Wonky threads using die

[Howard LewisParticipant @howardlewis46836]

Cutting an external thread with a Die involves removing a lot of metal in a few passes, possibly just one. Do use a lubricant such as Trefolex or Rocol RTD.

Don't be afraid to reverse rotation every half turn or so, just like a Tap, to break the swarf.

+1 for::

Holding the rod central (ESSENTIAL )

Lead In Chamfer on the end of the bar

Use a Tailstock Die Holder. One that can slide along an arbor, so that the newly cut threads are not stressed by trying to drag a Tailstock along the lathe bed. i e Don't hold the Die Holder in a drill chuck in the Tailstock.

You can make or buy. Making can be a useful learning exercise, and give confidence in using the lathe.

(Turning, facing, boring, drilling and Tapping )

If you decide to make, making and fitting an arbor to a soft stub M T arbor is a starting point.

This might also be the poiunt at which to do some more learning and make a Mandrel Handle, so that the chuck can be rotated by hand. Useful for Tapping as well as for cutting external threads with a Die. .

Whereever possible, I adjust the Die, using a good commercial Setscrew, Bolt or Stud as a gauge.

Investing in a 3 jaw chuck can save time in clocking work in a 4 jaw, where concentricity is not absolutely essential

It is MOST unlikely that a 3 jaw, even a new one of a good brand, will produce absolute concentricity. 0.075 mm run out would be quite good.. If you need two or more diameters to be concentric, they can can be done in a 3 jaw, by machining them all without disturbing the work in the chuck. In that way, all the diameters are machined about the same axis.

Howard

[Steve355Participant @steve355]

Hi Howard….

In fact I have a 3 jaw, but it has no backplate. Here’s the story…

You can’t buy a backplate for a Zyto as it has a 7/8” 9TPI spindle. So I have to make one.

I bought a suitable piece of cast iron and put it on the faceplate ready to start.

before I try to cut an internal thread in cast-iron, which I’ve never done before, I thought I’ll just have a go at some threading practice.

fairly quickly I realise that I can’t consistently get the thread dial indicator to start when I lift the carriage lever. It sometimes “jumps” and the thread starts in the wrong place.

after quite a lot of head scratching and taking it to bits and putting it back together again, I realised that the half nuts are engaging with the lead screw at slightly different times. This is down to (I believe) The little rods in the internal cam in the carriage lever not being straight.

So I need to make some more little rods, and I need to get them very straight, and exactly the right length.

 

Then I can do some threading practice, then I can make the backplate, then hopefully I have 3 jaw chuck!

Somebody said that if you buy a vintage lathe, you’ll spend more time working on the lathe than doing work on the lathe. Very true.

Edited By Steve355 on 20/11/2021 21:33:08

[egaParticipant @ega]

Can you sidestep your problem for the moment by leaving the half nuts closed throughout?

This should not be too laborious with a short backplate thread. Obviously, you need to withdraw the tool from the cut when winding the carriage back before taking the next cut.

No doubt it has been said before but before cutting the female thread it would help to prepare an accurate dummy spindle that you can offer up to the thread as you make the final cuts.

[Howard LewisParticipant @howardlewis46836]

7/8 x 9 tpi is 7/8 BSW. Fortunately, when I wanted to make a 7/8 x 9 to Myford adaptor, a kind friend loaned one to me for this One Off job. (See M E W 310 for the context )

Bolt to the faceplate, for drilling, boring and tapping (Tapping size is 19..25 mm, 0.7579" in old money, or 3/4" as the nearest standard size drill. But 19 mm would be closer if you can borrow one.

You may be able to find a secondhand Tap since BSW is now very much non preferred.

With a small lathe, and low power, metal will have to be removed in small stages so a lot of cuts needed to open up to tapping size.

Once the bore is to size, it is time to engage back gear, or use a mandrel Handle.

It is likely that once the tap is well started in the hole, the embryo backplate will have to moved to the vice to be gripped whilst the Tap is turned by sheer muscle power.

if you can produce the 7/8 BSW thread, the backplate blank will fit onto the lathe spindle.

I would be inclined to face the backplate, and bore the register for the spindle, if there is one, at this point..

Once this has been done, it can be reversed and faced and the OD turned to suit the register in the 3 jaw chuck.

To mark the position for the securing bolts, make up three short studs with pointed ends.

Use one to mark the position of the first securing hole, so that it can be drilled clearance size. Fit the two other pointed suds to the chuck, and with the backplate located in the chuck register, and secured by the one bolt, mark the position of the remaining holes, so that they too can be drilled clearance.

