Machinist question...O-ring boss machining

[37 boat]

Does anyone on here have the capability to machine a 3/4 16 O-ring boss thread in some blank fuel rail extrusions?

 

[RiverDave]

What is a 3/16 o ring boss thread?

 

[37 boat]

What is a 3/16 o ring boss thread?

It's basically a standard thread with a relief cut in to seal an o-ring. Used widely in AN fittings.

 

[Wheeler]

@Dana757 might be able to help

 

[37 boat]

What is a 3/16 o ring boss thread?

Here is a fuel filter with a o-ring boss thread

 

[traquer]

Seems quite simple, threadmill it in and undercut? I have parts that need random machining like this too but haven't gotten around to it

 

[RiverDave]

Here is a fuel filter with a o-ring boss thread
View attachment 879319

gotcha

 

[37 boat]

Seems quite simple, threadmill it in and undercut? I have parts that need random machining like this too but haven't gotten around to it

It needs to be pretty precise to get the right amount of "crush" in the o-ring. Needs to hold 60ish pounds of pressure for EFI.

 

[RiverDave]

It needs to be pretty precise to get the right amount of "crush" in the o-ring. Needs to hold 60ish pounds of pressure for EFI.

Still easy to machine if you know the sizes..

Kinda awkward holding it though.

 

[traquer]

Yeah for sure, not the place you want a leak lol! I'm not a machinist but I would imagine someone could do the whole job, from measuring and writing the simple cnc program to cutting it in under 2 hours. Clamp it to the side of the table somewhow since it's a long part. Might need to buy the threading tool though if they don't have it etc.

 

[37 boat]

Still easy to machine if you know the sizes..

Kinda awkward holding it though.

Yeah, I'm not sure if it could be chucked up in a 3 jaw chuck? Wanna try?

 

[RiverDave]

Yeah, I'm not sure if it could be chucked up in a 3 jaw chuck? Wanna try?

Id clamp it to the table vertically on a knee mill and then offset the head to reach it if it was me..

Might be able to grab it in a chuck though. Wouldn’t know unless I tried.

you in Havasu?

 

[Racey]

Yes, i do them on the lathe sometimes. For some fuel rails i have a collet i made that holds them concentric. You can indicate and 4 jaw it also.

This is why hack shops run NPT pipe threads in rails. It's completely incorrect to do so, but they are usually too lazy, or lack the skills and capabilities to do an ORB port properly.

The threads are a standard NF thread, 5/8, 9/16, 3/4 (don't remember them all of the top of my head, but it's nothing irregular) depending on the AN dash size. You just use a regular tap.

 

[37 boat]

Id clamp it to the table vertically on a knee mill and then offset the head to reach it if it was me..

Might be able to grab it in a chuck though. Wouldn’t know unless I tried.

you in Havasu?

Yes, I'm in Havasu. I can bring the fuel filter pictured above to measure dimensions. The thread itself is 3/4 16, the fuel rail I.D. is already sized for 3/4 16 at .6875

 

[37 boat]

Yes, i do them on the lathe sometimes. For some fuel rails i have a collet i made that holds them concentric. You can indicate and 4 jaw it also.

This is why hack shops run NPT pipe threads in rails. It's completely incorrect to do so, but they are usually too lazy, or lack the skills and capabilities to do an ORB port properly.

Since I'm doing a lot of this stuff myself I was tempted to tap it NPT but I agree its not the correct way.

 

[HB2Havasu]

Does anyone on here have the capability to machine a 3/4 16 O-ring boss thread in some blank fuel rail extrusions?
View attachment 879308

Do you mean a Seal Groove?

 

[Racey]

Since I'm doing a lot of this stuff myself I was tempted to tap it NPT but I agree its not the correct way.

I've seen more than one fuel rail split from the tapered fitting stretching the thin wall.

I always tell customers that pipe threads are for your garden not your fuel system.

