A question of scale: I’m making RichRap’s 3DR printer, and I’m wanting to expand the envelope a little right off the bat. As printed, the pieces I have an envelope roughly 6" in diameter.
One of the things I currently CAN do, it work aluminum (Mill and lathe in the garage), Each piece, being symmetric, means 6 drilled and tapped blocks, would allow me to expand the printer in the X and Y dimentions. I’d like an 8" envelope to work with.
Where my experience falls short is: NEMA 17 motors work in the as-built size, will I run into scaling issues if I make certain dimensions larger, but leave everything else alone? My knee-jerk thought is: no, there’s no additional weights, stresses, or loads, the effector just has farther to go.
So, going +20%, will I run into unexpected problems?
(Don’t worry, it’s not the final dimension…the bandsaw doesn’t cut parallel, I have to leave some extra meat to clean things up.)
You should be just fine. You will have different values in the firmware (from a vanilla 3DR) but that’s not a big deal. You can actually easily add much more than %20. If you I have a set of modified STLs somewhere that expand the 3DR about %40.
I figured the differences would be sorted in the initial calibration. It’s a catch-22 situation in that, if I HAD a printer, changing the dimensions would be easy, but I don’t have a printer yet.
Coming from hotrodding cars, it’s often a case of modding one part, only to find it affects a bunch of other things farther down the line (more horsepower means more cooling, bigger brakes, stronger transmission), I just wasn’t sure if that’d be the case here.
Looking at it a second time, however…1"x1" box section aluminum is cheap and easy to work with…I’ll probably use that instead of billet. It’s not a MILSPEC solution, but it’s not a MILSPEC need, either.
Check out +Richrap blog he posted an update, there are a few styles out to get your 8" build area with printed parts, if you need parts printed lmk I’ll help you out
Also another though to save some cash what about hardwood as your spacer? Then you can print replacements from your printer once going
Well, that’s the wierd thing: I can’t work with wood. 
I can get precision and repeatability with metal that I just can’t get in wood. 1x1 is pretty cheap, though. I’m not sure the wall thickness will be enough to tap and use or if I’ll need to drill a little larger and just use nuts and capscrews.
I appreciate your quest for accuracy on this but IMO alum is excessive for a expansion. as long as your verticals are equally spaced you are perfect if not that can be adjusted in marlin. But I doubt a few tenths would be detrimental to get you printing.
The alum will work great I just see it adding unneeded weight as it’s a pretty portable machine( depending on how tall). That’s my motivation for building one now. I’m up in the air ATM on what style expansion I will use , I already have a heat bed, or if I will design my own.
I’m starteing with PLA…I’ll consider retrofitting a heated bed at a later date. The portability aspect is an interesting thing I hadn’t considered with I started out, but IS pretty nifty, if only to move it from the kitchen to the study for long prints.
Expanding X and Y is fine, just remember to also extend your Push-Rods for the arms. To get the new length measure the distance between the vertical bar centres and multiply that by 0.8 to get the new push-rod distance from eye-to-eye.
Good luck and post more images as you go.
Also remember to update the firmware settings for the new size.
Thanks, Richard! There were limitations on the lengths of Rod and Aluminum extrusions that I could get, so I figured I’d see what envelope I could make with the materials I’ve got…so far the external vertical height of the rods make the printer 1.5 feet (457 mm), and the spacers give a corner to corner distance of 8.25" (210 mm)…using your blog recommendations, that’s a 6.75"-ish (171mm) arm length. That all looks roughly like this: https://drive.google.com/file/d/0B09sUvvteXCBVTZVVlBYbnRZOHM/edit?usp=sharing
(and yeah, I still need to sort the triangular centerpost…THAT I may make out of wood. )
Squinting and eyeballing it, that’s a 10" (254mm) vertical envelope and an 8" (203mm) diameter.
