End cutting in mill

I have recently bought a Sieg mill which I'm very happy with, and would appreciate some help on a job I need to do. It's not strictly speaking model engineering, but might as well be!

My old Jag has brass banjo unions in the braking system, one of which repeatedly leaks. The flat faces on the fitting that the copper washers seal against are not in great condition and I'd like to reface them. The OD needs to be 22mm, and ideally light concentric grooves would help the seal. Can anyone suggest a tool that would fit the Sieg mill to do this, preferably something that isn't £200?

Any help gratefully received.

Fine wet and dry paper and a glass plate. Milling operations do not necessarily give a flat smooth surface.

I don't know what you have in the way of other equipment but the cheapest solution would be to grind a pointed tool to make the grooves and put it in a basic fly cutter. You are only cutting brass so the tool does not need to be anything particularly hard. You can move the ground tool in the fly cutter to do different diameters of concentric grooves. Piece of hacksaw blade may be enough.

Martin C

Edited By Martin Connelly on 01/06/2023 10:37:11

Unfortunately I can't use a glass plate as the union is angled at one end, so won't sit flat on a plate (hard to describe...), hence the specific OD. Also the important thing is to get both faces absolutely parallel, which is tricky by sanding.

I like the fly-cutter idea, thanks. Obviously the key (as with anything, I suppose) is how to mount accurately for machining.

I wouldn't faff around trying to set it up in the mill. Make a suitable tool and do it by hand. The surface is only being cleaned up not really machined. I'd make the tool from silver steel and harden it, albeit not strictly needed for brass.

Andrew

Sounds more like a job for a lathe, you don't say if you have one. Incidentally, are you annealing the copper washers before fitting? I'm not sure that I like the groove idea.

Flycutter type arrangement will be cheapest, one up from that would be a boring head which would allow easy adjustment of the spacing of the concentric grooves.

Skim one side clean and do the grooves in one setting and then mount the part with the freshly machined surface clamped down flat and repeat skimming and rings on theopposite second face.

I'm assuming that the part is too big to turn on a lathe as suggested, which would be an easy job to face and cut grooves. An option on your mill is to get a boring head which you could use to face the end of the fitting. Then cut the grooves with a specially ground (pointy end) boring bar. (Jason beat me to answer)

Edited By Paul Lousick on 01/06/2023 11:40:33

Thanks all - the grooves are almost like 120 grit sanding marks really, but being concentric they help the soft washer to seal. The problem is compounded by the difficulty in purchasing decent (purer?) copper - the ones sold for this purpose are very 'brass' in colour and don't seem to soften much with annealing. I'm using the MAPP torch I use for silver soldering so I presume it's getting properly hot, but it gets the washers red all right but they never melt.

The unions might fit in my Super7, and I do have a 4-jaw chuck, but I'm not sure how easy they would be to mount. And of course the mount has to be repeatable on the reverse side and parallel to within a thou or so.

If these banjos are for the braking system, be VERY careful. Pressures in the hydraulc braking system can be very high.

Your life might depend on them!

The copper washers should be annealed..

In a banjo bolt / copper washer / banjo / copper washer / fitting situation there are EIGHT possible faces th\at can fail to seal.

Get it wrong and you could be worse off than when you started.

Turning (Facing ) the faces of the banjo will produce a spiral groove, so although an appealing way of producing a good finish, may well not be the best way to go.

Putting grooves or ridges in the face of the banjo will increase the unit loading , but will decrease the leakage path, and so make matters worse.

If grooves or ridges were the solution to the problem, LOTS of engine and vehicle manufacturers woukld have been using them; so probably mot the best solution

Lapping the faces with 600 grade wet and dry, may be a solution, but ifd the angled faces make this difficul bend your efforts to making up a suitable fixture to hold them. Thiks will help having the faces parallell as an end result.

Also, look to the faces of the banjo bolts. The coppere washer has two faces across which there could be a leak.

Be careful not to reduce thread enagagement so that the banjo bolt bottoms before exertinbg maximum pressure on the washers.

HTH

Howard

Thanks Howard - I have 4mm to work with before the threads can bottom in the cylinder.

The original unions and cylinder have these fine concentric grooves in them, and seem to be designed that way. I never used to have this problem as the washers would deform to seal even quite poor surfaces. As said above, I think it's the cheap washers the specialists sell these days that are the real problem. I've tried to buy C110 sheet to stamp out a few, but it's hard to find and not cheap! Which explains why the ones the specialist suppliers sell are not great...

Sounds like making a simple expanding stub mandrel to hold the banjo in the lathe would be a way to go.

And I would search out a better supplier of copper washers if you are not happy with what you have. They are used throughout hydraulic systems and brake systems everywhere so plenty are available.

PROVIDED The seal material is NOT attacked by your fluid then IF you can get a Dowty washer/ seal that would solve your problem, they will take about 6 times your brake pressure. If the banjo bolt is a standard one then may be 1/8" or 1/4" BSP, or 10, 12, 14 Etc metric, the seal can be viton,nitrile or EPDM. Are you using silicon fluid ? For copper take a piece of pipe eg 28mm, slit it down the side with a hacksaw, flatten out, cut to make your washers and anneal ! I would NOT groove the banjo. Good luck. Noel.

Thanks Noel, I actually not keen on polymer/rubber seals in braking systems for this application - I know Stat-o-seals claim they're OK with fuel and possibly hydraulic fluid but it doesn't sit well in my mind. The other problem is that the lands on the banjos and beneath the head of the banjo bolts are so narrow that I've not found a composite seal that will fit. I do not use silicone fluid, as 20 years ago I very nearly lost an Austin Healey 3000 through it boiling somehow, total loss of brakes which came back 10 minutes later. This happened twice on two different cars, so I went back to DOT4.

The best method of smoothing the banjo face, after further experimentation, seems to be to make a 'washer' of abrasive paper, hold this under the head of the bolt and twist it against the fit surface of the brass banjo union. This also gives the degree of 'groove' (probably the wrong word) that the unions had originally. The trick will be keeping the two faces parallel. I need to source some C110 sheet, and I like the expanding stub mandrel idea in the lathe, if the paper washer trick doesn't work.

What about trying some aluminium washers?

Martin.

Thanks Martin, that was another possibility. I did wonder about the propensity to corrode, but I have an old Mustang as well and noted that the Americans did use alumin(i)um washers on that back in the sixties, so it should do the job if I can't get this to work. The unions need to be as good as I can get them though, either way.

The seals in the master and slave cylinders will be some kind of rubber, so I wouldn't dismiss Dowty washers, or even o ring with a spacer. Just need to make sure you get the right material.

You could always try

https://www.greasemonkeydirect.com/collections/copper-washers

They have a very large range

You do of course anneal the copper washers before use?

Aluminium washers and brass banjo? NEVER! You will have electrolytic corrosion of the washer and leakage soon afterwards.

Getting the mating surfaces 100% flat is more important than getting them 100% parallel. The banjo bolt can tip slightly in its thread to cope with this.

If you're still having difficulty finding pure copper washers I can look in my ex-Lockheed tin and see if anything useful is left (since 1970). Just tell me your i/d. And I think you could consider Dowty washers (ie a rubber seal bonded to a steel washer), and used to keep the fluids in Concord etc. They are a bit thicker than coppoer washers so be sure you have enough thread engagement.

Cheers, Tim