Deep O ring groove in small ID.

I need to make a 0.984"(25mm) O ring groove in a part with a 0.610" ID bore (on a lathe). So far I haven't been able to find any ID grooving tools that can make a 0.187" per side groove in such a small ID bore. any suggestions?

commachines said:

I need to make a 0.984"(25mm) O ring groove in a part with a 0.610" ID bore (on a lathe). So far I haven't been able to find any ID grooving tools that can make a 0.187" per side groove in such a small ID bore. any suggestions?View attachment 321299

Click to expand...

Horn offers the 114 system, but nothing that'll do what you want off the shelf. The closest they've got is P/N RU114.0094.1.08 (.094" wide) or RU114.0125.1.08 (.125" wide) These will both do a DOC of .256" radially, but their stated minimum bore Ø is .650. You could solve this by modifying the insert and holder for the small amount of clearance you'd need.

The other option is to go smaller, and use RS114.0200.D2, which has an .079" width of cut and will do a max radial DOC of .157"... You could modify the insert to gain the extra .030" clearance you need, fairly easily. This tool has a minimum bore diameter of .551", and is, in my opinion, the better choice.

The holder for all these inserts is a BU114, you'd have to give me the shank diameter for a more exact part number. A BU114.0500.01 is a 1/2" diameter round shank.

Thinbit also offers their solid carbide ID groovers with up to .150" DOC... I'd imagine for a nominal fee they'd grind you the extra .037" clearance you need. They've always done good work for me, and shipped quickly, at quite reasonable prices.

Click the picture labeled "Microbit" for details: Grooving Products

Internal Tool also has groovers with .150" DOC off the shelf, and has always been happy to grind me a slight custom on a stock tool with no complaints.

Deep Slotting Groove Tools - Series 121

If you can make a drawing and submit it, MITGI will make a custom groover for you, for about the same price as any of the OTS ones, and usually can deliver in 2 weeks or less, with coating. Good tools, good people, good delivery. You can request a custom tool here: Custom Tool Request from Midwest Industrial Tool Grinding | MITGI

You don't say how many, but in a pinch I've ground down a keycutter to fit.

Hi commachines:
Have you tried having a custom tool ground, or several custom tools ground?
If I've calculated correctly, you can get a bar with a 0.4 shank diameter and a 0.2 stickout into your bore.
How far down the bore do you need to go?
What material are you cutting?

If it's a long way down in steel or in inconel or some other Godawful material you may not be able to turn it at all.

If that's the case, you have to hit the customer up for the cost of doing it another way.
I've had success with a sinker EDM making shit like this, but I charged a bloody fortune to do it, and after the disbelieving customer shopped the job all over town and got NO BIDs everywhere, they grudgingly agreed to pay me to do it.
Nice thing about a sinker is that the shank of the electrode can be super skinny, but it's SLOOOWWWW.

The secret to success here is to get agreement from the customer BEFOREHAND and then charge him out the ass for his ridiculous design and the hassle he put you through.
If he can't handle that...TFB for him.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining


(Man do I ever sound cranky this morning...must be the sore back talking).

Hi All:
Ignore my rant...I just saw the drawing.
Custom boring bar is the way to go.
Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

An o-ring you say? It'd have to be a -312, and without seeing the mating parts I'm very suspicious of this component functioning as a seal. Do you have any input to the design? I'd wager that you'll see better performance with a -208 and an appropriately shallower groove, but without seeing the rest of the system I can't say for sure.

BoxcarPete said:

An o-ring you say? It'd have to be a -312, and without seeing the mating parts I'm very suspicious of this component functioning as a seal. Do you have any input to the design? I'd wager that you'll see better performance with a -208 and an appropriately shallower groove, but without seeing the rest of the system I can't say for sure.

Click to expand...

thanks for all the input.
sorry if this is getting off topic from the OP, but the application is sealing 15mm stainless shafts through a sidewall into a tank of water based stain. the part shown is essentially an Acetal (Delrin) washer (with a gasket on the face and an O-ring on the shaft) that will be clamped against the outside wall of the tank.

My engineering department specced McMaster Carr 1295N424 as the O ring to use... I don't know anything about O rings... maybe they are wrong and I can get away with a smaller dia. O ring which would solve all my problems??

Hi again commachines:
If it's just Delrin, you can make almost anything and it will work.

Just grab a chunk of any hardenable steel and whistle up a home made tool.

