Upper cylinder covers

[dgehricke]

I Have been working on this Marine Steam engine for about 2 weeks now and I an stumped as to how I can machine the upper cylinder covers on my lathe.
I have purchased a 6" piece of 2" dia. brass and I made the lower cylinder covers but now I'm down to about 4" of brass and any mistake could get expensive
fast any advise would be greatly appreciated. Please view the plans that are attached.
Thanks
dgehricke

 

[7HC]

I Have been working on this Marine Steam engine for about 2 weeks now and I an stumped as to how I can machine the upper cylinder covers on my lathe.
I have purchased a 6" piece of 2" dia. brass and I made the lower cylinder covers but now I'm down to about 4" of brass and any mistake could get expensive
fast any advise would be greatly appreciated. Please view the plans that are attached.
Thanks
dgehricke

Is it making the domed shape that's the problem? It's easy to describe, just co-ordinate the movement of the cross-slide and the compound handwheels, but doing it accurately is another matter.

Whatever the issue, I would suggest investing in a regular wax candle, or maybe several, and practice on the inexpensive wax.
They sell 3"x 5" white candles for $1 each at my local Dollar Store.


M

 

[Bill Gruby]

I believe that is what he is asking Eric. Just what part of the machining are you worried about, the dome on top???

"Billy G" :thinking:

 

[dgehricke]

I did the lower cylinder covers as described in J but they give no indication how to machine the 3/8" radius for the Upper covers.

 

[7HC]

I did the lower cylinder covers as described in J but they give no indication how to machine the 3/8" radius for the Upper covers.

Very very basically, starting at the base of the dome, you turn clockwise on the cross-slide while turning counter clockwise on the compound, which means the cutting tool will travel in a curve as it moves to the center of the workpiece.

If the operator was experienced or the lathe CNC'd it would result in a smooth radius.

If it was me I think I'd do it in very small steps, measuring as I went, then polish it to the final shape.


I'm no expert, so others may have much bettter ideas.


M

 

[Tony Wells]

http://www.hobby-machinist.com/showthread.php/4422-Turning-to-a-profile?highlight=trace+profile

 

[dgehricke]

Very very basically, starting at the base of the dome, you turn clockwise on the cross-slide while turning counter clockwise on the compound, which means the cutting tool will travel in a curve as it moves to the center of the workpiece.

If the operator was experienced or the lathe CNC'd it would result in a smooth radius.

If it was me I think I'd do it in very small steps, measuring as I went, then polish it to the final shape.


I'm no expert, so others may have much bettter ideas.


M

Thats exactly what I did the piece came out alright as I also used a radius gauge for the 3/8" radius but the 7/8" base measurement is iffy, I still have to complete one more piece and I want them to match as they will be on top of the engine and any one that looks at it will be able to note any mistakes.
Thanks for the hint and everyone else that responded Thanks.
dgehricke

 

[Hawkeye]

Since you are working with brass, one possibility would be to grind a curved profile in the end of an old flat file to use as a forming tool. It would only have to be a bit less than a quarter circle, possibly with the left-hand corner rounded off to form the depressed ring around the dome. I would recommend using Tony's tracing method to get close to the end profile, then smooth it out with the form tool.

The form tool could be used by hand, rested on a strong bar supported in the toolpost, in the same way that a scraper is used on a wood lathe. With brass , be very careful to hold a bit of negative rake when making contact so that the cutting edge can't dig in.

 

[gheumann]

I make rounded brass domes all the time - in my case they become microphone grills. What I do is to use the compound to cut an approximation of the shape with angles about 20 degrees apart. Then I knock the intersections down with 80 grit sandpaper, and progress up to 600 grit before the buffing wheel. For a "machine finish" you could stop at 180 grit. 80 grit will remove a lot of material quickly- this doesn't take that long. If you have some 50 grit you can probably shape it even more quickly.

I don't know if this link will work but it is a photo of a recent brass grill. (I usually make them out of aluminum.)

387729_581875601838699_1939643459_n.jpg

/Greg
http://www.BlowsMeAway.com

 

[7HC]

I make rounded brass domes all the time - in my case they become microphone grills. What I do is to use the compound to cut an approximation of the shape with angles about 20 degrees apart. Then I knock the intersections down with 80 grit sandpaper, and progress up to 600 grit before the buffing wheel. For a "machine finish" you could stop at 180 grit. 80 grit will remove a lot of material quickly- this doesn't take that long. If you have some 50 grit you can probably shape it even more quickly.

I don't know if this link will work but it is a photo of a recent brass grill. (I usually make them out of aluminum.)

387729_581875601838699_1939643459_n.jpg

/Greg
http://www.BlowsMeAway.com

That's pretty interesting. I have always thought that shapes like that were either cast, or made using a press and a die, or were spun.
What size is the one in the pic?


M