I think so - very little difference. Well my instinct says for environment in general that
Another thing I must test though.
Rich S
Variable - you have many eccentrics, each with a slightly different throw?
I thought - one eccentric, but many different "pistons" with their "collar" they go through into the fluid volume.
Yes one thought is that the mechanism could be built onto the lower cylinder end.
With the "bar" driven by the eccentric simply pushing in and out of the cylinder volume. For the "170Tonne-force" test it would need to displace about 270cc - would be 70mm diameter and stroke (or some other combination of diameter and stroke which gives that displacement).
One advantage of this arrangement is, seeing as it's so stiff, plus bits can't fly around with being inside the cylinder, the test rate could be high. Fastest induction motor speed? 3000rpm on 50Hz supply = 50Hz test rate :-) That would be 60Hz on N.Am. supply.
Knowing the metallurgical and fatigue stuff has cost me a lot - money in various ways and time ...
Heating is pretty negligible. On a resonant machine you can test at up to around 300Hz and there is no drift in values obtained compared to at much slower rates. You have full elastic energy recovery.
Servo-hydraulic - not recovering elastic energy with the drive heats the oil away from the sample where you dump the pressure - and you dump that heat through "raditiators" (forced convectors transfering oil-to-air).
But the sample is seeing full energy recovery / negligible energy loss.
Variable - you have many eccentrics, each with a slightly different throw?
I thought - one eccentric, but many different "pistons" with their "collar" they go through into the fluid volume.
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One circular eccentric disk, mounted on an offset pivot pin so it can be centered or swung out as needed. The clamp for the swinging side might have to include a custom stepped bushing to withstand the torque, rather than just a bolt that holds by friction, but its surface finishes aren't critical like the eccentric's. Lathes don't necessarily leave surfaces good enough to be running bearings, that's extra hand work.
It's easy to turn two cylindrical surfaces with different centers when holding the work in a 4-jaw lathe chuck.
I can't easily hit the tolerances on a customer's drawing but I can still make two pieces fit each other although they may not be quite to spec, so my antique machines are fine for making single devices for my own use (and for fixing each other). From the reference above: "I turned the final diameter on a good portion of the bar and then machined each eccentric one at a time, individually match-fitting each eccentric strap."
The trick is that two parts of a complementary operation may not be equally difficult, for example the piston is easier to turn and finish than the cylinder, so make the difficult one first and fit the easier one to it. The boring head he used on the eccentric has a micrometer adjusting screw to change size, I have an identical one. Many shortcuts are possible when you control the design.
I made the prototype of an inch-long diode laser and lens mount in a few evenings that later cost $4000 apiece from a job shop that normally made parts for BAE. Mine wasn't quite as well finished but it worked and proved my ideas. First I needed approval to charge it as overtime, but the project engineer knew how expensive the company's main machine shop was. I suspect part of the high cost was due to the electrical engineers' inexperience with mechanical design and machining.
I think so - very little difference. Well my instinct says for environment in general that
Another thing I must test though.
Rich S
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Racing engine builders might know.
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I made a split bushing to hold short 3/8" Grade 8 bolts in a 5C collet like in the "I love this tooling." example shown. Grooves near the ends hold O rings that keep it together. Neither the hex head, shank nor threads run true to each other so I have to clamp the bolt by the section I'm modifying. OK, they are technically hex head cap screws when they go in a tapped hole but 'bolt' is their common name.
The bushing's center hole is 0.370" diameter to match the shanks of the bolts at the store, and before splitting I tapped it 3/8-16 to grab the thread crests without damaging them, as rolled threads can be larger than the shank. It lets me modify bolts to within as little as 1/2" from the head, for instance to trim back the slightly-long shank so a nut bears on the parts being clamped, or to cut a root-diameter pilot and pointed end on the threads for simultaneous alignment of multiple 40 Lb parts with 0.370" bolts in 0.375" holes. Those piloted bolts are longer and go at the outer ends to stop the trolley after using them to align the center splice. Most of the bolts joining my gantry track sections had to be modified to put their shanks in the shear planes and clear the moving trolley.
My previous 5C bolt-holding fixtures are bushings with tapped holes, but this version is more versatile and clamps tight on either shank or threads. I split it with a hacksaw after scribing the end with a tool point aligned with the 5C splits.
I haven't got this for certain. Not grasped the idea for sure, yet.
Forces would be in Tonnes to tens of Tonnes. The size of the eccentric - both what it will withstand as a bend or shear, and preesenting enough bearing surface for the bearing to take the load - can make these things quite big. Maybe 200mm diameter with
190mm shaft for 10mm "throw", for some enormous tests in high yield steels. As I calculate / estimate as best I can.If it came to making one of these things, there would have been a lot of proof-of-principle with "testing lab. scale" samples, and the stakes would be quite remarkable by that stage, if we got there.
