Abrasive Cutoff Saw Issues

"Jon Danniken" wrote: (clip) I checked the abrasive wheel arbor, and it doesn't seem to have any play in

^^^^^^^^^^^^^^^^^ I'm betting it's not the wheel. Since you don't feel play in the arbor bearings, it is likely due to flexibility/vibration in the entire saw. While this is going on, do you feel vibration in the handle?

Hi Leo, yes, I can feel it, I can even see the motor vibrating. It feels pretty smooth when it is up to speed, but at a slightly slower speed (I notice it when it is speeding up) it vibrates noticably.

Jon

"Jon Danniken" wrote: Hi Leo, yes, I can feel it, I can even see the motor vibrating. It feels

^^^^^^^^^^^^^^^^^ The fact that it occurs as the saw is speeding up, AND when you slow it down by loading it suggest that it is a resonant condition. I'm not sure how you can correct this, except maybe attach some weights to the saw. (Doesn't sound too practical, does it?)

It's possible, that, as Roy J suggested, the wheel may be out of balance, contributing to the problem. Rotating the wheel, as he suggested, recentering it, or trying a different wheel might be worthwhile. I was able to balance a fan, once, by holding a vibrating engraving tool against it while it was not running. The vibration overcame the friction in the bearings, and the heavy blade slowly drifted to the bottom. If you have an engraver you might try this trick. Or maybe a Dremel tool with an unbalanced stone or burr would work.

Thanks for that, Roy, it made a difference. Make sense, there's enough slop in there between the wheel and the arbor.

I also noticed that the hinge pin supporting the motor goes through a hole that feels a bit too big. I'm starting to think it might be a magnifier of sorts when the blade's imperfection is noticable, giving it a pivot point to translate into a sway that is perpendicular to the plane of the wheel. I'm guessing better quality saws might have a more precise hinge at that point than a pin and a hole through a cast yoke.

Jon

Thanks Leo. After I get the wheel as good as I can, I might put some shot in the recess to see if that stiffens it up a bit.

Here's a pic of what I think the culprit is, the sloppy hingepin holes:

I don't know how shiny I can get this turd, but I wonder if putting an epoxy concoction in the hingepin holes might stiffen it up a bit.

Jon

I use cut off saws all the time and they do not vibrate at all . This is an very dangerous situation , I've seen blades explode like an grenade and cut you all to hell. Return the saw if pivot pins or arbor bearings have too much play as this is not permissible.

Sal

You might also try running the blade backwards from it's current orientation. It obviously has a resonant issue since it only does it at certain speeds. I doubt it the pivot has much to do with it.

You might also want to take some scrap steel and do a lightweight cut > "RoyJ" wrote:

Bronze bushings perhaps? Readily available in standard sizes at even Depot or Lowe's.

Hey - first things first. I been using these things for years, from el cheapo Chinese ones to really expensive precision engineered ones. From your pictures, yours looks better than the one I have now.

In EVERY case of vibration as you describe, its either the wrong cutoff blade (ie, centre hub hole wrong size, too big) or it isnt fitted correctly, vis the blade must be a snug fit on the motor spindle, the screw on flat washer MUST be oriented correctly to clamp the blade but not stress it. Easy to get wrong. Check the instruction leaflet.

And check the blade you are now using, if its been damaged, smash it in half and bin it (so no one else can use it in error) - Actually, I usually buy them by the half dozen, their cheap, means you are likely to have one close at hand when you need it..and I have never had problems like yours even with cheap chines ones.

And its never going to be a precision tool anyway, as its name implies, all it is used for is cutting things to approx length and approx angle....

Hope this helps, if you could hold it up to the monitor so I can get a good look at it....remote diagnosis fills in the time but sometimes is totally wrong.

Andrew VK3BFA.

Put a new blade on it, and pay serious attention to all the details to make sure you got the spacers, nuts, etc, all right. If it still does it, take it back. A blade fracture can be catastrophic. They're supposed to work and work right. Yours obviously isn't for some reason, and if it is in the machine, you're entitled to a new one. Just be sure you got it right. If it still don't work, don't put yourself in harms way.

Steve

When I'd change blades, I'd put the spacers and bolts on there, and with the wheel loose, give it a spin to make sure it was centered on the spindle. Then tighten it down. More than once over the years, I'd have it askew, and if I had tightened it down, it would have spun askew.

Steve

Some one stole my last cut off saw, and if I ever find out who, I'll send them a Christmas turkey free. I got a band saw, and haven't looked back.

Steve

Hi Jon;

When your're using one of these don't push hard enough to bog the motor down (maybe 10% at most), experience will allow you to cut quick enough with a narrow kerf, and your saw and wheels will last a lot longer. You'll get done just about as fast and your wheel changes will be far less frequent.

The dry cutoff saws have a couple of issues (not a deal breaker though) especially if you're cutting cylinder rod or very thin sections.

Surface speed is the key to any abrasive wheel and the constant torque biased DC motor allows the wheel to cut at lower than optimum speeds without shutting down. A few things then happen.

First the wheel cools poorly and looses strength (also wheel breakdown occurs much faster).

Second and most important is that "at speed the wheel centers about its own axis by centrifical force".

Third the combination of the wheel making the transition through "critical speed" (changing the center of rotation and axis plane) over and over and losing strength (like pushing paper through a slot) it will displace a larger area. This causes the wider kerf.

Last is without coolant (wet machine) the wheel sharpens by the binder breaking down instead of abrasive fracture so a lot of free (sharp) abrasive ends up side cutting instead of face cutting.

Matt

Hey thanks Pete, I didn't think of bushings. I'll keep that in mind should I try to stiffen up the mounts.

Jon

wrote

THanks Andrew. I've checked and rechecked that mounting assembly, both clamshells and the washer/screw. I'm pretty darn sure I've got it right at this point, but I'm going to pick up another couple of wheels to try next.

Jon

"SteveB"

Thanks Steve, a new wheel or two is going to be my next step to investigate. I spun it up last night and noticed that the wobble in the current wheel is enough to generate a few sparks when it rubs up against the guard. Yikes!

Jon

"Jon Danniken" wrote

I wore out four chop saws before I went to a band saw. In that time, I had about half a dozen wheels that were just screwed up from the factory, particularly Pearl brand, which were the cheapos of the day.

Bottom line, if everything's right, it should work. If it don't, the wheel is out of kilter, mounted out of kilter, or something else is throwing it out of kilter.

Stop and figger it out before you launch yourself into the next zip code.

Steve