It Don't Add Up

Being a hard-core fan of Doctor Who about ten years ago I set out to make a working sonic screwdriver and did a brilliant job of it. But somehow I lost both the screwdriver and the plans for it, so I'm rebuilding it from scratch and memory

What I am now noticing is that I had a 1" diameter part that screwed into a battery compartment made out of a five inch section of 1" schedule 40 aluminum pipe. Supposedly such pipe has an internal diameter of 1.049" yet the part made out of 1" round aluminum bar fit perfectly. Does anyone know if the inside diameter of Al pipe is actually smaller than it's stated value or is bar stock a little larger in diameter than the stated 1"?

Reply to
Ron Hubbard
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My experience with aluminum bar stock dictates it is on size, not over. Size is important so it can be held by collets and other restricted holding devices. Likewise, schedule 40 pipe is unlikely to be a good fit, it should be a generous amount oversized, by the .049" you mention. Is it possible you built it from tubing, not pipe? That makes sense. Or is it that you had that much clearance but don't recall correctly? I'm real good at false memory.

Harold

Reply to
Harold & Susan Vordos

Great! I would love to see that once you are done. Take photos for the Dropbox.

My Dr. Who Scarf (the full 20' one) finally fell victim to moths, unfortunately.

Sometimes either can happen. Did you measure to determine which is off of the specified size? Often bar stock will be a bit oversized so you can finish it nicely to precise size.

Enjoy, DoN.

Reply to
DoN. Nichols

As to sizing of bar stock, I've seen *remarkable* differences. For instance, some

5/8 round that measures .638, or 3/8 x 5/8 rec bar showing .367-.382 x .619-.628. Or some variation within those dimensions. That kind of thing happens even when ordering "same lot" material. Kaiser is generally the poorest quality both for size consistancy and profile, surfaces often being convex/concave, out of square (parallelogram), twisted, etc. I try to avoid Kaiser material whenever possible. Regardless of supplier, you can't be certain if stock will be a bit over or under. Unless, of course, you are counting on it being over, then it will definitely not be such.

michael

Reply to
michael

screwed

bar

pipe

little

restricted holding

fit, it

Or is it

I don't even remember much about the project except for all the running around I did going to machine shops getting each piece worked on. But I used nothing but 1" pipe and 1" round bar.

Whatever inner diameter of the schedule 40 pipe, I had enough room to have the 1" diameter piece pipe threaded and it fit perfectly with no play. It's only now in drawing the new specs do I begin to wonder why they fit assuming each piece of pipe and rod was the size they're supposed to be.

Ron

Reply to
Ron Hubbard

That's real interesting, Ron. The one place I've noticed considerable variation is material size is in hot rolled products, particularly in steel, but that's not what we're talking about in this case. I checked variations in wall thickness in schedule 40 and schedule 80, but that wouldn't account for the fit. I also checked Jorgensen's stock book to see if there's any aluminum tubing available, but they don't show anything with a 1-5/16 OD in aluminum, so you must have had a variation of sorts, be it pipe with a small bore or the 1" aluminum bar of which you spoke. Maybe both.

In checking mill tolerance on aluminum bar, extruded bar in 1" diameter has a tolerance of +/- .010" (which is not normally stock used for machining). Cold finished rod, or standard screw machine stock in 1" diameter has a tolerance of +/- .002". Neither of these would account for the fit you described, assuming the pipe was per spec.

Aluminum pipe under 2" has an external tolerance of +.015"/-.031", with a minimum variation of nominal wall thickness of 12-1/2% less, but nothing mentioned about a thicker wall. Assuming the wall could also be oversized (thicker) by the same tolerance, I can see how you could have possibly come close to the type of fit you described. Chances of a repeat may be slim, though.

Harold

Reply to
Harold & Susan Vordos

out

it.

Don., I don't think it will be any time soon. I really forgot how hard it was to design those four little pieces to fit together in the first place. There were, are, a lot of pictures of various versions of the screwdriver on the Net, but no detailed specs for any of them. Because of the electronics involved I had to use a lot of brain power to figure out how I could make the smallest casing and still get the circuitry and batteries to fit. And of course, still keep the traditional design.

