Myford VMC Spindle Advice Please.

[Michael GilliganParticipant @michaelgilligan61133]

I hesitate to even mention the possibility, but here goes:

Is it feasible that the previous owner suffered a “crash” which ever-so- slightly bent  the quill ?

… that would explain a lot.

MichaelG.

[Nigel Graham 2Participant @nigelgraham2]

Thankyou Graham.

I will examine the quill’s fit and movement carefully. I’ll turn the top on its side as you suggest to make this easier.

I’ve not seen any sign of damage, and the quill was always stiff but seems to have worsened lately. It would not move under its own weight with the pinion, lock and depth-stop all removed. I saw the edge of the interpenetration between the quill and lock bores was very sharp, and I eased that a touch with a fine file.

One edge I examined carefully is the top of the quill, for any sign of burring or bruising. There wasn’t any.

Err, you can’t readily refer back up-thread once on a new page, but someone asked if a previous owner had managed to bend the quill. That would have to be a hefty crash! There is no evidence for that, nor of over-enthusiastic lock-tightening. Doing that would more likely break the lock itself, perhaps snap its small handle, than harm the major components. No sign of damage to the rack and pinion teeth.

The quill has no external lubrication point, so could well be stuck on glue that was once grease. I’ll clean everything thoroughly with white spirit before trying the quill back in the head.

 

I succeeded in removing the lower bearing, with the aid of a hide mallet, but more to the point having chilled the spindle using a plumber’s pipe-freezing kit. The blurb says it will cool down to -50ºC: I can’t vouch for that but it certainly created an impressive frost halo on the steel.

The worn-out locating-pin turned out to be a tiny grub-screw. Identifying it was hard but it seems to be 6-32 or 6-40 ANC. I was surprised because the spindle is all to nice tidy millimetre measurements, I found when I measured the bearing and shaft. Metric screws don’t fit properly; 4BA fits rather sloppily.

The spindle appears unhardened and it may be feasible to convert the pin to the slightly larger M4, easier to obtain and compatible with its metric home. An M4 screw does nestle in a collet’s keyway. I’d wondered about even moving it to above the bearings; though hopefully once the machine’s back in action that will become my executor’s problem!

The bearing is an SKF, its number partly illegible, but I will contact Townsend Bearings about a replacement, and take it with me so we are sure. It seems to have a very slight rough point but I probably damaged it trying to remove it. Had I been unable to remove it at all I would have found an engineering-services company (possibly Townsend) or HGV garage able to carry out the work.

The thrust bearing is fine: that is not held tightly to the shaft so comes off easily, and shows no sign of harm. The top bearing similarly turns smoothly.

 

I’ve wondered why the pin / grub-screw became so mangled. My guess is insufficient draw-bar tighting so the pin became a drive key rather than to aid tightening the bar; and once it started to wear the problem worsened. It still seems a curiously weak detail. I’d expected a rectangular key held by a small screw.

[Graham MeekParticipant @grahammeek88282]

I have been trying to find the photograph taken of the part of a broken tap that I removed from my Myford spindle, but to no avail.

It was not uncommon on the machines from the Far East during the late 70’s early 80’s to have Metric threads and Imperial sockets and vice versa.

From memory the keyway in the R8 collet is 5/32″ wide x 3/32″ deep. I would be more inclined to tap the spindle M5 and turn a spigot onto an M5 thread. Using a Hacksaw to put a screw driver slot to screw it in with. Play it really canny and only use the front portion of the taper tap. Screwing the key into a tight thread will stop it rocking when the collet is tightened and loosened. Otherwise use some Loctite stud retainer.

Be sure to check all the tooling that goes in the spindle to make sure the key is not too proud before you reassemble everything.

A small hole just above the fully home position of the quill would provide an access for oiling purposes. Bridgeport’s have an oil cup for this if my memory is right.

Hope this helps,

My best regards

Gray,

 

[Nigel Graham 2]

 

On Nigel Graham 2 Said:

 

Err, you can’t readily refer back up-thread once on a new page, but someone asked if a previous owner had managed to bend the quill.

Nigel,

If you Right Click where I have highlighted in green, then click on “open in a new tab” you can easily look at the post in a separate tab, and flick between reading and writing, in the two tabs.

Mark.

[Nigel Graham 2Participant @nigelgraham2]

Thank you.

 

I think it was Michael Gilligan who asked about damage in previous ownership, but I’ve not found any evidence of an accident.

[Nigel Graham 2Participant @nigelgraham2]

Progress so far… (I’vebeen devoting most of my tine to modifying the club’s loco driving-truck):

New bearing bought but not yet fitted.

No real sign of anything that could so effectively jam the quill, no obvious high spots or damage. A lot of effort with WD-40 and a strap-wrench seems to have made it a bit freer by a sort of auto-lapping process. I reached a point where I could just about slide it up and down by hand but it still seems to stick at the slightest opportunity.

Renoving the pinion again, which I’d put back in without the spring yet, it just stuck there, not falling under its own weight.

Managed to lose one of the small socket-screws that hold the pinion-shaft bearing in place. I’ve not yet established their thread but I suspect a Unified size. They are about 5mm dia but not M5.

