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Myford quick-change gearbox

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sparky mike27/07/2012 16:47:51
259 forum posts
77 photos

Can anyone explain the workings of the Myford quick change gearbox. I assume that the large external gear drives the input shaft. How does the box connect to the leadscrew shaft? How do the layshaft gears transmit the power from input shaft to leadscrew? I have downloaded the gearbox manual, but it does not show the drive path in various gears.It does not quite make sense to me at the moment, but no doubt it does work somehow !!

Mike.

KWIL27/07/2012 19:37:19
3681 forum posts
70 photos

If you look closely the gears are in an increasing number of teeth and you merely shift an intermediate gear along the shaft picking up in order. The lever on the top switches between various clutch drives. Easier when you have one in front of you.

sparky mike28/07/2012 07:03:39
259 forum posts
77 photos

I now know why the operation of the box seems impossible. It turns out by looking at other box photos that are for sale, that mine is different !! On my box, the lead screw does not pass through the box, but ends in a blind hole in the right hand side of the casting. The drive is taken from the other shafts by three gears that are on the right hand face, outside the box , where there is also an alloy cover, which in my case is missing. I am now wondering how many more parts are different to the normal box ?

Mike.

Swarf, Mostly!28/07/2012 09:19:13
753 forum posts
80 photos

Hi there, Mike,

Is your gearbox a 'made in Beeston' box? It would be helpful (and interesting) if you could create an album here and upload a couple of photos to it.

Laurence Sparey designed a Q/C gearbox for the ML7 and drawings for it were sold by the ME Plans service at one time. I've also heard of a gearbox kit being sold by one of the third party accessory firms, can't remember which one. Maybe your box is one of those.

If your box WAS made by Beeston Myford, maybe it is an experimental prototype that 'escaped' from the factory.

Best regards,

Swarf, Mostly!

John Stevenson28/07/2012 09:53:59
avatar
5068 forum posts
3 photos

You have the early Myford box, later ones had the leadscrew go inside and did not have the drive train on the right.

See here.

**LINK**

John S.

sparky mike28/07/2012 10:37:30
259 forum posts
77 photos

Hi John,

Yes that is the one. Certainly had me mystified ,as I could not figure out how the lead screw got through the box, going by the later manual !! If most of the parts for the early box are the same as the later one, I stand a chance of getting this one back in one piece. On the picture on Tony's lathe site, I believe that one of the gears on the right hand end of the box is just an idler and is held on to the end of the nine gear shaft by a washer and screw. If I could find out the number of teeth on the two corresponding gears, then the idler could be worked out from those.

I don't know how many early type boxes were made, but the serial number on my box is OC 1802 or possibly QC ****

Mike.

Swarf, Mostly!28/07/2012 12:22:47
753 forum posts
80 photos

Hi there, Mike,

Mystery solved!

John, thanks for that link. I've browsed the Lathes site a lot but I must have missed that page. I had encountered references to early boxes having unhardened gears but I'd always assumed that the layout of the gear-trains was the same for both early and later boxes.

Thanks again,

Best regards,

Swarf, Mostly!

David Littlewood28/07/2012 12:51:37
533 forum posts

The third party box mentioned by swarf could have been the kit marketed by Hemingway:

**LINK**

David

sparky mike28/07/2012 17:03:48
259 forum posts
77 photos

If the internal gears are the same on both boxes, then the same gearing must be employed to take the drive from the layshaft to leadscrew in either type of box or else the screw cutting will not be correct. Admittedly, the two driving gears could have more or less teeth, as long as the ratio was the same.(The idler gear as said before does not matter as long as it fills the gap and meshes correctly.

Perhaps someone can tell me how many teeth are on the gears in question in one of the later gear-boxes. At least this will be a start and something to go on. (Unfortunately, the pictures of the gearing on Tony's site are not sharp enough to cound the teeth on the right hand end of the box.)

The electric motor has been stripped and cleaned and checked out and is now in primer. I will have this part working before the lathe is anywhere near ready !!

Mike.

John Stevenson28/07/2012 17:33:21
avatar
5068 forum posts
3 photos

Mike, do you have any of the gears ?

Failing that you can count the top one easily, I make it 18 T

If you can now measure centre to centre on the holes for the other two gears it will be easy to work out what gears are needed.

John S.

sparky mike28/07/2012 19:13:00
259 forum posts
77 photos

Hi John,

No I don't have any of the gears on the right hand side of the box. However I also make the top gear 18. The middle is debateable at 32T and the leadscrew possibly 20T. Tony at lathes uk does the manual for the early box, so I have emailed him with a view to buying it. Could save a bit of time in the long run.

Mike.

sparky mike29/07/2012 18:11:21
259 forum posts
77 photos

I have now had a chance to measure the gear centers. It is 1 3/16" either side of the center gear.

If my calculations are correct, the top gear 18T (if that is correct size) , would measure around .956" over the top of the teeth. As the hole centers are equal, it would make sense that the small leadscrew gear is also 18T. If that is correct, then all that is needed is to select an idler gear for the center position that meshes correctly with the two smaller gears. Any comments welcome.!!

See photos on link below. There are some before and after pictures of the lathe bed. It is only in primer at the moment, but it is looking a lot better than when I purchased it. The slides are covered in masking tape while it is being painted.