 

[ka0tyk]

This is why hack shops run NPT pipe threads in rails. It's completely incorrect to do so, but they are usually too lazy, or lack the skills and capabilities to do an ORB port properly.

this oil pump i have has the oring business. i was expecting to just have a npt fitting in there but had to rebuy oring an fitting ones. i guess "flamable fluids" use orings as npt allows those fluids to naturally wick up the threads under pressure? not to mention npt will eventually stretch the material if dug in too much?

 

[Racey]

this oil pump i have has the oring business. i was expecting to just have a npt fitting in there but had to rebuy oring an fitting ones. i guess "flamable fluids" use orings as npt allows those fluids to naturally wick up the threads under pressure? not to mention npt will eventually stretch the material if dug in too much?

Correct, NPT is not a great sealing technology, it's a very forgiving, and legacy one. It was invented probably a hundred years ago, and didn't require much in the way of precision tooling to work. This is why it's always assembled with either a putty, or a gauze (teflon tape today). It uses the actual threads to do the sealing, the idea being that eventually if you go enough distance up the thread there is a bind point that will seal off the fluid from going any further, even if the two surfaces don't perfectly mate.

ORB, and AN JIC seal with the o-ring, or taper respectively, the thread just provides the mechanical means to hold the sealing surfaces where they need to be.

 

[Racey]

RD should be able to do this with a 4 jaw chuck on the lathe and a small boring bar or other high relief cutter.

You just need to make sure that your port has a greater volume cross section than the cross section of the o-ring (otherwise it will essentially hydraulic when you try to squeeze it and there is nowhere to go). And i usually shoot for 15-20% cord compression in one dimension, while accounting for that squeeze out in the other.

An o-ring with a cord thickness of 0.087" (a #908 o-ring for -8 which is probably what this is) should have a squeeze in one dimension of between 13 and 17 thou.

IMO it is probably better to squeeze the o-ring in the concentric dimension than the axial dimension. This helps to keep the fitting from working itself loose. In this case i would probably shoot for closer to 10% squeeze as you need to give a slight chamfer to the entrance in this case. I use 15-20% when calculating for an axial squeeze.

 

[37 boat]

RD should be able to do this with a 4 jaw chuck on the lathe and a small boring bar or other high relief cutter.

You just need to make sure that your port has a greater volume cross section than the cross section of the o-ring (otherwise it will essentially hydraulic when you try to squeeze it and there is nowhere to go). And i usually shoot for 15-20% cord compression in one dimension, while accounting for that squeeze out in the other.

When you refer to the cross section of the port are you referring to the depth of the relief for the o-ring? My crude measuring tools give me a cross section of .084 on the o-ring and I show approx. .100 on the depth of the relief on the fuel filter.

 

[elco]

You can buy pilot reamers to finish the port to size. Im not a machinist but if you google parker o-ring handbook there is lots of info and dimensions for port seals.

 

[Racey]

When you refer to the cross section of the port are you referring to the depth of the relief for the o-ring? My crude measuring tools give me a cross section of .084 on the o-ring and I show approx. .100 on the depth of the relief on the fuel filter.

Yes so the o-ring gets tight into the circumference of the bore and deforms into that oversized depth. Roll the o-ring back and measure the OD of the fitting where it seats, then add 2x the cord thickness, minus 2x your 10% squeeze, 0.008 x 2, this will give you the bore diameter appx that will seal.

Sorry for the brevity, typing this on my phone.

 

[RiverDave]

RD should be able to do this with a 4 jaw chuck on the lathe and a small boring bar or other high relief cutter.

You just need to make sure that your port has a greater volume cross section than the cross section of the o-ring (otherwise it will essentially hydraulic when you try to squeeze it and there is nowhere to go). And i usually shoot for 15-20% cord compression in one dimension, while accounting for that squeeze out in the other.

An o-ring with a cord thickness of 0.087" (a #908 o-ring for -8 which is probably what this is) should have a squeeze in one dimension of between 13 and 17 thou.

IMO it is probably better to squeeze the o-ring in the concentric dimension than the axial dimension. This helps to keep the fitting from working itself loose. In this case i would probably shoot for closer to 10% squeeze as you need to give a slight chamfer to the entrance in this case. I use 15-20% when calculating for an axial squeeze.

