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Post by akansan on Apr 12, 2008 14:13:01 GMT -5
Okay if you recall my saw was down with a wobble. The wobble was definitely the pulley, and a new pulley straightened it all out. However, I couldn't get a pulley the same diameter - had to step down to a 3" instead of a 3 1/2". The pulley that drives the blade is a 4" pulley.
Now my question - I can never remember if the smaller pulley size on the motor speeds things up or slows things down. Am I now going slower or faster? The motor is a 1725 RPM motor - am I going too slow or too fast?
I ask this as everything seemed to be bogging down as I cut today, the first day I've actually TRULY attempted to cut since the repairs. I cut a few pieces to verify it all worked after replacement, but nothing too exacting. Today, it was as if my motor was straining to cut. Could I have overworked my motor with the pulley replacement?
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Post by stoner on Apr 12, 2008 15:49:31 GMT -5
You've slowed it down, but not by very much. The old pulley and belt(did you replace the belt?) may have been slipping, and now that you have a nice new pulley that grabs the belt you're seeing the motor bog down.
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Post by akansan on Apr 12, 2008 16:34:21 GMT -5
Is it necessary to replace the saw blade pulley as well, do you think? Finding the exact same pulleys for different shaft sizes appears to be difficult, at least here. This might call for a trip to a larger hardware store in KC...
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Post by Tony W on Apr 12, 2008 23:26:05 GMT -5
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dshalldms
starting to spend too much on rocks
Member since January 2008
Posts: 113
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Post by dshalldms on Apr 13, 2008 9:39:06 GMT -5
Hi Arkansan,
Given that your motor pulley was 3.5" and your blade pulley 4"
your original speed would have been... 1509 rpm.
Your new motor pulley being 3" and blade pulley 4" would now
give a speed of 1294 rpm
Dividing 12000 by your blade diameter will give you the maximum
rpm that your blade can safely run at.
Hope this helps,
Derek
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DeanW
has rocks in the head
Member since December 2007
Posts: 721
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Post by DeanW on Apr 15, 2008 17:56:02 GMT -5
Hey Derek, what magic is the 12000 number based on? I'm just trying to understand it so that as I rebuild some saws for a friend I can make sure all is good.
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Post by johnjsgems on Apr 15, 2008 18:57:19 GMT -5
Ronda, according to Diamond Pacific's chart you are at 1290 rpm now and your 14" blade should run 750-1600 rpm. Covington says 820-1230 rpm. I think you are at the right speed now and was probably too fast before. If your autofeed is adjustable run at the slowest speed possible.
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Post by akansan on Apr 15, 2008 21:35:05 GMT -5
It's a drop saw, so my autofeed is the weight of the saw head. ;D
It looks like the actual culprit then was the rock I was trying to cut when I noticed it bogging down. Kim tells me now that it can glaze up a blade pretty quickly, not to mention the mess it made of my oil! Which brings me to my next question - is there something "local" I can purchase that would work as a dressing stick? I'd like to get through the rest of this rock sometime soon.
Does obsidian really work?
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Post by catmandewe on Apr 15, 2008 22:04:55 GMT -5
You can use a fire brick to dress your blade, obsidian does work, but you need to cut several slabs, whereas one or two passes on a fire brick will do it.
(That has been my experience anyways, this is by no means based on scientific fact, only what I have observed to work)
There, got my disclaimer in there!
Tony
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Post by johnjsgems on Apr 15, 2008 22:30:50 GMT -5
I sell dressing sticks and blocks but use broken pieces of cinder blocks in my saws. I have a friend that tried the obsidian and said it didn't work, his blade was no good. I talked him into trying a 60 grit dressing stick and he said it cut like new again. Somehow I just can't imagine obsidian being abrasive enough. The old timers saved their worn don S/C wheels for dressing.
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Post by akansan on Apr 16, 2008 1:48:05 GMT -5
I've heard of using the SiC wheels, unfortunately I passed those along when I went diamond. I'll have a dressing stick headed my way (thanks, John!), but just out curiousity - what makes a brick a fire brick? Is it any old brick? I have a few of those out in my yard for some reason. I could try one of those, I suppose. It'll match the color of my oil right now.  The only cinder blocks I have around are the ones holding my house up. I don't think my house would appreciate my borrowing one to clean up my blade.  |
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dshalldms
starting to spend too much on rocks
Member since January 2008
Posts: 113
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Post by dshalldms on Apr 16, 2008 2:10:30 GMT -5
Hi Dean,
In answer to your question... why 12000...
Given that as a general rule diamond saws should run at a
surface speed of 3150 fpm, then...
a 12" blade would travel at 37800 ipm now divide by 3.142
and you have 12030.
Do the same calculation for other blade diameters and you
will always get a figure of around 12000
Thus 12000 becomes the third constant, the other two being
3150 and pi.
Hope this helps,
Derek
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Post by johnjsgems on Apr 16, 2008 7:39:34 GMT -5
No one said there was going to be math!
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Post by catmandewe on Apr 16, 2008 8:49:32 GMT -5
The two main ingredients in fire bricks are aluminum oxide and silica oxide or silica carbide, depending on the application, (whereas regular bricks are mostly clay and water). They are made to withstand high temperature changes inside of fireplaces, etc.
Tony
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DeanW
has rocks in the head
Member since December 2007
Posts: 721
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Post by DeanW on Apr 16, 2008 17:18:14 GMT -5
Most excellent Derek thanks! The 3150 is a rule/number I was looking for (well, sort of looking; I hadn't actually put any effort into looking yet ;D).
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Post by deb193redux on Apr 16, 2008 17:59:07 GMT -5
Is it necessary to replace the saw blade pulley as well, do you think? Finding the exact same pulleys for different shaft sizes appears to be difficult, at least here. This might call for a trip to a larger hardware store in KC... Is swapping them around an option? Most blades can be run a little faster/ |
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Post by akansan on Apr 16, 2008 18:41:09 GMT -5
Nope - two different arbor sizes. Motor has 1/2", saw shaft has 3/4".
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Post by johnjsgems on Apr 17, 2008 7:51:31 GMT -5
Does your saw have a way to slow the saw drop? I bought a (possibly homemade) funky old saw years ago that had a hydraulic cylinder with a valve to regulate the rate of drop. The leather seal in the cylinder leaked and my attempt to make a new one wasn't very successfull. I used a bungee to the rafters as a temporary fix. Let's see, I think that was 8 years ago and still working fine (temporary of course).
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Post by akansan on Apr 17, 2008 9:27:35 GMT -5
My dad used to say that if it worked well, then it wasn't temporary.  There's not a built-in method to slow the rate of the drop, but I've been known to use my hand to relieve the weight on some trickier cuts. I think I'll try your bungee trick! |
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