lathe turning bullet bases

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  • Last Post 13 February 2019
porthos posted this 10 February 2019

question for John Alexander:

in your article in the last issue of the fouling shot ; you refered to lathe turning bases. i'm guessing that you did so to square up the base to remove the sprue lump? my guess is that you used a collet of nose riding size to shoulder against the front driving band and take a cut off the base to remove any excess sprue. is this correct?

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Ken Campbell Iowa posted this 12 February 2019

porthos .. my current smithing/hobby lathe is a southbend 13 inch ... if i can help you get going, let me know.   i prefer email, deltainc@grm.net .

btw, tailstocks are hardly ever ( ok, never )  in line exactly ...  too high, too low, varies with distance from spindle, you have to optimize for the length you will be using ...  ...  ... for most uses, it just results in a small taper, only you will know it is there.  hey, that is what knurling tools are for ... heh ...

a general rule is that if you keep your aluminum or steel work piece from the spindle nose less than 3 diameters you don't need a tail stock support, normal tolerances.

ken

 

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Ken Campbell Iowa posted this 13 February 2019

tip for crutching up a mis-aligned tailstock ( or  drilling from the cross slide )>>

chuck a 3/8 round aluminum plug in the tailstock or cross-slide tool holder, then center drill and drill from the spindle ... now you have a hole perfectly aligned with the spindle.    you did split it or put in a setscrew before you chucked it, right ?? ...  if you need to remove it, index-mark it for close replacement.  also, it is only perfect at the distance it was back-drilled .

and most hobby stuff, incuding cast squishing dies, don't need this much work .

hope this helps, ken 

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Ken Campbell Iowa posted this 10 February 2019

rudely butting in ( g ) ..  i thought lathe truing bases  improved the accuracy of my 22 castings.  i used standard 5c collet blanks bored to size in my hardinge chucker, chucked on the groove diameter as close to the base as possible ...very little chuck pressure and a very very sharp tool ... probably about 45 degrees of front rake ...  to put the least load on the casting.  alloy was 92-6-2 hardball not heated.   i fed into the casting base axially to lessen the load.

i don't think it is critical the amount you take off within a couple thou, and the improvement was with and without gas checks added later .  i also played with the base angle on plain base with no difference, they don't seem to need a 90 degree base, and i would fantasize that a bevel base doesn't damage so bad in handling.

*****************

however, i thought the same improvement came with " bumping " or " swaging " the bases flat in a die, and that was much less hassle .... well, after making a die, of course ...

hope this helps, i would like to see more reports on cutting or swaging " better " bases .   the best cast groups in my 222 were with " improved " bases .      this from base pour;  nose pour might not need that ??

ken

 

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porthos posted this 10 February 2019

thanks for the info. i thought that a bump die would do the same plus more. i'm getting to make some,but am having a problem getting my lathe (south bend)  centered properly

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John Alexander posted this 11 February 2019

Porthos,

I didn't mean to mislead anyone by using lathe turned bases as the alternate being tested for in my example of a good experiment.  It was an arbitrary choice.  I have never lathe turned bullet bases.

My experiments with near perfect bases vs. imperfect bases (non-uniformly rounded bases, small bumps) has made me extremely skeptical about the need for absolutely perfect bases -- at least down to the 1 moa level.  Yes, I know it is a cast bullet axiom I just had never seen evidence to support it before reading Ken's post above.  Like Ken, I would like to hear more. David Pape, who sometimes posts here has been experimenting with lath turned bases. Maybe he will chip in.

I do cut off sprues by hand and get extremely flat bases with no bumps and usually no rounded edges -- just in case I'm wrong.

John

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nosee posted this 12 February 2019

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nosee posted this 12 February 2019


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nosee posted this 12 February 2019

Endmill in a watchmakers lathe works,but it is still my shooting that is the problem! I try everything and still get a two inch group.

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R. Dupraz posted this 12 February 2019

Ken  wrote:

"btw, tailstocks are hardly ever ( ok, never )  in line exactly too high, too low, varies with distance from spindle, you have to optimize for the length you will be using for most uses, it just results in a small taper, only you will know it is there.  hey, that is what knurling tools are for."

Thanks for that Ken. I can now finally quit pulling my hair out!

R. 

 

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