author
16Instructables235,229Views90CommentsChicago, ILJoined September 18th, 2014
I'm a professor of physics and astronomy at Northwestern University. I do a lot of hobbies, including amateur astronomy, woodworking, and Lego modeling among many others.

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Epilog Challenge 9
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Audio Contest 2018
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Tiny Home Contest
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Explore Science Contest
Contest Winner Second Prize in the Explore Science Contest
Homemade Gifts Contest 2017
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  • gravitino commented on gravitino's instructable Falling Sand Art Picture Repair1 day ago
    Falling Sand Art Picture Repair

    I'm glad you found it useful! I was just looking at mine and it is time to fix it again. I'm also glad I wrote it up so I know what to do now!

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  • Wide Angle Reflex Finder for Amateur Astronomers

    Yay! I'm going to try and build one for my next scope project. I've never 3D printed before, so that will be new for me. My library has a print service, so I'm going to talk to them about it. I'll let you know how it turns out, and post here when i've done it. :-)

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    thank you! I'm glad you enjoyed it!

    I'm glad you enjoyed it! I added a new step with a few pictures of the Moon, which are all I have taken through Mariner (using my phone).

    I added a new step with a few pictures of the Moon, which are all I have taken through Mariner (using my phone). Most everything else is too hard to photograph with my phone, though you could upgrade the scope to be used for astrophotography.

    I added a new step with a few pictures of the Moon, which are all I have taken through Mariner (using my phone). I'm glad you liked the project!

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    • Cosmos Mariner: a Large Aperture Dobsonian Telescope
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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    Thanks! I'm glad you liked it.

    Thank you! I'm glad you enjoyed the instructable!

    It was definitely a lot more work than building the smaller one. As they get larger, it is harder to engineer them out of wood, though I do know of examples that are in the 36-inch range and made out of wood. A famous example is Tom Clark's "Yard Scope" (the mirror is a yard across!). https://www.cloudynights.com/gallery/image/22005-the-yard-scope-ii/

    Thanks! It was fun to build; hopefully it is all clear! The skies too (though not right now!). :-)

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    Yep, aperture fever is costly. :-( I don't have an instructable for Equinox because I built it so long ago, but the procedure is essentially the same outlined here, just scaled down to the size of the 12-inch mirror. You can do a scope like Equinox for probably less than $1000 -- the main cost is always the primary mirror. It looks like Agena Astro has 12-inch mirrors for $500. https://agenaastro.com/parts-accessories/mirrors-holders/primary-mirrors.html

    Wow! I never got to meet Dobson! I've heard a lot about him; it would have been fun to attend one of his classes!

    Thank you! It was fun, and it is fun to observe with too! Glad you enjoyed it!

    This was on the order of $10,000 when all was said and done (over half of that for the mirror). Motorizing is done easiest with an equatorial table; there are a couple of other comment threads below about that, but I just discovered last night there are a couple of nice Instructables about making equatorial tables. This one looks promising: https://www.instructables.com/id/Equatorial-Platform-for-the-North/

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    So you can make (or purchase) dual axis drives like you suggest, but operation is a bit more complicated because the two axes have to be driven simultaneously, but the rate and direction each one needs to drive at depends on where the scope is pointing in the sky. For instance, consider a star in the southeast sky. Viewed from above, the azimuth needs to rotate clockwise, and the atltitude bearing needs to lift the scope to track. For a star in the southwest sky, the azimuth again needs to rotate clockwise, but now the altitude bearings need to lower the scope. Systems like this usually need a central brain (computer) to figure out the right thing to do, and need to be alighned at startup. By contrast, an equatorial table preserves the elegance of the Dob bearings you note — the Dob si...

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    So you can make (or purchase) dual axis drives like you suggest, but operation is a bit more complicated because the two axes have to be driven simultaneously, but the rate and direction each one needs to drive at depends on where the scope is pointing in the sky. For instance, consider a star in the southeast sky. Viewed from above, the azimuth needs to rotate clockwise, and the atltitude bearing needs to lift the scope to track. For a star in the southwest sky, the azimuth again needs to rotate clockwise, but now the altitude bearings need to lower the scope. Systems like this usually need a central brain (computer) to figure out the right thing to do, and need to be alighned at startup. By contrast, an equatorial table preserves the elegance of the Dob bearings you note — the Dob sits on the table and still points using its altitude and azimuth bearings, but the table simple turns to track the stars. They are low and quite elegant. Here is a good example of one: http://www.reinervogel.net/index_e.html?/Plattform/Plattform_e.html

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  • gravitino commented on gravitino's instructable Barncaster Electric Guitar15 days ago
    Barncaster Electric Guitar

    A standard telecaster body is just under 16-inches in the long dimension, and just over 12.75 inches in the short dimension. I cut my boards long (maybe 17-inches?), but only had 13-inch wide across the body after I glued the reclaimed panels together, so that was the tightest constraint. For the thickness, I planed everything before I glued it (step 6) to give me the thickness of 1-5/8 inches. Standard telecaster thickness is 1.75" according to blueprints, but many custom shops make them 1.5" (thickness of dimensional lumber). I had a cardboard template I was using to lay on the wood at each stage to make sure I had the grain I wanted in the right places and to make sure I had the full shape!

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  • Wide Angle Reflex Finder for Amateur Astronomers

    This is really excellent. I always hack my Telrads and put a pulser in them, so it's great to see that built in. The wider rings will also be a great help, especially under moderately light polluted skies. I have a couple of questions:(1) What are the overall dimensions? I was wondering if my dew shield for my Telrad will fit this (I use the one from Astrosystems).(2) What do you do for the base? Does it fit in the standard Telrad base? It looks like you have a custom rail in step 6.Great build!

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    I'm always glad to hear when people fix their telescopes! It means you'll get out under the stars more! :-) I'm glad you enjoyed the instructable.

    No, I'm a completely visual observer. I keep notes about what I see and sometimes make (crummy) sketches, but don't do any astrophotography through the telescope (I will sometimes hold my phone up and snap a pic of the Moon, but I don't have any I'm sure came from Mariner). However, the views are *STUNNING*. I long ago finished my Messier Catalog with my smaller scopes, but the amount of more detail that can be seen with Mariner is amazing (eg. spiral arms on galaxies!), so I'm slowing revisting things I've already seen before just to look at them again. :-) I'm glad you like the instructable!

    Thanks! I'm glad you enjoyed it. Clear skies!

    Good question. I don't have any tracking. I work between 60x and 120x normally, and things stay in the field for a minute or more. To track along you just give it a bit of a bump; after observing with Dobsonians for so long, it's quite natural to track along. The easiest way to add tracking is to build an "equatorial table" -- I've thought about it, but it would require having power in the field to drive the motor. I've been fine so far. :-)

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    • Sonification of Gravitational Waves With Lego Mindstorms EV3
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  • Sonification of Gravitational Waves With Lego Mindstorms EV3

    I'm glad you enjoyed the instructable! Yes, it is calculated directly from a physical model, though I've done some streamlining (mostly factoring out constants and setting them equal to 1, since the true physical numbers are tiny). I'll see if I can boil the basics down to a 1 page PDF and add it to the instructable. You can certainly do it in Matlab/Octave or other environment. Most of us do it in python or Mathematica. The event you speak of was the first LIGO detection (there is a link to the detection page in Step 1). For those interested, you can download all of the data from all of our events at the Gravitational-Wave Open Science Center: http://gw-openscience.orgYou will also find there: tutorials on analysis, explanations of the events, and audio for each of the events we've d...

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    I'm glad you enjoyed the instructable! Yes, it is calculated directly from a physical model, though I've done some streamlining (mostly factoring out constants and setting them equal to 1, since the true physical numbers are tiny). I'll see if I can boil the basics down to a 1 page PDF and add it to the instructable. You can certainly do it in Matlab/Octave or other environment. Most of us do it in python or Mathematica. The event you speak of was the first LIGO detection (there is a link to the detection page in Step 1). For those interested, you can download all of the data from all of our events at the Gravitational-Wave Open Science Center: http://gw-openscience.orgYou will also find there: tutorials on analysis, explanations of the events, and audio for each of the events we've detected that we make with our professional tools (that page is here: https://www.gw-openscience.org/audio/ ).Have fun!

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  • gravitino's entry A Tiny Telescope Observatory is a winner in the Tiny Home Contest contest 2 months ago
  • gravitino commented on makeorbreakshop's instructable How to Make a Rubber Stamp2 months ago
    How to Make a Rubber Stamp

    Nice one. I've been thinking about doing this sort of fine scale carving with my xCarve but in some tests (trying to etch on anodized metal) I'm struggling with the right thing to do to get fine details, like around the "and" in your logo. So I have two questions: (1) The way you carved this with the V-big -- you did all the large areas with the V-point? So it just had to make a jillion passes? (2) You said you might do it with an end mill first -- would you have a separate pattern to do the large areas, then one like this for the fine patterns with the V-bit? Thanks! Nice instructable!

