Die-ing. Not literally

I cut a lot of BSF 5/16 threads as I restore Austin Sevens (e.g. new cylinder head studs).

I use button dies but have difficulty starting the thread. I turn the blank to the specified external diameter and chamfer it. But still have problems. I've improved my technique by coming under the nominal by about 0.10 mm - but it's still not great.

I have tail-stock die holders for my lathe ( Chester Super B - sorry!) but I can't run under 160 rpm which I feel is at least eight times too fast to die cut a thread, and to tackle it manually - blank in chuck, die in tail-stock etcetera - you need at least three paws.

Any thoughts?

Needless to say, I need to clean threads in the block, sometimes where I've removed broken studs. I don't have any real problem hand tapping, but wondered if my very wise and experienced colleagues on the forum would recommend one of those (very expensive) reversible tapping chucks for the drill press/mill.

Many thanks in advance and do keep well.

Martyn

There are some folk on youtube & I am sure on here that have made the tailstock type die holder that free rotates. They put handles on them. Bring it up to the work & put pressure on the bar to be threaded by the die. Then rotate the chuck by hand to get the thread started. Then carry on , or remove from the lathe & finish the started thread in the vice.

Steve.

I don't use dies very much, preferring to screwcut or use Coventry dieheads. But oddly enough I've just cut a 5/16" BSW thread in EN8 as I didn't have the appropriate insert for screwcutting. Rather to my surprise I managed a really nice thread. I turned to nominal diameter. I held the die in a tailstock holder from Arc. I started the thread by turning the chuck by hand while applying force from the tailstock handle. The die was secondhand from Ebay many moons ago. I think it's the first time I've used it. The important point is that it was a quality die, HSS ground thread by Warrior.

Andrew

Presumably the material is mild steel? Some of the not-so-mild steels like EN8 can be difficult to die-cut threads on without excessive force, with galling and a torn finish.

Thread depth on 5/16 BSF is about 29 thou per side nominal, so you could probably 0,25mm undersize without materially affecting strength.

Rocol RTD or other suitable thread cutting compound would probably help. I've used Castrol LM3 when I had nothing else, and it worked quite well.

If you're doing it in a lathe, sometimes a good deal of tailstock pressure on the die is needed to get it started. I've sometimes die-cut threads at 180 rpm on my Warco, mainly 'cos I'm too lazy to switch the belt to the lower speed range - perhaps I got away with it because they were smaller threads, on brass. If I'm hand-driving the chuck, I've got a short length of 10mm round bar that happens to fit the the chuck key square hole neatly, so I use that.

Three suggestions:

1 ) 160 rpm is too fast, so make a Mandrel Handle, so that YOU control the speed. Also, it makes it easy to reverse rotation so as to break the swarf.

2 ) Adjust the die to match a commercial 5/6 BSF bolt., so that it is not too tight.

3 ) If you are using a Tailstock Die holder, although it slides easily on the arbor, it may need a bit of end force to start it cutting. Once the die starts cutting, it should pull itself along the work piece. Trifolex or Rocol RTD are good lubricants for cutting threads.

Once, when I had trouble getting a die to start cutting, I found that the etched details were on the back of the die, and the lead in chamfer was on the other end! Turning it around, solved the problem!

HTH

Howard

+1 for a Coventry die head. I have a 1" size (CHS). For a smaller lathe the 1/2" size would be OK. If I need to cut threads on anymore than just a few components the die head is used. 160rpm bottom speed should be OK for 5/16" diameter threads

Ebay usually them for sale as are the dies are reasonable prices.

I have a Vertex tapping head, auto reversing, 3mm to 12mm, bought new and has performed faultlessly for many years. Again, plenty on Ebay at reasonable price.

John

My suggestion - cut the thread with the lathe and just tidy up with a die. So easy with a single point cutter.

It would be nice to have a slower spindle speed available. Don’t know what speed I use - I just adjust the VFD to suit the job - but (much) slower speeds are possible without really even thinking about it.

Either screwcut it (finish to size with the die) or make up a holder which fixes to the cross slide and use the leadscrew to drive the die along

I find that you need to press quite hard on the tailstock holder. I happen to have a num 2 morse taper extension holder which I put into the tailstock and then wind the die on using a normal die stock, stop it rotating by letting one handle rest on the cross slide but keep the pressure on from the tailstock, use back gear and sometimes slacken o0ff the motor tension so the drive can slip. Use EN8D which is the free cutting version (not so good for welding).

Bob. 1932 RN

Couple things I have found useful using a die in the tailstock die holder on the lathe to thread round stock:

1. try a 30 degree or 20 degree long chamfer rather than a 0.1 mm under 45 degree chamfer. You can leave a little extra stock length to trim back and make a finish 45 degree chamfer after you have the thread.

2. Use a sharp die. If using old ones they can sometimes be sharpened with a small stone in a Dremel style tool, dipping in water often to keep the steel cool and retain hardness. New good quality HSS dies do work best though.

