Super 7 stiff feedscrews

I recently purchased new imperial top and cross slide feedscrews and nuts from Myford /RDG for my mid 60’s Super 7 to replace the incredibly worn originals.

After fitting both feedscrews and nuts, the operation of both top and cross slides is very stiff (I haven’t adjusted any gib strips). It is worse the more they are screwed in, and in one revolution of the screws, they both seem to have a stiff part and a smoother part. I have adjusted the adjusting collars to provide varying degrees of clearance, with no avail. If I undo the two cap head screws slightly which hold the end plates on, I get an improvement but still not great.

Can anyone offer any advice? Many thanks.

Speak to RDG, sounds like they are not ‘fit for purpose’ so need replacing. Also oil the threads

Tony

Try loosening the end plate screws, and screw the slides inwards to their full extent before tightening them - this will bring the the 'screw bushing as close as is possible to the nut and hopefully help to ensure that the two share a common axis of rotation - sometimes a bit of wiggling / turning to & fro will help to find a 'sweet' spot before you fully tighten the screws..

When adjusting the collars, err on the side of favouring 'free rotation' over 'minimal backlash'..

.

My first advice would be two confirm which of these two separate limited companies you have purchased from.

Although the same persons are involved in both companies, [and the companies may or may not trade with one another], they are distinct.

If you are thinking of ‘fitness for purpose’ … you need to be very clear about the purpose.

Were the items sold as actual Myford parts ?

MichaelG.

Yes, they came from “Myford” in plastic bags with the yellow and blue cardboard headers on, purchased last week for £110 or so the pair.

I have oiled the thread copiously and worked them back and forth a number of times to no avail.

Were the nuts free to rotate on the screws before assembly?

John

.

Thanks for the clarification

MichaelG.

This doesn’t help with your predicament, but it makes interesting reading:

Longer - and with an extra T-slot - the Super 7 cross slide abandoned the loose "gib strip" and was fitted instead with a pair of rigid "gib blocks" screwed into the roof of the slide. The top slide was able to rotate through 360 degrees and employed an inverted tapered spigot mounting instead of a clamp. The micrometer dials were engraved (not cast), had much larger (adjustable) thrust pads and could be "zeroed" without having to slacken a locking screw, a wavy "belville" washer being fitted between the inner face of the dial and the support bracket. When correctly set-up the "feel" of a Super 7 cross and top slide assembly could be almost equal in delicacy to that of a Schaublin precision bench lathe, a point confirmed by several owners of both types.

Ref: **LINK**

http://www.lathes.co.uk/myford/page19.html

MichaelG.

Hi ,

Sound as if you are having similar problems to the Myford lathe in this posting https://www.model-engineer.co.uk/forums/postings.asp?th=173467 , all routes lead back to RGD.

The conclusion  was  on this posting  was

"An update, Myford suggested I return the screw and nut for appraisal, which I did. They detected tightness and suggested it was borderline on tolerance and sent a replacement "original" Myford screw and nut which I fitted today. The replacement is significantly better but lacks the silky smooth action of the metric screw and nut. I can't get it down to virtually nil backlash either.

I am reluctant to concede that it may bed in as I feel it should work out of the box."

Perhaps they just stuck the old one back on the shelf  for re sale!

I don't bother with such things now i just make my own  they work every time that way.

John

Edited By John P on 28/10/2021 08:32:44

You are presumably aware of this … but it’s perhaps worth quoting from the handbook:

When stripping the compound slides for thorough cleaning and lubrication re-adjust the slides without feed screws and screw support brackets, testing the slides by hand motion, re-assembling the feed screw units as the last operation.

[ none of which will help much if your purchased items are out of specification ]

MichaelG.

Micheal, mine does indeed have the two gib blocks instead of strips.

Prior to fitting them, I span the nuts up and down the threads and they seemed fine. With the old feedscrews they were lovely and smooth in action, they just had noticeable slip backwards and forwards.

