# Query: Is it possible to slow down a bench grinder



## sonofSon (May 25, 2020)

I inherited an old but very good condition, 1/3hp Baldor Model 612, two-wheel bench grinder from my late father. The motor, wired for 125VAC, runs at 3600 RPM, which for my personal use is way too fast. Half that speed would be much better. 

Can anyone please advise me: (1) Is it possible and practical to reduce the speed of the motor without damaging it?

(2) How might I go about it?

I'm not an electrician but have some knowledge of electrical circuitry, can read simple schematics, and have built small projects over the years. 

Thanks


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## DrRobert (Apr 27, 2015)

Google 120v speed control


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## woodnthings (Jan 24, 2009)

*Nope!*

You can not change the speed of an induction motor using a "variable speed controller" as you would on a router which is an AC/DC brush type motor. Unless the motor has internal windings that allow for two speeds, you are out of luck. The standard RPMs for induction motors are 3450 and 1725 RPMs. However, bench grinders do come in both speeds. It is for this reason that I do not sharpen my plane blade or chisels on a 3450 RPM grinder, it gets the metal too hot too fast. I use a belt sander with a "belt drive" which I can change the speeds by moving the belt on a step pulley. A direct drive bench grinder has no such feature. 

:|


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## CharleyL (Jan 13, 2019)

Try to slow that one down, and you will burn it up. It has a centrifugal start switch that will switch on the start winding if you succeed in slowing it that much, and the start winding will quickly overheat and burn, since it isn't rated to be on more than a few seconds at a time. Induction motors are power line frequency dependent to govern their speed. You need to change the power frequency to change the speed, but again, look out for that start winding. They make power controllers for 3 phase induction motors to vary the frequency of the power going to them, and this will allow changing the speed, but slow the motor too much under load, and the motor won't be able to cool itself.

So, in short, don't try it. If you do, you will burn it up.

Nice grinder. Leave it alone and enjoy using it at it's intended speed. Buy another grinder designed to run slower, if you need that.

Charley


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## JayArr (Sep 18, 2018)

You could take it apart and disconnect the start winding, and then buy a VFD (variable Frequency drive) but that's lot of work and you may spend more on the VFD than a new grinder.


http://www.electricmotorwholesale.c...40&attributevalues=,1/3&attSearchList=,40~1/3


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## johnedp34 (Jun 30, 2016)

I agree, I paid $15 for my bench grinder which came with 80 and 120 grit wheels plus a buffing wheel.
johnep


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## sonofSon (May 25, 2020)

Gentlemen: Thank you all very much for your helpful replies. You've saved me some grief, not to mention Dad's grinder. I can see this Website is going to be useful and enjoyable. 

Although Baldor no longer makes the grinder in question, a Wyoming distributor of my acquaintance still had the factory documents on its Website so I was able to download the motor schematic last night. From that, I could see the motor is an induction unit with a capacitor start and a drop-out relay instead of a centrifugal switch. 

After your timely warnings about what would happen if I reduced the voltage to the motor and the futility of altering the current frequency, I wanted to find out the grisly reasons so went to Quora and had it explained to me in grisly detail by a couple of E.E. types. 

I'll still use the grinder for metal work but my chisel and plane blades will not go near it. 

Stay well, all of you. 
Bill


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## DrRobert (Apr 27, 2015)

Then what is this?


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## JayArr (Sep 18, 2018)

That's an oversized light dimmer.



> The heart of the control is a triac fired in a manner to adjust phase and thereby vary speed.





> *It is not designed for capacitor start motors*_._


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## sonofSon (May 25, 2020)

JayArr is correct - my Baldor grinder is based on a capacitor start motor. Although I've taken apart, repaired and reassembled the Leeson Ph1 1.5hp TEFC motor Delta furnished with my tablesaw in 1986, I wasn't sure of the nature of this Baldor motor because it didn't have the usual external lump where a start capacitor would reside. It wasn't until I got hold of the motor schematic (attached) that I could see it was a capacitor start induction motor. 