Part of the problem is that you don't know the true size relationships between each section-- I had to consider where the electronics would go and still keep the ratio between each section intact and much of that was done by trial and error. Now I have to design it all over again and I have to say, this time it isn't that much fun the second time around. ;-)

Besides, the four main pieces cost me about $150 to $200 to be machined nearly ten years ago. I wonder what it's going to cost me these days.

Anyway it'll take a week or two just to finish the specs. If you like, I can email them to you when I'm done. At the moment most of them are finished, but there are still a few minor details I'm trying to remember and I am trying to decide on the traditional design for the end cap (a cone) or the kind of cylindrical cap shown in a picture where the fifth Doctor and Nyssa are holding up a subtly different but interesting looking screwdriver. I think it's a scene from Four To Doomsday if my memory serves me right (either that or a publicity still).

Ever go into a store and say you'd like to purchase a scarf maybe 12 to 16 feet long? It doesn't go well. So I went out and bought a cheapie knitting machine and less than two days later I had a 15' scarf; boy, I was creative back then.

Ron

Reply to
Ron Hubbard

Silly, too. ERS

Reply to
Eric R Snow

it, so

internal

aluminum

mention.

sense.

room

considerable

spoke. Maybe

Harold, that's what I am afraid of. It was a cheap and elegant answer to a design problem using tubing like that rather than lathing down !.250" aluminum bar down to size then boring it out and threading it. If I can't get the same kind of fit with stock material I'll have to redesign things. Greater flexibility using

1.250" aluminum bar but at greater cost and more time, work, and cost. As that horse on Ren & Stimpy used to say, "No, sir, I just don't like it." :-)

Ron

Reply to
Ron Hubbard

Of course.

I'll bet.

Where do you live? Hmm ... Germany. Not exactly next-door to most of us, and I've been reading things which suggest that hobby metalworking is relatively rare in Germany, so finding a hobby machinist is more of a problem. (Unless you come up with one in here.) Or are you simply using a German news server? If you are in the US, give us an idea where you are living (just roughly -- we don't need a detailed address) and perhaps someone near you will be interested in the project.

I would appreciate that -- but one caveat. Make sure that the final size of each e-mail is no larger than 30K (actually, probably better to aim for no larger than 25k, so the header growth doesn't push you past that limit). The reason for this is that I have configured my e-mail to reject anything larger than 30K in size, because the last large flood of virii was about 31K typical size. (They won't hurt my unix system, but they are a pain when 200+ arrive in a single day, and I have a couple of mailing lists hosted on this system, with lots of Windows users. Since I'm not in a position to feed everything through a virus scanner, this is the easiest way to protect them from themselves and each other. :-)

Unfortunately, the size limit is global -- I have no way to white-list it for individual mailers.

Hmm ... I will have to dig up my old books of pictures from the show, to see if I can spot any details.

A friend is a compulsive knitter, and my wife found the specs for the scarf (the red and dark purple version) from some other friends at a Science Fiction Con(vention), and they conspired to knit this for me in secret for a Christmas gift. She always had some other knitting project to hide it under whenever I came by. I didn't suspect a thing until they gave it to me. This qualifies as a serious surprise. (And she said "Never again!" after that much knitting.

Enjoy, DoN.

Reply to
DoN. Nichols

{snip of post}

Hey Don, Do you know of a place (too near Washington D.C.) that my wife, daughter, and family can park a vehicle for about 3 wks while they take a plane from Dulles to Europe that wont cost a small (not even very small) fortune? We are in Chatham VA now, they will be leaving on Tue. ...lew... Albuquerque. (been reading RCM for a long time)

Reply to
Lewis Hartswick

Sometimes hotels/motels will do that for a reasonable price (like 2 weeks free) if you buy a night's stay on the way there and/or back. They would have an airport shuttle too.

Best regards, Spehro Pefhany

Reply to
Spehro Pefhany

I've already answered the private e-mail copy of this.

Enjoy, DoN.

