ThomasPowers Posted July 22, 2010 Share Posted July 22, 2010 The moment arm of the rotor in a much larger motor does make a difference in what it can spin up to speed. (I saw one motor once that you could *walk* through the windings of---it ran a blower to push air through the Moffat tunnel IIRC) Quote Link to comment Share on other sites More sharing options...
nonjic Posted July 22, 2010 Share Posted July 22, 2010 To the best of my knowledge self contained hammers only use a 6 or 8 pole motor to save the gear reduction, which, as has been mentioned is costly in money, space and maintenance. Ive seen some old plans for mill steam engines and they have stated x 'good' horsepower manufacturers may have been economical with the truth a couple of hundred years ago ! Quote Link to comment Share on other sites More sharing options...
thecelticforge Posted July 22, 2010 Author Share Posted July 22, 2010 Okay, if I do get the hammer, I would do better to get a 3hp motor with low rpms. I also should pour a slab nigh on 3 feet deep with good rebar renforcements. Anchored with bolts and cushioned with oak. I am thinking of an oak/rubber laminate. Now pricing. I had been planning on making a Clay tire hammer. How much would that cost me to build from scratch? Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 22, 2010 Share Posted July 22, 2010 There's "old" and there is "low rpm", let's don't mix up the two. Many old motors were rated on continuous output and many modern motors are rated on peak output. Look at some of the air compressors that claim 7 hp. Not for very long! I've managed to replace two of those with HD 5 hp motors and they are bigger and run cooler. Same rpm though, it ain't rpm/torque that makes the difference, it's manufactures ratings. They don't build "consumer" 900 rpm motors. Most 900's are very heavy duty and have a high service factor. Fact is you have to gear down any motor. Or are you gonna run your hammer at 900 rpm? So for a 300 rpm hammer you gear it down 3:1 and a 1750 you gear down 6:1. Well, 3:1 is just easier to do. None of that changes the fact that "a horsepower is a horsepower"! Put a 900 rpm 5gpm hydraulic pump on a 900 rpm motor and it will stall at the same pressure as a 5gpm 1750rpm pump on a 1750 rpm motor. IF they are comparable duty motors. Hey Larry, bet your 100,000 rpm 1hp die grinder will remove metal faster than a 900rpm 1hp die grinder would! So it must have more power! Use the most suitable rpm and horsepower. Don't use a high speed motor on a low speed hammer or a low speed motor on a high speed grinder. Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 22, 2010 Share Posted July 22, 2010 Okay, if I do get the hammer, I would do better to get a 3hp motor with low rpms. I also should pour a slab nigh on 3 feet deep with good rebar renforcements. Anchored with bolts and cushioned with oak. I am thinking of an oak/rubber laminate. Now pricing. I had been planning on making a Clay tire hammer. How much would that cost me to build from scratch? Not a fair comparison! When you get done with the tire hammer, you still won't have a hammer that nearly compares to the Fairbanks. Quote Link to comment Share on other sites More sharing options...
thecelticforge Posted July 22, 2010 Author Share Posted July 22, 2010 Not a fair comparison! When you get done with the tire hammer, you still won't have a hammer that nearly compares to the Fairbanks. I was afraid some one would say that. I thought it would be Thomas though! Quote Link to comment Share on other sites More sharing options...
Timothy Miller Posted July 22, 2010 Share Posted July 22, 2010 I say your going to need 5Hp to get the most out of that hammer. Probably would work on 3 hp but its going to be a bit sluggish to get going. It will also trip the breaker when run hard. Quote Link to comment Share on other sites More sharing options...
David Browne Posted July 22, 2010 Share Posted July 22, 2010 I was afraid some one would say that. I thought it would be Thomas though! Celtic, If you are hoping for someone to "talk you down" into buying the smaller, more economical, completely practical, sensible hammer....well...good luck with that on this forum. -DB Quote Link to comment Share on other sites More sharing options...
thecelticforge Posted July 23, 2010 Author Share Posted July 23, 2010 Celtic, If you are hoping for someone to "talk you down" into buying the smaller, more economical, completely practical, sensible hammer....well...good luck with that on this forum. -DB All I am really worried about is parts. I will have to have them all machined because I don't think I will do business with the guy in PA who demanded to know how I got his phone #. That tells me he has had a LOT of unhappy customers. I don't think I will run it hard enough to cause any problems. Quote Link to comment Share on other sites More sharing options...
Timothy Miller Posted July 23, 2010 Share Posted July 23, 2010 If you need advise I have some experience fixing this brand of power hammer. Quote Link to comment Share on other sites More sharing options...
monstermetal Posted July 23, 2010 Share Posted July 23, 2010 Ok.... I'll give... But I still dont agree.. Both these are 7.5HP motors, both draw 20 amps at 230 volts.... Yet one produces 4 times the torque... And weighs twice as much... Yet they are both 7.5 hp... You think the high rpm one will take the strain and load over and over and over again of that the low RPM one will? Maybe on paper... Id rather have the beef.. Ok now Grant, I give up.... you win PS I purposelessly left the image huge because I know it irks u :D Quote Link to comment Share on other sites More sharing options...
