Need chucks and faceplate for Prentice Bros lathe
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  1. #1
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    Default Need chucks and faceplate for Prentice Bros lathe

    Hi! I'm a new member who has just acquired a Prentice Bros lathe. It is a 14" swing 36" between centers. It was originally set up to run from a 2" overhead flat belt. A previous owner mounted a 3hp 1750 rpm 220 single phase motor driving through an early GM 3 Spd auto trans. The modification was not done with the greatest of care or with the proper materials so I will have to re-do it. the seller wanted to retain the original legs and offered to include a framework made from 2x2" tubing and 2 x 2 1/4" angle which I agreed to. Plans are to replace the 3hp 1750 motor with a 1hp 3600rpm motor and replace the auto trans with a set of step pulleys and a jack shaft which will drive the spindle. The lathe has 2 lead screws one for turning and the other for threading and a fairly large set of back gears. The head stock has a 3 jaw scroll chuck and the tail stock has a dead center. A small (3") center rest was included along with a taper cutting attachment. I would like to add a 4 jaw independent chuck and a faceplate and a live tailstock center. The thread on the headstock spindle measures 2 1/8" x 8 TPI which appears to be an odd size. All the chucks, faceplates and back plates I have located are either 1 1/2 or 2 1/4" x 8 TPI. I joined this forum hoping to get a line on the attachments I need. My primary interest is automotive and the lathe will be used for making parts for disc brake conversions, transmission swaps, drive shaft mods and the odd bushings and spacers. None of it will demand high precision. This lathe though quite old seems to be in good condition and should suit my needs. Most importantly, it was within my budget! I am retired and am living on a fixed income.

  2. #2
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    They were all "odd" over 100 years ago when that lathe as made - so they will not be "found", and in all likely hood and will have to be made after all dimensions and features are taken and used to produce a THREAD PLUG GAGE - or duplicate of spindle nose. With such a tool, any competent machinist can make a back plate or several to mount whatever you want in the way of chucks or other spindle tooling

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    3600 rpm motor is way too fast for the lathe, even 1750 is too fast. You don't want any more than 600 rpm for the fastest spindle speed for a 14" lathe with Babbitt bearings.

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    And most were considerably less, like this 335 RPM 1916 Lodge & Shipley
    Attached Thumbnails Attached Thumbnails l-spg26.jpg  

  5. #5
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    Lots on info on the make in this older thread

    Prentice bros. Co. High speed lathe

    A cone head version

    Machining lathe, work benches, shelving - tools - by owner - sale

    ph
    Last edited by johnoder; 01-14-2020 at 05:04 PM.

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    Thanks for the input. You are correct that a hub could be machined to fit my spindle shaft but you gotta admit it would save a whole lot of work if I could find one ready made. That's kinda why I joined this forum

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    I guess I wasn't clear. I have no intention of turning my lathe at 3600 rpm. I plan to go through at least 2 steps. The 3600 rpm motor is one I happen to have on hand. If it turns out to be impractical to reduce the spindle speed enough I will replace it with a 1725 rpm motor. I do plan to run my spindle at more than 600 rpm for short periods while polishing only. I believe this could be done safely. Early auto engines had plain bearings without pressure lubrication and they ran at much higher rpms for extended periods. I would NOT run at more than 600 rpm while cutting. By the way, I forgot to mention that this lathe has a speed reducing countershaft.

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    studelvr:

    Something to bear in mind about running the Prentice lathe is the matter of dynamic balance. If you run an old 14" swing lathe with cone pulley & a chuck on its spindle at any kind of speed up above about 450-500 rpm, you are liable to find the lathe wants to get up and dance. Namely, the issue of dynamic balance will rear its head.

    A cone head lathe with the bull gear and locking pin mechanism already has some imbalance. Add the random nature of a lathe chuck and the result is a rotating mass that usually is anything but balanced. I know from experience that while a three-jaw chuck may look symmetrical about the centerline of a lathe spindle, it has some imbalance in it. It's your call as to running your lathe at higher-than-designed spindle speeds. Chances are the spindle bearings are worn-in and won't be an issue, but you should check the bearing temperatures when you start running a lathe at higher spindle speeds. The bearing should feel slightly warmer than ambient temperature, and should take their time in getting to that temperature. I am old school, so check bearing temperatures with the back of my hand ( front of fingers being too callused to get a good sense of temperature). The old rule of thumb (pardon the pun) is: if a bearing is too warm for a person to put their hands comfortably upon it, it is running too hot. Remember that the temperature you feel in the cast iron bearing caps is a bit lower than the actual temperature at the bearing and journal. Other thing to be aware of is: how quickly the bearing heats up when run at higher speeds. The bearing will get warmer than running at low speeds, even with little or no load on it. If it seems to be heating up rapidly, STOP the lathe, flood the bearings with oil, and loosen the nuts or bolts holding the bearing caps and let things cool down on their own.