I am nobody's expert on electic motors and I was really fascinated to see how the start circuitry was designed, using a relay that is sized and calibrated to energize the start circuitry when the main winding draws peak current on startup, and then drops the start circuit out as the current draw falls when the motor approaches running speed. The centrifugal switch on my Leeson is a nice piece of work and I'd guess expensive and difficult to scale down below a certain mass. At a guess.


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## JayArr (Sep 18, 2018)

Umm... I don't see a capacitor in that schematic.


The parallel lines are relay contacts not a capacitor. (google "3cr current relay")


I still wouldn't run it on the dimmer control but I thought I'd point out to you that there is no capacitor.


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## sonofSon (May 25, 2020)

You could have fooled me - I thought I was looking at a non-polarized capacitor symbol. Live and learn. I'll Google the link you mention and run it by you once I think I've figured out how this start circuit works. 

Thanks, 
Bill


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## sonofSon (May 25, 2020)

Well, I think I've made a start on understanding how it works. Let's see. Please check me on this: This is a split phase motor, the auxiliary winding consisting of relatively thin, high resistance, low inductive reactance wire, the obverse of the main winding. The two windings are initially in parallel. I don't understand what a "traveling wave" is but the phenomenon apparently serves to create enough torque to start the rotor moving, albeit the torque created is much less than what a capacitor-based start circuit can create. As the rotor approaches running speed and current draw diminishes, the auxiliary winding is dropped out of the circuit by either a centrifugal switch or a current-reading relay. From what I have read and _think _I understand, split phase motors would be used in low-torque applications like my grinder or a fan, say. 

Pass? Barely Pass? Fail? Clueless?

Thanks, 
Bill


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## TobyC (Apr 30, 2013)

It's only 1/3rd horsepower, if you slow it down it'll be useless, it'll bog down on a feather!


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## Bob Vaughan (Oct 29, 2008)

The Baldor 612 was the bottom of the Baldor line. Even then, they were sweet little grinders. Very smooth and quiet. Much better than the Asian made stuff offered for cheap today.
If you're having burning problems using a 3450 rpm grinder, you need better instructions on using a bench grinder. One can burn on the slow speed grinders as easily as a high speed grinder.


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## sonofSon (May 25, 2020)

Bob, 

Probably it's my age - I'm slower these days to deal with things that happen fast. Other than for dressing cut machine screws and smoothing edges of sheet stock, I had thought to use this grinder for squaring up a worn chisel or plane blade before putting a new edge on it by hand with stones. I've done that with slow grinders in the past and was able to keep the blade sufficiently cool that it didn't draw the temper. With the help of other members I've now come to understand Dad's grinder is a one-speed pony, which is o.k.

I'd be happy to learn from any wisdom you'd care to impart. With only a few exceptions, I'm almost completely self-taught and that is what makes this forum especially useful and enjoyable. 

Bill


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## Bob Vaughan (Oct 29, 2008)

The Baldor 612 is still listed with MSC for $456.39 so that's the potential quality level grinder you're putting together. I've bought many over the years for $20.00 from sellers that thought the 612 was the same as an Asian-made cheapie.
https://www.mscdirect.com/browse/tn...MIzvLk3PvY6QIVB9bACh1WAgG7EAQYASABEgJuPfD_BwE
The problem with the 612 isn't the grinder, but the tool rests. They are too light and flimsy for such a good grinder. I'll make my own out of thicker steel. Heavier tool rests make all the difference in the world. Add a few Kipp handles, and you've got a lifetime of convenience.

An 1800 rpm 6" grinder is incredibly slow in removing metal. I hate them. The trick is light quick passes. I can make 100 light passes on a plane iron or chisel in about 60 seconds. Keeping the stone clean and sharp is another key detail. Cheap stones aren't worth the trouble. They clog and heat too easily. By holding your fingers close to the cutting edge, you can feel the heat building so you know when to back off. The little rocks in the wheel only stick out so much so that's about all you can remove. To quantify with numbers, a light quick pass will remove about .001" to .0005" of steel. 100 light quick passes removes a lot of steel. Once the edge is formed, the steel goes right to the sharpening stones for sharpening.

