Threading Question.

[randyc]

I may have missed it but, is there anything wrong with using a nut if you have one the correct size and TPI to check?

Jim

Nothing wrong at all for the most part. There may be occasions where a bit more precision is needed or where it isn't practical to use the mating part to check the thread fit. Here's a hypothetical example, using your airplane avatar as inspiration - keep in mind that this is a very simple-minded hypothetical situation:

Vibration over time has caused a fastener from the engine in your home-built experimental aircraft to be lost. You want to make the replacement part and have obtained suitable high-tensile stock. The stock is chucked in your lathe and you've started to cut the threads when you realize that you have no way to check the fit of the fastener to the part.

If you remove the fastener from the lathe (to try the fit in the engine tapped hole) it will cause the threads on your part to be "out of time" with the lead screw when the part is replaced in the lathe for further thread cutting.

With a set of thread wires, or thread micrometers, and a copy of "Machinery's Handbook" this becomes a non-issue and does NOT require the part to be removed from the lathe. You simply look up the OD and PD of the required thread size and continue threading on the lathe until your measuring tools indicate that the part is within tolerance.

If the fastener is one of several fasteners of the same type in your engine, the task is even simpler: remove one of the other fasteners and measure the PD with thread wires or micrometers then machine the new fastener to the same dimension without removing it from the chuck.

(Note that if the new part was held between centers in the lathe using a lathe dog, it could be removed from the machine, checked for fit and then replaced in the lathe for further thread cutting. But this was just an example)

 

[randyc]

Talk of thread wires reminds me - I poke 'em into a wine cork at roughly the right spacing. Any excuse to open another bottle

Dave H. (the other one)

Dave, that is one of the cleverest ideas regarding thread wires that I've ever read ! I might well be able to use thread wires again, even with my shaky hands, using your idea. Thank you VERY much !

 

[Fldvr]

Thanks for all of the information, there is a lot I've not been exposed to as of yet but the discussion here is great for
me to think about.

I can see my technique needs a little more experience behind it but when I run the compound per the .0457 depth for
the 5/8-14 Bsp theads it comes up a little short. I ended up cutting until I could get a threading die on it and everything
worked out ok. Now to do 49 more.

 

[JT.]

http://www.driehoekberekenen.be/

i somthime use thise one

angle A is your cutting angle (30 ore 29.5 -29 etc.
angle C = 90 dg
side B is your(crosslide) depht
thenpush calculate and the side c is how mutch you need to move your compound to get your (crossslide ) cutting dept

 

[Fldvr]

Jt thanks for that visual representation. The math was not clear to me until
I could "see" it visually.