When you’re trying to figure out how to fit a part you want to make to something, oh, say, like an electric motor mount on motorcycle frame, it can seem pretty daunting – all those holes floating around somewhere in Space. People seem to like to make it pretty complicated, too, trying to work out a way to do it. Some of the “explanations” will make you want to take up knitting instead.
I’m a simple man. I’m not too CAD-savvy, and I hate maths even more, but there’s one thing I know. Photoshop.
Stealing a page from basic cartography, basically all I’m doing is taking a nice, straight-on photo of the frame (or whatever I’m trying to fit something to) and size it so it’s life-sized. Then I can measure directly off of it, or use it as a template – just like a satellite photo. Once you have a 1:1 image you can have all sorts of fun with it – from drawing on it with crayons and sharpies, to making some awesome high-tech shape, printing it and cutting it out to check the fit.
The slick way to do this is to start with a photo that’s shot using a telephoto lens. You can just use the “zoom in – zoom out” feature on any point-and-shoot, too – just zoom in as far as you can, and move further away from the frame. This makes it so you don’t as much get parallax distortion. Also it helps to shoot it with a ruler or tape right in the photograph. Make sure it’s at the same plane as your part, so you don’t get any enlargement or reduction… or you can simply measure out to details you see, after the fact, and crop the image to that size as I’ve shown in the video.
After you get your part drawn, you can use the image, or even just the print, to make a CAD drawing. I’ve made my own, and I’ve also just sent the file via email to the guys doing the milling and let them draw up the CAD to their specifications. If you’re hogging out the part yourself with a saw or something equally primitive (as most of my parts are made), you can use the drawing to trace to the part, or even use adhesive vinyl to print to, then stick on the stock for your guides.
I’ve done it a few times now, and the fit has been spot-on perfect. As a machinist friend of mine so graciously describes it, “A honeymoon fit.”. Oh, those machinists with their sense of humor.
Here’s the step-by-step video:
One little addition. If you use the “Ruler” tool, you can get very precise measurements between points, as well as the angles. Click the “Eyedropper” tool and hold it, and the Ruler can be selected.
When you use the Ruler Tool, just position the crosshairs where you want to start, click, and drag to where you want to end up. When you release the mouse, you’ll get something like this.
Click on the image to enlarge it if you need to, but you can see your Ruler between the top two holes, center-to-center, on the motor. At the very top of your Photoshop window you can see all your vitals – x-y coordinates of your start and stop points, the length out to 3 decimal places, as well as the angle from horizontal.
You can see how precise this can be. I’m seeing a length of 4.480, and an angle of 17.6º. If you start with a shot with a ruler or scale in the photo and you use that to crop precisely to dimensions, it’s probably the most precise measurement you’re going to get, especially when points are in different planes.
Now, I’ve been told that Illustrator can export vector files that are directly useable by CAD software. I tried it and failed miserably because, well, I don’t know Illustrator to save my ass. I stick with Photoshop and it works great for me. Give it a shot. If you know Photoshop well, it’s a piece of cake. If you don’t it may be a bit of a struggle, but even if you just use it to make a full-sized print of the frame, that will give you something you can measure off of.
So about a year later I hooked up with a guy, Clark Sopper, who then took the very same PAD drawing of mine and made this gorgeous bit of machining yummyness:
I agree that PAD and some printing of a few templates is pretty fast. Measuring the hole centers helps with scaling the picture and getting really critical dimensions… Measuring a bike in 3 dimensions is so hard to get accurate that I don’t spend too much time on it until I have at least a reference drawing based on a pic.
We built chassis for 5 CB350s, 1 Guzzi 500 single, and an MV Agusta triple from PAD and in some parts measuring to confirm scale.
For more on PAD, see these followup posts: