Don B.
having dreams about rocks
Member since August 2012
Posts: 52
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Post by Don B. on Sept 6, 2013 16:55:53 GMT -5
I just picked up the saw I won from E-bay a couple days ago. Everything is in good working order like was advertised. The saw had a 1/2 HP motor when the seller purchased it from an auction, but he upgraded it to a 1HP motor to cut larger rocks without issue. He gave me the choice of which motor I wanted, and I took the 1HP motor. The motor spins at 1725 RPM and has a two inch pulley on it. The arbor for the blade has a 7 inch pulley on it, so the blade would be spinning at right about 500 RPM. The PDF displayed in the "General lapidary saw info" topic says that the ideal speed for a 16" notched blade is 720-840 RPM. Should I put a three inch pulley on the motor to get the blade into the recommended range? As I typed that, it just occurred to me that the original motor had a 3 inch pulley on it, but the guy had been using the 1HP motor with 2 inch pulley for a while he said, and only put the 1/2HP motor back on when he was doing smaller rocks because it was quieter. Then again... he also mentioned it jamming up once or twice, so that was probably due to the slow blade not cutting fast enough to keep up with the auto feed?
Also, I already have a 1/2HP motor here that I figured I could use if I needed a quieter cut for something. It is a 3450 RPM motor though. It has a two inch pulley as well that would spin the blade at 985 RPM. Would that be two far outside the ideal range to use? I have some motors stuck to the side at my mother in laws house as well, so I will grab those if they are 1725 RPM motors, but just wanted to know if the existing one I have is ok to use if I need.
If you are reading this, thanks for taking the time to read the questions from a newb, and I appreciate any answers you can offer. I will get the saw all setup and running next week, and hopefully post some cut rocks soon.
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gerard
starting to spend too much on rocks
Member since April 2011
Posts: 218
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Post by gerard on Sept 6, 2013 17:36:41 GMT -5
I can not answer your question exactly - but I would think getting it in the recommended RPM's would be best. I have a question on how to make those calculations regarding the pulley diameters and the motor RPMs. It seems that you have a good handle on making those calcs - care to share?
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Don B.
having dreams about rocks
Member since August 2012
Posts: 52
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Post by Don B. on Sept 6, 2013 17:41:21 GMT -5
MRPM * (MPD / APD) = ARPM
MRPM = Motor RPM MPD = Motor Pulley Diameter APD = Arbor Pulley Diameter ARPM = Arbor RPM
So in my case...
1725 * (2 / 7) = 492.85 (I rounded to 500 RPM)
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Post by johnjsgems on Sept 6, 2013 17:50:27 GMT -5
Best speed depends on blade type. Most of the older charts are for the older notch rim blades. Barranca Diamond has a blade speed chart on their web site. Use the 301 for notch rims, 303 for 303 (continuous rim) and new style 301. If you don't want to do math Diamond Pacific has a nice pulley speed chart in their catalog (available on line). 3450 motors don't seem to work well reduced down that far for some reason. Half horse would be under powered unless it is a very heavy duty, capacitor start, high torque motor.
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robsrockshop
has rocks in the head
Member since August 2012
Posts: 715
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Post by robsrockshop on Sept 6, 2013 21:10:31 GMT -5
Jamming, could be too slow, dull blade etc. I use 1.5"inch to 5" on my 16". 7" sounds awful big on a 16" saw. Forget about using the 3450rpm motor.
And the idea of switching different motors out for noise issues vs rock sizes is ignorant and a waste of time. 1hp is really over kill and that would probably make it hum a bit, a good 1/2hp motor will work all it has to do is spin the blade as the feed has a seperate motor. Just depends on the condition of the 1/2hp and type. His 1/2hp motor probably wouldn't cut the mustard or he wouldn't had been switching them out. Of course you have what you have so make the best of it if money is an issue.
Don't take offense to the ignorant comment I wasn't referring to you, you are completely new to this. Something you will learn is that just because someone else was using it doesn't mean they knew what they were doing and a lot of times age has no bearing on knowledge i've gotten some pretty crappy advice from old timers and nine times out of ten realize I should've just done what I wanted to in the first place.
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Post by deb193redux on Sept 6, 2013 21:51:48 GMT -5
I can not answer your question exactly - but I would think getting it in the recommended RPM's would be best. I have a question on how to make those calculations regarding the pulley diameters and the motor RPMs. It seems that you have a good handle on making those calcs - care to share? many online calculators. math is our friend, but online pulley calculators are great too.
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Post by deb193redux on Sept 6, 2013 21:53:15 GMT -5
1hp is kind of overkill
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Don B.
having dreams about rocks
Member since August 2012
Posts: 52
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Post by Don B. on Sept 6, 2013 21:58:14 GMT -5
I will have to check what these other motors are, otherwise I will just get a new pully for now until I track down a different half horse motor. Even knowing all this, I probably would have still taken the 1hp motor. I usually see 1/3 and 1/2 ones at auctions, so it will be nice to have a 1hp around if i ever need it.
