What has happened to this die to cause this ?

[Brian JohnParticipant @brianjohn93961]

…or is it me again ?

[Brian JohnParticipant @brianjohn93961]

I have used this M3 HSS die to cut numerous threads on piston rods before. I hold the 3mm silver steel rod in the lathe chuck and I use the tailstock to keep things even. There has never been any problem before but today it just will not cut the thread properly. I hope you can see the photo. The die looks okay ( but what would I know ) although I am surprised by the gap in the split ; I thought it should close up more than that but it will not. The silver steel rod is 2.95mm in diameter.

 

Edited By Brian John on 29/04/2016 08:01:14

[JasonBModerator @jasonb]

Is that a bit of silver steel in teh background or an old screwdriver blade?

make sure your middle screw is loose before tightening the outer ones and nothing stuck in the slot

[Brian JohnParticipant @brianjohn93961]

That silver steel is the piston rod with the badly cut thread.

Yes, I made sure the middle screw was loose ; I even took it out to make sure.

Edited By Brian John on 29/04/2016 08:30:24

[John Stevenson 1Participant @johnstevenson1]

You didn't answer Jason's question.

Is that an old screwdriver blade because it certainly looks like it and as such has probably been heat treated

[Brian JohnParticipant @brianjohn93961]

No, it is the silver steel rod I usually use. It is not an old screw driver blade.

I remember that I did chip part of the cutting thread on my original M2 die but that was quite obvious to the naked eye. I cannot see anything wrong with this M3 die. I may have to buy a new M3 die just to eliminate that possibility.

While we are on the subject of dies : what are the advantages of having a non split die ? I am looking at the Bengs website (getting ready for another order) and all their dies are not split dies.

Edited By Brian John on 29/04/2016 08:42:27

Edited By Brian John on 29/04/2016 08:44:45

Edited By Brian John on 29/04/2016 08:45:01

[Chris Evans 6Participant @chrisevans6]

Did you cut 1/2" or so off the end of the silver steel before starting ? Silver steel is cut to size for dispatch with an abrasive cut off wheel, this locally hardens the end and may have coursed your problem.

[Rex HanmanParticipant @rexhanman57403]

Try using the die on a bit of mild steel. If it cuts ok it is probably the bit of silver steel that is the problem.

[Bernard WrightParticipant @bernardwright25932]

Why not try undoing the pinching side screws.

Then tightening the centre screw to make a bit larger thread.

It would show if the die is duff.

Are you threading dry or with lubricant.

The suggestion about the end of the rod is a good one too.

Bernard

[Brian JohnParticipant @brianjohn93961]

This is not the raw end of the rod ; I cut a bit off with the hacksaw to start.

I thread dry ; I have never had a problem doing it this way before.

If I opened the die up much more than I doubt it would cut at all but I have tried everything else so I may as well give that a go. The die was in the same setting as I used to successfully cut a thread on some rod three days ago….this is why I am so perplexed.

[Neil WyattModerator @neilwyatt]

Is it a bit you have used as a toolmaker's reamer?

Full diameter silver steel is a challenge to any die – you could either skim a fraction of a mm off it before threading OR make a first pass with the die sligthly opened up, and then do a final sizing pass if the thread is tight.

I would ALWAYS use a lubricant on any steel, and silver steel in particular, as it will rarely give a good finish cut dry. Plus it make expensive dies last much longer – cutting silver steel unlubricated could have bluntened it a bit but not enough to be visible.

Neil

[julian atkinsParticipant @julianatkins58923]

Hi Brian,

Firstly there is no need to make the piston rod out of silver steel, so you are making things far more difficult for yourself.

My guess is that the die is not lying flat in the die holder. A proper tailstock die holder is a better method, again making sure the die is inserted correctly.

The die may also now be blunt.

If the material is accurately dead central in the chuck or collet, then you can turn down the first section to 'core' diameter with a chamfer between core and OD.

Get some decent tapping compound. I use Rocol, usual disclaimer.

The correct closure of the die in holder can be tested by inserting a screw of known standard/size and same thread as the die into the die to check.

