Cutting threads

[Triumphman]

Hi Pete,
I could definately do with a new one!
Let me know what you want for it,
Cheers
Jon

 

[Lawnmowerboy]

Screw cutting Is definitely the way to go. If your doing a thread longer than about an inch the die wanders up and down making the thread off centre. The most accurate way is screw cutting it and measuring with grease wires of the appropriate size and a good mic. But irrelevant but useful!

 

[Mr shiney]

I have a screw cutting facility on the lathe. However I find it easier to use a tap or die held in the tail stock and turn the chuck by hand!!

 

[Lawnmowerboy]

It's far quicker using a tap or die but if you have to wait for a tap or die to turn up on a bit of an exotic thread it's a useful thing to be able to do

 

[brightspark]

I have a screw cutting facility on the lathe. However I find it easier to use a tap or die held in the tail stock and turn the chuck by hand!!

make one of these its easier

 

[Lawnmowerboy]

That's a really good idea. Is it an old file handle?

 

[brightspark]

That's a really good idea. Is it an old file handle?

yes and it can be disengaged and used on both my machines without having to take the drive plate out

 

[gordon stephenson]

Screw cutting Is definitely the way to go. If your doing a thread longer than about an inch the die wanders up and down making the thread off centre. The most accurate way is screw cutting it and measuring with grease wires of the appropriate size and a good mic. But irrelevant but useful!

I have been in the engineering game all my working life and never ever heard of "grease wires" only thing that springs to mind is Plastigauge, If not, please explain someone

 

[Mr shiney]

Brightspark, that's sheer genius! I am going to steal that idea immediately!

 

[MattF]

I have been in the engineering game all my working life and never ever heard of "grease wires" only thing that springs to mind is Plastigauge, If not, please explain someone

I'm assuming he means thread wires.

http://www.arceurotrade.co.uk/Catalogue/Measurement/Thread-Gauges-and-Wires

 

[Lawnmowerboy]

Yeah. Done with any accurately sized wires. I can't remember the formula to calculate the size of wires in relation to the thread. You use 3 pieces of wire 2 on the top and one on the bottom stuck on with grease and then measure with a mic. It basically measures the effective diameter of the thread as it's the smoothest part and both the crest and core of the thread has slight variation and possibly a bit of tearing. The grease is just there to stick the wires to the thread. To calculate the wire size the wires thickness must be twice the distance from the crest of the thread to the effective diameter. You can get away with about a thou difference maximum between the calculated size and the wires you have.

 

[MattF]

You could just run a nut up the thread and check it fits.

 

[Lawnmowerboy]

Where's the fun in that!! I make quite a lot of one off jobs to fit other parts with some quite odd threads where it isn't to suit a nut or we don't have a tap to make one. If I make sure it's right when it comes off the lathe inspection have no cause of complaint!