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ptjw7uk
03-18-2007, 06:58 AM
Hi all I have had my chinese lathe for over a year now and have never cut a thread on it yet but the need has now arisen. So the saga is I measured the pitch with some metric gauges and it says the thread is 100 so go to the lathe and the numbers on the lathe are not quite what I was expecting the nearest are 0.1 and 1 trying the what I think is 0.1 is not cutting a thread but gives anice finish to the bar.
I think the 1 is going to be 1mm pitch which is not quite fine enough as the thread I want to make looks very fine. The bit I want to make is to fit into a microphone goosneck and is about 16mm diameter.

Looking at my thread gauges I realise I do not understand them imperial is easy it says the tpi job done but metric!!!

Peter

aboard_epsilon
03-18-2007, 08:27 AM
metric thread comes in fine and coarse

http://www.gewinde-normen.de/en/iso-fine-thread.html

http://www.gewinde-normen.de/en/iso-coarse-thread.html

As the bolt size increases so does the pitch ..and jumps up every other... size sort of, as the diameter goes up...have a look at the charts .

sounds like you are not putting your lathe into threading mode when you make your choices

there should be a lever marked threading...on the head stock ..

when this is engaged you will see the threaded acme shaft that runs along the bed of the lathe start to turn

once turning there should be another lever to engage half-nuts on the apron, onto the shaft.

only then are you threading


ll the best....mark

Peter N
03-18-2007, 08:28 AM
Peter, metric thread gauges are simple, instead of TPI they tell you the pitch distance between the thread roots/crests in mm, so I imagine that the 100 you saw on the thread gauges was probably a 1.0mm pitch.

However, a quick google for microphone threads brings up 5/8" x 27TPI as a standard, which is very close to 16mm-diameter-and-finer-than-1mm that you listed.
Are you sure it's not this thread that you want?

But you might be snookered anyway - you have the Chester DB10G IIRC? When I briefly had mine there was no way it had enough change gears to screwcut many threads at all, although the threading chart on the headstock said it would do 8-35TPI.
I still have a picture of this to make me laugh a bit and whilst it has 24/25/28 TPI listed there's no combination on there for 27.
Doesn't mean you definitely can't do it, but may need a bit of maths with the gear train..

Peter

ptjw7uk
03-18-2007, 08:47 AM
Update,
Done a search on the web and find what I need is not a metric thread but I assume an american size as it is 5/8 27 which I think is impossible to cut on ametric lathe.
Now looking for reasonable priced taps what I thought to be a simple job is getting to be expensive.
I should have just bought a lamp for the lathe in the first place but nothing ventured nothing gained and I am learning, I think!!
Peter

aboard_epsilon
03-18-2007, 08:54 AM
there should be change gears that you swap out to convert your metric lathe into an imperial one just for dioing these threads

ptjw7uk
03-18-2007, 08:54 AM
Thanks -Peter Neill,
Its as you say the Chester is not that good at showing what you need to do.
It is also as you say a 5/8 27 but I might try and cut a sloppy 15.875 with a sloppy 1mm pitch (if I can work the gears out) and see if it will work as its only for a lamp fitting to a gooseneck.
Just looked at the prices of a 5/8 27 tap and they are out of this world which for a 2 off job is a no no.
Anyway thanks again - back to the workshop.
Peter

ptjw7uk
03-18-2007, 08:59 AM
Thanks -Peter Neill,
Its as you say the Chester is not that good at showing what you need to do.
It is also as you say a 5/8 27 but I might try and cut a sloppy 15.875 with a sloppy 1mm pitch (if I can work the gears out) and see if it will work as its only for a lamp fitting to a gooseneck.
Just looked at the prices of a 5/8 27 tap and they are out of this world which for a 2 off job is a no no.
Anyway thanks again - back to the workshop.
Peter

Peter N
03-18-2007, 09:02 AM
Peter, if sloppy is not a problem then 28 TPI will be closer than a 1mm pitch.

