Threading inserts - why different sizes? - Model Engineer

Looking again at the inserts (eg here https://www.shop-apt.co.uk/metric-iso-external-threading-inserts/16er-175-iso-t300-external-threading-insert.html – usual no connection, they are quick and reasonably priced). They have what looks like a 'parallel' cutting edge, would I be right in assuming that it will start cutting the OD if I try to cut beyond the thread depth?

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Which suggests a coarser pitch insert will cut finer threads no problem?

"Full Form" inserts have the correct rounding for the crests and valleys so are size specific, "partial form" are not rounded so will cover a range of pitches per insert but you may need to knock the corners off the crests with a fine file

Have a look at Cutwell, they show the range of pitches covered by partial form inserts here

Edited By JasonB on 20/11/ 12:39:54

There are two basic types of indexible threading inserts; those specific to one pitch, and those that cover a range of pitches.

Inserts that cover a range of pitches have the correct thread angle, but the root dimensions are set for the finest pitch, and will therefore be incorrect for coarser pitches. In addition they do not form the outer diameter or crest.

Those inserts designed for a specific thread pitch will correctly form both the root and crest for the particular thread pitch.

I screwcut a lot of imperial, mainly Whitworth form threads, and I prefer to use the pitch specific inserts as they give the correct root and crest radii.

For more information, please visit Threading Inserts.

Additional resources:
When to Replace Steering Rack Bushings and How to Check Them？

Note that external and internal threading inserts for the same nominal thread are different, to account for the differences in internal and external thread forms. As in this picture of external and internal full profile inserts for the same thread form, in this case 2mm pitch ISO:

Andrew

One gotcha with partial profiles is that they need a bit of extra infeed over book values for all except the smallest pitch. Due to the point dimensions being set for the smallest thread they are a little more pointed, and so longer, than book size for the other threads in the range.

One of the many reasons I like the Zero-2-Zero threading method is that its a lot easier to sort out what's going on and make corrections for such things.

Clive.

If your doing threading that don't require or can get away without the proper form and tolerance, choose a universal angle as mentioned above which purely cut a V. These will come either 55 or 60 degree designated by angle after the ER or IR number ie IR16 internal or ER16 then A55 A60 etc. Unless Sandvik that use special coding irrelevant to to what all the rest abide by.

Full form will be to the specific pitch ie ER16 1.25 which will be external 1.25mm pitch with correct radius for the root.

Personally do a lot of high tolerance stuff that require every morsel of strength, no play. Full form way to go as each cut takes down the root and o/d.
Major reason I like the set to zero and plunge in 90 degrees, no messing about way is you have a direct measurement of depth going in which will change with every pitch and tolerance.

Best inserts found that cut well and last longer than all others are Iscar and Seco. Do have cheapies from various places and they don't last in comparison by as much as 4 times.

If you want to learn more, please visit our website CNC Cutting Tools.

I'm looking for someone to educate me on the finer points of internal threading. As a baseline, I've never internally thread anything.

I recently ordered some tool holders/carbide-inserts from Aliexpress, and the learning curve on the insert/holder naming conventions was pretty steep. When I looked at the inserts and holders that arrived, I'm still confused.

Some base questions I have are:

Left hand vs. Right Hand internal threading

1. What side of the bore does the tool work? I've ready about inverting the cutter and running in reverse etc. but haven't put any of it into practice. My right-hand holder looks to cut on the left side of the bore, the left hand holder looks to cut on the right?
2. Does your chuck always run in the normal (forward) rotation?
3. Do you thread towards the headstock or away from it?

HSS vs. Carbide (laydown) insert
Pros/Cons?

ACME Threading

1. Internally, assuming a larger bore (1.5" or bigger), single-point or tap?
2. HSS vs. Carbide?

I know nothing -- all opinions welcome -- you can't hurt my feelings.

Bonus Question: My God, you want us to write a book?

I threaded few times internally. Once left hand (or maybe twice).

It is similar to external threading but you see less of what is going on.

Threading is easier and faster with DRO.

Regular threading I always go towards the chuck. I never needed to play with that.

For external threads I usually use an insert. For internal HSS. Mostly b/c most of my internal threads have been small.