Reply to
DoN. Nichols

photos

how

section

that

shown

it's a

Hey! That scarf is my one concession to flamboyance and it attracts attention. A lot of people tell me how cool it is, and it especially gets the attention of the ladies. A 6'2" guy in a long colorful scarf beats a guy in z business suit any day. ;-)

Ron

Reply to
Ron Hubbard

photos

how

Germany? LOL! No, our nearest neighbor across the Columbia is Vancouver,Washington (USA) although I love to vacation further north in Vancouver, BC Canada. News. Cis. Dfn.De or whatever it's calling itself these days is a free news server open to anyone who registers, and has access to more than forty thousand news groups-- way more than what my ISP has to offer.

probably

Don't worry about that. Since I use a CAD program that's not Autocad compatible what I usually do in such situations is to print out a drawing then scan it and turn it into a ,jpg or .bmp image which shouldn't be more than a few kilobytes. If you have a really decent imaging program like Photo Impact Viewer I can even send them as .PC X images which are smaller than either .JPG or .BMP images.

show, to see if I can spot any details.

Don't sweat it, Don. I've seen the screwdriver through all of its incarnations starting with the 2nd Doctor's stubby tubular screwdriver that looked like.. well, a screwdriver; through several designs the 3rd Doctor had; the 4th Doctor's is the most prominent since it has been focused on in shows like the Android Invasion and Full Circle; the fifth Doctor's screwdriver was seen only occasionally until its demise and it had the cylindrical end cap rather than the traditional cone; there was 6th Doctor's short-lived sonic lance; and nothing wasn't seen again until the movie as that slick, retractable version:

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(although I always thought it had to have been retractable since sometimes the screwdriver changed size from show to show and sometimes between scenes). I've seen

Most of the differences were cosmetic: the sound head was black, then it's red, then the cone is wider or narrower-- that kind of thing. The only one I never saw too clearly was Romana's little job in Horns of the Nimon. Now that one was slick enough for the Doctor to want to steal, heh heh.

Ron

Reply to
Ron Hubbard

[ ... ]

O.K. Then you should be able to find some hobby machinists somewhere nearby. Even better, if you get one who is a Dr. Who fan, and will dive in for the fun of it.

O.K. I run my own news server, so it is no problem for me.

[ ... ]

Have you ever looked at how big a .bmp file is? and .jpg is bad for line drawings, because the lossy compression creates artifacts near the intersections of lines.

Better by far (for a pure B&W line drawing) is ".gif". It compresses far better than a .jpg of the same image.

Quite a collection of intersting Dr. Who artifacts in there. :-)

I believe that at least one was built around an opthalmoscope (the thing that the doctor uses to peer into your ear).

Bear in mind that for most things, the prop men on TV and Movie set go for something easy to modify to look like what they need -- or even to use as is, if it is sufficiently unfamiliar.

Enjoy, DoN.

Reply to
DoN. Nichols

Even better for line drawings in black and white or with up to 16 colours is .PNG (Portable Network Graphics). This is rapidly taking over from .GIF for that application.

Ted

Reply to
Ted Edwards

north

fan, and

. Hmm, I don't know about that. This is Portland, and while there is much to recommend here-- well, actually there's nothing about Portland to recommend-- finding somebody with my interests could be highly problematic.

No, not lately as I seldom worry about file size. But I checked and even as a .GIF file the simplest drawing is over 10 _megabytes_; as a PCX file its a little over two megs. So...

Reply to
Ron Hubbard

Rapidly, but not always available on older computers without hunting down another viewing program.

One reason for the move from ".gif", other than technical qualities is that the compression algorithm used in ".gif" is patented, and only commercial programs are set up for paying the royalties. As a result, the freeware programs may have the decompression program for viewing .gif, but *not* the compression one for creating them.

Enjoy, DoN.

Reply to
DoN. Nichols

"DoN. Nichols" wrote: ...

...

US patent 4,558,302 expired about a year ago - 19 June 2003, see eg

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, which also says, "European patent EP0,129,439 covers Germany, France, Britain and Italy and expires on the 18th June 2004. The Canadian patent CA1,223,965 expires on the 6th June 2004. The Japanese patents 2,123,602 and 2,610,084 expire on the 20th June 2004."

I think it's actually LZW compression at issue, rather than the gif format itself, and if that's what the above patents address, then their expirations is more important than otherwise.

-jiw

Reply to
James Waldby

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