The holes can be larger than normal clearance, if this helps, since the location is by the register. The bolts are there to hold things in place while the chuck is being used (Ideally, the register OD should be a really snug fit in the chuck ).

HTH

Howard

[Grindstone CowboyParticipant @grindstonecowboy]

Lots of 7/8" BSW taps on Ebay from around £10. Might be worthwhile.

Rob

[Steve355Participant @steve355]

Posted by Grindstone Cowboy on 20/11/2021 22:10:30:

Lots of 7/8" BSW taps on Ebay from around £10. Might be worthwhile.

Rob

That would be fantastic, but I thought that backplates should be threaded on a lathe rather than tapped. Not entirely sure why, but that’s what I read somewhere.

[NimbleParticipant @nimble]

Hi Steve,

What I do is turn about the dies width down to the root diameter of the thread and put small chamfer on the end of the rod, either then slip the die over the reduced shank or if necessary proceed as if threading when you get to the full diameter of shaft commence threading as per normal.

Perfectly aligned!

Regards, Nimble Neil

[Dr. MC BlackParticipant @dr-mcblack73214]

Steve

Where are you located?

I have a number of 7/8 BSW taps (inherited from my late father when the family company was building Fire Escapes before WWII).

I you are local, you could borrow.

For security, I suggest you respond OFF LIST.

With best wishes.

MC Black (Dr.)

[SillyOldDufferModerator @sillyoldduffer]

Posted by Steve355 on 20/11/2021 20:37:40:

Posted by Tony Pratt 1 on 20/11/2021 19:40:39:

Posted by Steve355 on 20/11/2021 18:33:27:

Hi

thanks for the replies.

I only have a 4 jaw chuck, dialling in a 3/16 rod may not be easy.

As you have only a 4 jaw you must 'dial in' every work piece so surely you are an expert at it by now? 3/16" rod will be no more difficult than any other diameter.

Tony

 

 

 

I am considerably better at it than I was when I started, but I still find it a pain in the neck TBH. The 3/16 rods I need are only about 1 inch long. I can imagine the dial indicator face facing the chuck to get the probe in the part etc….

How are you adjusting the 4-jaw Steve? The stupid things only come with one key, which makes setting them up a right pain. Much easier with two keys used contra-wise to shift the rod horizontally until centred, then the chuck is rotated 90° and the rod shifted to centre it between the newly horizontal jaws. Surprisingly quick after practice – spend an afternoon doing nothing else. Making a second chuck key for their 4-jaw is a common beginner job. Doesn't have to be fancy or strong because it's only used as a sideways adjuster: the real key is used to tighten up and undo.

Altering the work plan might help. Rather than working with one inch long blanks, cut easy-to-hold two inch blanks, thread both ends, and then cut them in half. If you had a 3-jaw or collet, I'd recommend feeding, threading and cutting a long rod passed through the spindle.

I think parting off a 3/16" steel rod is more trouble than it's worth and would hacksaw it. If so, be careful not to accidentally notch the lathe bed by hacking through too quickly. Always put a bit of wood on the bed to protect it and always remember to remove the wood before restarting the lathe!

Dave

 

Edited By SillyOldDuffer on 21/11/2021 12:58:46

[Dr. MC BlackParticipant @dr-mcblack73214]

Does part of the rod need to be unthreaded?

If not, consider buying some 3/16 BSW studding and cut off the lengths that you need.

MC

[Bob Unitt 1Participant @bobunitt1]

Posted by Steve355 on 21/11/2021 00:13:04:

Posted by Grindstone Cowboy on 20/11/2021 22:10:30:

Lots of 7/8" BSW taps on Ebay from around £10. Might be worthwhile.

Rob

That would be fantastic, but I thought that backplates should be threaded on a lathe rather than tapped. Not entirely sure why, but that’s what I read somewhere.

I had a similar requirement the other day, but for an external thread. I got round it by first screwcutting the thread to a little bit oversize, and then using the die to get the correct thread-form. For an internal thread that size you could probably take a similar approach, by screwcutting a little bit undersize before finally running the tap through.

Edited By Bob Unitt 1 on 21/11/2021 16:44:46

[Earny49Participant @earny49]

If you have a faceplate and a three jaw chuck without a backplate could you possibly bolt the three jaw to the faceplate using bolts through the faceplate into the tapped holes in the back of the three jaw? Tighten the three jaw sufficiently to stop it slipping about the gently tap the three jaw until it’s periphery runs true then nip up the bolts tight. All adjustments done whilst turning the lathe by hand I hasten to add! I accept that you need some sort of dial gauge to get the chuck running true. However this might make an acceptable solution to having a three jaw on a temporary basis so would be useful for some of the other basic lathe work operations suggested in earlier posts such as the tailstock die holder.

