I need a internal threading tool recommendation

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fishingreg

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I am new at using a lathe and I need to be able to thread a minimum bore of .500 or maybe a hair less to give me wiggle room since I am new... I would rather the tool not take up .495 of the .500 bore... I only need to thread about an inch deep. I will be threading typical threads in the 24 to 28 pitch range. I'm using a BXA type quick change tool holder. I can use a flat or round bar holder. Does anyone have any recommendations on what I should get?
 
You have several options:
Micro 100 solid bars are very, very good. They cut accurate threads and hold an edge for years. If you need to sharpen them, you just lightly hone the flat on top of the cutting tip with an extra-fine diamond stone and it will keep on going and going. While their initial cost is a little high, they will save you money because it will outlast inserts by many years. I have used these tools for a very long time and I can testify that these are among the best tools of their kind. In fact, the one I use for tiny bores has lasted over 15 years and shows no sign of wear. To actually use these tools you also need an internal thread relief tool to cut a groove at the bottom of the bore. This is the matching tool that would go with the threading tool above.

Personally, if I need to go deeper I use Circle Machine solid carbide bars that take both grooving and threading inserts. These are an expensive option since CM was taken over by Widia. You can still get the bars and inserts on ebay but they are getting harder to find. For example, this one will go up to 2.5" deep but you have to either buy inserts at retail or wait for them to come up on ebay. I only see grooving inserts for it right now but the threading inserts will show up eventually. The grooving inserts allow you to cut a thread relief at the bottom of the bore so they're useful.

The big difference between threading inside a bore vs cutting them on the outside is that you're working inside a bore and your tools will bend and deflect. This requires you to use either a bigger steel bar or a carbide bar and the latter is more expensive. Still, carbide is the way to go in my opinion because the greater inherent stiffness of the bar gives you better accuracy.
 
I have several steel boring bars that use a tool bit. I have bars in various diameters from 3/8" to 1 1/4" Those bars are easy to make if you settle for a round hole for the tool bit. I also have some HSS bars similar Micro 100 Mikey describes. The Chinese internal threading tools with laydown inserts aren't bad.
 
Although I use a lot of carbide tooling, when I need a small or touchy finish, I use HSS cutters. In your case, I have (and saw recently) HSS 1/4 inch cutters that are ground for internal threading. It's only a couple of inches long, but you're only talking about going an inch in, max. The first time I saw one was on a UniMat, when I was still 17 years old. Didn't know what it was then, but it looked cool. I usually, or used to, cut 40 TPI fairly regularly. Instrument grade stuff. Most of that has now been replaced with silicon based sensors. Yeah well... ...

You are talking a little coarser thread than I'm used to working with. The basics are the same, you just need a couple of passes without any feed to smooth out any changes from flexing.

In most cases, I keep the half nuts engaged and reverse the machine to make the next pass. This is not for "precision" or metric threading, it is because my machine is old, and very sloppy. I'm just compensating for my lack of skill when I'm doing something tight.

Bill Hudson​
 
Another option is HSS one piece form relieved internal threading tools, they are sharpened on top only, made by Bokum Tool Co. in many sizes and lengths.
 
mikey said:
You have several options:
Micro 100 solid bars are very, very good. They cut accurate threads and hold an edge for years. If you need to sharpen them, you just lightly hone the flat on top of the cutting tip with an extra-fine diamond stone and it will keep on going and going. While their initial cost is a little high, they will save you money because it will outlast inserts by many years. I have used these tools for a very long time and I can testify that these are among the best tools of their kind. In fact, the one I use for tiny bores has lasted over 15 years and shows no sign of wear. To actually use these tools you also need an internal thread relief tool to cut a groove at the bottom of the bore. This is the matching tool that would go with the threading tool above.

Personally, if I need to go deeper I use Circle Machine solid carbide bars that take both grooving and threading inserts. These are an expensive option since CM was taken over by Widia. You can still get the bars and inserts on ebay but they are getting harder to find. For example, this one will go up to 2.5" deep but you have to either buy inserts at retail or wait for them to come up on ebay. I only see grooving inserts for it right now but the threading inserts will show up eventually. The grooving inserts allow you to cut a thread relief at the bottom of the bore so they're useful.

The big difference between threading inside a bore vs cutting them on the outside is that you're working inside a bore and your tools will bend and deflect. This requires you to use either a bigger steel bar or a carbide bar and the latter is more expensive. Still, carbide is the way to go in my opinion because the greater inherent stiffness of the bar gives you better accuracy.
Click to expand...


Thanks Mikey,

I agree, at this point grinding my own would be a really bad idea, it would look and perform horrible. Maybe one day but not as green as I am now... I ordered a Micro 100, thanks for the help. I like the look of that one and its what I imagined, I just could not find one since I have not learned the sites to check and I was worn out from looking at site after site to only find ones that are made for large bores and nothing under .500 bore to thread. I have also taken note of the tool to cut the relief as I will probably grab one of those as well but right now the piece I am thinking of I think I will drill it all the way through so it won't be a blind hole.

Thanks again,
Greg
 
martik777 said:
These work well and cheaper on ebay but you can read reviews here: https://www.banggood.com/Internal-L...-p-1032420.html?rmmds=search&cur_warehouse=CN

I have a full set of similar insert tools from them and they all work great, especially the parting tool.

You will want to get a thicker boring/threading tool for heavier cuts
Click to expand...

Thank you, I did see those but they were not super descriptive in saying what minimum bore size they could do so I was not sure about them. I appreciate you letting me know you have had good luck with them though because they are inexpensive so I will likely give them a try.
 
No problem. That bar should fit in the typical boring tool holder.

I suggest you download the Micro 100 catalog and go through it carefully. They make bars for almost any boring, grooving and threading application and you should be able to find what you need. Amazon and eBay will usually have them.

Don't discount the inserted carbide bars, especially the carbide ones. As you learn to bore and thread, these will become very handy. The main thing is to do your homework before you buy.
 
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