Reverse Engineering

Greetings All!

I am a teacher at a technical college. I teach mechanical drafting, so I am in the process of making a set of drawings for the RepRap machine. I downloaded a STL file viewer that can measure STL files, and I have started creating solid models of the parts in Pro/ENGINEER. It's been a little difficult working with the STL models to figure out dimensions, so I started this topic to ask questions that someone else may know.

Here's my first question. There is a teardrop shape that is used throughout the design (the corner bracket has many of them). When I measure its angle I get roughly 87.9 to 88 degrees. I've also measured from the arc center to the point of the tear drop and I do not get an even measurement either. Is the tear drop shape supposed to be a right angle (90 degrees)? Is there something special about 87.9594 degrees that I am missing here?

Rick.

Rick,

The .STL files for Darwin were originally made using Solid Edge but it is an academic license. The solid edge files are on source forge. I can help you with this if needed.

As for the tear drop I am not sure I thought it was 90 Deg. but it was desighned so that the part can be printed with out a support extruder.

As for the drawings for Seedling I believe there are .dxf files that Zach has made up..

Bruce Wattendorf

As far as I know, the teardrop is supposed to be 90 degrees. This is based on the RepRap being able to handle an overhang of up to 45 degrees without support material. Not sure why it's coming out off a couple degrees.

Is the STL measuring software free? and what is it please?

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Ian
[www.bitsfrombytes.com]

Greetings All!

I am going to use Darwin as a class project. We're going to create engineering drawings of all the RP parts and some of the purchased parts. Over the course of the semester I will try to work out the legal problems of using commercial software (academic version). I have the okay to do it if the information is not used for profit, from all four of the softwares we could use (Pro/ENGINEER, SolidWorks, Inventor, and AutoCAD); however, it was pointed out to me that there is no control to keep a business from download the files and using them for profit.

Steve, I'm going to use 90 degrees on the tear drops as that seems more logical.

Bruce, thanks for the tip about source forge. I will look for the files on Monday.

Ian, the STL measuring software is free. It is MYRIAD 3D Reader.

[www.myriadviewer.com]

It is not open source. It is similar to the Adobe approach. "Here's a free viewer showing the cool capabilities of the software. If you want to do more, pay us." The viewer does allow measurements, and seems to recognize when an STL is attempting to create a circle because you can measure from arc center to arc center and there is no definition of an arc in a STL file (only triangles and normal vectors). Hopefully this helps you in your STL quest.

You will be hearing from me and possibly my students in the near future!

Rick Montzka.

Excellent viewer very easy to use, for my

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Ian
[www.bitsfrombytes.com]

Greetings All!

A quick legal question... Can I use the RepRap logo in the titleblock of the drawings that my class creates?

By the way Ian, I will allow the students to use any software they choose. I am going to guess the majority will choose SolidWorks, followed by Pro/ENGINEER, Inventor, and finally AutoCAD. A single brave soul may attempt AoI, but I doubt it. My students want a portfolio to take with them to a job interview, so they will want to prove proficiency in a commercial CAD package.

Rick.

Hey Rick,

So long as you/they aren't claiming ownership of the RepRap name or logo, then go for it!

Greetings All!

Thanks to Bruce W. for sending me the IGES files! They have been extremely helpful to our class.

I believe I have detected a slight design error on one part. Since a picture is worth a thousand words, I have attached my drawing showing the slight error. Most of the time I can find a dimension that comes out to an exact metric number, so I consider that to be the design intent. This time, however, I couldn't find an even metric number describing the overall size of the part or the center to center distance. If one of these numbers truly is your design intent, that is okay, just let me know what is important about this part and the documentation will reflect your wishes. Otherwise, let me know what the corrected part should look like (or attach an updated IGES file).

I think the class is enjoying working on a real project, but they are getting frustrated with all the internal details and "strange" shaped hexagons. The next time I run the class, we will create and "Engineering Standard" to describe the shape and reference the engineering standard on all detail drawings.

Have you considered a part number scheme for all the parts? That would be another helpful piece of information for the documentation package.

Rick Montzka
Hennepin Technical College
Brooklyn Park, MN, USA

I'm part-way through building a Darwin but, as far as I can tell, the only important dimensions on the studding tie are the internal ones. The purpose of the part is to used the 2 trapped nuts to hold two rods a specific distance apart. One nut acts as a bearing against an M8 threaded rod. The other has an adjustment screw that pushes against an M8 smooth rod. The threaded rod rotates; the smooth one is stationary. As far as I know, the 4 hole along the side aren't needed.

In short, as long as you've got the internal slot and the 2 trapped nuts in the right arrangement, you can use artistic license on the rest. I'd keep the width of the slot slightly greater than 8mm and the distance between the nuts about what it is. You could probably round it up to 47 or 48 without causing any problems, since it's adjustable.

All Steve's post is good, but the 4 holes are very useful in assembly for retaining bolts. Any positioning rounding should be toward the centre.

Cheers Rick and Steve.

Ah, OK, so you can put bolts through these holes to keep the rods from slipping toward each other?

Yep, which stops the inserted nuts from spilling out...

Im in the same boat trying to reverse engineer some of the parts from their respective stl files. Until BitstoBytes has kits available again I am trying to develop prints to get one of our machinists going on machining the RP parts. Currently I have tried several stl viewers and none of them seam to mesh real well with what I have going here. As I type this message I am dl'ing the myriad viewer and from whats been said already my hopes are high. Keep your fingers crossed.
There was a comment in a previous post about iges files for the RP parts, does anyone have access to or a link to these files? I know that Inventor would have much nicer time trying to open them instead of the stl. thanks again and everyone keep up the good work.

Jason,

sorry here is a link to a ziped file of the robot parts made into an .iges file

I also started to make .dxf files of a lot of the parts. my machine is made from wood parts that I cut by taking the .stl files and converting them to .dxf drawings.

the link to the zip file is
[www.mediafire.com]

and here is a link to my blog if you want to see what I had done..

[repstrapping.blogspot.com]

Bruce Wattendorf

Thank you so much for the help. I have access to a machinist so Im thinkingof making the parts from either AL 6061 we have laying around or some sort of acetal copolymer (delrin) since we have so much of it in the shop.

That is awesome to make them from aluminum!
I was trying to make the parts so that anybody with the least amount of tools could make them.

There are a lot of parts I would have made from aluminum like the corner blocks I had to make mine from oak and it was a lot of trial and error..

Also if you need here is a PDF of drawings of some of the parts of the robot. this is also in the cartesian robot source forge download.

Bruce

Thanks for the link. That pdf file reinforces a lot of the decisions I made for the corner bracket. I have a question regarding the backlash spring in the "bed corner" piece. Since I will be machining these parts can I just thread the bottom of the bed corner where the driven nut is supposed to be? maching a hole for a nut when I can just thread the material instead doesnt make sense. Im sure Im missing some functionality thing with this. In input you have would be helpful.

There's some discussion on the anti-backlash mechanism here [forums.reprap.org] and here [forums.reprap.org]

Given that you're machining the part and the fact that the anti-backlash springs don't really seem to make that much difference, you might consider skipping the springs and nuts altogether and just tapping the entire length of the hole.

The only real requirements for the corner bracket are that it support the bed and fit onto the the Z rods. You could probably get away with a block with some holes drilled in it.

tapping would work I just used "furniture nuts" the nuts used in the making of furniture that have 3 spikes that drive into wood and then my bed constraint is made from wood.

the only thing you might want to think about is that you might want to use nuts at the very least so the z axis screws have room to walk as the table goes up and down.

Bruce