Britannia 70047 "Derek Stokes"

[David]

We all have days like that one where you try to take all the care you can and it still goes south.

I agree with increasing the tapping drill sometimes. I have a course metric tap & die set and the tapping drill sizes recommended just feel too tight and I go way oversize on them. I also might go oversize on 8 & 10 BA tapping holes.

It took me years to figure out what the sprung center was for - my father-in-law had been using it to emboss rivets on HO scale models! Now I know I use it as often as I can for tapping.

I find some of my taps don't sit straight in the tapping wrench. That's pretty annoying.

[dhamblin]

Having broken a 5BA tap last night and written off the locating dowel I was making I know exactly how you feel! Perseverance and make something simpler while mulling over how to improve for the second attempt.

Oh, and don't think you can get away with a 2.6mm tapping size when 2.65mm is recommended...

Regards,

Dan

[JonL]

Feb 6, 2019 21:23:02 GMT @greenglade said:

...I've learnt not to even start unless I'm feeling good. You'll be surprised how one day a job can seen a real pain and yet, sleep on it and it all goes smoothly the next day...

It's astonishing isn't it? The exact same job done one two different evenings, one with a result I'm proud of, the other will probably go in the scrap bin.

Thanks for everyone's support, much appreciated.

[Jim]

Feb 7, 2019 11:17:25 GMT JonL said:

It's astonishing isn't it? The exact same job done one two different evenings, one with a result I'm proud of, the other will probably go in the scrap bin.

Thanks for everyone's support, much appreciated.

Actually I think you've just described the hobby of Model Engineering to a tee. I suspect most of us have built two models of the same thing, the one every one sees working and the one that consists of a bin full of 'wasters'. I've had friends drop by who spot something and pick it up asking 'What's this?' and I have to admit it was a valve bobbin, coupling rod or what ever that somehow had a nasty accident like the spur gear I was cutting and realised I had the indexing wrong

Jim

[mugbuilder]

I have a drill chart put out by a major engineering company that lists 3 diferent drill sizes for each tap depending on the difficulty of the material being tapped. It covers most imperial threads and also BA. I always err on the side of caution and don't try to get a full thread in anything but brass. 8 and 10 BA taps are too fragile and too easily broken. I have only broken 1 tap in the last few years. Most likely break one now that i have said that.
Barry

[JonL]

Feb 8, 2019 7:30:09 GMT mugbuilder said:

I have a drill chart put out by a major engineering company that lists 3 diferent drill sizes for each tap depending on the difficulty of the material being tapped. It covers most imperial threads and also BA. I always err on the side of caution and don't try to get a full thread in anything but brass. 8 and 10 BA taps are too fragile and too easily broken. I have only broken 1 tap in the last few years. Most likely break one now that i have said that.
Barry

Thats interesting, can I ask where it came from? I'd like to score one myself!

[Roger]

Feb 8, 2019 9:44:47 GMT JonL said:

Feb 8, 2019 7:30:09 GMT mugbuilder said:

I have a drill chart put out by a major engineering company that lists 3 diferent drill sizes for each tap depending on the difficulty of the material being tapped. It covers most imperial threads and also BA. I always err on the side of caution and don't try to get a full thread in anything but brass. 8 and 10 BA taps are too fragile and too easily broken. I have only broken 1 tap in the last few years. Most likely break one now that i have said that.
Barry

Thats interesting, can I ask where it came from? I'd like to score one myself!

It's probably fair to say that we don't often need the full strength of a thread, but personally I wouldn't increase the tapping size unless it's a particularly difficult material. Stainless Steel, Silver Steel and Phosphor Bronze would probably be the only candidates I'd consider it on, and even then, by swapping between Second and Bottom taps you can get the full depth if you want it. (The most horrendous material I've had to tap is Molybdenum where you have to increase the tapping size a lot.)

I only use finger and thumb on the smaller sizes, say 2mm diameter and smaller, and always with a guide to make certain the tap is vertical. That's important not just because to snapping it off, but also it takes more force in both directions and its more likely to snag.

[JonL]

As you can see I've now made both ends of the piston sleeve assy. I got a bit of time in the workshop this afternoon (friday early finish from work!) so I managed to make my valve spindles. I used a split die and used the tailstock to keep the die square with the stainless rod whilst turning the die by hand. Backgear kept the chuck from moving.

