# Best Homemade Tools >  Lathe Cutting Tool for O-ring Grooves (and trepanning)

## Paul Jones

I machined an O-ring groove located a little too close to a parts inner corner for using my old lathe O-ring cutting tool. I tried running the lathe in reverse so I could approach the O-ring groove from the more narrow side of my O-ring cutting tool but still not enough room for the tool.

I have been wanting a more universal O-ring cutting tool so I ground a new O-ring cutting tool made from an old blank of Rex AAA HSS. The tool cutting face width is 0.095 and 0.5 long (to the shoulder) and ground at an offset of 30 degrees from the center line to provide better access. In addition to using the cutting tool for making O-ring grooves, it is also does a great job as a trepanning tool. I used it recently to remove a 3.5 diameter center section from a plate of T-304 stainless steel. The Rex AAA HSS had no trouble trepanning the stainless steel. I included some photos of the tool at work.

----------

billster (Apr 15, 2018),

C-Bag (Jan 15, 2016),

jjr2001 (Sep 1, 2016),

Jon (Jan 10, 2016),

JRock (Apr 15, 2018),

kbalch (Jan 11, 2016),

LMMasterMariner (Nov 22, 2017),

NortonDommi (Nov 16, 2017),

nova_robotics (May 12, 2022),

olderdan (Nov 17, 2017),

PJs (Jan 12, 2016),

Sleykin (Nov 18, 2017),

Tonyg (Dec 27, 2019),

Vyacheslav.Nevolya (Nov 17, 2017)

----------


## kbalch

OK, that's not what came to mind when I read "trepanning"!  :Lol: 

Ken

----------

Paul Jones (Jan 11, 2016)

----------


## DIYer

Thanks Paul! We've added your Groove and Trepanning Tool to our Lathes category, as well as to your builder page: Paul Jones' Homemade Tools. Your receipt:












Groove and Trepanning Tool
 by Paul Jones

tags: lathe, trepanning, grooving

----------


## PJs

Thanks Paul! Your grind work is beautiful and the radii...Wow! Never heard of the tool material but took a look at Crucible's site. Lots of tungsten (18%) and seems to have a balanced all around toughness, hardness and abrasion resistance at 64-66HRC. Did you have to grind it with diamond or special stone and are they good for particular metals? Can't see much of a rake (clearance angle) to it? Thanks for the tip on these!

Looks like your 4 jaw was about maxed out on that plate but the finish looked great from what I could see!! Made a custom trepan/o-ring cutter out of a P1 cuttoff blade a while back to use on acrylic. The thin undersection of the P1 worked great for cooling from the hot plastic...slow to work but did fine with it. Thanks for sharing your great work! ~PJ

----------


## Paul Jones

Thanks PJs. The Rex AAA HSS tool bit is one very tough cookie but can be ground with conventional aluminum oxide wheels on a pedestal grinder using a rough 36/46 grit to take away most of the material. The final grind finish was with 120 grit silicon carbide wheels. 

I have another pedestal grinder (toolmaker style) that has 100 and 220 grit diamond wheels but didn't want to waste the diamonds on this tool but may use the 220 grit to product an ultra smooth finish if needed next time. I ground a 10 degree side angle clearances on the sides of tool and added an undercut to the front tip by removing 0.22" for more clearance for the small radius O-ring grooves. In the trepanning work for the T-304 stainless steel plate, I had to run the lathe at 70 RPM and still ran into a lot of chatter and squeak (you know it is bad when even the dogs leave the garage because of the noise - I had my -30dB ear muffs on  :Big Grin: ). Thanks for the questions, Paul

----------

PJs (Jan 13, 2016)

----------


## PJs

> I had to run the lathe at 70 RPM and still ran into a lot of chatter and squeak (you know it is bad when even the dogs leave the garage because of the noise - I had my -30dB ear muffs on ).



 :ROFL:  I hear ya clear over here!

I get the side clearances for O-Rings, especially. Thanks Much! ~PJ

----------


## rossbotics

Good work Paul
I been needing one of those myself, wouldn't use it allot, but would be nice to have when the moment arrives, when I was coming up In the shop all we had was old rex95 tool bits,
Looks like it did a nice job on that tough old stainless,
Great post

Doug

----------

Paul Jones (Jan 19, 2016)

----------


## Ralphxyz

Trepanning
Trepanning, also known as trepanation, trephination, trephining or making a burr hole is a surgical intervention in which a hole is drilled or scraped into the human skull, exposing the dura mater to ... Wikipedia

Just had to google trepanning

Ralph

----------


## mklotz

> Trepanning
> Trepanning, also known as trepanation, trephination, trephining or making a burr hole is a surgical intervention in which a hole is drilled or scraped into the human skull, exposing the dura mater to ... Wikipedia
> 
> Just had to google trepanning



A better definition for "trepan" looks like this...

a tool for cutting out circular blanks or for making grooves around a fixed centre.
the operation of cutting a hole with such a tool; the hole so produced

In surgery, the hole in the skull is not "drilled" as one would use a drill in a drill press to make a hole. Rather a device similar to a hole saw is used to remove a circular piece of skull. The resulting hole gives access to the brain. When the procedure is done the circular bit of skull can be sown back into place and will heal over to close the hole quickly.

In surgery the intent is to save and reuse the material from the hole. In metalworking we do the same thing when we use a hole saw and then repurpose the slug removed from the hole.

In many metalworking applications the intention is not to make a complete through hole but rather to make a groove or depressed area in the workpiece. Many flywheels have a depressed center to lighten them without seriously diminishing their moment of inertia. The process of turning this depression is referred to as trepanning, the gerund form of "trepan".

----------


## Ralphxyz

Thanks Marv, I knew there had to be a metalworking definition.

Ralph

----------


## Jon

While cutting an access hole in a skull is a perfectly legitimate modern neurosurgical procedure (also see Craniotomy), trepanning was a ghoulish technique in ancient times, used to create an escape route for skull-dwelling evil spirits. Of course the antique medical trepanning tools are interesting.

----------

gunsgt1863 (Nov 20, 2017),

JRock (Apr 15, 2018),

Seedtick (Nov 17, 2017)

----------


## mklotz

It's worse than that. Many ancient societies, not yet out of the stone age, were trepanning people to release evil spirits. They were using flint knives! We know that this is true because skulls have been found with nice round holes and new bone grown at the circumference of the holes, proving that the patient survived the operation at least for a while. The holes are far too big to have been made by a survivable blow from a weapon. Any weapon large enough to make the hole would have penetrated too far into the brain to be survivable.

Even today, some nutbars think the procedure has beneficial effects and do it when not needed surgically. Full story here...

https://www.damninteresting.com/the-...n-trepanation/

If you're interested in trying this exciting form of self-medication, an antique trepanning brace is available...

https://ahp.apps01.yorku.ca/?p=268

If that's too slow, a Starrett hole saw in a Milwaukee cordless drill will do the job just fine.

----------

gunsgt1863 (Nov 20, 2017),

Seedtick (Nov 17, 2017)

----------


## Turboconqueringmegaeagle

It puts things into perspective, here in the UK complaining about our national health service is a national pastime, maybe those that are unhappy about waiting 4 hours to be seen for a completely avoidable drunken mishap should be relieved of their frustration in this traditional manner.
i'm absolutely full of admiration for our NHS and the many highly skilled folk working for them, having spent a fair bit of time around technicians carrying out ultrasonic non destructive testing on aircraft I thought i knew it all until i got shot in the arse with a high powered air riffle and the ultrasonic technician at hospital followed the entrance hole across my buttock until she found the pellet, marked it with an X and wrote 12mm beside it signifying its depth.

----------

