Author Topic: Next level on the lathe  (Read 12140 times)

cobbadog

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Re: Next level on the lathe
« Reply #15 on: 30 October, 2018, 04:45:42 pm »
Hi guys,
Cranky Crank, what is the reason for putting the cutting tool on an angle?
From what I understand and seen on the YouTube stuff they half the angle of the pitch. This would mean putting the cross slide on a 30' angle to cut a 60' pitch.
Franco, yes there is a little bit sticking out from the chuck, possibly just under 100mm but I did this to keep away from the chuck while I am in learning mode. No I did not have my live centre jammed into it so that is something I must do next time around.
With the gear for the dial
This second or third or even fourth hand Lathe did not come with a manual, well not something that explains very much other than how to plug it into the power source and turn it on. The rest I am working out a step at a time and I have tried contacting anyone that either sold these lathes or had one even tried to contact the manufacturer which was a good waste of time as their English is non existent and the same went for my Chinese.
Interesting that it may require 3 different gears for the thread chasing dial to cover imperial and metric. I did buy a dial that suits another common brand of lathe but the small gear on the bottom of it is very fine and I dont know how that would engage into a lead screw if all lead screws are based on a square pitched thread of various pitches. (if that makes sense). When I'm out in the shed next I will take a picture of what I have.
Cheers, John & Dee. Coopernook. NSW.

rustyengines

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Re: Next level on the lathe
« Reply #16 on: 30 October, 2018, 07:28:52 pm »
John you don?t have to put the tool post cross slide at an angle that is just an easy way of cutting a thread But the tool is still square to the job and you only use the tool post side for depth of cut
There is nothing wrong with a GOOD live centre that is all I use
If you got your lathe up to speed for the tool you are using the solid centre? Better known as Dead centre would burn out
Ian
Southern Cross Engines, Lawn Mowers and old tools * TOWNSVILLE

cranky crank

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Re: Next level on the lathe
« Reply #17 on: 30 October, 2018, 08:30:44 pm »
not me about tool on angle. my comment was to advance the cutting tool a little towards the chuck on each cut so you are cutting on the leading edge,not just winding the tool into the depth required and cutting on the trailing edge as well.

rustyengines

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Re: Next level on the lathe
« Reply #18 on: 30 October, 2018, 10:22:34 pm »
The tool is not an angle just the tool post slide
The method you mention is the way I was taught when doing my apprenticeship
I have tried the other way and it woks fine
Ian
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Kim S

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Re: Next level on the lathe
« Reply #19 on: 30 October, 2018, 11:36:50 pm »
Have been following this thread with a little curiosity? ...tool should be set at approximately half the thread angle by means of the compound rest and cuts on the leading edge so chips have room for leaving the cut, also helps using a decent heavy quality and rigid lathe i.e  Colchester, DSG, American Tool works, Monarch or VDF  for a good finish for cutting screw threads.

franco

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Re: Next level on the lathe
« Reply #20 on: 31 October, 2018, 01:35:29 am »
Interesting that it may require 3 different gears for the thread chasing dial to cover imperial and metric. I did buy a dial that suits another common brand of lathe but the small gear on the bottom of it is very fine and I dont know how that would engage into a lead screw if all lead screws are based on a square pitched thread of various pitches. (if that makes sense). When I'm out in the shed next I will take a picture of what I have.

John,

The three (or what ever number of gears are needed for a 3 mm pitch lead screw) do not allow you to use the thread dial to cut imperial threads on a lathe with a metric leadscrew: they are only there to allow you to cover the full  range of metric pitches. Don't worry about the fit of the various gears on the leadscrew. These don't need to be a precision fit. If you can find an original set they probably be stamped from sheet metal. I have seen thread dial gears made by hand with filed teeth which apparently worked OK.

Remember: with the class of lathes usually available for home workshops If you have a lathe with a metric leadscrew you can use the thread dial indicator to cut metric threads provided you have the right gear for the required pitch. You cannot use the thread dial indicator to cut imperial threads with a metric leadscrew, but need to leave the half nuts engaged.

If you have a lathe with an imperial leadscrew you can use the thread dial indicator when cutting imperial threads. You cannot use the thread dial when cutting metric threads with an imperial leadscrew, but need to leave the half nuts engaged.


Frank.
Cairns, Queensland

cobbadog

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Re: Next level on the lathe
« Reply #21 on: 31 October, 2018, 02:48:21 pm »
Once again, thanks to all who have commented and helped me out. I am at the moment trying to understand how to work out what size gears I require to cover the 3 common size metric threads (1.00, 1.25 1.75mm) on a 3mm lead screw. I have been offered a link to yet another Forum based around machinery work from Smokstak and as I have read it the theory is slowly coming together in my pea brain. I have to keep reading past some of the back biting to get to what I am after but I think I am getting closer. I now understand why I need 3 different gears, now I want to work out what sizes are required and where do I get some.
Some of the numbers offered were 28, 30 & 32 teeth but those were for a 4mm lead screw.

By the sounds of it it is almost a friction drive from the diameter of the gear and not maybe the teeth themselves.

I will keep reading and tomorrow will get back out to the shed and take a pic of the dial I have. Thanks again for all your input.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Next level on the lathe
« Reply #22 on: 31 October, 2018, 04:36:19 pm »
This s what I have been looking at. Some is not relevant to my lathe as he is discussing a 4mm lead screw but all those numbers and then he talks about a 'prime number'.  So what is the relevance of the prime numbers to the number of teeth?

