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Thread sizes on flexispeed meteor lathe

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Mark Edwards 119/08/2019 20:06:56
6 forum posts

I have obtained a little flexispeed lathe, and want to restore it. Being of a certain age I have only ever used metric fasteners. Obviously this lathe hasn't got metric fasteners. I also have a BA tap and die set and these do not match the smaller threads on this lathe. Any ideas what would have been used on s small British lathe made in the 50's. Whitworth, Inc,unf ? The threads do look quite course based on the diameter of the small bolts.

Clive Brown 119/08/2019 20:20:54
266 forum posts
7 photos

Very probably Whitworth threads for that era. Especially if tapped into iron castings

Mark Edwards 119/08/2019 22:01:25
6 forum posts

Thanks, will try and work out the exact sizes. Least I can now start looking through the whitworth specs

Neil A19/08/2019 22:35:40
47 forum posts

I think you will find that most of the threads used on the Flexispeed lathe are UNC. I had to replace the gib adjusting screws about 40 years ago, they were UNC, but I would have to search out the old packet to find what the actual size was. I think the cap screws in the tool post are 2BA, but I will have to check tomorrow to make certain.

Neil

Just had a thought, Flexispeed manufacture went though a number of different owners, there could be variations in what they actually used for their thread system. Whitworth and UNC are dimensionally very close on some sizes, best to check carefully before retapping any holes.

Edited By Neil A on 19/08/2019 23:04:01

john carruthers20/08/2019 08:33:21
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595 forum posts
172 photos

The spindle nose is 1/2" x 16tpi
If you look in my Flexispeed album there is a copy of the old type written manual..
flexispeed

not done it yet20/08/2019 10:21:36
3358 forum posts
11 photos

Whit and UNC are very similar, but not quite universally interchangeable. Whit is a 55 degree thread and UNC is 60 degrees, for instance. Pitches are mostly the same (1/2” are different by one tpi).

A set of thread gauges might be a useful addition to your toolbox.

Clive Brown 120/08/2019 11:07:56
266 forum posts
7 photos

A fairly good visual guide to whether a fastener is BS or unified is the size of the hexagon. Unified fasteners  have smaller hexagons, generally in 1/16" increments. BS fasteners don't follow this rule.

Eg; 3/8" UNC = 9/16" af hexagon; 3/8" BSW = 0.6", (later) or 0.71", (earlier) af hexagon.

Spanners aren't interchangable between the two systems.

Origin of the unified system is America and came into the motor industry post WW2.

Unified bolts often have a circular depression on the head, or at least, they used to.

Clive

Edited By Clive Brown 1 on 20/08/2019 11:08:53

Nick Clarke 320/08/2019 11:32:23
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390 forum posts
11 photos

While not relevant to a lathe, at least hopefully!, just because there is a BSF/BSW head size on a bolt does not necessarily mean that is the thread - Morris at their Coventry (ex Hotchkiss) engine plant used metric threads with BSW heads on Morris engines until 1954 and even later on MG and Wolseley engines!

Clive Brown 120/08/2019 11:45:30
266 forum posts
7 photos
Posted by Nick Clarke 3 on 20/08/2019 11:32:23:

While not relevant to a lathe, at least hopefully!, just because there is a BSF/BSW head size on a bolt does not necessarily mean that is the thread - Morris at their Coventry (ex Hotchkiss) engine plant used metric threads with BSW heads on Morris engines until 1954 and even later on MG and Wolseley engines!

I owned a pre-war Morris 20 with that type of fastener. IIRC the 8mm thread size was 1mm pitch, finer even than BSF.

Clive

Mark Edwards 122/08/2019 14:22:10
6 forum posts

it is the tiny screws in the gibs that I need to sort out, the threads in the castings are fine but the allen heads are all chewed up, so just need to replace the bolts. I do have thread gauges but are metric as this is all I normally need. Will also investigate UNC as well as Whitworth and see if I can figure it out. thanks Mark

John Baguley22/08/2019 16:07:12
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424 forum posts
46 photos

Hi Mark,

I've just dug my 1970's vintage Flexispeed out of it's box (been in it for years now!). The gib screws seem to a weird size that I can't find in my thread charts.

The pitch seems to be either 32TPI or 0.8mm and the diameter is 0.1305" or 3.32mm. Someone more knowledgeable than I may be able to help further.

Yours may be a different vintage to mine so the threads may not be the same?

I bought mine as a kit and it came with assembly instructions and a drawing but unfortunately there is no information on the threads used.

John

Edited By John Baguley on 22/08/2019 16:08:39

Frances IoM22/08/2019 16:09:03
643 forum posts
24 photos
I suspect you will find these to be BA as in this period use of such threads was common in UK - they are still available tho in a restricted set of sizes - it might will be useful to find your local ME club and beg a few examples of 0, 2, 4 and 6 BA machine screws + nuts as these are the most likely to be found and use these as test pieces - if you are going to 'do up' old British equipment then any metric purity needs to be lost and some relevant taps,dies etc obtained (ME societies again are a good source from their rummage/jumble sales) Quick guide is that 0BA had a 1mm thread and each BA step size reduced this to 90% of the previous size thus 2BA would be 0.9 x 0.9 mm or .81mm 4B = 0.81 x 0.81 or abt .65mm thread

Edited By Frances IoM on 22/08/2019 16:16:33

Neil A22/08/2019 16:24:51
47 forum posts

I have just checked the screws for the gibs on my Flexispeed, as I had remembered they are UNC thread.

The cone pointed adjusting screws are 0.135 OD x 32 TPI, this is No 6 x 32 UNC, the hex locknut is 0.25 AF.

The cap head locking screw is 0.110 OD x 40 TPI, this is No 4 x 40 UNC.

The spindle nose thread is 1/2" x 16 BSF as mentioned by John Carruthers earlier.

I find thread pitch gauges difficult to judge between 55 and 60 degree thread angle on these small size fasteners, not much flank to sit on.

My Flexispeed was made at the end of 1975 by the Norfolk Lathe & Tool Co Ltd at North Walsham, so there may still be some variation in the thread schemes that were used depending on who made them. Measuring the thread OD may be the best indication of what you have.

Let us know how you get on.

Neil

P.S. The tool post screws were 2BA.

Edited By Neil A on 22/08/2019 16:28:24

James Alford22/08/2019 21:52:56
351 forum posts
72 photos
Posted by Mark Edwards 1 on 22/08/2019 14:22:10:

it is the tiny screws in the gibs that I need to sort out, the threads in the castings are fine but the allen heads are all chewed up, so just need to replace the bolts. I do have thread gauges but are metric as this is all I normally need. Will also investigate UNC as well as Whitworth and see if I can figure it out. thanks Mark

I have a Flexispeed Meteor lathe (I was working on it this evening, finally getting a vertical slide fitted and working) and a spare cross slide and saddle. Whether they have been re-tapped in one of them, I do not know, but they gib screws are not interchangeable between the spare and the set in the machine. I have no idea what thread either set are, though, I regret.

Regards,

James.

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