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Gooseneck or spring-tool holder

petcnc

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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...

Simple blade.jpg

..to a more sophisticated one with inserts.
Insert parting.jpg

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

Back cutter1.jpg
...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!.

Spring tool use.png
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.

Gooseneck new.jpg
The basic shape will be as below.

3dSketch.jpg
With a cut from bottom to the large hole the tool will have the flexibility needed

3dSketch1.jpg
A piece of scrap metal volunteered to provide the flesh for the tool. The rest was just fun!

IMG_20191008_151704332.jpg
A printout of the design on the metal helped to decide the cuts needed.

IMG_20191008_151751242.jpg
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)

IMG_20191008_153004967.jpg


The tool gradually took it’s shape.

IMG_20191008_154324636.jpg


Next step involved some cleaning and drilling on the mill.

IMG_20191008_173814505.jpg


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

IMG_20191008_183955298NEW.jpg


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

IMG_20191009_004351622Parts.jpg


With all parts in place the spring tool looks promising…

IMG_20191009_005010262Fin.jpg


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

IMG_20191009_010437881.jpg

Thanks for visiting

Petros
 
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MikeWi

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

RJSakowski

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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.
 

ericc

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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

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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

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Here is a copy of the 1947 Armstrong catalog.
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.
 

petcnc

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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.
Very true RJ! In my tool around the 8mm hole there was a thick wall of material that gave very little spring action for the tiny blade (1.5mm X 5.5 mm) that I use. The only way to make the sourrounding material thinner, after the initial drilling, was to enlarge the hole.
 

savarin

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Is there a reason why these are no longer available?
 

Tim9

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Probably doesn’t need a lot of spring. Just needs a little bit of spring....or a little bit of give to smooth out a relatively fast operation. Even an older slower speed lathe like a South Bend, you’re still going around 500 rpm...or more. So it doesn’t have to give a lot. Just enough to smooth things out.
 

RJSakowski

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Is there a reason why these are no longer available?
Something that I pondered. Armstrong started making lantern style lathe tool holders in 1895. Their design was innovative in that it allowed replacement of a cutting bit rather than the whole tool. Armstrong became synonymous with this style tool holder. My Craftsman lanern style tool holders were made by Armstrong.

I suspect that the company ceased production of lathe tool holders when lantern style tool holders gave way to the QCTP, 4-way, and other styles. Armstrong began making industrial hand tools in 1909, including the Craftsman Professional line in its later years.

Armstrong was bought out by Danaher in 1994 and continued production of hand tools. Apex acquired Armstrong as part of the Dananher group in 2010 and ceased production of the Armstrong and Allen brands in 2016.

This style of cutoff tool holder was also made by J.H. Williams, acquired by Snap On in 1993.

Wholesale Tool still sells some lantern style tool holders made by RDX, an offshore brand.
 

benmychree

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One thing that I appreciated in the article was making a tool post ring the correct thickness to bring the parting tool on center, with no rocker wedge; when using a offset tool holder, it has a tendency to slip and allow the tool to cant over when things hang up, usually breaking the tool bit in the process, years ago before I went to Aloris holders, many parting tools were broken in that way, after I made the solid ring, very seldom was a tool broken in that way. I have no problems with parting on my 19" lathe, but do have problems with my 9" lathe, which is in excellent condition; the problem stems from having the tool holder overhung over the the front edge of the cross slide, and the tool tends to tip to the left, causing binding of the cut; when I move the holder to the right so that it is not overhung, the problem goes away, but then there are problems when using other tools and the compound tends to interfere with the chuck jaws; such is an imperfect world!
 

Silverbullet

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YouTube ,, Igorcowa,, or igorkowa ,,, Hes Russian I think but he's a darn good machinist , he made some on a videos. And it's quite easy to see when he uses them.
 

stioc

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YouTube ,, Igorcowa,, or igorkowa ,,, Hes Russian I think but he's a darn good machinist , he made some on a videos. And it's quite easy to see when he uses them.
Not finding him on youtube with those two spellings. Do you happen to have a link to his video/channel etc?
 

mickri

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Here is a video on how these spring tool holders work.

Here is another video showing how it works when making a cut. Fast forward to about the 7 minute mark in the video.
 
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RJSakowski

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Here is a video on how these spring tool holders work.

Here is another video showing how it works when making a cut. Fast forward to about the 7 minute mark in the video.
Thanks for sharing. A great explanation from Tom as to mechanics of the spring tool. If you think about it, this is exactly why using a parting tool upside down works so well.
 

petcnc

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Final finishing touches to the tool.
I did not like the bolt securing the blade on the holder so I made it a bit more sophisticated.
Started with a plain 6mm bolt, rounded the head and machined it to 8 deg angle

Bolt.jpg

It secures blade better than the previous one, plus the tool looks more "sophisticated" :grin:

Finished_Tool1.jpg

Finished_Tool2.jpg
 

ptsmith

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Ah ha! I'm reading this thread and not understanding how this works. Flex is the reason parting is a problem on smaller lathes. So you would think a tool holder that flexes would make matters worse.

The videos clarify that the key is the above the center line pivot point that causes the blade to kick out instead of dig in. And that makes total sense.

As others have mentioned, you have to wonder why they don't make these anymore.
 

mickri

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This is now my next project.
 

stioc

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If this really works I so need it because parting off for me always takes forever and/or end up in fireworks- even when I follow all the general advice. Since I have a threaded chuck running the lathe in reverse(for a rear mounted parting tool is not ideal.
 

mickri

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Don't have to make one. Found two for sale on Ebay. Should have them by the end of next week.

gooseneck tool holders.jpg
 
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