 

New locating-pin for the spindle made. I modified an M5 dog-point grub-screw and installed it a bit further up that section of the spindle so it will be under the thrust-bearing rather than radial bearing. It’s held with a dab of ‘Loctite’.

 

 

[Graham MeekParticipant @grahammeek88282]

You could try a trick I found to work over the years. Lubricate the Quill with Brasso as you re-insert the Quill. Oscillate the quill as you enter the housing, but not by much. Try and keep the Quill in about its working position. At the slightest sign of the Quill going tight. Retract the Quill slightly and give the Quill a squirt of WD 40, but not too much. The Ammonia in the Brasso tends to dry-out pretty quick.

It may take several attempts but I think you will start to feel an improvement. Add more Brasso as the Quill goes further in. Try working the Quill to and fro with the Pinion at the last go off with the guide bar attached. Clean everything off and lubricate with a little oil before assembling. The Brasso will probably show where the Quill was tight.

As regards the screw, no bolt will measure a dead nominal diameter. The crests are rounded from the thread rolling process. If the threads have a coarse appearance it could be 10-24 UNC. If the thread looks finer than this it is going to be a little more difficult as the 10-32 UNF and the M5x0.8 Pitch are nearly identical. Head size might differentiate between the two, but as I have had instances with the wrong head sizes I would not rely on this.

A known Nut or tapped thread would be the easiest route.

I hope this gets you nearer your goal.

Regards

Gray,

[Nigel Graham 2Participant @nigelgraham2]

Thankyou Gray.

As it’s for the club I am giving more attention to its project than mine so haven’t touched the mill for a few days.

However, I will try the Brasso. I assume it holds an extremely fine abrasive so I’m a bit worried about it taking up residence in the cast-iron head, but even if it does I doubt it will be enough to create serious problems. It’s likely only a few spots microns high that are causing the tightness so metal polish should suffice. If it proves where the lumps are, on the steel quill not in the casting, they might be removable with one of those abrasive rubber blocks.

 

I examined the parts diagram to see if it specifies the screws holding the pinion assembly, and that tells me they are M5. If so, not a problem, I’ve plenty of them in stock. It’s possible that the “M5” screw I used as a crude gauge was actually 2BA or something.  So I’ll try again with a definitely-known screw, not one from the “waifs and strays” collection.

[Graham MeekParticipant @grahammeek88282]

Hi Nigel,

There is no need to worry about the Brasso abrasive compound getting into the Head casting. The abrasive element if you can call it that is a very fine powder of milled Pumice and Chalk. It is not like valve grinding paste with Carborundum particles in. During the “Lapping” process the powder just gets finer and finer.

I have been thinking about this problem on and off. A possible cause came to me whilst looking at some Old Photographs taken during my apprenticeship of Forgings Weathering outside the Raw materials store at Dowty’s Staverton, Glos.

Most castings these days are “Aged” using a heat treatment process. I think your Head casting was either missed or it did not get a full cycle. This would explain why it has gone tight due to the locked up stresses coming out during service and natural aging.

Regards

Gray,

 

[Nigel Graham 2Participant @nigelgraham2]

Interesting suggestion! At the moment I’m spending more time and effort on our club’s driving-truck but have given myself a deadline of next Tuesday, as the loco and it will be needed within the next few weeks. One frustration there is that I orderd a quick-release hand-pump hose kit from one of Our Suppliers, and it’s still not arrived. I discovered they buy them from Another Supplier who has basically been lazy! So I’ve to either make a connector (probably a screw one like a washing-machine hose), find another supplier, or risk using one I have but which might not be happy with water.

 

Anyway, back to the mill…

Trying to insert the quill by hand tends to rock it as it enters, jamming it.

I found best for moving the quill in the head without the pinion, is a large strap-wrench I normally use to help loosen tight lathe chucks. With a fabric strap and aluminium lever it can’t hurt any of the machine components.

I think the cap-screws used are 10ANC, which is very, very close to M5 X 1mm.  They are short, with only about 5 or so turns available to enter the holes. Careful testing with a tap took a very light scrape off the threads, resulting in both the original screws and test M5 ones fitting with no appreciable difference in shake. A metric Allen key seems to fit the heads properly.

The Myford parts-list says M5, but my mill was made in Taiwan in 1981 (says the serial number plate), in the era when the Americans were trying to “Unify” industry generally, as they did with military equipment and many vehicles. The rather inadequate dial-locking thumbscrews have coarse threads that are neither metric nor BSW.

[Graham MeekParticipant @grahammeek88282]

Hi Nigel,

A couple of blocks of wood in front of the Quill bore. Adjusted using the Knee to get them in line with the Quill bore will make things easier when it comes to inserting the Quill. These can be removed to allow the Quill to go fully home.

A piece of wood in the top Quill bearing seating and a piece something like 50 x 25 mm (2″ x1″) to form a handle at the outer end. Both are clamped in place by a length of studding. This will probably be easier to use than the strap wrench, and it will not damage anything. It will certainly make oscillating the Quill easier during the “Lapping” operation.

Hope this helps,

Regards

Gray,

 

 

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