Author Topic: Gifts for relatives  (Read 2211 times)

Offline ddmckee54

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Gifts for relatives
« on: December 13, 2018, 02:35:22 PM »
Last year I made 3D printed fidget spinners for the nieces/nephews/great-nieces/great-nephews/whoever, this year I'm stepping it up a notch.  This year I'm going to arm them with rubber band guns.  I mean EVERYBODY needs to be able to defend themselves from the younger sibling that suddenly turns into a flesh eating zombie, right?  And you've got to be able to defend yourself when your older sibling turns into a snarling, drooling monster, right?  Mom and dad HAVE to be able to defend themselves from and the kids, right?

I think something the size of a Colt 1908 .25 caliber pistol would be just about right.  Small enough to be able to hide and still big enough to get the job done.  I wasn't able to find any blue-prints/drawings for the Colt 1908, but I did find a photo on blueprints.com.  The pistol is supposed to be 114.5mm long in the real world.  In the photo, at 100% size, it measures at about 120mm - close enough!

I just got this wild hair brilliant idea last night so I haven't completed enough of the design to be able to share anything yet.  I'm still learning how to work in a 3D world after 50+ years working in a 2D world.  Hopefully tomorrow I'll have something to show for my efforts.

Don
Too many irons, not enough fire.

Offline CHA5

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Re: Gifts for relatives
« Reply #1 on: December 14, 2018, 12:15:33 AM »
Are you looking for something like this :

https://www.thingiverse.com/thing:2294973

We used to make rubber band rifles out of a length of wood with a clothes peg for the trigger. When you tied a knot in the end of the band you could insert a chewed up piece of paper as ammunition.

This was great fun until 'handbags' lost his right eye. 50yrs later & he'll still chase you holding his glass replacement.

I thought we stopped giving kids toy guns in the 80's?

Last year, rather than just stuff cash in an envelope, I printed off several of these & stuffed a £20 reward inside (inflation) & handed them out at the big get together pre-xmas. It was amazing to watch them, all sat huddled together in a race to be the first to crack the puzzle.

https://www.thingiverse.com/thing:201097


Offline ddmckee54

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Re: Gifts for relatives
« Reply #2 on: December 14, 2018, 02:11:56 PM »
The kids are in a family of hunters/sport-shooters, and all are introduced to gun safety at an early age - even rubber band guns.

Besides, I'm of the opinion that great-uncles, corporate engineers, and seagulls are all birds of a feather.  We fly in, we squawk a lot, we sh*t all over everything, and then we leave.  I also plan to check with the parents before I actually commit to printing a bunch of these.

I've attached a PDF of what my version of the Colt 1908 will look like.  The blue artifact blocking half of the trigger guard is due to me forgetting that when I export a model to 3D PDF, the software exports EVERYTHING - not just the layers/objects that I have turned on.

I'm going to try printing a prototype this weekend to see what needs to be tweaked.

Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Gifts for relatives
« Reply #3 on: December 17, 2018, 02:52:54 PM »
CHA5:

I thought I was a trouble-maker but you sir are pure evil.  I printed one of your infernal gift boxes Friday night, and I can proudly say that I have assembled it - twice.  I got it apart once, but I think that was pure luck since I haven't been able to manage a repeat performance.

I'm printing them for the kids, it'll keep 'em busy for a while.  It takes about 8 hours to complete the print, so I start a print before I leave for work.

My rubber band gun prototype failed miserably.  It dry-cycled just fine, but when I loaded it with rubber bands, it wouldn't release consistently.   Sometimes it would work properly for 4-5 shots, sometimes it wouldn't fire at all, and sometimes it would fire all the rounds at once.  I'm still working on the rubber band guns, but I need to re-design the internals.  I suspect that the fiddly itty-bitty springs are the culprit so I'm getting rid of them.  Plus I lost 4-5 of the little buggers in the multiple times that I assembled/dis-assembled the prototype, so they gotta go.

I printed the next generation of the frame for the prototype last night, and I'll print the internals tonight.  We'll see if I've got a winner or just another dud.

