# How To Turn A Round Groove?



## dieselshadow (Sep 25, 2016)

How can I turn a round groove with a radius of .063 on a manual lathe. Seems like round insert tooling is fairly rare for a lathe, let alone find one with the correct radius? 

Any good ideas?


----------



## T Bredehoft (Sep 25, 2016)

Round groove as in "O ring groove"?, grind a HSS tool. Yeah, it's a tiny thing, but doable. I made rollers for bending 1/8 wire hooks, they are .062 (or so) radius.


----------



## JimDawson (Sep 25, 2016)

The normal way to do that is to just grind a HSS tool bit as needed.


----------



## Cobra (Sep 25, 2016)

As Jim said, I would grind a HSS tool to the round nosed shape you show in the drawing and then plunge it into the piece.
I have done the same a number of times when making small v-belt pulleys.  Just go easy because you are cutting over a large area as you go in.


----------



## 4GSR (Sep 25, 2016)

Once you hand grind the radius, take a oil stone and hone the edge to get a smoother radius.  Then you will be ready to cut the groove.  Use your favorite cutting oil to get a nice finish.  After that, if you want, use a piece of very fine emery to polish the groove to 32 or better finish.  Ken

Edit: after looking at your picture, If you have a Acme threading tool ground up, put  a radius on the tip of tool.  That way you can blend the radius in with the sides of the groove.  Ken


----------



## Bob Korves (Sep 25, 2016)

If it is for an o-ring, an o-ring groove is square cut, to close tolerances.
http://www.sealanddesign.com/category/O-Ring-Groove-Design/183.html


----------



## Tony Wells (Sep 25, 2016)

I use full radius inserts when I need to cut a precision groove. They are also used for profiling. Many are available. Here's one example. Look at the A3 style in this Kennametal catalog:

https://www.kennametal.com/content/...9_MasterCat_stationary_groove_cutoff_inch.pdf

It starts on page D27.


----------



## Eddyde (Sep 25, 2016)

+1 on the HSS. 
The carbide would be fine if you had many parts to make but might be costly to purchase the holder and insert to for a one off part.


----------



## dulltool17 (Sep 25, 2016)

With care, you can grind a HSS tool blank to about any form you need.  With a bit of patience (something I wasn't blessed with in abundance) I managed to grind an 0.042 square to cut threads in a 5/16 sq blank for threading a Marlin 336 barrel.  0.062 radius will be a bit more challenging, but is doable.  HSS is very versatile.


----------



## GA Gyro (Sep 25, 2016)

When I first played with machining... around 1970...
There were no CNC machines and few carbide tools (most were brazed onto blanks).

Custom grinding the end of a HSS tool blank to do specialty machining on a lathe... was the norm.
I have forgotten how to do it, however one time, under the leadership if a seasoned old guy... ground a tool to cut hard rubber bushings.  Worked just fine!  

If I remember... most of the information you will need... is in the Machinery handbook... 
However I have no idea where... [grin]


----------



## Wreck™Wreck (Sep 25, 2016)

Not rare at all, do a Google search for lathe profile tooling, Manchester springs to mind for large tools and Kaiser thin bit for smaller parts, Kennametal has an excellent selection of form grooving tools.   http://www.kennametal.com/en/featured/grooving.html

If you are making parts that will not be measured by the customers inspection department then improvise.

By all means grind your own tooling from HSS  or carbide blanks.


----------



## Andre (Oct 6, 2016)

When I cut o ring grooves, I cut the groove then round the bottom with a round file of the right size. Works OK, and saves me the trouble of grinding radii every time. Be careful not to widen the groove too much, it can happen if you're not careful.

Sent from my XT1053 using Tapatalk


----------



## Tony Wells (Oct 7, 2016)

Andre, ring grooves designed for seals should not be round bottom. They are designed to actually allow some elastic flow in the 'o' ring itself due to the pressure they see. They fill the designed profile and exert pressure against the seal surfaces in a very specific way. They cannot function as designed with a round bottom groove. The ideal groove actually has a 2-5° angle on the flanks, wider at the top, and depending on the overall size, maybe a 0.010-0.015 radius in the inside corner and a 0.005-0.010 edge break on the OD. 

