thread cutting

faced with having to cut a short length of M12x1.75 onto a 12mm bar, and
finding that the (cheapo) M12x1.75 die wasn't really up to it, I had a go at
getting the lathe to cut threads.
after a certain amount of discussion, calculation and guesswork (a mate of
mine was around at the time) we decided on which setting on the gearbox
would do 1.75mm pitch (oddly, it's not labelled - various other metric
pitches are, and the gearbox is metric-or-imperial).
I then ground up a 60-degree pointy tool, as I don't have a suitable thread
chaser, and, putting a bit of spare material in the chuck, set forth to see
if I could cut threads, which, after a few false starts, I did get it to do
a rather rough and 'orrible job, which I could then clean up with the
aforementioned die.
The main problem seems to be getting it to cut smoothly - I was operating at
very low speed, 'cos otherwise it's difficult to control, particularly as I
was only aiming to produce about 12mm or so of thread; just enough to screw
a nut onto.
Apart from having a proper chaser, any hints and tips about the process of
cutting threads on the lathe?
Reply to
Austin Shackles
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All you need is...
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BugBear
Reply to
bugbear
A good suggestion, I you require further reading the following is very good, and a useful addition to your bookshelf. It is a bit more technical in parts and Sparey is a good starter.
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Regards Brian
Reply to
brian
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Save yourself time and money but just buying a decent HSS die. Stick it in a tail stock holder at 100 or so rpm and use that with lubricant. Hit the stop butten when required.
The die will probably be around £15 books to read a few quid time to do all the setting up can be priceless (hours)
Adrian
Reply to
Adrian Hodgson
I've just tried my first bit of thread cutting - an M8 (1.25 pitch) thread on some silver steel... don't have a thread dial indicator, which made things difficult. Think what I have achieved is good enough to clean up with my cheap die set (and it's actually for self tapping into plastic anyway, so no great shakes). Still proud of my first proper bit of machining on my toy, though... :)
Reply to
Robin
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Silver steel isn't easy to get a good thread on, so maybe you can allow yourself to just a little more proud
Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
Tim Leech
Thanks, Tim... I'll hold my head a little higher!!
Reply to
Robin
Thread dial indicator won't work on a Myford for doing Metric threads.
You have to keep 1/2 nuts engaged and wind back.
. -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:-
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Reply to
John Stevenson
Robin
Make life a bit easier for yourself...try and find a bit of ordinary mild steel for your experiments, a leaded 'free-cutting' type for preference -
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sell in small quantities. It's much easier to cut and is likely to give you a better finish while you're learning. I'd be very happy to supply you with a couple of bits to practice on if you send me your address off list.
Remember too, on the Myford, that if you cut a thread with any multiple of eight threads per inch, you needn't worry about a thread dial indicator as you can engage the clasp nuts on the leadscrew at any point. Having said that, you are going to be a bit inhibited without a TDI - they are often to be found for a few pounds on e-Bay, one went about a week ago for about £12. Anyway, let us know when you have successfully cut your first half inch diameter, one inch long, sixteen threads per inch rod - with matching nut! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
Reply to
Chris Edwards
Robin
On reflection, a half inch diameter nut is perhaps a bit *too* challenging at this stage. Lets say *you* choose the diameter, depending on materials and tools available ....or that you can perhaps make! Nevertheless, well done so far, welcome to our world! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
Reply to
Chris Edwards
from Chris Edwards
As JS has already said that won't help with metric threads. One of the first 'accessories' I bought after the Lathe itself was a 127 tooth wheel - from Mary Poppins bag :)
The first thread I cut was a 12mm x 2mm ACME 150mm long in Silver Steel and the second was 250 long. The first ended up as the tap to cut the PB nut to fit the second !
JG
Reply to
JG
I've already bought a load of change gears - worked out which ones I needed for metric threads - can't remember off hand if I've got a 127 gear but according to the Myford manual, the ones I've got are OK.
I was watching a TDI on eBay the other day. It went for =A322. Looking at the Myford parts catalogue, a new one is =A317... can't put a price on heritage, I suppose...
John - you mentioned winding back the thread - would this be by putting a key in the chuck, for example, and using that as a lever to turn the whole system backwards?
So nice to be producing swarf at last - I've had the lathe for about 2 years!!!
Reply to
Robin
I think the original myford TDI had a black painted metal body and a nickel plated dial. Current ones are part or all plastic.
While the plastic one probably does the job perfectly, some people might prefer the older one.
-adrian
Reply to
Adrian Godwin
from "Robin"
For short threads you should have no problem but the only way to cut accurate metric threads on a lathe with an imperial leadscrew is to use a 127 tooth changewheel in the train.
Not necessarily. At the end of the thread cut, stop the lathe, withdraw the tool from the work, re-start the lathe in reverse far enough back to take acount of any backlash, stop the lathe, put the next cut on, re-start in forward . . . . repeat as necessary.
It took me all of 10 minutes after bolting the lathe back on the stand :))
JG
Reply to
JG
I don't where you got that information but it is unfortunately wrong. New ones are just the same as the old ones, at least around 4 weeks ago when I bought one.
Peter
Reply to
Peter Neill
The gears that Myford supply for metric allow accuracy to a level beyond most's ability to measure. The use of the 127 tooth gear makes the conversions EXACT! then the errors all rest on the operator. :-)
Look around online for crank handle plans. There are several out there. In general, they use an expanding mandrel fitted into the back end of the lathe spindle, and fitted with a handle to crank the spindle with/ Generally not used under power, as things get a little "jumpy"
Cheers Trevor Jones
Reply to
Trevor Jones
Pleased to hear it - but I'm sure I've seen some with a red plastic section. Sorry to mislead if it's just my imagination.
-adrian
Reply to
Adrian Godwin
For cutting metric threads Myford supply two 21T gears. These provide all the accuracy you could possibly measure. The calculation of a suitable gear train is a little more subtle however. Fortunately you can download a program to do it for you:
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Reply to
Charles Lamont
Ah, don't have a reverse switch... there's another thing to add to the list... looks like I'll be doing some tedious winding by hand...
Reply to
Robin
On or around Mon, 30 Oct 2006 17:51:08 +0000, Adrian Hodgson enlightened us thusly:
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yeah, well, that's what I do for smaller threads anyway, notably 8x1.25. however, the amount of cutting for the 12x1.75 is such that one or more of the work or the dieholder slipped. Now, of course, I could get a better tailstock die holder, but it's a bit difficult if the workpiece slips in the chuck, ther chuck will only go so tight; I suppose I could make a bigger handle for the chuck key...
this can be alleviated slightly by having an adjustable die and doing the first cut with it set as wide as possible, then cutting to final size.
Reply to
Austin Shackles

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