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Myford Super 7b lead screw end float

Adjustment

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Niloch16/12/2019 22:05:55
371 forum posts

How critical is the amount of end float on the lead screw of my lathe (1956 vintage)? Mine appears to be excessive or is it?

A thrust collar (part no 75/1115/1) fitted with a cup point socket set screw is fitted immediately adjacent to the right hand lead screw bracket.

Should there be a gap between the two and if so, how much? How is the adjustment made, the presence of the grub screw would suggest that an adjustment can be made.

The manuals by Myford and Ian Bradley are not helpful.

Mike Poole16/12/2019 22:41:04
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Moderator
3095 forum posts
72 photos

Leadscrew thrust
Hemingway do a thrust bearing mod for the Myford leadscrew. I would adjust for minimum float without any tight spots.
Mike

ega16/12/2019 23:05:27
2324 forum posts
190 photos

The adjustment is simply made via the Nyloc nut.

Zan16/12/2019 23:09:41
293 forum posts
19 photos

I don’t think it’s really important as you only drive the saddle in one direction at a time so any backlash is catered for each time you change the direction it’s being moved. It is of course consistent in value. As ega says, adjust the nylock nut in any case

ega17/12/2019 00:29:08
2324 forum posts
190 photos
Posted by Zan on 16/12/2019 23:09:41:

I don’t think it’s really important as you only drive the saddle in one direction at a time so any backlash is catered for each time you change the direction it’s being moved. It is of course consistent in value. As ega says, adjust the nylock nut in any case

However, in their "blurb" Hemingway do say:

"Axial slip of the leadscrew is a common cause of thread inaccuracies. A slight oscillation imparted to the screw will cause a periodic error in pitch. Georg Schlesinger adopted a pass-off criteria of half of one ten thousandth of an inch of slip for the 1920's German machine tool industry. To adjust clearance in the right hand bearing of the Myford Series 7 leadscrew is a difficult balancing act, generally resulting in excessive thrust loads."

What do others think?

Hopper17/12/2019 04:02:24
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5505 forum posts
137 photos

I think it's mighty fine marketing hype for the Hemmingway kit. The rolled thread on the Myford leadscrew was never as accurate as that when brand new and certainly has not improved with age. Then add in wear to the half nuts -- usually considerable by now.

Set it to the minimum clearance you can with no drag and be done with all this overthinking and get on with lathing.

Tony Pratt 117/12/2019 06:53:31
1757 forum posts
8 photos

I had a super 7 for nearly 50 odd years & as has been said previously just adjust with the Nyloc nut to obtain minimum clearance & don't worry about it. I won't comment on the Hemingway blurb!

Tony

Michael Gilligan17/12/2019 07:30:42
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19291 forum posts
960 photos

Posted by ega on 17/12/2019 00:29:08:

.

However, in their "blurb" Hemingway do say:

[…] Georg Schlesinger adopted a pass-off criteria of half of one ten thousandth of an inch of slip for the 1920's German machine tool industry. […]

What do others think?

 

.

I think I would like to see that in context ... Schlesinger was brilliant [*], and his advice was generally very practical.

MichaelG.

.
[*] https://www.gracesguide.co.uk/Georg_Schlesinger

.

P.S. ... I would instinctively distrust anyone who writes “a pass-off criteria”

 

Edited By Michael Gilligan on 17/12/2019 07:36:54

Michael Gilligan17/12/2019 07:46:57
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19291 forum posts
960 photos

With apologies for the digression:

I’ve just found this, which may be of interest to some: **LINK**

http://www.ebhsoc.org/journal/index.php/journal/article/viewFile/15/15

MichaelG.

Bill Davies 217/12/2019 08:05:30
246 forum posts
11 photos

Michael, that was very interesting, and similar to today's situation with products from China.

Bill

John Haine17/12/2019 09:05:01
4272 forum posts
251 photos

It's very easy to add needle roller thrust bearings either side of the LS bracket which allow more preload and give less friction.

Mike Poole17/12/2019 09:09:45
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Moderator
3095 forum posts
72 photos

The Hemingway sales pitch may be a bit over the top but the conversion should offer the possibility of zero float and improved feel, has anyone fitted the conversion? And could comment.

Mike

Nick Hughes17/12/2019 09:38:36
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256 forum posts
143 photos

From the Myford manual, dealing with replacing the Half Nuts, so ignore the reference to the Saddle and Carriage:-

annotation 2019-12-17 092702.jpg

derek hall 117/12/2019 10:08:54
182 forum posts

Hi I have fitted the Hemmingway kit some years ago and it was a fairly straightforward conversion and it is an improvement on the original design.

Regards

Derek

ega17/12/2019 10:24:50
2324 forum posts
190 photos

Michael Gilligan:

Thanks for the interesting links. At first glance they don't deal with "axial slip" and I suspect you are better than I am at locating the context for this.

Derek Hall:

Did you find the ability to reset the hand wheel index useful?

Michael Gilligan17/12/2019 10:37:52
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19291 forum posts
960 photos
Posted by ega on 17/12/2019 10:24:50:

Michael Gilligan:

Thanks for the interesting links. At first glance they don't deal with "axial slip" and I suspect you are better than I am at locating the context for this.

.

Although Schlesinger’s masterwork ‘Testing Machine Tools’ mentions “axial slip” ... I cannot find the source for the improbable number quoted by Hemingway.

My point was that I cannot trust their assertion until I see the source.

... This may take some time.

MichaelG.

Peter Sansom17/12/2019 11:20:42
97 forum posts
2 photos

I have allos fitted the Hemmingway leadscrew thrust bearing as part of reconditioning a 60yo S7. Certainly improved the leadscrew movment, negligible now.

Would say it is a worthwhile modification.

Peter

John Haine17/12/2019 13:13:08
4272 forum posts
251 photos

But just to note that Hemingway charge £27 for £10 worth of thrust bearings and some bits of steel and bronze. There's no need to replace the existing bush so you don't need the bronze; and the end caps to position and shield the thrust bearings can be made from a scrap of 1 inch steel bar that may well be in your scrap box.

ega17/12/2019 14:06:52
2324 forum posts
190 photos
Posted by John Haine on 17/12/2019 13:13:08:

But just to note that Hemingway charge £27 for £10 worth of thrust bearings and some bits of steel and bronze. There's no need to replace the existing bush so you don't need the bronze; and the end caps to position and shield the thrust bearings can be made from a scrap of 1 inch steel bar that may well be in your scrap box.

Fair comment but you also get a beautiful drawing, helpful instructions and support if you need it.

Plus one for making use of the scrap box. I always get a kick out of using up "unusable" short ends.

not done it yet17/12/2019 14:42:30
6438 forum posts
20 photos

​​​​​​£10? As much as that? Fymord charge £3.60 just for a single nyloc nut, so I don’t suppose some consider £27.70 as outlandish for an improvement kit?

At least fymord include postage on that single nut.smiley

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