# How do I cut o-ring grooves



## Grasshopper (Apr 7, 2020)

I'm new at this and wanted to know if there is an insert for cutting o-ring groves. I want to add one o-ring to a shaft that presently employs only one o-ring. Has this already been covered elsewhere on this site? TIA, Kent


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## kd4gij (Apr 7, 2020)

There are grooving inserts. Or grind a HSS bit to the with of the groove that is in there. The tool holder and insert won't be cheap. A parting blade can be ground to the right size.


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## Jimsehr (Apr 7, 2020)

Also might look at quad rings. It’s almost like having two rings in place of one. 
jimsehr


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## benmychree (Apr 7, 2020)

Proper O ring grooves are not straight sided as to be cut with a parting blade, they are tapered at the sides and have radii at the root.


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## Cadillac (Apr 7, 2020)

benmychree said:


> Proper O ring grooves are not straight sided as to be cut with a parting blade, they are tapered at the sides and have radii at the root.



Idk about that. I rebuild ALOT of hydraulic motors, cylinders and can't recall any being radiused at the root. Only time I can remember that scenario is some engines where a large oring is used to seal two mating surfaces. 
 I do know the groove size is critical to get the proper squish on the oring to seal correctly, and different pressure involved use different designs.


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## OTmachine (Apr 7, 2020)

O-ring groove sides are pretty much straight.  They can have taper, but are better if straight. Best tool profile is like a double hump camel face parting tool with the width of the tool narrow enough so that the top of the one hump will just pass over the surface cut by the top of the other hump.  My .02


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## benmychree (Apr 8, 2020)

So, look it up!


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## BGHansen (Apr 8, 2020)

Here are some options for O-ring grooving.  The inserts are MGMN style which are available in a number of widths.  Search on eBay for MGMN 150, 200, 300, 400, etc.  They are metric in size, divide the number by 100 for the width in millimeters (200 = 2 mm).  They are available in external and internal set ups.


These happen to be MGMN200 and MGMN300 bits on boring bars ($10 or less with 10 bits from China)



Insert is replaceable and double ended




External MGMN200/300 inserts.  I wrote the English width on the tool holder for DRO purposes ($10 or less with 10 bits from China).






Also pictured are a number of Rovi solid carbide pre-ground boring bars for grooving.  These are available from a number of sources (i.e. Micro 100, Rovi, etc.).


These work really well, much better than the MGMN bits, but they are more pricey (~$20 each).




Or, as mentioned above, you can use a boring bar and hand grind a cutter to the width you need.






Bruce


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## twraska (Apr 8, 2020)

benmychree said:


> So, look it up!



All specs I’ve ever seen were for a square bottomed groove.  Do you have specs for round bottomed?  I’d like a link for my information if you do.
Thanks
Tim


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## Janderso (Apr 8, 2020)

I checked MSC for grooving tools. The first few that popped up did have a radius.
For example,
*0.145" Groove Width, 1/4" Min Hole Diam, 5/8" Max Hole Depth, O-Ring Grooving Tool*
In the specs of the tool, it showed a .040" radius.
I have no opinion, I'm just a hobby guy.

I also found this guide, it mentions -radius
<<<<<<Metric o-ring groove designs vary greatly and choosing the right one for your application is important for maximum o-ring performance. This metric o-ring groove design reference guide will help you find the right radius, back-up, pressure and other o-ring dimensions for basic applications. Once you find the exact metric o-ring you need, you can easily order online from the world's largest o-ring inventory network. >>>>>>>


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## Jimsehr (Apr 8, 2020)

Of all the thousands of o-ring grooves I have cut . I have always cut them with straight sides and flat bottoms . The blueprints called straight sides or up to 5 degrees taper . Larger at the top. I have special depth mic rods to check the width and location of the grooves. I also have special gages to check dia of the Id grooves. And I mostly used hand ground old school tools. I remember hating to grind the tools in my 20s . But that was over 60 years ago and you could not buy all the store bought tools like today.
jimsehr


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## macardoso (Apr 8, 2020)

Take a look at ThinBIT by Kaiser. They have inserts ground for the correct O-ring profile. Not cheap (maybe $120 for the tool and the inserts), but a purpose made insert is the *right* way to do it.

These are certainly not the only inserts that do the job, but I've been very impressed with the Groove-N-Turn product line.

