Single Point Threading Help

[carolinamark]

I am trying to learn to single point thread.

What I'm coming up with has the right number of threads per inch and looks like a good thread but when I try to put a nut on it the nut will just start a little and then won't go any further.

Compound is set at 30 degrees from perpendicular.
Tool is HSS ground to fit "fish gauge" and set on centerline.End is ground sharp with no radius.

I am doing all of my infeed with the compound.

On a 1/2-13 thread I cut about .055" deep and the nut still won't go on. The thread has come to a crest and the flat is almost gone.

I have tried to cut other diameter and pitch threads and have had the same problem.

I have attached a drawing of what the tread looks like with a thread gauge.
The darken areas I added because it seems as if the thread gauge is making contact in these areas.

Any ideas or help would be appreciated.
Thanks,
cm

 

[chucketn]

Your setup sounds like your doing it right. I keep a nut the size of the thread i'm cutting at hand and when the thread is formed, I keep trying the nut and taking .001-002 passes until it does.

Chuck

 

[Woodster]

If your threads are "pointed" then you are doing something wrong. This may help - http://www.ring-plug-thread-gages.com/ti-thread-data-charts.html
You could truncate the thread or "top" it by simply skimming a few thou off of the O/D, but if your thread angle is wrong, even by just a couple of degrees, you will have problems.

 

[velocette]

Hi cm
It may not fit at all as a whitworth thread is 12 TPI 55 deg and NOT 13 TPI grab a UNC nut It will be 13 TPI. @ 60 deg
I fell for this as a lad many years ago.
The crests of the threads will need to be rounded off with a file or a die nut to get a decent fit to the nut.

Eric

 

[bb218]

I like to check my threading set up by measuring how far the carriage should travel with 1 turn of the spindle before I cut any thread. Divide 1 by 13 and the carriage should travel .0769 " per 1 rev after the slack is taken out. You can visually pencil a mark on the chuck and headstock and rotate by hand. If you are not really close to the .0769 value something is wrong, maybe in the wrong slot in the threading setup ?

This process has saved my many scrap parts over the years while threading.

Mike

 

[Walltoddj]

If your threads are "pointed" then you are doing something wrong. This may help - http://www.ring-plug-thread-gages.com/ti-thread-data-charts.html
You could truncate the thread or "top" it by simply skimming a few thou off of the O/D, but if your thread angle is wrong, even by just a couple of degrees, you will have problems.

I make a lot of special thread 1.400 x 20, 1.187 x 20 and I find I made a Gage for each. When I get close I'll take a light file pass or emery paper to the threads then take clean up pass no changes and check it. A lot. of times I find he's right you end up with a sharp thread which case the nut is not by taking the top and burr off it fits better.

Todd

 

[carolinamark]

OK,

I checked my pitch with an indicator and it was right. I also checked the 30 degree angle and it seems to be right.

I cut some more threads.....the nut still won't go on.

I've attached a microscope pic of the threads. The profile looks more like a check mark than a v to me. But I don't know what is causing it.

I'm thinking of trying to cut some using just the cross slide and not the compound.

Any other ideas?

Thanks for the help.

View attachment bad_threads.bmp

 

[velocette]

OK,

I checked my pitch with an indicator and it was right. I also checked the 30 degree angle and it seems to be right.

I cut some more threads.....the nut still won't go on.

I've attached a microscope pic of the threads. The profile looks more like a check mark than a v to me. But I don't know what is causing it.

I'm thinking of trying to cut some using just the cross slide and not the compound.

Any other ideas?

Thanks for the help.

Hi cm
At risk of sounding like a super critic by looking at the photo the thread is a bit of a disaster.
We all make mistakes it is part of the learning process.

Just looking at the photo it would appear that the crossslide is at 30 deg to the spindle Centre Line it needs to be set at 60 deg to CL or at 30 deg to the Crosslide CL travel

Sorry to sound critical but the intention is purely an attempt to solve the problem you have.

Keep up the postings and reading this is an excellent place to learn and pass on knowledge.

There are no problems just solutions not yet found.
No failures just a success not achieved.

