Plane Table Surveying - Repro Tables

Mike, best wishes. If you want to attach this to a tripod or to a reflector mount, I believe those threads are 5/8"-11. But maybe you have something different in mind.

If you used a reflector mount and a tribrach, you'd have the ability to level the board when it's mounted on a tripod. The circular bubble would be a little hard to see under the board. Of course you could attach two level vials to the board itself.

Do you have an alidade?

@rplumb314 Thanks!  I'm doing "old school" and do have several different alidades collected over the last thirty years (mostly from 1930's and newer), as well as tripods and a few boards.  All of my boards and tripods are set up for the "Johnson Head" which all use the 5/8"-18 threads.  BUT - One odd one appeared where the Johnson Head and Cap have been very nicely converted to 5/8-11!  None of the boards I have are the 5/8-11, but not any more difficult to make than the standard 5/8-18!  Interesting to note that both large and small diameter Johnson Head setups use the same threads - which makes sense

You can see the fine threads in the attached pic.  This is one of my smaller diameter Johnson Heads.

The pics of the boards a standard 18"x24" with case, and my prototype-in-progress (18x14).  Also shown are an original plate and one of my aluminum repros.

Interestingly enough - the hardest thing to find original is the boards!  And the hardest thing to reproduce is the threaded paper hold-down screws on the boards.  I have found a tedious way to make replacement screws - but if there is going to be a lot of them - there needs to be a better way!

Mike

So, does the Johnson head enable you to level the board? Looks as though it might have a sort of swivel action.

@rplumb314 - Yes - the Johnson Head has two parts that fit together.  After the tripod is set roughly level, the upper (larger) thumb screw allows the board to be swiveled and placed level.  Level is determined typically by the Bullseye level on the instrument base.  The board is free to rotate at this point, and after correct alignment is achieved, the lower (small) thumbscrew is tightened.  At this point the board is both level and aligned

When taking actual vertical measurements - after the target image is obtained, the instrument is then leveled using the "Striding Level" on top of the optics setting the vertical angle to "Zero", and then the target is identified, and the angle read on the vernier.  Sort of like the "Upper and Lower Motion" on the older transits.

The pics below show the larger of the two sized Johnson Heads.  This thing is HEAVY brass!  You can see the removable part with the long center is how the board is oriented after level is established.

Quite interesting!

I notice the original board has strips of wood on the ends, running perpendicular to the grain of the main part of the board. I've seen the same feature on old wooden drawing boards. Perhaps those strips serve to prevent warping.

@rplumb314 - yes, provides resistance to warping, and keeps the endgrain from absorbing moisture.  I'm skipping that detail and relying on the wood for the project being built from smaller.pieces, and am pretty sure nobody is going to use these in a wet or damp environment these days!

Very true. No more plane-table work is needed for the Panama Canal, among other projects.

What are the paper hold-down screws like?

@rplumb314 - here are some pics of an original and my repro/prototype.  Interestingly enough - instructions call for the user to place a pin through the paper into the board at the location of the instrument on the map!  At some point - especially on the ones I know came from a college - it appears that a heavy cardboard or perhaps foam core sheet was taped to the top of the board, and the project film/paper placed over that and taped to the BOTTOM of the board!  This of course simplifies a LOT of things for the user and the institution!  And - it was REALLY DIFFICULT to push a pin into the hardwood anyway - most of us just used the MkI Eyeball method.

Making those does look very tedious indeed.

Since you have the disc tapped and are soldering the screw in, perhaps you could use 8-32 threaded rod rather than screws. I suppose that's available in brass, though I've never had occasion to look for it. Or you could cut the heads off the screws before soldering them in.

The old-timers sure didn't want their paper to move around or blow away. Understandable, given the amount of original field data a single sheet might contain.

Never having owned an alidade, I'm wondering if the straightedge on the base was available in a variety of scales.

@rplumb314 - thanks!  I tested making the divots in the board and installing the inserts.  Couple lessons- yes I need to get threaded rods and/or cut the heads off! Also need a more aggressive router bit as the divots are getting too large in diameter for the depth achieved. The inserts go in much easier than anticipated, which creates alignment issues, so ordered the factory install tool.  Sighh. will need to regroup on the whole "hold down" set-up it seems! 

Oh the joys of prototypes!  

Had to work out a sequence to let me switch between drill bits for inserts and router bit (divots) on my only drill press to preserve alignments   If this goes much further will need to bring other DP back from girlfriends to  help!  Also pretty clear I need more clamps!

A related question...how many on this board have actually done planetable mapping? Probably only a few old timers. I did some on a Corps of Engineers crew in the early 80's. I wrote a program for the HP41 to reduce the data easier and faster. Anyone remember the Beaman Arc?

USGS quadrangles were originally done with planetable before photogrammetry. I only did small areas at large scale (1"=50'). But it definitely had it uses. 

A good alidade man could keep two rodmen busy running around.

Yes, I've used a planetable. I don't know what happened to the one that was hanging around the office, I suspect it was trashed during one of the cleanups, heck maybe some of the parts are still out there in the piles of stuff in the garage. Can't say I'm a fan. 

@john-hamilton For the record - I never used a plane table in actual survey work, but was fascinated by the whole concept and how it had been used up to when we had it in Survey Lab in early mid-1970's.  After college - worked for a couple of civil engineering firms and made extensive use of stadia methods for subdivision contour and general mapping work.  Lotsa field notes!  Often wondered if Plane Table would have been better/quicker, but never got the opportunity!

As a certified old-timer, I did use a plane table a bit early in my career.  I was mostly on the stick end of these stadia surveys, but got to observe the process up close when helping the PC fill in details.  We only used them on large-scale topos of limited size, and it wasn't long before the tables and alidades got relegated to a dusty corner of the equipment room.

Also a certified old-timer.

Used a Wild RK1 and plane table quite a bit in the early / mid 1980's.

The self reducing alidade is a pretty impressive (to me) piece of equipment.  One goal was to keep the mental math going.

You were directly reading a difference in elevation, adding/subtracting from the instrument elevation to get the point elevation and then plotting at the stadia distance.

We used mylar sheets taped to the plane table.

You can attach different scales to the instrument.

Ya another old-timer here. My chief was skilled at running the Alidade and drafting so our 3 man union crew did quite a few topo maps in the 60's and 70's. The Alidade bar did not have a scale and was not self reducing so after the chief got the stadia distance he had to plot the distance with a scale. We used a level and 25' rod for elevations and usually followed a contour elevation. It went pretty fast with the chief drafting in the contour and details like big rocks, trees, etc while I walked to the next shot. His maps were very good, actually a work of art that required a strong back (bent over the table all day), attention to detail and good penmanship.