Below are some shots of the 612s I've done over the years showing the tool rest components that I've remade. I hope these will offer some inspiration. Sharp tools are a joy to use and a properly rigged Baldor 612 grinder will offer a faster and easier way to get there.


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## CharleyL (Jan 13, 2019)

DrRobert said:


> Then what is this?



"*It is not designed for capacitor start motors*." You missed reading this statement in your link.

This speed controller will work fine on universal motors, like those in an electric drill, but they will not properly vary the speed of an induction motor whose speed is controlled by the power line frequency. Also, if you reduce the voltage of an induction motor to the point where it is no longer following the power line frequency, you will have lost most of the torque of the motor. Slowing it will also cause the centrifugal start switch to engage the start winding and capacitor circuit, which is not designed to operate for more than a few seconds at motor start-up. This will result in the start winding and capacitor being destroyed (you will let the magic smoke out).

Charley


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## sonofSon (May 25, 2020)

Bob, Thanks for taking your time to help me along. I can see you've put some serious beef in those tool rests. I've noted that what I have assumed to be the original rests are pretty light and awkward and don't want to stay in adjustment. I particularly appreciate the photos that illustrate the mods you made. I'm not much of a metalworker but I think I might be able to replicate what you've done. 

I can't identify for certain what wheels are on Dad's grinder except to say one is coarse and one is less so. I note that yours is set up with a wire wheel and a single stone. Do you use this setup for a particular purpose? Also, if you'd care to do so, recognizing that the primary purpose of my machine would be to sharpen edge tools, what brand and grade of wheels would you recommend? 

Also, almost forgot: Do you find it advisable to dip the tool in water as you grind or just use your fingers to feel for excessive heat?

Thanks,
Bill


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## Bob Vaughan (Oct 29, 2008)

Bill, I think those inside wheel guards on your grinder are cast iron. I’m envious. The later versions were cast aluminum.

I always keep a water pot and wiping rag near by when grinding. Grinding is a hand activity and errors in pressure and pace can and do occur. About 100 passes in 60 seconds is a good pace I’ve found. Light and quick. Your fingers will tell you when the heat is rising in the blade. Sticking a wet blade into the wheel introduces contaminates that gum up the surface of the wheel and makes the wheel heat more than it should. Adages referring to the tedium of grinding are very true, but the results are worth it. The grinder shapes. Sharpening is done on stones.

That setup on the 612 with the wire wheel was something I fixed up for the basement shop area when I needed a wire wheel. I got the grinder without wheel guards, a $15.00 buy at a flea market. I had an extra set of wheel guards in stock. I’ve got well over a dozen types of bench grinders I’ve accumulated over the years. I grind my own shaper steel profiles for slip knives. A handy cut-off wheel for your grinder is a Norton A60OBNA2. No other wheel is as good or as safe. For your amusement, I’ll link a thread below.
http://www.owwm.org/viewtopic.php?t=56115


Try using the wheels you’ve got for the immediate future. Those $100.00 CBN wheels won’t be much different right now. The kind of wheel can make a little difference, but what makes a BIG difference is the condition of the abrasive on the surface of the wheel. You need two things; a diamond (1/4 carat) wheel dresser and a star (Huntington #0) wheel dresser. These are long term investments that will last decades. The diamond dresser scrapes all of that mess off the surface of the wheel and trues up the wheel for very smooth running. It also makes a mess so wear a dust mask. While the diamond cleans and trues the wheel surface, it also dulls the exposed abrasive granules. That new, clean surface will burn like crazy. The next job is to beat the dulled abrasives off the surface. Take the star dresser and press into the wheel’s surface while moving side to side. The pressure should be hard enough to almost push the grinder around on the bench. Again, more mess. The duration of the star dresser use should be about five seconds and that’s it. You’ll be amazed at the difference. Once the diamond has been used, try grinding something and observe the few sparks generated. Try the same piece after the star dresser and you’ll be amazed at the amount of sparks generated and how much better the wheel cuts. You need both tools to get a good job. The diamond cleans and trues the wheel and the star dresser restores the sharpness. When the wheel’s abrasive gets dull, a few seconds with the star dresser cleans things up. You’ll use the star dresser much more often than the diamond. If you read on the internet that a diamond is all you need, disregard that source of information.


The below photos are from a 2004 catalog so the prices will be a little different but not a whole lot. There’s no need to spend a pile on the diamond dresser.


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## sonofSon (May 25, 2020)

Bob, Thanks very much for your extensive reply. I'll take your advice and work with the wheels that are already installed on the grinder, at least until I have a much better grip on technique and wheel maintenance. I'm going to lay in the accessories you mention and see what I can do with them. I'll report back - either progress or a cry for more help!

As I understand what you recommend, in the process of sharpening I should use the machine to establish a square edge and eliminate chips, then switch to stones. Should I set the tool rest for the bevel angle for the particular tool? e.g. 25 degrees for a low-angle block plane? I would guess so, but thought I'd better ask. 

Best,
Bill 

PS I've got some old tools from the bottom of Dad's barrel that I'm going to work with before I risk my small inventory of good stuff!


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## Bob Vaughan (Oct 29, 2008)

You understand it correctly about shaping on the grinder. It will take all day shaping with stones. I just checked tool pressure by pressing down on a postal scale. Wheel pressure should be about 1 ounce. Very light. As to angle, whatever looks about right will work. Once the edge has its burr off and honed sharp, the exact angle is not all that important. Hair shaving sharp is what you want, obviously. Initial shaping of a beater chisel or abused hand plane iron will seemingly take forever but it won't. Time it and you'll see. Once you've got the shape on an edge, restoring it generally takes just a few minutes.

https://www.woodworkingtalk.com/attachment.php?attachmentid=390485&thumb=1

A piece of 1/4 ply works good at keeping an index of tool rest to wheel ratio.

https://www.woodworkingtalk.com/attachment.php?attachmentid=390487&thumb=1

Kipp handles and custom made tool rest holders (from angle iron) on a 7" grinder showing what a good rest for chisels would be.

https://www.woodworkingtalk.com/attachment.php?attachmentid=390491&thumb=1
Magnifying glass mounted on the eye shield to better see the work area when a NortonA60OBNA2 toolroom cut-off wheel is being used.
https://www.woodworkingtalk.com/attachment.php?attachmentid=390489&thumb=1
Making your own brad point bit from metal working drill bits.
https://www.woodworkingtalk.com/attachment.php?attachmentid=390493&thumb=1
Another shot of the A60OBNA2 wheel grinding brad point bits

https://www.woodworkingtalk.com/attachment.php?attachmentid=390497&thumb=1

Tricked out Baldor 612. Its such a good little 6" grinder that it is worthy of this extra effort.

https://www.woodworkingtalk.com/attachment.php?attachmentid=390495&thumb=1

The back of the grinder enclosure showing a receptacle for a work light.


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## sonofSon (May 25, 2020)

That is, by far, the most tricked-out grinder I've ever seen. You've given me some great ideas.


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## kwoodhands (May 1, 2020)

Here is an old trick that works fine. Leave the motor at 3600 rpms. Turn the grinder on and let it come up to full speed. 
Now turn the grinder off and start grinding your tool. When the wheel stops, look at the grind, you may be surprised. 
If the grind needs more work, repeat the process.
About 50 years ago I stumbled on to this trick when the electric went off during a storm. I was grinding a roughing gouge and always had problems grinding a single facet. Mostly hit and miss back then. When the electric came back on I looked at the gouge and the grind was perfect. I thought it was dumb luck but decided to try grinding other lathe tools. 
Every tool I ground came out either perfect or nearly so. Then tried plane irons and chisels. Spent several hours sharpening every tool that needed it. I can't explain why, maybe because the grind is better controlled. 
It works, that's what is important.
mike


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## sonofSon (May 25, 2020)

I'll give this a try.


