O/T - Creating a CAD file from a simple template?

Terry Keeley · Dec 28, 2017

I need a 2D CAD file for a simple 1/4" thick poly-carbonate template, aprox. 36" x 2".

Google shows me many different ways this can be done, there's scanning, tracing, photo digitizing etc. Any way to do this w/o fancy equipment? If I do bring it somewhere what's the simplest, most accurate method? Costs?

FredC · Dec 28, 2017

I take it you do have a CAD program and can use it? With my old dinosaur CAD 2D for DOS I can print actual size and get a very accurate drawing. I sometimes print what I have drawn and compare to an actual part I am duplicating, then adjust as necessary. Not into that fancy scanning and digitizing, so I can not help there.
If you have a sample you are trying to duplicate, I think I would tape some masking tape to it and crank off pencil marks in the milling machine and measure at those points then transfer measurements to the CAD program.

DDoug · Dec 28, 2017

Would like to see what exactly the template looks like, complexity
wise.

What kind of accuracy are you looking for ?

DanielG · Dec 28, 2017

Here's my experience after doing a fair number of 2D profiles.

If it's a simple shape, take measurements and model it from your measurements.

If it's a complex shaped flat part, use a scanner. Unlike a photo, this won't have parallax error. You then import the photo into CAD and you can draw your splines on top of it. Take a few key measurements so you can check your scale.

Terry Keeley · Dec 28, 2017

FredC said:
I take it you do have a CAD program and can use it? With my old dinosaur CAD 2D for DOS I can print actual size and get a very accurate drawing. I sometimes print what I have drawn and compare to an actual part I am duplicating, then adjust as necessary. Not into that fancy scanning and digitizing, so I can not help there.
If you have a sample you are trying to duplicate, I think I would tape some masking tape to it and crank off pencil marks in the milling machine and measure at those points then transfer measurements to the CAD program.

I have Autocad 2013, I want to take this profile and do some virtual wind tunnel testing with it.

digger doug said:
Would like to see what exactly the template looks like, complexity
wise.

What kind of accuracy are you looking for ?

Pretty simple, I don't need the holes, just the outline. Doesn't need to have extreme accuracy.

johnoder · Dec 28, 2017

Measure part

Assign stations to assist with above

In Autocad, place points, draw splines, save as whatever, like dxf

All it amounts to is some "Y" dimensions and their locations in "X"

D Dubeau · Dec 28, 2017

I do stuff like this on a scanner. You will have to make dot's or reference marks so you can connect all the profiles in cad. They can be crosshairs, small punch marks, or pieces of scotch tape with pinholes in them. You need enough so that for every scan you have at least 3 in view. Bring all the pictures into cad (I use Rhino) and then line them all up and draw your profile. I also put a 6" scale on the scanner bed to double check the scaling is right.

For larger stuff that doesn't fit on the scanner bed such as a transmission, motorcycle case, etc I use graph paper, tape, and a good sharp knife. Just cut a bunch of pieces that fit all the way around the flange and over lap a good 2-3 inches each sheet. trim the outer profile to fit, mark any holes, then before you remove the paper poke small holes in the overlapped sections so that when you scan in all the sheets you can digitally line them all back up again. It sounds hokey, but it's really easy, and accurate if you put the time in.

DanielG · Dec 28, 2017

Terry Keeley said:
Pretty simple, I don't need the holes, just the outline. Doesn't need to have extreme accuracy.

From the picture, it looks symmetric. If that the case, this is very easy. As John said, mark off stations at known distances from the nose. Use calipers to measure the width at each station. Plug it into AutoCAD.

If it's not symmetric, I'd still do stations. First I'd measure width at each station as above. Next I'd stand the template on edge on a flat surface and measure depth from the top of the template down to the table. That gives you everything you need to model it.

Terry Keeley · Dec 28, 2017

Thanks for the help. From what I'm hearing I can do this myself by either measuring the part at different stations from the nose (height gauge and calipers?) or scanning it and converting to CAD with s/w.

It's not quite symmetrical, but only the first 12" or so from the nose is curved. From there back it's straight top and bottom, I know the radius of the nose. When I bring it into CAD does it "blend" the points to make a smooth curve? Obviously the more points the better.

As you can tell I have very limited CAD experience, I did a 2D drawing once to cut some foam to protect electronics parts but that was all radii and straight lines...

rcoope · Dec 28, 2017

Best would be to lay down the points from measurement and use a spine to go through as many points as possible. Then it will be smooth. It would be helpful to establish a tolerance in your mind for how close to each point you want to get. With lots of points you could use straight lines and fillets where they meet, but that may not be as accurate as splines.

Kyle Smith · Dec 28, 2017

You can use an indicator mounted in the spindle of the mill to get a better "X" increment to go along with the "Z" increment the dial indicator provides.

With the coordinates it wouldn't take much to get you a model if you want to send the numbers to me.

