Myford QC Gearbox

My lead screw suddenly stopped rotating and I found that the grub screw on the lever was loose and the lever just rotated on the rod without moving anything. There was no flat spot on the rod so I thought I had better look inside the box to determine. the correct position. The first three screws were easy to access, though extremely difficult to unscrew.The fourth one (top right hand corner) is directly under the oil cup and somewhat inaccessible.

Is there a correct way to remove and replace the oil cup if I have to, without damaging it. I have shortened the short arm on my allen key to reach the screw but was concerned that I might strip the head or hole in the screw considering the unusual force required to remove the first three screws.

Or maybe I shouldn't take the top off.

Any advice would be appreciated.

JC

John, I would not remove the oil cup, there is a wick taking the oil up to the bearing. My opinion is remove the gearbox, not so hard to do but you need to remove the lead screw first. You will need a small Allen screw and a spacer to draw the dowels on the RHS lead screw bearing cap, also remove the gears from the gear train so you can withdraw the leadscrew. The gearbox is held on with Allen screws into the bed I need to look but access is through the opening in the front of the gearbox.

Might have some detailed instructions from Myford, the above is from memory. Some gearboxes that have been retro fitted have a joint on the leadscrew to the right hand of the gearbox.

hope this helps. John

I have just had the top of my gearbox using a ball ended 3/16" Allen key on the back right hand screw. No problem but maybe mine wasn't so tight as yours.

Andrew M

Actually I was just preparing myself for the eventuality of my stripping the socket hole in the screw and the resultant mess trying to get the screw out.

All of which led me off on a tangent regarding the shortening of an allen key. I first tried with a hacksaw but then resorted to a bolt cutter, but was concerned if grinding the end smooth, with the subsequent heating, would change the temper of the key which was pretty hard. Luckily I have a box full of 3/16 keys so could experiment with a couple.

I might need some help on what is supposed to go where, when and if I get it open.

Thanks

JC

Hi there, John,

I gather from your mention of the oil cup that your lathe is a Super Seven rather than an ML7. The QC gearbox is the same for both machines except for a spacer strip on(I believe) early Super Sevens.

John F. has dealt with removing the lead-screw.

The QC gearbox is secured to the lathe bed by three screws. The upper two are 1/4" BSF cap-heads (maybe M6 if your machine is a recent one). They are best accessed after removing the top cover. IMHO, I guess you COULD get at them through the front of the gearbox but you'd need an extra long Allen key, a torch and four hands! (The more so when you come to refit the box to the lathe.)

The lower one is a 1/4" BSF slotted mushroom head, accessed by removing the plug on the front of the gearbox.

I suggest that you drain the oil from the box if you haven't done so already.

If you go onto the Myford web-site, chose 'Super Seven', then 'Spares', then 'QC Gearbox', then scroll right to the bottom of the page and click on 'Click for bigger picture' (in red letters). That will bring up a large .pdf version of the illustrated parts list (aka 'exploded diagram' ) - I'm sure you'll find that useful. (It's down-loadable. Ditto for all the other lathe sub-assemblies!)

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 05/08/2014 22:29:34

The wick does not go into the oil cup so the oiler can be removed. The hinged cover needs to be rotated to the left so the hinge clears the headstock casting. Turn the oiler anti clockwise to unscrew.

Hello John,

I shortened tha appropriate sized allen key to get in under the oil cup. It is a bit of a fiddle and take note that the 4 screws are paired for length. I didn't have a ball ended imperial wrench which would have been better.

It was easy enough with a junior hacksaw and just a touch on an abrasive wheel to smooth the end, no need for concern over drawing tempers etc done that way.

After that the lid comes off easily. Replace it making sure the top selector lever goes back into the same engagement it had before opening the box.

Regards Brian

Edited By Brian Wood on 06/08/2014 09:00:44

To go back to the beginning of my problem, the reason I needed to take the cover off was because the lever was rotating on the pivot pin and so I did not know what the original position was, so I do not know where the thrust block should go and in what position. There is no flat spot on the pin ,just a recess off the surface of the pin. My pin was scratched up with elongated rough grooves caused by the slipping grub screw. A new pin is £12.50 + VAT. I thought a little steep, as I would have to add postage here to the USA, so I will just try to smooth out the old one.

According to the chart the coarsest threads are with the lever to the right, so the fastest rotation would be on the left end of the gear spindle in the box. Getting the thrust block in and re-assembled looks like it might be a bit fiddly. When a the box has the cover on again I will just fix the lever in the right hand position and really torque it down.

Is my reasoning correct? Would appreciate an opinion or a better suggestion.

Thanks to all so far.

JC

Hello John,

Sorry to correct you, but your reasoning is actually wrong..

The thrust block is moved in the opposite direction to what you might expect and 8 TPI is obtained when it has carried the middle dog clutch section on the layshaft to engage the 16T gear on the right hand side. If you play about with it when the gearbox is open you will see that for yourself and by looking at the pivot/swing lever arrangement you will see why it happens as I describe.

Your way will lock the gearbox to the highest TPI ratios

I don't think you need to over torque things either, make sure they are secure of course.

Kind regards Brian

The 6 o'clock position of the lever corresponds with the central sliding gear being exactly in line with the gear it meshes with on the adjacent shaft. If you do that, the other two gear positions will be correct.

Andrew M

Sorry for delay, had to do some RPA (Revenue Producing Activity).

To go back to my original thought, there are only three different locations, with a dimple for each on the bottom of the quadrant plate and only one way for the quadrant plate to go in the top cover.

If I move the sliding gear to the left to engage the 32T gear then the only way that the thrust block can engage the sliding gear is if the lever is to the right i.e. 4 o’clock. So if I position the quadrant plate on the outside dimple then the only way you can move the sliding gear is to the right, or clockwise from the top, so that should be the position for fixing the upper lever as in the chart. This is what I meant in my earlier post where left and right positions may have been confused.

Am I right this time?

JC

Hello John,

Perhaps it might be best to adopt Andrew's approach and set everything up for the mid position. That will avoid any confusion with left and right and how they are viewed.

Mid position is when the layshaft slider inside the gearbox [the piece that has a dog clutch at each end with a 24T gear between them] is clear of the mating dogs at each end and has the 24T gear fully meshed with the 24T gear in the cone of gears below it

Niw you can put the thrust block into the gap made for it in the slider (just to the side of the 24T gear) and engage that with the quadrant plate in the cover, which will also be in the mid posit. I would use a little grease on these fitting operations to help thwart gravity and hold things in place.

Finally the operating handle on the outside surface of the gearbox cover can be secured in the mid position. On my gearbox, that is held with a roll pin, fitted blind from one side and not therefore extractable. I think it would pay you to made a proper dimple for the grub screw you referred to in the original post and give it something to get a grip on.

I still can't grasp why losing the grip on that grub screw would abruptly stop your leadscrew from rotating as it would have no influence on the selected meshing through the box; nothing would have moved to disengage the gearing.. .

I hope this removes confusion and you can get back to normal working again.

Regards Brian

Thanks Brian!

I will try that and let you know how I get on.

JC

All is well! I used the middle approach and everything is back together again and running smoothly.

Thank you all for your interest and advice on what was a rather minor problem.

As regards drilling a dimple on the pin for the grub screw I decided I was not skilled enough to do it dismantled and if I did it in situ I was concerned about damaging the thread on the lever, so I shelved it for now.

I have actually had this machine for 26 years,I made a visit to the factory in Beeston and brought it home here to the USA with me in 1988. Obviously minimal use so it is in pretty good condition.Bit heavy for carry-on!

Once again, thanks very much.

JC