Thread chart, help needed.

[Boris Ludwig]

Pitches and feeds chart on the Hercus 260 now has me baffled.

Last week I cut a M~14 x2 thread single point with no hassle. According to the chart #4 is engaged with B lever in position. Stud gear 18 was left on as I interpreted the chart that it can be either ~18 or 45.
See the chart.
Attachment 390189
20201223_161432.jpg


Beautiful thread that mates perfectly with a corresponding M~14 x2 internal cut with an M~14x2 tap.

20201216_122023.jpg

Today I tried to cut a ~1.5 thread in a brass sleeve. I checked my settings made a scratch pass. To my surprise, the scratch didn't confirm ~1.5 but ~ 0.8!

So I changed the stud gear to the 45 and got a scratch pass done that confirmed ~1.5 on my gauge.

So I proceeded to cut the thread. Being a little fine on brass it was difficult to see but as I proceeded it seems the peaks were cut as the valleys were broadened. It seems that each pass cut in the same pattern but not in the same position. I hasten to add this happened on my first attempt to single point a thread as I had the compound set at 30° so my advancement of the compound cut off the thread in the same way as this shows on each pass. Since then I have learned to set the compound angle to 60°

20201223_161415.jpg

So my questions are 2.
1. Why did the first scratch pass not conform to ~1.5 until I changed the stud gear from 18 to 45.

2. What am I missing to result in my thread being eaten?

Thanks for any help.

[pipeclay]

From what I can see with your first 2 mm thread at those settings it should cut .75mm pitch.

From what I calculate 1.5mm with 45 stud should be pos B hole 6.

1.5 mm with 18 stud pos A hole 4.

2mm with 45 stud pos B hole 3.

2 mm with 18 stud pos A hole 1.

Not sure how you got 2mm pitch with your first set up.

What gear is on the screw?

[Boris Ludwig]

From what I can see with your first 2 mm thread at those settings it should cut .75mm pitch.

From what I calculate 1.5mm with 45 stud should be pos B hole 6.

1.5 mm with 18 stud pos A hole 4.

2mm with 45 stud pos B hole 3.

2 mm with 18 stud pos A hole 1.

Not sure how you got 2mm pitch with your first set up.

What gear is on the screw?

Pipeclay,

I used a phone to post this before and lost a few attempts so my commentary isn't matching my first photo. The photo of the chart shows the setup I used for the 1.5. I should have written 6 B.

[jack620]

Stud gear 18 was left on as I interpreted the chart that it can be either ~18 or 45.

I've always believed the line between the 18 and 45 is in the wrong place, because there's no way you could get the same thread pitch with two different gears and with the levers in the same positions. I reckon that line should be in line with the line below the "B".

[jack620]

2. What am I missing to result in my thread being eaten?

You had your compound set on the 30 degree mark, which on the Hercus is actually 60 degrees off perpendicular. So when you advanced the compound you were getting too much movement to the left (Z axis). Hence you were removing more metal than you should have been with each pass.

[BaronJ]

Hi Guys,

Whilst I understand the reasons for angling the compound, for fine threads I just set the compound to zero and go straight in it makes virtually no difference to the thread being cut. I also use threading inserts and I believe that they are not intended to be used in an angled condition. All the pictures/illustrations in manufactures literature show them being used by going straight in.

[pipeclay]

Generally makes no difference with inserts if plunging or offset for vee threads.

[Michael G]

I've always believed the line between the 18 and 45 is in the wrong place, because there's no way you could get the same thread pitch with two different gears and with the levers in the same positions. I reckon that line should be in line with the line below the "B".

Agreed. 45/18 is 2.5, so that would make sense.

Michael

[Boris Ludwig]

I've always believed the line between the 18 and 45 is in the wrong place, because there's no way you could get the same thread pitch with two different gears and with the levers in the same positions. I reckon that line should be in line with the line below the "B".

That makes sense and same idea occurred to me but I believed they couldn't have made that type of error and let it pass.

[Boris Ludwig]

You had your compound set on the 30 degree mark, which on the Hercus is actually 60 degrees off perpendicular. So when you advanced the compound you were getting too much movement to the left (Z axis). Hence you were removing more metal than you should have been with each pass.

No, I didn't, I had it at 60', I'd already encountered this issue on my first threading. I agree, it looks similar but that's not it.

[pipeclay]

What method were you using to cut the thread?

[Boris Ludwig]

What method were you using to cut the thread?

The same method I use before. Set the cross slide at zero and advanced the compound. I didn't need to use the thread dial. Something else went on that I didn't notice...

In fact I've made a 1.5 a year ago in aluminum and it was fine. Looking back on my photos at the time I can reconstruct some of the details.

20200121_193204.jpg

Here I can see I chose lever 4 and pos A
20200121_192158.jpg

I even made a threaded sleeve nut for the outside sleeve. It was for an oversized fishing rod reel seat.



I should have checked my past records before I cut the thread. But I'm still no wiser why. I'm going to try again after Christmas and recheck my settings and execution. I could just have over looked something simple that I didn't notice. "Measure twice and cut once!"

[jack620]

No, I didn't, I had it at 60',

OK, well it's not that then. You are correct about not requiring the threading dial, so it's not that either.

The thread on the brass looks a bit like a buttress thread. Did you have the thread cutting tool set at the correct angle to the workpiece? I.e. the centreline of the tool perpendicular to the surface you are going to thread? I can't think what else would cause a thread to look like that.

[pipeclay]

So you left the half nuts engaged and reversed the spindle?

[Boris Ludwig]

So you left the half nuts engaged and reversed the spindle?

no, I disengaged the the half nuts at the shoulder, withdrew the cross slide, moved the carriage back, returned the cross slide to zero, then if needed moved the compound, or a spring pass which meant I left the compound in it's position. I proceeded to cut another pass by engaging the half nuts, etc