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 13, 2014 19:29:17 GMT -5
I have become the de facto maintenance man for a Lortone 18" slab saw in the lapidary shop in the senior center I go to to cut nodules. Nobody else wants to work on it, so when problems crop up the only way I get to use it is for me to fix it. This is in spite of the fact until 6 months ago I had never touched a slab saw. I'm learning more as problems come up. Sometimes when I've run out of things to do I familiarize myself with the operation of the saw. Recently I was traveling for a couple weeks and when I came back and visited the center there was a sign on the saw saying "Don't Use." The guys there said it was making bad noises and wasn't cutting anymore. To shorten the story, I've found what I think is the culprit. The blade is binding up in the cut. When the problem occurs I shut off the saw, and when I try to release and pull back the vise the blade is definitely stuck in the cut. The saw blade has quite a bit of run out (wobble). I've verified the run out isn't caused by arbor bearings going bad. When I was familiarizing myself with the saw I measured with a depth gauge the run out of the blade as .4mm or .015 inches. In some posts I've read .015 inches is about the maximum allowable. Others say half the width of the blade is allowable for run out. But now after measuring it after this latest problem the run out is .75mm or .030 inches. I'm assuming that is probably too much or close to it. I don't know where the blade came from. It's been in the saw for 3+ years. The edge is getting to or is rounded. The blade is segmented and looks looks similar to the 18" MK-303. Any writing or label on the saw has long since been obliterated so that's all I can give as a description. I was told we have a couple old spare blades. My plan is on Thursday (the shop is only open on Thursday and Friday) to try one of the spare blades to see if the problem is resolved. Of course there probably is a reason the old spare blades are spares, they might not work well. We'll see. If the run out is unacceptable on the problem blade, I'm assuming it is time for a new blade. I wouldn't want to try to fix it. And I'll need to justify to the money people there that the blade is kaput when we ask to buy another. I've found one document, Care and Feeding of Rock Saws at home.comcast.net/~eugenemineralclub/rocksaws.pdf that says a run out of as little as .005 inches is bad. Anybody else know of a good online document that addresses blade run out on rock saw blades? Thanks for your help with this. Without this forum I wouldn't be this far along in diagnosing the problem. Patrick
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Fossilman
Cave Dweller
Member since January 2009
Posts: 20,685
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Post by Fossilman on May 13, 2014 20:02:07 GMT -5
Sounds like the blade.......
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Post by Rockoonz on May 14, 2014 23:37:06 GMT -5
For runout I have always gone with half the thickness of the blade.
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Post by johnjsgems on May 15, 2014 11:03:19 GMT -5
The rounded edge will cause binding for sure. Hammer the edge flat and try it. If a 303S the core is very ridgid but I guess it could lose temper if it overheated enough. Remove the blade and see if it lays flat on a flat surface. If it does hammer the edge flat and give it a try. When my 24" notch rim blade dished it made a screaming noise and cut horribly.
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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 16, 2014 21:01:50 GMT -5
Thanks guys. Here is an update on what I found and did yesterday and today. In addition to the large amount of run out (wobble), the blade is also dished. From the center to the edge the dish is approximately .050 inches. So this MK 303 blade is probably toast. It's more than 3 years old and a conservative estimate is that it has accumulated actual cutting time of more than 1000 hours. So it's had a good run. It does have a lot of diamond left. That being said, I am going to try to bang some sense into it (straighten the run out and dish), and if that works, swage (or is it swedge) the edge. But only keep it around as a spare if that works.
The saw and blade have been used by a lot of people during this run. And I've heard that a number of rocks have broken loose from the vise during cutting and of course there have been the blade jams. Those all probably contributed to the run out and dish of the blade.
One of the spare blades I mentioned we have is a very old MK 301. It has less than 1/8" of diamond left. I installed it in the saw and it is working just fine now.
Now we just need to convince the senior center managers to pony up for the cost of a new blade. Hopefully that won't prove to be too difficult. Thanks again!
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jollyrockhound
spending too much on rocks
Member since March 2013
Posts: 409
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Post by jollyrockhound on May 16, 2014 22:18:42 GMT -5
Glad it worked out for ya I run two frantom 18" and love em when they get abused it will do that to ya! keep the berings greased s o it runs forever.
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rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on May 16, 2014 23:40:03 GMT -5
This is probably a dumb question, but have you tried dressing the blade with a dressing stick? Aluminum dioxide is the preferred according to Rockoonz, but an old grinder wheel works for me in a pinch. I had a blade that would bind every time, and as soon as I cut a few inches into a grinding wheel it started cutting good as new.
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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 17, 2014 1:04:48 GMT -5
Not a dumb question Jeff. Actually in the 6 months I've been using the slab saw at the center I've never seen anyone dress the blade. So the first thing I tried was dressing it with a fire brick we keep here for that purpose. But the problem persisted. There is a lot of equipment in the shop. But no real maintenance schedules. Volunteers run the shop. Only when the saws (one slab and three trim) start cutting slow does anybody think to dress them. Sometimes not even then. Since the maintenance for the saws seems to be falling on me I'm planning to dress the blades once a month to keep them tip top. I don't mind maintaining the saw and troubleshooting the problems that crop up as it helps me learn how the equipment works. Thanks.
