Gooseneck or spring-tool holder

[petcnc]

Since I bought my mini lathe, a decade ago, I had never managed to make a decent parting-off procedure.

I always put the blame on the tool so I moved from a simple blade tool (like the one in the next picture) that I have bought with my lathe...



..to a more sophisticated one with inserts.


No matter what tool I used the results were always similar. It was not a matter of “if” the blade digs in, but more “when” is it going do dig in. As a result, the whole process either stopped or the material ruined.

Needless to say that both tools were damaged in the process...

Researching the subject, I found out that the problem is very common even to larger lathes and many people suggested either a rear mount parting tool holder


...or to fix the parting tool upside down and run the lathe in reverse.

As I’m not convinced that the toolpost of my mini lathe were designed to work this way (i.e to accept forces that try to lift the tool up) I looked for something better.


My research lead me to the following article from Popular Mechanic magazine published in November 1944!.


The author claims that the best tool for the job is the “Spring-type tool” that works far better for the cutting process.
The working principal of the tool is that it works by flexing downward and away from the work as the loads change from the tool digging into the work, relieving the pressure momentarily.

As I could not find a ready-made one I decided to design mine from scratch.

I designed the tool based on my mini lathe capabilities and the blade I already owned from my first “commercial” tool.
Using eMachineshop (the simplest free-cad program) it was a matter of minutes to design it.


The basic shape will be as below.


With a cut from bottom to the large hole the tool will have the flexibility needed


A piece of scrap metal volunteered to provide the flesh for the tool. The rest was just fun!


A printout of the design on the metal helped to decide the cuts needed.


All necessary cuts were made on the band saw.

(A sharp eye will notice that the initial hole of my design was 8mm and the filal was made 12 mm! That change gave me the needed flexibility for this small blade I use)




The tool gradually took it’s shape.




Next step involved some cleaning and drilling on the mill.




After a final visit to the band saw for the last cut, the basic tool is ready.




A bar to the side needed to hold the tool to the tool post and a bolt to secure the blade.




With all parts in place the spring tool looks promising…




A test cut on the lathe proved its potential! No bites anymore! It cuts as it should!!!



Thanks for visiting

Petros

 

[thomas s]

Petros, Nice job.

 

[thomas s]

Petros, Nice job.

 

[MikeWi]

Man,I wish PM magazine was still like it was back then. Just garbage now.

 

[petcnc]

Man,I wish PM magazine was still like it was back then. Just garbage now.

I did not know it still existed!!!

 

[RJSakowski]

IMO, the two enemies of successful cutoffs are rigidity and available torque. These two factors a different for every machine and setup which accounts for the wide variation in prescriptions for successful cutoff. Unfortunately, mini lathes suffer from both. A large lathe is rigid enough to not flex as cutting forces increase and has enough oomph to keep cutting when the going gets tough.

Any lathe will have some flex somewhere along the mechanical chain from the cutting edge to the spindle. Flex can come in the tool itself, the tool holder, the compound, the cross feed, the apron, etc. all the way back to the work itself. How the cutting edge of the tool deflects will depend upon the relative effects of each of these factors. Interestingly, the spring parting tool has purposely added flex to the system which would seem counter intuitive

Available torque is another big issue. Some say the only way to part is to feed aggressively. Doing so with limited available torque means that you are almost to the point of stalling so any slight increase in cutting force will stall the lathe. As the lathe starts to stall, you momentarily increase the surface feet/rev. which increases the cutting force forcing the stall.

The spring parting tool will provide negative feedback to decrease the cutting force, preventing stalling of the lathe. It is interestng that the tool is no longer available. Armstrong had several in different sizes and configurations in the their 1947 catalog. I suspect that is possibly due to the relative scarcity of smaller lathes.

 

[petcnc]

I agree with RJ 100%. As I own a mini lathe the spring tool was the only way to go!

Totay I have put some finishing touches to the tool to make it look ...more like a tool.

 

[ericc]

In the Popular Mechanics article above, the hole looks positively tiny. I suspect that it has little spring to it. Is it just an illustration or artist's conception?

 

[Latinrascalrg1]

In the Popular Mechanics article above, the hole looks positively tiny. I suspect that it has little spring to it. Is it just an illustration or artist's conception?

I dont think the size of the hole is a huge factor in the drawing. The purpose for the hole is to relieve any stress that possibly built up within the tool that may be exposed by the cutting of the slit to keep it (the slit) from traveling past the point intended for the project.

 

[RJSakowski]

Here is a copy of the 1947 Armstrong catalog.

http://pounceatron.dreamhosters.com/docs/misc/Armstrong-Catalog-THB49-1947.pdf

The spring parting tool is on page 7. The hole at the end of the slot is relatively small on it. The size of the hole isn't as important as the width of the material surrounding it as that is what constitute the spring. Ideally, the tool would have been made from a hardened tool steel drawn to a spring temper.