The main point is to have plans in place. In a political world, you have to have everything covered, so every interjection, objection, etc. is smoothly put in its place. As I've experienced. I've certainly had the skill of predicting what the ploys might be tested. Having big efforts to derail the plan slapped down in seconds.
So it's about being able to see a way ahead, far along a perceived path. What would actually be going on, where you would actually be by then, what method you would use given experience had by then but ahead of you now - that might be a different story. But for now - you are "covered"...
With the beam tests, you can tune the testing force by moving the beam end supports in and out - present different spans. So one fixed throw / movement drive would cover all purposes.
For the "hydraulic inner fatigue test", I think different diameter "spuds" sliding in and out of the fluid volume, on a fixed eccentric drive, might be easiest?
I haven't got this for certain. Not grasped the idea for sure, yet.
Forces would be in Tonnes to tens of Tonnes. The size of the eccentric - both what it will withstand as a bend or shear, and preesenting enough bearing surface for the bearing to take the load - can make these things quite big. Maybe 200mm diameter with
190mm shaft for 10mm "throw", for some enormous tests in high yield steels. As I calculate / estimate as best I can. RS [[[[[[[[[[[[[[[[[[[ Lets say the 200mm eccentric is pinned to its mounting plate with two diametrically opposed 25mm round bushings. If the bushings are straight cylinders the eccentric disk runs in a true circle. If both bushings have a 5mm offset step in the middle to shift the eccentric disk sideways the throw is 10mm. The lathe setup to turn the bushings is the 5C collet block in a 4-jaw chuck, as in the posted reference.The bushings provide high shear and bearing strength. They would be slotted and keyed to prevent rotation. Making them is a reasonably simple lathe operation. To change the throw you make bushings with different offsets rather than changing the eccentric disk.
Two identical stepped bushings is simpler to describe, one stepped and one parallel is more rigid, triangle vs parallelogram. jsw ]]]]]]]]]]]]]]]]]]]
If it came to making one of these things, there would have been a lot of proof-of-principle with "testing lab. scale" samples, and the stakes would be quite remarkable by that stage, if we got there.
The main point is to have plans in place. In a political world, you have to have everything covered, so every interjection, objection, etc. is smoothly put in its place. As I've experienced. I've certainly had the skill of predicting what the ploys might be tested. Having big efforts to derail the plan slapped down in seconds.
So it's about being able to see a way ahead, far along a perceived path. What would actually be going on, where you would actually be by then, what method you would use given experience had by then but ahead of you now - that might be a different story. But for now - you are "covered"... RS
[[[[[[[[[[[[[[[[[[[ Been there, done that, I was the lab rat who built the proof-of-principles from sketches and gave the engineers simple, practical and economical ways to convert their concepts into products. I provided you several different approaches you could pursue, and mentioned possible sticking points like difficulty of fabrication or programming, and the skills and equipment to moved past them.A very handy trick I picked up to counter objections is to memorize the squares and reciprocals of numbers up to 32 so I could do engineering math rapidly in my head and present an off-the-cuff mathematical basis for my arguments. Above 31 [sqrt(1000)] they pair with lower numbers, 1/25 =
0.040, 1/40 = 0.025. Engineers not from the slide rule era don't learn the simplifying tricks we had to.For example I was running an error rate test on a satellite link when the chief engineer demanded to know how much longer I would be tying up the channel. The test was 10 million bits at 2400 per second. Knowing that 1/24 is 0.041666... I mentally figured the test duration as 4166.7 seconds, then converted that to 1 hour (3600), 9 minutes (540) and 26.7 seconds and gave him the answer. He pulled out his calculator, hesitated, then admitted he didn't know where to start and left me alone to complete the test.
I understand the physics but it's still weird to see something stored and later retrieved intact from empty space. jsw ]]]]]]]]]]]]]]]]]]]
With the beam tests, you can tune the testing force by moving the beam end supports in and out - present different spans. So one fixed throw / movement drive would cover all purposes.
For the "hydraulic inner fatigue test", I think different diameter "spuds" sliding in and out of the fluid volume, on a fixed eccentric drive, might be easiest? RS
[[[[[[[[[[[[[[[[[[[ The most demanding part to make is the piston/cylinder sealing surface, especially if you don't have machine tools. Any spud screwed into the end of the piston displaces a fixed volume of oil. There may be another way but I think the easy answer is to change the stroke length (lever?) unless you collect an appropriate assortment of polished rod stock and seals (car shock absorbers, gas cylinders etc). Modifying the rods into pistons and making packing glands to retain the seals are lathe operations. jsw
I took it a lathe would be available. Cylindrical "spud", cylindrical bush.
Maybe the "hydraulic fluid" could be grease - thick - tranmitting to oil or water through a rubber membrane. So the piston/bush sees viscous grease not thin oil.
I took it a lathe would be available. Cylindrical "spud", cylindrical bush.
