Compass Project -- STEP 1

Status
Not open for further replies.
Joined
Jun 2, 2003
Messages
23,591
Some of you may have wondered about what this thread was. I have decided to chronicle the whole picture intensive project for your pleasure (or aggravation). I'm not on a schedule, so finishing this project may take a while, months, maybe even longer.

The Project:

Modernizing and making 100% functional an old military compass
(No, it's not French, but the one in the picture was made for the French army. Mine was made for an English speaking market). Why? Well, because it's a fun project of course! Also, this type compass had a few features that set it apart from other, more typical compass designs. Unfortunately, the compass itself wasn't a fluid-filled compass, and as such the needle was not dampened. This made this compass comparatively slow and cumbersome. What to do? Fit a modern fluid-filled compass with a "global needle" in the old unique housing, what else?
grin2.gif


My old compass is very similar to this model (not my picture):

Compass_boussole_Bézard_AF_%2B_visée.jpg



Step 1: MAKING A NEW DIAL

This is the adjustable metal circle cutter ("General" brand, "Made in China") that I used. It's pretty well-built and doesn't seem to be cheaply made. It's at least sufficient for my needs. Both, the drill and cutting blade are replaceable. I removed the 1/4" drill bit and replaced it with a short length of steel tubing, because I did not want to use a drill press for this delicate job.
01.jpg


I took a 3"x1" piece of bass wood and drilled with my drill press a perpendicular 1/4" hole.
02.jpg


I drilled an 0.2" hole in a piece of 0.032" thin sheet aluminum. I used a precision drafting compass to scribe the two circles that would function as a guide when setting up the metal circle cutter. I scribed the circles on both sides of the sheet.
03.jpg



I used drill bits of increasing size in my drill press to widen the 0.02" hole to 1/4." I was worried the hole might not be sufficiently centric to the scribed circles, but it worked out just fine.
04.jpg



I tested the following procedure successfully during a trial run with a piece of 0.02" sheet styrene to make sure the tool was set properly and that it would cut the piece exactly right:

I placed the aluminum sheet on the piece of wood and inserted the steel tubing of the circle cutter. I clamped the metal to the wood. With the steel tubing (remember, there used to be a drill bit?) firmly inserted into the wood, I could now turn the cutter by hand, allowing me to use just enough pressure to gently cut the metal, following the scribed guide marks. The cutting blade was angled, so it was important to to rotate the blade depending on if I was cutting an inner or outer circle.
05.jpg


I needed about twenty trips around to cut about 1/3 of the thickness of the metal. I guess I spent two minutes on that. I did that with the inner and outer circle. Then I flipped the sheet metal and cut the inner and outer circle (Remember, I scribed the circles previously on both sides) in alternating steps until I could tell that the "donut" was about to pop out. That took me about 5 minutes, because I was working slowly.
06.jpg

For the close-up freaks:
07.jpg


08.jpg


The edge was pretty rough, but the size was where I wanted it: outer circle oversize and inner circle undersize by about 1/25 mm.
09.jpg


Not shown: I smoothened both sides of the donut on a flat diamond hone by hand to remove any rough edges. Next I taped the donut to a thicker aluminum sheet. I sanded the surface by hand and gave the donut a brushed finish. I removed the donut with dental floss, so I wouldn't bend it, from the aluminum sheet. I then sanded the outer carefully edge until totally smooth.
10.jpg


Here is the compass insert that has to fit into the hole of the donut. Let's call the donut a dial from now on.
11.jpg


As you can see, the compass has to fit tightly into the dial, because all that's preventing the compass from falling through the hole in the dial is that narrow edge formed pointed out by the red arrow.
12.jpg


It seems to fit tightly enough! I did have to widen the hole a little with sandpaper. I think I spent about 5 minutes with 400 grit sandpaper. I didn't care about the finish on the underside of the dial. It's ugly but it won't be visible.
13.jpg


The dial with the compass had to fit into this brass bezel. The dial is not completely done. I will cut a little window into it that will be filled with glow paint. This will make the pointer, which allows reading headings and bearings, stand out in the dark.
14.jpg


15.jpg




Money spent:

- one old compass: $35
- one new Swiss made compass with global needle (cannibalized!), $49 (heavily discounted)
- sheet styrene for mockup parts and testing, $2.99
- aluminum sheet, $4.99
- metal circle cutter, ~$20 with shipping
--------------------------------
~$112


The bezel with the compass will eventually be installed into the compass housing. Before I get to this, I will have to cast a spacer that allows mounting the compass in a secure but removable manner inside the bezel. I'll need another long weekend for that! After that, a bottom cover will have to be fashioned. I also will need to source, or fabricate, some very small metric brass set screws.