You can probably even just make it from a piece of 4140 and flame harden the end with a torch if you don't have too many Delrin parts to make.
You shouldn't be spending more than an hour to make something...less time than it takes to rummage through all the turning catalogs looking for something.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Old school

commachines said:

I need to make a 0.984"(25mm) O ring groove in a part with a 0.610" ID bore (on a lathe). So far I haven't been able to find any ID grooving tools that can make a 0.187" per side groove in such a small ID bore. any suggestions?View attachment 321299

Click to expand...

I would just silver braze a tip on a bar and grind it. And be glad it was not Inconel.
Jim

Here's what I came up with:

an AS568-208 standard size is a much more sensible cross section than that fatboi specified by your engineer. They can be had from McMaster in packs of 5 for nearly the same price as single o-rings of that other size. If you are stuck with the other o-ring I mathed out grooves for both. Looks like low pressure so the clearance to your tube is non-critical. I assumed your tube is 15±0.1mm for the calculations.



You need more width, both in the groove itself and the walls. I wouldn't be surprised if installation of the fatty blew out those paper thin delrin walls without even considering installation force. If you are width limited then you can cheat a little on the groove and/or walls, but almost certainly need to decrease the o-ring CS in that case.

BoxcarPete said:

Here's what I came up with:

an AS568-208 standard size is a much more sensible cross section than that fatboi specified by your engineer. They can be had from McMaster in packs of 5 for nearly the same price as single o-rings of that other size. If you are stuck with the other o-ring I mathed out grooves for both. Looks like low pressure so the clearance to your tube is non-critical. I assumed your tube is 15±0.1mm for the calculations.

View attachment 321343

You need more width, both in the groove itself and the walls. I wouldn't be surprised if installation of the fatty blew out those paper thin delrin walls without even considering installation force. If you are width limited then you can cheat a little on the groove and/or walls, but almost certainly need to decrease the o-ring CS in that case.

Click to expand...

thanks again for the help...
My engineer is stuck on using the fat O ring as apparently it is more forgiving for any intolerances and will last longer etc...
Since it is a low pressure application, he is suggesting that we make the bore size larger to allow me to use a standard ID grooving tool and avoid the wall blowout in installation. I am limited by space so cannot make the delrin disk any thicker so am stuck with the 0.027" walls... Can you see this working or are we stupid to not go down to a thinner wall O ring as you suggested?
see new dimensions.

Or, you could just machine a radius on the id of the Delrin and eliminate the o ring.

commachines said:

thanks again for the help...
My engineer is stuck on using the fat O ring as apparently it is more forgiving for any intolerances and will last longer etc...
Since it is a low pressure application, he is suggesting that we make the bore size larger to allow me to use a standard ID grooving tool and avoid the wall blowout in installation. I am limited by space so cannot make the delrin disk any thicker so am stuck with the 0.027" walls... Can you see this working or are we stupid to not go down to a thinner wall O ring as you suggested?
see new dimensions.
View attachment 321416

Click to expand...

So, that modification will make it easier to machine, but it still won't work. You have 0% squeeze at nominal, there's no "forgiving" of tolerances there, it's just a prayer that you'll have some interference if things tilt your way. In a low-pressure situation like free-standing liquid, you NEED the o-ring to provide the squeeze from its internal resilience, there is nothing else in the system that will affect a seal. Making everything line-line does not provide the fundamental driver of system function.

You gave me the shaft and o-ring size in mm, but your washer is in inches, so I'll make one more recommendation to you for now:

Get rid of one of the walls. Make the other .100" thick, leave the rest .150" wide as an open-faced groove. That's technically cheating both of those dimensions, even after removing one wall entirely. If you're clamping the washer against the wall of something, you'll be able to install it that way, and if you ever take it apart you will probably need to pull the o-ring off on its own, but that's the best thing I can think of. This is for the -208, I don't think there's much you can do about the 15x5mm ring other than make the part, wait for the leaks, and then do this. Diameter should be .837±0.003" for the -208 for a squeeze range of 7.4~15.6%. (the fatty gives about 9~15% using the same tolerances, it's so much more forgiving ). The o-ring is slightly larger OD (.887") than the .837 groove, so it will pre-set into place well enough to get it on the shaft without the forward-facing wall.

If the seal is static and you have some room to work with, a cord grip would work to seal against the shaft. Many of the have an o-ring to seal against the tank and a bushing that collapses against the tube: McMaster-Carr

I have also successfully drilled out a compression fitting to allow a tube to pass through: McMaster-Carr

Swagelock might offer these although they might be a special order item.