Cylinder drain cocks

[Steve101Participant @steve101]

I’ve made a couple of taper plug drain cocks to fit a Stuart 10V. On test under water pressure  (up to 60psi) its pretty obvious they leak when closed. I had a similar result from commercially made taper plug cocks for this engine.

I’m new to this so would like to know whether its fair to expect drain cocks of this type to hold a constant water pressure or whether the conditions resulting in an engine running on steam need less of a seal.

Steve101

[bernard towersParticipant @bernardtowers37738]

I think you may find that its matching taper problems. I have made some in the past and found that lapping before bending the handle pays dividends. i use a very old tin of lapping past made by the CARBORUNDUM Co.

[Harry WilkesParticipant @harrywilkes58467]

Ive used Brasso on mine

H

[Clive Brown 1Participant @clivebrown1]

With its slide valve a 10V doesn’t really need working draincocks.

[Steve101Participant @steve101]

Thanks for the replies. I cut the taper with a D bit made at the same time as turning the taper plugs and can’t think of any other way of making such a small tapered hole. I’ve also tried lapping the plugs in using metal polish first (didn’t work but seemed to reduce the weep) and then medium Timesaver, both after the drain cocks were finished so I could only do the lapping by hand turning the plug.

The two cocks were a fiddle to make, but look good. I’d like to have another go, meaning another taper D bit etc. but next time try lapping in before bending the handles as suggested and perhaps trying Brasso. The medium Timesaver left a very matt finish with obvious grinding score marks visible at x20 mag. so a bit too aggressive I think.

 

[Harry WilkesParticipant @harrywilkes58467]

You could get some tapered pegs and reamer ok the pegs would be steel but maybe could be used to set taper on lathe then just reamer the body

H

[bernard towersParticipant @bernardtowers37738]

contrary to popular opinion a matt finish seals better just put a little vaseline on the surfaces.

[Steve101Participant @steve101]

Thanks again. I’ll try the vaseline tip on the plug I’ve used the Timesaver on.

I’d thought about using a taper pin reamer as a basis for the drain cocks before I made this attempt but gathered that the plugs would need a steeper taper to  prevent them just jamming in the body. If memory serves I settled on an angle of 7 degrees for the taper. I’ll have to dig out my drawing to be sure.

On the taper turning side, any advice on setting the top slide accurately would be welcome. I think I’d be struggling to reproduce the same taper setting exactly now I’ve set the top slide back to a normal position for parallel turning. Using one of the plugs (I made a couple of extra plug blanks with the original two so could stick one of these in a collet) as a pattern would be a problem because of their size.

 

[Charles LamontParticipant @charleslamont71117]

To set the topside you can use a parallel bar in the chuck, a dial gauge mounted on the toolpost, and some trigonometry to work out how much the dial should move over a given distance of slide travel. Setting the topslide to reproduce the existing parts is not so easy.

[Clive Brown 1Participant @clivebrown1]

7deg. inc. angle sounds reasonable. The drawing that I have to hand for Allchin draincocks shows 6deg and they work well. I’d always favour making plugs and reamer at the same setting and then a very fine lapping compound. As said above, exact matching of existing tapers is not easy. If you must, I’ve found GHT’s gadget for micro-adjustment of the top-slide useful.

Going back to your leaky draincocks, although they obviously leak water at 60psi, the engine will run light on steam at a small fraction of that pressure and I’d suggest that steam leakage will then be barely noticeable, if at all.

[DalboyParticipant @dalboy]

Reading this with interest as in the future I need to make 4 small drain cocks

[Howard LewisParticipant @howardlewis46836]

When ever I have needed matching tapers, the internal and external tapers have been made without altering the angular setting of the Top Slide.

But for smaller sizes, a boring bar cannot be used, obviously.

What ever setting of the top Slide is used to produce the taper on the D bit will be reproduced in the drain cock body.

Probably, as long as the tapers match the exact angle will not matter too much, whether 7 or 8 degrees.

Lapping with Brasso, Duraglit,  or some similar metal polish should give good enough finish.  The finer the abrasive used the better the finish.  But make sure that everything is clean afterwards, the some abrasive will tend to stay in the material, and although not used too frequently, operation will continue the lapping process.

