, or should I not worry too much about it?

 

[benmychree]

Way too much clearance.

 

[markba633csi]

That's more than I have seen- usually there is less than about 1/16" movement if that
Whoever was boring the caps that day was asleep at the wheel

 

[westerner]

When the pressure in the cylinder comes up against a resistance, the ram will try to square up.
My wonderful old press has a carriage that allows the ram and pump to move a few inches each way from center while unloaded.
Sloppy as hell, but when the slack comes out of the setup you can watch 'square' occur.
Let off a smidge, and come right back with pressure a few times.

 

[Flynth]

Way too much clearance.

That's more than I have seen- usually there is less than about 1/16" movement if that
Whoever was boring the caps that day was asleep at the wheel

That's what I thought, but I wanted to check how loose others are.

Interestingly, the very bottom of the ram (the part that doesn't go inside the cylinder. Is exactly 10 though larger. So the cap is made to be a light press fit on the very end of the ram, but then loosens up by 10 thou (radially, double that on diameter). I have to measure if that skinny diameter is consistent along the rest of the length. If it is I'll make/buy some bushing for the cap to take up the slack. If its inconsistent... I might try cylindrical grinding the rod, or I might just buy a new one. The problem with just buying a new one is that I'll have to swap the piston which appeared to be pressed on in a peculiar way(more about it below) ,and there is some machining on the end that needs to happen. With this being a new hardened/chromed rod. It might be difficult to machine.

When the pressure in the cylinder comes up against a resistance, the ram will try to square up.
My wonderful old press has a carriage that allows the ram and pump to move a few inches each way from center while unloaded.
Sloppy as hell, but when the slack comes out of the setup you can watch 'square' occur.
Let off a smidge, and come right back with pressure a few times.

I wondered that too. When I did calculations designing my 50 ton press I looked at what they sell as "50 ton" presses and I thought to myself. No chance these stay rigid and don't flex a lot under these forces! So I built my press heavy. It weights ~350kg (~700lbs) and it is expected to flex symmetrically and exactly 2mm (80 thou) under full load.

I didn't think they designed a loose cylinder for a loose press.... With expectation that pressure rights it.

It seems to me this cylinder was specifically designed for the piston-rod connection to be flexible. After pulling out the rod/piston assembly one can hold the rod in one hand and the piston is free to revolve. It can be pulled 20 thou away from the rod and no more. Also it can be angled by pulling that 20 thou on one side and not the other. Someone purposefully made a relieved bore and a stepped shaft on that piston to allow for this free play.

My initial thought was that it is a loose threaded connection, because that's how it felt, but turning that piston didn't make any difference. I decided to try taking it off gently, but gently hitting it with a lead mallet didn't allow it to get off. I suspect one needs a press to press it off. Funny how I need the press to fix itself, but can't.

Also, it is interesting that piston can be pulled off by 20 thou and the ram/closing cap hole diameter is 20 thou bigger too.I thought It was almost by design, but then I find they did it that way, because they wouldn't be able to put a smaller hole on the rod as the very end is exactly 20 thou bigger. The rod is supposed to be nominal 63mm( 2.48inch) and that's what it is at the very end. Half inch further it is 62.8mm (2.46in).

Edit:Just to add something. The quarter inch of play with the ram extended is with the end cap not screwed in fully (loose). I was testing the clearances along the ram by inserting strips of copper tape between the ram and the hole and after it was immobilised I noticed it it tye actual cap that's moving.


I decided to drill holes for a spanner wrench in the cap so it can be tightened properly. Also I ordered some bronze filled Ptfe tape to make a sliding bearing surface. Hopefully that will resolve it.

 

[Karl_T]

Yep, you can learn to live with it, or fix it. Your choice.

Most of the time when I buy asian quality, this is the issue

 

[Flynth]

Yep, you can learn to live with it, or fix it. Your choice.

Most of the time when I buy asian quality, this is the issue

Yes, that is usually the case...

I ended up drilling holes in the cap to be able to tighten it with a pin spanner. I found only the first quarter inch of ram length is bigger diameter so J ground it to match the rest of the shaft.

I also discovered, 10 thou thick copper foil goes in nicely into the hole in the cap to take out the team-cap hole clearance. So I took this opportunity to see how it would work with very little clearance (before I modify the cap irreversibly).

So I put a strip of foil in. Initially I had to use a lead hammer to move that cap up and down, but after moving few times it became possible to move it by hand. That's how it looked once I pulled the cap eventually. It eve imgY

(the cuts and folds on top are there to prevent it from sliding out). It looks the same from the other side.

This made the cylinder very sturdy, but it also slowed down last 5 inch of return travel to even slower...

So eventually I took the cap off and I removed the copper foil - that's when I took the above photo). With the cap tight it appeared the movement with the ram extended is a lot less. More like a mm or two (up to 80 thou).

My other question to all owners of that "two stage hydraulic over pneumatic pumps" is also what they do with the fill screw when using the cylinder. I read the manuals, but they don't even mention the screw let alone specify what to do with it.

If closed, vacuum forms in the oil tank when pumping. This is good for retraction speed, but one has to pump fairly slow (to allow gravity to push oil into the pump, not electric).

Second scenario is to close it permanently. The cap is cast iron so one can cut a groove and put a standard wear/slip in there.