Threading ?s

[Naiveambition]

Adding some closure to this thread.

I was able to accomplish my threads but not without some complications and discoverys.
For this mission I switched to alum. The male thread went as planned but the female still presented issues. 1st being I found my leadscrew clamp was busted and with cuts under.01 it was fine but any more it would slip out of sync and kick the gearbox out of gear losing my place. So after fabing up another solved my issues there. The second issue was most likely cutter geometry. Was not cutting nice clean chips, more of a tear style chip. Under power it was enough to stop my little 7x10 so had to resort to hand turning the lathe and finally made it thru.

I chose 20 tpi and cut till I had one full turn on the dial or .1 I think.. Now granted I made my own 60* guage for setting the tool and prob made mistake of using small top rake. So not perfect but worked in the end will need some more practice but at least the steps are down and work on the finer points.

Here's a pic of my parts The iPad cam has no definition so they do look better than the photo.

 

[Sansspaceship]

Glad you had some success, will leave others to comment on cutting geometry as grinding cutting tools isn’t one of my strong areas. But something is definetly wrong if it gouging and not cutting, my initial thought would be too deep a cut, without enough horse power (as alu can be gummy) but won’t comment past that as am only guessing without more details.

Anyway good luck with you project, thanks for the update.

Cheers,
Adrian

 

[BaronJ]

Hi, From looking at your picture of the threads in the ring, make sure that the tool has enough clearance under the front and side edges. It looks as if it is rubbing and tearing the thread. I've had this problem with home ground tool bits. The problem gets worse with smaller holes. I have started to buy small carbide threading bits, which gets around this problem nicely. You still have to watch the hole size though.

HTH.

 

[JCSteam]

Just throwing this out there, with regards to the comment of Ali been gummy, have you tried cutting Ali with WD40. It stops the Ali cold welding itself to the tip, which may be another cause of the dragging that you've experience. For the sake of a couple of quid for a tin may be worth a try.
?? It did wonders on a part that I was turning, plus the chips just rolled off the cutting tool.

I by no means profess to be an expert, this is just my observations from my own work.

 

[Sansspaceship]

Just throwing this out there, with regards to the comment of Ali been gummy, have you tried cutting Ali with WD40. It stops the Ali cold welding itself to the tip, which may be another cause of the dragging that you've experience. For the sake of a couple of quid for a tin may be worth a try.
?? It did wonders on a part that I was turning, plus the chips just rolled off the cutting tool.

I by no means profess to be an expert, this is just my observations from my own work.

I might have added a bit of confusion by bringing up the gummy alu comment. To clarify I was just trying to read between the lines with the OP comment that he wasn’t getting good chips and it was more tearing which to me might have appeared gummy.

But you point is extremely valid though, when I first started with alu I used wd40 and it works great. Now I use a fog buster as just run it generally set and forget after program proofing on the mill which is where I cut most of my alu, but yes coolant would be recommended when starting out. Although i have had quite a bit for success roughing dry.

The other thought I had was if it wasn’t any of the culprits that have been mentioned by any of the previous posts it could be non heat tread alu, which can be a bear to cut and might explain the tearing, in my experience you want T3 or T6 (common) alu in a 2011, 6061 or 7075.

I too am no expert, but always interested and keen to learn about cause and effect of stuff like cutters and material.

Cheers,
Adrian

 

[DJP]

I'm sure that there are many cutting fluids available but if you want a 'home brew' try one part kerosene, one part Varsol and one part Automatic Transmission fluid.

 

[mcostello]

My experience is that any kind of light oil will work, penetrating oil bought at garage sales for a pittance works best as it soothes My wallet at the same time.

 

[rlukens]

It's an absolute must to have the compound rest set at 29 degrees. Make all your advancements with it, not the cross slide. Otherwise your plunging the cutter straight ahead and cutting on both sides. For your last pass, maybe move in on the cross slide a thou or two to clean up both sides of the "v".

 

[Cogsy]

Why is it 29 and not 30 degrees for a 60 degree thread? I've always wondered this, every time I see the 29 degree figure quoted. I've never tested it myself, having only every cut smallish threads on the lathe and never having an issue with plunging straight in, but it would satisfy my curiosity to know.

 

[BaronJ]

Hi Guys,

This controversy over 29-30 degrees and the insistence that this must be, verses plunging straight in, only serves to confuse and confound, newbies in particular. I would suggest that most of us would only cut relativity fine threads, say more than ten or twelve TPI, so plunging in is not a big issue, and I admit that this is exactly what I do !

For large threads cutting on the forward face, which is what happens when using a 29 degree top slide angle does, lowers the cutting forces because it creates back edge clearance. Doing Acme and square threads is an altogether more complicated proposition.