Groove-N-Turn Page 7-8 shows a nice boring bar and page 1-12 shows the inserts for the O-Ring.



			http://www.thinbit.com/documents/catalog_oring_grov.pdf


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## kd4gij (Apr 8, 2020)

I rebuilt hydraulic cylinders for 15 years in the past. All had straight sides and flat bottom.  Inserts do have a corner radius witch depends on the with. the smaller the with the smaller the radius, the larger the width the larger the radius.  The radius serves to purposes, 1 for preventing the part from cracking and also aids in too chipping.  That is for cylinders and rods or pistons.


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## BtoVin83 (Apr 8, 2020)

There are whole books on cutting o ring glands, static, rotary and reciprocating. I have seen tapered sides and straight sides, radiused bottoms and square bottoms. A lot depends on the application and that is what is called engineering.


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## Grasshopper (Apr 8, 2020)

Thanks for all of the great answers. You've given just the info and required reading to set me on my way. I can't thank you fellas enough. Learning is fun and this is a great place to learn from the "real life experience" crowd. Thx again.


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## Alcap (Apr 8, 2020)

I've used this ( hard copy though )  most of the engineering is way beyond me but did learn some info on O-rings https://www.parker.com/literature/Praedifa/Catalogs/Catalog_O-Ring-Handbook_PTD5705-EN.pdf


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## OTmachine (Apr 8, 2020)

Jimsehr said:


> Of all the thousands of o-ring grooves I have cut . I have always cut them with straight sides and flat bottoms . The blueprints called straight sides or up to 5 degrees taper . Larger at the top.
> jimsehr


I, also have been cutting o-ring grooves for the last 40 years and agree 100% with Jimsehr.  Most times the corner radii have been .005 to .010 maximum.  All of the Googling in the world will not give you “experience”.


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## epanzella (Apr 9, 2020)

Geez, this is getting complicated. Just grind a high speed tool to match the groove that's already there. Duplicate the the existing groove.


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## ErichKeane (Apr 9, 2020)

epanzella said:


> Geez, this is getting complicated. Just grind a high speed tool to match the groove that's already there. Duplicate the the existing groove.



This thread has (re)taught me how expensive being a carbide shop is!  $125 for an insert that I'll probably overfeed and destroy the first time I use it, then only use for 1 hole is crazy.  I'll stick to grinding and burning HSS thank you very much!


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## epanzella (Apr 9, 2020)

ErichKeane said:


> This thread has (re)taught me how expensive being a carbide shop is!  $125 for an insert that I'll probably overfeed and destroy the first time I use it, then only use for 1 hole is crazy.  I'll stick to grinding and burning HSS thank you very much!


I've got a drawer full of various HSS tools both ground by me and inherited. There are so many different sizes of O-ring grooves that more often than not I have to grind one because none of the half dozen or so groove cutters I've already ground are the right size. I can't imagine buying a new carbide tool every time every time I needed to set an O-ring. Even if I didn't mind spending the money (which I do) the wait for shipping in the middle of a project would annoy the crap out of me. (and I can't find toilet paper)


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## macardoso (Apr 9, 2020)

ErichKeane said:


> This thread has (re)taught me how expensive being a carbide shop is!  $125 for an insert that I'll probably overfeed and destroy the first time I use it, then only use for 1 hole is crazy.  I'll stick to grinding and burning HSS thank you very much!



I should have been more clear. The boring bar and clamping hardware would probably be $100. The inserts are around $15 each. Really nice quality tools. I've used their grooving line since changing inserts repeats the tip position and length within a tenth or two. Very impressive.

I purchased these tools for a paid CNC job where not needing to worry about offsets or grinding tools in the middle off the job was valuable to me.


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## srfallsallot (May 18, 2020)

If your assembly creates an issue with the o-ring staying in place consider a 1/2 dovetail groove


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## Grasshopper (May 18, 2020)

I ended up cutting a square groove the same dimension as the factory groove, 2mm wide x 1mm deep. The guy sold out in one day and sent me 20 more to turn today. If he only knew how inexperienced I am he'd pay a real machinist to do this. LOL. He is a friend so I thought I'd help him supplement his SS check. Beside, it's fun and I need all the experience I can get.


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## Jimsehr (Jul 6, 2021)

epanzella said:


> I've got a drawer full of various HSS tools both ground by me and inherited. There are so many different sizes of O-ring grooves that more often than not I have to grind one because none of the half dozen or so groove cutters I've already ground are the right size. I can't imagine buying a new carbide tool every time every time I needed to set an O-ring. Even if I didn't mind spending the money (which I do) the wait for shipping in the middle of a project would annoy the crap out of me. (and I can't find toilet paper)


I have often used a narrow tool to cut a wider groove. Easy to use a .100 wide tool to cut a .200 wide groove. 
Jim Sehr


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