Originally Posted by juergenwt  Mike - you are not giving us enough info. How many parts? What dia is the thread? It looks like a small thread.
First - since the part is metric I would stay with a standard metric fine thread.
Second - for the inside thread I would make an undercut and than cut from the inside out - or - I would try to find a metric standard fine tap. Buy two and grind one of them flat bottom going. Start with the first one and finish with the second one to the undercut. Don't forget to put a nice chamfer in front.
For the plug - you can cut as close as possible with a tool bit having a small tip.
You take a regular tool bit like a 5/16 x 5/16 and on the left side grind a 30 deg angle almost to the front. Than tilt another 30 deg. and grind to a small tip ( you can make a tip just slightly larger than the depth of your thread). You will than end up with a 60 deg. tip. Grind your clearance by hand.
Set compound to 29 1/2 deg and align the left ( first ground) angle with the face of your spindle or 90 deg to the thread. Cut to an undercut. The chamfer on the internal thread will help you - or - buy a die, cut with one (the chamfered side) and follow up with the other side of the die that is almost a sharp full thread. Check the die and make sure it has one side with a chamfered start and the other side starts with a thread that has a very short chamfer.
If you can not find one - grind one side. Juergenwt |
Thanks for the info!
How many parts - well it's a new product we are doing, so I will be running these in batches of 200-400pcs at a time.
Compound? Cross slide? What are those?
I'm making them on a CNC lathe... but a few folks and you have suggested threading from the inside and moving out... may I ask why? I've never done that, will I get a better finish or something? Or is that relevant on a manual machine to ensure you get right up to the shoulder?
The thread can be anything I want, I was thinking to use a very fine pitch thread to give as many threads to contact as possible, maybe a 48 pitch or something.
I have a laydown threading toolholder (ID and OD) so I was thinking to get an insert that will fit on that, like a full profile UN-48tpi and see how it works... if it doesn't, I can go from there. I will be sure to put a chamfer on the front lip - thanks for the tip!