I have a big collection of all sorts of dies my grandfather and father collected over 70 years in the auto repair business. Everything from UNF and UNC to left hand threads, BA, cycle threads, metric, you name it. Some still cut beautifully. Some never did cut worth beans and did not respond to sharpening. These last ones go in a special "not for combat" drawer. Can't bear to toss them due to the history but I won't use them if I have to faffle around to get a good thread.

My experience in this area is that the quality of the die is key to success. Try a new die from a reputable source.

Hi Martyn,

What I do is turn a short section of the stud down to the root diameter of the thread concerned, then proceed with threading with the die.

The root diameter holds the die parallel to the axis and allows the thread to start correctly.

Regards,

Nimble Neil

Put a little nick with a hacksaw on the chamfered end of the job so it catches the tooth on the die as it goes past .

I restore stationary engines,and many studs/ bolts need replacing,mainly Whit though my latest effort is a Stuart 600 which has lots of BSF studs, For smaller dia studs I use a sliding dieholder ,on en 8 studs over 1/2 inch dia I usually screwcut using a HSS machine chaser, in recent years the ER collet held in the hexagon holder has really made stud making much easier and quicker, the collets really do grip. and the hex holder allows bolts to be threaded as the hex leaves enough room at the back of the collet for the hexagon. I use home made sliding die holders the hole through the centre is 1/2 dia so that mating shaft can fit a 1/2 jacobs chuck The shaft is made from 3/4 dia steel is turned down at each end to 1/2 inch leaving a short larger dia central portion, this raised collar seats against the back of the holder allowing it to be pushed forward onto the work using the tailstock, the die holders have two or three holes for tommy bars to rotate the holder by hand to cut the thread, the lathe spindle (mandrel)being locked,this allows the thread to be started easily and the thread length to be controlled by hand without panic . particularly on a lathe with high bottom speed and no clutch. Threading on a lathe with forward /reverse clutch is quicker and easier, Work rotating slowly .the die holder prevented from rotating by a piece of mild steel square bar held in the top slide tool holder,dont use a lathe tool,or use a longer tommy bar resting on the lathe bed . On my Blackstone engine I needed a threaded 3/4 BSP water pipe slow bend for the cylinder barrel cooling,Curved the pipe in a borrowed pipe bender. then mounted the pipe bend on an angle plate on the cross slide, and the die was fitted into a home made die holder held in the three jaw chuck ,with the die rotating and the saddle fed forward by hand It cut a nice thread on the pipe, just like a commercial pipe threader, you might ask why not just screwcut the pipe before bending,well its the the problem of getting the bend in the centre, in plumbing it would not matter,but on a 1905 engine I wanted it to look correct. this method can be also used to make U bolts provided the die holder is made longer so that the chuck jaws do not hit the other end of the u bolt. I would not recomend using a forward /reverse tapping attachment on blind holes in vintage car parts,in that kind of work on valuable vintage parts it is better to use hand tapping particularly if it is a customers job. I have a good fwd/rev tapping head and a good Meddings drill to drive it,the head was used and passed on to me,but is rarely used and I would not bother to set it up for less than 25 holes they are ok for through holes but care needs to be taken with blind holes. I used a tapping head in my early work years, mainly on 3/8 whit holes in cast iron, the tapper was an Archer a popular make in the 1950/60s. they could be a bit fierce on the clutches,but generally reliable,the work must either be heavy or clamped down or if one was strong held down by hand, the tap when working reaches the set depth and then the tap carries on for a short distance to free the clutch,if the work is not held down securely the action of the tap can lift the work and not free the clutch,something has to give and its usually the tap,I cannot now remember if there was an overload friction clutch but if there was they did not work well. Archer also made small tap holders which held taps on the square as well as the shank ,they had a friction clutch,but relied on the machine(lathe or drill) to be able to provide forward/reverse motion,I was given a brand new one some time ago ok on the Colchester but useless on a standard Myford with no reverse.

Since you are working on a vintage vehicle, I would commend the use of the Mandrel Handle, so that you can feel the torque required. Hopefully, you will sense an overload, and stop before breaking the tap in an almost impossible to find vintage part. It also makes it so much easier to reverse rotation of Tap or Die, to break the swarf, and keep it short..

Also, there is very little risk of bending the Tap, which almost inevitably leads to breakage. Taps seem to be better able to withstand torsional loads than bending ones.

You may need long arms to turn the handle, and apply an end load to the Tap or Die in the sliding holder in the Tailstock, but once things bite and become self propelled, you can concentrate on the handle. Or even pull the chuck round by hand until cutting begins.

I have a Tailstock mounted Sliding holder for Dies, and made a sliding Tap holder to mount in the Tailstock.

My Tap holder uses ER collets, but a drill chuck would probably suffice. The advantage is that if things do get tight, the tap will slip in the holder, before it breaks!

The sliding holder minimises the load on the new thread, avoiding that of dragging a Tailstock along the bed of the lathe.

For tapping away from the machines, I have a drill chuck mounted on a spindle in a bracket on an repurposed drill stand. This avoids bending the Tap, allows feel, and keeps the tapping perpendicular to the work.

Howard

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