I need a better bench grinder

Has anyone bought from Northern tools? I am also looking at these grinders.

was looking at the one with the belt sander attached. Any help here on this?

Don D.

Was at Sears yesterday, and they had an 8" for $99. Looked pretty sturdy to me. When it comes to bench grinders, I found that those $20 miracle grinders just don't cut it. No pun intended. With bench grinders, you pretty much get what you pay for. IMHO, that is.

STeve

I've been watching the 8" harbor freight grinders for a sale. The seem to have 2 non-lighted versions, 1/2 and 3/4 horsepower. I think the 3/4 was 54.95 at the local store. Dunno how many amps though, so I don't know if it has any guts or not.

John

The "horsepower"/"HP" claims seem incredibly bogus in the US. Your "3/4HP" looks that way. 6inch + 3/4HP would be unstoppable - half that power but for-real would be capable machine.

Take this example. I've seen "5~1/2HP" vacuum cleaners (the workshop ones which can also draw up water) in the US, which plug into domestic 110V sockets. Now that no more happens than "2+2=5".

1HP=750Watts (actually 748W?) 5.5HP*750W/HP=4125W

and Watts=Volts*Amps

so Amps=Watts/Volts

Amps = 4125/110=37.5

37.5Amps from a domestic socket? I don't think so! The supply cable would have to be about 5/8inch diameter (about 15mm), for another thing! And that current draw is if the motor is 100% efficient (all electric power -> mechanical power). Electric motors are quite efficient, but still, you're talking over 40A current draw.

I think the current draw is a more accurate measure, as a contributor suggested. You could deliberately throw away current with an inefficient motor, but then the grinder would get hot doing nothing - which would be obvious - so that doesn't happen (a bench grinder has no vents or airflow, as have to keep out dust, so can't throw away waste heat like in say a vacuum cleaner). For sure a good machine would be icy cool doing nothing, for ever, while a cheapo one would get hot to the touch if left on for 15mins doing nothing. But that's less that a hundred watts wasted (less than an Amp at 110V).

Multiply:

current draw (Amps) * input voltage (110V or 220V - whichever it uses)

giving input power.

Then 750W = 1HP

So:

HP Watts Current @ 110V

0.25 188 1.7 0.33 248 2.3 0.5 375 3.4 0.75 563 5.1 1 750 6.8

Hope this helpful

Richard Smith

I saw a couple grinders that had low RPM's, I wonder if these would work better that the 3400 RPM's. I saw another one at the about 3400 RPM that said no load, would that mean it should not bog down? I did a small job biulding a tie post for a friend and I am using the money to buy a bigger grinder. I am looking at $80.00 - 100.00 if that helps finding a decent grinder

D>> I have a 6", 3/4 hp bench grinder I bought when a tool truck came to > town.

Don, the best bench grinder I have ever used is the one my dad and I built out of an old 1/2 hp motor--a real, honest-to-goodness 1/2 hp motor, like the kind you can scavenge for free out of a leaky washing machine. We bought one of those threaded shaft adapters from Woodworker's Supply, put on a wheel, and rigged up a guide/support. It does *not* bog down! It may be that one of these days the grinding dust will wear it out, since the motor is not sealed, but meanwhile it's been working great for quite a few years. One downside is that it only has one wheel, rather than the two that are common on store-bought machines; on the other hand, it runs at 1750 rpm, which is better for most of what I do. I keep meaning to make another one just like it for myself, since I've got one of those cheap tool-truck grinders that bogs down if you breathe on it ... and I do have two or three old washing machine motors lying around ... but I keep forgetting to pick up the shaft adapter whenever I'm at a store that might have one. (HD and Lowe's sometimes have shaft adapters, but only with the right-handed threads, and I need a left-handed thread.) One of these days ...

I have a Sears 8" diam, 3/4" stone face bench grinder , don't see HP rating printed on it but I recall 3/4 HP , it is a strong unit , I grind 1/4 inch mild steel plates all day long and does not bog down. paid $69 for the display unit since it was out of stock.

I'vealso bought >I have a 6", 3/4 hp bench grinder I bought when a tool truck came to town.

Unless US horses are different from Swedish 1 HP is 735 Watts. But newermind. I think the power specified for a grinder (or most other machines is based on max current drawn under full load. For an electric motor, that is when it is stopped. The higher the speed, the less curent is drawn. Some sort of torque measurement would be more useful. For high power machines here we use three phase wiring giving 400 volt. Same with all larger welding equipment. I have to make do with 220 V. Henning

No load would make me think it bogs down easily. Not that I'm suspicious or anything...

Steve

D> I saw a couple grinders that had low RPM's, I wonder if these would work

The revs of an induction motor is "locked" to the mains frequency of

60Hz (N.Am.), 50Hz rest-of-world. Under load an induction motors "skids" a bit with respect to this no-load speed. But not by much.

"electric drills", angle-grinders, etc. have DC motors with carbon brushes (the AC frequency is too low to matter - they work just fine on mains AC). Their response to load is more desirable for these applications than induction motors - steady decline in speed with load - but you have the brushes which have to be replaced. And induction motors can be very very efficient (high-90's percent), so very little waste heat, so can be fully enclosed. So no grit or anything in, and no wearable parts apart from the bearings - which are sealed, as we said.

There's good induction motors which are the right size for the job and they are made as they should be, and there are not-so-good ones. Hence this whole business about someone's grinder not doing so well.

I'm no electrician - anyone want to comment?

RS

Steve Smith wrote:

suspicious

There's a lotta replies...

One of the finest bench grinder I've ever used was a 220v single phase unit.

Almost instant on, and there was little way to stall it.

- "Don D." - spluttered in news:eOfLd.3352$6u.2097@fed1read02: