# 3D Drawing/Printing exercise in design



## ddmckee54 (Apr 27, 2018)

I got a Wild hair, Brain fart, idea the other day and decided to run with it for a while to see where it led. 

I was watching a video on YouTube, tutorial about how to build a wooden rubber band gun, and I started thinking I could 3D something like that.  I started looking to see if anybody had already posted the STL files for something like that.  I took a look around on Thingiverse but couldn't find anything that really jumped out at me.

I wanted something fairly small and kinda cool looking, kind of like 007's gun, and I'd REALLY like to make it clip fed.  The slide will be the rubber band clip.  I want an actual size sorta' replica of a Walther's PPK, BUT not be a true replica.  I'm NOT a rivet counter, and I'm trying to make this thing easier to 3D print - not make a museum quality replica..

Hmmm....Bond's Walther PPK.  Can't get much cooler than that and it's small enough that it shouldn't take forever to print the parts.  I love watching the 3D printer build a part, but I HATE waiting for it to get done.  I've got a Freebie g-code print simulator that gives me a pretty good idea of how long it will take to print a part.  For complex parts that will take HOURS to print, I'll start the printer before I go to bed and hope that by morning the printer hasn't turned out several hours of junk. 

Here's what my little design exercise looks like so far.  The first attachment is a screen shot of the 3D PDF file for my sorta PPK, the second attachment IS the 3D PDF.  You'll need to download it and then open the file with Adobe or whatever your software of choice is.

This is mainly just a solid model so far.  I have carved some hunks out it where I know it' will be required.  The trigger assembly so far consists of the trigger and the "hammer", but nothing between them.

Don


View attachment PPK.bmp


View attachment PPK RBG.pdf


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## stevehuckss396 (Apr 27, 2018)

Looks cool! This will be a rubber band gun?


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## Cogsy (Apr 27, 2018)

I came across plans/files on thingiverse a while back for a single action rubber-band revolver (think Colt Peacemaker) and I've printed 2 of them - one at full sized and one at 70% for the kids to use. They work well and are loads of fun. I'm interested to see how this one turns out, though for some reason the pdf is blank for me.


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## ShopShoe (Apr 28, 2018)

That does sound like a fun project. When I saw the rendering of the Walther, I just had to search for a picture of the real one as what was in my mind from the Bond movies didn't match.

You Learn Something New Everyday: It looks like the graphic artists and prop guys from the Bond franchise never saw the real thing.

--ShopShoe


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## lohring (Apr 28, 2018)

My current 3D project is a [ame="https://www.youtube.com/watch?v=C5hEarotKx0"]WWII Tiger tank[/ame].  I'll use a more conventional RC control since I have them as well as gear motors and servos.  I plan to use an Open Panzer control board.  I felt it needed a suspension so I redesigned the base section with Fusion 360 to be 3D printed with torsion bar suspension.  Most of the tank is now being printed as I write in PLA, but I want to try printing the track and wheels with PET.  We'll see how it turns out.

Lohring Miller


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## EddieV (Apr 29, 2018)

What materials will you use for the print? Looks good. Is there a grip texture going on the handle?


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## ddmckee54 (Apr 30, 2018)

Eddie:

I currently just print in PLA, I don't mind the smell of it while it's printing.  That's an important consideration since my printer is in my living room.

I ran a test print of the slide yesterday, to use up the last of the roll of white PLA and to see if there were going to be any problem areas in the print.  I found a couple and I modified the model to include some built in sacrificial supports in those areas.  I use the Prusa version of Slicer and don't like using the support generator that's built into it, why support everything if you've only got a couple of spots that need help?  I try to design with 3D printing in mind - I try to avoid overhangs that would require support.  I think I get a stronger better looking finished product that way.

I'm thinking about checkering the grips, but I'm not thinking too hard about it yet for two reasons.  First, those little pyramids would be a bear to model.  Second, my printer is just a relatively cheap Prusa I3 clone, I'm not sure how well it would handle printing the checkering.  If/when I get this designed and printed to a point where I'm happy with it, I might try printing checkered grips just to see if it would be as much of a disaster as I think it would be.

Don


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## EddieV (Apr 30, 2018)

Yea PLA is certainly the most living-room friendly material! Made from corn and smells pretty sweet like popcorn almost (to me anyway!) Good pick on that
I remember my first printer was a DLP resin printer, B9 Creator. I also had it in the living room next to the TV, resin stench and noisy mechanism - it was a miracle my girlfriend tolerated this eccentricity..

Have you tried acetone vapor polishing for a smooth and glossy finish? Can try it at a basic level with a biscuit barrel and kitchen roll. (would mean a switch to ABS though) 

Looking forward to seeing the print results!


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## ddmckee54 (May 1, 2018)

Eddie:

I haven't tried any vapor polishing since I've only been printing in PLA.  I've got a drafty old house and from what I've read PLA is a lot more tolerant of temperature changes than ABS is.

I think that there is a solvent that would be usable for vapor polishing PLA, but I'm also pretty sure that it is nasty stuff. 

Don


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## ddmckee54 (May 2, 2018)

I got some more design work done on the RBG.  I THINK I have a workable trigger assembly designed, but the proof is in the pudding as they say so I'll have to get it printed out and see if it works.  I also think I have a slide lock that just might work but I have been holding off on printing anything else until I'm relatively sure that what I've designed will actually work.

The first attachment was SUPPOSED to be just the trigger assembly, from trigger to rubber band wheel.  I had everything but those objects turned off in the drawing, but when I saved it in a 3D PDF format I got the whole freakin' thing.  So the first attachment is the 3D PDF of the entire rubber band gun.  Apparently my 3D software thinks it knows what I actually want to show better than I do.

The second attachment is just the trigger with its' built in springs.  I need to get the trigger printed out ASAP so I can find out how hard/soft those springs are.  That way if I don't like the way the trigger pull feels, I can play with the spring design to get what I want - at least that's the theory.

At this point I'm not sure whether or not I should design a separate frame to act as a test-bed for the trigger assembly and/or rubber band magazine/slide, or just use what I've already got designed as the prototype.

Don 

View attachment RBG.pdf


View attachment RBG Trigger.pdf


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## ddmckee54 (May 3, 2018)

I have discovered that I need to re-design the trigger assembly, or at least the sear.  I was planning on using a portion of a ball point pen spring to return the sear to it's normal non-firing position.  I had estimated that spring diameter to be about 3mm and designed the sear so that the sear spring would sit in shallow pockets to keep it in position.  My sear and all the rest of the trigger assembly is about 4.5mm thick.  I measured a few springs today and discovered that about the smallest I could find was about 3/16", or close to 5mm.  This obviously will NOT fit in a 3mm hole in a 4.5mm thick part.

I can see 2 possible solutions:

Option 1 - I print a small pin instead of a pocket to keep the sear spring in position on the sear.  I allow about 0.3mm clearance between printed parts, that gives me a free fit without too much slop.  With the clearance I already allow I SHOULD be OK as far as part thickness and sidewall clearance is concerned.  I may have to make the pocket in the slide that allows the sear to move a little deeper.  If I do have to modify the pocket then I'll allow a little more clearance in the slide around the sear at the same time, but that would mean that I'm still only modifying 2 parts.

Option 2 - I make the entire trigger assembly thicker, this assembly consists of several parts that would need to be modified.  Doing this would also affect the main frame because the business end of the trigger sits in a big honkin' pocket in the main frame, part of the sear projects into this pocket.  The sides of that pocket in the main frame are already as thin as I care to make them, so I'd have to make the main frame thicker.  This in turn affects both the left and right side frames and/or the left and right grips. I also need to alter the interior pockets in the slide that parts of the trigger assembly project into.  If I don't want to alter the exterior of the slide too, then I've got to compensate tor the extra thickness somewhere.  I'd probably take it out of the grips since I've got a quit a bit going on in the left and right side frames.  Parts of the clip and the slide lock mechanism are already going through there. 

Nope, Option 2 is NOT a viable option, I'm going with Option 1.  I can already foresee a printing problem with the overhang caused by the pin so I'll design a sacrificial support piece for it.

Don


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## ddmckee54 (May 15, 2018)

I printed the slide and part of the frame. There were a few trouble spots on the slide, too much overhang and not enough radius on that part of the slide and part of it didn't print well - it's not too noticeable, bit I know it's there. Also I'm not happy with the back part of the slide.  Right under where the actual hammer would be there is a noticeable gap that I need to fix on the next print. At 0.2mm layers, 3 perimeters, and 40% in-fill rate the slide takes almost 11 hours to print - so I don't want to print too many versions of it that don't work.

I printed the sear and the rubber band wheel/hammer too, all the moving parts in the firing mechanism only take about an hour to print. I'm pretty sure that the sear and wheel will work as advertised, but I'm also pretty sure that my trigger, in its' current configuration, will not work. The trigger needs to slide back pushing the sear to release it. In order to get the semi-automatic operation I had planned on the trigger sliding past the sear, that part's easey-peasey. The hard part is getting the trigger to slide back past the sear when the sear is in its' locked position as the trigger returns to its' normal non-firing position. This can obviously be machined out of metal, but I want to 3D print these parts and I want it to be a simple mechanism - simple is good, complex is bad. I've got a PDF copy of Ingenious Mechanisms someplace, maybe it'll give me some ideas. 

I've also come to the conclusion that 3D printed springs are pretty much useless, at least in this size. If they are printed thin enough to flex properly they don't exert enough pressure, and if you print them thick enough to exert the proper pressure they will not flex enough and they break - at least in PLA that's what happens. I've got a couple of 305mm lengths of pre-wound 4mm OD spring material ordered in 0.4mm wire diameter. So no more scrounging to find the right sized ball point pen springs, I can just cut off the length of spring I want. (Ebay, like Google, is your friend.)

No pictures, I haven't figured out a way to take a picture of a black object and have it show a reasonable amount of detail, never claimed to be a photographer. If it helps any to visualize this stuff looks like, I've been told that I'd get in a lot of trouble if I tried carrying it into an airport. I've got a cousin that works Homeland Security at LAX, but I still don't think I'd try walking through there with this thing assembled. I may be crazy, but I'm not that kind of crazy.

Don


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## ddmckee54 (May 25, 2018)

Since many people are of the opinion that "If you don't gots no pictures it didn't never happen."  I've got a couple of pictures for you.

I've heard a rumor that you are supposed to be able to copy and paste images, let's give it a shot.  The first is an assembled overview of what I've got designed and printed so far.



It's printed in black PLA, 40% infill, and 0.2mm layer height, the slide itself took almost 11 hours.  The blue painter's tape is holding in the pin the keeps the trigger in the correct position.  This pin will eventually be sandwiched between the left and right side frames, only the left side frame has been printed to this point.


This shows the slide, "actually the magazine/clip", removed.  Yes it is "loaded", but at this point it cannot fire.  I've found that I was a little too loose with my tolerances.  I've got enough play between the slide, the hammer, and the 2 spacers that I get "jams".  There's enough of a gap that the "ammo" gets jammed in the gap. - can't have that.


This shows the bottom of the slide and the space in the slide that the barrel slides through.  This locks the front of the slide in position on the front of the gun.  The side frames have wedges on them that lock the slide down on the rest of the "gun".  The slide will be locked in position by the "clip".  The clip will fit into the recess at the bottom of the handle and 2 locking tabs will extend through slots between the side frames and the hand grips - thus locking the slide in position - or at least that's the plan at this point.

Like I said earlier the current trigger design with plastic printed springs is trash.  I've been working an a different version and I'm waiting for my spring stock to get off the slow boat from China so that I can test it.  I think I can use part of my original sear design, but it will need to be modified and re-printed.

I have been working on a design for "checkering" the hand grips, but the more I think about it the more I'm leaning towards scrapping that design.  It looks good on the screen, but I don't think it will print well - if at all.

Later,
Don


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## ddmckee54 (Jun 6, 2018)

Well the slow boat from China made landfall yesterday.  I now have two 305mm lengths of 4mm OD spring made from 0.4mm diameter stainless steel wire in my grubby little hands.  I guess the yard can wait for a while, I've got more important things to do.

I have re-designed the trigger assembly around my spring stock, actually more of a design tweak that a re-design.  The down side is there were enough little changes that I will have to re-print every part I have already printed.  The re-design includes spring pockets to ensure the springs stay in the correct location, and modifications to the side frames to eliminate a gap at the rear of the slide.  Leaving the gap wouldn't hurt anything, but at the right angle you can see daylight between the slide and the frame at one spot - can't have that.

Last week I was running low on cash so I went to the money store to trade my signature for  some more folding money.  They always have an off-duty cop sitting in the lobby so I figured “Why not” and went out the car and got the little black bag containing the parts for my gun.  I handed the bag to the cop and asked him how much trouble the bag's contents could get me into.  Which for some strange reason, made him open the bag REALLY slow.  He took the parts out and assembled the gun.  He told me that legally speaking I was fine, because this wasn’t really a weapon.  However professionally speaking, it was just too damned realistic making it hard to determine that it wasn’t an actual weapon.  But he said it was REALLY cool – which I already knew.

After I double check the design and re-print the parts I'll take some more pictures so that you all know it actually did happen.

Don


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## ddmckee54 (Jun 11, 2018)

Printed out some parts over the weekend, actually most of them.  The only thing I didn't re-print was the slide, that's about a 9.5 to 10 hour print and I ran out of weekend.

The spring pocket idea turned out to be a bust.  Putting a 4+mm pocket into a 4mm part doesn't leave a whole lot of wiggle room.  My printer does a fairly good job, but sometimes the edges aren't exactly what you'd call crisp - especially in an overhang, and crisp edges are really what you need with parts this size.  I don't mind a small amount of fettling to get the parts to fit properly, but the present design involves more fettling than I want to do.   I think that next I'm going to try to print a small pin that the spring can locate over as opposed to a pocket that the spring has to fit into.  I'm also not happy with the fit of the clip to the clip detent in the frame, it's a little too snug.  I can fix that at the same time I fix the trigger spring pocket in the main frame.

Fortunately these changes will only affect the trigger group, the slide, and the main frame.  All toll, that's about 12-13 hours of print time.

Don


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## ddmckee54 (Aug 16, 2018)

Well I finally got back to this project, that darned work thing kept getting in the way of the really important stuff.  I'm going to have to do some experimenting, the temperature settings that I was using in May and early June resulted in semi-melted blobs of goo when I tried printing last night.  Who'd of thunk that a 15 - 20 degree rise in ambient temperature would have made that much difference.

Don


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## ssaxer (Aug 17, 2018)

Looking great Don, can't wait to see the finished product and download the drawings.