JM2PW.

 

[goldstar31]

ONE of the problems is that AFTER screwcutting in the lathe that it should be finished with a ground die.
The other possibility is that most lathes have 'protractors' which are inaccurate and the next exiting point is that the leadscrews on most older lathes are- em- knackered.

One way to find out what is happening is to cut a sample in half and use a high quality comparator which we all have -after we have carefully filed the quality control sample. Said he laughin' and scratchin'

Of course, we are all still reading something like McGraw's book Statistical Quality Control with a copy of Schlesinger for bed time reading.

In case of doubt-- YES:hDe:

Norm

 

[john_reese]

Here is my take on threading.
If feeding from the cross slide you have chips from both sides of the tool meeting and jamming together. Not good, especially on coarser threads.
In feeding from the cross slide a 30* angle may seem right, but it is likely you would see"steps" on the flank of the thread. By setting the compound slightly less than 30* the trailing edge of the tool shaves a tiny amount off the flank of the thread eliminating the "steps"
In general I set my compound 1/2* less than half the included angle of the thread.

On CNC the feed is always straight in but is commonly fed to cut alternate flanks of the thread.

 

[rlukens]

The tool has a 60 degree "point"... 30 on each side of center. Plunging straight in will cut equally on the left and right side of the tool. If you watch in slow motion, you will see the chip from each side curling towards each other. They collide, push back, and snap off. Although not the end of the world, this does give rise to a ragged thread.
Why 29 and not 30 degrees? Only because backing off of 30 by 1 degree wipes the right side of the thread slightly on each pass.

 

[Cogsy]

AFTER screwcutting in the lathe that it should be finished with a ground die

I was watching a professional machinist cutting a thread on his industrial lathe a few months ago and he did not follow with a ground die, of course the fact that the major diameter of the thread was around 450mm (18 inches) probably limited his options...

 

[goldstar31]

Whilst I can appreciate that a very small number of people are still engaged in Screwcutting- as you say 60 degrees and whatever, there are vast numbers of people making and using 'non standard' threads and these, if they are studied carefully have rounded crests.

If you read what the vast majority of people should be reading-- and doing something about it, the sea is full- endemic proportions of screwtop bottles. Again in my cupboard of my real needs, I note that all the 'lightweight' glass has closures which would cut through the lacquer on metal closures and as for the plastic ones, cause difficulty or annoyance if not some thing like 85 R3 which was the standard in the past.

On a more perhaps mundane level, Britain still has 55degrees, 47.5 and still uses metric sized threads in what can be laughingly called' 'British Association'

If I have ruffled a few feathers, might I humbly apologise.

Norm

 

[Hopper]

No need for setting the topslide at an angle. You can have five bob each way by leaving it in the standard position. When screwcutting, advance the topslide by half the amount the cross slide is wound in. EG, if taking a 10 thou deep cut on the cross slide, advance the topslide by 5 thou. This combination moves the tool bit in a path equivalent to a bit under 27 degrees, so works perfectly for both 60 degree and and 55 degree threads. Most of the cutting is done on the leading edge, with the trailing taking a light clean up cut so no steps are generated.

 

[mcostello]

I hardly ever finish off a thread with a die. If the lathe is set up to thread I will finish that way. More practice means better parts for Plan B.

 

[rlukens]

No need for setting the topslide at an angle. You can have five bob each way by leaving it in the standard position. When screwcutting, advance the topslide by half the amount the cross slide is wound in. EG, if taking a 10 thou deep cut on the cross slide, advance the topslide by 5 thou. This combination moves the tool bit in a path equivalent to a bit under 27 degrees, so works perfectly for both 60 degree and and 55 degree threads. Most of the cutting is done on the leading edge, with the trailing taking a light clean up cut so no steps are generated.

Agreed, but without DRO's (I'm old) how can you accurately advance in the "Z" direction.

 

[Herbiev]

I was watching a professional machinist cutting a thread on his industrial lathe a few months ago and he did not follow with a ground die, of course the fact that the major diameter of the thread was around 450mm (18 inches) probably limited his options...

Come on Cogsy. We all have an 18 inch UNC die hidden away somewhere :hDe:

 

[RichD]

Check out this guy...his videos are short and to the point. I already know a bit about threading, but darn if I didn't learn more tips from this guy.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwj8usX6jp_YAhXC5lQKHRrJD_gQtwIIMDAB&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D-hqYyPWSltk&usg=AOvVaw21gNbsNihEWLJRonx3hf0Z

I usually try to cut the female thread first if I can, then make the male piece last. Depending on the job, you can test fit the female threads onto the male thread and adjust as needed for a good fit.