    Plain bearings (bronze, or babbitt or cast iron) typically will be setup with a certain clearance between the bearing and the spindle journal. This clearance is needed for a wedge-shaped film of oil which is developed when the journal rotates, and it is what actually supports the journal. Lathe spindle bearings tended to be setup a bit tighter than similarly sized plain bearings on things like line shafting. The clearance set on lathe spindle bearings was often set with the bearings cold, then the lathe was run and the spindle bearings got to a "running heat". The lathe was then stopped and the clearance rechecked and adjusted as needed if the bearings were running too hot. I worked on one old lathe with plain spindle bearings, and the bearing clearances were finally adjusted (shims) once the spindle reached a running heat at the highest speed for that lathe. I changed pulley steps on the motor/countershaft and jacked up the speed, and the headstock bearings actually got a good bit hotter to the point I had to shut the lathe down. I flooded the spindle bearings with oil, and "threw off" the flat belt from the steps on the cone pulleys. I then tried to turn the headstock spindle by hand, and could feel a bit more drag.

    My own habit, when adjusting spindle bearings on plain bearing spindles, is to set the clearances using a dial indicator. Once clearances are set, I then try to turn the spindle over by hand and feel how things turn. If the spindle kind of glides smoothly, I know things are likely OK. If the spindle feels a bit stiff or does not "glide" when turning the spindle (chuck helps act as a flywheel for this test) over by hand, I know that the clearance is probably right on the edge of being too tight. Usually, adding a 0.001" shim to one side of a tight bearing cap will do the trick. Not entirely according to Hoyle, but it is what some fine oldtimers taught me ages ago.

    Auto engine bearings are a bit different animal than a lathe spindle. Namely, even if the early auto engines did not have pressure lubrication, there were slingers or dippers on the con rods that forced oil into the big end bearings on the rods. In addition, the slingers or dippers on the rods often splashed the lube oil up into troughs and channels and maintained a flow to the other bearings. The bearings in an early automobile engine were also not set up with the close clearances of lathe spindle bearings. Even with the splash lubrication systems, the early auto engine bearings were flooded with oil. A lathe spindle bearing gets its oil from an oil cup, possibly with a felt wick, or possibly with a drip oiler, or possibly with a ring oiling arrangement. Nowhere near the oil flow to the spindle bearings is provided when compared to an early auto engine with splash lube. The old auto engines had an oil pan with maybe a gallon or more of lube oil and it was constantly being slung up and into the bearings. The other consideration is the diameter of the auto engine bearings vs rpm. Surface speed of a journal along with bearing material, hardness of the journal, clearance and type of lubrication may be quite a bit different than a lathe spindle and its headstock bearings.

    It's your lathe, and you can do with it what you please. I've been around a lot of babbitted and bronze bearings on anything from small machinery to large engines as well as powerplant hydroelectric turbines and generators. Simply put, your Prentice lathe was designed in an era when carbon steel cutting tools were likely the standard, so spindle rpm/surface speeds were low. High speed steel tools were the next evolution from the forged carbon steel cutting tools, and with that came a need for somewhat higher rpm and heavier cutting tool loadings. Even with that evolution to HSS tools, spindle rpm of lathes did not take a huge jump. By way of example:

    If the cutting speed for a finishing cut on mild carbon steel is 100 feet/minute with HSS tools, and a piece of 1" diameter stock were to be turned in a lathe for a finishing cut:

    the approximate formula for determining RPM is: RPM = (4 x Cutting speed in feet/minute) divided by diameter of the work in inches.

    plugging in 1" diameter and 100 feet/min cutting speed: RPM = (4 x 100 ft/min)/1", or rpm = 400. This would explain the maximum rpm on a lot of the old lathes.

    If higher rpm was needed, the job was probably of small diameter, and it would be done in a "bench lathe" with a spindle designed to run at much higher speeds. We referred to the larger lathes as "engine lathes" because they were "too big to be run by foot treadle and needed an engine to turn them", and "bench lathes" was the catch-all term for the smaller lathes. It was a carry-over from 'way back when. Bench lathes typically had sets of collets for holding smaller diameter work, and were used for the smaller jobs. It was only when carbide cutting tools really took hold that spindle speeds of the engine lathes really took an increase. I remember in 1964, as a student a Brooklyn Technical HS, we had quite a few machine shop classrooms dating to the '20's. Overhead/lineshaft driven lathes, with relatively low spindle speeds. Some shop classrooms had geared head engine lathes such as Reed & Prentice 16", Lodge and Shipley, and Bradford. These were late 1930's or "War Production Board" machine tools, and high end speeds on them were only around 400-500 rpm. In one class room, a modernization had been done, and we got brand-new 15" LeBlond Regal "square head" engine lathes. We were amazed to find top speed on them was up around 1200 rpm. The shop teachers told us we were not to run the engine lathes that fast with chucks on them, or with work held between centers with lathe dogs. Later on, working in shops, I've felt a lathe want to get up and dance when the imbalance in the headstock rotating parts and the chuck made itself felt. There are a multitude of reasons why a lathe like your Prentice lathe should not be run up around 600 rpm or faster. You may be fine in doing it, but if it were my own lathe, based on my own experience, I'd not do it.

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