I have a six jaw.. I was wondering if I could remove the number 6 jaw and see if it would tab.. or remove 6&3 and try..

little concerned about messing up this guys fuel rail.. also wondering if it would even be worth charging a normal rate to do it.. lol.

 

[LuauLounge]

I’d guess he’s not looking for 3 bids.

 

[lbhsbz]

From the Bible...incase anyone doesn’t have their Machinery’s handbook handy.

It’s not rocket surgery...as long as there is some o-ring compression...60psi isn’t enough to leak past much. Look at the exposed area of the o-ring once things are assembled...it’s relatively nothing.

If we call it a .75” ID o-ring, and with the appropriate shoulder on the female fitting, we will likely be less than a .020 section width exposed to the 60psi.

That leaves with about 0.04” of exposed material, which at 60psi has 2.4lbs pushing against it

Not rocket surgery...

If I had to spitball this one and the customer insisted on an O-ring for some dumbass reason, I’d match the OD and ID to the free o-ring dimension and give her .020-.030 crush...done.

If I was lazy (and I am) and wanted to do it the easy way, I'd hand tap some straight threads in it and use a crush washer...which would work just fine if not better.

 

[236eagledave]

looks like what you want is an MS33649-8 port. That's the spec for a port to accept an AN fitting with a 3/4-16

 

[traquer]

^ Nice! Here's another visual that might help:

On second thought, it won't be as sexy but it'd be a lot easier to find someone to do this:

 

[37 boat]

looks like what you want is an MS33649-8 port. That's the spec for a port to accept an AN fitting with a 3/4-16

View attachment 879360

Yes, there is a tool available to machine it in one step but it's pricey and I don't have a mill or a lathe and I sure wouldn't want to attempt it in a drill press.

 

[Rajobigguy]

Don’t weld it. RaceY has the right idea although if I we’re doing it I would shoot for 20% axial compression and 10% radially.

 

[JUSTWANNARACE]

Yes, there is a tool available to machine it in one step but it's pricey and I don't have a mill or a lathe and I sure wouldn't want to attempt it in a drill press.
View attachment 879365

I'd offer @RiverDave to, (you)buy the tool, a couple cases of beer and he gets to keep the tool!! Next time(at shop rate) you or a buddy needs it done, you know where to go.. jmo

 

[37 boat]

Hey @lbhsbz, what happened to your post about using a crush washer? Not a good idea? I had not seen that in a EFI application before but they are used in brake systems that have way more pressure. Discuss...

 

[lbhsbz]

Hey @lbhsbz, what happened to your post about using a crush washer? Not a good idea? I had not seen that in a EFI application before but they are used in brake systems that have way more pressure. Discuss...

I edited it into my first post (at the end). Plenty of EFI systems use crush washers....Like almost everything Toyota made up till about at least 2003 (haven't worked on much past that)....even though toyota typically runs about 45psi I thing (never checked toyota fuel pressure...the pumps don't suck like GM ones). It's just a gasket. I'd not hesitate to even use a firm fiber washer in a pinch, although the material will need to be suitable for gasoline, which is likely why it's easier to just pick copper or aluminum for the crush washer/gasket material. While brake systems typically run under 1300psi on the street, it's not uncommon to see over 3000psi.,,,And copper washers work fine if all sealing surfaces are parallel and in good condition.

 

[37 boat]

I edited it into my first post (at the end). Plenty of EFI systems use crush washers....Like almost everything Toyota made up till about at least 2003 (haven't worked on much past that)....even though toyota typically runs about 45psi I thing (never checked toyota fuel pressure...the pumps don't suck like GM ones). It's just a gasket. I'd not hesitate to even use a firm fiber washer in a pinch, although the material will need to be suitable for gasoline, which is likely why it's easier to just pick copper or aluminum for the crush washer/gasket material. While brake systems typically run under 1300psi on the street, it's not uncommon to see over 3000psi.,,,And copper washers work fine if all sealing surfaces are parallel and in good condition.

