Creating a GROOVE inside a very small TUBE (on the lathe)...

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chugbug
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Joined: Fri Jan 17, 2020 3:32 pm

Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by chugbug » Fri Jan 17, 2020 5:02 pm

Hello All,

This is my first post here, so I hope I'm posting in the correct forum category! As the subject states, the basics of what I want to do is cut a groove inside a very small tube. I make custom fountain pens, and I want to cut a groove around the inside of a pen barrel about 1.25" in from the end for a retaining spring that will hold the lever in place (for a 'lever-filler' pen). The hole in the barrel is 9mm, and the slot only has to be deep enough so the retaining or snap spring will seat into without moving.

My Idea (that didn't quite work)... was to make a tool that I mounted in the tailstock that reached into the barrel. The cutting end was a straight piece of spring steel wire with a 90 bend on the end that was ground with a cutting edge. I mounted the cutter into the end of a wooden dowel so it was off-center and mounted it in a chuck in the tailstock. With it off-center once it is moved up inside the barrel the cutting edge rubbed against the inside of the barrel. Then to cut the slot I just added finger pressure to increase the force of the cutter. It seemed to work at first, but will only cut a shallow scoring groove. I can't get it deeper.

I think the technique will work, but need something I can put a better cutting edge on, and/or will be stiffer. Any suggestions? As I mentioned before, the hole is only 9mm in diameter, so I need something small. Attached is a photo showing the cutting tool and parts.

Thanks...John
Attachments
jeb_slot_cutting_parts.jpg

whateg0
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Location: Wichita, KS

Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by whateg0 » Fri Jan 17, 2020 5:32 pm

If I was making this part, I would grind a tool to put on the toolpost. That way, I can control the depth of the groove. That looks like just a wire, and I can't see what the cutting edge looks like in the photo. I think you would have a hard time getting consistent results that way, even if you do get a good cutting edge on it. 9mm is plenty of room for a small boring bar-style tool made for that specific groove.

Dave

whateg0
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by whateg0 » Fri Jan 17, 2020 5:35 pm

Here's an example of the style of tool I would use.
boring.jpg

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liveaboard
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by liveaboard » Fri Jan 17, 2020 6:45 pm

What Dave said.
I've never made one quite that small, but pretty close.'
I like snap rings.

whateg0
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by whateg0 » Fri Jan 17, 2020 7:04 pm

You don't have a location in your profile. I know a lot of folks here are willing to help somebody learn. I am going to guess from the tool you were using that you don't have a lot of training on running the lathe?

Dave

Harold_V
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by Harold_V » Sat Jan 18, 2020 2:52 am

As your post relates to lathe work, it would be best placed there, but it's not a requirement. It's fine where it is.

Dave's advice is spot on. It's not all that hard to hand grind a proper tool, one you'd mount in your tool post. That will allow you full control over where the groove is located, and its depth. Width can be controlled by the width of the cutting edge, or you can use a tool that is narrower than your requirement, and move the carriage for a second plunge cut. The use of a long travel indicator makes that very easy.

One work of caution. If you don't understand cutter geometry, you're most likely to fail in this endeavor. If you need guidance, ask, as many here are seasoned machinists and can help you gain the needed understanding.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

John Hasler
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by John Hasler » Sat Jan 18, 2020 11:38 am

One way to make such tools is to start with an HSS drill bit.

chugbug
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by chugbug » Sat Jan 18, 2020 4:28 pm

Hi Everyone, Thanks for the suggestions!

Harold, I considered the lathe section, but the description of that section read to be that it was for discussions relating to lathe models or brands.

I figured it out! I basically made a tool similar to the one WHATEG0 shows in his photo. After I thought about it for a few hours and dug around in my junk metal looking something suitable, I realized I had a box full of the perfect cutters-- metal paint can openers! The metal on most is pretty hard and they already have a hook on the end, that I was able to grind to a nice sharp point. I had some with flat sides, that allowed me to mount one in the center of a wooden dowel (after cutting off the round end). I drilled through it and installed a hinge pin so it could swivel allowing me to pull it down into the part to make the cut, then bring it up out of the way. I still mount it in the tailstock (rather than holding it), thinking it would be easier to duplicate the same cutting depth (length from the end) every time. I used another can opener to pull down at the front (in front of the dowel) to apply cutting pressure. It worked so well, I cut my first test piece in half! After making a few more test cuts I was able to anticipate when I was deep enough based on the sound of the cutting.

I also have plenty of can openers in case I need a new cutting edge. Attached is a photo of the new tool (and my first test piece).

Thanks again! John
Attachments
jeb_slot_cutting_new-parts.jpg

pete
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by pete » Sat Jan 18, 2020 9:11 pm

Already hardened metal items will obviously work, most of it will be some type of high carbon steel with unknown quality's. And yes high carbon steel was and still is used today and it was the only tool steel available for multiple century's. But it's now mostly used in home shops to come up with custom tool shapes. Most will use a known type and grade of high carbon tool steel to make those tools since the hardening and tempering temperatures as well as oil, water or air quenching is published for the type of steel your buying. In most home shops without a temperature controlled furnace the temperatures are judged by eye by there colors that can be found with a Google search. The finished tool will also have known quality's for hardness or at least ball park numbers, but more importantly the maximum speeds it can be used up to. I'd say most small lathes and especially the off shore ones are incapable of going slow enough to use high carbon tools on anything of any size. High carbon steels wouldn't last for very long at all. Commercially and for multiple reasons it's probably seldom used for cutting tools while machining today. High carbon steels durability or cutting edge life span and it's cutting speeds are well under what actual High Speed Steels (HSS) can provide. And high carbon steel is easily damaged while grinding or even trying to use it at higher cutting speeds than it's capable of. HSS can survive up to red heat cutting temperatures. But it's not normally heat treatable in any average home shop so the tools are ground from already hardened HSS. Your tool worked and you should be commended for thinking outside the box. But I'd highly recommend Googling for and reading in detail the book How to run a Lathe published by South Bend Lathe. The correct cutting tool angles and shapes as well as what they might be used to do are fairly well covered.
Last edited by pete on Sat Jan 18, 2020 9:15 pm, edited 1 time in total.

whateg0
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by whateg0 » Sat Jan 18, 2020 10:18 pm

For cutting plastic, whatever you are using will likely be just fine, but your method is not the preferred method. If you try to cut steel, or other harder metals, your tool will not last, as mentioned by Pete.

Magicniner
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by Magicniner » Sun Feb 02, 2020 12:43 pm

Iscar MGCH06 bar and the appropriate GIQR8 grooving cutter/insert good for holes down to 8mm on the lathe

For cutting plastic and the forces involved you could make your own holder rather than buying the MGCH06 bar, you can buy individual GIQR8 grooving cutters for a few dollars.

https://www.google.com/search?q=iscar+g ... e&ie=UTF-8

whateg0
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Re: Creating a GROOVE inside a very small TUBE (on the lathe)...

Post by whateg0 » Sun Feb 02, 2020 5:38 pm

Magicniner wrote:
Sun Feb 02, 2020 12:43 pm
Iscar MGCH06 bar and the appropriate GIQR8 grooving cutter/insert good for holes down to 8mm on the lathe

For cutting plastic and the forces involved you could make your own holder rather than buying the MGCH06 bar, you can buy individual GIQR8 grooving cutters for a few dollars.

https://www.google.com/search?q=iscar+g ... e&ie=UTF-8
Those are some neat looking inserts. I might pick up a few, and as you suggested, make my own holder. TBH, since the OP was using a piece of wire for the tool to begin with, I doubt he is going to spring for anything painted ISCAR green!

Dave

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