rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on Sept 24, 2013 11:40:23 GMT -5
I have a question on aligning blades. I have an 18" saw that appears to have what I'd call a "wobble". I don't know if that's the actual technical term for what's happening, but it's the best word that my vocabulary can come up with.
What happens is this - I will put a rock on a vice and place it next to the front of the blade. As I slowly rotate the blade, I will use the rock as a visual point of reference and monitor the position of the blade. The blade oscillates left and right with respect to the reference point as it rotates (probably by a total of ~1/8").
I've done the blade alignment I know how to do... using a pencil on a vice and checking the distance from the vice to the blade as I move the vice through its range of motion. As near as I can tell, the blade is aligned this way.
Does anybody have any suggestions on what the wobble could be? It's almost a brand new blade (Covington Gold series, less than 10 hours on it), so I hope it's not a dished blade.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,184
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Post by jamesp on Sept 24, 2013 13:17:59 GMT -5
Make sure the clamping components are clean before bolting down the blade. That's a lot. A rock did not come loose while sawing,did it? Remove the blade and spin the arbor or bump the motor and see if the arbor is bent.
Clean the washers and clamping area and reinstall to see if it changes. It is either the arbor is bent or the blade is warped i imagine. You may try the blade at different locations on the arbor to see if things change. Try tightening blade at different torques.
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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 24, 2013 17:53:12 GMT -5
Keep cutting at 20" per hour. Watch what happens.
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Post by catmandewe on Sept 24, 2013 19:23:51 GMT -5
I'd guess it is your blade but check your alignment first.
Mark a spot on the blade, then clamp something into the saw and adjust it so that it just touches the spot you marked while the spot is at the front of the blade. Then rotate the blade to the back of the saw and move the carriage towards the back and see if the pointer is still just touching the mark while the mark is at the back of the saw. If it is off then it is your alignment. If it does just touch then it is your blade. You can fix the blade but it takes time and patience.
Tony
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Post by johnjsgems on Sept 24, 2013 19:54:28 GMT -5
Try loosening the blade nut and retighten just enough to stop blade from slipping. Over tightening can cause a wobble. With the Chinese crimp rim blades if the bade ever overheated it could lose tension and wobble as well. The old style 301 notch rim on my HP 24" saw always wobbled from the time I bought it used. It always cut very well and never a saw mark until I finally dished it trying to cut a rock a little too tall. If your saw is cutting well I would not worry. Replace it with a BD/MK 301 when it is time and you will be very happy.
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rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on Sept 24, 2013 20:43:18 GMT -5
Try loosening the blade nut and retighten just enough to stop blade from slipping. Over tightening can cause a wobble. With the Chinese crimp rim blades if the bade ever overheated it could lose tension and wobble as well. The old style 301 notch rim on my HP 24" saw always wobbled from the time I bought it used. It always cut very well and never a saw mark until I finally dished it trying to cut a rock a little too tall. If your saw is cutting well I would not worry. Replace it with a BD/MK 301 when it is time and you will be very happy. Thanks, I'll give that a try. I did gronk the nut down pretty tight.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Sept 24, 2013 22:34:28 GMT -5
I agree with catmandewe - It's the blade. I've gotten 2 of the gold series Covingtons and BOTH had visible "angular anomalies". You could see the dings or depressions in the edge, especially if you turned the blade by hand. The second one I was able to hammer flat but it still left saw marks, just not as bad.
So I bagged it and bought the next one "up" in "quality"(?) - The "Black" series with a wide, continuous rim. Dang if *that* one didn't have "ruffles in its ridges", and leave saw marks as well! So, I laid it out on the garage floor and - with a 3lb hand sledge and a block of 2x4 - hammered that one in a radial sequence, inside to out - almost perfectly flat. Saw marks are now all but invisible.
My thing is - Are ALL of the Covington blades this bad??? I mean, I went 0-for-3 right out of the boxes! Next time, I'll try another brand, methinks... C-ya, Rick
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Post by catmandewe on Sept 24, 2013 22:49:33 GMT -5
I am 0 for 2 on Covington blades, An 18" and a 30", 2 was enough.
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rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on Sept 25, 2013 0:31:51 GMT -5
Okay, I bought a dial indicator today and took some measurements... my calibrated eye apparently needs some work.
When I eyeballed it earlier, I guesstimated 1/8 of an inch.
With the dial indicator, I measured a total "wobble" of 32 mils (0.032 inches, or about 1/32 of an inch) around the outer perimeter (just inside the cutting edge), and 12 mils misalignment from the front to the middle of the blade. So, not nearly as bad as I had thought. Still not perfect though. But maybe good enough?
