1940 Le Blond Regal Backing Plate Installation Instructions

[Shiseiji]

Stumbled across this on the Home Shop Machinist forum with credit to member "Nicholas"

" . . . the info is taken from my 1940 Leblond manual "Running a Regal".'

Key points.

1. Good thread fit.
2. Key contact surface is the spindle shoulder.
3. If the backing plate has a tendency to "stick", use blotter paper on the spindle register (Note. A factory supplied backing plate would generally be supplied with proper clearance over the spindle register, however LaBlond notes a skim cut may be necessary. Mr. Google reports a general use "blotter" paper is .010" thick, and a coffee filter is a good substitute. Just my $.002. I believe it's reasonable to 'assume' the spindle clearance was ~ .008" to provide any clearance for the blotter paper. )

A 1942 version of "Running a Regal" is available on the Vintage Machinery site.
________________________________________
PROPER FIT OF FIXTURES MOUNTED ON SPINDLE NOSE
_________________________________________
The small face plate is usually used only as a drive plate for work held on centers. As a general practice work is not mounted on the small face plate. For this reason the fit of the small face plate on the threads of the spindle nose is not important and may vary from snug to loose without harm.

With the use of the large face plate and chuck plates, however, the work is held and positioned by the plate, and any shake in the plate from a loose thread fit on the spindle nose would show up as an inaccuracy on the finished work.

Therefore, large face plates and chuck plates are finish tapped and fitted to the lathe spindle as tight as the plate can be screwed on the clean well lubricated spindle nose.

On a well fitted thread the bearing will be distributed evenly on the sides, and the position of the plate will be the same each time it is mounted.

EDIT: I have added the nomenclature and illustration below to try and provide a uniform nomenclature in this post. Credit to Scott Logan's site for the spindle illustration. NOT to any scale!

Spindle Nomenclature*
Shoulder Dia. - “A”
Register Dia. - “B”
Thread Minor Diameter - “C”
Thread Major Diameter - “D”
Thread Pitch - “E (3 wire method shown)”
Register Length - “F”
Spindle Threaded Length - “G”
* http://www.lathe.com/spindles.html

Backing Plate nomenclature
1. Counterbore to pass over spindle register.
2. Protrusion or "Spud" to press fit into the chuck counterbore.
FITTING CHUCK PLATES TO CHUCKS

The accuracy of a three or four-jaw chuck in holding work in the proper position is largely a question of the care used in fitting the chuck plate to the chuck.

It is imperative that the chuck plate should have a good fit on the spindle nose threads. The chuckplate should be screwed on the spindle nose without undue force and yet not be loose enough to allow shake on the threads. The chuck plate on all Le Blond Lathes is held true to the lathe spindle axis by the fit of the spindle nose threads in the threaded bore of the chuck plate. The chuck plate is held square with the lathe spindle axis by the fit of the chuck plate shoulder against the square face of the spindle shoulder.

Chuck plates are supplied by Le Blond in both semi-fitted and full-fitted styles.

A semi-fitted chuck is machine bored, tapped and counterbored, and is then finish hand tapped, to a plug screw-gauge fit, before being shipped.

The full fitted chuck plate, as its name implies, is completely machined and assembled to the chuck so that no further work is necessary.

So much of the accuracy depends on the thread fit (accurately obtained only by the use of a precision ground finish tap (emphasis added) such as we use in our plant) that we strongly recommend the use of genuine Le Blond semi-finished chuck plates in fitting up chucks to Le Blond Lathes.

The procedure to fit plates is as follows:
First, screw chuck plate on spindle in regular position about two-thirds of way up to shoulder so that bearing of chuck plate is entirely on threads. Take rough and finish cuts on face of chuck plate so that this finished surface will be square with thread and large enough to clear diameter of collar to be used in Step No. 2. (Note. I don't understand how this can be done without installing the plate until it makes contact with the register.)

Second, reverse chuck plate on spindle and insert a collar with true parallel faces between spindle shoulder and part of chuck plate just machined. (Note. In lieu of making a collar, precision spacers can be used.)