Here is picture of the change gear set up from my DB10G - of course this assumes that you have all the gears required, which is a bit of a gamble with Chester products....


http://www.btinternet.com/~p.neill/DB10G_threadcutting.jpeg

Peter

Randolph
03-18-2007, 09:34 AM
There is one more variable left in the "anxiety closet" of thread cutting. If you are trying to cut metric threads and your lead screw is TPI, or vice versa, your thread dial will not be of any use. You will have to engage the half-nut and then reverse the spindle between each cut to return to the starting point.

ptjw7uk
03-18-2007, 02:04 PM
Thanks all,
I cut a thread at 1mm and it fits a treat not to sloppy and the first I have cut with the 'lathe'(not sure if it should be called a lathe with so many questionable bits)
Peter Neill
All the gears on mine are all whole numbers 2 x 40,1 x50,1 x 60, 1 x 80 and 1 x100, it was not easy getting them all apart as instructions are none existant but I got it done.
Now to make the mountings, not sure whether to make permanent or magnetic only time will tell.
Thanks for all the replies its good to know ones not alone!!
Peter

Peter N
03-18-2007, 04:03 PM
Well done on your first bit of screwcutting.

The lack of a full set of change gears doesn't surprise me, but I seem to remember that these were all Module 1 gears so shouldn't be too hard to find some more as and when you need them.

Peter

Yankee1
03-18-2007, 09:39 PM
Hello Peter,
If you go to this website "http://www.varmintal.com/alath.htm" you will find a real neat free program that will enable you to calculate different threads. It was written by a Canadian machinist and can be downloaded to your computer. It works well. It isn called "Pauls Gears".
Regards
Chuck Marsh

Yankee1
03-18-2007, 09:41 PM
Hello Peter,
If you go to this website "http://www.varmintal.com/alath.htm" you will find a real neat free program that will enable you to calculate different threads. It was written by a Canadian machinist and can be downloaded to your computer. It works well. It's called "Pauls Gears".
Regards
Chuck Marsh

Evan
03-18-2007, 09:57 PM
http://vts.bc.ca/pics2/echo.gif

Paul Alciatore
03-19-2007, 02:05 AM
Thanks -Peter Neill,
Its as you say the Chester is not that good at showing what you need to do.
It is also as you say a 5/8 27 but I might try and cut a sloppy 15.875 with a sloppy 1mm pitch (if I can work the gears out) and see if it will work as its only for a lamp fitting to a gooseneck.
Just looked at the prices of a 5/8 27 tap and they are out of this world which for a 2 off job is a no no.
Anyway thanks again - back to the workshop.
Peter

I had a 10 or 12 piece order a year or so ago that needed the same thread.

KBC Tools, # 1-372-254, 5/8-27 HS SPECIAL TAP , $14.10. I was working in brass and it worked just fine. I'd offer to loan it but you could probably own it for a little over the two way freight.

ptjw7uk
03-19-2007, 04:46 AM
thanks Paul Alciatore for the offer but I think the pieces I cut will suffice for now.
I seem to have the bug now and want to try an internal thread for no other reason than it will be good proctice.
On another tack if I wanted to try a 2 start thread using the same 1mm pitch should I change it to 2mm pitch for a 2 start thread!!

Also (brain going into overdrive) could I cnc the screw threading operation then I should be able to cut virtually any thread!! Or is this a falacy!!
Peter

John Stevenson
03-19-2007, 05:12 AM
thanks Paul Alciatore for the offer but I think the pieces I cut will suffice for now.
I seem to have the bug now and want to try an internal thread for no other reason than it will be good proctice.
On another tack if I wanted to try a 2 start thread using the same 1mm pitch should I change it to 2mm pitch for a 2 start thread!!

Also (brain going into overdrive) could I cnc the screw threading operation then I should be able to cut virtually any thread!! Or is this a falacy!!
Peter

That's one of the main reasons that lathes get converted to CNC.
Hang fire though as Tony Jeffree has a got a single axis conversion in the pipeline at the moment to do just that.
He's converting my old ML7 to semi CNC on it's way to becoming a full CNC so you take your pick at what point you want to build to.

Obviously the methods will apply to other machines and not just the ML7.

.

Evan
03-19-2007, 09:44 AM
There is another trick I have used to cut threads that I don't have change gears for. If the item is something that doesn't need a lot of holding power such as a camera filter or similar then only cut two or three turns of thread using the closest available thread.

If better holding and/or alignment is required then set the compound parallel to the long axis. Cut two sets of two or three threads on collars spaced by whatever distance is appropriate using the compound to adjust and compensate for the difference in pitch. This of course requires that the entire process be done without disengaging the half nuts and the threads must be cut with a straight in plunge. It does work with a few calculations to determine the required spacing.