[Steve355Participant @steve355]

Hi all and thanks for the responses.

I have a collet Chuck coming tomorrow. Now I need to order a tailstock die holder.

Looking at the options there are 2 types, imperial and metric. Metric is not allowed in my workshop. But I’m worried that my dies, despite being for imperial threads, are metric. They measure 24.97mm or 0.983” across.

I definitely don’t want to buy a tailstock die holder that my dies are not central in.

Any thoughts on this? I really want to get the tailstock holder ordered?

cheers

Steve

[not done it yetParticipant @notdoneityet]

Any thoughts on this?

Making your own would be one option for you.

[Bob StevensonParticipant @bobstevenson13909]

You don't actually need a tailstock die holder….you can use an ordinary die stock and use the tailstock barrel to steady it and keep it accurate……I've been cutting threads in the lathe for many years but, as yet, I don't own a tailstock die holder although I do use one in the club workshop sometimes and i can't truthfully say that one is better than the other but of the two, I tend to prefer the ordinary 'manual' die holder steadied against the tailstock.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Steve355 on 22/11/2021 10:53:36:

…

Looking at the options there are 2 types, imperial and metric. Metric is not allowed in my workshop. But I’m worried that my dies, despite being for imperial threads, are metric. They measure 24.97mm or 0.983” across.

I definitely don’t want to buy a tailstock die holder that my dies are not central in.

Any thoughts on this? I really want to get the tailstock holder ordered?

cheers

Steve

My advice, don't get hung up on metric vs imperial. Perfectly reasonable to specialise on one, but sooner or later Imperial workshops have to work in metric and vice versa.

There's quite lot of advantage in exploiting both systems, for example using metric drills (available in straightforward 0.1mm increments) rather than Imperial Letter and Number drills, which are bonkers illogical. Depending on popularity, materials come in an odd mix of UK and metric sizes. You can waste a lot of time trying to source obsolete Imperial Sizes, or the unobtainium metric equivalent of common imperial stock.

Imperial is suited to restoring old British equipment, making models from imperial plans, older folk familiar with the system, and whenever someone gives a younsgter a fully equipped imperial workshop. US 'English' measure is similar to British Imperial, but not identical. This can lead to beginners trying to buy US specified nuts and bolts, stock sizes and alloys rather than cheaper and more available British equivalents.

Metric is suited to restoring recent machines, general-purpose engineering, and youngsters. Cost and availability-wise, metric is slowly squeezing Imperial and US measure out. For example, most once common Whitworth fasteners have become hard to find and expensive, whilst their metric equivalents are easily found and cheap.

In the case of die-stocks, it might pay to get a tailstock set that does both. Otherwise, you have to be a little careful buying dies. For example, M8 x 1" and M8 x 25mm are both available and hard to tell apart as exhibition bargains!

Dave

[File HandleParticipant @filehandle]

" for example using metric drills (available in straightforward 0.1mm increments) rather than Imperial Letter and Number drills, which are bonkers illogical. "

I have often wondered how number and letter drill sizes came about. does anyone know or is it lost in history?

A mixture of metric, imperial and letter / number drills does give you even more choice for fine tuning sizes.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Keith Wyles on 22/11/2021 14:54:14:

…

I have often wondered how number and letter drill sizes came about. does anyone know or is it lost in history?

…

Best answer I've heard is the sizes come from the way wire was originally handmade by pulling metal through dies.

The apparatus consisted of a stout bench with a large lever at one end. At the other a long bar was bashed through a fixed die until the end could be gripped and the rest drawn through the die by heaving on the lever. The diameter, or gauge, of the die was limited by the maximum force the lever could apply to swage the metal down to size without breakages.

Smaller diameters were made by pulling a large gauge wire through a smaller die, with the size of the hole adjusted again to avoid breaking anything. Thus wire gauges step down through a series of diameters that don't have an obvious numeric relationship – they depend on ductility, the strength of the metal being pulled, the strength of the die, and the power of a manually operated lever. The sizes were found by experiment, not calculated, and the resulting series of gauges became de-facto standards.

When the Victorians upgraded to drawing wire with steam they could draw wires in any diameter. But because many customers were committed to the old gauge sizes, they carried on producing them. There were dozens of different gauge systems, and my 1948 Engineer's Handbook spends half a page introducing them: quite easy to order the wrong one. Gauge sizes have gradually been supplanted by rational diameters but there are still survivals.

