2017-05-27

Drilling Holes in all the Right Places



There are 2 common ways to drill accurately placed holes: floating or indexed.

The floating method:
  1. Layout the part, scribing lines to the accuracy desired.
  2. Prick punch (a fine 30-50deg punch) the scribed intersections. Done correctly, you should be able to feel the intersecting lines with the point of the punch but use a magnifying glass to confirm. An optical center punch is another option here, but again confirm.
  3. Drift the center mark as necessary until it is at the line intersection.
  4. Enlarge the mark with a center punch.
  5. Optionally, with a divider using the center punch mark as an anchor, scribe witness circles the same or slightly larger diameter than the desired hole.
  6. Select a very small drill with a tip that fits properly in the center punch mark. Some people prefer to just make the center punch mark larger than the web of the pilot drill they intend to use.
  7. Drill while allowing the work to float on the drillpress table such that the drill will align with the punch mark.
  8. Select the next drill, which should have a web thickness smaller than the original hole or punch mark and have a diameter slightly larger than the web thickness of the final or, if necessary, intermediate drill.
  9. Drill the final size.

The indexed method:
  1. Clamp and index the part to a known feature. If you index off a punch mark, use an appropriate measuring tool to pick up the mark.
  2. Crank the table to the desired hole location. If using a drillpress, you can index each hole to drill.
  3. Use a short spotting drill or, if it's all you have, a center drill.
  4. Drill to the web thickness of your final drill.
  5. Drill to final size.

General notes:
  • The floating method relies on a moving work-piece and flexing drill to align with a center punch mark. Horizontal rigidity is bad. Do not clamp down the vice or fixture and use jobber length drills. When drilling large holes, remember drill safety and consider indexing instead.
  • The index method relies on rigidity. Clamp and lock everything down. Use stub-length drills where possible. Use spotting drills if you have them.
  • Mixing the two approaches, using stub-length drills when floating to center punch marks for example, will give less accurate results.
  • Layouts on work to be clamped down and indexed will help with error checking but a center punch mark will not, in itself, correctly line up the drilled hole. It's up to the operator to correctly index to the mark.
  • When using the floating method, if the initial hole has gone off center then you can drift it back a slight amount. Use a cold chisel to notch the far side, the side you want to move away from, and then drill the next size up drill available, possibly repeating several times. Witness circles help with this approach.
  • When using the index method, if the initial hole has gone off center then you can re-index and use an endmill or, if large enough, bore it back.
  • If holes in multiple parts are to align, bolt, clamp, or even tack weld them together and drill all at the same time. Another option is to make a drill guide (jig) that is then clamped to each part in turn.
  • The tables on light-duty drillpresses will often flex down with drilling pressure, thus going out of square. For this reason, deep holes are best done on more rigid machines. If necessary on a light-duty drillpress, block the table up to reduce flex. Optionally, shim the work on the table to compensate for the expected flex for the drill pressure being used.
  • Tramming the table is also important on deep holes.
  • A poorly sharpened drill can drill oversized holes.
  • Accurately sized holes require reaming or boring.
The above is the received wisdom learned from various posters and topics on the Home Shop Machinist forum, as well as other places.

2017-01-06

Getting Started with a MonoPrice Select Mini 3D Printer

This post documents my entry into 3D printing via Linux. Obviously, I'm no expert. Rather, this is where I'm recording what I learn along the way. The intent is, more or less, just sharing my study notes. I needed a place to write things down... might as well share. Nothing original here, no great insights, just organising information in a way I find useful so I can find it again. That's all. If you find it useful then buy me a cup of coffee.

This is a living document... Still printing, and starting to figure out the Cura settings. Now experimenting with TPE-80A filament.

I decided to get into 3D printing with a MonoPrice Select Mini 3D Printer. Why? Because it's cheap, because it's getting rave reviews, and because there seems to already be a great community building up around it.