[[[[[[[[[[[[[[[[[ It's difficult to create innovative mechanical solutions with only stock parts meant to solve standard problems. At Segway which was an engineer's playground by official policy the CNC lathe and milling machine were almost always tied up making someone's wild idea. I used their manual lathe or my home shop machines but my main task was custom electronics.Maybe the "hydraulic fluid" could be grease - thick - tranmitting to oil or water through a rubber membrane. So the piston/bush sees viscous grease not thin oil.
[[[[[[[[[[[[ It's known that high pressure oil seals work if done right, so I'd bin that with the minor issues that can be solved later by throwing enough money at them, and concentrate on identifying and resolving the show-stoppers.I'm glad I read the Amazon reviews before applying the thick black tire bead sealer goop. A reviewer advised to let it set somewhat before inflating the tire lest it spray out. I did, and only soapy water rubber lube sprayed me before the bead seated when I inflated it.
Here is a racing engineer and technology historian who might know about metal fatigue in oil:
I'd wish - but lots of slightly different sizes - and you are going to be able to find a seal for each diameter?
Maybe one could get a list of stock seal diameters, and find that yes, the pressure and therefore test force you'd end up with would be just fine - sits just where it needs to be to plot the S-N curve for fatigue performance. Throwing aside minor vanities like getting the stress which should mean the mean-average sample break is at exactly
250k cycles, etc.Rich S
Off-topic but...
Two great leads in there!
Engine Development and how done. Empires were at stake then and technical folk got resources - amazing what they did.
The Calum Douglas lead - never met or seen a pic. of the brittle lacquer method for stress distribution in-action. ****! it's effective! The "perspex / polarised-light" method - I wanted to use that when I knew a Finite Element Analysis modelling engineer must be talking <...nonsense!...>, before I could FEA. I actually blagged some "perspex" from a nearby company - but the Finite Element Analysis engineer then made such a bad political slip-up that we lost the job it was for anyway.
"Yale" / Segway lead... The one about engineers "kissing a lot of frogs to find a prince". Exactly! Yes, that's the reality of a scientist too! You have to be able to think and process things that way, to be a human having an effective channel of perception into the Natural World. I almost envy people living in what they think is a determinate world.
I'd wish - but lots of slightly different sizes - and you are going to be able to find a seal for each diameter?
Maybe one could get a list of stock seal diameters, and find that yes, the pressure and therefore test force you'd end up with would be just fine - sits just where it needs to be to plot the S-N curve for fatigue performance. Throwing aside minor vanities like getting the stress which should mean the mean-average sample break is at exactly
250k cycles, etc.Rich S
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This is a US company selling inch-sized products, but it shows what to look for.
The cylinders were $10 and $15 each and the right very compact size for my bucket loader design so they were worth the trouble.
I suspect that seals are available for all cataloged sizes of chromed and polished hydraulic rod stock, a part I can't make. Then you only need to make (or buy) the packing gland that adapts the seal to the cylinder end cap, and a crosshead to keep the piston running straight, both fairly easy on a thread-cutting lathe. They could be combined into one part. Instead of machining a hex you can drill two holes for a pin spanner wrench to tighten it.
Last night the air cleaner cover latch on the Chinese engine of my sawmill broke off so I made a stainless sheet metal replacement. I've stopped hunting for spare parts that are difficult or impossible to find and no better than the originals.
A -good- lathe is an investment that may appreciate. Collectors restore the better examples of mine, like classic cars.
"Yale" / Segway lead... The one about engineers "kissing a lot of frogs to find a prince". Exactly! Yes, that's the reality of a scientist too! You have to be able to think and process things that way, to be a human having an effective channel of perception into the Natural World. I almost envy people living in what they think is a determinate world.
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I have a BS in Chemistry so I understand how a scientist must think and operate. It's a very hands-on discipline that applies to almost any industry and we received a broader training than I've seen in other types of engineer and scientist, such as Materials Science (the properties of steel) and two years of Physics.
The profs told us a BS degree doesn't prepares us to do useful work immediately, only to understand the explanations wherever we go. Advanced degrees were essential, they said self-servingly. (Mitre was like that too.) I was chosen for summer research grants and did learn more about real life applications, and what it's like to hole up in the lab all night and not see other humans for weeks at a time. I was disturbingly comfortable with that.
At graduation time I still needed 4 more credits in any subject and, being somewhat burned out by then, signed up for 6 credit, certain-to-pass summer theatre as a carpenter, and was packed in with as many touchy and demanding humans as I could stand for 12-16 hours a day, good training I suppose. I was dancing on stage when Armstrong landed on the moon.
When I graduated the grad school draft deferment had ended, taking with it my Chemistry career, but the Army was glad to find someone they could train to maintain complex electronics along the lines of your Colossus machine. The few who survived that school all had technical degrees. The integrated circuit was enabling electronics' Great Leap Forward and I got in it at the start.
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