[justgary]

All -

I told Randy I would post pictures...

My recent BSOD episodes nearly drove me crazy as I tried to complete these, but even without the problems I could never sell these for their actual value. I knew I was doing them for free when I started, but the time I spent on them was surprising. Since it was purely a labor of love, cost was no object, right? The frustrating thing is that I'm sure they'll get pocketed quickly and never seen again. Hopefully, I'm wrong.

They are Geocoins, which are tokens used for Geocaching. The idea is that each coin has a specific mission that participants should help fulfill. Our local Boy Scout Council is encouraging scouts to create and search for caches as a part of the 100th anniversary of scouting in America.

Each coin is cut from 1.5" bronze propeller shaft and faced to 0.150" thick. I reeded the shaft first on the lathe by mounting the tool sideways and feeding it toward the head stock (with the motor off), then indexing 6 degrees and doing it again (and again, and again). The rims on the top and bottom of each coin are 0.020" deep, and the lettering is 0.010" wide by 0.010" deep.

The front (obverse) sides are roughed with a .125" and then 0.025" endmills, and finished with a 0.010" mill (all using a router-HSS). Finally, the inside corners on the BSA logo are squared up with a 30 degree engraving point starting a few thousandths deep (using Rest milling in SprutCAM).

The back (reverse) sides are pocketed with a .125" mill and then lettered with the 0.010" mill. Finally, I inked the lettering before I sprayed them with clear lacquer. All told, it's about three hours of machine time per side per coin plus nearly two hours of cleanup, inking, and spraying each.

Regards,

- Just Gary

[DSL PWR]

They look great!

[zephyr9900]

Those geocoins are awesome, Just Gary! Very impressive work. So the "BSA 2010" is flush with the surface of the coin and the panel recessed around them? What handwork did you need to do other than the (I assume) sanding toolmarks off the flat surfaces?

Randy

[mrcodewiz]

Those are excellent!

[justgary]

Thanks, guys.

The "BSA 2010" is recessed about 0.006" from the rim (the original surface) of the coins.

Sanding and Scotchbrite were pretty much all the prep, and I didn't bother to get *all* of the tool marks. Some of them are worse than others. I inked the blue ones with layout fluid and then Scotchbrited them again, and the red one is done with a Sharpie. The red doesn't show up as well, but I wanted it different and didn't have red layout fluid.

I had to work most of the ink back out with alcohol, Q-Tips, and paper towel to keep it from running out when I sprayed the lacquer. I had to strip a few of them and start over because of that. Even then, I had to spray very lightly and let it dry until I built up a protective layer. I had to strip a few of them and start over because of the runout problem.

I was surprised that it took almost two hours each just for the hand work and spraying, but at over three hours per side on the mill, it's not like I had them stacking up waiting on me.

The fellow I delivered them to put them on a scanner and got much better pictures than I did. You can see where I removed too much ink from the bottom of the fleur-de-lis in the first zero.

Since they are bronze and a decent size, they have a really good feel in the hand...

Regards,

- Just Gary

P.S. I didn't show you the one where the first side came out great, but when I flipped it over and started with the .125 pocket, things went bad. I watched the mill start in the center with a ramp, then start interpolating circles. I had just gotten to the door when I heard the spindle (a router motor) bog down. By the time I ran back to stop it, the mill had pulled far enough out of the collet that it was cutting through the full .150" coin. I used a wrench on the .125 mill after that. Finger tight is plenty on the small stuff. That sixth coin is now my pocket souvenir.

[justgary]

Here's the one that got away...

Most of what look like tool marks in the scan are actually lissajous patterns made by the scanner sampling pixels at a rate different from the actual tool marks. The fly cutter gave me a really nice surface to work with, and the .125 mill at 15000 RPM and only 20% stepover (to control side loading on the router) left a nice surface also.

I had hit the first side with scotchbrite to check it before I took it out of the vice, so some of the tool marks are gone. The stains on the back are a reaction between the bronze, the aluminum soft jaws, and the coolant.

Hand-tightening the collet had worked just fine several times before this one, but as soon as you figure that you have it all down to a process, Murphy comes calling.

I should finish the back anyway, and then make the hole look more like a bullet went through...

Regards,

- Just Gary

P.S. One more thing I didn't mention before. The main reason I reeded the edges was so I had a decent mark to use to index the two sides. I have a line engraved on the top of the vice jaws, centered on the shallow circular pocket in the jaws (a la Randy). Marking one "reed" with a Sharpie allowed me to easily place the coin properly when I flipped it over.

[ATRepair]

Wow, amazing work and a great thing to do for the Scouts!

[zephyr9900]

Just Gary, thanks for the extra description, and putting up the pic of the "one that got away". It oddly reminds me of Lt. Dixon's gold coin from the Hunley...

And I'll echo ATRepair's sentiment that you are going above and beyond for the Scouts. They are fortunate to have you as a resource.

But I think that you were thinking of Moire pattern in describing the spatial beat frequency between the scanlines and tool marks.

smart-a$$ Randy

[justgary]

s-a Randy -

The Hunley is an interesting story. Of course, I'd be glad to trade my bronze trinket for Lt. Dixon's gold coin.

Thanks for pointing out my brain f@rt in identifying the pattern. I'm Moire embarrassed than you can imagine. Even after attaching the link I never even made the connection, and had wondered why Wikipedia didn't have a better description of it, Moire or less. I must have been Moire tired than I thought. I pledge to be Moire careful in the future!

Regards,

- b-f Just Gary

P.S. One Moire of these jokes and I'll gag, but at this point I'm Moire afraid of reading your reply.

[zephyr9900]

Oh, I know when to sit back and just let you run with it...

