Will a Colchester Bantam cut 5tpi?

[David YeowartParticipant @davidyeowart59915]

Hi , Guys, I have a metric Colchester Bantam 2000 mk2 lathe, I would like to know if I can cut 5 tpi with it? I have a job that I would like to do, looks like the max tpi is 3

Cheers Dave

[David YeowartParticipant @davidyeowart59915]

[Howard LewisParticipant @howardlewis46836]

Pure guesswork, but would expect the Leadscrew on a lathe of that size to be 3mm pitch, so for 5 tpi it would need to be rotating faster than the spindle by a ratio of 1:0.59.

With 3 tpi to be the coarsest thread that can be cut, this is about 8.4mm pitch, needing the Leadscrew to rotate about a third faster than the Spindle. (1:0.3543307 ratio).

Do you have a 127T or even a 63T changegear? That should allow you set up a train, (and the Norton box) to cut Imperial threads, of various tpi.

As a starting point, 5 tpi (0.2" pitch) at 0.59:1 would seem to need the 127T gear driving a 75T, ( or a 63T driving a 37T) AS AN APPROXIMATION in an otherwise 1:1 train. Greater precision can be obtained by moving away, slightly from the supposed 1:1 ratio.

But then I could be wrong! Anyone else got any suggestions?

Howard

[MuzzerParticipant @muzzer]

I have a Bantam 1600 but assuming they are very similar, it should be simple enough. Here's is the std range of threads for the imperial model. If you have the metric version, you need the 100/127 gears or similar and there is a different chart on the machine / in the manual.

Do you have the various operating and installation manuals? PM me if you don't. As I said, mine's the 1600 but unless I'm mistaken they are very similar under the skin.

Murray

Edited By Muzzer on 02/06/2017 12:59:09

[BazyleParticipant @bazyle]

As you say 'the max tpi is 3' it implies you have parts and information for cutting imperial threads so is your question about the possible strain on the parts in cutting a coarse thread? Tables and gearboxes are sometimes more for completeness of the list rather than implication that it is a good thing to do – rather like car speedos going up to 150mph.
If that is your concern then one way round it is to push or pull the saddle manually while using the gear train to impede its movement to the correct pitch rather than providing the force needed to pull it along.

[Simon Williams 3Participant @simonwilliams3]

Try this for size, copied out of the manual for my Bantam Mk2.

I saw some comments a few days ago about rotating the pictures, so I loaded this to see if I could rotate it after loading it. Fail. Sorry Neil, you haven;'t fixed it – or more likely I'm too incompetent to follow the instructions!!

 

HTH Simon

Edited By Neil Wyatt on 02/06/2017 13:37:33

Edited By Neil Wyatt on 02/06/2017 13:39:19

Edited By JasonB on 02/06/2017 14:03:33

Edited By JasonB on 02/06/2017 14:03:53

[Neil WyattModerator @neilwyatt]

I never fixed it, I just thought I had found a solution, but it only lets mods rotate images. You may or may not be able to see the rotation I've done, you can probably see the random spaces.

Neil

[JasonBModerator @jasonb]

Well at least I can sweep up after you and get rid of the random spaces

[MuzzerParticipant @muzzer]

I selected the text behind the picture and pasted it into notepad to view it.

Technology, eh!

Edited By Muzzer on 02/06/2017 14:32:38

[Simon Williams 3Participant @simonwilliams3]

Thank you Neil, at least I don't have to lie down now to read it!

Rgds Simon

[Simon Williams 3Participant @simonwilliams3]

Posted by Simon Williams 3 on 02/06/2017 13:05:43:

Try this for size, copied out of the manual for my Bantam Mk2.

I saw some comments a few days ago about rotating the pictures, so I loaded this to see if I could rotate it after loading it. Fail. Sorry Neil, you haven;'t fixed it – or more likely I'm too incompetent to follow the instructions!!

HTH Simon

Edited By Neil Wyatt on 02/06/2017 13:37:33

Edited By Neil Wyatt on 02/06/2017 13:39:19

Edited By JasonB on 02/06/2017 14:03:33

Edited By JasonB on 02/06/2017 14:03:53

For the sake of clarity, the bit that got overwritten in this post as adjusted above was that the table of threads came from the handbook for my MK 2 Bantam, so it shows how to set up the change wheels for 5TPI as requested.

There does seem to be a little bit of confusion going round – if the lathe can cut everything down to 3.5 TPI as shown in the manufacturer's table, then all those finer threads (of which 5TPI is one) are available. Cutting coarser threads – numbers below 3.5 TPI – might be difficult and certainly needs extra care or a different approach. But a Mk 2 Bantam is a pretty robust beast, and I wouldn't expect to have too much difficulty doing 5TPI on it. Mind you it's a lot of thread to whittle out, it's going to take a bit of patience (and a lot of concentration) to make a reasonable job of it.

I'm sure I'm not the only one who'd like to see a piccy of the finished result.

[David YeowartParticipant @davidyeowart59915]

Many thanks for all of the help, I need to make a travelling steady first before I can start my project, I will post pictures when it is finished

Thanks for the help Dave

[Simon Williams 3Participant @simonwilliams3]

Looking forward to seeing it. Can we have some " in progress" pictures too please?

Good luck Simon

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