**LINK**

John Stevenson29/07/2012 19:27:26
avatar
5068 forum posts
3 photos

1 3/16" =1.1875 take away half of the PCD of an 18T gear at 0.450 and you are left with 0.7375

Muktiply this by two and you get 1.475 which doesn't match up to any gear.

Now if we do the sums again with a centre distance of 1.200" which is only a bit bigger and probably more correct we get 1.200 - 0.450 = 0.75 x 2 = 1.5" which equates to a standard 30 tooth gear.

Try measuring again a bit more accurately and I'm sure you will get 1.200"

John S.

sparky mike29/07/2012 19:49:13
259 forum posts
77 photos

Hi John,

I will find some rods to fit the bores and measure with a micrometer.

Mike.

Alan Worland29/07/2012 19:56:36
247 forum posts
21 photos

Mike,

I have the same box as yours and just been out to remove cover and I counted 18 tooth gears either side of a 30 tooth idler - hope this helps

My box is s/n QC 2268 and is mounted on bed s/n K16170 and was purchased assembled by Myfprd 30/3/1951

I think the internals are the same as I had a broken gear (20 tooth I believe) and obtained a replacement from Myford - and to be honest I didn't even realise I had the early box till I read your post!

I guess you could obtain the correct tooth gears fromm a screwcutting geartrain and adapt?

Alan

sparky mike29/07/2012 20:32:06
259 forum posts
77 photos

Hi John,

Now re-measured and they came to 1.203 and 1.180.

However, Alan has kindly posted the gear details above so I can now find some blank gears and bore them out to suit. Possibly some of the stock Myford gears will fit or adapt. The 18 teeth gears will need the keyways, but I think that the idler gear has a plain shaft.

Mike.

DMR29/07/2012 22:17:43
136 forum posts
14 photos

Mike,

You are not getting the full story. So before you get in too deep......
In no particular order:
1. The last gearbox of the type you have was Serial No. QC (for Quick Change) 2500. QC2501 was the first "modern" one.
2. It is thought that many early gearboxes were retrofitted in the factory with hardened cogs, but no records were kept. Also quite possibly from some point before QC1950, hardened cogs were fitted as standard.
3. The leadscrew on your none-gearboxed machine has quite probably got a different plain diameter at the headstock end, as in smaller than what you require.
It must fit the hole in the gearbox casting closely for obvious reasons.
4. It is somewhat trickier to align the gearbox with the leadscrew, but it must be done and done carefully or the hole in the casting for the leadscrew becomes worn. The "modern" box is almost self aligning as it goes right through, but it still needs doing.
5. To align the gearbox properly, you need a spacer strip between the gearbox and the top two fixing screws along the bed shear. It is just a flat strip with two holes in, but I have no idea what the thickness is. That is a left over from the earlier ML7 fitting.
6. Your gearbox runs at half the speed of the "modern box" to cut the same thread. That is to say, your output gearing at the right hand end is 1:1, whereas the modern box is 2:1 at the left hand end. There is no chance of you altering the principle to be the same as a modern one as you won't make it fit!
7. A consequence of this that you also need a 12/30T FINE FEED TUMBLER GEAR A1974A/1 as it is termed on the Myford/RDG website to drive the standard fixed quadrant geartrain. The modern box uses 24T/30T and hence does not have to be a combo cog.
8. Do not try and use the Myford modern screw cutting details as in a later manual as you will end up with a times 2 factor as above, but you can do far better none imperial threads than the earlier Myford tables.

9. The guts of the boxes are identical and interchangeable apart from the shaft differences of course

Think that's it.

You have some way to go to get going.

Dennis

sparky mike30/07/2012 07:17:45
259 forum posts
77 photos

Hi Dennis,

Many thanks for the in-depth information on the early box. I did not think it was going to be easy !! The lathe was picked up from an estate sale by the previous owners son. There is a slim chance that some of the missing parts are still at the same address so I am taking steps to check on that, now that I have a better idea what is not actually here !!

My lead screw is full length at the moment, but at some time in the past it looks like it was fitted to an early box, as now there is a thicker tube portion that might have been welded/brazed on to take it back to standard length. It can not have been used on my lathe with a box ,as there are no holes drilled and tapped on the side of the bed for the box fitting.

While on that subject point, I would like to drill the box fixing holes while the machine is stripped down. Does anyone have a drawing for the position of them ?

One part of the box I can't yet figure out. The smallest gear on the internal cluster is a 16 teeth gear. There is a cross hole in the shaft where this gear should be. Is this for lubrication , or is that single gear pinned? All the others are secured by a long key and they are all here. If you could explain how the drive is taken from the cluster gear shaft to the layshaft and also the purpose of the dog clutch, I will then have all the facts. (I hope !!)

One last question, should there be a ball and spring under the top cover to act as a detent for the quadrant. ? The small grub screw is present but no detent here.

Mike.

Swarf, Mostly!30/07/2012 09:57:42
753 forum posts
80 photos

Hi there, Mike,

Check your personal messages.

Best regards,

Swarf, Mostly!

Swarf, Mostly!30/07/2012 10:00:24
753 forum posts
80 photos

Hi there, Mike,

Another thing,

It's quite common for ML7 leadscrews to have that coupling sleeve. I've heard it said that the securing cross-pin acts as a mechanical 'fuse' in case there's a lock-up anywhere.

Best regards,

Swarf, Mostly!

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