Help. Myford Super 7 threads not equal gearbox chart

I am a novice. I inherited my Dad's Myford Super 7. I used this as a youth with my dad, but now I'm really getting into it. I know how to read my gearbox. I am trying to get 18 TPI. When I try using 2B, I get 21TPI. 1B gives me 19.3 TPI. 8A gives me 17 TPI. I measured both with a thread gauge, and manual calculations from 3" test runs. What am I doing wrong? No setting equates to what it should.

Oh, and how in the dickens do you grease the fitting that is too small to accommodate a grease gun? I ended up pulling the spindle out and packing it by hand. Is there such thing as a british grease gun that has a smaller head?

I don't have a Myford but I do know that what looks like a greasing point might be an oiling point. Do not apply grease unless you know for certain it is a greasing point.

Martin C

In some sense, you are starting in the middle of the problem, not at one end or the other.

Begin with the leadscrew. The gearbox settings are based on an 8tpi leadscrew. It is vanishingly unlikely that this is incorrect, but is so easy to verify (hold a rule against it and check there are 16 threads in two inches), it is worth taking the time to eliminate it from your enquiries.

Now concentrate on the gearbox. You tell us 2B, which we assume is supposed to be 18tpi, gives you 21tpi. Work out the ratio between supposed and actual. Do so for the other two piches you mention (you only tell us gearbox settings and results not what those settings are supposed to represent). If the ratio between actual tpi and gearbox-set tpi is the same, it is something upstream of the gearbox causing a consistent error.

Open the rear cover of the machine. Check that the gears installed between gearbox input and spindle are sized (tooth count) and meshed (what is driving what) as per the manual.

Welcome to the forum, first point the nipples are exclusive for oil NOT grease, if you have greased them better to strip down, clean and re lubricate with oil.

Regarding the gearbox I have attached a link to a pdf document file for full instructions and use of the gearbox. From what you have said none of the gearbox TPI's are correct so the first place i would look is the main spindle and tumbler reverse gears -- make sure they are the correct tooth count.

https://groups.io/g/myfordlathes/files/s7gbox2.pdf

Another interesting post on here

https://www.model-engineer.co.uk/forums/postings.asp?th=86738&p=1

John

1B (16) cuts 19.3 TPI error = 1.206

2B (18) cuts 21 TPI error = 1.167

8A (14) cuts 17 error = 1.214

Which says to me that the mandrel input gear is a factor of 1/1.2 smaller than designed.

My recollection is that the input gear should be 30 teeth (someone confirm please?), divide by 1.2 gets you 25 teeth.

So count the teeth on the first gear of the changewheel train, driven by the tumbler gears. I'm expecting it to be 25 teeth.

Fix is to remove the compound gear, the outer one separates on a keyed bore, swap it for 30T. The manual explains in more detail.

Now try any gearbox setting, you should find your TPI matches that shown on the label.

HTH Simon

It's worth checking that the tumbler stud gear (the one concentric with the tumbler train output gear) has 24 teeth.

It sounds like you have the wrong stud gear on the tumbler. Perhaps it has a 21 or 22 tooth fitted? 21 would be more normal to find there but it doesn't quite fit with your selected vs actual TPI results.

Have a look in the spares box for a 20T gear and fit that, it should correct your issue.

Thank you Brian, and good morning. I was hoping you would chip in with the rights of it soon.

If I adjust my arithmetic with a broad smile as if nothing was ever wrong I suggest Matthew has a 20 tooth gear (24 / 1.2) on the mandrel.

He's cutting more TPI so the leadscrew is running slow, hence the gear he's got driving the gear train is smaller than the one intended.

Apologies for the confusion.

Best rgds Simon

Edit - at least I could spell the OP's name right!

Edited By Simon Williams 3 on 09/07/2023 10:40:20

You're not the first of us to be caught out by oiling nipples

they use these kind of pumps

edit: you can get grease out by pumping air through first

Edited By Ady1 on 09/07/2023 10:40:10

I stand corrected the gear should be 24 not 20. A 21 in place of the 24 would give the error the OP is seeing.

DC31K thank you, I check the lead screw and it is 8 TPI, so we can cross that off the list. I will start to check everyones input this morning, and in the mean time I will attach a few photos. Wow, that is an oil nipple? ok.

It looks like I have a 21 in place of the 24. I'll be dipped. Thank you guys for the help. This place is great! I've spent two months learning how to cut threads. This has been quite the boggle. Simon, Chris, Pete, Brian, Ady1, you guys are the Best!

Matthew the 21T gear would have been fitted by your father for the cutting of metric threads, so keep it handy.

Have we got to the bottom of this yet? By which I mean - on the basis of this additional info from Matthew - I don't think the input gear is the only consideration.

If Matthew's diagram of gear numbers is correct, there are some odd looking gear ratios in the gear train.

My understanding - based on my old MK1 S7 - is that the final gear is 72 teeth, the two idlers are each 51/17 (ie 3:1 each giving a 9:1 reduction for the fine feed, a 1 : 1 straight through for the threading application) and a 24T (not 30T, thanks Brian) on the mandrel as the input gear.

As I say, if Matthew's hand written sketch is correct those gears won't do what we're expecting.

The 45 T gear as the first driven doesn't look right, isn't this a 30 with the 24T (mandrel gear ) compounded to it. Does this iteration of the S7 have a 45T gear on the tail end of the spindle? On my older machine the gear on the tail of the spindle is a 30 T.

And having a 70 T gear driven by a 21 on the g'box input shaft doesn't look right at all.

Any thoughts?

.

This is not proof … but it’s supporting evidence

**LINK**

https://www.lathespares.co.uk/myford-oil-nipple-raised-1-4

MichaelG.

Mattthew, + 1 for the (corrected ) advice above. It seems farirly clear your father modified the change wheel layout , probably to cut metric threads as suggested by Pete above.

If you rearrange the change wheels as in the advice above or in your handbook, then all should be well. there is almost no chance of a fault in the gearbox itself, it's just a matter of arranging the right wheels into the right order. The wheels are designed to be able to be rearranged to enable the lathe to cut a wide range of threads.

Possibly the first thread to test the corrected arrangement on is 8tpi as all the numbers should cancel and end up with a 1:1 ratio between spindle and leadscrew.

+ 1 from me for reducing this to very first principles, as everything points to your Dad doing something "off piste"

If you strap a Sharpie to the tool post you can mark out an erasable thread without cutting metal at all.

Do let us know how this turns out.

Rgds Simon

Well, I think you have figured out the problem. I will take off all gears, count all teeth...again, and set back to the original. I dont know why my dad had a metric configuration setup. He was building a sterling steam engine before he passed. Let me get my shop clothes on and I will start at this. And maybe go to the store to get an oiler. Thanks to everyone, I thought only the little oil cylinders needed oil. So, I'll be off to the store to get an oil tube. Oh, and then I get to loo forward to cleaning out everywhere I greased. That should be fun. I think the big gear is a 72, not 70, but I will count again. I love the sharpie idea, I will waste less.