Thread cutting on a lathe.

[God mode restorations]

Morning guys.
At some point I will be purchasing a lathe. Unfortunately not a big ol English one as funds will not stretch. But I have been watching lots of videos and reading books on lathe operations. I have seen metric and imperial cutting done. But how are unc unf bsw threads done. I have seen a die stock holder attachment for a lathe but these are limited in length. Just curious.

 

[awemawson]

UNC, UNF & BSW are all Imperial threads and only differ in the cutting tool profile as far as single point threading is concerned. BSW has a 55 degree included angle with a rounded tip making a round root profile. UNC and UNF have a 60 degree included angle with a slightly different tip radius specification.

http://www.me.metu.edu.tr/courses/me114/Lectures/screw_threads.htm

 

[RonA]

Morning guys.
At some point I will be purchasing a lathe. Unfortunately not a big ol English one as funds will not stretch. But I have been watching lots of videos and reading books on lathe operations. I have seen metric and imperial cutting done. But how are unc unf bsw threads done. I have seen a die stock holder attachment for a lathe but these are limited in length. Just curious.

The die holder can be used to start the thread so it's perfectly aligned on the stock, remove the die from the holder, then using a convention die wrench you can make the thread as long as you want it.
RonA

 

[God mode restorations]

UNC, UNF & BSW are all Imperial threads and only differ in the cutting tool profile as far as single point threading is concerned. BSW has a 55 degree included angle with a rounded tip making a round root profile. UNC and UNF have a 60 degree included angle with a slightly different tip radius specification.

http://www.me.metu.edu.tr/courses/me114/Lectures/screw_threads.htm

Got ya. So it's all down to the different tool profiles.

 

[Rannsachair]

For tooling, I find one of these gauges handy:

 

[brightspark]

For tooling, I find one of these gauges handy:

not just handy they are needed if u are sharpening your cutting tools to the correct angle

 

[slim_boy_fat]

not just handy they are needed if u are sharpening your cutting tools to the correct angle

And they cost next to nothing, even I've got one......

 

[Richard.]

not just handy they are needed if u are sharpening your cutting tools to the correct angle

Dam right. All my thread cutting tools are diy hss bars. Those angle gages are a god send. Get a set of thread pitch gages too. Also cheap.

 

[Pete.]

The fishtail gauges are great but you should always use them with a magnifier especially for the smaller threads. It's incredibly easy to grind a curved flank or miss the angle by 5 degrees and simply not spot it with the naked eye. Another thing you could do is zoom in on it with a smartphone. If it has good macro capability you can get incredible detail.

 

[slim_boy_fat]

All my thread cutting tools are diy hss bars

As are mine, but thanks to advice from @Hood I'm researching indexable ones - I'm not 'flush' enough to lash out on a set at the moment but will buy one at a time for different functions.

 

[brightspark]

90 percent of cutting can be done with hss tools self sharpened

 

[slim_boy_fat]

90 percent of cutting can be done with hss tools self sharpened

I'm in the position where I'd have to buy in the blank HSS bars of the right centre height [or grind down larger ones] so thought I'd give the 'bought' tooling a go.

 

[Richard.]

Cutting a thread on the lathe when you read about it sounds far more complicated than it actually is.
It's actually very easy providing you don't take short cuts and follow the sequence properly.
I learnt to cut a very nice thread on mine in a matter of a couple of hours.

 

[Richard.]

As are mine, but thanks to advice from @Hood I'm researching indexable ones - I'm not 'flush' enough to lash out on a set at the moment but will buy one at a time for different functions.

I like the indexable tools for finishing up (my hss grinding doesn't produce as nice a finish) but for thread cutting and rough machining my home grinds are great.

 

[brightspark]

I like the indexable tools for finishing up (my hss grinding doesn't produce as nice a finish) but for thread cutting and rough machining my home grinds are great.

practice makes perfect. a good oil stone helps after grinding

 

[slim_boy_fat]

Cutting a thread on the lathe when you read about it sounds far more complicated than it actually is.
It's actually very easy providing you don't take short cuts and follow the sequence properly.
I learnt to cut a very nice thread on mine in a matter of a couple of hours.

That's my next big hurdle with the lathe, still got to get my head round gear sets for different thread(s), and traverse speed(s). First, I'm trying to get my feet clear of all the little jobs/projects I have on the go , then thread-cutting will have my undivided attention.

To be honest, I'm not [yet] sure if the change gears which came with the Myford are imperial or metric. I've assumed the former, since the leadscrew pitch is in imperial.....afaik Might have to get to counting teeth..........

 

[Richard.]

It certainly does mate. Internal thread cutting tools took some effort to get right but got there in the end

 

[brightspark]

That's my next big hurdle with the lathe, still got to get my head round gear sets for different thread(s), and traverse speed(s). First, I'm trying to get my feet clear of all the little jobs/projects I have on the go , then thread-cutting will have my undivided attention.

To be honest, I'm not [yet] sure if the change gears which came with the Myford are imperial or metric. I've assumed the former, since the leadscrew pitch is in imperial.....afaik Might have to get to counting teeth..........

herehttp://www.modelenginemaker.com/index.php?topic=795.0

 

[slim_boy_fat]

herehttp://www.modelenginemaker.com/index.php?topic=795.0

Just the very thing. I have the Myford manual by Ian Bradley but haven't really have time to sit down & study it - your link is a good, quick reference source which I might print out and fix on the notice board in the cave.

 

[Seadog]

Join the dark side. Insert tools are a doddle