Author Topic: Help, British threads !!!  (Read 11519 times)

Offline Darren

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Help, British threads !!!
« on: November 23, 2008, 04:06:10 PM »
I have found a chap on Ebay that may have a backplate for my lathe, he's saying it's a BSF 2" x 7TPI thread.

I guess he's wrong on two counts, lathes as far as I know use BSW not BSF, and I've never heard of a 7TPI being used?

He says he's measured it with a BSF guage. Could that mislead him, if he had a BSW guage would it tell him it was 8 TPI?

I have neither guages so I'm hoping one of you good fellows out there has....fingers crossed, these backplates are hard to get hold of...!!
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bogstandard

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Re: Help, British threads !!!
« Reply #1 on: November 23, 2008, 04:45:22 PM »
Darren

What is the spindle thread on yours?

This site might give you a bit of info on your particular lathe. It looks like S&B were 1.75" x 8TPI

http://www.lathes.co.uk/smartbrown/index.html

You shouldn't really jump to conclusions, almost any thread can be used on the spindle. And is usually determined by diameter and thread pitch, plus angle of thread, I suspect that US made machines were 60 degrees, and UK machines 55 degrees. Boxford backplates will fit American Atlas but I don't know if it works the other way around if there is an angle difference. Thread gauges don't normally come for a particular thread, just a range of pitches. If he says it is 7 TPI when measured with a pitch gauge, I would tend to say he is right, 8 TPI will go nowhere near.

Here is a link to a BSF threading chart, which shows 1.75" and 2" do in fact have 7 TPI, which makes it a nono for your lathe.

http://shopswarf.orconhosting.net.nz/bsf.html

If you can get the cast iron, it is a fairly easy job to make your own backplates in any size and pitch you desire by single point cutting. But you really need the spindle nose off the machine so that you can check it whilst machining.

John
« Last Edit: November 23, 2008, 05:36:13 PM by bogstandard »

Offline Darren

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Re: Help, British threads !!!
« Reply #2 on: November 23, 2008, 05:46:41 PM »
Hi John,

The S&B's are normally 1.75x8tpi with their own design collets, but mine unusually has a 5C spindle. For this they upgraded the nose to a 2" x 8tpi thread.

That's why the backplates are hard to find, cos it's hard to find a 5C S&B.


The chap says it's a BSF thread, which I understand is a fine thread system. In the picture I have of his backplate it doesn't look like a fine thread. So I guessed that it is really a BSW thread, but I am guessing of course.

I would cut one, but would the mini be able ? That's a big thread...for a little lathe, even turning by hand.

Darren

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bogstandard

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Re: Help, British threads !!!
« Reply #3 on: November 23, 2008, 06:25:22 PM »
Darren,

I think you are getting confused by a name. BSF means what? There is nothing to compare it with except BSW. It is just a size, pitch and angle. The chart I showed proves it.

The metric threads you normally use are called metric coarse, only because they are more coarse than metric fine, but I don't consider them very coarse at all. It is just a name.

Your mini lathe wouldn't stand a chance, not only wouldn't it fit diameter wise, it would most probably burn it out just trying to turn a lump of metal that size.

I can make backplates for you, but it will have to wait until my workshop has been cleared of all jobs and tidied up, it could be a few months. But it would mean you removing your lathe spindle, I wouldn't even attempt it without. Just a couple of thou out and it wouldn't fit or be too sloppy a fit. Cast iron is the only material I would use, again, I wouldn't attempt it with anything else. Just get a quote for material, and be sitting down when you read it. Expect around £30+ per inch for 8", around £10+ per inch for 5".
It all depends on what sized chucks you want to fit, 5" would be reasonable, 8" might be a second mortgage type of job, especially as it seems the S&B has a longer than normal thread, so would require a longer length of material. It would need a length from the back datum face to the end of the threads, plus 3/8" to allow for machining and thread front recess.

John
« Last Edit: November 23, 2008, 06:43:05 PM by bogstandard »

Offline Darren

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Re: Help, British threads !!!
« Reply #4 on: November 23, 2008, 06:50:04 PM »
Hi John,

Yes I probably am confused, VERY !!.
I'm really lost around British threads and measurements, only just getting my head around what a thou is. Well I know what it is, but relating to it when machining is another matter. I try to convert it to metric all the time. One thou = roughly 0.4 of a mm...

A bit like when someone around here speaks to me in Welsh, I have to convert it to English to be able to speak back...

I've prob got this wrong, but I understood BSW was British Standard Whithworth and BSF was British Standard Fine (or a fine Whitworth)

TPI should just be Threads per Inch no matter what the standard type is. Even metric can be measured this way but we tend not to as they have a standardised TPI. And because it would be mixing metric with imperial which we tend not to do.

6mm is 26 tpi I believe.


I'll do some studying on the matter.....oh and look at your links which I have yet to do.......thanks

Darren

PS, I have one backplate, would that help in making another? 6" chucks seem to be about right for this lathe.



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Offline Darren

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Re: Help, British threads !!!
« Reply #5 on: November 23, 2008, 07:17:29 PM »
Annoyingly I have have two backplates for the standard size, 1.752 x 8 tpi, came in a box of spares. Dia is a bit small though.
I'll dig them out tomorrow and see if anything can be done with them. Have a better look like....


Darren
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bogstandard

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Re: Help, British threads !!!
« Reply #6 on: November 23, 2008, 11:32:20 PM »
Darren,

Just to prove that yours isn't a standard BSW thread, here is the BSW chart

http://shopswarf.orconhosting.net.nz/bsw.html

Notice that the standard 2" BSW has a pitch of 4.5 TPI.

