Thread: Question about threading

Usually you would only take 0.1mm cuts most I ever take is about 0.3mm which is what I was taught when I done my trade. You could probably run the spindle faster if you want to cut them faster, with carbide you can cut threads alot faster as you can run the spindle faster but you got to watch out when going up to a shoulder.

Thanks for the reply, never realized threads are achieved by using small cuts,
its more time consuming then originally thought.
had used 70 rpm, due to the shoulder, tried 170 rpm, all too often had failed to stop it in time, so wasted time sharpening bits.
when using a boring bar for internal threads, have not broken any tips, seems like the flex in the boring bar helps, even when it hits the end of a threads it just flexes away saving the tip.
next time will perform a test using a boring bar for OD threading.

Lather does the thread have to go all the way to the shoulder or polished shaft section?
Can you machine a "runout" section on the shaft first?

The top one in the drawing is something like I think you are making. The bottom has the runouts machined into it.

Stuart

Here is a vid I made years ago

[ame=http://www.youtube.com/watch?v=U9oTVc7L-cA]YouTube - how to thread[/ame]

Originally Posted by lather

Do carbide tips cut deeper than HSS ?

I use carbide for most threading on my AL960B and generally run it a bit faster than I would with HSS. For an M16 thread I'd probably use 4 passes. I use a heavy cutting oil and find that helps a lot.

Are you cutting a run-out trench at the end of the threaded section, that helps when getting to the end of the threaded section.

If you find the lathe laboring at 1mm with HSS I doubt that you would be able to use Carbide tooling.

If others here with your model machine are useing Carbide with that depth of cut or greater I would think that there is some type of problem with your lathe.

I have a 960 but I'm not sure how much I take off in mm as I do most of my machining in imperial units, I'll have to take notice when I do a thread tomorrow. Are you setting the compound at 55 or 60 degrees and using that for the depth of cut adjustment or is it left in the normal position with the DOC being adjusted with the cross-slide?

How deep are you cutting your threads?

240mm shafts, with 80 mm M16 threads at each end.

Is the 240 the diameter of the stock?

Gavin/ Stuart, sorry.
the shafts were 240mm long, 80 mm thread at each end, and m16 thread up to the polished surface being 16.5 mm.
had not made cut out trenches towards the ends, as the design was to lock 2 m16 bolts + a washer at each end, which would be easy to adjust the side clearance for the bush.
if using a trench the washer would not be centered, although it wouldnt make a difference if a nut was used without a washer.
Will try this next time.
At the moment i do not have a thread depth chart, so when first making a new thread i use small increments until the nut fits, then take note of the depth.
I keep the compound alone and use the cross slide for depth.
Will use the topslide next time.
The first cut is 1mm (as read from the dial), had noticed it doesnt take much material out, as the cut is narrow.
the 2nd pass cut depth is 0.5mm or 1.5mm overall.
from this point on the cut depth is 0.25mm as the cut gets wider.
On the M16 the total depth until the nut had a good fit was 2.30mm.
( it may not have been zeroed properly when first starting the job).
On the last setting alone (without adjusting the dial) it needed 3 passes until no more material was cut from the thread, its as if it doesnt cut the thread properly at each depth.
If using a 0.5 mm depth on the final passes, when looking at the hand dial it jerks due to strain.

Could trefalex be used, or does it contain abrasive material ?

RC, thanks for the vid, may decide to go imperial, being able to hand wind the carriage back would save time.
In the 960b manual it states that when making metric threads the only option is to reverse the lathe without disengaging the half nut.
Is this true ?

One problem i had noticed is that the surface under the post has bad wear and tear.
This started only after using for the first time, 2 toolholders in the post.
When trying to rotate the post was almost jammed, took great effort to rotate the post.
even the top slide was a little tighter.
The springed button didn't lift the post at all.
Now only use 1 tool at a time in the post.
since then its been a little tight when rotating using only 1 toolholder, still need to lift the post up by hand to avoid damaging the surface in case some specs get under it. (more farting about).
if its not lifted it grinds due to the rough surface.
only used the tools supplied and dont go crazy when tightening.

would like to correct this before it chews too much out of the surface, though this may be normal for cheap lathes.
Hope it hasn't warped causing problems.

For washers you could make a 10mm thick washers if there is room or use captive washers on the nuts(if you can get them in M16) or maybe flange nuts.



TrefOlex is for hand tools only

The tool post, are you talking about a 4 way tool post? I wouldnt lift it to turn it. Holding it down will help wipe swarf off, if you lift and turn you could be lifting swarf between the faces. If its that dirty take it off and clean it. (pictures?)

Stuart

Stuart

the post originally used to lift up due to a springed button.
until this problem occurred, only loosened the post a little, when rotating, as it had a smooth action.
this is not possible now as its still tight against the surface unless lifted, the rough surface has a grinding feel to it when rotating if this is not done causing more wear and tear, its very rough when touched.
considered using an oilstone, then realised it wont solve whatever warped causing the tightness.
May need to get the surfaces re-machined and the post shaft checked.

will post pics tomorrow.

as far as the washers go there is a space restriction when fitted .
the design will be changed for the remaining bushes needed.

Originally Posted by lather

At the moment i do not have a thread depth chart, so when first making a new thread i use small increments until the nut fits, then take note of the depth.

A M16x2.0 thread would be 1.0 mm deep by my calculations

I keep the compound alone and use the cross slide for depth.

That's one of the reasons why it's hard work, you are trying to cut on both side of the tool at once and wedging the tool in the cut, if you use the compound set over method then you are primarily cutting on one side of the tool, thus reducing the load markedly.

This link may help www.discoverlivesteam.com/books/threads.pdf

Could trefalex be used, or does it contain abrasive material ?

If you are referring to the paste type of Trefalex the answer is most emphatically NO. The instructions specifically point out that it shouldn't be used where fumes are likely to be generated and is restricted to hand tools only - the fumes are very bad for you. I used to use the RTD liquid in the orange bottle, it's very good stuff. Nowadays I use a Fuchs cutting oil which I buy in 20 litre drums. In your case I'd be going for the RTD stuff.

In the 960b manual it states that when making metric threads the only option is to reverse the lathe without disengaging the half nut.
Is this true ?

Yep.

One problem i had noticed is that the surface under the post has bad wear and tear.
This started only after using for the first time, 2 toolholders in the post.
When trying to rotate the post was almost jammed, took great effort to rotate the post.
even the top slide was a little tighter.
The springed button didn't lift the post at all.
Now only use 1 tool at a time in the post.
since then its been a little tight when rotating using only 1 toolholder, still need to lift the post up by hand to avoid damaging the surface in case some specs get under it. (more farting about).
if its not lifted it grinds due to the rough surface.
only used the tools supplied and dont go crazy when tightening.

If this is the standard 4-way toolpost then that's definitely not right, I routinely run 3 tools (turn, bore, part) in mine for a job I do often.

that looks to easy RC....what did you use for the trick photography..lol

cant wait till my threading holders get here so I can try it

Gavin, thanks for the tips.

yeh, it was the trefalex paste, had been using it in the drill press.
no wonder i felt like crap after drilling hundreds of holes.
A neighbor gave me a can, and mentioned that it saves time and slows wear on the drill bit, couldn't read the label, as it was badly scratched.
Thanks for clearing up the difference between using the cross slide, and compound.
Thinking about it in terms of geometry it makes sense.

As for the post, will first try to make a new bolt for it, perhaps it bent for some unknown reason.

no wonder i felt like crap after drilling hundreds of holes

Get some Rocol RTD liquid, it's much better than the Trefolex for drilling. Keep the Trefolex for hand tapping.
Shop around for the RTD, it seems to vary widely in price.