SJPatrick
starting to spend too much on rocks
2 1/2 years into rock hounding and I'm still a newbie!
Member since September 2013
Posts: 124 
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Post by SJPatrick on May 26, 2014 13:58:46 GMT -5
In my quest to learn more about slab saws, especially the Lortone LS18 I've been working on, I came across the table at www.mkdiamond.com/lapidary/tec_speed.html . I've cut and pasted it at the end. A prior version has been included in some previous posts. The table specifies the recommended surface feet per minute (SFPM) for the MK-301 and MK-303 saw blades and the blade RPMs required to get the recommended SFPM for different diameter blades. For the MK-301 the SFPM should be between 3000 and 4500. For an 18" saw blade that amounts to an RPM range of 640 to 960 according to the table. For the MK-303 the SFPM should be between 4500 and 6000. For an 18" saw blade that amounts to an RPM range of 960 to 1270 according to the table. My first question is, why the big difference in recommended SFPM and RPM between the two blades? Maybe I'm interpreting the table incorrectly. I sort of doubt it, but if so, let me know and skip the rest of this post. Now the LS18 has a 1/2 HP motor that runs at 1725 RPM. The motor pulley is 2 1/2" in diameter while the arbor pulley is 7". That works out to an arbor RPM of 616. We are using an MK-303 blade. So an arbor RPM of 616 is below the minimum recommended RPM of 960 and way below the max allowed for that blade. So, if that is correct, you probably see where I'm going with this  , why can't I put a different pulley on the arbor and bump the RPM up into the 1200 range. Changing the arbor pulley to a 3 1/2" diameter would give an arbor RPM of 1232. That could theoretically double the cutting speed. I must be missing something, misinterpreting something, miscalculating something, lacking some knowledge of saw operation, not understanding SFPM. I'm still a newbie after all. Please let me know. Like they say, if it seems to good to be true, it probably is to good to be true. Thanks. Lapidary Blade Speed Recommendations Approximate Arbor Shaft RPM Range Blade Diameter MK-301 MK-303 Surface Feet Per Minute 3000 - 4500 4500 - 6000 4" (102mm) 2860 - 4300 4300 - 5730 5" (127mm) 2290 - 3440 3440 - 4580 6" (152mm) 1910 - 2870 2870 - 3820 7" (178mm) 1640 - 2460 2460 - 3270 8" (203mm) 1430 - 2150 2150 - 2870 9" (229mm) 1270 - 1910 1910 - 2550 10" (254mm) 1150 - 1720 1720 - 2290 12" (305mm) 960 - 1430 1430 - 1910 14" (356mm) 820 - 1230 1230 - 1640 16" (406mm) 720 - 1070 1070 - 1430 18" (457mm) 640 - 960 960 - 1270 20" (508mm) 570 - 860 860 - 1150 24" (610mm) 480 - 720 720 - 960 30" (762mm) 380 - 570 570 - 760 36" (914mm) 320 - 480 480 - 640 |
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Post by Rockoonz on May 26, 2014 14:56:24 GMT -5
Bach in the day with the old style blades 2500SFPM was the norm, so 616rpm was about right for that.
I would get a 4 inch pulley. On the motor it would give about 980 rpm and on the blade it would give about 1080.
On the blade is probably better since it will fit in the belt guard better. Remember to change the feed to the slowest setting since it will speed up too.
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SJPatrick
starting to spend too much on rocks
2 1/2 years into rock hounding and I'm still a newbie!
Member since September 2013
Posts: 124
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Post by SJPatrick on May 26, 2014 20:17:15 GMT -5
Thanks Lee. It's good to know that the 600RPM made sense at some point in time. Have you or others changed pulleys to take advantage of the increased speeds at which these newer blades can turn? If some have tried and a low number of them have had bad experiences doing it I would recommend it to our lab people.
I thought about the increase in feed rate after changing the pulley. But hadn't worked any numbers. I would use the 4" pulley you recommend, and Lortone sells one. But for illustration let's use a 3.5" pulley because it would exactly double the RPM. And it will thus double the feed rate so the feed rates in minutes per inch would be halved from the 3, 4.5, and 6 minutes per inch to 1.5, 2.25, and 3.
In our environment we have been running with the LS18 standard set up and its highest feed rate of 3 minutes per inch which we all agree is not a good thing to do. After changing the pulley we will use the slowest feed rate but it will still be 3 minutes per inch. And since the blade is running twice as fast as before we shouldn't run into problems cutting hard material. Having close to the same feed rate will make our users very happy.
Of course some will want to try going even faster than 3 minutes per inch. Last week when we were discussing making the standard middle feed rate of 4.5 minutes per inch the only option we wondered how we could enforce it. We laughingly discussed welding the door to the pulleys shut, or installing a lock on that door. The lock is looking like a good idea if we go ahead with changing the pulley.
Can anybody think of other issues that might arise from nearly doubling the blade RPM? There must be some.
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Post by Rockoonz on May 26, 2014 21:57:25 GMT -5
While increasing the feed speed of the saw will increase the cutting efficiency of the saw, 3 min per inch is still way too fast.
I replaced the pulley behind the blade pulley with a smaller one when I increased the blade speed on my 14 inch HP to keep the feed speed down. I run a 3"/5" pulley combination on my hydraulic 18 inch saw for 1035 rpm and have the speed control set so the FASTEST it can ever travel in one inch every 6 minutes, the slabs come off looking like they are already sanded to 60 grit or so, and the blade is still square after about 5 years with no swedging and one or two sharpenings.