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  • gravitino commented on gravitino's instructable A Tiny Telescope Observatory2 months ago
    A Tiny Telescope Observatory

    Yep, I built both my telescopes (the one in my profile pic, and the one in the observatory). They've been very dependable. :-) Glad you liked the build.

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  • gravitino's entry A Tiny Telescope Observatory is a finalist in the Tiny Home Contest contest 2 months ago
  • gravitino commented on bcrocker1's instructable Truck Camper Platform/Bed2 months ago
    Truck Camper Platform/Bed

    This is great! I've been thinking about this in my Tundra to make camping quick and easy. I've been trying to find a high rise shell like the 122 you used. How much headroom do you have from the top of your rails to the top of the shell? Great build!

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  • gravitino commented on gravitino's instructable A Tiny Telescope Observatory2 months ago
    A Tiny Telescope Observatory

    Thank you! I'm glad you enjoyed it!

    Lol! Of course, I never get much sleep if I'm out observing. :-) When I built this one, my wife said "There are worse things you could be doing!" I hope you build one -- if you do, make sure to show us the result here on Instructables!

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  • gravitino's instructable A Tiny Telescope Observatory's weekly stats: 2 months ago
    • A Tiny Telescope Observatory
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  • gravitino commented on gravitino's instructable A Tiny Telescope Observatory2 months ago
    A Tiny Telescope Observatory

    The lock is "to keep the honest people honest." With only single panel wood for construction, I decided there are any number of ways that someone could destructively get into the observatory if they really wanted to. Popping the roof is one, as you note, though it would be at the cost of destroying the overlapping ridge panel. It also would be difficult to get the telescope out that way, as you'd have to lift it over the wall!

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  • gravitino commented on gravitino's instructable A Tiny Telescope Observatory2 months ago
    A Tiny Telescope Observatory

    Hi Stephen, I'm a completely visual observer, so I don't have the constraints of the photography crowd. IN practice, the floor is a bit over-built, and the observatory is so small there are seldom people walking around inside, so I get very little transfer from the floor to the scope. In the Note to MarkF147 below, I put a picture of another observatory I built where I put the Dob on a wooden pier (because people could walk around), and it worked just fine for visual work. If I was going to do photography, I would have done a pier, but didn't want to pour one. :-)

    That's a neat idea; I've never seen lift-off ends, though I have seen people fold the peak down (typically the south wall). In this case, given the light I have in the north and south, I'm not sure I needed to do that. But I'll put that idea down for the next observatory... :-)

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  • gravitino commented on gravitino's instructable A Tiny Telescope Observatory2 months ago
    A Tiny Telescope Observatory

    My Dob is a 12.5" f/4.8 that I built when I was in graduate school. It's been a great scope, and is still the one I use most nights. I collapses down in the style of many truss style Dobsonians into just the lower cube of the mirror box, and can easily be transported in a car. Looking at zenith I can look through the eyepiece without a ladder, though I keep a short two-step ladder around because I can't quite get to my finder when it's pointing straight up (though it has a Telrad too, which I use most often).

    The roof cap is a piece of 4" x 4" step flashing. You'll find it with the corrugated metal roofing at your hardware store, and is meant to seal the top of a metal roof, kind of in the fashion that I've used it here; the difference is I've only bolted it down on one side of the roof ridgeline. If you look at the 4th picture in step 7, you see the inverted "wavy wood" piece I put on top of the corrugated roof panel? That's where all the sealing is happening. When the roof is closed, that is the piece the ridge cap rests on, providing a seal. You could probably put a line of weather stripping on it, but I never had anything make it through. The only issue is at the ends, where there is a small hollow, but the rails I hung the counterweights on covered gaps there. I'm a...

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    The roof cap is a piece of 4" x 4" step flashing. You'll find it with the corrugated metal roofing at your hardware store, and is meant to seal the top of a metal roof, kind of in the fashion that I've used it here; the difference is I've only bolted it down on one side of the roof ridgeline. If you look at the 4th picture in step 7, you see the inverted "wavy wood" piece I put on top of the corrugated roof panel? That's where all the sealing is happening. When the roof is closed, that is the piece the ridge cap rests on, providing a seal. You could probably put a line of weather stripping on it, but I never had anything make it through. The only issue is at the ends, where there is a small hollow, but the rails I hung the counterweights on covered gaps there. I'm attaching a quick diagram to this comment -- does it help show how it works?