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## ddmckee54 (Aug 17, 2018)

Ssaxer:

Thanks, for a while I was wondering if there was anybody out there.  I was pretty sure that I was just talking to myself - again, and that gets old after a while.  I mean it just seems a little - one-sided?

This isn't the first time I've noticed a lack of heat dissipation on small-ish parts.  I've found that when printing a large part each layer had enough time to cool before the next layer was printed.  The way I solved this issue in the past was printing multiple small parts, of about the same height, at the same time.  That way each part had some time to cool before the its' next layer was printed.  This time I was trying to print the entire trigger group which is 6 pieces: the two parts of the actual trigger, the sear, the hammer, and the two spacers that center the hammer in the slide.  When I finally decided to cancel the print, the top of all of the parts looked like molten puddles of goo.

I guess it's time to re-design the filament cooling fan/shroud - again.  I've been using a 40mm x 10mm axial fan and I've been debating whether I should switch to a blower for filament cooling.  Last night I was watching a couple of videos where they were testing various fan/shroud combinations, printing the same part on the same printer.  They came to these conclusions:
An axial fan with no shroud is better than nothing.
An axial fan with a shroud is better than just the fan.
A blower with the same shroud will be better than the axial fan and shroud.
This is because blowers handle the higher pressures that the shrouds cause better than axial fans do. 

There are a couple of 50mm by 15mm blowers on their way to me, courtesy of our friends at Flea-Bay.  By the time they get here next week I'll have the shroud re-designed and hopefully printed.  It should be a big enough part that layer cooling won't be that much of an issue.

Don


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## ddmckee54 (Aug 22, 2018)

Well, I got the new radial blowers in the mail yesterday.  I also got the filament cooling fan shroud redesigned and reprinted over the weekend.  So last night I changed from the old fan/shroud combo to the new fan/shroud combo - HOO-BOY howdy what a difference.  I need to do some more work on the design of the discharge from the shroud, it's blowing onto the extruder hot block too much.  I had my fan minimum speed set at 60% which was never a problem before.  But when I tried a test print last night and the fan came on, my extruder temperature dropped over 30 degrees before I figured out what was going on and turned the fan speed down to a point where the extruder heater could cope.  I plan to experiment a little bit with some masking tape and aluminum foil until I get the discharge shape worked out, then I'll print a new shroud. 

This should also help my overall print quality, especially on overhangs and when bridging which were always problem areas before.

Don


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## Buchanan (Aug 22, 2018)

Keep the updates comming please.  I bought my first 3 d printer (Zortrex 200 ) a month ago, So i am following with interest.


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## johnmcc69 (Aug 23, 2018)

Keep the updates coming Don. I'm finding all this very interesting as well.

 John


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## ddmckee54 (Aug 30, 2018)

I stumbled across an interesting video Tuesday night, but I couldn't find the link today to save my soul.  The video was the first part of rebuilding a Creality Ender to rival a Prusa Mk3 using a Duet board and other parts.  That in itself was interesting, but the really interesting part was he redesigned the filament cooling fan shroud and how he tested it.  He used a shallow pan of water on the print bed and brought the nozzle down low enough to see the air flow pattern in the surface of the water.

Well I said I was going to do some experimenting, so last night I did.  My cooling fan shroud used to look like this, with the axial fan at the back of the printer.






I switched to this shroud when I got the blower to use instead of the axial fan.  Again, the blower is on the back side of the printer just like the axial fan was.




As I said earlier I found that I had plenty of air movement, too much of that air was directed at the extruder hot block.  In fact so much air was hitting the block that the heater couldn't maintain extruder temperature with the fan speed set at 60%.  I had to lower the fan speed to about 10-15% in order to maintain extruder temperature.

When I first tested the shroud with the pan of water,  I found that I also had plenty of air hitting the surface of the water.  Unfortunately where the air streams hit the water was about 6-8mm away from the nozzle on all sides.  Out came the aluminum foil and the masking tape and I started blocking off parts of the shroud openings.  Bottom line, I've blocked off the entire opening on the back side of the hot block and I've blocked off all but about the from 8-10mm of the openings on both sides of the shroud.   This gave me two indentations in the water about 6-8mm long on both sides of the nozzle, about 1-2mm away from it.  Sorry, didn't think that I should have gotten some pictures of that until I was typing this - but I promise it did actually happen.  (The checks in the mail too - just in case you're wondering.)  I did find out that with the discharge blocked off as it is now I can maintain extruder temperature, even at 40-50% fan speed.

Anyway, this is what the next iteration of the filament cooling shroud will look like.  I left the walls on both sides of the openings plenty thick and solid, about 1.5-2mm.  Just in case I need to get out the file and do some more "adjusting" to the air flow later on.





We'll see if this works.

Don


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## ddmckee54 (Sep 10, 2018)

I changed the fan shroud over the weekend and repeated the water test to check the airflow with then new shroud.

I'm halfway there, the air from the right-hand discharge is hitting right where I want it to hit - at the tip of the nozzle.  The left-hand side is still hitting about 6-8mm away from the tip.  I can maintain extruder temperature with the fan running at 60% constantly and I can bump the fan speed up to 100% temporarily for bridging, just like you're supposed to do.

