Question for the PRE-CNC machinists

[SPiN Racing]

Morning all,

I have a project I am working on. And I need to be able to turn a shape on my lathe.

Picture a candlestick shape, or a table leg. Any quasi complex shape like that for example.

I need to turn it on a piece of stainless steel appx 3-4 inches long.

In the past I would make a drawing with all the curves and dips in the shape.. fire up the lathe, spin it up nice and quick.. then with a very sharp indexable turning bit, would cut in the profiles by hand... around a 20 minute process if I was quick.

Then part it off.. slide out another 3 or 4 inche length and TRY to duplicate what I had just made.

SO if I need to fabricate 4 ornate small stainless table legs, or candle holders, or fan pulls... that are 1/4 to 3/8 inch in diameter.. Is there even a way to make a repeatable pattern or something?

If I need to make say... 20 of them... were talking a LOT of work to get them done. And very hard to duplicate what I made.


I was trying to think of some sort of duplication tool like they use on wood lathes... or possibly a piece of tool steel profiled, and hardened to make the entire part in one plunge.. but I think I would get chatter.

If there are links and or ideas.. I would love to hear them.. I have b een wrangling with this for a long time percolating trying to figure how people did it before CNC.

Thanks!
Scott

[David Jupp]

Sounds like you need a copying attachment - the cross slide lead screw is disconnected, a follower protruding from back of cross slide rests on a template positioned behind the bed.  A spring  pulls the cross slide towards the template.  As the saddle is moved along the bed, the shape of the template is reproduced.

There is a bit more detail to it than that.  I've seen plans for this in a magazine (for a Myford I think), but should be possible for most lathes.  I've never used one - am sure others can add more detail.

[kvom]

One way to get pretty close is to use one of the pattern measuring tools; there are a large number of fine wires that slide independently in a locking holder to mold to a profile shape.  You'd hold it against eash part to gauge where to cut; you'd likely then need to file/sand to the finish shape.

[75Plus]

Could you possibly use a ball turned as Ralph did in this thread?

http://madmodder.net/index.php?topic=284.0

Joe

[SPiN Racing]

Could you possibly use a ball turned as Ralph did in this thread?

http://madmodder.net/index.php?topic=284.0

Joe

 

Been there got that 

Made one of those a good while back.... here is the thread for it:

http://madmodder.net/index.php?topic=548

Im interested in some sort of pattern follower.. that might work well.. coming off the tailstock.

[andyf]

Scott, this is probably overcomplicating it:

Rig up a sturdy table behind the lathe, and bolt a template down to it, with a straight edged plate on top, the plate being fixed independently of the template so the plate can be moved without disturbing the template. Fit a finger on the back of the cross-slide, so it bears on the template and straight-edge. Start with the straight-edge positioned so that only the "peaks" on the template are exposed. Take a cut, traversing the carriage with one hand and using the other on the cross-slide handle to keep the finger in contact. For the next cut, move the straight-edge back a bit to expose a little more of the template. Repeat, moving the straight-edge back a little bit more, and so on until the troughs on the template have been fully exposed. Then start on the next piece of stock, and carry on until boredom sets indo it all over again.

A more sophisticated table would have a feedscrew to take it, with template attached, a little further way from you between successive cuts. That would avoid fiddling with a straight-edge, which wouldn't be needed.

Andy

[picclock]

@ Andyf

Wouldn't it be simpler to just move the pattern into the work ?

Best regards

picclock

[SemiSkilled]

Saw this on another site, not my work.

Food for thought.





Lee

[SPiN Racing]

Ohhh very nice!

I have done some more research.. and lathe duplicators seem to be the term.. mostly wood lathes though.

That looks like a nice piece.. but how do you control the depth is my question.. since its a compund curve..

here is one that is nice for like.. brass. but I would be chicken to hold that in my hand with stainless steel.
http://plsntcov.8m.com/Duplicator.html

[John Stevenson]

Spin,
Take a look at this machine I did yesterday.

http://bbs.homeshopmachinist.net/showthread.php?t=48916

John S.

[HS93]

I have used lots of wood turning lathes with copying devices they would work on metal lathes if the material was not to hard , they mainly had a tool that was spring loaded (in and out)  which was controlled by a follower ether a single rounded end or very small ball race depending on the item being turned , you will find that you have to play with the follower and patterns as you will find an exact copy of what you want to turn will not be the ideal shape especially if you use a ball raced follower

Peter

[Rob.Wilson]

Not bad John 



Rob 


Was thinking about making an attachment to fit on my tapper turning dood dad 

[Lew_Merrick_PE]

Ohhh very nice!

I have done some more research.. and lathe duplicators seem to be the term.. mostly wood lathes though.

That looks like a nice piece.. but how do you control the depth is my question.. since its a compund curve..

Spin,

In terms of a traditional machinist's mechanical tracing attachment (we also had hydraulic tracing lathes and mills), think of it as a free-form taper-turning attachment.  Instead of a single bushing or block bearing following a straight bar, it is a pair of spring-loaded roller bearings that follow a template's contour.  With practice and standard care, you can hold +/-.002 on such a set-up.  With more practice and massive attention to detail (and more than a bit of luck) I once held +/-.0005 on such a set-up (note the modifier once -- across four parts).

The "pointer version" shown above can be quite challenging (to say the least).  If you replace the pointer with a travel dial indicator, you can stack the deck a bit more to your side of the handwheels.  It all depends on how "close" is "good enough."

[SPiN Racing]

Wow.. I really appreciate the input.

I have been thinking hard about it for a while now. And the ideas and thoughts are appreciated.

Im thinking that the setup you made on that lathe there John is exactly what I am looking for.

Now to try to decide if I wanna make a changable setup for my existing lathe.. or just pony up and buy one of the cheapie chinese lathes from Harbor Freight, or WHolesale Tool, and convert it over, and park it in its own spot.. so I am not taking my main lathe offline.

Thanks again everyone.. When I start making the conversion, or new parts, I will make up a project log of it. (I have three projects in the works, that I am building, but have not started threads yet LOL)

Scott