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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 17, 2014 11:49:19 GMT -5
A slight correction/addition to my last post. I haven't seen a maintenance schedule. But for the slab saw there is one weekly task that gets performed by one of the volunteers. Each week he uses a scoop to gather a few scoopfuls of the the accumulated rock snot from the previous week and puts it in a paper grocery bag to let the oil filter out. He then tops off the saw with previously filtered oil or fresh oil if there isn't enough of the filtered oil.
The oil is never fully drained out. Heck the drain on the bottom of the saw might be frozen for all I know. I've drained and cleaned a couple of the trim saws that use oil for a coolant/lubricant. I'd hate to have to do a full drain and cleaning of the slab saw.
The slab saw is remarkably clean too. The saw is a supposed to be clean at the end of the day. So typically the last person using the saw cleans it. That pretty much amounts to cleaning off the debris that collects on the slab catcher, vise, and carriage. I think this cleaning and the once a week snot removal is a great way to go, especially since it eliminates the need to drain the oil and remove the snot accumulated over a very long time. It's a little effort once in a while to save a lot of effort later.
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Post by Rockoonz on May 17, 2014 23:51:04 GMT -5
This is probably a dumb question, but have you tried dressing the blade with a dressing stick? Aluminum dioxide is the preferred according to Rockoonz, but an old grinder wheel works for me in a pinch. I had a blade that would bind every time, and as soon as I cut a few inches into a grinding wheel it started cutting good as new. Some grinder wheels are Aluminum Oxide, at least the ones that are good for dressing blades are. You don't want to use Silicon Carbide wheels, they can make the blade worse.
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Post by Rockoonz on May 18, 2014 0:03:16 GMT -5
If the edges are rounded swedging with a light hammer, as John suggested, will help. The instructions for this are here, bottom of page 5 and on to page 6... lapidaryworld.com/pdf/rocksaws.pdfI lay the blade flat on a table with just a little hanging off the edge and mark my starting point with a sharpie so I can easily know when I have made it all the way around the blade.
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robsrockshop
has rocks in the head
Member since August 2012
Posts: 715
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Post by robsrockshop on May 18, 2014 9:37:11 GMT -5
I went round and round with a supplier over one of the 18" import blades they couldn't seem to understand it was NOT my saw and it was the blade. Funny that the MK doesn't wobble on it. I've seen guidrails with roller bearings on saws before I could try that but haven't got around to it.
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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 18, 2014 21:09:25 GMT -5
Thanks guys. I'm almost certain the blade is an MK-303. There is a small portion of the label remaining and that portion matches the label on another MK blade and it's a segmented blade. Therefore I'm assuming it is a 303. I also found a document in the lab that says a replacement should be an MK-303. Don't know if that's what they did last time it was replaced, but it looks like it.
I have the "Care and Feeding of Rock Saws" instructions. I plan on using it to swedge the blade. But I don't know if the MK-303 can have the run out and dish fixed. I heard that some blades can't have that done without heating them. And also I'm not sure I understand the instructions on page 7 for fixing it. If I do it I'll be doing it just to see if it can be done and for practice. I'm fairly confident we will be able to get the senior center to buy a new blade. In the meantime we have the real old 301 to use as a spare. Thanks.
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mikeinsjc
spending too much on rocks
Member since June 2010
Posts: 329
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Post by mikeinsjc on May 21, 2014 19:49:39 GMT -5
Patrick, I personally think .050 is way too much runout for a blade. Even if the saw manages to finish the cut, the slab will probably be so rough that it will be time-consuming or impractical to further work it. The problem is surely rocks coming loose during cutting. When this happens, the blade is quite often toast.
I have never seen a really robust vise on a saw, and therein lies the problem. I have an 18" Covington, and two 24" Highland Parks. The Covington vise is hopelessly inadequate. So here's my fix. On every cut (no exceptions) I make I use either a bar clamp or C-clamp across the top of the vise. I check the rock in the vise, and if I can move it at all I don't cut. I have never lost a blade using this system. You cannot grip a rock too tightly when your blades are that expensive.
The problem of saws producing junk slabs is pervasive. Most people rely on just the factory vise. I see tons of slabs at shows that are nice material but have been cut on saws with excessive blade runout, on cheap blades, or on saws that are not maintained. I bought an estate collection that included at least 600 slabs. Nearly every larger slab was junk because the guy evidently thought a bent blade, if it finished the cut, was good enough.
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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 22, 2014 0:17:25 GMT -5
Hi Mikeinsjc, from what I've read about run out and learned on this forum I agree. And a like amount of dish can't be good. And that dish is very obvious when the blade is laid flat on a flat surface. But oddly the slabs come out smooth as silk if a jam doesn't occur. The only complaint I've heard is that a slab will once in a while have a slightly different thickness from end to end. Unfortunately that occurrence is so rare I can't reliably reproduce the problem. So I can't really trouble shoot it.