Definitely making progress, along with a bunch of junk prototype parts - but that's another topic.

Don


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## elcid (Sep 11, 2018)

Cogsy said:


> I came across plans/files on thingiverse a while back for a single action rubber-band revolver (think Colt Peacemaker) and I've printed 2 of them - one at full sized and one at 70% for the kids to use. They work well and are loads of fun. I'm interested to see how this one turns out, though for some reason the pdf is blank for me.


I use foxit reader which has a beta program for showing 3d pdf files, I can rotate it but only see a solid black image.


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## ddmckee54 (Sep 14, 2018)

elcid:

I use Designspark for my 3D work, the price was right - free - so I'm not too sure about the "quality" of the PDF file that it generates.  I'm able to "see" the file on several machines using the freebie Adobe runtime package.

I've been threatening to devote the time to learning Fusion but just haven't done it yet.

Don


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## ddmckee54 (Sep 17, 2018)

Been thinking about the checkering on the grips of the PPK and how I could 3D model/print that.  While I was printing a part for another project I had a epifany, epipheny, brain fart.  I got to wondering what a  part that was printed with cubic infill would look like if you printed NO top layers.  I whipped up a quick test part, 40mm X 40mm X 5mm with a 3.5mm dia. thru hole.

The attached file is is what I got.  The best description I can think of is that it's kind of an inverted checkering.  It's a crappy picture, and this was the BEST of the bunch.  I covered part of it with a green highlighter to try and get a little better definition - didn't help THAT much.

I printed this with a 0.4mm extrusion width, 0.2mm layer thickness, 6 bottom layers, NO top layers, with 10 perimeters.  This SHOULD give me about a 4mm border around the part, never did measure it to verify that.  I don't think I could use this trick on any part that didn't have a flat top, at least not with my current Slic3r.  I think that you can print multiple parts simultaneously with Simplify3D and use different slicing settings for each part.  If you can print a solid part with infill, NO perimeters and NO top - this might allow you to sculpt the top of the infill.

Don


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## ddmckee54 (Oct 31, 2018)

OK, it's about time I got back to this project.

Scratch the idea about printing a part with no perimeters and then sculpting the top of the infill.  When the infill is printed the printer doesn't print one line across the part then just move to the next line to be printed.  Nope, it prints a line across the part, then prints around the inside of the perimeter until  it gets to where the next line across the part will be, then it prints the next line across the part.  If I tried to sculpt the top of a part with no perimeters I'd still get lines where I didn't want them.  The only way I can see to do that right now would be to model the infill myself and I'm not that crazy dedicated.

I have mocked up the trigger mechanism using the 4mm spring stock that I got a couple of months ago and have discovered that I need to modify the pins I'm using to keep the springs in place.  That or glue one end of the spring in place.  I need something to keep the springs in the proper place while the Rubber Band Gun is assembled.  Once it's assembled  they are trapped in position and won't go anywhere.  I'm re-designing the pins now and will try printing a prototype tonight. 

Don


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## ddmckee54 (Dec 17, 2018)

Haven't updated this in a while.  I have been working on smaller simpler version RBG that I had hoped to be able to arm the great-nephews/nieces with for Christmas - probably not gonna happen.

I planned to use the simpler RBG's to field test the trigger mechanism.  I printed a prototype, my version of a Colt 1908, and it failed miserably - at least that's my opinion.  It dry cycles just fine, but when I load it with rubber bands, it does not behave consistently.  Sometimes it would cycle through 4-5 shots properly, sometimes it wouldn't fire at all, and sometimes it would fire all the rounds at once.  Totally unacceptable behavior and not something that I'd ever try passing off onto a kid, even if they are over 30.  Since I copied all of the internals of the PPK directly into the Colt, I know that the PPK won't work either. 

I'm re-designing the internals, both to get a more consistent release of the rubber band, and to get rid of those fiddly little springs.  After losing the 4th or 5th spring, either on assembly or dis-assembly, I realized that those things have got to go.  I don't know of too many boys that won't try tearing something apart if they get the chance, and losing a custom made spring turns this into a paperweight.  I'm trying to replace the itty-bitty springs with rubber bands, gotta love it when you can use the ammo to replace a broken spring.

I printed  a new test frame last night, and I'll print the new internals tonight.  I'll let you  know  if we have a winner, or just  another dud.

Don


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## ddmckee54 (Dec 18, 2018)

Well, it's not exactly a winner, but it's not exactly a dud either.  I did print out the re-designed internal parts last night, they appear to work correctly.  In my haste to get this thing working, I didn't pay too much attention to the appearance of the beast, so it looks a bit like Frankenstein's monster with bits added on or clipped off here and there.  

I've got a good feeling about the release mechanism, it seems to be working properly.  I got rid of the custom fiddly itty-bitty springs, instead I'm using a rubber band.  You gotta love it when you can use the ammo to make replacement parts.  I was originally making the wheel/hammer and the two spacers as three separate parts.  I found out last night that loading the rubber bands onto the wheel would separate these parts allowing the rubber bands to jammed in the gap.  The hammer/wheel/spacers are now printed as one part.