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Post by Donnie's Rocky Treasures on Sept 27, 2013 9:53:14 GMT -5
Do what John said with the nut. I had mine tightened too tight & when I loosened it, much better!
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rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on Sept 27, 2013 10:24:50 GMT -5
I took the blade off the other day, spent a couple of hours trying to get the misalignment down (took it from 12 down to 2), and put the blade back on with the nut just finger tight... so much better!
Thanks for the help everybody!
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Post by Rockoonz on Sept 27, 2013 11:14:28 GMT -5
Generally if the runout is less than half the blade thickness it is considered acceptable. When I get blades that exceed that I straighten as much as possible and keep them for cutting where blade marks are not as big a problem, like thick wood slabs or bookends that can be lapped flat while I am busy elsewhere.
Lee
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Post by DirtCleaner on Sept 30, 2013 21:49:36 GMT -5
Just something I was taught by an old blacksmith about large circular wood blades. He would true them up for his customers. He showed me one in his shop one day. I remember it to be about 36" or a bit bigger. The blade was not flat, it had a bit of a cup to it. And his magic was knowing how much cupping a blade should have so that when it was spun and cutting wood it would straighten out and cut better than a flat one. Flat blades would wobble. I don't know if this correlates to rock blades or not. Anybody know more about this?
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robsrockshop
has rocks in the head
Member since August 2012
Posts: 715
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Post by robsrockshop on Oct 1, 2013 9:56:11 GMT -5
So on that design of saw since the vise would be stopping at different points depending on the rock size and how far the top vise plate sticks out of the back of the vise............I assume you aren't able to make a stop in the feedshaft to where it can't drive the vise any further?
So what happens? Is there enough give in the feedmotor belt that it won't drive further as the belt will slip or does it start warping the feedscrew and cause problems? Which I realize isn't a problem if you set the auto-shutoff and don't leave the saw unattended.
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Post by Rockoonz on Oct 3, 2013 0:02:28 GMT -5
Screw driven saws will have a section of the feed screw threads machined away so the carriage will stop at that point. Mine have adjustable auto shut-off as well.
Lee
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robsrockshop
has rocks in the head
Member since August 2012
Posts: 715
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Post by robsrockshop on Oct 3, 2013 9:26:28 GMT -5
Screw driven saws will have a section of the feed screw threads machined away so the carriage will stop at that point. Mine have adjustable auto shut-off as well. Lee Right. But what i'm saying is that this style of vise has the top plate extend out the rear of the vise, possibly as far as the entire length if you were cutting something narrow that needed the entire height of the blade. I have not seen this setup in person and in my mind it seems it would have different stopping points which would make machining out a stop point impossible. Gravity feed wouldn't be a problem, but this would unless you had a good clutch setup which is unlikely. I suppose you could cut a hole in the rear of the saw and let it extend and put a catch pan under it. I really have no idea since I haven't seen one i'm just wondering about it maybe my line of thinking isn't catching on to something here I don't know. I mean I suppose you could reclamp the rock longways etc etc etc.
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rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on Oct 3, 2013 13:45:51 GMT -5
I see what you're saying. The length of the vice is only slightly longer than half the length of the blade... by the time you add in clearance between the blade and the rear of the saw, you have plenty of space between the rear of the vice (even if fully closed) and the rear of the saw.
This is assuming you don't traverse more than half the blade diameter (which my saw is mechanically prevented from doing by the screw threads being machined away and auto-shutoff). I guess if you had a big cube or something that needed to be cut that could be a problem because of the curve of the blade, but then I think you just need a bigger saw.
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robsrockshop
has rocks in the head
Member since August 2012
Posts: 715
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Post by robsrockshop on Oct 3, 2013 17:02:24 GMT -5
You have plenty of room but if the vise was clamped on a smaller rock that would require the stopping point to where the flat bar sticks out the back is a different stopping point than where a larger rock would be so my as well not even have a one because you'd never reach it with a small rock or vs. you'd never be able to cut a large rock.
The only way to alleviate this problem would be by adding a clutch to where it wouldn't matter if it did hit the rear of the saw.
Don't ask why I rack my brain with such crap I know all about the auto-shutoff etc etc. I realize anyone that knows how to operate the saw none of this would be a problem but I could see a newbie having things go to hell in a hurry.
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rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on Oct 3, 2013 17:33:19 GMT -5
I guess I'm not seeing what your concern is. If you set the stop such that if the vice is fully closed (bar sticks out fully from the back) it doesn't hit the back, then obviously having a larger rock (vice open) would be safe too.
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Post by Rockoonz on Oct 3, 2013 20:32:04 GMT -5
You could always install a normally closed micro switch through the back wall of the saw so whatever you're talking about (I would need a pic to visualize it)would trip the switch and shut down the saw when it contacted the switch.
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