Author Topic: Metric Thread On Imperial Lathe  (Read 42967 times)

Offline doubleboost

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Metric Thread On Imperial Lathe
« on: December 11, 2010, 03:50:20 PM »
Hi
I have been buisy making a ER32 collet holder
This link should take you to a screw cutting video
Sorry about the geordie accent

Offline DavidA

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Re: Metric Thread On Imperial Lathe
« Reply #1 on: December 11, 2010, 04:49:16 PM »
Nice demo.  I've had to do exactly that on numerous occasions at work;  but without the variable speed reduction to help. Always was a bit nerve wracking as the last turn approached.

Dave.

Offline Jonny

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Re: Metric Thread On Imperial Lathe
« Reply #2 on: December 11, 2010, 06:28:24 PM »
Nice video.

Precisely why i sworn blind i would never buy another lathe that wasnt dual metric and imperial, no faffing around with change wheels.

Had to do similar at work with just the on/off switch and couldnt alter the speed, so used to revolve by hand and power it back.
Luckilly the Harrison i can disconnect lead screw wind carriage back and re engage lead screw again any where for most metric. I try to avoid shutting motor down as it blows a 13a fuse 1 in 3 startups else would wait for motor to stop, start in reverse etc.
Also would scare the crap out of me without a clutch, spindle stop etc.

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Re: Metric Thread On Imperial Lathe
« Reply #3 on: December 12, 2010, 08:12:21 AM »
 :bugeye: very good clear video John  :clap: :clap: :clap:

I nass  what yu saw tarkin aboot  :lol: :lol: :lol:


Rob  :D

Offline Bluechip

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Re: Metric Thread On Imperial Lathe
« Reply #4 on: December 12, 2010, 09:04:01 AM »
:bugeye: very good clear video John  :clap: :clap: :clap:

I nass  what yu saw tarkin aboot  :lol: :lol: :lol:


Rob  :D

I pasted  that into Babelfish, and translated into German ... look what I got

Nass I, welches yu tarkin aboot sah     :scratch:

No better ... but certainly no worse, will have to try Mandarin or summat next ..

我nass什麼yu看了tarkin aboot    :lol:

Ah, that's fixed it. Why didn't you say that in the first place ????  :bang:   

Dave BC

« Last Edit: December 12, 2010, 09:07:04 AM by Bluechip »
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Offline Bogstandard

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Re: Metric Thread On Imperial Lathe
« Reply #5 on: December 12, 2010, 11:08:04 AM »
Very good instructional vid John.

All you need to do now is make a swing up toolholder, and halve everything that you had to do.

But honestly, can't fault what you showed.


Nice one


John
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Offline doubleboost

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Re: Metric Thread On Imperial Lathe
« Reply #6 on: December 12, 2010, 06:18:04 PM »
Thanks John
I will have to make one
I should have videoed the other end
1 i/2 inch 8 tpi internal that was great fun  :D :D :D :D

Offline Ned Ludd

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Re: Metric Thread On Imperial Lathe
« Reply #7 on: December 13, 2010, 01:46:53 PM »
Hi There,
I like your video clear and concise as all training videos should be.
I hope you will forgive a small criticism, have you not set the top/compound slide to 29.5 on the scale? Surely it should be 29.5 to the lathe axis, which should read 60.5 on the scale? If I have misread the situation I apologize.
Ned
EDIT It should be 29.5 to cross slide not lathe axis but otherwise info is correct
« Last Edit: March 08, 2011, 08:00:42 AM by Ned Ludd »
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Offline Blade

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Re: Metric Thread On Imperial Lathe
« Reply #8 on: December 13, 2010, 07:08:46 PM »
Nice video!

Offline Bogstandard

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Re: Metric Thread On Imperial Lathe
« Reply #9 on: December 14, 2010, 02:04:41 AM »

Quote
have you not set the top/compound slide to 29.5 on the scale? Surely it should be 29.5 to the lathe axis, which should read 60.5 on the scale?

You are quite right Ned, but there are actually two ways of doing it, the way John has shown, which gives much better control on the depth of cut, and to me, if doing super fine threads, I would use, but only with 60 deg thread forms, the sidewards feed is a little too much for 55 deg or lower threads, and you risk actually cutting the threads away and so going undersize on the OD.
Or the normally accepted way, which you mentioned, and gives a more aggressive depth of cut, but less sideways feed, and is the way I would use most of the time.

So if you are not into the fine complexities of single point threading, you are quite correct

In fact, I have marked up my cross slide with datums on all main points of the compass, so that whatever type of threads I want to cut, both left and right hand, I can set up the degree scale for the types of threads and tapers I need to cut, as the scale on my compound only goes to 45 degs either way of zero, and so I can't set it to the required 60.5 for 60 deg threads against the normal datum mark.