To be continued...
 
mori...excellent work.

I'm becoming a "bash it into serviceable shape" engineer at present...not sure that I like it.

However, after spending some time with an engineer named Steve back in May/June, I am becoming enamoured with the wonders of dental casting putty.

It won't stick to anything, forms a very good negative impression, even of some small returns.

Been meaning on doing a BITOG "article" on making a negative in dental putty, followed by a positive in epoxy...'cept I can't photograph to save my existence.
 
Thanks for the flowers. I have fun recording that sort of project. Besides, it might inspire others.

I haven't worked with dental putty, but I do have some experience with mold making and casting various kinds of resin (polyurethane, epoxy, polyester etc) and metal alloys. It all started with me casting my own tin soldiers at age 9. Yes, my parents let me play with fire and run with scissors!
grin2.gif


What sort of thing would you like to cast?

Originally Posted By: Shannow
I'm becoming a "bash it into serviceable shape" engineer at present...

We used to have a plumber who had only three tools: a screwdriver, a hammer, and a plumber's wrench. Oh, and he always carried a length of hemp twine. That was his whole gear.
 
ahhh tincasting...had one of those.

'cept there was no internet, and once I'd run out of hex pellets and tin, I had to try to find anything that would burn, and that greyer more available form of "tin" (well it melted, and I was 10/11).
 
I used the sand casting method for casting tin soldiers. I still remember the smell.
 
No drill press mori? You could have chucked the cutter into the press and turned it by hand. Drilled any pilot holes at the same set up as well. Would have saved you a few steps.
55.gif
 
Originally Posted By: Tempest
No drill press mori? You could have chucked the cutter into the press and turned it by hand. Drilled any pilot holes at the same set up as well. Would have saved you a few steps.
55.gif



I don't believe I could have achieved the required precision that way -- at least not on the first try with only one trial run. But I'm sure you know my drill press and my other gear much better than I do, Tim Taylor.
wink.gif


PS: Can you fit an 0.5 mm (0.02") drill bit in your drill press? In order to scribe the aluminum, I had to drill such a small pilot hole.
 
mori the aluminum donut looks really good. The adjustable circle cutter did the trick. It looks like a decent quality tool even though it's made in the far east.
55.gif


You'll probably find more uses for the circle tool I'm sure, so the $20 investment should go to good use.
 
I'm happy with the piece that I cut out. The cutter is alright. It doesn't seem fragile and has a decent finish. Although, I have no idea what would happen if I were to use it with a power tool on a more substantial piece of metal...
 
Step 2: Modifying the Existing Bezel & Fitting the Dial

Here is a shot that shows the main components of the project. Step 2 focuses on fitting the new compass module inside the original brass bezel. In order to do this, I have to design and fabricate various adaptors and spacers. It is crucial that every part fits precisely and accurately. Proper alignment is crucial, because this compass is a precision instrument.

Bottom row, left to right:
- custom made bezel adaptor: this adaptor allows mounting the new compass module in the original brass bezel. This is not the final adaptor, bust just a mockup made from styrene. I will make a mold of this piece and cast it in very durable urethane resin.
- brass bezel: original part
- custom made styrene spacer: I will make the same part out of aluminum later, because styrene does not meet my requirements for heat resistance.
- custom made aluminum dial: your may remember this part from Step1. I have since drilled various holes, as described in one of the more detailed pictures below.

The compass module (top right) will fit into the original bezel, which will fit into the original compass housing (top left)

2_01.jpg



To the left you see the mockup of the spacer that I have to cast. The spacer contains a groove, just like the compass module contains a groove. I will describe how those grooves (see red arrows) will be used to hold the compass module securely in place much later. For now it doesn't matter. Important is that the grooves match up when the compass module is inserted into the bezel.
2_02.jpg



A closer look at the adaptor with the spacer on top of it inside the brass bezel. Note the groove (see red arrow), not the notch (I will explain its function later), and note how the adaptor butts up against the bottom end of the brass bezel. This is important.
2_03.jpg


The dial. Last time you saw the dial it was just a plain donut. Now it sports various holes. Note the taper to accommodate flat head screws for a flush fit. The cardinal points will later be filled with glow paint (glow powder and urethane resin mix). The registration holes have to be dead-on. During the final assembly, aluminum pins will be inserted (press-fit). These pins align the dial with the spacer and the adaptor below the spacer. The top of the pins will be sanded flush with the dial.
2_04.jpg