Right before I quit for the night I found that the rubber bands are getting jammed in the gap between the wheel and the frame at  the shooty end of the RBG.  What's happening now is that when the trigger is pulled, the sear releases the wheel and the wheel/hammer starts to move, but the wheel gets jammed by the rubber band pinched in the gap.  I'm going to open up this gap to see if this corrects the problem, then I think I'll have a working semi-auto RBG - only time will tell. 

If/when I get it working tonight I'll take some pictures of this monstrosity in all its' glory?  I'll let you know tomorrow if we've got a working RBG, or just another plastic paper-weight.

Don


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## ddmckee54 (Dec 21, 2018)

There's still no joy in Mudville, and I don't have pictures but I've got the next best thing a bitmap and a 3D PDF.

The bitmap below shows the current working bits of the RBG.





This shows the RH side of the test frame that I have printed, the Hammer/wheel, the Sear, the Trigger and the link, labeled Trigger2, between the trigger and the Sear that causes the Sear to release the Hammer/wheel.  For some reason, that I have yet to figure out, I cannot change the layer/color of the trigger, the link or the sear - they're always blue. (Maybe they're sad because they don't work?)

The problem that I'm having right now is that as a single shot RBG this works just fine.  When I load multiple "rounds" onto the hammer/wheel, it goes into MetalStorm mode discharging everything at once.  While impressive, it's not exactly the result I was after.  I've even tried loading just one rubber band, then rotating the wheel as if multiple rounds were loaded.  This should cause the RBG to dry-fire until the loaded band comes around.  Nope, wheel just rotates.

Sitting here looking at it I may have had an idea, it was either that or a brain-fart - too early to tell.  I'm starting to think that the problem is where I have the rubber band that I am using as the sear spring attached to the sear.  It is currently wrapped around the sear, so I don't think the rubber band has much leverage to move the sear back into position to stop the hammer/wheel.  I know it's possible to make this work, I've watched videos of a guy building a semi-auto RBG out of plywood that uses a similar set-up - principles are the same anyway.

I'm going to try adding a lever at the bottom of the sear that will project toward the rear of the gun.  I should be able to double or triple the amount of leverage that the sear spring can apply on the sear.  Of course I'll have to modify the existing cavity for the sear, but that's what mills were invented for wasn't it?  If it works, then I'll modify the print files, print the parts again, and see if it still works.

Attached is the 3D PDF, it doesn't have the rubber bands modeled, or the additional text.

Don


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## Cogsy (Dec 22, 2018)

A little difficult to tell from the pic alone, but to me it looks like the trigger rod would be acting on the sear in such a way that it would be next to impossible for the sear to return to position without a lot of spring force.  Basically it looks like the trigger would be overriding the ramp on the sear.


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## cds4byu (Dec 22, 2018)

I think you beed an escapement type of.mechanism.  When the sear releases the rubber band wheel it should simultaneously insert a stop that limits tje wheel rotation to a fixed angle.

Carl


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## ddmckee54 (Dec 22, 2018)

Cogsy:
When the trigger is pulled to the stop what you are calling the trigger rod slides past the sear, allowing the sear to swing back to the stop position.  I'm starting to think I've got too much trigger travel between when the sear allows the hammer to release, and when the trigger rod releases the sear.  I REALLY need top look at the geometry and timing of those actions.

Carl:
I've thought about an escapement, but I must have a block of some type when I think about them.  Every time I come up with an escapement design, it releases the rubber band on trigger release, not on trigger pull - and that just feels wrong.  I must be doing something wrong.

Don


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## cds4byu (Dec 22, 2018)

Yeah, you need to have the escapement set so that the rubber band comes off when the escapement is in place.  I checked out a commercially produced multi-shot rubber band gun, and it used an escapement mechanism, coupled with a rubber-band lifter connected to the trigger.  I may take a look at your system and see if I can figure out how to design such a mechanism for your gun.

Carl


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## Cogsy (Dec 22, 2018)

My post yesterday was a bit brief as I was dealing with a horrible toothache that started while I was typing. Again, it's difficult to tell from just the drawing, but to me it looks like the part of trigger 2 that acts on the sear to fire a 'round' must then release the sear to let it revolve exactly as the round is fired. If there is any delay in the trigger 2 holding the sear after the round is fired the hammer will freewheel from the tension of the next loaded rounds and the thing will go full auto. It looks like trigger 2 can/does pivot downwards as the sear resets, but to my eye the sear cannot put the downward force on trigger 2 until the catch that activates the sear has released. I think this timing is wrong and that's giving you the issue.

I don't know the terminology for it, but how about a sear that has a sort or 'U' shape? So as the sear is rotated to fire a round, the back portion of the 'U' becomes a stop for the hammer wheel so it can only rotate enough to release one band and holds the hammer wheel at roughly 3/4 cock. Then as the sear rotates back to position the back part of the U releases the wheel and it is caught by the front of the sear at full cock, ready to fire again. I could draw it easier than I can explain it, but hopefully you get my meaning.


