Internal threading lathe tool...left-handed

[JackOfDiamonds]

I often need to turn threads inside bores, to make adapters and rings/flanges.

I prefer to do this with the lathe moving from the left to the right, so that the tool doesn't "bottom out" in the bore.

For a right-hand thread, this means you either need to cut with the tool facing up, on the back surface of the bore (side away from the operator), which is my preference, or else cut with the tool facing upside down, and cut on the front surface of the bore (side closest to operator).

I'm having a hard time grinding HSS tools for this because an enormous amount of steel has to be ground away from a HSS blank in order to make an internal threading tool. I have a tool which I made by brazing a little piece of HSS to a bar, but it's a bit crude for my tastes.

Most of the affordable indexable tools I can find for internal threading are right-hand configuration, as a rule.

Any ideas either for left-hand indexable tooling, or how to make such a tool from HSS without having to grind away a huge amount of material?

 

[DocsMachine]

Just ordered and received this one a week or two ago, for my gang-tool CNC lathe. In my case, I'll be using it on the OD, the direction is simply a requirement of how the tools are set up in my lathe. But in your case, turn it backwards with the bar on either side, and it should work just fine.

Doc.

 

[matt_i]

Just general ideas not sure of your resources and or friends.
- use laydown insert upside down - I think Dorian's flips over with a 2 bolt flange (edit lets scratch that one, a 180 rotation of the RH tool doesn't make it a LH tool)
- braze a piece of carbide to a standard cold rolled steel flatted rod or square backer, shape and sharpen the carbide to get the 60 degree form - the HSS is just an edge and doesn't help rigidity, so CRS can be your basic structure and the carbide edge should be better than HSS if not abused.
- wire edm the HSS blank to the shape you need (beg for small job from WEDM shop or friend or send them a few to be done). By hand an abrasive cutoff wheel bulk-removes HSS a lot faster than it can be ground into dust by a spinning stone.
- an inserted tool (is there a LH laydown insert?) just needs the pocket CNC or manually machined, probably easier to make tweaks with a CNC program if its not exactly right the first time out.
- if a friend with a turning center it can chase via RH right to the very end of a blind hole and won't miss.

 

[gorilla]

Not sure what size bore your dealing with could you use an old fashion round boring bar with a brazed carbide threading tool in the end?

 

[JackOfDiamonds]

Well I can't grind carbide right now.

I guess I have a few ideas I'm just surprised this is not a more common thing. Does it actually work to use a tap as a threading tool?

 

[matt_i]

Grind carbide with a "green wheel" in a bench grinder (? not sure if that's an issue) I cobbled together a slow turning 3ph motor to sharpen solid machine-scraper carbides with a 3000grit thin wheel, its a 1/4hp x 3 phase motor running a VFD @ 7Hz.

I suppose if you could fixture the tap (guessing you want to use one flute like a single point tool) but its pretty flexy at the cutting edge and not optimized as to where the "hook" is for your (thinking larger) diameter. So you'd need some flexibility to tweak the rotation of the tap to get it cutting and not rubbing.

Personally I'd get some LH laydown inserts and try to mill the pocket and drill+tap the center hole. Really all you need is 1 good edge to keep the insert from spinning/rotating if you are using light cuts. I'm picturing in my mind you are making camera lens adapter rings and its like a 3.0 inch x 32tpi thread....

I just want to ask how you re-reference the tool for the next chasing pass, do you keep the half-nuts closed the whole time and then enter the tool til it bottoms out, turning the chuck by hand so you don't crash under power, then infeed & power-thread-cut out? Does your compound face away from the chuck as you infeed to form the deeper thread (vs pointing towards the chuck on classic threading)

It sounds like an interesting thing to try someday if I can ever get a day off.

 

[cmandp]

Carbide for a cutting tool is best ground with a diamond wheel. The green silicone carbide wheels more "hammer" the carbide and micro fracture the edge. I do usually use the green wheel to rough out a shape but then I go back and finish with the diamond wheel.

 

[metlmunchr]

Bokum Tool in Madison Heights MI makes hss form relieved threading tools that are the best tool I've ever found for relatively short internal threads to be cut with a manual lathe. A form relieved tool will last darn near forever in a hobby setting because you sharpen it by grinding only a bit off the top of the thread form and rotate the tool slightly to bring it back on center. The rest of the tool geometry remains untouched, so it doesn't vary from grind to grind.

