Cutting threads with dies

[John CoatesParticipant @johncoates48577]

Am wanting to cut some threads to make various workshop tools and am making a die holder for my lathe tailstock and mill spindle. The lathe is imperial so I bought some imperial taps and dies at Harrogate (1/4″, 3/8″, 1/2″, 7/16″, 5/8″) to go with a metric set I already had.

 

Now some of these have a split in them (imperial) and some are solid (metric). When I make the die holder am I supposed to design it so that grub screws close the split up for the imperials to get the right thread cut? The metric ones will just have to hold the die centrally

 

Never thought about this until I got to making the die holders and thought I had better check with you lot before making a costly mistake !

 

John

[John CoatesParticipant @johncoates48577]

My dies are different

[John CoatesParticipant @johncoates48577]

Oh forgot to add. In a tap set what is the difference between the first, second and plug taps?

 

I presume first means first cut and second the second cut (?) but plug has me

[Chris TriceParticipant @christrice43267]

The split allows some fine adjustment so you can control the fit of a nut on the thread. The solid ones just cut at whatever they’ve been ground at. One of the retaining screws should engage in the split when fitted in the holder and two other screws either side are used to adjust the gap before tightening everything down.

 

The first tap, as you’ve correctly guessed, has the most lead taper and used for starting a threaded hole. The second has less of a lead taper for following the first and the plug tap has no taper so you can fully form the thread all the way to the bottom of a drilled hole. Some of the smaller size taps only use a first and plug.

 

Edited By Chris Trice on 01/11/2010 13:15:57

[Howard JonesParticipant @howardjones35282]

notice that the tap on the left has more taper. the tap in the centre has shorter taper and the tap on the right almost no taper.

from left to right we call them start, intermediate and bottom taps.

if the material you are trying to tap is difficult to work with then cutting the thread in stages will cause a lot less tool wear than attempting to cut it to full depth in one go.

I recomend the use of “Trefolex” brand sulphurised lard while tapping. it significantly makes the task easier.

the rest as for Chris Trice’s comments

[adyParticipant @ady]

If I’m using taps and concentricity etc is important, I cut the first thread on the lathe and use it to guide the tap.

 

Things like spindle nose threads need to be pretty much 0.000″

 

Just depends on the job at hand.

 

[Sub MandrelParticipant @submandrel]

Most of my split dies need a little adjustment to cut a spot on size thread – they have the advantage that you can create a thread to be a loose or a tight fit.

 

‘Unsplit’ dies are called ‘die nuts’ and many of the cheap metric sets that used to be out there were really only meant for truing up old, battered or rusty threads. That said my metric set has unsplit dies and they are the dog’s – spot on every time, even on stainless steel. The bootsale purchase of a lifetime, £20 for 3 taps and set of dies 3mm to 12mm, all HSS.

 

Neil

[John CoatesParticipant @johncoates48577]

Posted by ady on 01/11/2010 19:40:00:

If I’m using taps and concentricity etc is important, I cut the first thread on the lathe and use it to guide the tap.

I agree. I tried to cut the first threads in the drill chuck in the mill but it didn’t get in far enough as the tap started to turn in the chuck. I intend to make a kind of collet, with a circular bore for the round shaft of the tap and a square bore at the end for the square section at the end of the tap. This should hold the tap tight so all I need is a collet holder with a locating hole for  tommy bar to be able to turn the tap into the body of the material to cut the thread. This will be on an MT3 shaft so it can go in either the mill or the lathe tailstock

[Sub MandrelParticipant @submandrel]

Hi John,

 

If an M3 tap is slipping in a properly tightened drill chuck, then perhaps the tap is blunt, you haven’t got good lubricant or the hole is too small. Try using a hole for 65% thread engagement (2.65mm for M3). Forcing teh tap to turn could just result in a breakage.

 

Neil

[John CoatesParticipant @johncoates48577]

Posted by Stub Mandrel on 01/11/2010 20:59:00:

If an M3 tap is slipping in a properly tightened drill chuck, then perhaps the tap is blunt, you haven’t got good lubricant or the hole is too small. Try using a hole for 65% thread engagement (2.65mm for M3). Forcing teh tap to turn could just result in a breakage.

Hi Neil

Sorry for not mentioning the tap is 8mm x 1.25. I realised that I should be lubricating the cutting as I snapped the tap tonight. I’ve got soluble cutting fluid. Managed to get the tap out (it was a cheap metric set £14 from the local auto store some years ago before I got into this home engineering lark) by filing the top square and getting a wrench on it. Since got the top of the shaft all nice and square on the grinder so it fits back into the tapping wrench for further use until I buy a better quality one.

 

Mea culpa !

 

John 

[Eric CoxParticipant @ericcox50497]

When tapping don’t forget to “back off” the tap every so often to stop it from jamming and breaking.

 

“This should hold the tap tight so all I need is a collet holder with a
locating hole for  tommy bar to be able to turn the tap into the body of
the material to cut the thread.” 

 

If you are using the lathe to tap a hole keep the
tap stationary and rotate the lathe chuck by hand. Same applies when
using a die on the lathe. Saves having to make a fancy tap holder

[Anonymous]

You were able to file the tap?   Bin it immediately, that’s not low quality, it’s zero quality!

 

Regards,

 

Andrew

Edited By Andrew Johnston on 02/11/2010 10:59:29

Edited By Andrew Johnston on 02/11/2010 10:59:51

[Ian S CParticipant @iansc]

Diamond file? Ian S C

[Anonymous]

Well, I did think of that before my tongue in cheek post, but it’d still take a while to file a square sufficient to use a wrench. Dunno, may be I’ve got duff taps, but I’m pretty sure I couldn’t file any of them!

 

Regards,

 

Andrew

[Ian S CParticipant @iansc]

If you must attack the end of a broken tap, dremel tool and cutting wheel, you can even put a slot for a screwdriver, but mine when they break are usually below the surface.Ian S C

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