n00b needs help with design drawings

john_partridge

I used Onshape to design a mechanical puzzle and am happy with the prototype that I 3D printed. Now I want to give the design to a machine shop to have it made from aluminum.

Many of the machine shops I've spoken to are happy to take .STEP, .IGES, or other file formats to program their CNC machines. I can easily generate those files from Onshape but I need actual drawings so that I can discuss some of the design features and their tolerance requirements. I'm not a mechanical engineer so I have no training in GD&T and need help making the drawings. So my first question is where can I post a design drawing job? I think this is a couple of hours of work and I would expect to pay for it.

My second question is this. I want to engrave markings on the flat surfaces of the outside of the puzzle. I have .DXF files of the markings but I don't know if I should add them in Onshape or simply give the machine shop separate instructions on the size, the location, and the depth of the engravings. What's the standard practice?

Apologies if I've posted to the wrong forum - I'm new here!

owen_sparks

Hi @john_partridge, what a great topic. I can't offer any real advice as pretty much every shop we use is different.  Some will take a back of cigarette packet sketch others require a little more.  Some will be happy with just 3D, others want 2D.

Might be worth posting where in the world you are (as conventions vary) where you want them made, in what quantity and to what quality.  5 units from a good old boy down the road would be rather different to 10K units form China.

Good luck,
Owen S,

john_partridge

Owen, thanks for the reply. I should have added some more detail. I'm looking at machine shops in the Boston / Metro West area (any recommendations?). The puzzle consists of two pieces, each about 7" x 2" x 1", and I'm looking to have quantity 100 pairs made.

michael3424

Unless there are some high tolerance or fussy geometry in your parts, you probably don't need to provide GD&T specs - simple dimensions with page wide tolerances are often enough.  If you are picky about some features, call out their tolerances explicitly in the dimension.  Never *ever* dimension tighter than actually needed, though.  Machining cost goes up quickly as the inverse of tolerance

When you call out the dimensions try to reference from a point on the part that will be easy for the machinist to locate.  For a rectangular part that might be the top left corner; for the face of a cylindrical part that would probably be the center.  If you have inside radii in pockets, make the radius slightly larger than the common milling cutter sizes - say 0.270" rather than 0.250".  That gets you a better finish at less cost.  And in case you didn't know, never design any sharp (0 ° radius) inside pocket corners - to get those you need EDM which gets expensive.

If you post a screen grab of the parts, I'm others here could offer a lot more suggestions.

If you decide against doing it yourself and no one else offers, send me a PM and maybe we can work something out.

john_partridge

Michael, thanks for the pointers. My problem is that I don't have enough experience with machining to know when I am specifying a tighter tolerance than I need. I'm trying to solve that problem, perhaps incorrectly, by talking to machine shops about what I need and getting their guidance on tolerances. In order to have that conversation, I need a design drawing with dimensions and tolerances that I can discuss with them. 

Yes, machine shops can open .IGES and .STEP files and read dimensions off but that doesn't let them understand where my tolerances are important, where they're not, or where the reference datum on the part is. So that's why I've concluded I need a proper design drawing and wishing I had the GD&T skills to do it myself.

I'm a little surprised there isn't a jobs posting board or something in the Onshape forums so I guess I'll go try to find someone through Upwork.

lni64

I can generate the drawing for you. I sent you a private message with my contact data