Cheers,

Julian

[Brian JohnParticipant @brianjohn93961]

I have checked the die with an M3 screw it threads okay.

I opened up the die a bit and applied some tap magic to the die : the result is still a mess. It just will not cut.

I think we can assume that the die has become blunt so I will order a new one tonight. That is the only way to find out for sure. When the new die arrives I will use tap magic every time. The lack of a cutting compound might explain why it has become blunt.

If the new die does not cut then I have a problem.

I also tried the die holder. I ordered this months ago but when it arrived it did not fit in my tailstock drill chuck. I then ordered a larger drill chuck which arrived many weeks later. At the time I was busy with something else and I never actually got a chance to use the two of them together until now. It still did not solve my problem

I am 99% certain that a new die is required. I cut a thread on this material only yesterday with no problem.

Edited By Brian John on 29/04/2016 12:14:17

Edited By Brian John on 29/04/2016 12:15:18

Edited By Brian John on 29/04/2016 12:27:48

[davebParticipant @daveb17630]

I have had silver steel that was much harder than normal, I heated it with a torch and let it cool slowly, made a lot of difference.

It's possible to sharpen dies with a Dremel, poke a cylindrical point through the circular holes.

Dave

[Phil PParticipant @philp]

Looking at the photo, it does not have a makers name on that die. I am guessing it is a cheap one of dubious origin.

I had the same problem when I bought a cheap M9 x 1 die on ebay, I got a really badly formed thread from it.

You could actually cut into the die's thread form with a file it was that soft, I got my money back and ordered a known make of HSS die, that worked perfectly. The good quality die cost four times as much as the useless one.

It might be worth checking how hard the teeth are on yours.

You get what you pay for in my experience, buy cheap buy twice.

Phil

[Brian JohnParticipant @brianjohn93961]

No, these are good quality HSS dies purchased from the UK. I bought them at the same time I bought all my taps. I should have used tap magic on it to preserve the sharp edge. I will order another one and see how it goes…this time using tap magic.

I never buy cheap taps and dies or carbon steel either…been there, done that !

Edited By Brian John on 29/04/2016 13:47:45

[Ian S CParticipant @iansc]

Get a Sutton or P&N die, Australian/NZ made, probably as good as you'll get. I'v been using a 10-32/ 3/16" UNF die, with broken chipped teeth (from cutting threads on steel too tough), it has been working well on mild steel.

Ian S C

[Howard LewisParticipant @howardlewis46836]

All the foregoing advice is good. To which I would add,:

Chamfer the end of the rod, to help the die to start cutting.

Use lubricant (Rocol / Trefolex / Bacon Fat – Don't laugh, it works very well!)

Use a Tailstock Die Holder (Make one?) You are asking a lot to ask a M3 thread to drag the Tailstock along the bed. AND the Drill Chuck does not allow the Die to float to pick the rod.. The Tailstock Die Holders will be a relatively slack fit on the Arbor for just that reason.

Commercial Tailstock Die Holders usually have the ability to accept a variety of sizes of Dies.

I made myself a Sliding Tap Holder, to fit the Arbor for the Die Holder, for Tapping. Again, a slack fit to ease picking up the drilling. (Mine uses ER25 Collets).

Making your own tools is often time well spent, since you can make exactly what you want, you learn, and save money, (and in view of your location, time).

Hope that you get things sorted.

Howard

[mechman48Participant @mechman48]

Chamfer a new piece of steel; turn the die round & try to cut thread with back of thread to see if teeth are blunt all the way through, you may get by using die this way, I have on a couple of occasions, get / make sliding arbor for your die holder, as pulling the weight of the tailstock is counterproductive, & always use some form of lubricant, even veg / cooking oil or soap has been put to use if you have absolutely nothing to hand.

George.

[Peter KroghParticipant @peterkrogh76576]

By simply not tightening the chuck jaws and allowing the die holder to rotate in the chuck, you can hold the die holder by hand while running the lathe or, with the lathe still, turn the holder to thread the rod. This assumes that the problem is caused by dragging the tailstock…..

