Myford S7 large bore apron and half nuts.

[brickyParticipant @bricky]

Boring on the lathe I realised that I hadn't measured the bore of my chuck and having been boreing for some time I didn,t want to remove the work.I decided to fit the depth stop,leaving it loose so that when I got to depth I would lock it.I put in the wrong depth rod and the lathe came to an abrupt screaming halt.I had to saw the rod out to release the half nuts,the pressure was so great the saw kept jamming and had to cut a second slot into the firat and this closed up ,I released it with a sharp tap with a hammer.The lathe runs well but the top half nut dose not seat properly and the feed keeps stopping.I wish to remove the apron to discover what is wrong, but before I do I want to know the pitfalls I might encounter.I need advice please.

[brickyParticipant @bricky]

[JohnFParticipant @johnf59703]

Bricky, are you using the 6 station bed stop ? or a similar "dead" stop? It sounds as though you are and have run the carriage into the stop which is a disaster on this type of traverse — there are no shear pins or clutches as a fail safe. I made a stop that has a safety feature to prevent this.

If my supposition is correct you will probably have damaged the half nuts and maybe other items ?? hopefully only the nuts which will be Mazak if the same as the earlier machines.

What you need to do first is withdraw the lead screw, to do this [assuming it is the same as the power cross feed S7] first remove the large gear inside the gear train and the banjo etc then withdraw the dowels and screws from the RH end of the leadscrew support bearing — you need a tool to do this in the form of a miniature puller to extract the dowels. At this point the lead screw can be withdrawn left to right.

When the lead screw has been removed you can remove the apron — if memory is good ! Then the half nuts can be removed and examined. Replacements are available from Myford

Its pretty obvious what's needed as a puller for the dowels and the thread is I think 6BA but if you need to PM me and I have the details in my workshop — I need to remove mine some years ago to do some maintenance on the apron.

Hope this helps John

[brickyParticipant @bricky]

Hi John.

Thanks for replying.I have a dead stop fitted and I am sure that it is the half nuts.I am glad that you posted as I didn,t know that I had to remove the leadscrew before attempting to remove the apron.The dowels have been removed by the previous owner or Myfords and not replaced as I was informed by the ex Myford fitters who seviced my lathe which I purchased from the Myford closure sale.I have had a straight edge on the leadscrew to check I have not bent it but without removal of the apron I can,t be 100% sure .Thanks again John.

Regards Frank

[JohnFParticipant @johnf59703]

Frank, there is often a small and I do mean small bias in the straightness of lead screws — we are talking under 0.010" and generally less than 0.005" so don't be too critical. I would replace the dowels at the tailstock end BUT do use ones with a threaded hole for extraction in the future if need be. The thread in mine is 4BA but should you make some form say silver steel any suitable thread will do.

I also removed the compound and cross slide before removing the apron — take care re- installing the cross slide with the power cross feed, easy to do but make sure you get the key in the gear lined up as you screw in the feed screw.

John

[brickyParticipant @bricky]

John, Rang RDG today referance the availiability of the half nuts and a new leadscrew if needed,Yhey do not have them in stock and when enquired when they would have them he said that he didn,t know as they were getting a new supplier and he said that he had no idea when they would be in stock.Then they wonder why we buy from abroad.I have not dismantled it yet as I am going to familiarise myself with the gear box before I start.Thanks for your advice and if I get into trouble I will PM you.

Frank

[JohnFParticipant @johnf59703]

Frank see your messages John

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