# Internal Threading Tool For 7x10 Mini Lathe



## mzvarner (Jul 8, 2016)

I finally have my mini lathe all setup with change gears and new bearings. Im ready to start learning how to thread with them. What do you guys recommend as a worth while internal threading tool? I currently have a QCTP from LMS. The set allows me to use the 3/8 boring bar tool holder or the square/ rectanhular style tools. Pros cons? Advice appreciated.


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## T Bredehoft (Jul 8, 2016)

If you feel up to it, use a piece of 3/8 drill rod, drill a 1/8 hole through the end and put a broken No 0 center drill in it, (locktite or set scsrew), grind a flat on the top and form a thread tool on the end. If it sticks out 1/8, (none on the back) you can thread a 5/8 11 thread.


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## Bob Korves (Jul 9, 2016)

What kind of material are you threading?  If it is mild steel or softer material I would recommend a simple round boring bar with a square or round cross hole to hold a short piece of HSS ground to the thread shape.  Like Tom mentioned, it can all be made with leftover metal and broken tools if you have some.  If it is harder than mild steel, good luck.  I have no experience on a mini lathe, but would expect it to be a fussy job.  Insertable carbide tooling is a lot more expensive and I do not think you would gain any performance using them on a mini lathe.


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## mzvarner (Jul 9, 2016)

Yep.... should have clarrified. I mainly use soft materials, aluminum, brass, mild steel, and occasional stainless. 

If i do make my own threading tool whats the best way to drill the center whole? I have a small central machinery drill press and a center finder ( 45 degree angle that rpughly points to center), but it seems people do not think highly of these.


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## mikey (Jul 9, 2016)

If you bore and thread smaller holes (1/4" to 3/8" or so) and they aren't too deep (maybe 2" deep or less) then the solid carbide internal threading tools from Micro 100 are superb. They are very sharp, very accurate and cut really great threads. They produce internal thread relief tools in the same series and I highly recommend you take a look at these tools.

For deeper holes I like/use a 3/16" Circle Machine CCMI inserted carbide threading/grooving tool for holes up to 2" deep. This will cut an internal thread relief at the bottom of the bore and very nice, accurate threads. Beyond 2" deep I use a Circle Machine QCMI boring/threading/grooving bar to do the same thing. My 3/8" bar will go nearly 4" deep and my 1/2" bar will go 5" deep. There are times when you need to bore a deep hole with a threaded section down deep in the hole. Just as often, that hole will not have a large ID so you cannot fit a big steel threading bar in there so carbide is the only option.

I'm all for making your own cutting tools but making very small but accurate 60 degree tips on very short tools is not that simple. I have taken to using the tools above, which are very sharp and cut quite nicely on my Sherline and Emco lathes with no issues whatsoever.

If you opt to try these tools, get them on ebay. They are stupid expensive retail.


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## T Bredehoft (Jul 9, 2016)

whats the best way to drill the center hole?

In reality, the cross hole should be just below center, so the tip of the tool is on center, but fret not, by rotating the boring bar, the tool can be put  on center nevermind where the hole is. 

It's all a crap shoot, anyway. Its a hobby, not rocket science.


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