That and some good cutting oil.

If the die is toast then replace the die and do the above.

Pete

[Ed DuffnerParticipant @edduffner79357]

Could the die be the wrong way around i.e. the work piece not starting into the tapered part of the die? Is there a way to tell the tapered end/side easily on small dies?

Just an FYI, I tried cutting an M8 x 1.25 thread yesterday and found it just would not start. I measured the OD of an M8 screw and found it to be about 7.94mm. After turning the OD of the part to that size and retrying I could then cut the thread with the die. I always use the brown cutting grease.

Ed.

[MWParticipant @mw27036]

for materials that chip easily rather than curl it is better to cut once with the die open and not twice to finish,

it may sound strange but that is my experience,

because if i closed the die up on brass or silver steel it tends to mutilate the bar and chew the whole thing up right down to the core depth of the die, not good i can tell you.

So if it looks ok after 1 cut and the part fits, leave it be.

Michael W

[duncan webster 1Participant @duncanwebster1]

OP hasn't answered Julian's point, silver steel is not the best material for piston rods, make life easier by using a machining grade stainless or if you're not after corrosion resistance use EN3. Silver steel is for making cutting tools, jigs etc

[SillyOldDufferModerator @sillyoldduffer]

Posted by Brian John on 29/04/2016 12:07:17:

I have checked the die with an M3 screw it threads okay.

I opened up the die a bit and applied some tap magic to the die : the result is still a mess. It just will not cut.

I think we can assume that the die has become blunt so I will order a new one tonight. That is the only way to find out for sure. When the new die arrives I will use tap magic every time. The lack of a cutting compound might explain why it has become blunt.

If the new die does not cut then I have a problem.

I also tried the die holder. I ordered this months ago but when it arrived it did not fit in my tailstock drill chuck. I then ordered a larger drill chuck which arrived many weeks later. At the time I was busy with something else and I never actually got a chance to use the two of them together until now. It still did not solve my problem

I am 99% certain that a new die is required. I cut a thread on this material only yesterday with no problem.

Edited By Brian John on 29/04/2016 12:14:17

Edited By Brian John on 29/04/2016 12:15:18

Edited By Brian John on 29/04/2016 12:27:48

Can anyone advise on the correct way to cut a thread using the set-up shown in Brian's picture? I have the same type of die holder and am not clear on how it is meant to be used.

The die holder simply consists of a wide tube at one end to hold the die with a hollow narrow tube or shank at the other. The die holder doesn't have any arrangement that allows the die holder to move forward as the thread is cut. Nor is the holder obviously intended to be hand held.

A few ways of using the tool occur to me none of which seem quite right.

1. The drill chuck is wedged into the tail-stock so that it can't turn. The shank of the die holder is firmly gripped by the drill chuck. The tail-stock is unlocked and free to slide on the ways. Whilst the lathe chuck is rotating, possibly under power, the die is engaged with the end of the rod and the whole tail-stock pushed towards the lathe as the thread cuts.

2. Exactly as above except the tail-stock is locked and pressure applied by winding in the quill.

3. The shank of the die holder is loosely aligned by the drill chuck but not gripped by it. The die holder is held by hand and pressed on to the rod by moving the tail-stock. As the lathe chuck is turned by hand to cut the thread the die holder slides out of the drill chuck.

Methods 1 and 2 in my hands are likely to mangle the thread. Method 3 works but doesn't feel like "industry best practice"

I now use a more conventional sliding die holder. The way that's used on the lathe seems obvious in comparison to the simple type.

Thanks in anticipation,

Dave

[Neil WyattModerator @neilwyatt]

Posted by duncan webster on 29/04/2016 19:42:34:

OP hasn't answered Julian's point, silver steel is not the best material for piston rods, make life easier by using a machining grade stainless or if you're not after corrosion resistance use EN3. Silver steel is for making cutting tools, jigs etc

Brian has a specific issue of needing a very good fit of piston rod in gland for a stirling engine. He was recommended to use silver steel so he could make a matching toolmaker's reamer.

Neil

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