Metric is always measured by the metric length of pitch.

Anyway, back to your problem.

Those old backplates should be fairly easily opened up to fit your machine, there should be enough meat on them. But again, the spindle would be required for an accurate fit. I suppose a dummy spindle nose could be turned up to fit one of your backplates, but that increases the workload, and because yours is a fairly old machine, the backplates might be worn, and any resulting backplates might not fit your lathe spindle correctly.

I have seen faceplates made using large brake discs, with a hub being made from a smaller piece of cast, and then bolted together, but I don't think I would trust that sort of build up to support a heavy chuck.

BTW 1" = 25.4mm, so 1 thou = 0.0254mm. When doing a quick mental calculation, 1mm = 40 thou (actually 0.03937", but close enough for quickie calcs).

If you are going to get deeper into this, a basic understanding of Imperial is definitely required, as most British and American plans will be in imperial. Over time, you really should be able to think and work in both systems, otherwise major conversion errors can creep in.

There is a bit more to this model engineering lark than you thought. But it seems you are picking all the difficult bits to begin with.

John

Offline Darren

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Re: Help, British threads !!!
« Reply #7 on: November 24, 2008, 03:56:38 AM »
Thanks John, I'm beginning to realise that you can make any darn thread you want.....and they did !!

A thread type is little more than a shape or angle. BSF & BSW are just two sets of standard pitches of the same shape for a given diameter.
The beginnings of thread standardisation.

The lathe nose is not of one of those standards. Nonetheless, it works well.

Oh and the thou = mm thing, I shouldn't post so late, I got that backwards. I do hope it becomes more natural in time without too much thinking. I'm not getting any younger for all this new language I need to learn  :smart:

Anyway, I doubt my lathe nose is too warn, it was set-up as a dedicated capstan lathe using collets. There was plenty of collets with it but no chucks or backplates.
The spindle nose in front of you would be best, but darn inconvenient, not that I've ever removed it.


Quote
"There is a bit more to this model engineering lark than you thought. But it seems you are picking all the difficult bits to begin with."

Oh I do hope so, it should be downhill from there on  :D



No worries, I'm in no hurry, might even find a backplate yet, I have found one so far.....


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Offline John Stevenson

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Re: Help, British threads !!!
« Reply #8 on: November 24, 2008, 04:37:36 AM »
Once you get into these items they are all specials.
2" x 8 BSW is the same as 2" x 8 BSF, what they are trying to say is that they are 2" x 8 tpi at 55 degrees thread angle.

Any lathe that needs plenty of attachements needs a spare spindle nose. This in turn is then uses as a master gauge to reproduce new fittings.



John S.
John Stevenson

Offline Darren

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Re: Help, British threads !!!
« Reply #9 on: November 24, 2008, 05:09:53 AM »
Hi John,

Yes thanks, it's starting to become a bit clearer (and simpler).

This is a cracking and very solid little lathe. It does what it was designed for very well.
But thread cutting is not part of that program. Maybe I should be looking for one that has more capabilities in this department.
Not right now though, it'll have to wait a while, got to build a garage first, after some other renovations. I spent the most of yesterday pulling ceilings down. Should give you a picture of where I'm at.....will all come good in the end  :D

Main thing is, I enjoy playing with metal, always have. Funny really, so demanding on the resources at times, yet so relaxing....sure makes time fly.... :thumbup:
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Offline CrewCab

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Re: Help, British threads !!!
« Reply #10 on: November 24, 2008, 06:56:20 PM »
This is a cracking and very solid little lathe.

Darren,

I had a trawl back through a few old posts to find a little more info about your lathe ........ (just colour me "nosey  ::)  ) ............. Smart and Brown Model L ......... let's be honest here ...  I'm no expert but as far as I can see anything made by Smart and Brown is going to be top quality and that little Model "L" looks a cracking machine .......... well done for managing to find one.

Before I bought my Boxford I had a look at all sorts and one place had a Smart and Brown 1024 (I think) ........... that is a "Very, Very, Nice" piece of kit ........... it was never going to folow me home for a variety of reasons .......... size and weight being a fairly major factor, it weighs over twice as much as the Boxford and the footprint is about 45% bigger .............. and the other  deciding factor was .............. I could have bought 6 Boxfords like mine for the asking price of this 1024  :bugeye: .......... got to say though it's a seriously nice machine  ::) if you have the space and budget.


Anyway ............... back to reality ..............  my cross slide is just a nad's "wibbly - wobbly" near the centre ........  metinks I need to do a little investigation etc. and perhaps follow your lead  :bow:

Thanks for all the input Darren ........... it's very much appreciated   :thumbup:

CC

Offline Darren

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Re: Help, British threads !!!
« Reply #11 on: November 25, 2008, 04:02:38 AM »
Yes I don't think S&B ever made what is considered to be a "bad" lathe. Even the smallest they made the 2" Pultra is sought after. Very similar to the L model but half the size. Mind you, the cabinet is the same unit so it takes up the same footprint.

I was lucky when mine was delivered, we had a team of builders around at the time. It took four strong men to move my little lathe. There was no way two alone could move it. It had to be lifted off the pallet with nothing but muscle power.

The 1024 is a beauty, as far as I know they were not too common in production machine shops. More often found in research labs I believe. So most are still in excellent condition with little wear.

For such a big machine a couple of things let them down a touch. Spindle through bore and throw. A gap bed would have been nice.
But having said that, they were built for precision and were extremely well made, just look at the size of that apron & bed casting ....!!! 

I would love one....



You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)