Checking flatness of something (or any data really) on the cheap! - Page 1
Forum section: electronics / projects

author: Erwin Ried
author_rank: Regular Contributor
timestamp: August 13, 2013, 05:48:59 pm
content: Hi, time ago I wanted to check the flatness of my 3d printer platform (critical thing, usually underestimated) and I find a way really cheap to do it. I think this thing can be applied almost to any data collection process so it seems interesting to share.First, the setup. One digital depth caliper with a custom holder:Then, a webcam "looking" at the caliper screen:Software for recognition in this case was "Webcam laboratory" (too bad isn't available anymore because some legal things: I think it was sold to intel, but I guess is available in somewhere). This application can map dial gauges, bars and digital ones:Finally a macro for windows built in vTask:http://www.vtaskstudio.com/this macro moves the platform via the usb control (just directly clicking buttons in a dialog) and reads the webcam laboratory caption (with the value, as you may know, every control in Windows is part of an GUI thread, and has a handle, so you can manipulate individual controls with ease, and in this case asks for another value in another window just via his handle:http://www.codeproject.com/Articles/42780/UI-Control-Data-Spy)The data produced by this setup is pretty useful for my purposes:All the files available here:http://www.thingiverse.com/thing:28135(including macro source and excel data)

author: robrenz
author_rank: Super Contributor
timestamp: August 13, 2013, 06:25:15 pm
content: Very nice! But technically you are measuring the parallelism of the platform to the travels of the machine, not flatness. You could have travels with significant roll and still get a flat reading.

author: fcb
author_rank: Super Contributor
timestamp: August 13, 2013, 07:08:07 pm
content: Many digital calipers have an SPC port on them, which is basically serial data output. This might be useful if the kinematics of your printer make using a webcam difficult.

author: Erwin Ried
author_rank: Regular Contributor
timestamp: August 13, 2013, 08:25:19 pm
content: Quote from: robrenz on August 13, 2013, 06:25:15 pmIn general terms, I think you are correct. This approach is exclusive for that particular aluminium sheet, so I think I can say it is flatness no? (there are just 6 anchor points bending the platform)Quote from: fcb on August 13, 2013, 07:08:07 pmYes, this one has a serial port (I have another caliper vernier with a similar port too) but I was not able to find the connector anywhere and I usually try to avoid destroying the things (if I can replace the plug = ok, but in this case they use pcb pads for the connector)

author: BillyD
author_rank: Regular Contributor
timestamp: August 13, 2013, 08:54:22 pm
content: Very resourceful, that's what I call engineering, well done!

author: robrenz
author_rank: Super Contributor
timestamp: August 13, 2013, 10:25:29 pm
content: Quote from: Erwin Ried on August 13, 2013, 08:25:19 pmNo. lets say your one axis moves in a gradual arc or bow in the vertical direction with a .005"chordal height. So that axis is not traveling a straight line (measured vertically). Now you adjust you platform so you get a 0.000 reading over the full travel of that axis. You have made the platform parallel to the axis but the platform is out of flat .005" just like the axis travel is out of straight by .005" Not trying to be a jerk, just helping you see flatness is not the right term. Aligning the platform to the axis travels might be a better description and is all you really care about for this application anyway.

author: MacAttak
author_rank: Unknown
timestamp: August 14, 2013, 01:16:57 am
content: However, if you have a known flat surface (within a certain tolerance), then you could use it to produce a set of correction offsets for the gantry's horizontal axes (axises?), and combine that data with the data above to produce actual flatness data for the deposition platform.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 14, 2013, 08:02:46 am
content: Mechanics use a straight edge & a set of feeler gauges!

author: G7PSK
author_rank: Super Contributor
timestamp: August 14, 2013, 10:08:59 am
content: Just use the eye, surprising how accurate the eye is.

author: Erwin Ried
author_rank: Regular Contributor
timestamp: August 14, 2013, 02:52:04 pm
content: Quote from: G7PSK on August 14, 2013, 10:08:59 amIt looks flat to the naked eye, differences are between 0 and 0.1 mm usually (plastic will not stick properly on some zones of the platform)

author: eKretz
author_rank: Frequent Contributor
timestamp: August 15, 2013, 02:57:50 pm
content: Rob is definitely correct. In this case it might be OK to use a small granite surface plate to set your axis travels and check for flatness. You can also check axis squareness with a granite master square. These items aren't cheap however, it would be a good thing if you could borrow one or both from a machinist friend if you would only use them once. You could also have a plate surface ground/machined from a stable material and checked for flatness and squareness by someone with that capability and use that. Then you would be able to use MacAttack's idea and also check any future items you put on your platform for flatness/square if you need to.