# How to make this thin wall brass part?



## timo_gross (Oct 3, 2022)

Hello, 

i am trying to make some engine, which is probalby to big of a challenge  , but I decided just to go on piece at a time and see if I can get all the bits and pieces machined.
Now this smoke stack is next on the list. Yet I did not come up with a clever idea how to get on with it, because it is rel. long, has some tapers from both sides and it has rel. thin walls
. 

Maybe someone sees this and has some good hint how I could do it. 




part with the stock around it. It is approx 25 mm (1") diameter brass piece an the part is about 60 mm long (2"-3").



There are rel. Thin wallls, and I am not sure how I should approach it. Maybe someone has a good idea.


Part as it roughly should look like. 


Greetings Timo


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## Ghosty (Oct 3, 2022)

Use an overlength stock, machine the inside, then machine the outside, then part off
Cheers
Andrew


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## Jasonb (Oct 3, 2022)

Face to length
Bore the short bottom taper and the parallel part.
Reverse in chuck and bore the long top taper
With the topslide still at the taper angle turn a tapered mandrel
Place long taper onto mandrel, add tailstock support 
Turn the outside profile.

That's for manual machining but your first image suggests you gave it in F360's CAM and intend to CNC.


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## timo_gross (Oct 3, 2022)

Jasonb said:


> Face to length
> Bore the short bottom taper and the parallel part.
> Reverse in chuck and bore the long top taper
> With the topslide still at the taper angle turn a tapered mandrel
> ...


Hello Jasonb,

That sounded very logical. And it turned out to be. 

"With the topslide still at the taper angle turn a tapered mandrel" this was the crucial trick. To turn this mandrell I used the boring bar and just reversed the spindle rotation. 

I exactly followed the instruction and was able to make a 1st test piece from Al. Just to make sure before I use the brass bar. 





Yes it is indeed a fusion 360 cam picture, but that was only to illustrate how my stock looks like.
No CNC lathe in the workshop  (yet), as those seem to be very expensive.

Greetings Timo


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## werowance (Oct 3, 2022)

i have been learning and experimenting with metal spinning with some really good results for my crude setup.   what i have been doing is 3d printing a form to spin the metal around.  im just using a lathe/mill combo hobby machine similar to a "smithy" that i made a tool post to hold my rod for spinning.   but the thing i liked best so far is 3d printing the form.  i give it an extra length for my chuck to hold and then start spinning.  if the part is "stuck" to the form afterwards a little heat and the plastic melts away.    only thing is its very time consuming especially with brass because i have to keep removing it to anneal it.  cant anneal on the plastic forms else it melts it.


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## timo_gross (Oct 3, 2022)

werowance said:


> i have been learning and experimenting with metal spinning with some really good results for my crude setup.   what i have been doing is 3d printing a form to spin the metal around.  im just using a lathe/mill combo hobby machine similar to a "smithy" that i made a tool post to hold my rod for spinning.   but the thing i liked best so far is 3d printing the form.  i give it an extra length for my chuck to hold and then start spinning.  if the part is "stuck" to the form afterwards a little heat and the plastic melts away.    only thing is its very time consuming especially with brass because i have to keep removing it to anneal it.  cant anneal on the plastic forms else it melts it.


Spinning seems also an interesting method, probably even more useful for more complicated shapes. The test piece that I made today following jasonbs instruction took me 2h, but I am sure the next one will be at least 1 min faster.


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## timo_gross (Oct 5, 2022)

Finally that one part is done.




lots more to go...


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