Have a look at Parker's seal design guidelines. There are several scenarios where the profile and specifics are discussed as to how and why they are specified the way they are.


----------



## bfd (Oct 7, 2016)

a .063" radius is .125" dia. so if you don't have a radius gauge drill and ream a 125" hole in a piece of sheet metal and cut it in half. this makes you a .063 radius gauge. then using a high speed steel parting tool grind the end to match your gauge. lots less grinding  this way. turn the lathe to one of the slowest speeds you have and plunge cut the radius. lots of cutting fluid don't let it chatter by feeding to slow. practice on a scrap part until you like the results. the is also a round emery cloth to fix up the groove if necessary. hope this helps bill


----------



## Downunder Bob (Oct 7, 2016)

Tony Wells said:


> Andre, ring grooves designed for seals should not be round bottom. They are designed to actually allow some elastic flow in the 'o' ring itself due to the pressure they see. They fill the designed profile and exert pressure against the seal surfaces in a very specific way. They cannot function as designed with a round bottom groove. The ideal groove actually has a 2-5° angle on the flanks, wider at the top, and depending on the overall size, maybe a 0.010-0.015 radius in the inside corner and a 0.005-0.010 edge break on the OD.
> 
> Have a look at Parker's seal design guidelines. There are several scenarios where the profile and specifics are discussed as to how and why they are specified the way they are.



Excellent advice O ring grooves should never be round bottomed, they have very specific dimensions and can be found in the Parker handbook.


----------



## Billh50 (Oct 7, 2016)

I don't see any "O" ring groove in that pdf. Looks like a pulley type roller. A simple tool bit ground with the angle and radius would work just fine.


----------



## Andre (Oct 7, 2016)

Tony Wells said:


> Andre, ring grooves designed for seals should not be round bottom. They are designed to actually allow some elastic flow in the 'o' ring itself due to the pressure they see. They fill the designed profile and exert pressure against the seal surfaces in a very specific way. They cannot function as designed with a round bottom groove. The ideal groove actually has a 2-5° angle on the flanks, wider at the top, and depending on the overall size, maybe a 0.010-0.015 radius in the inside corner and a 0.005-0.010 edge break on the OD.
> 
> Have a look at Parker's seal design guidelines. There are several scenarios where the profile and specifics are discussed as to how and why they are specified the way they are.


My mistake, I just used an O ring groove as an example. 

Sent from my XT1053 using Tapatalk


----------



## dieselshadow (Oct 7, 2016)

Well this project got passed by. I don't have any hand ground tooling, or a grinder setup to do it, and lastly I don't have the knowledge to actually grind my own tooling. This would be a handy skill to have. Clearly I can see the benefits and needs. 

Is there any reason not to use carbide blanks and grind those?


----------



## Tony Wells (Oct 7, 2016)

None at all.


----------



## Downunder Bob (Oct 8, 2016)

dieselshadow said:


> Well this project got passed by. I don't have any hand ground tooling, or a grinder setup to do it, and lastly I don't have the knowledge to actually grind my own tooling. This would be a handy skill to have. Clearly I can see the benefits and needs.
> 
> Is there any reason not to use carbide blanks and grind those?



None at all except you will need special grinding wheels for the carbide. There are numerous books and many schools run courses on how to grind machuine toolss from drill it to complicated profile cutters.


----------



## JimDawson (Oct 8, 2016)

dieselshadow said:


> I don't have the knowledge to actually grind my own tooling. This would be a handy skill to have. Clearly I can see the benefits and needs



The way you gain the knowledge and skill is to just do it.    The cutting edged sticks out further than everything else, all of the other surfaces are just clearance.  If you can sharpen a cold chisel, you can grind lathe bits.

A cheap bench grinder or belt/disk sander and a random piece of metal makes a pretty good practice platform.  Useful tool bits can be ground from many different broken tools.  Broken taps, broken drill bits, broken end mills.  I save all of the broken bits and I tend to generate quite a few .