This collar should be wide enough to extend from spindle collar to the first full depth thread, since the face of chuck plate is not counterbored as is the back. Next take a skim cut off end of hub. Clean up counterbore of hub at 45 degrees and true up diameter of hub and take cut off back of chuck plate.

Next take chuck plate off; remove collar; clean spindle nose and chuck plate thread and screw chuck plate on spindle in proper position. Rough face front face and rough turn out-side diameter 1/32-inch above diameter of counterbore in chuck. Also counterbore tapped hole at 45 degrees to 1/8-inch across flat; next, take finish cut off face of chuck plate.

Caliper counterbore of chuck and transfer size to outside mikes. Finish turn OD to fit counter-bore allowing for a slight tap fit.

Next transfer the holes in the chuck to the chuck plate, using the chuck as a drill jig.

Lightly tap the chuck plate into chuck counterbore and spot drill through the chuck body to the plate with body size drill. Without removing chuck plate, drill in the spotted holes with the proper tap drill for the screws furnished with the chuck.

Start taps into tap holes, tapping from front of chuck to insure proper tap alignment.

Center punch plate and chuck for location; remove chuck plate; finish tap holes and file off burrs.

The plate can also be mounted with the chuck bolts going through both the chuck body and plate and held with nuts on the face of the chuck plate. The procedure would be the same as the foregoing, omitting the tapping operation. If the hub on the plate is shorter than the width of the nuts, the latter method cannot be used.

When body holes are not drilled through chuck, chalk chuck plate face thoroughly, wipe off mating face of chuck back, then tap chuck plate in position in chuck counterbore. Outline of bolt holes will show up on chalked surface when chuck body is removed. Center punch plate and chuck for location and remove. Mark off holes, center punch circle and center for drilling. Drill with body size drill to allow clearance for chuck screws.

Clean chuck counterbore and chuck plate thoroughly. Reassemble in proper position and insert and draw screws up tight.

When chuck plate assembly is put on the lathe spindle the body of chuck should run true.

A true piece of short shaft when clamped in a universal chuck should run true within .002" if work has been properly done.

 

[benmychree]

Seems way overcomplicated ---

 

[Shiseiji]

Not really any different from many other write ups on the site. What I found interesting is there in no mention if a requirement for a tight interference fit between the register and the adapter.

1. Install the plate as it will be used tight against the so called register and face the chuck side. Remove the backing plate.
2. Measure the OD and length of your register.
3. Install a collar or spacers to cover the register. Reverse the plate, tighten it, and ensure there is a sufficient counter bore to cover the register. Opinion. Make the counter bore a little bit longer if the chuck may be moved from a Southbend to a Logan. Aim for the ID to have a close interface fit to the register. (Logan reportly machines the ID to fit the slightly larger Southbend register and states they have never had a return.) Opinion. I think stuck chucks are often due to too tight a tolerance between the register/backing plate.). La Blond suggests a 45° chamfer on the ID.
4. Reverse the backing plate again. If needed, machine the backing plate for a tight fit to the chuck counter bore.
5. Last step is to mark and drill the backing plate for the bolts.

These same 5 steps are repeated at least 30+ times on the forum, admittedly not in a succinct 5 steps, and none with a factory citation. And almost every one of the 30+ threads include comments that the backing plate/register must have not more than a .003" gap. A requirement not mentioned by La Blond. Or any source other than opinion.

But many believe in the need, so when I found a source I thought I'd share it. To be fair, a La Blond provided plate for a La Blond lathe would be expected to have the correct interface. But the factory mention of blotter paper on the register suggests a gap larger than .003"

 

[benmychree]

There absolutely should NOT be an interference fit between the register and the adaptor, to do so would invite galling and sticking; there should instead be a small amount of clearance, for a small lathe, a few thousandths would suffice, on larger lathes, I have seen the register and threads quite sloppy fit, yet, they still run concentric. Neither the threads nor the register should be fit tightly; so far as the threads are concerned, when I need get a new machine and need to fit a new chuck or other spindle accessory, I make a plug gage according to thread wire size, and use it to fit the thread snugly to fit the spindle; if the gage fits the backplate or other accessory, it will fit the spindle with about the same class of fit.