Their website is bokum.com but unfortunately it's probably one of the worst sites on the entire web. You can look thru the general catalog pdf there and see what the tool looks like, but you'd likely need to call them to get specifics. My guess is most all their business is repetitive stuff from high volume turning shops, so they don't pay much attention to the website.

 

[paulsomlo]

Take a look at this: https://www.mesatool.com/product-page/1-2-thread-grooving-tool-id-od

 

[matt_i]

I think ToolFlo.com deserves a look, they have an on-edge catalog of inserts and holders.

The SI-MTHOL series might be what you are looking for....but...costs not listed.

 

[JackOfDiamonds]

After striking out everywhere I ran across this on Amazon. I bought it and will see how it works.

kiKinRite 5/8" SNR0013M16 SNL0013M16 External/Internal Threading Boring Bar Turning Tool Holder with 10pcs External/Internal Threading Carbide Inserts 16IR 16ER AG60 https://www.amazon.com/dp/B098FMJ9VY/?tag=atomicindus08-20

To make the threads, it depends if I need to leave the half-nuts engaged or if I can use the threading dial. If I have to leave the nuts engaged I back the lathe up, the last bit by hand. I use a dial indicator to indicate when the carriage is back to the starting position, and also index the chuck itself using a mark so the chuck goes back to the exact starting rotation. Then I don't make any attempt to take out the slack, and just kick in the lathe on. For aluminum I usually don't use the compound and just feed with the cross-feed usually.

 

[RoninB4]

Carbide tooling, to me, either means high speed, massive production, or difficult material. For single point threading none of the previously mentioned conditions usually apply. Too easy to chip an edge and SFPM is less than optimum for carbide. I prefer HSS for ease of grinding non-standard sizes, clearances, and rake angle. HSS is less susceptible to edge chipping, and thermal fracture during grinding. JMO from my experience. I like using carbide in a rigid machine for some machining operations but single point threading in a manual lather isn't one of them.

 

[MushCreek]

I have a carbide insert threading tool (external) that I use all of the time on my clunky old lathe. It works just fine. The best part is that if you do chip the tip, you can put in a new one and continue working without having to pick up the threads again.

 

[Farrier]

i miss Enco a lot. spent major bucks there back in the day

 

[paulsomlo]

i miss Enco a lot. spent major bucks there back in the day

And their 20% off, with no min and free shipping.

 

[MushCreek]

Enco was the Harbor Freight of machine tools. They did fill a need, though. A buddy of mine had an Enco mill, and was tearing the head apart to work on it. Buried deep inside were four socket head cap screws. One of them had no internal hex in the head. There was a hole, but the hex had never been broached. The mystery was that the bolt was good and tight, and there was no way to get something like Vise-Grips on it. It was down deep, and it took hours to grind sort of a hex on the outside and drive a socket onto it to get it out.

I bought a granite surface plate from them. Less than $300 for a 36 X 48, 1200 lb. plate. That included shipping it from China to New York, and from NYC to Tampa, FL. It was actually very accurate, too.

 

[RoninB4]

I used to live near one of the main warehouses for Enco on Cicero in Chicago. Lots of junk tooling but some things that were decent buys here and there. Still have a set of gauge blocks ($20) I use for less demanding work, hardened 1-2-3 blocks (reground by me), and a few other items. The warehouse closed back in the mid-late 80's and I was sorry to see it go.

 

[ojh]

Why don't you use a tap? If I need a piece of tubing threaded I put a jacobs chuck tool loose in the tailstock, tighten a tap in it and run it up into the drilled hole to be tapped. I'm careful with the feed, let the chuck spin like a tapping head clutch I recon, I've never broken a tap and been doing it like this for 20 years I guess, dunno if I've done 8-32 but do lots of 10-32 and up to 3/4 left & right hand threads. Drill the hole, replace the bit with a tap and loosen the taper on the chuck and run it on into the hole.

 

[JackOfDiamonds]

The Amazon tools worked just fine, as expected for aluminum. I made this lens flange with them, cutting on the front side of the bore but from the left to right. I cut on the front side, because it allows use of the compound rest. I haven't figured out a way to use the compound rest when cutting the far side of the bore.