John
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Offline andyf

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Re: Metric Thread On Imperial Lathe
« Reply #10 on: December 14, 2010, 06:26:31 AM »

Quote
have you not set the top/compound slide to 29.5 on the scale? Surely it should be 29.5 to the lathe axis, which should read 60.5 on the scale?

You are quite right Ned, but there are actually two ways of doing it, the way John has shown, which gives much better control on the depth of cut, and to me, if doing super fine threads, I would use, but only with 60 deg thread forms, the sidewards feed is a little too much for 55 deg or lower threads, and you risk actually cutting the threads away and so going undersize on the OD.
Or the normally accepted way, which you mentioned, and gives a more aggressive depth of cut, but less sideways feed, and is the way I would use most of the time....

John

John, I'm feeling a bit stupid, because I don't understand that  :scratch: . I can see that it gives finer control over the depth of cut. But I should have thought that increasing the depth of cut using a topslide set at just over 30 deg to the lathe axis (rather than just over 60 deg) would result in a thread with its LH flank correct but the RH flank wrong - a lopsided 90 degree thread. If it's not too much trouble, would you explain a bit further so I can grasp how it works?

On the subject of threading, it might be worth mentioning G H Thomas's method of getting to the right depth when using an angled topslide, for anyone who doesn't already know it:
1. Feed cross-slide forward until tool just touches the work (nip cigarette paper if desired). Set both the cross- and topslide dials to zero.
2. Move saddle to the right, so tool is clear of the work, advance the cross-slide by the depth of thread, and reset its dial to zero.
3. Withdraw the tool using the topslide, move saddle to the left, advance topslide until tool just touches the work, and then start cutting the thread in the usual way, applying depth of cut using the topslide. Unless you have a swing-up toolholder, pull the tool clear of the work with the cross-slide when traversing back, and re-advance the cross-slide so its dial reads zero before applying more depth of cut with the topslide for the next cut.
4. The thread depth is correct when the topslide dial has got back to zero again. Of course, if the thread is a deep one, the topslide dial may need to go round more than once before you get there, but when passing through intermediate zeros it will be obvious that the thread is only part formed.

This avoids resorting to things like trig or Pythagoras; I always was a bit of a duffer at sums.

Andy
« Last Edit: December 14, 2010, 02:20:21 PM by andyf »
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Bogstandard

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Re: Metric Thread On Imperial Lathe
« Reply #11 on: December 14, 2010, 12:07:06 PM »
Andy,

I am not putting it off, but I am having trouble with my comp and it might be a few days, but I will definitely get back to you on this one.

I have just lost around ten years, about 300GB, of engineering archive material, and I am trying to get it back. Not my fault, my archive drive (almost new) has decided to say that it is an unformatted disk. So I may be offline for a couple of days.


John
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Offline Pete.

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Re: Metric Thread On Imperial Lathe
« Reply #12 on: December 14, 2010, 12:51:15 PM »
On the subject of threading, it might be worth mentioning G H Thomas's method of getting to the right depth when using an angled topslide, for anyone who doesn't already know it:
1. Feed cross-slide forward until tool just touches the work (nip cigarette paper if desired). Set both the cross- and topslide dials to zero.
2. Move saddle to the right, so tool is clear of the work, advance the cross-slide by the depth of thread, and reset its dial to zero.
3. Withdraw the tool using the topslide, move saddle to the left, advance until tool just touches the work, and then start cutting the thread in the usual way, applying depth of cut using the topslide. Unless you have a swing-up toolholder) pull the tool clear of the work with the cross-slide when traversing back, and re-advance the cross-slide so its dial reads zero before applying more depth of cut with the topslide for the next cut.
4. The thread depth is correct when the topslide dial has got back to zero again. Of course, if the thread is a deep one, the topslide dial may need to go round more than once before you get there, but when passing through intermediate zeros it will be obvious that the thread is only part formed.

This avoids resorting to things like trig or Pythagoras; I always was a bit of a duffer at sums.

Andy

What a great method - I for one didn't know that!

Offline RichardShute

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Re: Metric Thread On Imperial Lathe
« Reply #13 on: December 19, 2010, 07:09:46 AM »

Quote
have you not set the top/compound slide to 29.5 on the scale? Surely it should be 29.5 to the lathe axis, which should read 60.5 on the scale?

You are quite right Ned, but there are actually two ways of doing it, the way John has shown,
<....>

John

John, I'm feeling a bit stupid, because I don't understand that
<....>

[/quote]

Nor can I understand it, given the good description at 3:40 into the video, which relates one of the normal methods very nicely. With the compound slide set as shown the resulting thread form will be like the pic below. The purple is what you would be hoping for, but the saw-toothing on a right flank and reduced peak on a left is what you will get.
It's not a question of a fine thread or otherwise, it's a geometry issue, just at a different scales.

You can leave the compound parallel to the spindle axis and apply half the infeed to that and the resulting tool path is near enough the same as with the rotated compound method (arcTan0.5=26.6deg from the cross slide), but that is not the description here.