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Post by jakesrocks on Sept 6, 2013 22:45:04 GMT -5
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,555
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Post by jamesp on Sept 7, 2013 6:33:53 GMT -5
I would avoid a 3450 rpm motor. My 18 inch covington saw has a good 1/2 HP cap start motor and i like it. If i have the blade adjusted to cut straight it easily cuts thru a jaw full of hard rock. It tells me that i have the saw adjusted to cut straight and the blade well dressed.
When the blade needs dressing i can hear the saw straining and simply dress the blade.
I changed from a continuos to a segmented and speeded the blade up like 25% as recommended. To speed the blade up i changed to a 25% smaller pulley on the blade shaft.
All it required was to go from a 5 inch pulley on the blade shaft to a 4 inch pulley.(about a 25% reduction in diameter). Shorter v-belt too.
The carriage feed comes directly off the motor so i chose not to change the motor pulley. i.e.-same carriage feed speed but increased blade speed.
Sounds like you just need to replace the 7 inch pulley to a
7 divide by 5 times 500 =700 rpm blade-----use 5 inch pulley
7 divide by 4.5 times 500=780 rpm blade-----use 4.5 inch pulley
7 divide by 4 times 500 =875 rpm blade-----use 4 inch pulley
Segmented blade cut fine. I love mine.
By the way, 2 inch motor pulley + 7 inch blade shaft pulley and 1725 rpm motor is 2 divide by 7 times 1725rpm motor = 500.250000000 rpm. So 500 sounds bang on.
I would do a 4.5 to get speed in center of optimum at 780. I guess you run a segmented blade faster because it has less diamonds per revolution than a continuos blade. I used my saw to cut specimens in half. Then i polished the faces. Saw marks were not allowed to get a polish so good alignment was absolute necessary. That segmented blade can cut with a 400 grit finish if you feed the rock nice and slow. Have fun. Ace hardware has a lot of pulleys.
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Don B.
having dreams about rocks
Member since August 2012
Posts: 52
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Post by Don B. on Sept 7, 2013 18:16:40 GMT -5
1725 * (2 / 7) = 492 on every calculator ive tried Well, none of the motors here are the size i want so i will stick with the one horse for now and get a 5 inch pulley to run the saw. hopefully ill be able to share some slabs by the end of next week. Hopefully the tub of rocks ive been waiting to cut has something good in it.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,555
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Post by jamesp on Sept 7, 2013 19:11:33 GMT -5
I was using a metric 1725. Ha ,never was much w/math but OK w/formulas. Should not hurt a thing having 1 horsepower
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Don B.
having dreams about rocks
Member since August 2012
Posts: 52
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Post by Don B. on Sept 7, 2013 20:22:26 GMT -5
Yeah, if I can get the blade speed right, I didn't think it would be a problem other than using more electricity than I need. My brother in law has a 3/4 HP motor he is bringing me. If its quieter I may use that. . Will the motor noise even be a factor once the blade is cutting into rock?
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,555
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Post by jamesp on Sept 7, 2013 22:53:35 GMT -5
No. Because the motor should be under very little load if your saw is set up correctly.
But a 16 inch blade makes a fair amount of noise. Well over the motor noise, definitely .
I cut through a 6 x 8 inch agate today and the saw hit the shut off switch early. So the blade was totally imbedded into the rock when it stopped. So i grabbed the blade and gave it a spin and it took a couple of seconds to stop. Meaning it is not scrubbing at all. I feel like i could cut with a 1/4 hp motor if oil is clean. Muddy oil takes a lot more HP by coating the diamonds and constipating the kerf. If you run muddy oil you may need more HP. I am cheap skate and run kerosene and motor oil mix. Smells strong but has excellent lubricating ability.And particles settle to crystal clean oil over nite.
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Post by jakesrocks on Sept 7, 2013 23:28:29 GMT -5
If you were anywhere near Aberdeen, S.D., I've got a nearly new 3/4 HP motor gathering dust in my shed. I'd swap it for a box of rocks.
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Post by johnjsgems on Sept 8, 2013 8:14:35 GMT -5
Power consumption is based on load, not motor size. If your 1 hp motor draws 12 amps turning the saw the 3/4 hp will draw the same. You could have an overheating issue if the running amps are less than 1/2 the rated amps but I think you will be OK.
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Don B.
having dreams about rocks
Member since August 2012
Posts: 52
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Post by Don B. on Sept 8, 2013 20:47:18 GMT -5
It would over heat if it is using LESS power?
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Post by Rockoonz on Sept 8, 2013 22:44:08 GMT -5
I am cheap skate and run kerosene and motor oil mix.quote] Cheap enough to replace everything after the fire? I bought some rough last summer from a guy whose shop burned down. Kerosene has a low flash point. Lee
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Post by johnjsgems on Sept 9, 2013 19:10:37 GMT -5
I don't know why but found during my 30 years in HVAC/Refrigeration that severely underloaded motors do indeed run hot and fail early. Motors run best at about 3/4 the rated load amps. I too have heard of fires from the old diesel and diesel/kerosene saw coolants. High flash point is very important.
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