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Posted:
Thu Sep 07, 2006 5:49 pmby R_T
Everybody makes their bench out of wood, I can make a water tight bench out of 3mm steel plate fairly easily and probably cheaper.
I would like to build a big inch bench
Has anybody done this before ,or had any problems, or can think of any problems that will make this not feasible?
Posted:
Thu Sep 07, 2006 10:03 pmby Thomas Vaught
I am presently building a steel bench for one of my projects at work.
2x2 square tubing for the uprights and basic frame and 1x1 for the individual divider sections.
8 115923 motors.
Will be used to measure a 4 cylinder engine for proper intake manifold distribution using a block with orifices in the cylinders.
Tom V.
Posted:
Thu Sep 07, 2006 11:58 pmby Tony
My most recent bench uses a welded 2"x 2" steel angle frame with one inch MDF panels bolted onto the outside. Actually, it is two steel rectangles bolted together with a central bulkhead sandwitched between both steel frames.
It is a simple way to build a very strong bench without any air leakage problems, especially at the corners. A steel frame also allows rapid and easy access by having removable front panels.
Studs and nuts + large washers always go back togeter quickly and reliably limitless times without any concerns with strength reduction or air leakage. The main outer panels were glued and bolted to the steel frame. The two removable front panels using thick rubber gaskets.
The nuts on the front are not pretty, but one day I will replace them all with internally threaded plastic star knobs. At least I can use my air wrench on the nuts, and I can remove or replace a panel in less than a minute.
Wood screws are fine the first time you assemble the bench. But I bet the 13th time you replace those wood screws to get at the bench internals, those little suckers are getting a bit loose and just might rip out under positive internal air pressure.
I welded up my own frame, and distortion during welding was a constant worry. It had to be straightened by using chain and a turnbuckle to pull across diagonals (in three dimensions), or a bottle jack to push across diagonals. It all worked out extremely well but was a fair bit of work. If the panels are going to fit neatly without leakage, the frame must be perfectly square.
After building two conventional wooden benches, and one steel frame bench, If I ever build a fourth bench it would also be steel frame construction with MDF panels. An all metal top panel is an interesting idea, but this one is MDF with a layer laminex glued on top.
Posted:
Fri Sep 08, 2006 1:04 pmby Unkl Ian
As long as there is access panels in the appropriate places,
for repairs and modifications,there shouldn't be a problem.
Posted:
Mon Sep 11, 2006 3:36 pmby R_T
I not only wanted to build the frame out of steel but also wanted to use 3mm steel plate for the sides fully welded excepted for sealed hatches
I was a bit worried about vibrations of 12 motors shaking manometers, pitots, electronics etc
Thanks
Posted:
Mon Sep 11, 2006 6:43 pmby Tony
I would also be a bit concerned about how a large flat area of 3mm steel plate may respond to several thousand pounds of bursting or implosion force.
If by accident you suddenly totally block the airflow, the vacuum motors may be able to pull a hundred inches vacuum (or more). That is 3.6psi, or 514 Lbs per square foot. A three foot by three foot panel may suddenly have to resist 4,628 Lbs of air pressure. Will it ?
Thick wooden panels may be considerably stiffer than thin steel plate.
Steel may still be practical, but it may require some sort of pressure limiting safety valve system that will limit the maximum pressure.
Posted:
Mon Sep 11, 2006 7:07 pmby jsa
[color=#000000]I did some testing on the motors I'm using to build my bench.
They generated 95.7" H
Posted:
Mon Sep 11, 2006 8:52 pmby larrycavan
[color=#000000][quote="jsa"]I did some testing on the motors I'm using to build my bench.
They generated 95.7" H
Posted:
Mon Sep 11, 2006 10:47 pmby jsa
Posted:
Mon Sep 11, 2006 11:33 pmby larrycavan
IF you somehow managed to block the exhaust side of the motor, it can't move any air through. It won't affect the bench structure from a pressure standpoint. The fan will continue to spin and create heat. The heat will either shut down the motor if it's thermal protected or eventually, if left running, could go up in smoke.
Absolutely though, if you were testing exhaust and the valve managed to get shut on you [like you mentioned] with the head clamped to the test stand, you'd certainly stand a chance of finding the weak point in the bench......I must be tired tonight....that never even entered my mind.... ???
Posted:
Tue Sep 12, 2006 10:35 pmby Tony
Suddenly blocked flow can happen in a whole variety of unexpected ways, and the results can range from blowing the fluid out of your manometers, to catastrophic structural damage to the bench.
I once had a rag wedge itself into an inlet port. It took quite a while to refill my test pressure manometer, and restore an accurate fluid zero point. Believe me, it is at all too easy to have a nasty little overpressure accident, and when it does happen, it will happen in a heartbeat.
It is one more reason why I hate vacuum motor benches. The two stage motors especially. They develop inconveniently high pressures at zero flow. That plus the high noise level and the inefficiency.
My current bench uses a single large diameter centrifugal blower, driven from a VFD. Even absolutely flat out it just reaches sixty inches, but it does that over a very wide range of flow. If I am running the VFD at 28 inches test pressure, and the flow suddenly drops to zero, I would not expect to see more than perhaps 35 inches maximum test pressure. It is much safer like that.
But the whole scenario of suddenly blocked flow can develop some truly frightening forces if you work it out. Provision of a spring loaded relief valve around the motors, may be simpler than just trying to build sufficient strength into the basic structure.
Posted:
Wed Sep 13, 2006 8:47 amby larrycavan
Yes...I remember the annoyance of refilling the manometers. What an aggrivating thing to have to stop and do. That aggrivation goes away with electronics though. Haven't refilled the fluid in my FP1 a single time yet.. 
The only over pressure situations I have ever had happen to me were on intake testing...never on exhaust testing.
Posted:
Mon Sep 18, 2006 9:39 amby R_T
The steel plates will be layered over a steel frame
There doesn't seam to be many problems or no one has made an all steel flowbench to talk about problems
Posted:
Mon Sep 18, 2006 9:14 pmby Thomas Vaught
I am presently making a steel bench for a work project.
I will try and post pics when it is finished.
Tom V.
Posted:
Tue Sep 19, 2006 6:48 pmby R_T
That will be good
wondering if motor vibrations will upset manometers or electronics, pitots etc
Thanks