Myford S7 Saddle/Carriage wear twist and gib adjustment

[Russ BParticipant @russb]

1953 (glass sight) Myford Super 7

[Russ BParticipant @russb]

Ok, I bang on here, I know, I'm just outlining what I have already (hopefully) understood and read on other threads, I don't think I actually ask much of question on this thread, I'm just looking for comments/reassurance I think?

If you can find 5 minutes for a little head scratch please grab a cup of tea, thanks in advance, and here goes!

Well, I thought the Myford I bought was in superb condition but I'm seeing conflicting info, the front and rear shears deviate a minimal amount in width and thickness from factory standard, and the carriage travels just by pushing it forwards and backwards the full length of the bed – ever so slightly tighter near the tailstock but oddly the apron fouls the leadscrew bearing block – too close but beautifully even, free and smooth – with my DTI clamped to the bed and resting on the front edge of the cross slide about 4" from the lathes centreline and with one hand grabbing the front of the cross slide, one on the back bearing down and twisting left/right with very firm force I get no more than 0.11mm of movement on the needle, locking the carriage reduces this to 0.7mm and moving towards the tighter end and locking reduces unclamped movement to 0.8mm – its pretty dam smooth, consistent and deflection free IMO despite being so free to glide about – I could reduce this figure as I can feel some rocking in the crossslide but its minimal – I don't have to time to go over the adjusting procedure again but I could get it better

I have set up the carriage gib by adjusting the first 3 screws which bear on the short inner hidden fast side (fast side bears on the inside face of the front shear, ie narrow guide) first by adjusting the outer 2, then bringing the centre in snug, and then finally adjusting the 4th one at the tailstock end gently so as not to twist the carriage or wear the corner off the fast side at the tailstock end.

Now I did notice when checking for the common "twist" on these narrow guide Myfords that the gap between the rear face of the rear shear and the carriage was slightly uneven from left to right but almost spot on, Further researching and reading Nigel B's comments in the thread "Lathe Turns Convex" and following various links here and there – points towards the general consensus that this gap should measure 0.0625" (1/16th" or 1.5875mm)

Measuring in metric, but talking in imperial for consistency with the community and past threads, I have a gap of just 0.014" aka 0.35mm on my metric gauges (headstock end) and 0.010" – 0.025mm tailstock end. this gives me 0.004" – 0.1mm deviation which I feel is exceptionally low/evenly worn, could anyone confirm this?

Now if the gap is supposed to be 1/16th – I'm obviously a very long way off – indicating that what appears to me (a novice) to be an exceptionally good condition, low wear machine and "straight" machine is actually very very worn albeit evenly?! this explains why my apron fouls the leadscrew bearing block at the tailstock end – I thought this was uncharacteristic of the general design and build quality but cracked on as it was all so nice and smooth……..

I'm just a bit confused, I don't have any large diameter stock or a faceplate to run a DTI on, I do have a very nice surface plate and a 150mm length of 75×12 mild steel flat bar – I'll grab that in the 4 jaw if I can, and give it a skim but I expect it to turn nicely given the carriage gaps described above and hopefully slightly concave – blue on the surface plate will be the test and given its long and thin I can probably slip a feeler gauge under it in the middle and quantify something – maybe

Has anyone seen a machine "this" worn before? – I'm thinking perhaps it was converted to wide guide and the 1/16th strip has fell out, or perhaps someone has scraped/corrected the fast side and took a to much out of it…….. I don't know – but now after gib adjustments its running better than it ever has….. happy and worried at the same time!

Thanks for reading – what a long thread…….

Edited By Russ B on 09/09/2014 12:53:54

[Chris TriceParticipant @christrice43267]

If you loosen the bolts holding the apron, wind the saddle to the the less worn tail end and then retighten the bolts, you should find it more consistent all the way along.

[Chris TriceParticipant @christrice43267]

The easiest way to measure any wear on the bed is use a micrometer to measure the distance between the inside shear and the outside shear along the length of the bed.

[CotswoldsPhilParticipant @cotswoldsphil]

I've just measured my ML7, I've had it nearly all of it's life – well from 1969 (1965 vintage) I know it has little wear 0.0005 width and thickness variation – 6 inches from chuck to tailstock end. The vertical gap between the rear shear and the saddle casting is 0.022 both ends. 1/16 sounds too much. The Super 7 (1972 vintage) which will replace the ML7 has 0.014 gap both ends and is in a likewise condition. Someone may tell me that it is wrong to have equal measurements bearing in mind the the lathe should face convex.