Thanks for the reply, this would definitely be the easiest solution. I have a 3/4 16 tap...the only concern I would have is making sure I tapped the hole dead straight.

 

[lbhsbz]

Thanks for the reply, this would definitely be the easiest solution. I have a 3/4 16 tap...the only concern I would have is making sure I tapped the hole dead straight.

It's not hard...use a guide. Dunno where you're located...but if near Long Beach, bring it by and we can make it dead straight. If not local, I'll PM you my number...give me a call and we can talk about what junk you have laying around and find a way to make a "straigtness" jig.

One of my favorites is a couple chunks of thin hardware store aluminum angle...cut a long piece and hose clamp it to the round thing...then stack a shorter piece...or a few shorter pieces on the business side to act as a guide for a tap or welding or whatever. If angle isn't available in the appropriate thickness to match the ID and guide your tap...use some sheet stock....an old sign, the CG tag on the gunnel, etc...all it needs to do is take up space. Angle is good for jigs.

 

[37 boat]

It's not hard...use a guide. Dunno where you're located...but if near Long Beach, bring it by and we can make it dead straight. If not local, I'll PM you my number...give me a call and we can talk about what junk you have laying around and find a way to make a "straigtness" jig.

Thanks, I'm in Havasu but I get to O.C. fairly often. I'm sure I can "McGyver" some type of guide/jig, I just need to put some thought into it.

 

[Racey]

C

Hey @lbhsbz, what happened to your post about using a crush washer? Not a good idea? I had not seen that in a EFI application before but they are used in brake systems that have way more pressure. Discuss...

Crush washers are only good if the fitting was designed for them, don't use one on an ORB fitting.

 

[lbhsbz]

C


Crush washers are only good if the fitting was designed for them, don't use one on an ORB fitting.

A crush washer is a gasket suitable for use between any 2 flat and parallel surfaces...what do you know that I don’t (with respect to crush washers)?

 

[Racey]

A crush washer is a gasket suitable for use between any 2 flat and parallel surfaces...what do you know that I don’t (with respect to crush washers)?

That the two surfaces need to have appropriate surfaces machined for this, and that the crush washer needs to register for concentricity on one of them. So finding a copper washer to do that might be a problem for an AN ORB that is not machined on that surface, for a washer that doesn't cannot fit over the threads since the OD of the sealing area is smaller than the major thread diameter, and onto the end of a fuel rail that has no guarantee of being cut perfectly perpendicular to the threading or bore.

Copper crush washers are great as long as they have 3 things working in their favor, concentricity, and two parallel surfaces with an appropriate amount of torque.

 

[RiverDave]

I'd offer @RiverDave to, (you)buy the tool, a couple cases of beer and he gets to keep the tool!! Next time(at shop rate) you or a buddy needs it done, you know where to go.. jmo

I would just do it with a boring bar and the compound on a lathe. Don’t need the tool

 

[RiverDave]

Here is a fuel filter with a o-ring boss thread
View attachment 879319

Bring it all over after the weekend and I’ll take a look at it. I can tell you in a few minutes if it’s going to be quick and easy or not

 

[Dana757]

I would just do it with a boring bar and the compound on a lathe. Don’t need the tool

I turn them with a boring tool on lathes but on a mill a porting tool makes life easy. Look up SAE J1926 for correct dimensions.

 

[Dana757]

@RiverDave I could send you a porting tool as long as you send it back.

 

[DaveH]

Listen.to.Shane.

i have him machine all sorts of stuff for the EFI systems i work on.....he KNOWS what he is talking about.

 

[Dana757]

Here is all the info you need. It's a 15* then 45* angles.

https://www.inserta.com/PDF/AI-STR-THD-PORT-DIM.pdf

 

[37 boat]

Bring it all over after the weekend and I’ll take a look at it. I can tell you in a few minutes if it’s going to be quick and easy or not

Thanks Dave, I will hit you up next week. I think I might join you guys on the ride tomorrow night as well.