Don
Too many irons, not enough fire.

Offline CHA5

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Re: Gifts for relatives
« Reply #4 on: December 18, 2018, 01:24:00 AM »
CHA5:

I thought I was a trouble-maker but you sir are pure evil.  I printed one of your infernal gift boxes Friday night, and I can proudly say that I have assembled it - twice.  I got it apart once, but I think that was pure luck since I haven't been able to manage a repeat performance.

I'm printing them for the kids, it'll keep 'em busy for a while.  It takes about 8 hours to complete the print, so I start a print before I leave for work.


If you map out the path with a felt pen onto your own secret internal, which the kids need never know exists, then it's much easier to solve. I actually had it in memory last xmas. I suspect they'll abandon the £20 & run away & hide if I try similar this year :-)

Rather than try to get a rubber band gun working reliably, how about something simples . . . like a Xbow?

My mate often wraps his kids pocket money around arrows, which he shoots 100's of yards out into the fields !

Offline ddmckee54

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Re: Gifts for relatives
« Reply #5 on: December 18, 2018, 01:34:47 PM »
When I printed the second gift box, I used it as a map to open the first.  I haven't got the solution committed to memory yet, but I will.

I re-designed the internals for the rubber band gun and I'm getting much more reliable operation.  It's still not working properly, as the hammer/wheel it tends to pinch the rubber band between the wheel and the frame.  I think I just a simple fix away from my goal now.  I want to get this figured out, because what started this whole mess was me deciding - a long time ago -  to build a clip fed semi-automatic rubber band gun.   I'm close to getting a reliable firing mechanism, now I've got to get the clip part worked out.

Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Gifts for relatives
« Reply #6 on: December 21, 2018, 02:29:31 PM »
There's still no joy in Mudville, and I still don't have pictures - but I've got cartoons.

The first attachment is the bitmap of the working bits of my test RBG.  It shows the RH side of the test Frame, the Hammer/wheel, the Sear, the Trigger and the link between the trigger and the sear - Trigger2.  For some reason, that I have yet to figure out, I cannot change the layer/color of 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 thing 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 no 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 gun 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 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 stopping 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.

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

Don
Too many irons, not enough fire.

Offline WeldingRod

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Re: Gifts for relatives
« Reply #7 on: December 21, 2018, 10:24:44 PM »
It looks like your trigger2 might be holding the sear open.  You might want to dream something closer to an escapement, so you get one tooth per pull.
Or come up with something so the the sear can return to position without interference from the trigger bits.
A thought:  a double sear.  One sear cycles with the firing pull.  The second sear catches the wheel after the first releases.  Then the first sear has time to reset.  Releasing the trigger pops the second sear, putting the wheel onto the first sear and ready to fire again.


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Offline ddmckee54

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Re: Gifts for relatives
« Reply #8 on: December 22, 2018, 09:55:34 AM »
When the trigger is pulled back to the stop Trigger2 slides past the Sear.  The Sear then has the clearance it needs to swing back into the stop position.  But you may be right, Trigger2 may not be releasing the Sear soon enough.  I'll have to look at the geometry of where I've got Trigger2 releasing the Sear.  I've probably got too much time overlap between hammer release and sear release.  Back to the proverbial drawing board to see what this looks like.

I thought about using an escapement, but I must have some type of a problem with that.  I may be doing something wrong because every time I try an escapement, the design I come up with releases the rubber band on trigger release not trigger pull - and that just feels backwards to me.  The escapement location may wrong maybe, but there's not a lot of interior room in this thing - it's only 120mm X 80mm X 25mm max.

My whole problem may be that I'm starting with a gun and trying to fit the guts into it.  Maybe I should start with the guts and when I've got them working, fit a gun around them.

Don

 
Too many irons, not enough fire.