May have to make a phone call!

Edited By Twf on 28/10/2021 09:16:08

Good Luck

MichaelG.

TWF,

You've not shared just how much backlash that you now have.

To be honest this "With the old feedscrews they were lovely and smooth in action, they just had noticeable slip backwards and forwards". just says knackered.

As someone who has just changed the 1/2" x 10tpi LH cross-slide screw on my lathe (Rockwell Delta 10" by getting a length of Acme rod of Ebay from a nice man in Wales who makes leadscrew nuts. I've now gone from 50 thou lash to 10 thou. All I did was turn a tenon on the new screw, hacksaw the old thread off and drill what's left and Loctite the two together.

It seemed quite stiff holding both nut and screw and turning them, when fitted it seemed much looser, but given what I did is asking for a screw wobble, but there is no tight and loose.

Have you tried rolling the screw on a granite tile or glass plate to see if it wobbles?

You no doubt have Gib wear in the middle so each end may now feel stiffer.

Compare old nut with new.

I have had the same issue when making new nuts for old feedscrews

The nut fits the end of the screw for testing and I put it all together but...

The leadscrew wear is uneven, and it gets really tight towards the handle which is the area with the least wear in the screw

Lathe beds are the same, most of the wear is around the headstock end and the saddle gets tight at the tailstock end

A tight screw will even out over time but it is not ideal

Edited By Ady1 on 28/10/2021 13:59:44

.

But presumably that would have been noticed when following Myford’s instruction

MichaelG.

the problem with the screws which when assembled go tight and slack in one revolution,is possibly due to the threads being rolled and the rolling process is not correctly set up,a nut in a free condition will spin freely down the thread as any wobble would be difficult to detect,when assembled in the lathe the nut and thread are constrained at the mounting points so the nut cannot wobble so the assembly goes slack and tight in one rev. it is probable better to use the new nut and screwcut a new spindle on your lathe.I know that I will get criticism for the following,but I have made a cross slide screw from leaded mild steel and it lasted for around 12 years so far,the advantage of free cutting steel is that a smooth polished thread can be screw cut easily , and subject to the condition of the lead screw it will be surprisingly accurate, That cross slide screw was for a Colchester , a new screw and nut was quoted at £550 plus vat 12 years ago,so that prompted me to make a new screw as the old was badly corroded due to the trough in the saddle which clears the screw was filled with some high performance cutting oil and left standing before I bought it. I cut the screw on my S7 and that screw has been used on a lot of commercialwork with power feed when required.

Have you considered the following,

The nut thread as cut, is not axial to the outer tubular nut extension and therefore upon fitting is causing an out of alignment with the correct leadscrew axis.

Did you loosen the 2BA screws holding the slide endplates, wind the leadscrew fully in and then tighten the 2BA screws?

If you do not do this the leadscrew may tighten as you wind it in as the misalignment then gets progressively worse

TWF if you refer to my earlier post commencing much the same problem whilst the replacement "original Myford new old stock " imperial cross slide screw and nut was better than the" new Myford" screw and nut having used the lathe again recently it is inferior to the original metric screw.

I think the old stock item was "work in progress" at Myford before the Nottingham factory closed, the Myford process was one of selective assembly and maybe lapping.

As I mentioned in my post I converted my machine to imperial, replacing all components, the top slide was perfect. I have since fitted DRO and will probably revert to the metric feed screws as they were as good as anyone could reasonably expect.

Robert Butler

I bought some German made spray oil on ebay and tried it on the extremely stiff leadscrew and nut for the drill mill X axis. It was unbelievably good after having removed the bed several times without being able to sort out the problem.

I can recommend this:

WURTH HHS 2000 highly adhesive synthetic lubricating oil.

.

I’m glad you mentioned that,Robert

I can’t find it on t’internet, but I am almost certain that I have seen the lapping process ‘officially’ documented by Myford [Beeston] sometime, somewhere.

MichaelG.