homebrew pedestal grinder

[Tony]

even'n folks..
i have a pair of grinding wheels down in the shop that've been around forever. the recent threads on balancing, and the HSM press got my gears turning...

not to mention the arbour press (pictures to come) works wonderfully ... though is in line for a larger/longer handle.

i'm going to put these two wheels to use but have never built a grinder. off hand, doesn't seem very challenging, but i thought i'd ask.. to be on the safe side.

the wheels are 60 and 80 grit 1" wide x 10" diam. they seem a bit thin for the diameter, but maybe thats how they made them 'back in the day' ?

they're grey wheels (corobundumoniumate??) and they 'ring' kinda nice. i think they're safe.. have been boxed and shelved the whole time.

these wheels have 1" holes in them. i plan on using two 1.25" pillowblocks so the shaft will have shoulders for the wheel washers to butt against.

questions:
1) how far apart could i set these wheels on a 1.25" shaft without worrying about the shaft deflecting? (the motor will be mounted underneath, with dual v-belt pulleys to the center of the shaft).. i'm wondering if i 'pull' too hard with the belts, and the pillowblocks 'self-align' ... will i get into some weird vibrations?

2) the wheels are marked 2500rpm. that seems mighty fast to me for 10" wheels. then again, i have ZERO experience with grinder design (i've always just bought mine 2500 sound about right?

3) every grinder i've ever met has a left hand thread on one end of the shaft. i'm guessing this is so the wheels don't spin loose. can i get away with using a jam nut?
turning a LH thread on the shaft is no prob.. inside a 24mm nut, thats something i'd prefer to avoid.

thanks to anyone who made it this far.
-tony

[brunneng]

I don't know that I can answer your questions but I'm real interested in the answers as I have a couple nice, new 1"w wheels that won't fit my grinders and I'd like to make a grinder for them.

It seems to me that your plan would work just fine. That's about the same thing I was thinking and it's like a large toolpost grinder. Unless you used a nut with a positive lock, like a cross pin, I'd go with the left hand thread. Complete safety beats a little work when you have a couple pounds of rock spinning at 2500rpm.

Kevin

[wierdscience]

Okay,maximum I would run on the length of a shaft in your situation is about 18",12" of which would be between the pillow blocks,since the motor will only have one out put shaft and it will be on the end of the motor the natural choice for the pulley location is up against one pillow block,with the pulley located just inside the bearing you should not have any problems with vibration.

2500rpm is fine,any faster and it would burn and glaze over,to slow and it wouldn't cut effectively.But I would shoot for 2250 to give a little safty margin.

As for the left hand threads,you could get by without them by cutting a keyway in the shaft through the threads and drill and press in a matching pin in the wheel washers.

[jstinem]

Check with your local hardware store. they should hace a ball bearing mandrel with correctly threaded ends, nuts and washers. It should even have a pully mounted. All for about 30.00 USD. then all you need is a motor, wheel guards, and a tool rest.
good luck.
Joe

[Forrest Addy]

Been lot of them made that-a-way. It's called indirect drive.

Generally bench grinders are made with the wheels some distance apart and over hung on their shafts so the operator has roon to maneuver awkward work on the inside between the wheel and the stand or the bulk of the motor. sicle sharpening comet to mind.

Your wheels are a good choice if the hardness designation is between "K" and "M" and they ring out OK.

I suggest a 1 1/2 HP motor which is the largest you can run on 115 Volts from a 15 Amp wall plug but no less than 1.

I suggest 8" to 12" between the bearings and the shaft overhang to be no greater than 4". 1 1/4" bar stock is pretty stiff. Make some 3/8" thick wheel washers 1/4" smaller thant the wheel's blotter diameter. Relieve 1/32" deep the wheel side of the washer to leave a 3/8 wide face in contact with the wheel .

Don't forget the left wheel needs a left hand nut and the right wheel a righty. Use loosely fitted threads. I believe you can get 1 - UNC LH nuts from stock. Make the shaft from heat treated stock if you can. If something goes sour you don't want to bend the shaft.

Mount the pillow blocks on pedestals or a fabrication tall enough to allow 3" under the wheel. The base the pedistals mount on should be heavy steel plate and it should be arranged so the V-belt drive can be changed without removing a ton of parts. The base plate should be long enough to support the wheel guards and the tool rest. It should be possible to quickly remove the wheel guard and mount a wire wheel.

Make a couple of portotyles from wood and cardboard to proove your design. There's a lot fo trial and error in practical ergonomics. Think with the cheap stuff so you only have to make the one of a kind product once.

Vitrified grinding wheels used in general shop work run most efficiently at 5500 peripheral feet per minute. 10" x Pi = 2.6 feet. 5500 FPM / 2.6 per rev = 2100 RPM grinder shaft speed.

10" wheels are usable down to 6" diameter. It would be nice but not necessary to run the wheel at a constant FPM meaning a variable speed ranging between 2100 RPM to 3500 RPM. If you wanted to get fancy, you could run a DC motor and adjustable voltage drive, a single phase supplied VFD to run a three phase motor, or a variable motor pulley (such as still offered by Lovejoy) and the single phase motor on a lever operated swing mount.

If the motor is exposed to the dust use a TEFC motor. Open motors hate magnetic dust.

Use a 3V belt and pulley of you decide on a fixed belt ratio grinder drive. The variable pulley belt would depend on the makers reccommendations.