Offline ddmckee54

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Re: Gifts for relatives
« Reply #9 on: December 26, 2018, 03:18:48 PM »
I tried adding a lever to the sear, all I got for my efforts was another paperweight.  I've got it re-designed - again, and I've printed both frame halves.  I'll print the internal parts tonight and we'll see if I add another paperweight to the pile.  Maybe I'll get really lucky and it'll work this time.

I think I figured out what my problem with the escapement was, I was trying to keep the trigger and the escapement linked together all the time.  This time around I'm using the trigger to release the sear/escapement which in turn, lets the wheel cycle through only one tooth on the wheel.  It takes the forward and backward movement of the sear/escapement to cycle through each tooth.

I know pictures or even cartoons would help this explanation, but I don't have any right now.  If this works I'll show what it looks like.  If it doesn't work I'll probably show you what is looks like, and I'll be wondering what I did wrong this time.

Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Gifts for relatives
« Reply #10 on: December 27, 2018, 10:23:55 AM »
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 and 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
« Last Edit: December 28, 2018, 09:52:30 AM by ddmckee54 »
Too many irons, not enough fire.

Offline Alphawolf45

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Re: Gifts for relatives
« Reply #11 on: December 27, 2018, 08:15:44 PM »
 My first "gun" was a single shot rubber band firing contraption that looked nothing as nice at this one.
  I hope to see you develop a mag fed repeater.. That would be awesome. Per your own words-  I want to get this figured out, because what started this whole mess was me deciding - a long time ago -  to build a clip fed semi-automatic rubber band gun.   I'm close to getting a reliable firing mechanism, now I've got to get the clip part worked out.
    I scratch build actual rifles and pistols for serious  competition but the interest that I have begun as a child with rubber band pistols and later it was spring fired small shafts with suction cup tips.. Then a BB gun and then pellet rifle and finally actual smokeless powder firearms.. You may be starting a junior or two onto a lifelong appreciation of firearms. Good for you!
I am not actually retired ,I merely find myself disabled by an intolerance for productive activity.

Offline ddmckee54

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Re: Gifts for relatives
« Reply #12 on: December 29, 2018, 09:33:13 AM »
I printed out the real version of the RBG, damned thing donít work.  When I checked into what was going on I discovered that I hadnít 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 30į rotation, until the trigger is fully pulled.  At that point the sear will slide past the trigger bar and snap back to itsí normal position.

On my test version I cut and filed this catch to make it work.  I modified the searís print file before I reprinted everything, but I didnít give it enough clearance Ė it still wouldnít 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 wasnít right, but itís 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 itís supposed to - so Iím 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

Too many irons, not enough fire.

Offline ddmckee54

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Re: Gifts for relatives
« Reply #13 on: December 31, 2018, 12:33:36 PM »
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
Too many irons, not enough fire.

Offline ddmckee54

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Re: Gifts for relatives
« Reply #14 on: February 06, 2019, 02:19:47 PM »
OK, time to fess up.

When I started this project for the relatives, my original intention was not to arm the great nephews and great niece for a parental insurrection - that was just a perk.  The real reason was more self-centered.  Sitting way back on the back burner is a project that's more or less for my own funsies.  I'm designing/printing/building a 1:1 mostly scale replica of a Walther's PPK.  I wanted it to resemble a PPK, be semi-automatic, have the same capacity of "ammo", and be clip-fed.

I took the guts of my PPK as the first iteration of the Colt 1908.  Since that design didn't work in the Colt, I know it won't work in the PPK.  Now that I've got a working design in the Colt, I need to start transitioning that design back into the PPK.  I wound up moving bits and pieces around a lot in the Colt, so I won't know if that transition is actually possible until I actually fire up the CAD software.

I'm currently  using the slide of the PPK as the "clip".  I want to try and keep this feature since it seems like the simplest way to pre-load the rubber bands.  Loading the rubber bands is a fairly slow process and I can appreciate why the early gun designers wanted to have some form of rapid re-loading system.

I'm going to play around with the 3D CAD a little and see how difficult getting the working Colt hammer/trigger group design into the PPK is actually going to be - while still keeping the slide as the "clip".

Don
Too many irons, not enough fire.