 

[stupoty]

There absolutely should NOT be an interference fit between the register and the adaptor, to do so would invite galling and sticking; there should instead be a small amount of clearance, for a small lathe, a few thousandths would suffice, on larger lathes, I have seen the register and threads quite sloppy fit, yet, they still run concentric. Neither the threads nor the register should be fit tightly; so far as the threads are concerned, when I need get a new machine and need to fit a new chuck or other spindle accessory, I make a plug gage according to thread wire size, and use it to fit the thread snugly to fit the spindle; if the gage fits the backplate or other accessory, it will fit the spindle with about the same class of fit.

I think he means the register on the chuck for the back plate to fit in.

Stu

 

[benmychree]

Sorry, wrong terminology, what I meant to say was the diameter that the spindle fits the ID of the chuck behind the threads, the diameter that the chuck fits on the backplate could also be rightly called a register, in that case, I have always fit them "metal to metal", that is the same diameter for both the ID of the chuck and the OD of the (register) of the backplate; this could be called an interference fit, as they will simply not just fall together of their own weight.

 

[Shiseiji]

I think he means the register on the chuck for the back plate to fit in.

Stu

No. Many have a firm belief the register, not the spindle shoulder, fit to the backing plate must be as tight as possible. ~ .002"

FWIW I don't share that belief and am simply providing a factory source for the spindle shoulder/backing plate fit side of the argument.

 

[stupoty]

No. Many have a firm belief the register, not the spindle shoulder, fit to the backing plate must be as tight as possible. ~ .002"

FWIW I don't share that belief and am simply providing a factory source for the spindle shoulder/backing plate fit side of the argument.

Their would be a risk of movement if the chuck register isn't a tight fit to the back plate I would of thought. Unless you did the "buck chuck" style screws to lock it in place.

If you had no interference fit you would need to indicate it in as you tightened the chuck bolts to the backplate.

Is that what you do and then just check it every now and again for concentricity ?

My photo in the "remove a stuck chuck" is a LeBlond factory made and fitted backplate. It required a bit of a tappidy tap to pop it off the register when the bolts were removed. Definitely an interference fit.

The spindle nose only has a flat face and a short cylindrical area to radially center the chuck.

Stu

 

[Shiseiji]

I've read more arguments for facing off the backing plate. headstock side, hence the need for a collar over the register to space the backing off the spindle nose, to ensure concentricity with the spindle and square with the lathe spindle shoulder, than for using the backing plate as supplied.

Not surprised to read about the tight backing plate, hence the La Blond recommendation for paper. In your case tobacco paper, .001", would probably be perfect.

I have a BP M-Head with B&S #7 taper. The Chinese import collets are too long. A Post-It note is just the right thickness to get the collet to pull tight. Or grind off the unthreaded part to make the collet closer to the old spec length.

 

[stupoty]

I've read more arguments for facing off the backing plate. headstock side, hence the need for a collar over the register to space the backing off the spindle nose, to ensure concentricity with the spindle and square with the lathe spindle shoulder, than for using the backing plate as supplied.

Not surprised to read about the tight backing plate, hence the La Blond recommendation for paper. In your case tobacco paper, .001", would probably be perfect.

I have a BP M-Head with B&S #7 taper. The Chinese import collets are too long. A Post-It note is just the right thickness to get the collet to pull tight. Or grind off the unthreaded part to make the collet closer to the old spec length.

When I've made backplates for my lathe I have held the blank in the three jaw faced bored and threaded then tested with a thread gauge (clone of spindle thread) then threaded the backplate onto spindle (with the three jaw still attached just in case ) then made the register to fit the new chuck.

I have always tried to get it as close as possible to the chucks register step.

Stu