biednick
Member
Hello,
Is there a wayto cut internal thresds on a metal lathe without a tap?
Thanks,
Nick
Is there a wayto cut internal thresds on a metal lathe without a tap?
Thanks,
Nick
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Paul in OKC
Member
You can use a small bar with a threading tip on it. Look for miniature boring threading tools. Several places sell them, just can't think of one off hand, other than MSC.
biednick
Member
Okay, thank you both
penmaker56
Member
Enco has a miniature internal threading bar that will go into a hole a little larger that 1/4", if memory serves me, but, it is only good for fine threads and it works great. The only problem is that it is very expensive.
Another possibility is to use a thread mill like this:
Harvey Tool - Thread Milling Cutters - Single Form - Threadmilling Cutters
You would have to mount it in a rotary tool which would mount to the tool post, but they give very clean threads. You could use this for both internal and external threads.
Harvey Tool - Thread Milling Cutters - Single Form - Threadmilling Cutters
You would have to mount it in a rotary tool which would mount to the tool post, but they give very clean threads. You could use this for both internal and external threads.
It's hard to find an miniature internal threading bit that will do less than about a 3/8 hole.
You can grind one from a very small HSS boring bar, but with bores that small it is a really touchy operation to do the threading this way.
Doing an external thread on some appropriate sized drill rod then carefully filing flutes into it will usually make an adequate small threading die for softer materials, heat treating it after getting the final shape finished will make it last for a long time unless you're trying to thread something hard (a MAPP gas torch is best if you don't have an acetylene rig available, but very small rod can usually be done adequately with propane). Heat treating it is really a very simple operation, just heat it till it becomes non magnetic (something close to yellow hot depending on how you see the colors), hold it there a minute or two, then quench it in the appropriate media (Oil for "O" rod, salt water for "W" rod and simple air cooling for "A" rod).
I should mention, if it's a standard thread you can also make a soft material tap out of the right sized grade 8 bolt (but you don't get to play with the lathe as much that way, not to mention the yellow hot steel). Look at some self threading bolts to get the basic idea then experiment some.
You can grind one from a very small HSS boring bar, but with bores that small it is a really touchy operation to do the threading this way.
Doing an external thread on some appropriate sized drill rod then carefully filing flutes into it will usually make an adequate small threading die for softer materials, heat treating it after getting the final shape finished will make it last for a long time unless you're trying to thread something hard (a MAPP gas torch is best if you don't have an acetylene rig available, but very small rod can usually be done adequately with propane). Heat treating it is really a very simple operation, just heat it till it becomes non magnetic (something close to yellow hot depending on how you see the colors), hold it there a minute or two, then quench it in the appropriate media (Oil for "O" rod, salt water for "W" rod and simple air cooling for "A" rod).
I should mention, if it's a standard thread you can also make a soft material tap out of the right sized grade 8 bolt (but you don't get to play with the lathe as much that way, not to mention the yellow hot steel). Look at some self threading bolts to get the basic idea then experiment some.
Proper internal threading boring bars can get a bit expensive.
shars.com - Miniature Internal Threading Tool Holders
I would be hesitant to attempt threading a <1/2" diameter hole manually unless the material is transparent.
shars.com - Miniature Internal Threading Tool Holders
I would be hesitant to attempt threading a <1/2" diameter hole manually unless the material is transparent.
biednick
Member
Lookingat the options I have, I think I'll do better with taps. thanks for all the responses.
Rich L
Member
It's really not hard to find threading tools that will thread inside holes less than .25 inch. e.g. MSC part number 09884503 for an independent tool bit. You can also find this stuff in the Micro 100 catalog. I don't think the Shars indexable tool holder was particularly expensive (this is the way I go) as it will last forever and a typical carbide insert for acrylics and softer metals lasts about as long.
Also, the question was curious as the OP didn't say whether he was talking about a lathe with or without a lead screw. I have a hunch it was without because it's pretty clear on lathes that have lead screw that they can cut threads and the lathe doesn't know internal or external.
Tiny threads in small holes means you really have to manage backlash on a manual lathe and trust your dials.
Good luck!
Cheers,
Rich
Also, the question was curious as the OP didn't say whether he was talking about a lathe with or without a lead screw. I have a hunch it was without because it's pretty clear on lathes that have lead screw that they can cut threads and the lathe doesn't know internal or external.
Tiny threads in small holes means you really have to manage backlash on a manual lathe and trust your dials.
Good luck!
Cheers,
Rich