Eric

 

[Walltoddj]

Hi cm
At risk of sounding like a super critic by looking at the photo the thread is a bit of a disaster.
We all make mistakes it is part of the learning process.

Just looking at the photo it would appear that the crossslide is at 30 deg to the spindle Centre Line it needs to be set at 60 deg to CL or at 30 deg to the Crosslide CL travel

Sorry to sound critical but the intention is purely an attempt to solve the problem you have.

Keep up the postings and reading this is an excellent place to learn and pass on knowledge.

There are no problems just solutions not yet found.
No failures just a success not achieved.

Eric

I'd have agree with velocette the thread looks wrong, compound is usually set to 29-29 1/2 deg I use 29 it seems to clean up better and the tool should be square to the work piece with a fish. When you cut it should just skim the back side of the cutter to give you a clean thread. Look it the downloads I think they have some books on how to if not let me know I'll send you a couple.

Todd

 

[Swifty]

Irrespective of the top slide angle, it looks as though you threading tool is not presented at the correct angle to the work. Hold your fishtail gauge against the work and line up your toolbit. However, looking at the angle of the thread, it appears to be at least 80deg included, has the toolbit worn on one side?

Paul.

 

[Walltoddj]

Here are a few pages that show the proper way to set up and cut a thread these are from the Army manual. It might help because it shows how to set up the compound and the tool for cutting threads. Also had another thought be sure that you are reading the right angle on the compound mine has two marks so I have different number they both read the same but one is for "0" and the other is for "90" ( it will read "60")

Todd

View attachment Thread cutting.pdf

 

[MachineTom]

It appears that you have the compound incorrectly, as already stated by previous poster.

The compound should be to the right of the crossfeed handle 29°, when cutting external right hand threads. and to the left of the handle when cutting internal RH threads.

So compounds are marked with "0" at the point where the compound is parallel to the bed, if this is your case, then you need to move the compound to the 61° marking, which would be 29° from parallel to the crosslide axis.

 

[lathe nut]

I was to open the attachment interested in seeing what is going on, I am far from being what most the fellows are here but that was the most rewarding thing that I have learned on a lathe was to thread, don't give up, took me about 30 tries to get it, what kind of lathe do you have, don't give up and don't give in, Lathe Nut

 

[rodw]

I know the feeling!

There is quite a good tutorial directed at me on page 5 of my shed thread
http://www.homemodelenginemachinist.com/f15/rods-aussie-shed-19885/index5.html

A bit different for you with an imperial thread perhaps (as you can use the chasing dial) but you could try running a die over it to clean it up.

 

[goldstar31]

I'm not going to argue with any of the foregoing remarks but perhaps the problem is one of two other things.
The first is the difference of 12 and 13 TPI which is not a lot- until it jams up.
This continues with the question of whether the all important gear contains the prime number '13' and not some multiple of 2.
The next is 'wear' or fit of the leadscrew and if the leadscrew is not accurate, you will get some funny results.

Maybe we should all go back to Martin Cleeve's book- Screwcutting in the Lathe. I have!

Regards

Norman

 

[danstir]

One problem I had that I have not seen mentioned was figuring out the proper diameter before I started threading. I was leaving the blank to large and after threading it would just start but never got beyond a full thread.
As other's have said persevere.

 

[Swifty]

I always turn to the finished thread diameter OD, a few thou under.

Paul.

 

[carolinamark]

Well I cut a good thread last night using just the cross slide.

That eliminated the gearing setup, leadscrew, tool presentation etc.

I'm thinking using the tailstock center will eliminate the problem with using the compound. I have not had time to confirm this yet.

Using the cross slide worked fine for this size thread. It may not work as good for larger size threads. It would probably work for any threads I'll be cutting.

Thanks to everyone for their help and suggestions.

 

[lathe nut]

Great glad for you practice, practice, I have a 14X40 HF lathe and if I tread with the cross feed its perfect every time, pleased to hear you did it.

 

[Swifty]

Theory tells us to use the top slide at an angle for infeed, I don't, I only use the cross slide for infeeding. Perhaps if I was cutting larger threads, say above 3/4", I might think about using the angled top slide.

Paul.