I have 3 gears on the stem of my metric thread cutting dial and they are 28, 30 and 32 teeth. Those give you the prime numbers 2,3,5 & 7, which combined with a few different gears will give you all the metric thread pitches you will need. Not quite as straightforward as cutting TPI on an imperial lathe, but 95% of the world's machinists cope. I can take a photo of my thread chasing chart, ie dial teeth v pitch, if that will help.



4mm Leitspindel:

Thread pitch - Gear - Segment on dial (to engage in)

0,45 - 27 - Segment 3
0,5 - 20 - Segment 4
0,6 - 27 - Segment 3
0,75 - 27 - Segment 3
0,9 - 27 - Segment 3
1 - 20 - Segment 4
1,2 - 27 - Segment 3
1,25 - 20 - Segment 4
1,5 - 27 - Segment 3
1,75 - 21 - Segment 3
2 - 20 - Segment 4
2,5 - 20 - Segment 4
3 - 27 - Segment 3
3,5 - 21 - Segment 3
4 - 20 - Segment 4


So that means I would need a 20, 21 and 27 Tooth gear to get all the thread pitches my lathe allows for....

can anyone confirm this??
Cheers, John & Dee. Coopernook. NSW.

Kim S

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Re: Next level on the lathe
« Reply #23 on: 31 October, 2018, 05:21:45 pm »
but 95% of the world's machinists cope.

With out beating around the bush 95% of machinists are now on at least CNC machines and for most manual machines basically all but few change gears are built in the machines geared head and Norton box, basically the older machines and some of the newer hobby? class machines using detachable change gears all the gears were generally supplied with the machine when new, beware buying second hand lathes with the extra detachable gears missing! or for that matter any of the other accessories missing.

franco

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Re: Next level on the lathe
« Reply #24 on: 31 October, 2018, 06:46:23 pm »
QUOTE: By the sounds of it it is almost a friction drive from the diameter of the gear and not maybe the teeth themselves.
No! The teeth must engage the leadscrew: they just don't have to transmit much power.

See if this helps:
 https://www.homemodelenginemachinist.com/threads/al320g-threading-dial.26720/
It gives some calculations for thread dial indicator gears for a 3mm pitch leadscrew. I had a look at the AL320 Manual (the lathe in the link) and there is no mention or illustration of a thread cutting dial, which is not helpful!

I can't answer your question referring to the calculations for the gearing for a 4mm pitch which you quote, but I suspect (without doing the math) that they probably won't all apply to a 3mm pitch.

 In the link above the author refers to pages 81 and 82 of Martin Cleeve's book "Screwcutting in the Lathe". If you want to sight these pages I have a copy of the book and might be able to get legible copies if you want them, if the explanation in the link is not sufficient. This book (Workshop Series #3) is worth having for reference purposes, but if you read it and absorb all the information you will know much more about cutting threads in the lathe than you ever wished to know!

Frank.
Cairns, Queensland

rustyengines

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Re: Next level on the lathe
« Reply #25 on: 31 October, 2018, 06:58:02 pm »
**tool should be set at approximately half the thread angle***
Sorry Kim that is not what was taught at Tafe collages, yes it is all everybody seams to use these days
You don't need those brands of lathes you mention for a good lathe
we have talked all about this once before China dose make some very good machinery
Ian
https://kaida-machine.en.made-in-china.com/product/lKdEzhiHZLrC/China-Professional-Manufacturer-of-Lathe-Machine-for-66-Years-DC1440-K.html
Southern Cross Engines, Lawn Mowers and old tools * TOWNSVILLE

Scott

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Re: Next level on the lathe
« Reply #26 on: 01 November, 2018, 07:00:50 am »
Hello Cobba
Are the cutting tips and tool holder your using suitable for thread cutting?
I'm just thinking of how our threading machine has the dies set and how the cutters are sharpened.
Cheers Scott

Kim S

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Re: Next level on the lathe
« Reply #27 on: 01 November, 2018, 07:36:36 am »
A good example of the correct methods employed for the screw cutting of threads.

https://www.youtube.com/watch?v=9Hb-96Z7cRc

rustyengines

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Re: Next level on the lathe
« Reply #28 on: 01 November, 2018, 09:13:19 am »
**Are the cutting tips and tool holder your using suitable for thread cutting? **
Yes Scott
I mainly use high speed steel and grind the tool my self
Ian
Southern Cross Engines, Lawn Mowers and old tools * TOWNSVILLE

cobbadog

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Re: Next level on the lathe
« Reply #29 on: 01 November, 2018, 05:21:44 pm »
Thank you once again guys for the helpful tips. That link Frank is a ripper and is very helpful to me. Yes that chart was for a 4mm lead screw but it was just an example of what it was I was looking for. Now I'm armed and dangerous, I think !

The carbide tips I am using are of the correct angle. A diamond shaped tip is 55' for cutting imperial Whitworth but in my first run I used a tip that is basically diamond shaped with a funny little bit sticking out just behind the cutting edge and is at 60' the same as metric.
I did buy some HSS with the intention of grinding it to shape but have not gone down that road as yet.

I have taken some pics of my dial that happened my way but it is listed to suit another brand of lathe,  a Sieg C2, C3, SC2 & SC3 and I have no idea of the size off the lead screw on those machines.
Now I have seen that the common teeth numbers are up around  20 teeth up to 30 teeth all doing different metric pitches. The bit I now find confusing is that a 3mm pitch on the lead screw does not look as if a 20 tooth gear on a dial would connect and drive. Is this correct?
Cheers, John & Dee. Coopernook. NSW.