Thread cutting dilemma

[iron bark]

Hello all,

I have just been experimenting cutting my first threads (1/2 UNC) and now have a question which I am sure someone will know the answer to. I have read a fair bit on the forum, and watched all of Tubalcain's UTube videos with great interest.

I thought I had everything set just the way I've heard about and seen on the net, but here is the result. Looks like a factory roof!!!!!

235196
I had the compound set at 29 deg.,the tool sharpened at 60 deg and vertical to the piece being attacked, and fed only using the compound just as Tubalcain does in his videos. At the end of each cut (about 5 thou DOC), I back off the cross feed, wind the carriage back, reset the crossfeed to zero, advance the compound about 5 thou and make the next cut.

To me it looks as if the tool wasn't aligned properly, but I double checked it about half way through, because I could see the beginning of the end result, so after checking, continued on to see what would happen.

I don't see how this could happen with a plunge cut, which I will try tomorrow, so why does it happen with this method. I have very obviously screwed up somewhere and would appreciate any constructive criticism.

Cheers,

Ned

[Bryan]

Wrong angle on the compound. Some lathes use the bed axis as zero degrees, some the cross axis.

[morrisman]

Hi

First . I would say that your tool isn't sharp enough . Are you using a HSS tool , and has it been honed to a sharp edge ?

Also, your tool may not have enough side clearance .

Can you post a close up pic of the tool ?

And did you use any lubricant ?

Mike

[iron bark]

Wrong angle on the compound. Some lathes use the bed axis as zero degrees, some the cross axis.

Bryan,

On mine the bed axis is zero.

[scottyd]

Id definately say wrong angle on the compound. It will need to be set to 61º, not 29º. Specifically, it needs to be 29º away from being parallel to the crossfeed axis. The surface finish is about right for hot rolled stock. If youre concerned with more than just the incorrect angles, try doing your practise threads on some 12L14. Itll make getting them right a bit easier.

[Jon_77]

I could be wrong but it looks like there are multiple threads being cut there - Are you re-engaging the half nut at the correct number on the thread dial? some lathes require the half nut to remain engaged throughout the threading process with no dis-engagement until threading is completed - my lathe is one of them and it frustrates me massively.

5 thou per cut is fine for the first few cuts...the closer you get to full depth thread the smaller DOC you need to make, finishing with 1 thou cuts generally otherwise you will end up with a rather ordinary thread finish

Cheers
Jon

[toolman49]

G'Day,
My lathe had the same problem referred to by Bryan, to overcome it I set the compound with a protractor and stamped a new index line on the cross slide, no problems since.
Regards,
Martin235229

[iron bark]

Hi

First . I would say that your tool isn't sharp enough . Are you using a HSS tool , and has it been honed to a sharp edge ?

Also, your tool may not have enough side clearance .

Can you post a close up pic of the tool ?

And did you use any lubricant ?

Mike

Mike,

The tool is HSS sharpened on a white wheel, but not honed I only had a bit of Hyd jack oil at the time and used it on the last couple of passes. Pics of tool attached.

Sharpening is still on my "yet to get right" list.

235231 235232
Cheers,

Ned

[iron bark]

I could be wrong but it looks like there are multiple threads being cut there - Are you re-engaging the half nut at the correct number on the thread dial? some lathes require the half nut to remain engaged throughout the threading process with no dis-engagement until threading is completed - my lathe is one of them and it frustrates me massively.

5 thou per cut is fine for the first few cuts...the closer you get to full depth thread the smaller DOC you need to make, finishing with 1 thou cuts generally otherwise you will end up with a rather ordinary thread finish

Cheers
Jon
Jon,

I always engaged the half nut on the same index number, even though the placard said I could use 1, 2, 3, or 4.

[morrisman]

Ned

The tool looks pretty good . Only thing I can see that may need changing is the top rake

I hope this pic will help you . Fig. 190 shows the top of the tool has a sloping rake , sloping down from the cutting edge

As somebody pointed out, the type of steel you are using is the cause of the rough finish

have you got any bright mild steel ?

Mike

[iron bark]

Guys,
Many thanks for your inputs. I just went back and checked Tubalcains videos, and sure enough, the 29 deg. I was setting was relative to the longitudinal axis, and not the cross feed axis. How could I be so stoopid?? Very easily apparently.
First pic of my compound set parallel to the bed.235242

Second pic of my compound set at 90 deg to the bed. 235243
Any suggestions on how best to remark it so I can get accurate angles relative to the cross feed??

EDIT: Disregard the question - I just re-read Martins post on this subject, thanks

[iron bark]

Ned

The tool looks pretty good . Only thing I can see that may need changing is the top rake

I hope this pic will help you . Fig. 190 shows the top of the tool has a sloping rake , sloping down from the cutting edge

As somebody pointed out, the type of steel you are using is the cause of the rough finish

have you got any bright mild steel ?

Mike

Thanks Mike. Obviously identifying metal is still on my "yet to learn" list. I will try to get some bright mild steel rod and try again.

[scottyd]

My tip on the identification of metals is to simply ask exactly what grade it is when you get it. Its pretty hard to pick apart some steel products without working on them or doing some exstensive tests on them. Ive got some S7 and some 1020 at work and without cutting it, youd be hard pressed to separate them. What youre working with is probably 1045, common as muck mild steel in the hot rolled condition. 1020 is cold rolled mild steel, but because of the different manufacturing processes, they behave differently. Bright steel has a work hardened outside layer and some different ingredients to make it behave itself for cold rolling. 1045 is still "mild steel" though...go figure!

I find the interlloy datasheets to be really interesting reading, gives you a much better idea of what to look for when shopping for metals.

[Jon_77]

Looking at the markings, they go up to 60 degrees so you could probably eyeball it from there and be close enough to 29 degrees (61 degrees)

Another alternative is something like this > https://www.machineryhouse.com.au/M970

Cheers
Jon

[Bryan]

How could I be so stoopid?? Very easily apparently.

Don't worry, you're no orphan. :wink:

[iron bark]

Guys, I would like to say thanks to all who helped me out with threading.

I cut another thread tis morning in some bright steel (I think) and got a much better result thanks to your collective inputs , in particular the feed angle. Pic attached

235321

I still have some more work to do on my tool sharpening
(Edit) it is 3/8 UNF

[morrisman]

Hey

That's looking the goods :2tsup:

I seem to stuff up every time I do thread cutting . You need to concentrate 100% , if your mind wanders off in the middle of the job, its usually a stuffup, with me anyway . :C

Some people run a button die over the thread to make it look better , but real machinists don't do that of course :o

[scottyd]

I run a die over my threads, but not because i cant measure them right, but because threads arnt supposed to have perfect peaks and valleys. Both are supposed to have a small fillet and rather than buying specific thread chasers for all the pitches I work in, its just easy to use a die to get them right without having to think too hard.

That aside, that thread looks a hell of a lot better iron bark!

[toolman49]

G'Day,
That looks a hell of a lot better than some of my early efforts - congratulations.
Regards,
Martin