Richard - confused
« Last Edit: December 19, 2010, 07:12:27 AM by RichardShute »
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Offline doubleboost

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Re: Metric Thread On Imperial Lathe
« Reply #14 on: December 19, 2010, 08:58:27 AM »
Hi
Richard
I hope these scans will help
I dont fully understand how it works but it is the method i have always used.
I should have stated on the vid that the last cut was made on the cross slide (only about 5 thou )
I have looked at the thread through a magnifying glass and it is as good as the thread on the nut.





Hope this helps
John

Offline RichardShute

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Re: Metric Thread On Imperial Lathe
« Reply #15 on: December 19, 2010, 10:17:40 AM »
Thanks John,
that is the method you described very well in the video and I agree it is one of the widely accepted methods. The query/confusion comes because in the video, you had the compound set so as to have the angle shown in the diagrams as 27.5deg actually set to 61deg.

You seemed to have set the compound at 29 deg from the spindle axis as I tried to show in my sketch, not 29 deg from the cross slide axis as shown in your scans. Maybe I've got the wrong end of the stick because your threads look fine.

Richard
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Offline doubleboost

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Re: Metric Thread On Imperial Lathe
« Reply #16 on: December 19, 2010, 10:47:32 AM »
This scan is taken from the boxford hand book
the angle is 29 deg

Offline RichardShute

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Re: Metric Thread On Imperial Lathe
« Reply #17 on: December 19, 2010, 11:37:53 AM »
Hello John,
Maybe I was making things worse, I'm not worried about whether it's 29 or 29.5 or 27.5 deg, but where the degrees are measured from.

From what you are saying, when your compound slide is parallel to the cross slide, the degree scale must read Zero. On my lathe the compound reads Zero when it is parallel to the spindle axis. There's the difference/confusion.

Richard
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Offline doubleboost

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Re: Metric Thread On Imperial Lathe
« Reply #18 on: December 19, 2010, 11:48:16 AM »
I will go have a look :) :) :) :) :) :)

Offline Pete.

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Re: Metric Thread On Imperial Lathe
« Reply #19 on: December 19, 2010, 12:04:13 PM »
I agree with Richard. It all depends on how the scale is marked up on the lathe. In the video, the compound is angled 30° off parallel to the spindle axis, where it should be 30° off perpendicular. My lathe is the same I have to set the scale to 60° (or actually 60.5) for a metric thread. The way it's set in the vid will give a 91° angle thread rather than a 60.
« Last Edit: December 19, 2010, 12:05:58 PM by Pete. »

Offline doubleboost

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Re: Metric Thread On Imperial Lathe
« Reply #20 on: December 19, 2010, 12:12:32 PM »
That means the boxford hand book is wrong :( :( :( :( :(

Regards
John

Online BillTodd

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Re: Metric Thread On Imperial Lathe
« Reply #21 on: December 19, 2010, 12:17:36 PM »
I agree with Richard. It all depends on how the scale is marked up on the lathe. In the video, the compound is angled 30° off parallel to the spindle axis, where it should be 30° off perpendicular. My lathe is the same I have to set the scale to 60° (or actually 60.5) for a metric thread. The way it's set in the vid will give a 91° angle thread rather than a 60.

Yes, On my Hardinge it is 59°


« Last Edit: December 19, 2010, 12:28:14 PM by BillTodd »
Bill

Offline doubleboost

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Re: Metric Thread On Imperial Lathe
« Reply #22 on: December 19, 2010, 12:22:43 PM »
I am really confused now :doh: :doh: :doh: :doh:
Interesting stuff though
I would go and cut some threads if it were not below freezing in the shop :( :( :( :(

Online BillTodd

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Re: Metric Thread On Imperial Lathe
« Reply #23 on: December 19, 2010, 12:52:38 PM »
I think the difference (and thus confusion) is down to how the trailing side of the thread form is to be cut.

If the top-slide angle is less-than the the thread angle ( i.e 29.5° for a 30° thread) then the trailing edge is cut by the back edge of the tool.

If the angle is greater than the thread angle then the trailing edge is cut by the tip of the tool, (as the back edge clears the face) and is thus defined by the angle of the slide.

If the slide is set to exactly the thread angle, then the cutter just scrapes the edge.


Bill
« Last Edit: December 19, 2010, 01:17:15 PM by BillTodd »
Bill

Offline RichardShute

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Re: Metric Thread On Imperial Lathe
« Reply #24 on: December 19, 2010, 01:06:40 PM »
That means the boxford hand book is wrong

Regards
John

Well it's not really 'wrong', just rather ambiguous. It says '...set at an angle of 29 deg...' which a legalese pedant would argue is not quite the same as saying 'set the compound slide so that the scale reads 29deg.'
It is very poorly worded, but at least we've got to the bottom of it.

Richard
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