Threading toolholders

You said "low cost" and to "make a few" pieces. Just grind a bit of HSS to make a threading point.

A bit of HSS held in a boring bar. Or just braze a bit of HSS to a steel bar.

Spend some time at the library, or $15 including postage, and get a copy of the book by the South Bend Lathe Company titled "How to Run a Lathe". You'll be way ahead of the game if you buy the book, buy a bench grinder, and a handful of High Speed Steel cutting bits. Get a pair of vice grips, too. That way you can grind the living crap out of the HSS bits without burning your fingers. You can't hurt the HSS with heat, but it can fracture on it's surface a bit if you cool it too harshly, like when you plonk it into the water when its red hot. All told that should save you at least $60 over the cost of the threading kit you are looking at.

Carbide inserts have their place in the scheme of things, but they are a bit unforgiving for learning to thread with at anywhere from a couple to many dollars each.

Cheers Trevor Jones

Bruce:

As others have stated it is best to grind this sort of tooling yourself.....you save big $$$. And the South Bend book (or a high school text from days of yore) would be a great help.

But, threading in the lathe is the type of operation that's best learned by being shown and emulating it under supervision.

I would strongly recommend that you join a model engineering club, take a night school course, or failing that, locate a friend/neighbour/family member knowledgable in this art. It will save you endless frustration!

Failing all that you CAN do it on your own. Just obtain a text on the subject, study it, and ask any remaining questions on this NG.

Good luck!

Wolfgang

Bruce Barnett wrote:

Yeah, don't waste your money. Grind your own for the OD and for the ID, these are available:

I have that book and several others. But griding a bit for inside threading is briefly covered. Hmm. I guess I can make a boring bar. However, if I want the thread to go to the bottom on the hole, I'd need to upgrade.

Thanks.

That's the bit I was looking for. Thanks!

My questons were mostly related to internal threading. I checked my books for tips on cutting internal threads. I listed the amount of text devoted to this topic in each book:

How to Run a Lathe 1/2 page Running an Engine Lathe Nothing The Care and Operation of a Lathe 1/2 page Machine Shop Essentials: Q&A 3 1/2 pages

The last one, by Marlow, has the most complete information.

Well, it seems you are a bit frustrated???

How about you simply consider how an internal threading is different from external threading?

My first guess is you can't see what the *** is going on. Right? If you agree with that premise, then you isolate part of the problem.

My suggestion is draw yourself a circle the size of the bore before you start threading. (tap drill size) Enlarge to whatever scale necessary to make sense to you. Then working from the centerline, draw the size threading tool you wish to use. You'll have to know in advance how deep the thread is, and the size of the threading tool holder. (I usually mounted hand ground tools into a boring bar) Then you can see that an internal threading tool requires a much different 'end clearance' than doing external. Your drawing should show what kind of clearance needed to prevent the bottom of the tool dragging in the thread. Also, don't forget to allow room for the chips. If you go thru this 'exercise', you'll probably see why so many posters say they grind up their own threading tools from scratch, especially for the smaller threads.

Next consider the necessary clearance required to retract out of the thread. (usually accomplished with the cross feed) Then you can pull out of the thread bore, reset cross feed for next threading pass.

Can't see where to stop the threading pass? Simplest way lacking a trav-a-dial is to set up a dial indicator with enough travel (maybe 1" travel?) to monitor your depth into the thread bore.

You might want to practice boring up against a shoulder to develop the technique of stopping at a predefined depth.

Probably last, but not least, learn how to do external threading first.

Good luck!

Well, my primary question was in buying vs. making a toolbit. But thanks for your answer. I'm archiving it.

================ see MINI BORING & THREADING SET(Reference #BTS & BTS12) at

Unka George (George McDuffee) ............................. I sincerely believe . . . banking establishments are more dangerous than standing armies, and that the principle of spending money to be paid by posterity, under the name of funding, is but swindling futurity on a large scale. Thomas Jefferson (1743?1826), U.S. president. Letter, 28 May 1816, to political philosopher and Senator John Taylor

I make my own, have cut inside threads from 6 TPI to 60 TPI,including some fine threads in holes as small as 0.25 dia. For larger bores I silverbraze an HSS toolbit crosswise on the end of a suitably-sized shank and grind to shape. For the little ones I just use a broken or dull 3/8" endmill as rawstock and grind the whole thing from it. These don't go very deep, but I don't have to go very deep in small holes.