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## ddmckee54 (Dec 26, 2018)

Cogsy:

I was trying to get the sear to release the hammer with a single action, I have since given that up.  I HAD the internals re-designed by late Christmas Eve when I decided to make one final change.  I should have left good enough alone, that last change caused the software to lock-up and I lost all my work.  I've been working with computers for decades, and I STILL haven't learned that I need to save  - OFTEN!!!

Between having to re-create my work and needing to do some emergency printer repairs, I didn't get the printer running again until late on the 25th.  With all the changes, I have to print everything over, there isn't one part of this RBG that didn't get modified, even the hammer.  I went back to a multi-part hammer because it just prints better that way, but I did modify it to make the assembly easier.

I printed the frame halves yesterday and I'm going to print the internal parts tonight when I get home, according to the slicing software they should take about an hour to print.  Then we'll find out if the latest idea is a winner, or if I just got another paperweight.

During the day the printer is busy cranking out gift/puzzle boxes for Christmas presents.  It's printing the last one now, takes about 8 hours to print.

Don


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## willray (Dec 27, 2018)

You could either use, as others have said, an escapement mechanism so that the wheel is trapped into only "one band" rotations, or, you need a mechanism to definitively move the trigger2 bar off the sear, so that only the hammer/wheel is supporting the sear and preventing it from rolling back.

Weak leverage pulling the sear back into position might contribute, but, your larger problem is that once the trigger2 bar pushes the sear far enough that it disengages the wheel, it disengages the wheel - and it holds the sear disengaged.  It's not until the trigger moves far enough to let the sear begin to be supported by the hammer/wheel that there's any possibility of the sear falling back into the hammer notches.  If you manage to get that to work, it's only going to be by fiddly luck, and as tolerances and friction change, it'll almost certainly stop working and need readjustment.

The escapement mechanism is foolproof.   If you're determined to use just a plain single-disengagement sear, then you need to _force_ the trigger to disengage as soon as the hammer/wheel starts turning.  You could make the trigger2 bar "sprung" in an upwards direction, and add a link such that rotation of the hammer pushes the trigger-bar down, disengaging it from the sear and allowing the sear to come to rest on the hammer.  This is still fiddly but would allow the sear to ride the hammer and stop it at single-band rotational increments as you have envisioned the mechanism.


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## ddmckee54 (Dec 27, 2018)

We have a winner, I went with an escapement mechanism for the sear. Printed out the internal parts last night.  I had to do a little tweaking, files and razor saws are great for removing the offending extra bits of plastic.  I attached a picture of the test gun sitting on a CD jewel case.

I had two problems, first the sear wouldn't move far enough to release the hammer/wheel.  I must have modified that part of the sear and not realized that I had changed it.  Second, once I got the wheel to release, the trigger bar wasn't rotating the sear enough to release the wheel.  I put a couple of windows in one of the frame halves so that I could see what was happening.  I had a ramp that pushed the trigger bar down to ensure that the sear was released to return to it's normal position.  The ramp was causing the trigger bar to release the sear too soon.  I removed the offending ramp and I now have a functioning 6 shot semi-automatic rubber band gun.

I'm using #16 rubber bands, they are too large but they were all I could get at the office supply store.  I've ordered some #12's ands some #10's to see which will work best. 

Last night I copied the internal parts of the test-bed gun into the 3D model of the Colt 1908, so I now should be able to print out the actual RBG's.

Don


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## ddmckee54 (Dec 29, 2018)

I printed out the real version of the RBG, damned thing don’t work.  When I checked into what was going on I discovered that I hadn’t modified the sear properly.  There are two tabs on the sear that catch the hammer/wheel.  One releases the wheel and the other holds it in a half released position, about 30° rotation, until the trigger is fully pulled.  At that point the sear will slide past the trigger bar and snap back to its’ normal position.

On my test version I cut and filed this catch to make it work.  I modified the sear’s print file before I reprinted everything, but I didn’t give it enough clearance – it still wouldn’t release the hammer.  I then scribed where I had cut/filed the test sear onto the newly printed version, intending to measure how much more it needed to be modified.  Turns out there were no flat surfaces that I could get an accurate measurement from so I had to guestimate them.  I wasn’t right, but it’s real hard to guess at a 0.5-0.75mm distance, especially for an Imperial guy.  I really had cut it off twice and it was still too short.

Now if I fully load the RBG the damned thing shotguns, releasing all of the bands at once.  However with just 2 bands loaded, it dry fires just like it’s supposed to - so I’m real close.  Hopefully all I have to do is modify the sear one more time and this thing will be ready to print multiple copies.

Don


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## ddmckee54 (Dec 31, 2018)

I did a little "gunsmithing" yesterday, I now have a working prototype 6 shot, semi-automatic, Colt 1908 rubber band gun.