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## sonofSon (May 25, 2020)

Bob, I tried a magnet on the wheel guards and they are definitely magnetic, as are the other painted parts. I know heat-treating has come a long way and the aluminum tables on my little suitcase planer and Toshiba miter saw seem reasonably stout, you just can't been cast iron for vibration dampening. 

Bill


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## Bob Vaughan (Oct 29, 2008)

As I said, your grinder is cast iron and a good quality USA-made cast iron to boot, not Asian peanut butter iron.
A lot of the cheapie grinders these days have stamped steel inside and outside guards that seem to be rejects from a low-end frying pan factory.
You've got an industrial quality grinder that will never be made again.


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## ajdragon (Jul 26, 2017)

Hi


If your looking for a grinder that you can control the speed on, then try looking for a older belt driven grinder and use a DC Motor out of a treadmill and a AC Speed-controller. You can get those DC motors down to some pretty low RPM's.


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## sonofSon (May 25, 2020)

*Vaughan has shown me the Way*



ajdragon said:


> Hi
> 
> 
> If your looking for a grinder that you can control the speed on, then try looking for a older belt driven grinder and use a DC Motor out of a treadmill and a AC Speed-controller. You can get those DC motors down to some pretty low RPM's.


Thanks for your suggestion and that certainly would be a feasible project. However, in response to my original post, @member Bob Vaughan graciously has taken a considerable amount of his time to provide me with know-how and show-how; hopefully so I can learn to properly use Dad's old grinder to reshape blades for sharpening without drawing their temper. He has put up a very useful series of photos of re-worked tool rests and guards to aid in the task. And he has pointed me to some maintenance tools needed to prep the existing wheels on my machine to do good work. Armed with these lessons, I'm encouraged enough to give my machine a good trial with some old worn chisels and plane blades Dad left lying around - although not the good stuff, at least not yet. 

I'll report back how it works out. 

Bill


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## sonofSon (May 25, 2020)

Bob Vaughan said:


> The below photos are from a 2004 catalog so the prices will be a little different but not a whole lot. There’s no need to spend a pile on the diamond dresser.


Bob, I've ordered the Desmond star dresser you recommended. MSC carries it and they've been reliable. There has been a little inflation - twenty bucks instead of twelve. I tried at first to include a diamond dresser in the order. However, none of the single point tools MSC listed (that I could find) had handles on them. I wound up buying a "shop grade" quarter-carat dresser on an 8" shank and plastic handle, from Penn Tool Co. for about $28. 

Big Brown is supposed to get them here in about a week. I look forward to trying them out and I've already figured out to do this on my driveway with a mask, to avoid adverse comment from the War Department.


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## Bob Vaughan (Oct 29, 2008)

Looking at your original wheels, they are going to take some time to get that layer of aluminum out and some of the other contaminates. Doing this outdoors is excellent strategy. Once the wheels are clean, the occasions you'll use the star dresser won't make such a big mess. As I said, for routine sharpening of the wheel's surface, you'll only push the star dresser into the spinning wheel for about five seconds and then you're done.

Consider making your own grinder stand. Its a fun little workshop project that can have great storage benefits and a good way to use up wood that wouldn't be of a grade that quite fits in a nice piece of furniture. Side hung drawers are very efficient. I like 5/8" thickness for the sides and backs. Having the grinder stand on casters makes things easy to move around and it keeps your bench uncluttered for larger projects.

Some examples of stands I've done for various grinders I've got:


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## sonofSon (May 25, 2020)

*Everything has to be on casters*

Bob, I particularly like the touch of the tray mounted above the motor and between the wheel guards. Is it secured to the motor case or the table top? 