For inside threads I usually mount the cutter upside down and cut on the far side of the work. I can see better that way, and I don't have to reverse the compound angle because it's advancing in the same direction (away from me) that it would for an outside thread on the near side.

I don't try to thread to a shoulder on inside threads. I either cut a relief groove at the bottom, or I bore a bit deeper and put a plug in the bottom after threading.

========================= Also remember that you do not have to thread under power.

It is relatively trivial to rig up a hand crank for your lathe spindle. Makes it easy to come to an exact depth (even easier if you rig a test [dial] indicator stop). Almost a necessity if you are using metric/inch change gears to thread a blind hole.

for one example see

Unka George (George McDuffee) ............................. I sincerely believe . . . banking establishments are more dangerous than standing armies, and that the principle of spending money to be paid by posterity, under the name of funding, is but swindling futurity on a large scale. Thomas Jefferson (1743?1826), U.S. president. Letter, 28 May 1816, to political philosopher and Senator John Taylor

Thanks, Don and Unca George!

=============

Your more than welcome. I like to think this is partial payback for all the help I received when I was starting to learn machining.

One more item if you want to try using a hand crank for threading. Don't ever "back-up" with the tool in the cut. This will have a tendency to break/crack the tip off the tool if HS steel and is almost certain to break or crack it if you are using a carbide tool. Use the cross-slide or top/compound slide the clear the cut before backing the tool out. [I suggest leaving the half nut engaged.]

Also check about using the compound set at 30 or 29_1/2 degrees [for a 60 degree thread] so that the tool only cuts on the forward edge giving the affect of positive rake [equal to the helix angle]. By cutting on only the forward edge the width of cut is reduced by 50% greatly reducing chatter and imporving the thread quality/appearence.

Unka George (George McDuffee) ............................. I sincerely believe . . . banking establishments are more dangerous than standing armies, and that the principle of spending money to be paid by posterity, under the name of funding, is but swindling futurity on a large scale. Thomas Jefferson (1743?1826), U.S. president. Letter, 28 May 1816, to political philosopher and Senator John Taylor

I think this is exactly what happened with my carbide E toolholder, and why I was thinking of getting an indexable set. Harbor freight has a set of 5, including an "E", and I stopped to pick it up (it's been sitting on the shelf at the HF for 6 months - untouched). Well, the store was moving everything around, and put that stuff on clearance. It was gone, dangit! I'll probably wait until they re-stock it, and get the indexable one, or order one from enco. At least when I do something bonehead, I'll have another edge to use.

This I know, although it's amusing to read that 29, 29.1 and 30 degrees are also recommended. I think some engineer came up with the

I'll second that one. It can be quite upsetting to realize that one now has an _extremely_ negative rake tool because most of the cutting edge has just pinged across the workshop :-(

Mark Rand RTFM

Those five-piece sets tend to lack the carbide anvil to support the carbide insert -- and the inserts are too thin, making them easy to break. And the inserts tend to be more expensive than those for better tools, too.

I prefer good (more expensive) insert tooling -- and for threading, insert tooling made for the purpose and for a specific range of thread pitches. The "E" is not usually a good choice -- too much radius on the tip for finer threads -- and not rigid enough for coarser ones.

Good Luck, DoN.

I'm wondering why you are set on carbide tooling? Unless you are cutting hard material, HSS works fine, is more durable, and is a lot cheaper. Carbide is great where one wants to maximize production speed and get long runs with in-spec tolarance before having to regrind and re-locate a cutter. In a home shop where the usual materials are mild steel, aluminum, brass and plastic and production is not an issue, HSS works very nicely. I have a few carbide bits but rarely use them. I have never (in 30 years) cut threads with carbide. I am not a "real" machinist, but I can still make pretty decent threads.

I do use carbide drills for drilling tiny holes in abrasive materials like fiberglass.

I just bought from Enco the cheapest indexed internal threading tool I could find -- still almost $80. The reason I bought it is so I can cut unusual inside threads in relatively small holes. It will fit in about a .310 inch hole. I have a small 90 deg boring bar that I made a HSS threading bit for, but the smallest hole I can thread with that is about .75 inch.

Do you grind a HSS tool for threading that will work inside small holes?

I though about trying to make something from a 5/16 or 3/8 bit, but it seemed like it would take a lot of skill and time to accomplish. It also had potential to go bad from a mistake after a lot of time had been invested.

I'd be interested to hear a description of how to make a tool for inside threading in smaller holes. A link to pictures would be even better.