Identifying the pitch of threading inserts

[Bill PhinnParticipant @billphinn90025]

I was sent five randomly selected external threading inserts a while ago when I bought an indexable threading tool from a well known ebay seller of lathe tooling.

The seller didn’t tell me what inserts were in the package. That didn’t matter for two of the inserts, because their markings identify them, but the markings on the other three aren’t quite enough of a help.

I gather from the appearance and markings that are there that all three are partial profile inserts and two of them are 60 and one 55 degrees. The 55 degree one has Q788 on it, one of the 60s has M412 on it, and the other 60 degree one has no markings on it at all.

Ed. Sorry, I’ve somewhat booboed here, haven’t I? These are partial profile inserts, not full form, therefore the pitch isn’t fixed.But how do I know what the biggest pitch they can do is?

 

 

[Andrew CrowParticipant @andrewcrow91475]

Hi Bill, looking at the radius of the tip of the tool I would suggest that the minimum pitch would be more the question as they all seem to have quite a large tip radius. The maximum pitch would be governed by the depth that it would cut.

Alternatively perhaps you could contact the supplier to see if they can provide more information.

Andy.

[Mark RandParticipant @markrand96270]

AG55 and AG60 are, as you realised, partial profile ‘general purpose’ inserts. assume .5 to 3mm pitch or 48 to 8 tpi. US and ISO threads for the AG60. BSW and BSF for the AG55

Being old before my time (less less the case as the years progress!), a bit of a pedant, and having a preference for Whitworth and BA threads, I’d say that the AG inserts are OK for stuff that really doesn’t matter or in an emergency.

Full form inserts produce a far nicer thread form especially if you are interested in root and crest geometry.

[Mark Rand]

On Mark Rand Said:

Full form inserts produce a far nicer thread form especially if you are interested in root and crest geometry.

+1

Probably 99% of my screwcutting is done with full form inserts. Especially good for Whitworth threads when the proper rounded roots and crests are formed.

Julie

[Bill PhinnParticipant @billphinn90025]

Thanks for your replies, Andrew and Mark.

I wasn’t fully aware there might be a minimum as well as a maximum pitch, Andrew. That’s important to know.

Mark, the two other inserts I can identify are of course identifiable because they’re full-form inserts.

Two threads I hoped to be able to cut at some point soon are 1” BSW and M24 coarse. I can single-point cut a 3mm pitch on my lathe, but not an 8 tpi unfortunately. I tried tapping a piece of 36mm af mild steel hex bar the other day with an M24 tap, having bored out to 21.2mm.

I did it, but it was very hard going, and I think the nut moved in the chuck causing a slight skew in the finished thread.

While we’re on thread cutting, what’s the consensus on which is the better of the two lathe options for reduced laboriousness in single point threading: an ELS or a gearhead lathe?

[Bill PhinnParticipant @billphinn90025]

The full form inserts aren’t exactly unaffordable, so I will bear your and Mark’s advice in mind, Julie Ann.

[JasonBModerator @jasonb]

What about the third option of a couple more change gears to be able to do 8tpi or 3.175mm pitch. It really comes down to how often you thread cut and what you may want that is outside what can be done with change gears. But if you are otherwise happy with your lathe then go with the ELS conversion but bear in mind that just like you a small lathe may find 8tpi hard going.

Myself I don’t thread cut much so am happy to use change gears on the banjo and 100% of threads cut with inserts are partial form, againjust don’t do enough to justify having inserts for each.

Also be aware that partial form inserts need feeding in further than full form

The other question is why did you tap a hole but buy external inserts presumably for the same job? or is it the mating male thread you now want to cut?

[Bill PhinnParticipant @billphinn90025]

Thanks for your reply, Jason.

Getting an extra change gear or two is certainly an option I’d consider, as discussed a while ago in this thread: https://www.model-engineer.co.uk/forums/topic/1-2-x-25-uns/page/2/

The only snags are I didn’t actually find any ebay or Amazon offerings that had the raised integral key-wayed spacer like my gears have (some pointers on where to buy would be appreciated), and trying to get an answer from Ride the Gear Train on what gear or gears I need for 8 tpi in addition to my current line-up (20, 30,40, 40, 50, 50, 60, 60, 70, 72, 80, 80) is proving difficult. Every time I click “find a new gear” after completing boxes 1-5A and skipping number 6 as instructed I just get the error message shown in the screenshot. So, again, some help with where I’m going wrong would be appreciated, for both now and in the future.

The external inserts were obtained 6 months ago basically as freebies with a 12mm external 16ER compatible threading tool. What I’m aiming for at the moment is to be able to do 8 tpi internal with two small projects in mind (adaptor for mounting collet chuck on my woodturning lathe, which has an 8 tpi screw fitting, and making two replacement 1” BSW nuts for a large cast-iron nipping press I’ve got).

My experience with the M24 tap tells me tapping the whole thread from scratch with a 1” BSW tap isn’t really going to be viable and single point threading is the only way to go. I’ve got a 10mm shank 11 size internal threading tool, but I believe inserts of the size needed for either M24 or 8 tpi won’t go in an 11 size tool and I need to get hold of a 16 size internal tool.

One snag with that is that the minimum shank size I can find for an internal threading tool in steel that will take 16 size inserts is 16mm, which I fear may not allow me to get the tool down low enough to find the centre height on my 210 lathe. A 12mm shank internal threading tool for 16 size inserts is available in carbide at APT, but it is almost a three figure sum.

[JasonBModerator @jasonb]

Looking at that older thread I think you actually have a 3mm leadscrew as the gear train assuming a fixe d40T on the spindle for 1mm pitch is 0.333 and that for 1.5mm is 0.5.

So try this.

40T spindle

Any gear as an idler on the first stud

35T being driven by the idler and a 60T driver on the second stud

65T on the leadscrew being driven by the 60T of the pair above.

maths is

40/35 = 1.143

60/65 = 0.923

1.143 x 0.923 = 1.056

Therefore 1.056 turns of the 3mm leadscrew per turn of the work = 3.167mm pitch not far off 3.175 (8tpi)

Just needs a 35T gear, you will  have to come up with  away to cut a keyway or you could just pin the new gear to an existing 40T

[Bill PhinnParticipant @billphinn90025]

Thanks, Jason.

The tooth count on the fixed spindle gear on my 38mm bore lathe is 60 (though I think it may be 40 on the 20mm bore version) and the leadscrew is definitely 2mm pitch.

[JasonBModerator @jasonb]

Same combination will give the same result.

60/35 = 1.714

60/65 = 0.923

1.714 x 0.923 = 1.582

1.582 x 2 leadscrew = 3.164pitch

[Bill PhinnParticipant @billphinn90025]

Just an update.

35T and 65T gears 3D-printed for me in PLA and installed.

Looks like it’s going to work just fine.

Thanks to everyone for your help and guidance.

[old martParticipant @oldmart]

I only stick to full form inserts in ACME and trapezoidal, unless the thread is finer than 18tpi or 1.5mm

[Author]

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