It's hard to imagine a greater convenience on a bench grinder than a dust collector. A shop vac is barely adequate and very noisy for this application. I wouldn't reccommend it. You need more volume. A better choice would be a 8" squirel cage blower with a screened inlet driven by a 1/6 HP motor but a cheap leaf blower will do.

Arrange the duct capture to suit the conflicting requirements of full capture and maximum accessibility and convenience. That can be a real trick. Arrange a trap with a door under the wheel guard so you can retreive little stuff you might fumble. The air flow should make a U turn in the trap to eject the heavier dust before it goes to the blower. The blower discharge should flow tangentially into a faux top discharge cyclone made from a 15 gallon steel drum. Use 5" ductwork. Make the filter sack from chamois flannel or seferal pleated filters of some common size and make it bag as you can fit under the grinder.

Somehow make all this stuff compact, fully enclosed, quiet, and easy to clean. Right.

That's how I would make a home made bench or pedistal grinder. If someone held a gun to my head.

[This message has been edited by Forrest Addy (edited 05-27-2004).]

[Betterhalf]

RPM is about right. Wheels if they are old could act harder than the grade shows on the wheel.

[Evan]

.

[This message has been edited by Evan (edited 05-27-2004).]

[Paul Alciatore]

I don't like the idea of a jam nut in an application like this. Consider:

The main nut will have the outer side of it's thread pressing on the inner side of the thread on the shaft. A jam nut will lessen this pressure when it's tightened. Unless you apply enough torque to compress the wheel's cardboard facing enough to then bring the inner side of the main nut's threads into contact with the shaft's threads, then the main nut will be floating and provide less or no holding torque. Tightening the jam nut this much may overstress the wheel and cause cracks.

For this reason, I don't like the idea of a jam nut except where both nuts are free and clear when the jam nut is tightened.

If you really want to avoid the left hand thread, you might consider a castle nut and wire or cotter pin it in place. Or just a hole for a cotter pin outside of an ordinary nut to prevent it from spinning off.

Paul A.

[Tony]

holysmokes, forrest! thanks for the input but after all of that i might as well go buy one!

*pause*blank stare* *blink*

i'm building this thing because "its there"
.. that is, the parts are. 1.5hp motor, bearings, and wheels.

no dust collection involved unless you count the air filtering the 1.5motor will be doing for the shop

and no guards. at least not for the wheels. maybe boneheaded, but i just dont like them. i plan on closing everything else. i feel guards on pedestal grinders to be dangerous and have always removed them in the past. the only thing i keep guards on are small fast tools like 4"angle grinders, air-cutoff tools, . . . and my girlfriend.

plus i have two other 'real' pedestal grinders that should even out the accident statistics.

what i would like to do, however, is add some bells and whistles.. like really nice STURDY rests... maybe with built in angle adjusts for bit sharpening. or something crazy like a built in collet on the shaft ends to take 1/4" diegrinder stones.

or pillowblock bearing mounts that double as bottle top openers.

ok maybe those last two are stretch.

anyway, if i see this through, the most work the grinder will probably ever see is forming 3/4"x3/4" hss squares for lathe toolbits -- we dont do alot of heavy fab in the shop that would require "leaning" on a grinder.

maybe to make the project *really* exciting i'll drive the shaft with dual chainsaw chains. (kidding)

good night everyone!
-tony

PS.. LH nut it is.

[Tony]

i got in the habit a few years back of drawing mock-ups in good 3d cad packages.

generates all the prints that i work from and is by far my handiest tool. (next to my hammer).

here's what the thing will look like:

http://www.sigma-f.com/pub/grinder.gif

the yellow base is a large C-channel.
getting the belts off shouldn't be too hard as there are only 4 bolts holding the whole thing together.

i plan to bolt the gizmo to a wall.

-tony

[brunneng]

Which package did you render that out of?
I use AutoCAD 13 for my cad work and I've got TurboCAD 8 that I'm starting to learn for 3d work.

[ulav8r]

You need to add a shield to prevent dust from the right end wheel being sucked into the fan on the back of the motor.

[ibewgypsie]

Rhino 3d?

Neat drawing. I wish you was around to help me out here. I bought bobcad but not had enough t ime in the last few weeks to learn much.

IF it is rhino3d I posted a free toolpath generation that works with it on another post here.. I lost that hard drive and don't have the link handy. Neat simulation via truespace too... I wanna copy of that someday.

David

[Tony]

solidworks.
not the newest version, but you can find
more info at www.solidworks.com

i think the new versions do full-blown simulations and can calculate stuff like component failure (such as bearing life, in this case).

amazing what "they do with computers"

if anyone needs anything drawn up, i'd be happy to do it (free)... i could use the practice. -- so longs its not an entire petroleum distillation plant... that might take a few days.

(ps, i think i can export models in that fancy format they like to turn into Gcode. STL? IGS? ABC? so if you need a complex 3d (curvy?) model to rip Gcode out of, let me know. (engraving, too)

-tony

[Forrest Addy]

I see discussion of using RH threads on both ends and using a jam num to back up the nut on the left wheel. Don't do it. Use a LH thread and nuts. Jam nuts are of no use in LH situations where relative rotations are involved one initial tension relaxes. There's no self tightenting.

If You absolutely positively have to use a RH thread in a LH situration, use a keyed washer between the nut and the driven element. Mush less hassle and much safer than a jam nut and it's less hassle.

Left hand threads are no biggie. You make them the same way as you make the right hand ones. You simply reverse the direction sense between spindle and lead screw and use left hand threading tools to bore the internal thread.