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Mini prism for column lines
Posted by Adam P on March 17, 2018 at 1:52 amDoes anyone use a mini prism set to stake column lines? I??ve been in the field for 7 years but have only don??t column lines 3 times. I??m not particularly fast with a plumb bob. Is a mini prism set accurate enough?
Ben Davidson replied 5 years, 9 months ago 13 Members · 20 Replies- 20 Replies
Yes it is, what concerns you about the accuracy?
I use this setup
Almost exclusively…..Leica GMP101 Mini Prism
I like the GMP 111, there may be a small step down in centring from the 101 but it has better ergonomics.
I have a knockoff of the GMP 111 with 30mm offset for Sokkia with thread adapter on top of SECO prism pole point 5194-05 and like the style very much.
The 30 mil o/s ruins it, try tilting the prism when pointed at an instrument that is locked on and watch the distance and elevation swing a few hundreths, no such swing with the 17.5 o/s.
Oh I’m curious about your experience with the mini prism with -30mm as when i do controls with target prisms, i do not have such problems with -30mm targets
For control shots the minus 30 is usually to a bigger piece of glass and the distance is farther, for close up tight staking the difference between the nodal center and the pivot point of the prism assembly makes for some slop that would normally be acceptable but if you are shooting for millimeters you want to remove what you can.
It is my opinion that the Leica folks have it right when it comes to prism offsetting and housing while just about everyone else has it wrong, which is weird.
thats interesting. Gonna test out that one day, when projects are not so back logged
Hi Lee,
Would you mind sharing a video of the Seco Monopod in action please?
I’d like to see how it works.
Thanks
Hi,
When working with columns.. be extremely careful which prism you use when doing any measurement ontop of a column.
Most prisms are fine when used in horizontal plane.. but as soon as you’re measuring under steep angles, then you can’t use 360prisms.Greetings,
Floris.- Posted by: leegreen
I use this setup
Hello, LeeGreen
Where can I get a monopod like that? The only one that I see is for use with the seco 6000 miniprism and it attaches to the top of that prism. I would like one like in the picture to use with my sliding mini prism seco kit that I have. I assume the clamp is not small enough on the mini poles, but I bet I could glue some rubber inside of it to make the diameter smaller to fit.
It is a combination of the Seco 6000 with a RAM Ball mount to standard 1 1/4″ prism pole. I have 3d printed plastic adapters to make the pole clamp fit the small diameter slide prism pole.
- Posted by: leegreen
It is a combination of the Seco 6000 with a RAM Ball mount to standard 1 1/4″ prism pole. I have 3d printed plastic adapters to make the pole clamp fit the small diameter slide prism pole.
where could I get the ram ball mount?
Did you make the plastic adapters yourself?
@ben-davidson You can find the ram ball mounts on Amazon, or Sitech in Knoxville can probably order it if they don’t have it in stock.
I find it’s easier to mount a prism on the bottom of a regular rod for this type stakeout, assuming you can see low enough. I’ve got a couple of old geodimeter brick prisms that have 5/8 threaded holes top and bottom, so it can be mounted between the bottom of the rod and the point. Much easier to level it up since you can use the rod bubble at the top, which also minimizes the error at the bottom even if the rod isn’t exactly plumb. Plus I can stand up to do it, and the controller can stay mounted to the rod. This is robotically of course.
For anchors, I would NOT want to carry a standard prism pole with a prism mounted at the bottom. For one the bubble is too high when the measurement is on a wall chest high working from a latter. Second I would think a prism so close the rod point would be subject damage very easily while working on a construction site.
I can make a 3d model of the adapter for a 1 1/4″ to a smaller diameter pole and you can upload the OBJ to http://www.shapesways.com to have in 3D Printed. What is the diameter of the slide pole?
Thanks all for the messages.
Steve, I will check on the ball adapter order.
Lee: I will measure the slide pole and follow-up.
As far as prism on the bottom, I think that would be cool for a lot of stuff I do but for this mini prism, I am looking for something that I can sit atop narrow fabricated walls for as-built locating and something for precise anchor bolt stake-out. I can’t walk the walls and keep my rod tip on the corner edge, plumbed up, and hit the shot button on my data collector too well. I do have reflectorless, but sometimes that is hard to utilize too depending on the situation and obstacles. For critical shots, I think the mini setup would work well.
I have a zero offset mini slider, but may buy a mini nodal prism eventually.
Much appreciated.
We purchased a short rod with a small bipod on it for column work. The rod is about 1.2 feet tall and has an 8′ bubble. The miniprism and rod combo was tested extensively before use. Once things were tuned up we scribed alignment marks on each part. Works like a champ..
The sliding pole has a diameter of 0.05′.
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