Enforcing your feed rate is easy, take off the stepped pulley and replace with a single pulley in the diameter you want. I have a single pulley on my 24 inch FranTom replacing the original 3 step pulley, it's set to run at about 7 min/inch. BTW pulleys cost a lot less at your local hardware store than they do at Lortone, and no shipping cost. You may be able to fit a larger pulley at the front of the saw to keep the feed rate slow.
Just out of curiosity how much do the members pay for slabbing?
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SJPatrick
starting to spend too much on rocks
2 1/2 years into rock hounding and I'm still a newbie!
Member since September 2013
Posts: 124
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Post by SJPatrick on May 26, 2014 23:49:12 GMT -5
Hi Lee, anybody over the age of 50 and living in the county can use the lapidary shop after filling out a registration form and signing a liability waiver. For the lapidary lab there is a $1 per day "donation" to use any or all of the equipment. Additionally for the slab saw there is a 45 minute use limit per day if others are waiting to use it. So you can see why speedy cuts are a big concern. The lab is open 2 days a week for 4 hours each day. The lab gets anywhere from a few to a dozen or so users on any given day. I'd say it averages about 7 or 8 a day, and 3 or 4 for the slab saw, but those are just guesses.
I'm a little confused. If we can roughly double the speed of the blade, but can't roughly double the feed rate, then the benefit of increasing the RPM is negated, unless there is some other benefit I don't know about. And that is definitely a possibility since I'm new to this.
I understand that a 3 minutes per inch feed rate with the blade turning 600 RPM is not good for cutting hard material. But it's been said that 6 minutes per inch is acceptable. If the blade is turning at 1200 RPM won't it be able to cut twice as fast and therefore allow for a 3 minutes per inch feed rate. What is the limiting factor that forces the best feed rate to remain at 6 minutes per inch despite being able to cut material twice as fast? Does it cause the rock to become too hot when cut at faster speeds? I'm just guessing here. And curious.
Thanks for the tip on pulleys and where to buy them. I appreciate all the inputs you've been kind enough to provide. I'm learning a lot.
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Post by Rockoonz on May 27, 2014 20:31:30 GMT -5
When we were talking about feed rates originally the blade speed was not mentioned. Once it was mentioned it became clear that your feed was too fast AND the blade was too slow. The old style continuous rim saw blades cut in a different fashion and slower was better. The new style sintered blades run more efficiently at a higher RPM but that does not translate to faster cutting, only proper blade speed.
In other words, apples and oranges.
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Post by Rockoonz on May 27, 2014 20:39:59 GMT -5
Seriously, do people actually complain about how much rock they get cut in 45 minutes for a buck?  Our shop for the local club charges $7.00 per 4 hour session plus 50 cents per linear inch of rock cut in the slab saws. We have had to turn people away. |
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SJPatrick
starting to spend too much on rocks
2 1/2 years into rock hounding and I'm still a newbie!
Member since September 2013
Posts: 124
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Post by SJPatrick on May 28, 2014 0:38:23 GMT -5
Oh yeah. Complain they do. They have lots of rocks to cut. And it 's the only saw available to them.
Have other slab saw owners modified their pulley arrangements to up the RPMs and cut the feed rates for these sintered blades so they operate efficiently? I never met the fellow who maintained our saw. He passed away before I started going to the shop. He was supposedly very good at it from what I've heard. He may have already modified it. I've been going by the standard LS18 configuration as specified in the manual. I'll check it. But offhand I don't think he did as the arbor pulley is pretty big. I'll see if it is the standard 7", and check the other pulley sizes as well.
Being new to this I'm not familiar with blade technologies. But like with the workings of the slab saw I want to learn. I've heard the term "sintered" used when referring to some blades. But I'm don't know what it means, yet. I'll study up on it and on blade design and history as well.
I'm sorry to be a pain. I'm just trying to learn and keep our saw working the best it can for our environment.
Thanks again.
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Fossilman
Cave Dweller 
Member since January 2009
Posts: 20,723
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Post by Fossilman on May 28, 2014 13:04:43 GMT -5
Great info......thumbs up
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Post by johnjsgems on May 28, 2014 13:22:52 GMT -5
Can't help with Lortone feed issues but can explain the 303C versus 301 speed differences. The chart is outdated and the 301 on the chart is the old mild steel core notched rim blade. The 301 (for last 3 years or so) uses same high carbon steel core so use the 303C speeds and you would be fine. Speeding up the 303C/301 blades gives you better cutting but I would not speed up feed rates. Slow (5 min. per inch) cutting with either blade gives you a 220 or better smooth cut.
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SJPatrick
starting to spend too much on rocks
2 1/2 years into rock hounding and I'm still a newbie!
Member since September 2013
Posts: 124
|
Post by SJPatrick on May 28, 2014 16:54:45 GMT -5
johnjsgems, Thanks! I was wondering about that. We're debating whether to purchase a 301 or 303S to replace the dished blade. Should an 18" 303S run at the same RPM as the 303C? I've read that the 301 is the better blade. But I haven't read why it is considered better and I don't know how to convince the people at the center that it is a better blade other than saying it must be because it costs more. Can you fill me in? Thanks.
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, why can't I put a different pulley on the arbor and bump the RPM up into the 1200 range. Changing the arbor pulley to a 3 1/2" diameter would give an arbor RPM of 1232. That could theoretically double the cutting speed. 
