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rbertalotto
09-20-2011, 08:39 AM
I will be making a Unertl style rifle scope mount and I need a materials expert.....

The prototype is in aluminum and I used the internals from a set of micrometers to get the hardened threaded shaft and insert

http://images15.fotki.com/v2/photos/2/36012/10064964/P1020971-vi.jpg

I want to do away with using the micrometer internals so I ordered taps and dies at 3/8-40 and 1/2-40 (not sure what size I'll use as I want a large bearing area on the scope tube.

http://images51.fotki.com/v628/photos/2/36012/10064964/P1020962-vi.jpg

So help me with materials.

There will not be much wear as the turrets are turned relatively infreaquently.

But I'm thinking about making the entire mount out of some type of bronze.

I've never worked with bronze.........

Questions:

Ease of machining?
Ease of threading / taping?
Bronze against bronze OK?
What type of Bronze should I use? (there are lots of different types)

C510 PHOS BRONZE
C544 PHOS BRONZE
C630 ALUMINUM BRONZE
C642 ALUMINUM BRONZE
C655 SILICON BRONZE
C863 MANGANESE BRONZE
C932 BEARING BRONZE (SAE 660)
C954 ALUMINUM BRONZE
SAE 841 OIL-IMPREGNATED PWDR. BRONZE
SAE 863 POWDERED IRON-COPPER

Full article on the prototype mount I built:
http://rvbprecision.com/

Thanks in advance!

38_Cal
09-20-2011, 10:13 AM
I've been thinking about this since I read your post this morning on the ASSRA site...I think that I would go with aluminum and loctite/press in steel threaded bushings. It will hold up better in the long run, and the aluminum is cheaper and easier to work with than the bronze.

My dos centavos worth. :D

David

dalee100
09-20-2011, 10:35 AM
Hi,

I wouldn't be too overly stressed out about which alloy to choose for this application, well, the oil impregnated wouldn't be a good choice, unless you like oily things.:) Anything on the list would be usable. I'd probably choose based mostly on price and availability in this case.

I do like the idea of steel inserts for threads. But if you're not turning them much, it probably isn't overly important. Kind of a 'How good does good enough really need to be?' question.

Bronze isn't difficult to machine. Any of the tooling you have right now will work just fine.

dalee

rbertalotto
09-20-2011, 12:38 PM
Thanks folks...........I'm trying to stay away from inserts as it is just one more thing to make and one more thing to be a slight bit out of alignment and screw up the repeatability of a device such as this.

The bronze was suggested for two reason..........wear and it would look very "period correct".................

Aluminum would be much easier to be sure.........

JCHannum
09-20-2011, 01:01 PM
Any of the external mounts that I am familiar with were aluminum castings finished bright. To keep them period correct, aluminum would be the choice. Steel inserts would not be add that much of a difficulty factor.

HWooldridge
09-20-2011, 01:45 PM
How about 353 or 360 brass and let it tarnish similar to the furniture found on period muzzleloaders? Bronze is really no "better" than brass in this application and more expensive to acquire in bar stock.

rbertalotto
09-20-2011, 01:54 PM
"Brass".......the other gold colored metal!

You might be right. Brass is probably a much better option. And a clear coat would keep it from tarnishing if the customer requested this.

rbertalotto
09-20-2011, 02:03 PM
The price difference is staggering..........

1" X 2" X 12" Piece

Bronze $94.22
Brass 360 $71.01
Alum 7075 $26.85
Alum 6061 $10.62

HWooldridge
09-20-2011, 02:22 PM
The price difference is staggering..........

1" X 2" X 12" Piece

Bronze $94.22
Brass 360 $71.01
Alum 7075 $26.85
Alum 6061 $10.62

Yeah, anything containing copper is crazy $$$ right now. World market prices have been high for several months and supply has not gotten any better. However, you might want to quote a bar drop from your supplier - they may have something close to size without charging list price.