DIY VASI

[UniFoxOs]

I'd like to make a small VASi, or something similar. To explain the background, I am doing some extensions using a small excavator. I have to scrape off about 500mm soil over a largish area of the site. I'm not really an ace digger driver, and I tend to drift up or down over large areas. Therefore I was trying to invent some simple device to help me keep level. Big excavators have all sorts of fancy laser levels, probably cost more than a small digger, but I just wand something simple.

I was thinking along the lines of a small version of a VASI at a suitable height, with the "glide slope" set horizontal, and a mirror or lens on the digger "dipper" - i.e. the arm with the bucket on the end, so that when the dipper is vertical, and the bucket sitting on the bottom of the excavated ground, I would get the "on the glide slope" lights to help me keep level, with appropriate lights for too deep (below glide slope) or too shallow (above).

So - anybody know how to make a VASI out of bits and pieces from my "come in handy" box? I have access to plenty of LEDs, but no fancy fresnel lenses or such like. Something about the size of a brick would be about right, that I could mount on my site level tripod.

Cheers
UFO

[PEI_3721]

You may wish to consider making a homemade PAPI.
PAPI differs from a VASI (often the descriptions are interchanged) in that PAPI is a projector system and thus can be very accurate. PAPI is like an old style 35mm slide projector. It requires a white/red ‘slide’ defining the boundary of high/low, a suitable lens to focus the beam, a light source, and a containing unit.
IIRC early test versions (RAE Bedford) were made from clear plastic sheet / coloured glass or stick-on plastic. The lens was the most difficult item to find – unless you have a spare HUD. The casing was a large diameter plastic drain pipe / gas pipe / water pipe, depending on which utility was working in the local area. A bubble spirit level was preset to the required angle and stuck on the side; I assume that your system will be level. (With due acknowledgment of engineer extraordinaire Mr Sam Kidd, RAE circa 1970s).

As an alternative there are some cheap and relatively powerful ‘laser’ type lights (presentation pointers) which are effective over reasonable ranges and might be seen in daylight – use a target board on the excavator and a spirit level on the light.
In Canada, try ‘Canadian Tire’ for a $6 light / pointer.

[UniFoxOs]

Thanks for that, PEI, however I am not sure the PAPI would do what I want. As I understand your description the PAPI would throw a beam divided into three zones - I will call them upper, middle and lower. I am assuming that the zones would be parallel, so that across my site I would have a beam of (say) 2 inches depth of the middle "slice" and (say) 4 inches depth of the upper and lower slices. If that is the case, then I can certainly see that it could be set up to be very accurate, but I am assuming that the beam would only be a certain width (so that, if circular, it would be the diameter of whatever size lens was used). Similar would apply with a laser, whereas with a VASI-type device it could be made so that the central light band was visible over an area of, say 90 degrees horizontal (so it could stand at the corner of the site and be seen anywhere), and the upper and lower bands were visible at quite wide vertical angles, say from the horizantal to 30 degrees up or down. What I am having difficulty in visualising is how these bands could be created. I have been assuming that there are some sort of baffles employed so that the lights can only be seen in certain directions, maybe like what are now fitted to some traffic lights to prevent drivers from seeing signals not intended for them.

Thanks again,

UFO

[Nick Thomas]

As an Architect am wondering why you need to be so accurate with your excavations. I presume they are for the foundations of your extension. Normally hardcore is laid before pouring the concrete. The hardcore will take out any irregularities. I hope that helps

[PEI_3721]

UniFoxoS, my description probably lacks the required detail.
With PAPI there are only two zones in the beam, the upper (white) and lower (red) which are projected from the white/red ‘slide’. The horizontal dividing line (constructed on the slide) gives a sharp transition which should give high precision. The beam width of PAPI is whatever the slide / lens / casing allows.
The problem with VASI (no lens system) is that the division between white and red is very diffuse and offers little accuracy as well as lower beam power.
Try Google for more info; you will only need a single tube system.
IMHO the laser pointer option would be much simpler, although this has no lateral spread.

[Luc Lion]

UniFoxOs,

why don't you use a PAPI of the poors ?
Just erect two or three crosses set so that they are perfectly aligned on an horizontal line at the level of your eyes when you sit in your excavator.
That system is used in many small aerodromes (often in montainous region) ; three crosses aligned on the correct glide slope.

Luc

Use a transparent plastic tube filled with water to get an horizontal reference over some distance.

Edit: seemingly, the english term for that is "boning rods"
Paving Expert - AJ McCormack and Son - Setting Out - Boning Rods

[hval]

Batter Rails

What you should be using are called batter rails. Google it. Plenty of gen on them

[UniFoxOs]

OK, chaps, this is what I envisaged. As you can see the level of the driver's eyes bears no relation to the digging level required, so any suggestion based on a type of sight gauge is a non-starter.

I was envisaging some sort of simple receiver on the dipper, just a lens or reflector of some sort and I was hoping for some simple beaming arrangement as shown in the sketch top right, the middle zone needn't be too accurate - plus or minus an inch or two would be good enough. Doing it by eye I can't keep level very accurately, can easily be out by 3 or 4 inches in either direction after a couple of yards, so a couple of inches over the whole excavation (10 yards or so) would be pretty good.

I'm quite happy to use a PAPI as I think I understand from PEI's description, but I don't understand (well, can't remember from school 50 years ago) what sort of lens would throw the required beam out with a 90 deg (or thereabouts) spread in the horizontal plane, and for some reason giggle seems to throw up pages and pages of stuff about camera lenses, nothing as basic as this, so any advice on this would be appreciated.




Cheers
UFO

[Nick Thomas]

Hi UniFoxOS
I still think you are over complicating things. If you feel unhappy at just excavating and using hardcore to level the bottoms, the batter rail proposal is a simple and effective way of staying level. On small jobs such as yours a builder will just suck it and see. If you slightly over excavate it's not the end of the world. What is important is to ensure that the bottom of your excavation is solid. If you find soft spots you should excavate the soft spot down until you reach reasonable ground and then backfill. There is no need to remove adjacent solid ground to the bottom of a soft spot. The building inspector will want to inspect the bottom of the excavation to ensure that you have a solid bed. He will not be worried if the bottom is not perfectly level.

[UniFoxOs]

Hi Nick,
Maybe I've misunderstood the batter rail. I thought it was a way of levelling reference the drivers eye, not the digger bucket. I'll have another google of it and see if I can understand it better
Cheers
UFO

[Nick Thomas]

I expect you have investigated whether there are any services in the vicinity of your excavations. Can be expensive and dangerous if you hit say a gas main.