This shows how I drilled the holes for the screws that will hold the assembly together. I also drilled the all other holes, including two small ones that allow perfect alignment of the dial within the bezel. You can see temporary plastic pins protruding from the dial. The plastic spacers that your see between the edge of the bezel and the dial are temporary and only an alignment aid.
2_05.jpg


For the close-up freaks:
2_06.jpg


The bezel temporarily put in place. See the two small registration holes on the dial? They will be pretty much invisible once the registration pins have been pressed in. Note the brass screws that will later hold the bezel assembly together:
2_07.jpg


I didn't have to buy any materials or supplies for this step, so it's mostly labor (1 hour all in all).
grin2.gif


To be continued...
 
I noticed a few gaffes. Most notably I called the "adaptor" a "spacer" a few times -- which is not incorrect, since that's what it is. I should however have called only the thin styrene disc a "spacer" and called the thicker spacer an "adaptor" in an effort to clearly differentiate between those two parts. At least I don't call every part doohickey. Oh well, it's all probably confusing anyway!
grin2.gif


PS: The two shots showing the drill press are editorial shots (set up sloppily after the holes had been drilled). I did not want to interrupt working on the piece just to take a few pictures.
 
Oh, sure. The good old "pull the already roasted turkey out of the oven" food show trick. I get it.


Escapist goat!



No way am into that level of detail on anything in the physical universe. Good show.
 
Not much to tell. It's a very simple small Proxxon drill press with a cross slide. The Proxxon power tools that I use are a bit smaller than a typical Dremel. Dremel neither offers small enough tools nor the selection of tools that I require. Proxxon specialized in what I'd almost call miniature power tools. They do have a couple small mills. The smaller one runs about $1,100, the larger one costs about twice that and is very nice. Google PROXXON MINI MILL MODEL # FF400.
 
STEP 3 -- MOLD MAKING & CASTING

I took the mockup styrene adaptor and stuck it via double sided tape on a styrene sheet.
3_01.jpg



I made a mold frame out of LEGOs.
3_02.jpg


I filled the mold frame with RTV silicone.
3_03.jpg


12 hours later the silicone had cured and I removed the mold frame and the mold. This is the mold:
3_04.jpg


I filled the mold with a two parts casting urethane. I added black dye because I didn't want the cast part to be white. After 15 minutes I removed the cast spacer. I heat cured the spacer for a couple hours (not really necessary) in my toaster oven. All pilot holes were present.
3_05.jpg


The adaptor fit perfectly into the brass bezel.
3_06.jpg


Four tiny brass screws and nuts were used to hold the dial and bezel assembly together. The four nuts must not protrude from the bottom of the adaptor. I widened the four screw holes at the bottom of the adaptor so the nuts almost fit inside the holes. I used a brass screw with a washer and pulled the nut into the screw hole. That's good enough to keep the nuts from falling out and from spinning when tightening the screws.
3_07.jpg


3_08.jpg


The dial and bezel assembly were put together by stacking the dial and the spacer (now aluminum), dropping them into the brass bezel, then inserting the cast adaptor from below, and by finally screwing it all together with the four brass screws and nuts, which I had already trimmed to proper length. Thread locker was used. Metal pins in the registration holes were used to line up everything during assembly. The tiny gap between the dial and the bezel was filled with epoxy resin mixed with aluminum powder. The cardinal point markers will later be filled with luminescent material. Right now the markers look white because I painted the spacer that's under the dial white. The two prominent registration holes will be filled later.

3_09.jpg


Cost: None, besides using materials and supplies I have anyway.
Labor: About 45 minutes, not counting waiting for silicone and resin to cure.

The dial is now almost ready. Almost!

To be continued...
 
I haven't gotten around to continuing the project, but maybe someone can tell me where to find this kind of tiny brass set screw: 1.2 mm diameter, 2.4 mm long (without head), 0.2 mm pitch.

1point2times2point_eight_si.jpg


PS: The half sanded-off friction ridges are not due to criminal intent. It's just wear and tear.
grin2.gif
 
Ah ..I'm sure Crown Vic-man and the Xth St. sniper have just figured that they now have a good sampling of your fingerprint. Thankfully, you've already moved to retina scan security measures.
 
Status
Not open for further replies.
Back
Top