As you can see from the attached photos of my garage "shop", everything HAS to be on casters unless it's hung on the wall; and I'm running out of wall space so, in order to be accessible and useful, the little Baldor grinder will need to have it's own rolling stand. What is not shown in the photos is the 800 board feet of rough white oak in what was once a car bay. That subject is a little touchy around my house - particularly since another thing not shown is the motorcycle still parked in the garage...

I'm going to need to build something like what you've illustrated. I believe I've even got a set of casters suited to the job. I'd assume from the working height of the stand that you either have weights in the bottom drawer or don't put large sideways forces on the machine while in use? The wheelbase doesn't look very long in relation to the table height. I need a fairly high working height myself, so will build one similar. 

Dad did a pretty fair amount of metal work with this grinder, although he also used an old Craftsman narrow-belt vertical sander for similar purposes. He had several different gas welding rigs in addition to his big arc welder, a pre-1940 Southbend lathe and an Enco drill/mill (which latter he cursed regularly for its sloppy build). Along with a supply of exotic metal stock that had somehow stuck to him (as a retirement gift from colleagues) when he retired from Shell Oil. I can't imagine what all residue is on the grinder wheels. To give a small example: A machinist friend and fellow employee gave Dad and Mother a beautiful barbeque grill made of high-grade stainless steel, the firebox having been insulated with "spare" tiles of hybrid metal from a run made for the re-entry nose cone of an early NASA space vehicle. (He later found out the material was considered carcinogenic and disposed of it.)


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## Bob Vaughan (Oct 29, 2008)

It looks like your shop is coming along pretty good and you’ve got most of the things needed. That’s a great story about the nose cone materials used in the making of the barbeque grill.

I, too, have disrupted domestic tranquility with storage of a big lumber buy that was too good to pass up. Twice I had piles of lumber that stayed on our covered back porch until I had room to store things in my lumber storage areas. It took several years to accomplish this. The drawer cabinet base will be a good opportunity for you to use up some of that lumber that may not be of a quality level suitable for fine furniture. Drawer sides and backs are real lumber alligators. I’ll joint and glue up wide panels and then rip the drawer sides out of that. I’ll start with 4/4 lumber, face flatten, skip dress, and joint the edges. Once the drawer sides are roughly ripped out, back to the jointer for finish flattening and then to the planer for final dressing to 5/8” thickness. The relatively short lengths makes good use of wood that may be twisted or bowed too much for longer parts.

The grinder drawer stand is pretty heavy and won’t move against pressure put against the grinder when grinding. If it does, you’re putting way too much pressure against the wheel and will burn the steel. On many of my stands, the grinder is screwed to the top. There’s a ¾” space left between the top of the top drawer and the bottom of the top to allow clearance for the bolts. That can be seen on one of the photos shown above. You’re essentially building a casual lingerie type drawer cabinet. Its good practice. I’ll use an easier to make locking joint on the drawers rather than dovetails. The sides and back of my cabinets are made of ¾” plywood, either birch or oak veneer. Having a back of ¾” plywood is crucial to squareness and stability. The cabinet is set on a floor float that has casters placed wide enough so that when turned under the cabinet, there won’t be imbalance.

The tray tops on some of the grinders are attached directly to the grinder’s body with an angle piece and stand-off spacers. The original through bolt is discarded and usually replaced with 10-32 all thread long enough to hold things in place. This is possible with the larger grinders with four through bolts. The Baldor 612 only has two through bolts, so this isn’t possible and thus the two upright pieces of plywood behind the grinder. I’ll try to get some photos.

… lots of blather here and lots of thread drift but I’ve nothing more interesting to do this morning.


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## Bob Vaughan (Oct 29, 2008)

More photos including a drawer side glue-up.


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## faith michel (Sep 10, 2017)

Good job Bob.. it looks so beatiful your grinder and your stand... welldone...
This is my grinder and my stand..
I will add simple led light. .









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## Tool Agnostic (Aug 13, 2017)

Is there a name for that style of base?


