Starting out - Digital Calipers, How would you measure? (Sorry) 1

[BlackBag]

Hello,

I am sure this is a really stupid question, I'm in the process of learning, so I appreciate any input. I am starting out learning Sketchup for some personal mechanical design projects and I'm learning the basics of the software, etc..

I'm getting pretty decent in just "drafting" up some things, but, I need to measure some small parts that I have with my digital calipers, and then actually draw them up in Sketchup.

I know how to use the digital calipers that I bought, which are the green Insize 1108-200 and seem to be pretty decent.

However, the simple things that I can measure, there are no problems - but I have this one small part that, I do not know how to accurately measure the placement/alignment of the (2) holes on each side - in relation to the top of the main circle. I will show you a picture of what I'm trying to do.

What I am trying to do is to find the correct measurement/distance for both holes on each side (from the center of the main piece)as well as the bottom with my calipers. The 2 holes on each side ( right and left top) are lined up with each other, but are above the midpoint on the centerpiece, and of course, the hole below is just to the right of the center as well.

I hope this makes sense. I know there's a "right" way to do this instead of scratching lines on the piece, using a wood ruler, etc..


I really appreciate any constructive input guys.



Thanks!
J

 

[zeusfaber]

I suspect that that the right answer is to use a different measuring tool, but here's what I would do (to be honest, making this up as I go along)...

First, I'd make the brave assumption that the mounting holes are all the same distance from the "centre" of the part.

Take the mounting holes two at a time (so there are three pairs) and measure the distance between the holes in each pair. Measure each twice - once using the "inside" jaws of the caliper on the nearest faces of the mounting holes and once using the "outside" jaws on the opposing faces of the mounting holes. Subtract the "inside" distance from the "outside" distance to give you the distance between the centres of each of the mounting holes. WRONG: Add the two measurements together and divide by two! Original post written far too late at night!

Now, I'd plonk the part down on a piece of paper and spot through the holes with a pencil (the beauty of doing this is that you can do trig, geometry and real life measurement all on the one bit of paper, making it much easier to spot the inevitable cockup before you build much of an edifice on it.

Join the three dots to make a triangle. Mark the lengths of the sides using the numbers you measured with your calipers.

Use the cosine rule to calculate the three angles of the triangle. Mark these on the paper. Mark them A, B and C.

Find the midpoints of two of the lines that form the triangle (say AB and AC) and draw lines perpendicular to those. The point where those two lines cross is the centre of the pitch circle of the mounting holes (and, by assumption, of the whole object. Use basic trig to calculate the precise distance from (say) point A to the centre. (You could draw a right angled triangle between the centre point of AC, the centrepoint and the intercept of AB's perpendicular to calculate the distance between the centrpoint and the perpendicular's intercept, then use that to calculate the distance from A to the centrepoint).

Once you know the radius of the pitch circle, the angles between the mounting holes and measure the outer diameter of the shell, you have essentially defined the part.

A.

 

[Skogsgurra]

A common method is to use the zero button. Like this:
1. Measure the hole diameter.
2. Zero the calipers.
3. Measure wall-wall distance between holes.
4. Read center-center distance from the calipers.

The reason it works is that you, by measuring the diameter, actually also measured two radii and then zeroed them away so that you get the center-center distance when you measure between holes near walls. There are a few variations on this, but if you get the basic method you can do a lot of intricate measurements with simple calipers. Add some trigonometry and you can do just about anything.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[MikeHalloran]

The photo with the hand clearly shows that the three small holes are not on the same bolt circle.
... but the technique outlined by zeusfaber can let you measure the radius from the large counterbore's center to the center of each of the small holes, and trig will eventually get you the numbers you need.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

This is a case where some trickery can work well.

1) I'd toss that thing into any all-in-one printer.

2) Scan it like a document.

3) Bring it up in your engineering drawing tool as an image. In this case I'm using free DraftSight. I took your image and brought it into Paint that comes with Windoz. From there simple "insert object".

4) Expand it until it barely fits on the screen.