    My neighbors all know it's a scope and observatory. I think the lights get left on by habit or accident, and at midnight I don't think I should be knocking on doors! My improvised screen works pretty well for the times it happens. But you're absolutely right -- having an impromptu star party for your neighbors does wonders for relations. :-)

    Far and away the best thing to do would be to pour a pier for the Schmidt-Cassegraine -- that is not an uncommon practice in amateur observatories. You need to bury it past the frost line, make sure it is reinforced with mesh/rebar, and pour it to a convenient height for your needs. At the top, as you note, you'll have to put lugs in that will match a wedge or interface plate for your scope. The big deal there is the permanence, as you note. If you want to stick with your tripod, you can isolate it with a little more wood working. If you're doing photography with your scope, I think that is the right way to go. If you're just using your eyeballs though, the tripod is probably easier. I built another observatory where I did that for the Dob by building a platform in the center of the obs...

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    Far and away the best thing to do would be to pour a pier for the Schmidt-Cassegraine -- that is not an uncommon practice in amateur observatories. You need to bury it past the frost line, make sure it is reinforced with mesh/rebar, and pour it to a convenient height for your needs. At the top, as you note, you'll have to put lugs in that will match a wedge or interface plate for your scope. The big deal there is the permanence, as you note. If you want to stick with your tripod, you can isolate it with a little more wood working. If you're doing photography with your scope, I think that is the right way to go. If you're just using your eyeballs though, the tripod is probably easier. I built another observatory where I did that for the Dob by building a platform in the center of the observatory. I framed the floor joists around an open square, then built a mini frame of joists that sat in the square on its own footings that went to the ground. I put weather stripping around where the mini-frame and the main floor joists interfaced to keep critters and bugs out. It worked pretty well; you could probably do something similar with your tripod footing. I clipped together some old photos to show the framing, and the only shot I have that shows the footings.

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  • gravitino commented on gravitino's instructable A Tiny Telescope Observatory2 months ago
    A Tiny Telescope Observatory

    Mostly that choice was made to keep the walls low. If the center peak of the roof was tall, then either the walls would have been taller for the same size roof panels, or the roof panels would have been larger (steeper angle) and not able to (easily) rotate out of the way. Either way, they would have blocked more of the sky than I was willing to not have access to when the observatory was open. The scope can store either upright or horizontally. I actually have a protective cover I put over it at star parties, and I used it in the observatory as an extra layer of precaution. The natural storage state for that cover is horizontal, as you see in the photos.

    Thanks, I'm glad you liked it! I can't take credit for thinking of this, though. I was sketching out ideas for something that kind of worked like a dumbwaiter system with pulleys and suspended weights when I stumbled on this system on a few other observatories. It was very simple, and very effective. It worked so well, I've thought about doing it on a much larger observatory, though you'd probably have to have a steel frame instead of wood for larger weights.

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  • gravitino commented on gravitino's instructable A Tiny Telescope Observatory2 months ago
    A Tiny Telescope Observatory

    I'm glad you liked it!If I had been willing to expand the observatory to a full 10x10 size, I would have been within the permitting limits, and could have gone down below the current cut-offs I have. In practice, I haven't found the cut-offs to be that limiting for what I've been observing, so in the end it worked out just fine.One "improvement" I made is I put C-shaped electrical conduit brackets in each interior corner to hold vertical dowels -- my neighbor sometimes leaves his backlight on, so I just drape a black sheet between the dowels to shield me from the direct view of that light when it happens.Something I've been considering is that I use a red LED-light clipboard I made for notes and charts, but I was thinking I could mount a red LED light (kind of like musicians ...

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    I'm glad you liked it!If I had been willing to expand the observatory to a full 10x10 size, I would have been within the permitting limits, and could have gone down below the current cut-offs I have. In practice, I haven't found the cut-offs to be that limiting for what I've been observing, so in the end it worked out just fine.One "improvement" I made is I put C-shaped electrical conduit brackets in each interior corner to hold vertical dowels -- my neighbor sometimes leaves his backlight on, so I just drape a black sheet between the dowels to shield me from the direct view of that light when it happens.Something I've been considering is that I use a red LED-light clipboard I made for notes and charts, but I was thinking I could mount a red LED light (kind of like musicians have on their stands) on my chart table, and always have light when I need it -- it would be easy to wire up and tuck the electronics support under the board the chart table is made of.

