Help with making threads

[oregonsteam]

I have a chart for using a tap for 1/4 20 threads that says drill 13/64". However, if I want to make external 1/4 - 20, do I turn the stock to 1/4" before threading with the die?

I have been having trouble making threads with the dies, i seem to have no problem with the taps. Any advice would be appreciated.

Thanks,


Mike

 

[doc1955]

Depends on what class thread you want.
class 1a =mojor dia of .2489/.2367
class 2a = major dia of .2489/.2408
clas 3a = major dia of .2500/.2419

 

[oregonsteam]

I have a chart showing major diameter, is that what the "raw" stock should be before threading?


Thanks!

 

[doc1955]

Yes

 

[bob ward]

I would try a few practice pieces at .248, then .246 diameter etc. If you measure a commercial 1/4" bolt it is probably .245 over the threads.

 

[jonesie]

i agree with bob i do a lot of single point threading and i always turn down the o.d. by .003 to .004 before cutting the external threads , like bob says try some practice ones .

 

[cobra428]

oregonsteam,
This may sound like a silly question but are you starting the external threads with the right side of the die?
There is a starting side, usually the side with the die size etched into it. This side has a larger opening to start easier.

Tony

 

[oregonsteam]

Thanks for all the advice!

Mike

 

[Bourne Bill]

does anyone have a printable chart for this?

 

[Blogwitch]

Where a lot of people go wrong with external threads, they try to die cut it all in one go.

Getting a good external thread is a technique, not just a stick it on and cut it.

What you should really do, is using the diestock centre screw, screw it in and spread the die a little. Be careful, as some cheap diestocks are not very well made and can allow the die to spread too much, and it is liable to break the die. DAMHIK

Nip up the two side screws, then take your first cut. Then by releasing slightly on the centre screw and nipping up the two outer screws, another cut is taken. Then do this, say 1/4 release of the centre screw each time until you get a nice fit with the female screw thread.

The die should have a tapered lead in, as mentioned before, and that should be fed onto the part being cut. After finishing the cut, and if you are going to a shoulder, turn the die around in the diestock, and repeat the above exercise. This should cut a full depth thread almost to or completely up to the shoulder. If you don't want to go to the trouble of turning the die around, cut an undercut next to the shoulder to the depth of the thread and about 1.5 pitches wide. This should allow the nut to run up to the shoulder.

Brass and cast iron you can get away without lube, everything else needs it.

You wouldn't want to cut a good internal thread without using the three tap system. Die threading is no different, the thread should be brought down in stages.

I personally wouldn't use dienuts (the dies without splits), they are really for cleaning up threads that have been damaged, not for cutting new ones.

For anyone with Msoft Excel, I have attached a chart for almost any threads you are liable to come across in your travels.


Blogs

View attachment all threads.xls

 

[Artie]

Blogs, thanks mate I ve saved a copy of the chart. Wonderfull resource!

Artie

 

[Tin Falcon]

As far as charts hear is a nice one from Little machineshop.com
http://www.littlemachineshop.com/Reference/TapDrillSizes.pdf

split dies can also help when threading. I have a craftsman die set and it is a bugger to get going on steel . cutting a generous chamfer also help start the die and use plenty of good cutting fluid.
Tin

 

[AlanHaisley]

Blogs,

While your description of the use of split dies for threading is quite clear, I really don't understand your reference here:

You wouldn't want to cut a good internal thread without using the three tap system. Die threading is no different, the thread should be brought down in stages.
Blogs

Other than various classes of fit, which are more obviously critical in a manufacturing setting, all I am aware of when it comes to taps is "taper", "plug", and "bottoming". Could you explain what you meant please?

Alan

 

[Blogwitch]

Actually Alan, the use of the three tap system is designed to bring you to the correct sized thread in easy stages, and no, a bottoming (we call it a plug) tap isn't just a way to get a thread to the bottom of a blind hole, but to bring even a thru hole to the correct diameter and profile of thread.

As you mentioned, for use in a home shop, it isn't really necessary to go beyond your plug (our second cut), as the thread cut by it will be very close to what is required, but it will not be exact.

What I am trying to get at is that to cut a perfect internal thread, the three tap system should be used, and so the same method should be used to bring an external thread to size, by doing it in stages.

A lot of people will blame a badly made die when they get a sloppy or tight fit with the female thread. Invariably it is the chap who has the tap and die in his hands that is to blame for the bad fits of screw threads.

Blogs

 

[SAM in LA]

Blogs,

Great thread!

I was not aware that the dies were adjustable for depth of cut.

Which means that I was never curious enough to wonder why there was a set screw in the side of the die.

My tap and die set only has one tap for each thread type.

Please explain the proper way to tap an acurate internal thread.

Thanks for the links to the thread reference charts.

SAM

 

[joeby]

Most tap and die sets will only have one tap of each size. If you look closely at the tap included, it will be a plug tap (U.S. nomenclature) because a plug tap has been given the honor of being the "fits-all". In other words, a bottoming tap will be a real bear to get started, and a taper tap, although being easy to start, will not thread near enough to the bottom of the hole. The plug tap is a sort of happy medium.

A plug tap will do a reasonable job of threading a hole on it's own; but care must be taken to get it started correctly (straight) and it will take more torque to cut than a taper tap. The taper tap spreads out the depth of cut over numerous cutting edges, instead of a few as in a plug tap.

The dies included in a tap and die set are usually the non-adjustable die-nuts as stated by Blogs. These sets are normally intended for cleaning up or "chasing" existing threads to clean them up or repair damage.

Kevin