CotswoldsPhil

[Russ BParticipant @russb]

hmm, very reassuring thank you CotswoldsPhil, it's nice to know my numbers are not unusual since you have 2 similar machines there – I assume your super 7 is before SK108892 as from that one onwards they were all wide guide's using a slightly longer casting (so I'm told )

Chris, thanks for the Apron advice, I will do just that, I didn't realise it would float – I wrongly assumed it would be keyed or doweled to the carriage!. I also notice on the parts diagram a gib strip for the half nuts – looks I need to read up on aligning and adjusting that too.

I'm not sure I grasp if your referring to the front or the rear shear – or a combination of them both.

From what I gather the outside of the rear shear (ie the one at the back looking away from the operator) shouldn't have been touched on a pre-1972 narrow guide machine like mine so I will use that as a reference to gauge wear on the inside and outside of the front shear.

I read this before I bought the machine, and found it very useful, I'll re-read it **LINK**

 

Edited By Russ B on 09/09/2014 14:17:49

Edited By Russ B on 09/09/2014 14:18:20

[Chris TriceParticipant @christrice43267]

Early Super 7’s and later Super 7’s used different vertical faces of the front and rear bed shears for the saddle to slide against. Whichever version you have, two of the vertical faces will be (should be) unworn and the other two subject to wear so you have a true datum to measure wear against. Since the saddle tightens as it traverses towards the tailstock (not unusual), there is clearly some wear present. Just measure and compare the width of both shears at the tailstock end with shears at the chuck end. Wear on the top surface unless severe doesn’t have as much impact on turning accuracy so worry about that later.

Edited By Chris Trice on 09/09/2014 16:00:10

[CotswoldsPhilParticipant @cotswoldsphil]

My machines both use the early narrow guide setup ie only the front shear is used, making the rear shear (both vertical faces) potential datums.

CotswoldsPhil

[Russ BParticipant @russb]

Once again, I apologise for the use of both metric and imperial units – I'm sort of used to using both at work with imperial pipe, flanges, fittings and volumes on metric parts and machinery!

Measured at 1 inch intervals, none of the measurements deviate more than 0.015mm (0.00059&quot start to mid to end, most of it in 4" to 9" range peaking at 0.015mm at exactly 6" and that is the front shear width.

Interestingly the unused rear shear is not that accurate, its width tapers down towards the tailstock end – opposite of what I expected. it starts at 30.03mm and tapers down to 30.01mm at the tailstock – so its probably not a good datum but I still think that's pretty accurate.

thickness is 12.67mm the full length front and rear (front where measurable) but does thin out for just a inch or 2 around that 6" mark where it drops to 12.667mm (it was below 12.67mm but not 12.665mm so I went with that )

Overall it still seems relatively good, the "stiffness" I describe is nothing more than increased drag, I can still push the saddle to and fro with my hand – so I absolutely have to lock the saddle when doing any work as it moves so freely – I sort of wish it would be a bit stiffer. I faced a piece of 6" 2×1/2" hot rolled flat bar, I'll measure it flatness once I get some more time in the workshop – I didn't have to time to adjust the apron, another job for another day I think

[Neil WyattModerator @neilwyatt]

I think it's in Improvements and Accessories for your Lathe that J A Radford describes his modification to allow the saddle of an early ML7 to run on the outer shears.

Neil

[Chris TriceParticipant @christrice43267]

It doesn’t sound too bad assuming your measuring is accurate. The next thing would be to check for wear in the saddle, the plain face that slides against the shear. You need to check it’s straight and not worn slightly curved. If it is, it’s still not a disaster. You could have the lightest of remachinings by someone competent or you want to seek out the modification Neil posted.

Edited By Chris Trice on 09/09/2014 22:12:53

[Russ BParticipant @russb]

Chris,

I will go back and double check a few measurements to ensure consistency.

I would really like to fit locking screws to the top and cross slide gib so perhaps I'll do this at the same time I'll align up one face in the mill and then check the other and compare – one to the other and each to the unused rear face while I'm in there.

I'd really like to get things running sweet and nice as I go back to Uni this year (in a few weeks) so summer breaks (if I'm not busy working on assignments) will be the only gaps I get for bigger jobs.

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