Machining internal thread

Im needing to machine an internal thread so a hydraulic ram can be screwed into it. The outside diameter of the thread of the hydraulic ram is 4.1/2" by 12tpi. What size of internal hole do I have to start with before threading. Can machine external thread no bother. Using an indexable thread cutting insert. Have a Zeus book but just insure what measurement I use. Thanks in advance.

Depends whether it is Imperial (55 degrees) or American (60 degrees). From your Zeus tables, find the depth of thread for any 12 tpi thread which is 53 thou for Imperial or 51 thou for American. Double this and subtract it from your 4.5 inches.

That's the way I would do it.

Rod

I think that,s the way most people do it.

Don't forget to truncate the thread slightly to ensure the crest does not foul in the root of the ram thread, I would suggest around 0.008" on the dia i.e. calculate as above and add the truncation to the bore size calculated.

No need to do this if you were using a modern full form tip but if not full form I would defiantly truncate the crest.

John

If you have no experience of cutting internal threads then I would suggest you practise on some scrap before doing the real thing.

On the assumption that you cannot offer up the ram to the work in the lathe it might pay to first produce a dummy male thread to use as a gauge.