Metric Dies

[BOB BLACKSHAW 1Participant @bobblackshaw1]

Hello all. Can anyone recommend a metric die brand that have a lead on the front of the die and  flat on the back,I know I could grind the lead but would rather not. I don’t know why they make them with a lead front and back, any ideas for the reasoning.

Thanks Bob

[BOB BLACKSHAW 1]

On 25 January 2024 at 07:31 BOB BLACKSHAW 1 Said:

… I don’t know why they make them with a lead front and back, any ideas for the reasoning.

Thanks Bob

My guess would be that it’s a misguided attempt to make them ‘simpler’ to use [!] … if they’re symmetrical there is no risk of the naive using them the wrong way round.

MichaelG.

[JasonBModerator @jasonb]

Two cutting edges for the price of one die, just like a Stanley knife blade

I don’t think you will find any with a totally square back, there will be some form of chamfer even if it is smaller than a single leading edge

[DC31kParticipant @dc31k]

The difficulty with your question is that dies are made to a Standard so they can be sold into a world (plus US) market.

Metric dies are likely to be made to ISO 2568 or a local implementation thereof. Note 1 on page 2 of that Standard mentions two chamfers.

Dies are also made to suit the demand from their users. That’s what happens in a free market economy. If there were 999,999 other people like yourself who had a plausible use case for a single chamfer die, the manufacturers might respond and produce a variation of their product line.

Consider that it is easier to remove the unwanted chamfer from a two-sided item than it would be to add a second chamfer to a single-sided item.

[JasonBModerator @jasonb]

Alternative is a shallow relief at the base of the thread if you are threading to a shoulder or a shallow counterbore of the mating hole. Engine I’m working on at the moment has quite a few shouldered pivot pins in M3 and M4, I’ve just cut a relief in all and they screw in OK after threading with the chamfered end of the die.

[Anonymous]

Without a chamfer one of the cutting edges will most likely be very thin and will break off when used anyway.

Andrew

[EmgeeParticipant @emgee]

If you want to maintain full diameter of the threaded part drill the hole entry to suit to allow the full diameter to enter.

 

Emgee

[BOB BLACKSHAW 1Participant @bobblackshaw1]

Thanks for the replies. I do use a small relief to get a nice edg to the finished thread but when I’m threading short 3mm threads or smaller it doesn’t leave much. I have a few metric dies that have no relief, all my model engineering dies ME which are a specialist die, I would of thought they would be the obvious norm for that type of die. I shall  order some more dies and grind up my old ones.

Thanks Bob.

 

[Howard LewisParticipant @howardlewis46836]

Dies are made with a chamfer on the front edge

a) to help guide the Die onto the work

b) To allow for any radius between the shoulder and the diameter.

To an extent, this can be accomodated by cutting then thread nornally, and then reversing the Die so that back face cuts closer to the shoulder. Closer, because there will still be a little chamfer on the back of the Die.  But usually, this does not cause a problem.

If an undercut is made against the shoulder, the problem doesn’t arise, since there is no longer anything for the matching component to butt against.

If you are worried about stress raisers and fatigue, this is a downside.

Howard

[JasonBModerator @jasonb]

Howard, Bob’s problem is that many dies these days have the lead chamfer on both sides so turning them round won’t get the thread any closer to a shoulder. These are also quite often “gun nosed” where a second angle is ground onto the leading edges to drive the swarf forwards much like a spiral point tap does as the dies are often intended to be use din diestocks with the work rotating under power so no backing off to break the chips.

If it’s a part where I’m worried about stress rizers I have a 1mm half round (0.5mm Radius)parting insert that will do the relief with the minimum risk of stress spreading from an internal corner. However most of the time on a lightly loaded model a flat ended parting insert is OK. This M10 x 1 thread on a stuffing gland would be the sort of low stress part where the plain cut is OK. I would not do it on the end of say a crankshaft that may have the thread retaining a propellor or heavy flywheel.

Interesting bit bottom right of page 155 about this maker (one of the brands Cutwel do)doing short chamfer on request but not that short. Also note that generally they are unsplit like most of what is now made.

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