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  • gravitino entered A Tiny Telescope Observatory in the Tiny Home Contest contest 2 months ago
  • gravitino's entry Barncaster Electric Guitar is a winner in the Trash to Treasure contest 7 months ago
  • gravitino's entry Barncaster Electric Guitar is a finalist in the Trash to Treasure contest 7 months ago
  • gravitino commented on gravitino's instructable Barncaster Electric Guitar7 months ago
    Barncaster Electric Guitar

    Thank you! I'm glad you liked it!

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  • gravitino commented on gravitino's instructable Barncaster Electric Guitar8 months ago
    Barncaster Electric Guitar

    That's a nice looking bass!

    Yes, it is fun to play -- I like the look and feel of it, and have been picking it up first (instead of my off the shelf Squier tele) since it has been done. :-) That is a nice looking guitar! How was making the neck?

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  • gravitino's instructable The Doodle Game's weekly stats: 8 months ago
    • The Doodle Game
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  • gravitino's entry Barncaster Electric Guitar is a winner in the Epilog Challenge 9 contest 8 months ago
  • gravitino entered The Doodle Game in the Paper Contest 2018 contest 8 months ago
  • gravitino commented on gravitino's instructable Falling Sand Art Picture Repair8 months ago
    Falling Sand Art Picture Repair

    I have always used distilled, and never had an issue in my sand pictures. I always shy away from tap water, because we are on well water that is high in minerals ("hard water") and I didn't want it in the art. In principle, distilled water is boiled off and then reclaimed from water vapor, so should be much lower in any sort of contaminants like minerals. If you ever heard why, I'd love to hear the reason!

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  • gravitino's instructable Barncaster Electric Guitar's weekly stats: 8 months ago
    • Barncaster Electric Guitar
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  • gravitino's entry Barncaster Electric Guitar is a finalist in the Epilog Challenge 9 contest 8 months ago
  • gravitino commented on gravitino's instructable Barncaster Electric Guitar8 months ago
    Barncaster Electric Guitar

    I've done this test before, and I apparently don't have a dominant eye -- it always splits the difference between my eyes. :-)

    Ha! Well, I'm not to the shredding yet. But soon... very soon! :-)

    Thanks an interesting idea to glue the screw head on. To be honest, I don't notice it is missing; I would be more worried if the bridge was wiggling around.

    I'm glad you liked it! It was a lot of fun to build; I'm humbled by how much everyone seems to like it. :-)

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  • gravitino commented on gravitino's instructable Barncaster Electric Guitar8 months ago
    Barncaster Electric Guitar

    I think it was always natural for me to pick it up left-handed so I did. I write right-handed, and I bat right-handed, but I do a whole bunch of other stuff lefty: guitar, shoot bows and rifles. Only a few things can I do with both hands -- I'm can shoot pistol both hands, and I think I could teach myself to write left-handed -- I'm not too bad. I've tried batting lefty and it is way hard. :-)

    Happy to be a bad influence on you. :-)

    Ah, excellent idea -- I kept the template, but hand't thought about trying to repair it. Will definitely do this. :-)

    I bought the neck (~$40), the controls (~$50), and pickups (~$100), so about $200 for the parts.

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  • gravitino commented on gravitino's instructable Barncaster Electric Guitar8 months ago
    Barncaster Electric Guitar

    Thanks! Finding the wood with some character was the fun part. :-)

    Thank you -- it was a learning process, so I hope all the detail helps other people try their own too.

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  • gravitino entered Barncaster Electric Guitar in the Trash to Treasure contest 8 months ago
  • gravitino entered Barncaster Electric Guitar in the Epilog Challenge 9 contest 8 months ago
  • gravitino commented on gravitino's instructable Barncaster Electric Guitar8 months ago
    Barncaster Electric Guitar

    Thanks! It was a lot of fun being able to make all my own choices for how it would look. :-)

    I entered it over there; it just hasn't appeared yet! I'm glad you enjoyed it -- this was a lot of fun!

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  • gravitino's entry Personalized Lapdesk is a winner in the Homemade Gifts Contest 2017 contest 10 months ago
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