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## Bob Vaughan (Oct 29, 2008)

It would be a pedestal base.
Baldor makes them. The Baldor GA16 is the cast iron type. The Baldor GA14 is a steel box with shelves. Pricey little devils. The GA14 was the inspiration for my drawer pedestal bases. I'd seen some of them in school shops and noticed that an unbalanced wheel could vibrate things out of the shelf. I figured drawers would be better.
I like the wood pedestal base. The bottom is heavy and that's necessary.


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## Tool Agnostic (Aug 13, 2017)

Bob Vaughan said:


> It would be a pedestal base.
> Baldor makes them. The Baldor GA16 is the cast iron type. The Baldor GA14 is a steel box with shelves. Pricey little devils. The GA14 was the inspiration for my drawer pedestal bases. I'd seen some of them in school shops and noticed that an unbalanced wheel could vibrate things out of the shelf. I figured drawers would be better.
> I like the wood pedestal base. The bottom is heavy and that's necessary.


Thank you for the quick response, but I was referring to the "four point" style on the very bottom of @faith michel's base. I wonder whether there is a specific name for that style of bottom on the pedestal base itself?


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## sonofSon (May 25, 2020)

Bob Vaughan said:


> More photos including a drawer side glue-up.


Bob, thanks for the photos - and the encouragement. I expect I'll have some offcuts from the upstairs project, from which i can construct a base cabinet for the grinder. Things have slowed down for the last week because I dropped a 20' red oak S2S 1x6 board on my left foot, just aft of where the steel toe in the shoe stopped. Next time, wear leather gloves instead of cheap cloth from HD. 

PS - something perhaps of modest value to other members: Profit from my experience. Last Saturday I placed a Web order with MSC Direct - good folks - for a star grinder wheel dresser. Then, Sunday, I realized I needed two 303 stainless M6 thumb screws. Back to MSC and placed a separate order. By the time I could get hold of a live person on Monday morning, they'd priced the shipping on the two orders separately and packed them up. To make a long story short, the dresser was only twenty dollars, the two thumb screws were $8.50 each -- about $37 for the actual stuff in both orders-- but the total shipping was SIXTEEN DOLLARS, even after I screamed loud enough to get a four dollar discount. Don't get me wrong - MSC is a blessing because it will sell you one or two pieces of tool parts that you are not going to find locally, for which I'm grateful. Yes, the thumb screws were priced like they were made of Unobtainium but I needed something very specific - exactly 25mm OAL, in a metric thread, a decent sized knurled head, and made of hard stainless steel. (It's for a drill press quill stop/lock mini-project). I needed exactly two - not the 500 the manufacturer likes orders for. The moral to the story is think about what you might need and get it in a single order! 

If I don't show some performance on the upstairs paneling and rails and baseboards and window trim soon, I may be sleeping in the garage shop and hot weather is upon us.


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## faith michel (Sep 10, 2017)

Tool Agnostic said:


> Thank you for the quick response, but I was referring to the "four point" style on the very bottom of @faith michel's base. I wonder whether there is a specific name for that style of bottom on the pedestal base itself?


I am really so sorry.. I am too late for your question Tool Agnostic.. I am looking online.. but i am not online.. my phone and my computer open 24/7 at this forum... My univercity opened today.. This is first open afther corona pandemic.. My school friends and i studyed lesson allday at school's library.. we come back our normal life with slowly slowly mini steps..
Anyway we call it geometric shapes.. I honestly said. I am an engineer's student.. I hate mathematics..and especiatly geometri..

An arabic scientist El Harezmî – (Ebu Abdullah Muhammed bin Musa el Harezmi) finded this geometric shapes at 16th century. .









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## Catpower (Jan 11, 2016)

sonofSon said:


> I inherited an old but very good condition, 1/3hp Baldor Model 612, two-wheel bench grinder from my late father. The motor, wired for 125VAC, runs at 3600 RPM, which for my personal use is way too fast. Half that speed would be much better.
> 
> Can anyone please advise me: (1) Is it possible and practical to reduce the speed of the motor without damaging it?
> 
> ...