The attached picture is a family shot of the working prototype and "most" of the reject pieces.  Counting the versions that are in the gun, I made 2 versions of the trigger bar, 4 versions of the trigger, and 6 versions of the sear.  Plus 2 versions of both the left and the right half of the frame which aren't shown in the attached picture.  This was all to fix 2 problems, the shot-gunning problem that you already know about, and the problem of the trigger jamming.

The first modified version of the sear fixed the shot-gunning problem.  From then on it was trying to determine why the trigger would jam, usually in the fully pulled position.  It took me a long time to determine that the rubber band used hold the trigger bar up was getting pinched between the trigger bar and the sides of the frame.  The trigger bar runs through a cavity in the frame, there's some clearance, but not too much since the cavity is used to keep the trigger bar and sear in approximately the same plane.  I increased the depth of the cavity at the trigger end to allow room for the rubber band, while keeping the original depth at the sear end so that the sear and trigger bar stay lined up.

This mostly worked, the trigger no longer jammed in the fully pulled position, but it didn't ALWAYS return to it's normal position.  This I eventually tracked down to the trigger catching in the surface of the frame.

The way that I  print the frame halves is with the outside surface up, and the flat inner surface on the print bed.  This gives me the best surface finish on the outside where it is most exposed.  Unfortunately this also means that the first printed layer over all of the required cavities will be a "bridge".  I don't care what 3D printer you've got, the bottom side of a bridge layer will be a corduroy surface at best.  I finally figured out that the square leading edge of trigger was sometimes catching on this corduroy surface.  I radiused the leading edges of the trigger where they contact the sidewalls, and problem solved.

Don


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## Cogsy (Jan 1, 2019)

Looks good - how about a video of it in action?


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## ddmckee54 (Jan 2, 2019)

Cogsy:

You'd need steadier hands than I've got to do that.

My original intention with the Colt was to unilaterally arm my nieces, nephews, great-nieces and great-nephews this Christmas, we're gong to be getting together when my brother comes up from Mississippi in a couple of weeks.  When it didn't look like I'd get the bugs worked out in time I went to Plan-B and printed out some puzzle boxes instead.  The plan now is to take the prototype along and I'll take orders for the rubber band guns.  That way "mom and dad" have a say in whether or not the kids are armed.

I expect that there'll be a little "field-testing" by the kids and maybe we can get some video of that. 

Don


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## Cogsy (Jan 2, 2019)

I once printed out a puzzle box for my kids. Basically a round tube with a maze on it that slides inside a hexagonal tube with a locating lug. The idea was you have to solve the maze blind to get the tubes to separate and get to the rewards inside. I chucked some cash in there and let my kids loose, not really expecting they'd solve it. 10 minutes later they had it apart and pocketed my cash! Turns out the locating pin wore down very quickly as they worked it and it eroded enough that it wouldn't engage again. One of these days I'll have a look at fitting an improved locating pin without showing its location on the outside.


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## ddmckee54 (Jan 3, 2019)

The puzzle box you described sounds a lot like the ones that I printed.  Especially since the first one that I printed did about the same thing as you described.  However, I beefed up both the number of perimeters and the infill percentage and I haven't had that problem since.


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## cds4byu (Mar 20, 2021)

ddmckee54 said:


> I did a little "gunsmithing" yesterday, I now have a working prototype 6 shot, semi-automatic, Colt 1908 rubber band gun.
> 
> The attached picture is a family shot of the working prototype and "most" of the reject pieces.  Counting the versions that are in the gun, I made 2 versions of the trigger bar, 4 versions of the trigger, and 6 versions of the sear.  Plus 2 versions of both the left and the right half of the frame which aren't shown in the attached picture.  This was all to fix 2 problems, the shot-gunning problem that you already know about, and the problem of the trigger jamming.
> 
> ...


Don, 

Do you have any files available for the final gun?
Carl


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## ddmckee54 (Mar 22, 2021)

Carl:

I can dig up the STL files.  The CAD files probably won't help you much, I use Designspark 3D as my CAD.  It uses Rsdoc as its' file format and I'm not sure if I can save them in any other useful format.  I'll check on saving the CAD to a different file format when I get home tonight.

I could probably post the STL files here, or PM me and I'll send you the files.  These files will be for Colt 1908 wannabee.  If I remember correctly it takes about 7-8 hours to print the parts, I usually print at 60mm/sec so YMMV.  It takes a couple of hours to clean and assemble the parts after printing, and then do a little gun-smithing to get it to work reliably.  The fasteners I used were M3 button-head cap screws nuts.  I used a piece of 4mm OD brass tubing for the rubber band wheel axle.  It uses #10 rubber bands for both the ammo and the springs.

Don


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## cds4byu (Mar 22, 2021)

Looks like DesignSpark only creates STEP/IGES files if you buy the paid Exchange add-on module, which goes for the low price of $558!

But DesignSpark Mechanical is free, so I could open the files in DesignSpark if I wanted to.

The STL files would be nice.

I'll send you a PM.

THanks,

Carl


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