Thread: Threading Advice…..Again!

Simon,

It would depend on how much thread engagement you need, which would depend on what you are using the nut and bolt for.
The actual position, sizing and thread face shape of the thread in relation to the centreline (axis) of the bolt and nut do not change; the variances in major and minor diameters only affect the amount of thread engagement between the nut and the bolt.
For most purposes you can use major and minor values midway between the given values, but clearly the minor and major diameters on the nut will need to be large than those on the thread to prevent interference.

I would make the nut first and then make the bolt thread to give a good fit, unless you need other existing nuts or internal threads to fit the bolt.
It wouldn't matter exactly what dimensions you use if nothing else needs to fit your nut and bolt.

Andrew.

Hi Andrew,

Thanks. When making stuff like threads etc. I prefer to make them compatible with the outside world. Eventhough on this case it would not need to be so. WRT the thread engagement etc. I thought that was taken care of with the class of fit, for instance a 6g 6H which is a standard fit.

I think I may have since answered my own question. The depth of thread = 5/8 x H where H = √3/2 x pitch. This gives a figure of 0.811mm (depth of thread for bolt) however I found another figure of 0.920mm for the bolt and 0.812mm for the nut which is different from what I calculated. Which is correct for metric pitch of M22 x 1.5mm in a 6g 6H class of fit?

Cheers,

Simon

Simon this is the way I work out thread depth not sure of the tolerance , you need to remember two constants.
For an external thread its .6134 x pitch
Example 0.6134x 1.5
= 0.9201mm
For an Internal thread use .5412x pitch
Example 0.6134x1.5
= 0.811 mm
Hope this makes sense I am on my phone.

Much appreciated Andre,

Thanks mate.

Simon

Simon,

you want to cut an external M22x1.5 6G thread.

This is a metric fine thread. And with metric fine threads, you need not to worry what its diameter is. You only need to worry what its pitch is and what is the tolerace you are going to use. This is how its is, a metric fine thread is completely and soley defined by its pitch and the tolerance, and nothing else.

I personally use thread tables, not formulas. This is what my table says about an ISO 6g 1.5mm external thread:

minimum outer diameter: d -0.268
maximum outer diameter: d -0.032
thread depth: 0.920
radius in thread valley: 0.217

d being the nominal thread diameter, in your particular case 22mm. Meaning min diameter 22 - 0.268mm, max diameter 22 - 0.032mm.

And this also answers your question "how does thread depth change with thread diameter". The thread depth of a metric fine thread does not change at all with thread diameter, it only changes with pitch. However, the thread depth is different for bolt and nut thred.

You need some thread wires... Then measure with the three wire system as you go.... It is the only way to really be able to cut accurate threads when it matters...

Ausee in melbourne sell a chinese set, but they are not as good as the US made Pee Dee wires which are around $20 a set..

I use the infeeds tables at the bottom of this link. http://www2.coromant.sandvik.com/cor...061/tech_c.pdf

Richard, I should get myself some thread wires, where does one obtain the Pee Dee variety?

Originally Posted by bob ward

I use the infeeds tables at the bottom of this link. http://www2.coromant.sandvik.com/cor...061/tech_c.pdf

Richard, I should get myself some thread wires, where does one obtain the Pee Dee variety?

I got mine from Little Machine Shop in the US...

Hi Simon,
I agree with the use of thread wires as it is really the only way you can get any dimensional accuracy (if required) when screwcutting. Mind you I 'still' don't have a set but the one Richard pointed us to is likely to be my next purchase.
In the meantime I normally go down to Spotlight armed with my micrometer and the ball park size of the thread wire I need to measure the thread I am cutting and buy three sewing machine needles to suit.
It is surprising how accurate they are for the job at hand. Probably worth a crack until your thread wires arrive.
I may also have a brand new tap here that is the size you are after that I could post out to you. I have several I think so it would be yours for the keeping.

Phil

Hi Richard,

Yes it looks like I should look into getting some thread wires but they are designed to get you spot on go - no go, you still need to know the depth of thread to get you to ball park figures. Looks like I'm shopping for thread wires….

CBA, Thanks for the info. It had never occured to me that the thread dimensions were purely derived from the pitch. It makes sense.

Hi Phil,

Thanks mate for the generous offer but I would feel bad relieving you of an (expensive) item for my one off use. Besides, if I keep relying on taps then I will never have a need to finally do some internal thread cutting. Sewing needles eh? I love spotlight, it's such an underated store for males!

Hi Bob, are you talking about the infeed rates (ap) at C7 where it says 0.94mm for 1.5mm metric external pitch and 0.90mm for internal nut? These figures are still slightly different to others quoted. Not by much though.

Simon

Originally Posted by simonl

Hi Phil,

Thanks mate for the generous offer but I would feel bad relieving you of an (expensive) item for my one off use. Besides, if I keep relying on taps then I will never have a need to finally do some internal thread cutting. Sewing needles eh? I love spotlight, it's such an underated store for males!



Simon

No worries Simon, they were given to me in the first place though I do understand what you are saying about cutting threads yourself.
I actually consider Spotlight my pseudo engineering supply store

Phil

For anyone else interested, heres a link to the set mentioned by Richard from Ausee on their ebay store. Out of interest, how do they compare to the more expensive brand sold at The little Machine Shop?
http://www.ebay.com.au/itm/Thread-Me...item4633be0e2b

Simon

Originally Posted by simonl

.........................

Hi Bob, are you talking about the infeed rates (ap) at C7 where it says 0.94mm for 1.5mm metric external pitch and 0.90mm for internal nut? These figures are still slightly different to others quoted. Not by much though.

Simon

No, right down the bottom, page C26 and on.

Originally Posted by bob ward

No, right down the bottom, page C26 and on.

Thanks Bob, found them. They are the same values as stated before, 0.94mm for external and 0.90mm for internal. These are slightly different to the values obtained using Andre's calculations. It's probably neither her nor there but it intetrests me why the variation.

Anyway, I cut the M22x1.5mm thread using my "usual" technique. I then took it out and bought a standard M22x1.5 nut to test fit and found it fits like a glove. Of course once you remove it from the chuck it's pretty difficult to make any changes if you find it a little tight. I see the benifit of thread wires. No guess work! Mind you, if you make your major diameter within the specified tolerance and you feed in at the correct depth, how can you get it wrong anyway? It's just a recipe.

Simon