Randy

[neilw20]

Use your CNC to make the tolls for a press like this.
Then it will be coins per hour instead of hours per coin.

You could also make the positive on the end of copper bar and use that to spark eroded the dies, even with grooves on the side.

Just a thought, or make almost finished coins and engrave the last bit on them.

[justgary]

neilw20 -

All of those things are true, but I really only needed one each of the five different coins. Also, I had the bronze rod, but not 1.5" tool steel to make dies.

Randy told me about seeing a drop hammer in action making coins, and that would have been a lot of fun, but even more work to get right. Had I needed more than one of each, I would have given it a try.

Besides, I learned a lot. Mostly, I learned how to not produce parts in high volume...

Regards,

- Just Gary

P.S. I would have *really* liked to have gold plated them!

[neilw20]

Try lost wax process.
You can achieve rally good precision, fast machining. Easy on tooling.
It is really jewelery you is creating. (wrong) ??? :withstupi

[justgary]

neilw20 -

I'm with you on the lost wax, also. I'd love to try it except for two things:

1. I don't have a furnace (or a set of leathers).

2. I'd prefer to start with aluminum (lost foam) and work up to bronze and beyond (both mulled sand and lost wax).

Granted, I can melt the amount needed for a single coin with the torch, but it makes more sense to do a whole batch of them with a larger melt. For this project I seriously considered diving right in and casting silver, but I had a major distraction when I was about to buy the silver grain. By the time I got back to it, I was out of time to play with new (to me) technology.

Lost foam aluminum casting sounds like a very interesting way to make things that would otherwise need a lot of material removal. I intend to try it sometime.

Regards,

- Just Gary

[David Bord]

Man, super impressive Gary... Great job!

david

[zephyr9900]

Like to produce one offs faster? Try lost wax process.

??? How can machining wax masters, investing them, melting bronze, casting, despruing, and cleaning up the resulting castings to the equivalent finish be faster than just machining the one-offs directly? The machining of the wax itself will not save time on the Tormach because the machining time is determined by the axis acceleration and not ultimate velocity on small, detailed workpieces like these coins.

What Just Gary is doing is the essence of rapid prototyping--the creation of functional, one-off components by direct fabrication. No other, specialized equipment, excessive energy use, creation of extra and possibly hazmat waste products, etc, etc.

If we were to go down that path, Just Gary might as well send out his solid models to be laser sintered out of bronze powder.

Randy

[justgary]

Randy -

I admit that casting would be fun, and I'd like to try it. With my luck, I'd only have to machine 20 or 30 wax masters to get the process good enough to use. I guess the real luck would be not having the molten bronze blow up in my face, too. One day I'll muster the courage.

Yes, I probably took way to much time on these, but I would rather take the time than buy a whole lot more tooling. I set the feed rates to the values recommended in MachMate and only broke one 0.010" mill. The feed rate was correct, but I got it a few thousandths off center when I put it in the collet. It didn't take it very long to fatigue and break off. I was much more careful mounting them after that.

Since it broke at the very top of the helix with a tiny stub of a tooth left on each side, I simply dressed the bottom with a little diamond file (to put some draft on the bottom edges) and used it for the rest of the project. At 0.010", who's to say you are actually cutting all of the material anyway? Pushing it out of the way just makes a slightly bigger burr...

Many Regards,

- Just Gary

P.S. I did a few calculations this afternoon, and it looks like a 110 pound bar dropped from about 7 feet high will impart about 240 tons per square inch on a 1.5" coin, assuming about 0.010" of total deformation in the coin. A smaller coin would get even more force due to the smaller area. No wonder they come out of the dies hot. I just might have to order some larger drill rod for dies and give it a try.

[Fastest1]

All I know is that it is a pleasure to see yours and others here who share their projects. Success or not, it is excellent. I think the coins were fantastic and a worthy effort. I really want to thank you for the mistake. After having a pile of attempts that went wrong it is refreshing to see people who do great work make mistakes too. I just learned to pull an end mill down against the grub screw (if not using a collet), I had always pushed the mill in as far as it could go. I was at a meeting and a man explained that the end mill is being pulled into the work so if the screw loosens somehow it goes thru the work. It made sense. I do know this, on a cnc machine if it can come loose it usually will at the last line or 2 of a long code! Btw Good Work in case that long post didnt say it!

[justgary]

Fastest1 -

Thanks for the kind words.

It's funny how Murphy waits until the best time to strike. In that particular case, I had just gotten complacent about tightening the collet and left it too loose for that endmill. With all of the BSOD problems I was having at the time, I'll say that I was distracted by the computer... Thumb tight *usually* works just fine on it, but it is amazing how much down force even a .125 mill 0.020 deep has.

By the way, I'm using a router as a high-speed spindle, and I hold the tooling in a little collet holder that I posted last year. I have a few little issues with it, but mostly it works great (well, great enough to not do anything about its issues).

I'm also amazed how Murphy seems to like brand new tooling. I had a new undersize reamer about 8 months ago, and I decided to try it out on a little fixture so I could use .125" alignment pins. I fretted for quite a while over the feed and speed to use, but that didn't matter much since I apparently set the Z height wrong when I chucked it. If I remember correctly, I took out the drill and put in the reamer and pressed start without actually setting the Z height.

The mill reamed the first hole just great (it was a through hole), and then started to rapid to the next hole... without fully retracting first. Before I could do anything, I saw several parts of the reamer fly past my head. I heard the biggest piece loudly hit the wall about 10 feet behind me. I always keep the clear guard up now, even without coolant running.

Show us your projects!

Regards,

- Just Gary

[ebrabec]

do either of you have a dxf. dwg. file of the boy scout logo. we want to put it on our arrow of light plaques for our transitioning weblos