With all non-standard "new" insert types as well as "faking standard" to create company proprietary inserts (like Kennametal at $10 per insert or throw your facemill at a wall) I am also confused. Why do not manufacturers put insert size on their tool? They *never* do that. They could put in something like "recommended size TNMG 322" or in metric format or both. On the flip side, why they do not even sometimes put size on a BOX the inserts are in - but "catalog" number. Trying to lock us into their insert brand?

I only own HSS taps and dies both for regular V threads as well as ACME. I assume tapping 1.5"+ with ACME tap would be an issue - I have large V thread taps in 2" and 2.5" so I guess it is possible. Measure the torque needed and post it here, better yet make a video. Also would be of interest how straight this all went. @kevin.decelles : there are some good you tubes on the threading. This old Tony and Blondihacks and and Vintage Machinery have lots of help.

Left hand vs. Right Hand internal threading

1. What side of the bore does the tool work? I've ready about inverting the cutter and running in reverse etc. but haven't put any of it into practice. My right-hand holder looks to cut on the left side of the bore, the left hand holder looks to cut on the right?

For the internal left hand threads you can cut them with the lathe running in reverse, forward feed and on the far side of the bore. Makes things easier to see. tool facing up

You can cut them on the nearside of the bore with the lathe running forward and the feed running in reverse, but you start the tool inside the bore and you cannot see what is happening as easy. Also you will typically make a few spring passes to finish the threads and it is easier when you can see how much is coming off. tool facing up

1. Does your chuck always run in the normal (forward) rotation?

It doesn't have to - see above

1. Do you thread towards the headstock or away from it?

You can go either way depending on your set up and if you are trying to thread a landing that doesn't go through the whole way

ACME Threading

1. Internally, assuming a larger bore (1.5" or bigger), single-point or tap?

You will need to pretty much single point as a tap would be $$ . I have single point made bushings down to 9/16 ACME LH and single pointing 1" ACME is not too stressful once you are on your game

1. HSS vs. Carbide?

I ground the HSS for the smaller bores and carbide insert for the larger bores. The ACME HSS ones that you can buy are typically pretty expensive if they are one piece construction - like ground into a 1/2" piece of HSS If you are making a dedicated pair from scratch, meaning threaded shaft & nut, make the external thread shaft first & internal nut tread second. Why? Because you have the means to measure the external thread either with 3-wire method or thread mic or whatever else is appropriate to verify the pitch diameter & OD is within class target tolerance. Then machine the nut to fit y creeping up on depth. Reason is there isn't a great way to measure internal pitch diameter. Unless you're Tom Lipton & who probably has some tricked out indicator from a Skunkworks tool shop.

Even if you have a tap & intend to use it, there still could be case for machining the threads to 80% depth & let the tap do the finishing work because the load on it will be substantially less. Here I'm talking big TPI threads or tough materials where taps are spendy. Thanks Kevin for starting this thread. I searched for acme threads and found this one. As much as I feel ok about cutting internal threads, finding the cutter is proving to be a difficult or expensive, if I understand correctly. But I think I might have what I need already, with some coaching....that is where you all come in...

I want to cut 3/4" diameter or more internal acme threads.

Is this a start?

TMX,TMX 5/8 SIR--L11 RH INT THRD BOREBAR,6-821-009,KBC Tools & Machinery

TMX,TMX 5/8 SIR--L11 RH INT THRD BOREBAR,6-821-009,KBC Tools & Machinery
I have watched a couple of Tony's videos on it and in one, he just says he shaped an old end mill and then he brazed it into a piece of steel rod. I am good with everything except shaping of the cutter. Perhaps my sharpening equipment is what is holding me back....a misshapen green wheel . Tony does show a neat little guide. I made one up years ago that could probably be tweaked. Here is what I have to work with currently. Perhaps the next project is sharpening equipment, then the tool, then the job....

Here is my grinder used only for tools. The left is the standard wheel. The right is a green wheel. I have wondered about changing one out for a "white" wheel but then the question of straight, cupped, etc.



If I was to be able to shape a profile, then these are a couple of boring bars. The larger is a 1/2" and the smaller, a 3/8". I would think that the 1/2" would be good for a 3/4" acme tool bit? Wondering about how much tool has to stick out but that info can come from the Machinist's handbook.



I don't have an acme thread gauge. Is that where I am stumbling cause I cannot see how I can shape a tool based on only dimensions. But I suppose if I use the same tool bit for internal and external, then it will work but that sounds like a poor practice.

Suggestions?