My second attempt galled up badly, maybe I didn't keep the swarf cleaned out enough. I was doing a full rotation, 1/3 to 1/2 a turn back. Third attempt was good though, so I have a pair.



Next up I plan to make the bobbin, containing some Fluorosint supplied kindly by Roger. I've got some Meehanite which looks like it would do the job nicely, or I might be able to find some brass. I have a split-bobbin plan which should hold it all together securely whilst still allowing for adjustment. 

[Roger]

Excellent progress again! Personally I'd never go a whole turn with a die, a half turn is about the limit when I do it. These days I make screwed parts like this about 3-4mm longer than they need to be and put a centre in the end. Then I screw cut the thread instead, it's much less brutal to complete the thread with more than one deep cut. If you don't have carbide threading inserts, you can cut the bulk of the thread with screw cutting, and finish it to size with a die. You'll find that you can get a much better finish that way. Once done, you can cut off the excess and tidy up the end. Yes, it takes a bit longer, but it's a good way to get consistent results and less scrap.

[Jim]

Hi Nobby,

Just looking at your piston valve covers I was wondering how you intend to fit the slide bar assembly for the piston valve's crosshead.

Jim

[JonL]

Feb 8, 2019 22:01:52 GMT Jim said:

Hi Nobby,

Just looking at your piston valve covers I was wondering how you intend to fit the slide bar assembly for the piston valve's crosshead.

Jim

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It's a good question... let me investigate further and get back to you. I haven't actually thought that far ahead. It's all part of my carefully considered plan.

[Jim]

Hi Nobby,

This is a photo of Boadicea's valve slide bars, support pillars and base. As you can see from the drawing in the back ground it is all one piece with the valve's end cap.

I made up a jig to hold the parts together and at the correct spacing while they were silver soldered together. I suspect there were originally two castings for these two end caps and if so they weren't in the box of parts I was given hence the fabrication of the parts.

This is a close up photo of the above.

Hope this clarifies things a bit.

Jim

[Cro]

Jim,

The 3 1/2" Brit as drawn doesn't have the valve guide supports as the 5" design does. Doesn't mean they couldn't be added but drawing doesn't show them.

Adam

[92220]

Having been away for a few days, I hadn't read the posts, above, about tapping until today. I got fed up with breaking small taps, and when I thought about it, I realised all my BA taps were carbon steel, having originally bought a 0 - 12BA set......easily broken. I looked on Ebay for HSS taps and have now got taps down to 14BA in HSS. Broken taps have not been a problem since getting together a full set of HSS taps. As far as tapping sizes go, I use the Zeus charts for all my tapping sizes and haven't had a problem. One thing I ALWAYS do is lubricate the tap with Rocol RTD liquid regardless of material being tapped. Occasionally I will use an oversize tapping drill if I am being lazy and tapping in steel with the tap in a drill chuck in the quill head on the mill, but generally I find the Zeus sizes don't give me any problems. They quote a recommended size and an alternative size. I do think the Rocol liquid is what considerably reduces the risk of breakages though.

Bob.

[Jim]

Feb 9, 2019 8:04:05 GMT Cro said:

Jim,

The 3 1/2" Brit as drawn doesn't have the valve guide supports as the 5" design does. Doesn't mean they couldn't be added but drawing doesn't show them.

Adam

Thanks Adam, I'd forgotten it is a 3 1/2" not a 5" Britannia.

Jim

[simplyloco]

Feb 9, 2019 10:32:30 GMT Jim said:

Feb 9, 2019 8:04:05 GMT Cro said:

Jim,

The 3 1/2" Brit as drawn doesn't have the valve guide supports as the 5" design does. Doesn't mean they couldn't be added but drawing doesn't show them.

Adam

Thanks Adam, I'd forgotten it is a 3 1/2" not a 5" Britannia.

Jim

Adding the valve guides to my Brit was my first 'deviation' from the LBSC drawing. It was the beginning of my undoing...

[JonL]

Is it a worthwhile addition? On my drawings they are fixed to the frame.

[JonL]

Not the final shape I hasten to add! Making the spindles tonight. Productive night in the workshop, hopefully more to come tomorrow.

[JonL]

Well I used the techniques discussed to make my bobbins and they seal beautifully. With a little oil in the bore they move quite sweetly. I've made the bobbins as advised so they can be adjusted from the front of the locomotive easily.

[Deleted]

Great work Nobby...you're putting me to shame as I still haven't done my cylinders...I best address that soon....keep up the good work sir..

Pete