new power for st louis 10" flat belt bench grinder

looking to figure out how much and the type of new electric motor for a old St louis 10" flat belt bench grinder it has 10" grinding wheel and 10" wire brush on it i use this more than any other tool in the shop

thinking 3 hp 1725 rpm farm duty motor high torque start needed to get this thing spinnin and a fresh flat drive belt too.


have existing 3/4" output shaft wooden drive pulley maybe bout 3" OD that came off old 50 plus years underpowered 3/4 hp emerson motor it is giving up wont start right and get up to speed when its cold fresh capacitor and motor shop on monday for more bad news $$$$ that i need rebuilt or just replace

and new motor update as the grinder will stall if u lean into the brush to much so im thinking more hp same rpm but hp question looms?

any help is always appreciated

proteus

Ps: my champion 20" camelback drill press is still here sleeping in the shop waiting for the next round now its all painted up and pretty

Do get your ratio right, you would not want to be around if the wheel explodes. Makes ugly holes in your noggin

Halsey's "Handbook for Machine Designers, Shop Men, and Draftsmen" (1916) table 25 page 346 puts the power requirement for a "Diamond Wet Tool Grinder" at 3.29 horsepower "observed maximum" and 0.97 horsepower "average". This a machine with one 20 inch wheel. A similar "Leland & Faulkner" with two 24 inch wheels shows 0.41 to 0.82 average horsepower.

Looking to 10" commercially available grinders puts the horsepower at 1-1/2. (Edited out a Home Depot 10" Dewalt Grinder - *Database Error*- Link - you can find it like I did.)

Thus I'm sure your 3 horsepower motor is MORE than adequate - in fact you may want to tone that down a bit to possibly even one horsepower - horsepower ratings on modern tools are particularly suspect. Nameplate horsepower ratings on loose motors considerably less suspect.

Grinding is one of those operations where horsepower is ENTIRELY dependent on the strength and attention of the operator - most of us do this irregularly (called "duty cycle" in welder parlance) and the motor has a chance to cool while we're less attentive or easing off a bit. (hence the "observed maximum" and "average" of the Halsey numbers.)

As to John's comment on speeds, keep in mind that today's fully vitrified wheels are CONSIDERABLY higher quality than original semi-vitrified wheels - but still, an accident is an accident and can be just as disfiguring, if not outright fatal.

My flat belt bench grinder was designed for 10" wheels. I use 8" wheels rated at 10K RPM - and run it about 2800 RPM. These normally mount on an 8" electric grinder at 3600 RPM. But I have no guards hence the conservatism.

One is advised to AT LEAST this level of conservatism - if not more based on the fact that an antique grinder sleeve bearing doesn't rotate as consistently about a center of gravity as a ball bearing does - and the lateral vibration can be a cause for root failure of a grinding wheel.

It is, of course, a matter of what your tolerance level for risk is - as it is with ANY machine tool operations, even modern.

Joe in NH

this old St. Louis flat belt grinder runs low and slow once enertia and old belt quits slipping , mainly used as a 10" wire brush it has a modern weiler 10" wire brush medium wire that i use for buffing rust dirt and grime off of dirty parts and ocasional light grinding or deburring ,rounding or shaping a part.

grinder has bronze bushings and oil cups very worn few drops of oil is good to go

original motor is a vintage and very heavy 3/4 hp emerson 1725 rpm motor, just put a new capacitor on it ,

going to hamilton electric in Austin ,to see if they can fix armature shim spacing it had a carbon insulator washer that fell apart when dissasembled for cleaning and paint has been rebuilt once, with a new starter fork ,
has some stamped numbers on case, maybe ill get lucky and they can fix it worked fine before , not burned at all just dirty and weak cap,

see how my luck goes has 3/4" output shaft and a wooden pulley on it which is very obsolete

new options r very spendy 2 hp ok ?

3 hp seems overkill to also for flat belt setup

farm duty motor with high torgue and sealed housing to keep dirt out, 1725 rpm 125 or 220 volt /

just trying to get this going again and not be disapointed with performance after spending the big bucks

im out of old washer machine motors what my dad would do ,

proteus