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The Artful Bodger
10-11-2010, 03:21 PM
You may have seen the thread where weighing a shipping container was being discussed and WeirdScience (?)**** suggested a hydraulic load cell.

So I started making the bits, the piston is 20mm thick plate of 113mm diameter and I carved out a matching 'cylinder' from some much thicker steel, right at the end of this process I found a void in the metal!

I know how it got there, these pieces are scraps from a plasma cutting place and the original 'round' had a slot in it from where the plasma cutter had started, I thought I had welded it up but obviously not good enough.:mad:

So what can I fill it with, expoxy? Soft solder? Drill it out and Loctite a bit of rod into the hole?

The hole does not extend to the outside and the O-ring will not pass over it.

BTW, the piston size is chosen to read 100Bar at 10 tonnes, I dont expect to be going that heavy, least I hope not! (100Bar is 1450PSI)


****[Later] It was Camdigger.

Dr Stan
10-11-2010, 03:34 PM
When ever I have had a student remove too much metal I generally sent him or her looking for a metal stretcher. :D

Liger Zero
10-11-2010, 03:58 PM
When ever I have had a student remove too much metal I generally sent him or her looking for a metal stretcher. :D

Left or right handed version?

Dr Stan
10-11-2010, 04:06 PM
Left or right handed version?

Either, I was not too picky. :D

The Artful Bodger
10-11-2010, 04:28 PM
Ohhhhhh, I am feeling sorry I asked!:(

Black_Moons
10-11-2010, 04:34 PM
Id drill it out, Countersink the hell out of it, then fill it up with my mig welder and hope I did'nt warp the hell outta everything else nearby.

The Artful Bodger
10-11-2010, 05:21 PM
Id drill it out, Countersink the hell out of it, then fill it up with my mig welder and hope I did'nt warp the hell outta everything else nearby.

Yes, I agree and that was my first inclination however the machining is now at the finished size and I am afraid I would have difficulty machining true without becoming oversize.

I guess the crux of my question, does epoxy get attacked by hydraulic oil? What about Loctite?

Arcane
10-11-2010, 06:25 PM
The hole does not extend to the outside and the O-ring will not pass over it.

Is it a big enough void to cause a stress riser that would cause the cylinder to fail? Is it deep enough to result in a thin spot that might blow out under pressure? If the answer is no to both of these, leave it as is.

KiddZimaHater
10-11-2010, 06:31 PM
JB Weld ???

spope14
10-11-2010, 06:44 PM
When working to hold in oil, weld the hole.

davidh
10-11-2010, 08:10 PM
oring type seals of that size are very forgiving. . . . weld it. . . . .

jdunmyer
10-11-2010, 08:11 PM
Perhaps you could drill and tap the hole? Wind in a screw w/LocTite, then cut off the end of the screw.

That pressure isn't super-high as far as hydraulics go.

Evan
10-11-2010, 08:47 PM
The hole does not extend to the outside and the O-ring will not pass over it.


Drill it out, tap it and put in a setscrew with some pipe dope (as per Jim). Call it a bleeder. :D

oldtiffie
10-11-2010, 08:49 PM
AB.

I'd be more concerned about the small diameter to depth ratio (113:20 = 5.65).

If the load and its axis is not precisely on and normal to the centre/axis of the piston, the piston will be inclined to tilt and if it jams in the bore you will have a new set of problems.

The "rod" in most hydraulic cylinders attends to this matter as it keeps the piston parallel to the cylinder bore.

How much piston travel does the 113mm bore allow for?

How are you going to bleed the air from the oil under the piston?

The Artful Bodger
10-11-2010, 08:59 PM
Good points OT.

I am putting a 'knob' on the centre of the piston, about 20mm diameter, to take care of any tendency to tip.

The piston travel should be minimal, just enough to operate the gauge, stretch the hose and maybe compress any air, I expect a couple of mm.

I will be putting the hose connection on one side of the cylinder and a bleed screw on the other, as Clamdigger showed. I might even be able to use the troublesome void as a point for one or the other (as Evan suggests).

whitis
10-11-2010, 09:05 PM
Ok, let me see if I have this straight:

The hole does not affect the structural integrity
The hole does not affect the o-ring seal
The hole does not affect the vertical projection of the piston shape and therefore does not affect measurement accuracy
It is not a visible blemish on the outside
Fixing it carries some risk of creating a problem.
You have enough work to do as it is moving a shop


Might be time to quit while you are ahead.

oldtiffie
10-11-2010, 09:30 PM
I will be very surprised if you can limit the piston-to-cylinder lift/relative movement to 1mm (~0.040") as it implies that the "packing" is such that the "ball" is in contact with the underside of the shipping container and that there will be no further strain or compression etc. to "take up" (as "slack"?) before the container actually lifts.