Background Info:

The Tools:

The slicer: Cura  This is the part that takes the model and converts it to printer-specific gcode.
  • Install under linux via custom PPA:
    sudo add-apt-repository ppa:thopiekar/cura
  • Update and then sudo apt-get install cura
  • Add custom printer to Cura with settings from Tyler Gibson's blog (above).
  • Add your material(s) with specifications.
  • Apparently, it's possible to import settings from a demo gcode file supplied with the printer. (never bothered). I've learned that it will only do this if the gcode was created by Cura and the versions are compatible.
  • Cura's interface is a bit odd and takes some figuring to get the profile info to stick. It also updates daily via the PPA, or so it seems so far. But, it seems to do well as a slicer.
The graphics gcode terminal: Pronterface.py from Printrun. This is used to set some parameters, upload gcode files to the SD card via USB, and can directly print a gcode file as well.
  • Linux prep:
    sudo apt-get install python python-serial python-wxgtk3.0 python-tk git-core python-pyglet python-psutil python-numpy
  • Use GIT to get the scripted app:
    git clone https://github.com/kliment/Printrun.git
  • Running via commandline: (seems to require admin privs)
    cd Printrun
    sudo ./pronterface.py
Inventor: The very expensive CAD to gcode option. (I can use it at work)
  • Adding a 3D printer model involves going into the 3D Print environment, Other printers, and making some change to any existing printer (like setting it to default). This creates an xml file under %appdata%\Autodesk\Inventor 2017\3DprinterDescriptions.xml. Manually edit that file, duplicating a line, and setting a random GUID and other values as appropriate.
  • Download and install Print Studio (a free Autodesk add-on)
  • Restart
  • At that point, using the 3D Print environment and from there running Print Studio gives various options under the media type (advanced tab).
  • Settings do not seem to be quite as fine as with Cura, but there are more options for editing supports.
Fusion 360: The free for hobby/student CAD to gcode option.
  • Starting to use this for a variety of reasons. I quite like it actually. It uses the same Print Studio that Inventor does, and I've still not figured it out. Still using Cura.
  • I am starting to really like Fusion 360. Even the Render environment is a lot of fun.

Things to do after unpacking the box:

  1. Update firmware (seems to be 2 halves). Mine is 24.42, newer than the blogs say.
  2. Enable and configure the WIFI settings. Not yet.
  3. Change PID setting for printhead temp regulation and, optionally, the table heater regulation. Used Printrun's pronterface to set them to values in Tyler Gibson's blog.
  4. Apply table covering of choice. (I've bought tape but it appears tablet screen glass protectors are now the rage). Mine came with tape, so I left it. Had to trim off the corners to get at the levelling screws.
  5. Level table and set print height. Uses the same 4 screws. Mine appears to be slightly crowned, so I set it for the middle. Note that using pronterface to move the table around is way easier than the printer menu and jog wheel.
  6. Lots of reports of loose screws and connectors, so a once-over may be in order. Didn't bother, feels nice, no odd noises.
  7. Set up the printer and filament in Cura, mostly as per Tyler Gibson's blog.
  8. Print the first demo (as specified in the manual) and adjust the print height accordingly. Didn't bother, went straight to printing a token I made in TinkerCAD, exported as an STL, sliced with Cura to gcode, then loaded the gcode into pronterface and told it to print. Came out well. Once it was finished, I raised the bed temperature to 70deg and popped the trinket off. Pictures in a bit.
So, all things considered, it works way easier and better than I had expected. It was, as intended a very easy first print, but still... 

I think I'm going to have a lot of fun with this.