They say the gauge of modern railway track is derived from Roman Chariots axles for much the same reason: once a standard is embedded they take forever to change, even if the original reason has become daft!

Dave

[Brian MorehenParticipant @brianmorehen85290]

Die holders seem to have mostly metric sizes BA and small Whit & Bsf that i Have are 15/16 which from memory will only go to 1/4 Whit 5/16 Whit and similar go to a 1. 5/16 Die holder which i think stops at 1/2 whit. I also have some BA Dies that go from 10BA to 4BA that are 9/16 Dia . To get a perfect fit you may have to make small ring to fit your Die to then hold your Die , A poor fit may break your die? I maybe slightly wrong about these sizes as i am reliying on my memory

Good luck and time you will win.

[Steve355Participant @steve355]

Posted by Howard Lewis on 20/11/2021 21:11:15:

You can make or buy. Making can be a useful learning exercise, and give confidence in using the lathe.

(

right, I have changed my mind, i am making a tailstock die holder. The reason I was hesitant was that I am not confident in turning a morse taper. But I realised I have an MT2 collet which a die holder could easily be fitted to. If I can’t turn a die holder shaped thing with a rod sticking out the back I may as well give up.

What is the handle that sticks out if the back of the die holders for?

[Howard LewisParticipant @howardlewis46836]

Ideally, the Tailstock Die Holder should be able to "float" on the arbor, so that the chamfer on the end of the work centres the Die, and the newly cut threads do not have the task of pulling the Tailstock along the lathe bed.

(With fine threads that is very likely to strip the thread; certainly with ME 40 threads which are only 0.016" (0.406 mm ) deep ).

I ensured that my Die Holder body, and the Tap Holder body were a loose fit on the arbor for just that reason.

Howard

[Steve355Participant @steve355]

Posted by Howard Lewis on 23/11/2021 21:06:11:

Ideally, the Tailstock Die Holder should be able to "float" on the arbor, so that the chamfer on the end of the work centres the Die, and the newly cut threads do not have the task of pulling the Tailstock along the lathe bed.

(With fine threads that is very likely to strip the thread; certainly with ME 40 threads which are only 0.016" (0.406 mm ) deep ).

I ensured that my Die Holder body, and the Tap Holder body were a loose fit on the arbor for just that reason.

Howard

That is interesting. Do you have any pictures of it? Or is there something similar online?

my 1.5” bar I bought to make it is coming tomorrow!

thanks

Steve

[Steve355Participant @steve355]

Ok, I just watched blondiehacks video on the subject and I think I know what to do now.

[Mike PooleParticipant @mikepoole82104]

The Arrand tailstock die holder allows the actual die holder to be adjusted to be axially true, this is achieved by the holes for the attachment screws being oversized to allow the holder to be perfectly aligned before tightening. Although Arrand has closed as far as I know there is still some available, I think Rotagrip listed them not long ago.

Mike

[Howard LewisParticipant @howardlewis46836]

I am a coward where turning Morse Tapers is concerned, on the grounds that I may not get the angle right, and the turned surface finish will certainly be inferior to that of a commercially ground one.

So the Stub Morse Taper arbor is mounted in the Headstock spindle and drilled / reamed /bored to suit the arbor that will be fitted.

Often the arbor size is determined by the size of material available, quite likely to be Silver Steel.

The arbor is then chamfered and faced to length, and pressed / Loctited into place.

The bore in the body of the Holder is then deliberately made a few thou over size, relative to the arbor, so that it can float to self centre on the chamfer on the end of the job.

The Holder is bored to take the largest OD Die, and holders made that have a spigot the same OD, and length as the largest Die, with a bore that accepts the smaller OD Dies.

The holders are drilled and tapped with three holes for grubscrews, at 45 degree spacing around the circumference.

Or you can cheat by making your main holder body and buying the smaller Die Holders

I put a tapping into the OD of the main holder body, so that a stud can be screwed in, to rest against the edge of the Toolpost, to resist rotation whilst in use.

I made a similar holder taking ER collets, to hold Taps . There is a chanfer on the end of the bore, to help the Tap to self centre on the bore.

Sometimes the torque required is such that the Tap slips inn the collet. In such case the Tap is usually sufficiently engaged for the work to be transferred from chuck to vice, so that tapping can be completed by carefully using a Tap Wrench and muscle power

Although this entails cutting a 1.5 mm pitch thread for the size of collets that you choose.

(It seems that the thread dia is that of the next collet size up. 25 mm for ER 20, 32 mm for ER25, and so on. )

Howard

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