traveler
starting to shine!
Member since July 2010
Posts: 37
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Post by traveler on Nov 29, 2010 17:08:37 GMT -5
I've been toying with the idea of making a 18-24" saw for a while now and one of my last problems is power feed. I've got the feed per minute figured and now I'm looking to the power requirements for an electric motor. My idea is that the gearmotor will drive a 1/2-13 feed screw to slide the vise. I've seen a few references on 14" saws the say 1/250 HP motor will work. This doesn't seem to be enough power to me. Does anyone know any more specific info? Do you know what your saw uses? Any info would be appreciated.
Tom
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Post by Hard Rock Cafe on Nov 29, 2010 18:01:27 GMT -5
Given the slow feed rate, I think 1/250HP would be adequate. My 10" saw uses a tiny motor and most of the big saws I've seen either use a lot of pulley reduction or a small motor. My 18" saw uses gravity feed, which is plenty of power and I really like it.
Chuck
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Post by catmandewe on Nov 29, 2010 18:39:13 GMT -5
I would go gravity feed also. Cuts faster in soft material and slower in hard material. A constant speed motor doesn't take that into consideration unless you use a clutch and the clutches that I have seen on saws are kind of hokey. Hydraulic or pneumatic feed would feed constant depending on hardness and thickness but you can achieve the same thing with a weight feed far easier and faster.
Good luck with it............Tony
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Post by tkrueger3 on Nov 29, 2010 19:09:18 GMT -5
My old Royal 18" has a little bitty motor that drives a reduction gearbox, which turns a little pulley, which turns a big pulley on the threaded rod. Seems to work pretty well for me, anyway. I do agree, though, that gravity feed would do a much better job of varying the cutting speed according to the density of the material being cut. That might also produce smoother slices, as well, I would think.
Tom
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riverbendlapidary
fully equipped rock polisher
Member since September 2006
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Post by riverbendlapidary on Nov 29, 2010 19:32:37 GMT -5
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Post by deb193redux on Nov 29, 2010 20:59:26 GMT -5
You need torque.
I just got a 4RPM gearmotor for my LS10, and it seems ot be more like 1/10 not 1/250
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Post by jakesrocks on Nov 29, 2010 21:17:48 GMT -5
My Covington 16" has a 1/10 HP gearhead motor drive.
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traveler
starting to shine!
Member since July 2010
Posts: 37
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Post by traveler on Nov 29, 2010 23:34:06 GMT -5
Thanks for all the advise and still a wide range of motor sizes. The set up I'm looking at is 1/100 hp gearmotor with a 439:1 ratio. Do you think that will bring the torque up enough? I also matched it with a rheostat so it will go from 1-6.9 rpm. This has a final feed of roughly 4-30 inches per hour. I will look into higher HP gearmotors but the price climbs quickly. As far as a clutch, I was planning on using a plastic pin to connect the drive screw so it would fail if the blade jammed. It sounds like some of you are quite fond of the gravity feed. It always seemed like it would be hard to control the break-out at the end of a cut. Does the water bucket trick work to reduce the force at the end of the cut or do you use another method?
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Post by jakesrocks on Nov 29, 2010 23:43:19 GMT -5
Many folks disconnect the weight just before the end of a cut, and finish by hand. Not advisable for a saw that throws a lot of oil.
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Post by Rockoonz on Nov 30, 2010 0:41:02 GMT -5
If your gearmotor is AC the torque will drop off when you reduce RPM so you should be at or near full speed as much as possible. With a 7 RPM motor in a 18 inch or larger saw I would use a belt and pullies to reduce the feed speed an additional 2.5:1 to keep the speed at or below 1 inch every 5 minutes. (12"/hr) My 18 inch saw is a air over oil hydraulic feed, it will adjust it's speed to the size and hardness of the rock like a saw with weights, but the blade won't beat itself up bouncing off the rocks, and it has a speed control to limit the fastest it can travel.
Lee
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Post by Hard Rock Cafe on Nov 30, 2010 10:46:11 GMT -5
My gravity feed also has hydraulic regulation (it's a Great Western, if that helps). I can adjust the speed by varying the hydraulic resistance. I rarely have breakout as I keep the speed low to begin with, but I can adjust for a faster cut in the middle of the rock, then slow it down at the end.
Chuck
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riverbendlapidary
fully equipped rock polisher
Member since September 2006
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Post by riverbendlapidary on Nov 30, 2010 14:33:45 GMT -5
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NDK
Cave Dweller
Member since January 2009
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Post by NDK on Nov 30, 2010 21:09:52 GMT -5
I don't know anything about large saws, so take this with a grain of salt. This would be another + I suppose for gravity feed. While researching for building my own saw (which is still only in my head), I read that when you see a slab with uneven cut lines along the slab face, it's from the current alternating in the feed motor. Supposedly gravity fed cuts are much more smooth along the face, because of even constant pressure on the blade. I hope that makes sense.
Nate
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riverbendlapidary
fully equipped rock polisher
Member since September 2006
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Post by riverbendlapidary on Nov 30, 2010 22:37:52 GMT -5
Could be but I think it has to do more with the blade. I've had some blades that left marks and others that left an almost polished face on the slab on the same saw.
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Post by texaswoodie on Dec 1, 2010 7:58:20 GMT -5
I prefer the auto feed for convenience if nothing else. I've never had a problem with hard material. I think JR is right about the blade. I have a 14" MK 303 Pro and it cuts a smoother cut than any blade I've used.
Curt
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drjo
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Honduran Opal & DIY Nut
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Post by drjo on Dec 1, 2010 8:38:47 GMT -5
Sorry NDK, but the alternating current idea isn't possible, screw lag (or any drive mechanics for that matter) will take up any slight movement if it were.
Dr Joe
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NDK
Cave Dweller
Member since January 2009
Posts: 9,440
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Post by NDK on Dec 1, 2010 16:24:34 GMT -5
Ok, well I just wanted to throw that out there. Me and electricity mix like oil and water, but it sounded logical . Nate
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