Timothy Miller Posted July 23, 2010 Share Posted July 23, 2010 Ok.... I'll give... But I still dont agree.. Both these are 7.5HP motors, both draw 20 amps at 230 volts.... Yet one produces 4 times the torque... And weighs twice as much... Yet they are both 7.5 hp... You think the high rpm one will take the strain and load over and over and over again of that the low RPM one will? Maybe on paper... Id rather have the beef.. Ok now Grant, I give up.... you win PS I purposelessly left the image huge because I know it irks u Put a shaft coupler on them and see who wins Quote Link to comment Share on other sites More sharing options...
monstermetal Posted July 23, 2010 Share Posted July 23, 2010 Put a shaft coupler on them and see who wins I would have to run the fast one through a gear box to make it fair.... and that would be a heck of a demo... Although I dont think It would prove my point because Im pretty sure it would destroy both motors... :huh: Quote Link to comment Share on other sites More sharing options...
monstermetal Posted July 23, 2010 Share Posted July 23, 2010 I was just re reading all this stuff and I gotta say Im sorry.... I kind of got off track... I think your much better off buying the Fairbanks even if you do end up having to do a bit of work, its true you might have to build some parts, But hey you have to build ALL the parts of the tire hammer... Plus when your done the Fairbanks would be easy to sell for a good chunk, Tire hammers, even good ones... are a pretty tough sell... I know at this point resale is not what your thinking but its always nice to have a tool you know is worth at least what your into it at a moments notice, Kind of like having savings in the bank.. Quote Link to comment Share on other sites More sharing options...
Sask Mark Posted July 23, 2010 Share Posted July 23, 2010 For what it's worth, I recently picked up an old Rockwell 12" disc grinder. The cord was cut off at the motor (1/2 hp, 1745 rpm) in order to decommission it from the shop at a highschool years ago. I took it to a local electric motor shop to see what it would take to wire the motor and put in new bearings. He said it wasn't worth while because it would cost way more than the price of a new motor. He recommended replacing it with a 1 hp motor as he said the older, physically much larger motor was much more robust than a new 1/2 hp motor. My $25 disc grinder has become a $250 grinder... Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 23, 2010 Share Posted July 23, 2010 So, "he who shall remain nameless" in PA made another friend, eh? Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 23, 2010 Share Posted July 23, 2010 Well Larry, even thought I didn't open it, your picture tells a very compelling story. Like we talked about with the big diesel vs the race engine, they may have the same power, but when it comes to pulling a load, go with the diesel! There never was any argument on which was better or more desirable, only on "a horsepower is a horsepower", (which it IS) :lol: Quote Link to comment Share on other sites More sharing options...
nonjic Posted July 23, 2010 Share Posted July 23, 2010 From my readings (ok, only looking at the internet) there is not a shortage of mechanical hammers in the states,. Im sure you could find another one from a friendly vendor. If someone is that bad on the phone just asking about it imagine trying to arrange rigging etc. Now, just to continue with the off topic a little bit.... If you have a machine that requires a 3ph motor, and you fit a 6hp (assuming same duty cycle motors etc), will the 6 hp , working at 50% of its capacity draw the same ammount of electric through the meter (the bit we all worry about $ ) as the 3hp running at 100% work?? Quote Link to comment Share on other sites More sharing options...
youngdylan Posted July 23, 2010 Share Posted July 23, 2010 So, "he who shall remain nameless" in PA made another friend, eh? is he who shall remain nameless who I think he is? Quote Link to comment Share on other sites More sharing options...
youngdylan Posted July 23, 2010 Share Posted July 23, 2010 If you have a machine that requires a 3ph motor, and you fit a 6hp (assuming same duty cycle motors etc), will the 6 hp , working at 50% of its capacity draw the same ammount of electric through the meter (the bit we all worry about $ ) as the 3hp running at 100% work?? If they were both equally efficient, ie mecahnical power out = same % of electrical power in in, yes they would draw the same when running the same load ..................................... on paper :) Quote Link to comment Share on other sites More sharing options...
thecelticforge Posted July 23, 2010 Author Share Posted July 23, 2010 Which one? http://www.baldor.com/products/ac_motors.asp Quote Link to comment Share on other sites More sharing options...
BryanWillman Posted July 23, 2010 Share Posted July 23, 2010 At risk of stirring the pot... A HP is a HP if they are measured the same, which they almost never are, but it's kind of irrelevent anyway... In the real world where ships, cars, and machines don't run at constant speeds and constant loads, things like torque, inertia, acceleration, etc. matter. And even electric motors do not have flat torque or power curves, and how even the power is throughout a rotation can matter (hence the value of 3 phase motors.) And yes gearing helps, by getting things into the right part of the torque curve. But it won't change the shape of the curve. So both points of view ("a hp is a hp if measured the same" and "but in the real world big and slow is better for this") have merit. (And be very glad that you aren't trying to run these things off line shafts driven by gasoline engines...) As for the OP's project - start with the motor it has and see what happens. There's no law saying you cannot change the motor out in the future... Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 23, 2010 Share Posted July 23, 2010 The six horsepower will draw a little more due to friction but the biggest loss is due to power factor. Very similar to the fact that a small car engine running at near full output gets better economy than a large engine running at a small % of output. Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted July 23, 2010 Share Posted July 23, 2010 is he who shall remain nameless who I think he is? Yes, that would be him! Quote Link to comment Share on other sites More sharing options...
thecelticforge Posted July 23, 2010 Author Share Posted July 23, 2010 (And be very glad that you aren't trying to run these things off line shafts driven by gasoline engines...) If I were closer to the creek, I would build a weir and run it with water power. Quote Link to comment Share on other sites More sharing options...
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