BTW, I use my bench grinder with a standard aluminum oxide gray wheel for 99% of my carbide grinding, you just have to push a little harder.  Grinds pretty fast once it gets red hot.


----------



## dieselshadow (Oct 8, 2016)

Thanks for the tips guys!


----------



## Wreck™Wreck (Oct 8, 2016)

I have never seen a radius form O-ring groove specified by an engineer in 25 years, however I do currently make parts as drawn by a Customer employing dovetail O-Ring grooves in large parts for high vacuum applications, this is a far more difficult task to accomplish, as mentioned above Kaiser makes such tools.

I have no relationship with Kaiser. I just use their tools.

http://www.thinbit.com/pdfs/thinbit_sec_2.pdf


----------



## kd4gij (Oct 8, 2016)

dieselshadow said:


> Well this project got passed by. I don't have any hand ground tooling, or a grinder setup to do it, and lastly I don't have the knowledge to actually grind my own tooling. This would be a handy skill to have. Clearly I can see the benefits and needs.
> 
> Is there any reason not to use carbide blanks and grind those?



 Now that you passed on it. I would get some scrap and try and cut the groves. Would be a good learning project.


----------



## dieselshadow (Oct 8, 2016)

Yup. That's a good idea. I'll order me up some carbide tipped tooling to grind.


----------



## Bob Korves (Oct 9, 2016)

If the part is not too hard, you can grind the back end of a 1/8" drill bit to a sharp edge at a few degrees off a 90 degree angle and make a holder if necessary from a piece of key stock with a 1/8" hole in it and a set screw to hold the bit.  Quick, easy, cheap, and with a little care, accurate.


----------



## Tony Wells (Oct 9, 2016)

Shanks of drills aren't all that hard out where the chuck has to be able to get a bite on them, so cut off a little to get closer to the fluted area. It's harder there. Or, you can use a broken center drill, or on-size end mill shank. They're all hard. Carbide works great for that, but it's a little hard to get the set screw to bite into. But you can make a clamp type holder for that, and it works very well.


----------



## Downunder Bob (Oct 10, 2016)

Bob Korves said:


> If the part is not too hard, you can grind the back end of a 1/8" drill bit to a sharp edge at a few degrees off a 90 degree angle and make a holder if necessary from a piece of key stock with a 1/8" hole in it and a set screw to hold the bit.  Quick, easy, cheap, and with a little care, accurate.



Good idea except the back end of a drill shank is not usually fully hardened, use a broken drill bit. Broken centre drills also make great little cutting tools for various jobs, make up boring bars by drilling a suitable hole across the end of a suitable sized bar to take the brocken centre drill, also drill and tap an axial hole from the end fit with grub screw to clamp tool. Or simply weld a small piece of HSS to the end of a bar  then grind it up to make a quick boring bar


----------



## Bob Korves (Oct 10, 2016)

Or just use a 1/8" round HSS tool bit.


----------



## Jimsehr (Oct 13, 2016)

If you order a Kennametal insert     VNGA-434T 0820   It has the right size radius and shape to do that groove. You would have to set the 15 degree angle off a little as the v shape of the insert is 35 degrees and do one side of part at a time. I'm sure you could get other inserts to work also.
jimsehr


----------



## Downunder Bob (Oct 14, 2016)

Jimsehr said:


> If you order a Kennametal insert     VNGA-434T 0820   It has the right size radius and shape to do that groove. You would have to set the 15 degree angle off a little as the v shape of the insert is 35 degrees and do one side of part at a time. I'm sure you could get other inserts to work also.
> jimsehr



Maybe so, but Kennametal tooling is so expensive in Australia, yes I know it's good quality, but just too expensive for the hobby machinist.


----------



## Downunder Bob (Oct 14, 2016)

Jimsehr said:


> If you order a Kennametal insert     VNGA-434T 0820   It has the right size radius and shape to do that groove. You would have to set the 15 degree angle off a little as the v shape of the insert is 35 degrees and do one side of part at a time. I'm sure you could get other inserts to work also.
> jimsehr



Maybe so, but Kennametal tooling is so expensive in Australia, yes I know it's good quality, but just too expensive for the hobby machinist.


----------

