Here are the Cad drawings for the Digitising probe in pdf format so everyone should be able to view print etc.


Shaun........

Here is the dxf file for Prop.txt I translated with CamBam.

http://www.brusselsprout.org/CAMBAM/   (Free)

Paul, Central OR

Hello everyone -- I'm new to this forum. I just finished building my first probe and thought I would share some of my design ideas. I basically started with Shaun's plans using them as a rough guide for the overall size of things. I kept the circuit board and ball spacing the same size, but made a major revision to how the board and the balls are configured.

Here's what I did:
Made the housing out of two pieces. The top is shaped like the original housing except it is shorter. The bottom housing is shaped like the top, i.e., it has a hollowed out center. This new bottom housing combines the function of the "platern" and the "cap" into one piece.

The top has a hole for the arbor like the original. I made the arbor with a spring retaining extrusion similar to the one on the part known as the "hub" (refer to Shaun's drawings). The top and bottom housings were milled from HDPE.

In my design, I soldered the balls to the circuit board, holding them in place tighly against the PC board with a piece of metel tubing with an I.D. a bit less than the balls. This makes the assembly a bit easier than playing the dimple and ball puzzle game. This also eliminates any problems of contact between the balls and the circuit board. Soldering the balls would not be a bad idea in the original design too.

The PC board is then mounted upside down in the bottom housing. This eliminates the need to mill out the three cut outs for the pins on the circuit board because now the pins are on the top side of the balls and the PC board is on the bottom side of the balls. It also eliminates the need to mill the dimples for the balls as on the old "platern" (now part of the bottom housing).

The clearance between the protruding spring retainers (one on the hub and one on the arbor) was made small enough to keep the pins (and the hub) from rising far enough to allow the hub to turn and thereby displacing the pins from between the balls.

I used three countersunk through holes in the sidewalls (about 0.165" thk) of both the bottom housing and top housing to accomodate #2-56 screws and nuts to hold the housing halves together. The amount of the counter sink I used was enough to allow me to use some #2-56 x 1.25" screws I had on hand. They can be hard to find at that length, so anyone copying this idea may want to make the countersinks deeper. (I got the 1.25" screws at www.boltdepot.com, by the way.)

In summary, I made the assembly much simpler by soldering the balls to the PC board and flipping it upside down (with the balls on the top side and eliminating the pin cutouts), combining the platern and the cap into one piece, adding a spring retainer to the arbor and spacing the arbor and hub to keep the hub from over-traveling.

It is working quite nicely, but I need to cut some of the spring off because it is tighter than it needs to be. Just needs a little fudging.

Now I am looking for the easiest and cheapest way to get the point output of the digitizing wizard to a .dxf file.

That sounds good. Show us some pictures please. We like the sexy pics.

Brett

So you want the sexy pictures, eh?  Okay, but it may take me a day or two to get around to it. I should probably start a web page for my mill and lathe and put my pix there.

I am definitely going to build a second probe just to streamline the design. My first prototype is taller than it needs to be and that cuts down on the range. Another modification worthy of note is that I used brass rod instead of "silver steel" rod for the pins. I figure the forces involved are so small that brass will last a long time. The pins are simply pressed into holes in my HDPE hub and the fit is tight enough that they stay in place without glue which won't stick to HDPE anyway. Since my last post I clipped a bit off the spring and improved the sensitivity. I will fine tune the spring length for the second probe.

Since I will be building a second probe, I will document it in pictures throughout the fabrication. I will probably do some ACAD drawings of the new parts too -- maybe. In the meantime, I will take some pix of the first one and post them in a day or two as soon as I get the time.

Maybe I should mention my equipment:

Taig Mill (came with CNC ready motor mounts) with Xylotex 4-axis controller, Sherline rotary table, running the latest Mach3 on 1GHz Dell.

Grizzly Model G8688  7 x 12 lathe -- all stock equipment except for a quick change tool post from LittleMachineShop.com.

I started my second probe and redesigned my redesign and didn't get far before I decided to draw it up in ACAD before going any further. So this .dxf file shows everything except the stylus (will add one to the plans later). There are no dimensions on the drawing since this shows a complete unit, but it is a simple matter to check the dimensions on the drawing. I will extract separate drawings of the individual parts later and add dimensions to make a set like Shaun's. I put everything on a separate layer in this drawing making it easy to visualize in AutoCad by turning off the layer that holds the housing.

Some notes:

The spring is made from .025" dia. music wire formed by wrapping tightly around a 1/4"x20 threaded bolt. I chucked the wire and bolt in the lathe and turned the chuck by hand while holding the wire tight agaist the threads of the bolt. The number of coils, diameter and length in the drawing is accurate for a spring made this way on a 1/4"x20 bolt.

The balls are 3/16" diameter.

The pins have shoulders to make sure they extend the same amount out of the hub. The pin diameters are 1/8" and 3/32".

The screw that holds the arbor to the housing is #8-32x1/2" socket cap head and the cap is just the right diameter to hold the spring during final assembly. The washer is a #8 flat washer. the arbor shaft is 3/8" diameter.

There is a hole in the top of the housing for the wires to go through. A well-placed knot in the wires will act as a strain relief.

The three long screws are #2-56x1.25" and they serve to hold the PC board to the bottom cap as well as holding the cap to the main housing by virtue of two sets of nuts.

I still haven't taken any pictures yet.

Note (Added June 5, 2007): For my latest design, ignore the download here and go to my page at http://tetralite.com/mach/downloads.html

Here is an image made using my first probe prototype. The sampling grid was a 1 inch square with x and y steps of 0.005" (200 steps per inch and 40,000 points total) and the probe stylus is stainless steel with a tip diameter of about 0.027". The quarter was held in place with double-sticky-side fiberglass carpet tape. You can actually make out some of the weave pattern of the tape in the image. If I used a needle point stylus I think I could make a pretty good looking picture of a quarter! Anyway, this demonatrates a darn good degree of resolution -- not bad for my first attempt at building a probe if I do say so myself!

After the scan I took the point cloud file generated by the Mach3 digitizing wizard into Global Mapper (mapping is another hobby of mine) and applied one of the shading options (I used the "Gradient Shader") and then exported the JPEG image. Then I took it into PhotoShop and desaturated the image to remove the color generated in Global Mapper.
Here is a picture of my first protoype probe set up to scan the quarter:

Pretty nice job!!

Art

Looks good, you have done well in my book. You should be proud of yourself, I am. Are you going to make any to sell?

Brett

Thanks for the praise Chaoticone and Art!

Since I started my second probe my first one seems really crude to me now, but it works okay as you can see. If I were to use it in the manner it was intended (for scanning real parts probably with less detail than a quarter), I think it would suffice nicely.

I am considering making them to sell. I have no idea yet how long it would take me to make one (or several at a time) and how much I would charge for one. Any ideas/comments as to what a reasonable ballpark price might be would be most welcome. I wonder how big a market there is also. My lathe has no CNC on it but I'm considering a conversion. If I started making more things on it than I already do (not that much really) and started to sell them I think I would definitely want to automate the lathe a bit.

Btw, I have the meager beginnings of a web site up for my Mach3 related stuff at http://tetralite.com/mach -- not much there yet -- just started today.