Howard

[ZephyrinParticipant @zephyrin]

the annoying thing about taking the tap back to polish the cone is that the cone may sink too far into the body of the tap and protrudes beyond the bottom, so it’s no longer possible to tighten it with the small screw from the bottom…  and a new cone has to be made !
the little washer with a half-moon hole isn’t easy to do either!

[noel shelleyParticipant @noelshelley55608]

Half moon holes or any other shape are easy to do once you have built a spark eroder. Plan B is to laser cut them but making one of those is above my pay grade. Noel.

[LukerParticipant @luker]

Hey Steve, have a look at the Ballaarat series published in ME. All the steam valves including the sight glass and drain cocks were taper cocks and they work very well. How to make them is described including the pitfalls when making these types of steam valves. The washer with the D-hole is necessary, but, is easy to make and included in all my designs.

A little leakage on the drain cocks is not the end of the world, and helps to lubricate the valve (the steam valves cannot leak otherwise they will seize). I’m not surprised commercial ones leak, but home-made ones should be perfect…

[Steve101Participant @steve101]

Thanks again, other things have got in the way over the last couple of days so I’ve not progressed the valves any further beyond putting some vaseline on one and sticking it on the test rig, which was made for hydraulic testing a boiler. Something else I’ve not got round to yet.

Luker, I’ve not got the ME issues relating to Ballarat and haven’t seen any detailed description of making this type of valve. They would be helpful so if the information’s readily to hand, can you let me know which issues to get hold of? If it means you having to search please don’t, I’m sure I can do that myself on-line.

The washers were a bit of a game, though I used a square hole rather than D shaped. Luckily I had a broken 1/8″ hand reamer with a square on the end that converted pretty easily into a sort of broach.

[LukerParticipant @luker]

From part 8…

The drain cocks
Some people battle to make taper cocks, claiming that sealing is an issue, but there are a few tricks to make this little valve an easy job. The first item that needs to be made is the taper spindle. This is a taper cutting operation using the taper slide and a collet in the lathe. You need to cut at a high speed to make sure you get a good quality finish, which is easy with stainless if your tools are ground properly. Without changing the taper setting, the reamer for the brass body needs to be machined, leaving roughly a 1mm flat at the end (from silver steel). The reamer is then filed to half-way, quenched and tempered the normal way and, using an oil stone the cutting surface is dressed to a keen cutting edge. Sandpaper on a piece of steel works just as well and I generally go that route. Back to the lathe (using the same setup) machine a 16 or 20mm BMS bar to the same taper with a sharp dimple at the end; this will be used with a DTI to set the taper for any future taper spindles. There’s a few on this loco!

The body of the cock is made using a forming tool and the threaded part using a knife tool and thread cutting operations, but don’t part off. The bar is then moved to the milling machine and a pilot hole drilled centre through the ball of the body and the reamer is incrementally plunged into the hole until the taper spindle fits correctly. A stop collar can then be fitted to the reamer for the following bodies. The spindle is fitted in the hole and tightened with the square in the desired position, returned to the lathe and the through hole drilled. These two parts are now married and shouldn’t be parted for too long; well, the body parted from the bar, but you know what I mean!

Finally, the spindle is removed and, using 600grit sandpaper any burr is dressed and the cocks reassembled with a little light grease. Don’t turn the cocks before removing the burr; they will leak if you do.

The small washer at the end of the spindle is to prevent the nuts from rubbing against the body. These are drilled and parted from brass bar stock and the oval hole in the centre made using a home-made press tool with a lead-in the same size as the pilot hole. This is probably not necessary with the locking nuts, but technically more correct and makes the movement of the spindle smoother.

All the steam valves are made using a similar setup so it will be a good idea to machine all the taper spindle blanks while you’re at it.

Images/drawings won’t upload sorry….