I've been using this saw for six months. This is the first slab saw I've used as I'm a relative newbie. Before using it I was taught to check the rock in the vise before cutting, and if it can move at all then try mounting it again so it doesn't. I really crank it down, use wood shims to help with the grab, but every once in a while I have to try again. I'm happy to say that I haven't had one come loose so far. But I'm not the only one using the saw. It's in the senior center lapidary shop. And there are at least six others using the saw. Others might not be as conscientious. But I've never heard a rock come loose while sawing. But then again I'm not there all the time.
The blade also has a rounded edge. I think that might have contributed to the problems. The saw's feed is always running at it's fastest speed, a little over 3 minutes per inch. There is no consideration given to the hardness of the rock being cut. That might have to change, maybe moving to using the medium feed rate at all times. But that would decrease the amount of rock that could be cut in a day. So a slower feed rate might meet with some resistance. Well see.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on May 22, 2014 4:02:30 GMT -5
If you can see that the cut is actually curving on the uneven ones, you're probably dished AND feeding too fast. The curve can come from the blade bending/dishing. It could also happen if the rock rides up on the blade, though your vise carriage shouldn't be able to flex enough to let it climb too far up.
Three minutes per inch works out to a whopping 20 inches per hour. That's way, WAY too fast. An 18" saw should be fed something on the order 5-8 inches per hour. I think you need to slow it down, especially on harder stuff like agates. You'll end up going through a lot of blades feeding it so fast. C-ya, Rick
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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 25, 2014 16:21:11 GMT -5
Hi rykk and all. The LS18 has three feed rates of about 3, 4.5, and 6 minutes per inch. Since I started using the saw 6 months ago it has been set for 3 minutes per inch. Speaking with some "old timers", they said it had been set for 4.5 minutes per inch for many years. Note that the feed rate is not easily changed because the saw's pulley side is up against a wall and the saw must be moved to adjust the pulley. But somebody unhappy with the feed rate moved the saw, made the change to the fastest rate, and moved the saw back. It was sometime later that it was discovered that it had been changed.
They know the danger in having too fast a feed rate. In discussing it with the volunteers that run the shop, I think the initial decision made years ago to use the middle speed was a compromise between cutting speed and possibly damaging the blade. Two blades have been used in the saw and have had short lifetimes of 3.5 years each, that's about 1000 hours of actual cutting time for each. The thought seems to be that 3.5 years is okay in our multi user environment. It costs about 30 cents for each hour it actually is cutting. When we get a new blade, the feed rate will be set to 4.5 minutes per inch.
When I spoke with them on Friday it seemed like they were leaning towards replacing the wobbly and dished MK-303 with another MK-303.
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Post by Rockoonz on May 25, 2014 21:58:32 GMT -5
No wonder they had problems. The LS18 I take care of for my clubs shop is set and will remain at the slowest setting. The blade speed has been increased for the newer style blades so that makes it closer to an inch every 5 minutes. Anything faster than the slowest feed rate on pretty much any saw should only be used if cutting softer rocks. If you use a faster rate of feed with hard agate and jasper the spring on the feed half nut will slip and cause unnecessary wear on the half nut and possibly the feed screw if both are steel, and the rock won't cut any faster anyway.
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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 11:22:06 GMT -5
Thanks Lee! I think you just verified the theory I developed for another issue I noticed. When I came back to the shop after the binding problem had started happening, I noticed the blade was binding but never getting fully bound up in the cut. When it was in this situation one could hear a short, muffled, clunk sound, followed by 8 seconds of normal cutting sound followed by 4 seconds of a swooshing sound building in volume, and then the clunk sound again. Every 12 seconds this repeated. I noted that the vise wasn't advancing, but the feed rod was turning and everything else was turning. My theory was that the half nut was worn or the spring was weak, and the binding blade was putting pressure on the feed mechanism causing the half nut to ride up the threads of the feed rod and when it had reached the top of the threads the pressure pushed it back a thread or more (the clunk sound). Then the half nut reengaged, and the sequence started all over again, repeating in 12 seconds. I inspected the feed rod threads and they looked fine. I couldn't check out the half nut because I would need to remove parts that I wouldn't want to remove unless really needed (I'm still a rookie dealing with this saw and I don't want to needlessly screw up something ). My plan was to replace the spring first, as it's the cheapest, and then if that didn't work, the half nut. But then I figured that this slipping action of the half nut might be a good thing. It is sort of acting like a clutch preventing the blade from completely binding up and possibly causing additional damage. And you mention that it could be slipping when cutting hard material like jasper and agate. I usually know how long it will take a cut to complete. But there are times when I notice that it takes much longer than I thought it should. I never heard any different sounds coming for the saw though when this happens. But it makes sense that the nut is slipping. Of course this slipping isn't normal. And I'll have to fix it sometime. I'm gaining confidence in dealing with the saw thanks to posts like yours and others on this forum. Thanks!
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Post by johnjsgems on May 26, 2014 13:04:02 GMT -5
Baranca runs most of their saws at 5 minutes per inch. I would set it at the 6 minute option and keep blade well dressed.
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