Cutting BA Threads on Minilathe?

This topic has 9 replies, 8 voices, and was last updated 2 November 2017 at 15:20 by Neil Wyatt.

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1 November 2017 at 20:24 #324871
Jared Martin
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@jaredmartin42239
I'm thinking of getting a mini lathe like the SIEG C3 7×14 Mini Lathe. Since I live in El Salvador, getting the BA screws called for in the project I'm attempting will be very difficult to get. How feasible would it be to make the needed threads with the mini lathe I'm ordering? I know the manual doesn't have any tables for those threads, so how would I do it?
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1 November 2017 at 20:24 #8948
Jared Martin
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@jaredmartin42239
1 November 2017 at 20:33 #324873
Ian Skeldon 2
Participant
@ianskeldon2
I can't actually help with your question, however, if you are happy to buy from the UK lots of suppliers will sell BA screws and bolts. Just a couple of examples below.

**LINK**

or

**LINK**
1 November 2017 at 20:39 #324876
Brian H
Participant
@brianh50089
Hello Jared; you will have difficulties screw cutting BA threads on almost any lathe because of the unusual threads per inch or cm.

It might be as well to convert the threads to the nearest metric or US threads. I'm afraid that I don't know what threads would be common in El Salvador but I assume either metric or US. Do you have any taps and dies for one of those or are they easy to obtain?

I wish you all the best with your project and if you need more help then you know where to come.

Regards, Brian
1 November 2017 at 20:43 #324881
Jared Martin
Participant
@jaredmartin42239
Yeah, I'm trying to build a Simplex, and I've bought 5/32 and 1/8 taps to start with, I just thought having the lathe might make it feasible to make the right bolts
1 November 2017 at 20:45 #324882
JasonB
Moderator
@jasonb
I would not bother to screw cut them, get yourself a tailstock die holder and split dies of the BA sizes you want to use and cut them with that, if doing large numbers then a diehead may be worth considering but I have done batches of 50 or so with a tailstock dieholder quite easily.

J

Edited By JasonB on 01/11/2017 20:46:05
1 November 2017 at 20:54 #324883
mechman48
Participant
@mechman48
FWIW- Sounds like you're in the region of 2-3 BA with what you have… so 3 & 4 mm will be close to what you need, if your looking at 6 – 7 BA then you would be looking at 2 -2.3 mm taps & dies.

George.
2 November 2017 at 01:55 #324932
Hopper
Participant
@hopper
Do what I do living in a remote region with little access to exotica such as BA fasteners etc. Use the nearest metric size and buy the fasteners locally.

If you really want to screwcut BA (and I wouldn't) there is a good online change gear calculator for the mini-lathe here **LINK** All you have to do is look up the pitch of the BA thread you want to cut and enter it in the box. A standard set of gears can cut more threads than what is usually listed on the lathe maker's chart.
2 November 2017 at 09:48 #324954
Brian Wood
Participant
@brianwood45127
Hello Jared,

Gearing tables for BA threads in the range 0-16 BA for mini-lathes do now exist in 'Gearing of lathes for Screwcutting' published by Crowood in their metal worker series. The ISBN number is 978-1-78500-250-2 and it is available via Amazon for something like £12.50 plus postage.

Despite being the author of the book, these tables were published more on the lines of mathematical exercises to show that threads in that range could be generated to decent accuracy for either 16 tpi or 1.5 mm pitch leadscrews, using Neil Wyatt's 63 tooth wheel and the standard gear set together with 25 and 75 T wheels. The book also gives the gearing for other thread pitch series not shown in the mini-lathe handbook. The extra gears and the book are available form Arceurotrade

I would though agree with JasonB that the more practical route by far is to use split dies to create them; or use the metric equivalents instead.

Regards Brian
2 November 2017 at 15:20 #325011
Neil Wyatt
Moderator
@neilwyatt
The original mini-lathe tables I produced, including BA sizes, have been up on this site since 2014.

http://www.model-engineer.co.uk/news/article/mini-lathe-changewheel-tables/18722

There are a couple of errors to look out for which Brian corrected for his book, but I don't think they affect BA threads.

Neil
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