Reverse engineering tools and techniques

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sprior
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Reverse engineering tools and techniques

Post by sprior » Mon Jul 07, 2014 11:32 pm

It seems that in my new hobby of 3D printing there is a significant need to reverse engineer things in real life so some of their dimensions can be entered into a CAD tool to make either replacements or accessories for them. Measuring overall dimensions is a fairly straightforward issue, but what I find the most challenging is holes. Let's use as an example some of the extra holes in the frame of the M2 and you want to design a tool caddy that has holes that line up with those on the M2 - getting that done precisely ends up being pretty tricky, especially when the holes are small like for machine screws.

I'd like to hear what tools and techniques others are using in these kinds of situations to get a precise result without a lot of trial and error.

I'm starting to imagine a tool which measures the distance and size of a hole from a reference edge with a conical tip that self centers in the hole and provides a hairline indicator of the distance to center.

Besides the basic ruler and caliper, what are your favorite reverse engineering tools and special tricks for using them?

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jimc
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Re: Reverse engineering tools and techniques

Post by jimc » Tue Jul 08, 2014 1:12 am

Honestly i always use either my calipers or a machinist ruler. With those two i can get alignment pretty darn close. I did the whole m2 electronics box with just my calipers and everything was all dead nuts on the money. I think you ahould be able to get the center of a hole fairly accurately. With all that said though i am always on a hunt for new usefull tools. I have made it my lifes ambition to buy every tool i would possibly ever need. I think im fairly close with about 5000 sqft of shop space full, but ultimately that goal is unattainable. I think i find more tools i need faster than i can aquire them. lol. I would certainly like to hear what others use as well.

sprior
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Re: Reverse engineering tools and techniques

Post by sprior » Tue Jul 08, 2014 2:53 am

One way you can use a dial caliper is to measure the depth of a hole by butting the end up against the rim and extending the smaller part out until it hits bottom. I'm thinking the end of the caliper you but against the rim were wider so it could stay square against a surface. Instead of ending at a tip the small part that protrudes could have a cone shape centered at zero that self centers in the hole. So the way you'd use it would be to insert the cone into the hole then extend the bar and hold it square against the edge, then read the course units off the bar and the fine units off the caliper dial. I'd actually put the cone on a shaft that insets into a recessed sleeve so it can extend and retract into different sized holes while still staying flush with the surface. This way it could work in holes for small screws up to maybe 1/4" inch in diameter. That's just one design, but I think it would be fast and accurate to use.

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jdacal
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Re: Reverse engineering tools and techniques

Post by jdacal » Tue Jul 08, 2014 3:25 am

I don't have these, but they look interesting for measuring from the hole centers...

http://www.amazon.com/Starrett-PT26151- ... le+caliper

Edit: Just found these in a search but my wallet is crying:

http://www.amazon.com/Mitutoyo-573-605- ... le+caliper
Last edited by jdacal on Tue Jul 08, 2014 3:29 am, edited 1 time in total.
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sprior
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Re: Reverse engineering tools and techniques

Post by sprior » Tue Jul 08, 2014 3:29 am

Interesting, but at a "you could've just said no" price...

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Tim
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Re: Reverse engineering tools and techniques

Post by Tim » Tue Jul 08, 2014 3:40 am

> Interesting, but at a "you could've just said no" price...

Sure, but those attachments look like a nice 3D design project, hint, hint. . .

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Re: Reverse engineering tools and techniques

Post by jsc » Tue Jul 08, 2014 4:25 am

I've just been measuring outside to outside and subtracting inside to inside. That gives you twice the diameter. Add back half to the inside measurements and you get center to center distance.

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Re: Reverse engineering tools and techniques

Post by Josh » Tue Jul 08, 2014 5:13 am

Jsc's method generally works best when you want precision, but honestly I generally just eyeball it and round to the nearest mm (/ half quarter etc. mm) or .001" (depending on what unit system the rest of the part uses - on the M2 we mix a bit, but generally use metric, so most of our holes are on hard mm or half mm centers). For general modeling it really is just measure everything to some good reference and model it up - one of the models I'm quite proud of is from when I was just learning SolidWorks, I modeled up a SD card, with all the tiny little features (write lock switch, tiny little grooves on the side and bottom, etc.).

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ednisley
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Re: Reverse engineering tools and techniques

Post by ednisley » Tue Jul 08, 2014 5:53 pm

holes that line up with those on the M2
On rare occasions, there's an STL model that you can use as an overlay:

http://softsolder.com/2013/10/25/makerg ... ire-cover/

That worked surprisingly well.

Most of the time I apply a millimeter scale and digital calipers to the object, then drop those numbers into an OpenSCAD model. That's a key advantage of OpenSCAD over a CAD drawing program: the object recalculates itself from scratch based on the input measurements, so you can change one dimension and run off another object that's exactly the same, except for whatever depended on that change.

Two or three iterations later, you've got a perfect fit: rapid prototyping in action!

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Re: Reverse engineering tools and techniques

Post by jsc » Wed Jul 09, 2014 12:21 am

Here ya go: http://www.thingiverse.com/thing:388933

Use the customizer to adjust the fit for your calipers. Mine are the cheapest plastic ones sold at Lowes.

I used them on the two top vertical holes on the right side of the M2 and got 44.98. Seems about right.

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