Setting 16 TPI on Colchester Bantam Lathe

[Frank SmallParticipant @franksmall87776]

Hi Guys,

I am trying to cut a 16 TPI thread using a Colchester Bantam 1600 Lathe for the first time.

It is fitted with a metric pitch lead screw (6mm)

The settings I have used are as follows as per information plate.

Gears

120 V-42 W-36

The Gear levers are T5

but I find that the measured TPI is aprox 18

I notice that there is also 127 adjacent to the 120 on panel. Could this be the problem. I am using a mandrel as I have no thread dial but I think that should not be causing the problem.

Any ideas would be very welcome

Thank you

[Frank SmallParticipant @franksmall87776]

[JasonBModerator @jasonb]

Can you post a photo of the front plate on the lathe to confirm things.

EDITED for a 1600 machine.

You need to have the 42T gear driving the 120T. Then on the same shaft as the 120 you need the 127. The 127 should drive your 36T gear

 

Edited By JasonB on 07/08/2017 20:42:41

[Simon Williams 3Participant @simonwilliams3]

+1 for Jason's post above.

Just to confirm, the thread you are actually cutting without the 127 gear should be 16.93 TPI if I've understood things correctly, i.e. 1'5 mm pitch. Would you like to check the pitch you are cutting and confirm it is 1.5 mm pitch. If it helps an M10 coarse tap makes a good 1.5 mm pitch gauge.

Best rgds Simon

[Frank SmallParticipant @franksmall87776]

Thanks Guys,

I am sure that will solve my problem. I did not notice the 127 gear on the plate and also not realise that it is possible to place more than one gear on the same shaft.

Regards

Frank

[Frank SmallParticipant @franksmall87776]

Hi Guys,

I now have a different problem relating to the same subject.

I simply want to attach a couple of views of the problem, is there an easy way. I can send it in any format jpeg etc.

Otherwise is there a tutorial on how to do so using this post system?

Thank you.

Frank

[Thor 🇳🇴Participant @thor]

Hi Frank,

There is an explanation on how to post Photos and create Albums here. Use JPG format.

Thor

[Frank SmallParticipant @franksmall87776]

Hi Guys,

Thank you all for your kind help.

I am now ready to ask the next question!!!!!

The instruction requires the mounting the 127 tooth gear outside the 120 gear , to do this the retaining nut must first be removed..

I purchased the lathe secondhand and the change gear 100T was replaced by a much smaller one about the size of the retaining nut (see photo and drawing below). The problem is that the gear is about the same size as the nut and I find it impossible to hold the gear (without damaging it) whilst I try to open the nut which is very tight. If the gear were larger say 100T it would be very easy to deal with it.

Any idea how I can hold the gear under the nut without damaging it. I have tried a (chain) strap wrench but it is too wide to retain the gear as the nut is very tight.

I look forward to you ideas.

Thank you

Frank

Hi Guys,

Thank you everyone for your kind help.

Now I am ready to ask the next question!!!!

The instructions require the mounting the 127 tooth gear outside the 120 gear

[JasonBModerator @jasonb]

As it is in your photo the two gears are on the same splined shaft so you can hold the larger of the two while you undo the nut. It's the larrger of the two nuts you want to be undoing to remove the gears the other is to allow the stud to be moved along the banjo to mesh the gears

If you can't easily hold the big gear then engage screw cutting and lock the saddle to the bed that way all the gear train will be static while you undo the nut

[JasonBModerator @jasonb]

Forget that from the drawing the larger gear may not be a splined one.

You may have to unscrew the stud which will then allow you to hold the sleeve in a vice by the end that goes against the banjo

 

 

Edited By JasonB on 08/08/2017 17:22:02

[Frank SmallParticipant @franksmall87776]

Hi Jason,

Thanks for the prompt reply.

You are right Gear T120 is not splined. For that reason also I think jamming the gear train will not work, so it seems that holding the brass sleeve in the vice is the only option unless I can hold the small gear in a pipe wrench and accept any damage to that gear

What do you think?

Regards

Frank

[JasonBModerator @jasonb]

Not much bronze to get hold of there and a harder part to make if damaged.

What about grabbing a couple of bits of scrap aluminium and sawing/filing a couple of rough teeth into them like a short rack so they engage in the small gear and then gripping those.

Don't know what gear ratio they were trying to get but presumably as the very small gear can't be pinned to the larger one they did it up extra tight so they would not slip.

[Frank SmallParticipant @franksmall87776]

Jason,

Thank you

I agree about the bronze

I will focus on trying to hold the small gear and the rack idea.

I also may reconsider if I can pin the gears together although it is rather small

Will let you know how I get on

Regards

frank

[Simon Williams 3Participant @simonwilliams3]

Dont start graunching things yet, hopefully you dont need to.

Undo the centre small nut. This fastens the pivot in the banjo slot. Now see if you can pull the two gears and the big nut off the centre pivot, together with the centre bronze sleeve.

Now youve got the two gears, still fastened together, but off the lathe. Grip the bigger gear in the vice edge on, see if the big nut will now undo. Its a RH thread. Protect the jaws of the vice so not to chew up the faces of the bigger gear. This bigger 120t gear should have a female spline in it if I remember right, and the bronze sleeve has a matching male spline so they should be held secure while you loosen the bigger nut. Its the 127t gear which is smooth bored I think, will check in the morning.

 

Plan B is to sacrifice the smaller gear, but you shouldnt need to

Rgds Simon

Edited By Simon Williams 3 on 08/08/2017 22:08:30

 

Edit: My aplogies Ive misled you slightly.

Just been to check, and on mine the 120T gear is smooth bored, and both the 100 and the 127 T are splined. So holding the bigger gear 120 t wont stop the centre bronze bush from turning. You need to grip the little gear somehow – maybe pump pliers – to hold the bronze centre. Try it gripping the big gear as above though anyway, you might be able to get the big nut to loosen off.

Edited By Simon Williams 3 on 08/08/2017 22:36:05

[Frank SmallParticipant @franksmall87776]

Hi Simon,

Thanks again for your interest.

Firstly its good that I have confirmation that I am not overlooking something

I think I now have a plan to do as little damage as possible.

I will make an aluminium clamp along the lines suggested by Jason that can be held in the vice against the T120

gear. One minor problem I anticipate is that the width of the clamp may not be wide enough to accommodate adequate clamping bolts, but I as sure I will think of something. What a lot of problems over what should not even be a problem.

Mind you I have now decided that I will now borrow a decent socket rather that the wrench supplied by Colchester which could reduce my difficulties down the line!!!!!!!

It is great to have such an exchange of ideas

Regards

Frank

[JasonBModerator @jasonb]

I would use the ali jaws to hold the small gear as the big one will stay still and the nut & bronze spline turn within it, though Simon says his 120 is splined anmd yours is not?

If you hold the gears so the small one is at the bottom and rest it on your bench vice and make the Rack from say 6mm thick material you can close up the vice onto these and get a spanner in from below.

Edited By JasonB on 09/08/2017 08:01:14

[Simon Williams 3Participant @simonwilliams3]

Sorry Jason, my mistake, I'm wrong about the 120 being splined, it's not. I got that wrongg, see edit above.

So your idea of clamping the outer dia of the gear in a pair of shaped racks should work. But I'd try the 120 gear held edge on in a vice, then pump pliers on the od of the little gear. Frank has only got to provide enough friction to stop the bronze bit turning with the big nylock nut enough to crack the thread loose.

I agree with him not to nadger the bronze bit, but minor damage to the teeth of the little gear will be repairable.

Best rhds Simon

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