The container will flex under load (it is a hollow rectangular beam) and for your calculations to work (if they work) will require the container to be lifted at the piston such that all of the container - other than the opposite end - will be clear of any likely load support and so that the load is actually fully and only supported on the piston ball and the very edge of the opposite end of the container.

This process will need to be repeated at each end of the container.

I'd have repeated it for both sides as well in case the centre of gravity of the container and its load was not on the container longitudinal axis.

I hope it all works out but there is a good chance that this will be a case where practice does not match the theory as there are a lot of variables, possible errors and unknowns.

Best of luck.

The Artful Bodger
10-11-2010, 09:41 PM
OT, I actually intended to lift the container with a jack and lower it onto the load cell, the packing will be under the load cell and the container's end beam will rest on the load cell.

I am thinking of lifting one end and putting a support somewhere near the centre line with the one corner clear of its support, then lifting at the other end again more or less on the centre line and adjusting that position to find a point where the box is balanced, i.e. the c.o.g. is somewhere on a line between the jack and the support at the far end. Weigh both points for total weight.

Yes, it may well prove less than very accurate but it might be good enough to make good use of the shipping rate without incurring a penalty for overweight.

wierdscience
10-11-2010, 09:49 PM
Wash it out with acetone,fill with JB weld and work it out flush.

If there is sufficient wall thickness left and it's not going to fall in the seal area ,then it should be fine.

gmatov
10-11-2010, 10:53 PM
Stan,

I've used what you might call a "stretcher" when I mad on OD fit too small or an ID too large. Roller mounted in the head of the mill, and down pressure on the feed handle or wheel to "grow" the metal.

Won't work when you cut a finished bar off too short, but it does have its place in the BIG shops.

If you have time and material, why don't you make 2 load cells, connected by hoses, and with one guage, and weigh both ends at the same time? The pressure divided by the combined area of the 2 pistons will give you the weight of the whole thing.

I think, but don't know for sure, that the leverage effect of weighing each end separately will give you some error. The closer to CG, the higher the pressure reading. You might wind up with a total of 1000 lbs on an 800 pound package.

Else get it as close to CG as you can, and lift the heavy end by hand to weigh the whole thing in one shot. I don't think you would be 1 % off with the little lift it would take to teeter any package. If you can't lift the off end, you are not close enough to the CG.

Cheers,

George

Dr Stan
10-11-2010, 11:35 PM
Stan,

I've used what you might call a "stretcher" when I mad on OD fit too small or an ID too large. Roller mounted in the head of the mill, and down pressure on the feed handle or wheel to "grow" the metal.

Cheers,

George

I've also stretched metal by knurling. Straight knurling a bearing diameter oversize then turning it back to size is a long standing emergency shaft repair. Usually lasts long enough to purchase or make a proper replacement.

I've also "shrunk" holes using a ball bearing and a ball peen hammer, or "knurled" the pin with a center punch to make a press fit.

In reality there is such a thing as a metal stretcher, an English wheel used in sheet metal and body work. In die work we also had to be concerned with too much stretch or thinning of the part being stamped, otherwise it would not meet specs.

However, it was all in fun and I'm sure Art took it as such. :D

The Artful Bodger
10-12-2010, 01:48 AM
However, it was all in fun and I'm sure Art took it as such.

:) :) :) :)

Evan
10-12-2010, 02:19 AM
In reality there is such a thing as a metal stretcher...

metal stretcher:

http://ixian.ca/pics7/stretcher.jpg

Paul Alciatore
10-12-2010, 09:23 AM
metal stretcher:

http://ixian.ca/pics7/stretcher.jpg


You just had to, didn't you.

gmatov
10-13-2010, 01:37 AM
AND, HF also sells a Metal Stretcher AND Shrinker. Cheaper, I think, than the one you show, but might not last as long, UNLESS the Chinese make THEIRS too.

Stan and the prick punch to make a shaft fit the bearing is known as a "Hunky stipple". We used that a lot, and we were all Hunkies, so no Antidefamation League getting on our asses.

"However, it was all in fun and I'm sure Art took it as such."

So far as I am concerned, EVERYTHING said here is to be taken in a laisez -faire attitude. I don't intend to make any of you pis*ed off.

As in this post, I have done most of those thing, for much the reason Stan says. You don't have the time to wait for a new shaft to come in. Get the machine and the department back in operation, tear the machine down over the weekend.

I have been ordered to weld up 20 foot line shafts on overhead cranes that I could not get back within 1/2 inch of true, 4 inch steel, and comealong, "Weld it up. We'll replace it over the 4th of July."

Sumbitch ran like a crankshaft. Too bad we couldn't connect something to it to take advantage of that oscillation. Run a compressor, maybe.

Ah, well, that is all in the past. Retirement is nice.

Cheers,

George