Single Point Threading Help

[edenaus]

Yes It would seem that the cutting tool isnt being presented at 90 degrees, The two ways of cutting using the cross slide or the compound slide both need the tool at an angle of 90 degrees. You possibly might be placing the tool properly but then adjusting the top slide so the angle ends up skewed. So for doing the cut with the top slide/ compound slide turn it to half the angle of your thread, actually slightly less. Then put the tool in so its point is at 90 degrees to the work. Then by moving the top slide you keep the thread equal

 

[Tin Falcon]

use a fish tale gauge to check tool grinds and set perpendicular to part being threaded i usually set parallel to lathe chuck.
Tin

 

[Walltoddj]

I don't use a fish any more I butt the QCTP up to the squared work piece of work. It's seems to be easier for me and the threads look great. I'll have to find the articles but they all so stated to cross feed fine threads and to compound feed coarse threads due to amounts of material being cut. I don't cross feed my threads but when I finish it I plunge about .001 just to clean it up.

Todd

 

[Tin Falcon]

I don't use a fish any more I butt the QCTP up to the squared work piece of work. It's seems to be easier for me and the threads look great.

Sounds like good tip

It's seems to be easier for me and the threads look great.

Results and ease.

I'll have to find the articles but they all so stated to cross feed fine threads and to compound feed coarse threads due to amounts of material being cut. I don't cross feed my threads but when I finish it I plunge about .001 just to clean it up.

One of the best articles I have seen on threading is here :
http://www.machsupport.com/wp-content/uploads/2013/02/Mach3_Threading.pdf

It is written as a guide for threading with Mach 3 CNC but many of the points apply to manual threading.


I want also add that IMHO that a fishtail gauge removes variables from the setup . If you are using a QCTP and the tool is squarely in the holder and the tip is symmetrically ground then the above method will give great results.
however if one is using a less than symmetrically ground tool or tool ground at an angle favoring one side or the other an the tool is at an angle in the tool holder then the fish tail is the way to go. .
Tin

 

[ShopShoe]

Just one more thing. Check the threading toolbit to make sure that it is the measurement for the thread you want to cut. The first time I ever tried cutting threads (in the same week I bought my lathe) I had terrible luck, then I realized the "60-degree threading bit" that came with the cheap set of toolbits included with my lathe was more like 70 or 75 degrees. Luckily I had also ordered some HSS blanks and ground one the next night and successfully cut my first thread. I did, and do, chase my more-common threads with dies after cutting.

Keep practicing,

--ShopShoe

 

[Walltoddj]

If you have a surface grinder I made a fixture to grind it the same every time it takes longer to start the grinder than to touch up the tool. You can do the same with a belt sander or a bench grinder if you take the time to make a proper tool to do the job. It's worth the time to make a fixture to me because there is no fuss to sharpen the tools. I have different grinds on about 6 tools tight left hand, tight right hand, and in the middle I have an internal threading bar set up so it's very simple to just get the tool and cut the thread.

Todd

 

[Hopper]

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.

Pic indicates that the compound slide is at too shallow of an angle, looks more like 30 degrees from the lathe bed, not 30 degrees from the cross slide.

As an apprentice toolmaker I was taught to avoid all this faffing about with compound slide angles and leave the compound slide at its normal zero position.

Then when you wind the threading tool in by using the cross-slide, wind the compound slide forward by HALF the amount you moved the cross slide.
This will move the actual toolbit in at a 60 degree angle and give nice cutting on one side of the tool.
For example, if you wind the cross slide in .010", move teh compound rest forward .005".

This way, when you get to the theoretical thread depth but the nut is still tight, you can simply advance the compound rest a thou or so and take a cut to provide some clearance.

In addition to starting with the turned OD a couple of thou undersize and running a three-sided file along the crown of the thread to remove burrs should give you a quick, accurate thread.

I am not sure if this technique is any of the modelling books, but it was standard industry practice back in the days when we still had industry.

 

[Tin Falcon]

As with any setup question a picture can be worth a thousand words.
An experience eye can pick up on thing a newbie does not see.
So post a pic of the setup if you can.
Tin