Terry Keeley · Dec 28, 2017

rcoope said:
Best would be to lay down the points from measurement and use a spine to go through as many points as possible. Then it will be smooth. It would be helpful to establish a tolerance in your mind for how close to each point you want to get. With lots of points you could use straight lines and fillets where they meet, but that may not be as accurate as splines.

Thanks, will try that once I get the points.

Kyle Smith said:
You can use an indicator mounted in the spindle of the mill to get a better "X" increment to go along with the "Z" increment the dial indicator provides.

With the coordinates it wouldn't take much to get you a model if you want to send the numbers to me.

Thanks for the offer, I have some local help to draw it once I get the points.

That's also what my toolmaker buddy suggested (actually we both came to the same conclusion). Clamp the template on the mill table and use an edge finder to get points every .100" or so from the nose...

SeymourDumore · Dec 28, 2017

Terry Keeley said:
Clamp the template on the mill table and use an edge finder to get points every .100" or so from the nose...

Actually, that part is much easier than that method.

Put the part into the vise with edge-up, pick up the tip of the radius for X0, then put a dial indicator in the spindle with a sharp tip, zero it on the straight edge
then move the table by say .100 increments ( or less if you need better accuracy ) and read the dial for each increment.

When done, take the table you've created and put a point at each of the coordinates in Autocad.
Then use the Spline command and connect the dots.

To make it easy, in the Autosnap settings select NODE so all you need to do is click the points in the proper order.

pcasanova · Dec 28, 2017

don't think r13 will do raster. But Draftsight free is an autocad clone. install it and attach the image then just trace it and scale to some known points.

What I did here for a friend. Found a jpg of the logo and mopar and traced it.

Terry Keeley · Dec 28, 2017

SeymourDumore said:
Actually, that part is much easier than that method.

Put the part into the vise with edge-up, pick up the tip of the radius for X0, then put a dial indicator in the spindle with a sharp tip, zero it on the straight edge
then move the table by say .100 increments ( or less if you need better accuracy ) and read the dial for each increment.

When done, take the table you've created and put a point at each of the coordinates in Autocad.
Then use the Spline command and connect the dots.

To make it easy, in the Autosnap settings select NODE so all you need to do is click the points in the proper order.

That's an even better idea!

Scruffy887 · Dec 28, 2017

Autocad r4-5. Take a pic with a high res camera from as far back as you can. Stay perpend to the part. Put 2 scales in the pic on the same plane as the part, one in x, other one in Y. Import raster image into autocad and scale image to match scales in pic. Trace with splines and done.

SeaMoss · Dec 28, 2017

To some extent, you guys are giving bad advice. If his goal is a smooth curve, the fewest points will give the smoothest curve. If the goal is to accurately reproduce something he has, then the largest number of points will be the most accurate but not the smoothest. There's a whole technique to the curve-smoothing thing, and Autocad is not the top end of that software group.

If he's trying to do both, Alias Design Studio is maybe the most approachable with Class A surfaces, smooth accurate curves, etc etc - Autodesk bought them, like a black hole swallows light - I think they have a thirty-day free evaluation program. But you'd have to learn how to use it, which is sort of non-trivial.

DDoug · Dec 29, 2017

SeaMoss said:
To some extent, you guys are giving bad advice. If his goal is a smooth curve, the fewest points will give the smoothest curve. If the goal is to accurately reproduce something he has, then the largest number of points will be the most accurate but not the smoothest. There's a whole technique to the curve-smoothing thing, and Autocad is not the top end of that software group.

If he's trying to do both, Alias Design Studio is maybe the most approachable with Class A surfaces, smooth accurate curves, etc etc - Autodesk bought them, like a black hole swallows light - I think they have a thirty-day free evaluation program. But you'd have to learn how to use it, which is sort of non-trivial.

I think it would be cheaper to have it Cordaxed, than buy a new CAD sytem.

We still don't know the accuracy required. It looks like an airfoil,
and some have some pretty tight requirements.

Terry Keeley · Dec 29, 2017

Scruffy887 said:
Autocad r4-5. Take a pic with a high res camera from as far back as you can. Stay perpend to the part. Put 2 scales in the pic on the same plane as the part, one in x, other one in Y. Import raster image into autocad and scale image to match scales in pic. Trace with splines and done.

Will give that a shot, sounds like a fairly simple solution, thanks.

digger doug said:
I think it would be cheaper to have it Cordaxed, than buy a new CAD sytem.

We still don't know the accuracy required. It looks like an airfoil,
and some have some pretty tight requirements.

It's a side profile for one of my R/C boats. I'm going to make a diffuser at the back of the hull to help keep the prop planted, I want to try different shapes/angles in Autocad CFD.

Not proficient enough to quote accuracy requirements, as long as it's "close" that'll do.

Joe Gwinn · Dec 29, 2017

digger doug said:
We still don't know the accuracy required. It looks like an airfoil,
and some have some pretty tight requirements.

If it's an airfoil, it will be described by a relatively simple equation that generates all the surface location points. It will not be described only as a point cloud.

O/T - Creating a CAD file from a simple template?

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