Manually cutting a curve

[wdp67]

Hi,
Just needing some advice on the best way to ogive like radius on a manual lathe. It is a pretty large peice made out of aluminum, but I need to do many of them so I need a fast accurate way of doing it.

Thanks!!
Walt

 

[tattoomike68]

A ball turning tool would work for that.

If its not to big a ground form tool would work too.

I fake most things I turn like tapers and curves. set the feed to cut away from the chuck and run the cross slide.

A 4th method would be to make a quick and dirty tracer Like I use to make a wooden ball.

Its just a Popsicle stick and a peice of cardboard.

 

[DickDastardly40]

Walt,

I made bullet Ogives using the method described in this post:

http://www.homemodelenginemachinist.com/index.php?topic=723.msg6116#msg6116

I can't link the pictures here as I'm at work and have no access to photobucket. I made two bullets in 0.5"cal and 2 in 5.56mm cal using this method for a display and they came out both well and similar.

Marv Klotz has an Ogive calculator amongst his utilities on his fantastic site of highly useful stuff.

http://www.myvirtualnetwork.com/mklotz

Best Regards

 

[Mcgyver]

lots of different ogive profiles - http://en.wikipedia.org/wiki/Nose_cone_design

If not space shuttle parts, I like Mike's Q&D tracer idea. if many means 10's, this should work, if means 10's of 1000's, buy a cnc I take it large means too large for a form tool?

 

[wdp67]

Thanks for all the idea's!! Many means probably 100's if not thousands, depends on the popularity of the item, hopeing for thousands. But I can not afford to get into a cnc lathe at this point. If the product is succesfull then I will pursue that. I am not sure how to make a profile tool. I did take a used up file, and ground the shape into the side of it and tried to use that as a profile cutter, but I have not had much success with that yet. Maybe someone could guide me with that, as that is what I came up with before I posted the question, just did not have any success.

Thanks again!!

Walt

 

[Mcgyver]

Walt, a profile tool is commonly made out of hss, leave the top flat and grind into it, with some front clearance, the profile. The grind in part is quicker said than done, but its not hard. rough grind on the bench grinder then finish off and fine tune with a Foredom tool or die grinder. The challenge with them is that the depth of cut (length of the edge of the form tool) quickly becomes too large for a small lathe unless the form is quite small.

putting on a business hat instead of an amateur engineer's for a moment here's an alternate suggestion....

once you're past a few prototypes, with that potential quantity, consider outsourcing the turning. You can't compete for throughput and efficiency against someone with a 100k bar fed cnc lathe. Well, you can, but you have value your time at next to nothing....and our time is finite. Since compared to the job shop you are the poor cousin in terms of efficiency, you can't claim turning is a core competency. What then is the core competency? the idea and product itself, design, sales, marketing etc. These then are the activities where you should concentrate the finite amount of time you have....where you will maximize your returns. btw, the job shop suffers through life with low margins - the service is a bit of commodity. Given their small margins, there's not a strong economic argument to bring the work in house.

the other argument might be "but I like working in the shop and want to make them myself" ....not after the first 1000

 

[tattoomike68]

If he needs 1,000's farming the turning out is a good deal.

I had orders for 1,000's of small parts before. quoted @1.25 each but farmed it out to a screw machine shop and had them made for .29 cents. Easy money. I never had to touch them.