[LukerParticipant @luker]

From part 14…

The water gauge
The water gauge is designed to match the prototype gauge, which used a taper cock arrangement for the top and bottom glass valves and for the blow-down. Tricky construction to say the least! These taper cocks have not received much favour in the model engineering fraternity. I have seen taper cock arrangements with compression glands to prevent leakage, but this seemed like extra work, and space was somewhat limited. In the end I did a little experimentation on materials, taper angles, holes sizes and manufacturing methods which helped in making a steam taper cock that had no leakage on my model and functioned rather well. All the steam valves are made using this method so repeatability throughout makes machining a little easier and quicker once you get the hang of it. Other than the design considerations there are two fundamental manufacturing tolerances that need to be perfect. Firstly, the taper needs to be identical for the spindle and the hole, and secondly, the taper spindle needs to tighten on the taper itself and not the nut or washer at the end. The machining of these tapers and tapered holes is identical to that of the taper cocks described in Part 8 so I won’t go through that again.

 

After machining the taper it can be parted off or cut with a hack saw if you’re not yet confident with parting, and pushed into a taper mandrel for facing and drilling. The mandrel needs to be short enough so the back end of the taper spindle is accessible to tap out. If the taper spindle spins when drilling then your matching tapers are out and the valve will not seat properly. A push of the thumb into the mandrel should be enough to face and drill the hole.

With the hole drilled a piece of stainless steel rod can be fitted and silver soldered in place. For this operation it’s a good idea to hold the spindle in another mandrel to protect the taper surface from oxidation and to hold it upright when soldering. Using this same mandrel the handle is bent into the desired position, cut and the end rounded with a fine file. All told, you will need six of these taper spindles for the various steam valves.

 

 

The body component of the sight glass requires mostly lathe turning and is relatively simple. The soldering and final match machining operations, however, may catch you out a little. For all my valves, or any component for that matter, with two similar cylinders that need to be soldered, I machine the end of the soldering component to match the mating body, i.e. the end of the t-piece will have a milled half round. This neatens up the joint considerably and makes soldering a little easier. My standard practice of placing a locating dowel (screw or bolt) through the hole to align the component with a little Tipp-ex makes sure the holes line up nicely.

 

Most of the holes through the stainless steel spindle need to be drilled after the components have been soldered with the exception of the sight glass drain spindle. This needs to be done before soldering to the main body. All match drilled spindles need the same treatment as described in Part 8 and they will not be interchangeable after drilling is completed. Fair warning: when drilling through the brass into the stainless spindle, the two different materials need to be drilled differently and a careful hand is needed when you hit the stainless to prevent the drill from breaking. Likewise, don’t overdo the drilling through the stainless, otherwise the drill will jam and break when you punch through into the brass. I normally pilot the holes in the brass before soldering, but I do not drill straight though. Starting the drilling directly on the stainless through a pre-drilled hole will cause drift due to the curved surface that the end of the drill starts on.

When assembling the water gauge to the boiler make sure to line up the glass holes properly by slipping a drill or piece of ground bar stock down the holes before tightening the back locking nuts. These nuts shouldn’t be messed with when the glass is fitted!

Again there’s a few sketches and pictures that didn’t upload…

[LukerParticipant @luker]

The steps are shown here: https://youtu.be/xQ36UoWpisc

And for the taper reamer https://youtu.be/qDnJSOXbqmo?si=qNdfvjDScuVZJGmm

You should have enough info to make your drain cocks with this…

[Steve101Participant @steve101]

Many thanks Luker, Not looked at the videos yet but the text gives me a lot to chew on. I suspect one of the reasons my valves were leaking was the finish I’d got on the (brass) plugs. They’re pretty small and I just used a standard RH knife tool to make the taper on the plugs and the D bit. I’ll make a special cutter for the next attempt with attention to getting a fine finish. I was basically copying the Stuart drain cocks but a little smaller to fit the cylinder of my 10V which didn’t end up too close to the drawing, dimension wise.

The advice to make a large taper setting piece makes obvious sense. Should have thought of that but didn’t.

Thanks again all. I’ll let you know how the second attempt goes

[Jan BParticipant @janb]

One my latest locomotive, a 3.5-gauge Juliet, I made the draincocks as described by Kozo in his book about the Pennsylvania A3 Switcher. I drilled and reamed the hole through the valve body 2.5mm and then turned a piece of brass to fit the hole.

This design works verry well and they don’t leek. I have not pressure tested them, but cylinder pressure is a lot lower than boiler pressure, as indicated by the pressure gauge attached to the steam chests. Boiler pressure is 80 psi and steam chest pressure has never gone above 40 psi.

 

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