I know you have been given a lot of advice here but I have been in the HVAC/R business for over 40 years so I have dealt with thousands of motors from 3 VDC timers to 4160 VAC 17,500 HP centrifugal compressors, and yes you can use a light dimmer to adjust the speed of a split phase motor. They do it differently now days, the electricity is "pulsed" through the dimmer so it is getting 120 V and the schematic for that motor shows a start relay so it would stay in the circuit and keep the B or start windings out of the circuit, so there in no centrifugal switch 



But if you are worried when ever you start the grinder have the dimmer turned up all the way then slow the motor to your desired speed. It won't have the original power, but that was what was causing you to burn in the first place, plus you need to work on the operation too


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## sonofSon (May 25, 2020)

Catpower said:


> They do it differently now days, the electricity is "pulsed" through the dimmer so it is getting 120 V and the schematic for that motor shows a start relay so it would stay in the circuit and keep the B or start windings out of the circuit, so there in no centrifugal switch


Thank you for trying to help me. I'm a little slow on these things so please be patient if I ask what may seem to be a stupid question. Asking stupid questions is how I learn things. My (very limited) understanding of how a start relay works is that it reads the amperage demanded by the motor on startup and closes to energize the start circuit coil as soon as the amperage exceeds normal running amperage. With the start coil engaged, the motor spools up and approaches running speed, at which point the current demanded begins to drop, eventually to normal running amperage. At some point the start relay opens and drops the start coils out of the circuit. 

I think I understand that keeping the B winding out of the circuit, after running speed is achieved, is important to avoid damage because the start coil is not designed for continuous use. I'm not sure what you mean by saying the start relay would "stay in the circuit" Perhaps I've got it backward. Is the start relay normally (when un-energized) open or normally closed? 

I think you are telling me that the dimmer pulses current to the motor in such way as to keep the start coils from re-energizing. I'm not clear how it accomplishes this. I don't question your expertise. I just don't have a good grasp on what you're saying. Thanks, Bill


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## Catpower (Jan 11, 2016)

sonofSon said:


> Thank you for trying to help me. I'm a little slow on these things so please be patient if I ask what may seem to be a stupid question. Asking stupid questions is how I learn things. My (very limited) understanding of how a start relay works is that it reads the amperage demanded by the motor on startup and closes to energize the start circuit coil as soon as the amperage exceeds normal running amperage. With the start coil engaged, the motor spools up and approaches running speed, at which point the current demanded begins to drop, eventually to normal running amperage. At some point the start relay opens and drops the start coils out of the circuit.
> 
> I think I understand that keeping the B winding out of the circuit, after running speed is achieved, is important to avoid damage because the start coil is not designed for continuous use. I'm not sure what you mean by saying the start relay would "stay in the circuit" Perhaps I've got it backward. Is the start relay normally (when un-energized) open or normally closed?
> 
> I think you are telling me that the dimmer pulses current to the motor in such way as to keep the start coils from re-energizing. I'm not clear how it accomplishes this. I don't question your expertise. I just don't have a good grasp on what you're saying. Thanks, Bill





There are two types of start relays for single phase motors, a current relay and a potential relay, you described the current relay. On your machine it is a potential relay, as the motor ramps up the start winding starts producing a back voltage or "Back Electromagnetic Force" that we refer to as Back EMF, when it gets to a certain speed the back EMF is great enough to give the coil enough strength to open the contact in the relay to drop the start winding out of the circuit


That is why you should start the motor with the dimmer maxed out then once it gets to speed dial it down to the desired speed. If you slow it down too much you will hear the relay drop out, but it would have to be less then about 30% of the full speed you don't want to go that slow, it probably wouldn't hurt the motor but probably toast the dimmer if run for extended periods


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## sonofSon (May 25, 2020)

Thank you for the explanation, which makes sense to me. After reading it, I found an ACHRNews article, "Know Your Potential Starting Relays" that helped me understand further how and why the Back EMF is being generated. I would have expected to read line voltage across the start coils and the relay coil in the same circuit with it. There's always something new to learn.


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