Second Print

Feeling lucky, I decided to print a bigger file that I downloaded. A smartphone stand: (3.5 hr print)
  1. I uncompressed the ZIP.
  2. Loaded the STL into Cura.
  3. Rotated to print it on its side.
  4. Chose a "grid" fill for this print as it seemed more sensible.
  5. Cura said it was nearly a 3hr print. Good enough as a real test.
  6. Saved the gcode file.
  7. Loaded the gcode file into Pronterface.
  8. Connected the printer (in menu - printer was already connected via USB)
  9. Chose SD from the bar above the model pane.
  10. Chose to Upload (note the status bar at the bottom that shows progress).
  11. When done, I used the printer menu to print it.
  12. I disconnected Pronterface during the print. No untoward effect on the printer.
  13. The printer is not that noisy, though it gets annoying when everything else is quiet. I actually find it very difficult to sleep with, even in the next room. Just something about the non-regular whistling and lower tones mixing together... no more overnight printing for me.

More Prints

Going great. I'm still printing at what I've found is "medium" resolution, with a layer height of 0.175. No issues with adhesion at the start, and all the prints are turning out better than I had expected. Settings as follows:
  • Bed temp of 50deg to print, cranking up to 60deg to separate when done.
  • Layer height of 0.175
  • Wall thickness set to .8 (x2) for some prints. A bit thin but works. I'd say the finish is a little rougher though.
  • Speed is 50, with a wall speed of 25.
Starting to run out of the obvious test things to print so now it's a matter of getting into the editing side. Oh, and I created superfine to superrough profiles in Cura to match the layer thicknesses as suggested in the wiki, with other settings that seem to match (just guessing at this point). The 0.175 seems to be about middle. Haven't tried these alternative settings yet.

My Cura Settings

I'm not recommending these... I've no idea what I'm doing yet, but these are the settings I'm playing with at the moment and needed to write them down. This is as good a place as any. Note that the settings includes a page that makes these settings visible.

PLA-SuperFine:

  1. layer height = 0.0437
  2. initial layer height = 0.175
  3. line width (all) = 0.4
  4. Wall thickness = 0.4 (1 count)
  5. Top/bot thickness = 0.6
  6. Top/Bottom Pattern = Concentric
  7. Infill = 15%
  8. Pattern = defaulting to grid but may change depending on print
  9. Printing temp = 210 (pla)
  10. Printing temp initial layer = 215
  11. Build plate temp = 50
  12. Material diam = 1.75mm
  13. Material flow = 100%
  14. Enable retraction
  15. Print speed = 30mm/s
  16. Infill speed = 30mm/s
  17. Wall speed = 20mm/s
  18. Top/Bottom Speed = 15mm/s
  19. Travel speed = 100mm/s
  20. Initial Layer speed = 15mm/s
  21. Skirt/Brim Speed = 15mm/s
  22. Number of slow layers = 2
  23. Enable print cooling
  24. Support = default to off, model dependent
  25. Build plate adhesion = default to skirt, model dependent
  26. Skirt minimum length = 350mm
  27. Print sequence = all at once

PLA-Fine:

  1. layer height = 0.0875
  2. initial layer height = 0.2188
  3. line width (all) = 0.4
  4. Wall thickness = 0.8 (2 count)
  5. Top/bot thickness = 0.8
  6. Top/Bottom Pattern = Concentric
  7. Infill = 20%
  8. Pattern = defaulting to grid but may change depending on print
  9. Printing temp = 210 (pla)
  10. Printing temp initial layer = 215
  11. Build plate temp = 50
  12. Material diam = 1.75mm
  13. Material flow = 100%
  14. Enable retraction
  15. Print speed = 40mm/s
  16. Infill speed = 40mm/s
  17. Wall speed = 20mm/s
  18. Top/Bottom Speed = 20mm/s
  19. Travel speed = 120mm/s
  20. Initial Layer speed = 20mm/s
  21. Skirt/Brim Speed = 20mm/s
  22. Number of slow layers = 2
  23. Equalize filament flow
  24. Enable print cooling
  25. Support = default to off, model dependent
  26. Build plate adhesion = default to skirt, model dependent
  27. Skirt minimum length = 350mm
  28. Print sequence = all at once

PLA-Normal:

  1. layer height = 0.175
  2. initial layer height = 0.3
  3. line width (all) = 0.4
  4. Wall thickness = 1.2 (3 count)
  5. Top/bot thickness = 0.8
  6. Top/Bottom Pattern = Concentric
  7. Infill = 20%
  8. Pattern = defaulting to grid but may change depending on print
  9. Printing temp = 210 (pla)
  10. Printing temp initial layer = 215
  11. Build plate temp = 50
  12. Material diam = 1.75mm
  13. Material flow = 100%
  14. Enable retraction
  15. Print speed = 50mm/s
  16. Infill speed = 50mm/s
  17. Wall speed = 25mm/s
  18. Top/Bottom Speed = 25mm/s
  19. Travel speed = 120mm/s
  20. Initial Layer speed = 25mm/s
  21. Skirt/Brim Speed = 25mm/s
  22. Number of slow layers = 2
  23. Equalize filament flow
  24. Enable print cooling
  25. Support = default to off, model dependent
  26. Build plate adhesion = default to skirt, model dependent
  27. Skirt minimum length = 350mm
  28. Print sequence = all at once

PLA-Rough:

  1. layer height = 0.2625
  2. initial layer height = 0.3
  3. line width (all) = 0.4
  4. Wall thickness = 1.2 (3 count)
  5. Top/bot thickness = 0.8
  6. Top/Bottom Pattern = Concentric
  7. Infill = 20%
  8. Pattern = defaulting to grid but may change depending on print
  9. Printing temp = 210 (pla)
  10. Printing temp initial layer = 215
  11. Build plate temp = 50
  12. Material diam = 1.75mm
  13. Material flow = 100%
  14. Enable retraction
  15. Print speed = 60mm/s
  16. Infill speed = 60mm/s
  17. Wall speed = 40mm/s
  18. Top/Bottom Speed = 30mm/s
  19. Travel speed = 120mm/s
  20. Initial Layer speed = 30mm/s
  21. Skirt/Brim Speed = 30mm/s
  22. Number of slow layers = 2
  23. Equalize filament flow
  24. Enable print cooling
  25. Support = default to off, model dependent
  26. Build plate adhesion = default to skirt, model dependent
  27. Skirt minimum length = 350mm
  28. Print sequence = all at once

PLA-Super Rough:

  1. layer height = 0.3063
  2. initial layer height = 0.3063
  3. line width (all) = 0.4
  4. Wall thickness = 1.2 (3 count)
  5. Top/bot thickness = 0.8
  6. Top/Bottom Pattern = Concentric
  7. Infill = 15%
  8. Pattern = defaulting to grid but may change depending on print
  9. Printing temp = 210 (pla)
  10. Printing temp initial layer = 215
  11. Build plate temp = 50
  12. Material diam = 1.75mm
  13. Material flow = 100%
  14. Enable retraction
  15. Print speed = 75mm/s
  16. Infill speed = 75mm/s
  17. Wall speed = 37.5mm/s
  18. Top/Bottom Speed = 37.5mm/s
  19. Travel speed = 120mm/s
  20. Initial Layer speed = 37.5mm/s
  21. Skirt/Brim Speed = 37.5mm/s
  22. Number of slow layers = 2
  23. Equalize filament flow = off
  24. Enable print cooling
  25. Support = default to off, model dependent
  26. Build plate adhesion = default to skirt, model dependent
  27. Skirt minimum length = 350mm
  28. Print sequence = all at once

TPE-80A-Normal:

  1. layer height = 0.175
  2. initial layer height = 0.3
  3. line width (all) = 0.4
  4. Wall thickness = 1.2 (3 count)
  5. Top/bot thickness = 0.8
  6. Top/Bottom Pattern = Concentric
  7. Infill = 40%
  8. Pattern = defaulting to grid but may change depending on print
  9. Printing temp = 240
  10. Printing temp initial layer = 240
  11. Build plate temp = 0 (using double-sided tape on top of masking tape)
  12. Material diam = 1.75mm
  13. Material flow = 100%
  14. Enable retraction = No
  15. Print speed = 20mm/s
  16. Infill speed = 20mm/s
  17. Wall speed = 20mm/s
  18. Top/Bottom Speed = 20mm/s
  19. Travel speed = 60mm/s
  20. Initial Layer speed = 20mm/s
  21. Skirt/Brim Speed = 20mm/s
  22. Number of slow layers = 2
  23. Equalize filament flow = No
  24. Enable print cooling
  25. Support = default to off, model dependent
  26. Build plate adhesion = default to skirt, model dependent
  27. Skirt minimum length = 350mm
  28. Print sequence = all at once

More Printing

Had some failures, mostly with adhesion. I was printing a model downloaded from ThingiVerse, a Dremel nose finger guard, and part of it kept breaking free during the print. I first tried replacing the stock masking tape with some green painter's tape and that was worse. After much futzing around with using brims instead of skirts, adding supports, and sanding the tape, I managed to get a print that stuck. After that, I realised that the tape is way slipperier than regular masking tape. I replaced the tape and had better luck, though still not as good as the factory tape. I've got a couple of iPhone 5S tempered glass screen protectors on the way from China... which are supposed to be the solution to this problem. Time will tell.... (update) and, no. I had no luck with the glass and went back to regular masking tape, sanded a bit, and now with glue stick before each print. Seems to work well enough. I may try the glass with glue stick at some point, but I'll also see if I can find any of that fabled "blue painters tape" everyone keeps mentioning.

Another print, a whistle (another ThingiVerse download) also failed due to adhesion. This time it lifted up on one side from warping, but I let it print through. That was a mistake as... well... it's a whistle and compressing the tube you blow in kind of changes things. Live and learn. Anyway, after my initial success, I've now got a small but growing collection of failed prints. More successful ones as well... that ThingiVerse can be quite addictive and the printer has been working hard. The first roll of filament is noticeably down so I've ordered 2 more PLA. I think I'll avoid ABS until it's warm enough to put the printer outside while printing.

Note that I'm uploading designs and prints on PinShape. No point duplicating the pictures here.

Filaments

I've ordered a 12-roll variety pack from Filament.ca as well as some TPE-80A and Nylon-645. At this point, I've spent more on filament than the printer, which I consider to be a good thing. I'll be working through the various types, seeing how they do, over the next while.

TPE-80A Filament

I've been experimenting with this soft filament, somewhat rubber-like though it's not. I'd say if feels like it would make good drive belt material. That kind of strength and texture. Actually, I'd say the filament would be a very useful addition to the toolkit, but it is quite difficult to print with. First off, it is too soft to easily feed down the Bowden tube, instead going out sideways at the feed mechanism. Thus, I had to make a part to fill in the spaces so it couldn't escape. That part is here: MSM MK-IV Space Eraser, on PinShape. Solving that problem, the next issue is that it appears to shrink so much after printing that getting it to stay stuck to the bed is near impossible. After a few failed attempts, I decided to use double-sided carpet tape on top of masking tape (to protect the bed). It stuck quite well to the carpet tape but I still had issues with the carpet tape separating from the masking tape. Yeah, it pulls that hard. The next issue appears to be that it slips when trying to feed directly from the spool, and that causes missing lines in the print. The solution to that will be some kind of ball-bearing roller for the spool. Yes, a lot of hassle, but if I can figure out this filament, the rest should be easy.

Some Pictures

Some downloaded models from Thingiverse and PinShape:

The surprisingly hard thing to print:


And, some stuff I drew in Inventor and uploaded to PinShape
Tomy Plarail track bits...




Current Stats:

Nearly 1KG of PLA printed, with about 17% of that as waste. Yeah, I've been keeping all my failures, and supports, in a bag so I can weight it. Just curious.