5) Use the drawing functions to 'digitize' all the features you care about.

Notice how I used lines across the holes? Then I used snap-to-midpoint. As I write this I recall that a superior method as discovered by the Germans for their gun-sights are to use circles. The human eye can very accurately align concentric circles. Just draw circles that don't need to even be the same size as the holes. Your eyes will allow you to accurately center them in the image holes behind them. Then snap your lines to the centers of the circles.

It is important to scan the original as I describe, as taking a picture causes no end of parallax issues as seen in my hack-job of your photo.

Once you have all the geometry you want drawn you then pick any single dimension you've drawn that can be accurately and easily measured with your calipers on the actual piece and you 'scale' your drawing to arrive at that same dimension in your drawing. All the other dimensions will, of course, automatically scale correctly simultaneously.

Notice too in the lower left I could easily use the arc function to create the same radii in things like the ears - if you care.

When appropriate you can blitz the photo image out or turn it into a 'block' move it to its own layer and turn off that layer.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BrianE22]

How accurate do you need to be? The following would probably get you to +/- .005". If the hole sizes allow, press 3 ground pins in the holes. Then lay a ground flat rectangular bar on top of the two of the pins and measure the distance between the bar and the edge of the part. Then you can measure from the bar to the edge of the 3rd pin. Knowing the width if the bars and the diameter of the pins gives you the info you need.

 

[unclebob]

Draw/Trace the thing on a paper sheet, including the holes. Measure needed lengths.

 

[BlackBag]

Wow - Everyone here has really great suggestions. I really appreciate everything you guys suggest and will try them

The reason for me learning how to measure correctly is that I have the real project that I have had a friend help with. It is a hand sized clutch basket for a motorcycle. She has produced a 2D CAD drawing, but now the machine shop requires that I provide a 3D drawing. Now she doesn't have time to work on it anymore so now I am stuck and thought I could learn, which I need to do. CAD software is so expensive. I originally tried Auto CAD 2017 but found that by the time I started to figure out how to do what I needed to do, the trial version would expire. Sketchup is much easier but still expires.

Here is a pic of the PDF that shows the 2D drawing..

And this is the original part that she measured up..

Turning the 2D into a 3D for me will take a very long time since I am learning the tools, how to use them, correct terminology, etc...


I hate to be annoying, but if any of you guys that look at the pics and the 2D drawing would be willing, I would gladly pay you to help put this in a 3D format so I can finally move forward. If you tell me what you would charge, I'd gladly UPS the original clutch basket to you and paypal/send you cash.

I really appreciate all the input guys, I didn't expect to get so many responses.


Thanks,
J

 

[Skogsgurra]

I used to work with CEJ (Jo-Blocks) a lot. We developed 3D Co-ordinate Measuring Machines and when I google them, I see that they are still in the market.

http://www.hexagonmetrology.se/eng/CMMs-Small--Medium_100.htm#.WExmCIWcGZ8

There is software that can turn the measurements into drawings and the accuracy was around 5-10 microns (back in the eighties) and that should be good enough if you compare with what can be achieved using calipers.

Contact a company that sell CMMs. They can do the job in one or two hours and you get better accuracy, more measures and probably also a drawing or a set of data that can be fed to a 3D printing system.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

If you're willing to pay.. Then just pay for a 3D scan or 3D scanner.

Google for "3d scan service". Lots of places do it for a reasonable charge. Look for service in your town.

Or look around for a scanner. There are several under $1k.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BlackBag]

I thought about a 3D scanner, but was uncertain of which one would be the best for my efforts, all marketing BS claims aside.

 

[3DDave]

Maybe FreeCAD? The price is right and it has an active user forum, so it's not a dead end. There are videos on Youtube, so that may help decide.

Supposedly there's a DXF export add-in for Sketch-up that is suitable for CNC work.

 

[MacGyverS2000]

If I need measurements, I get surprisingly accurate results by laying it on a scanner and doing similar to what smoked suggests. Certainly better than I would get using hand calipers.

Dan - Owner

http://www.Hi-TecDesigns.com