What causes slitting blade mistracking?

[WobblyHand]

McMaster will deliver a replacement arbor tomorrow. No need to return the defective one. They didn't offer to replace the saw blade, but hey, it was worth mentioning to them. When I get the replacement arbor, first thing I will do is check the screw runout. Kind of sad to have to do this, you'd think the manufacturer would have drilled the hole in the right place to begin with...

Once I get the replacement and it checks out ok, I think I will attempt fixing the bad arbor. Might put in an M10 screw. Got to go check minor diameters... Edit, yes, an M10x1.5 would fit.

 

[wachuko]

Following as I believe I bought the same arbors and saws…

Still in their packages…

 

[homebrewed]

Feeding too fast is always the answer when I've had that problem with thin blades. Getting the saw to run true so most of the teeth work is the magic bullet, but it can be tricky!

How DO you achieve that? I always end up with just a few of the teeth actually doing any cutting.

I'm making a (prototype) touch detector that uses the change in resistance as the cutter contacts the work, thinking that might be a way....if it works at all. All other approaches I've considered look like an endless round of tinkering.

 

[mikey]

I was using an effective feed rate of 0.05"/minute. Is that too fast?

If you ask me, your problem is that you were feeding too slow and heat/expansion caused the saw to bind and break. I've used 0.020" thick saws many, many times in multiple materials and never had one snap like this. I always take a full depth cut, feed by hand so that I can feel a slight resistance to the feed and always in a conventional direction (how do you do it any other way?). The feed rate is always far faster than you're feeding, that's for sure.

 

[WobblyHand]

Following as I believe I bought the same arbors and saws…

Still in their packages…

Put them in a mill or lathe and indicate them. It's easy. Never expected to get a lemon, figured they'd be good at that price point. One arbor wasn't. Couldn't even imagine I'd get a bum unit. I will do more incoming inspection now. Shame to adapt such an attitude. Guess I'm back to trust but verify.

 

[WobblyHand]

If you ask me, your problem is that you were feeding too slow and heat/expansion caused the saw to bind and break. I've used 0.020" thick saws many, many times in multiple materials and never had one snap like this. I always take a full depth cut, feed by hand so that I can feel a slight resistance to the feed and always in a conventional direction (how do you do it any other way?). The feed rate is always far faster than you're feeding, that's for sure.

I hear what you are saying, but my experience with this mill is that faster feed rates stall the motor. I don't think that 99 IPM in steel at 125 rpm for a 2.75" diameter HSS saw is remotely possible using my PM25. That being said, I would gladly be wrong.

I can attempt to estimate the feedrate on the PF and run a test with a different saw. If it works, I'll be delighted. Is 6 IPM worth trying? That's 1" in 10 seconds.

Slitting has always been dreadful on this machine. It could be I am doing it wrong, so I'm asking for some guidance.

 

[mikey]

I hear what you are saying, but my experience with this mill is that faster feed rates stall the motor.

If you feed by hand so that you feel a slight resistance to the feed then there is no way you're going to stall the motor. Forget power feed, forget the DRO. Feel the machine cut.

 

[jmkasunich]

I hear what you are saying, but my experience with this mill is that faster feed rates stall the motor. I don't think that 99 IPM in steel at 125 rpm for a 2.75" diameter HSS saw is remotely possible using my PM25. That being said, I would gladly be wrong.

I can attempt to estimate the feedrate on the PF and run a test with a different saw. If it works, I'll be delighted. Is 6 IPM worth trying? That's 1" in 10 seconds.

Slitting has always been dreadful on this machine. It could be I am doing it wrong, so I'm asking for some guidance.

Let's walk through both speed and feed. Earlier you said 150 RPM, just now you said 125RPM. The 2.75" cutter has a circumference of 8.63" or 0.72 feet. So 150 RPM is 108 SFPM, and 125 RPM is 90 SFPM. To be honest, I'd go a little slower if possible. But if you have a variable speed motor and no gear/belt reduction then spindle torque will be a problem...

Now the feed. At 150 RPM and 0.05 inches/minute, that is 0.00033" per revolution. Even if you only had three teeth, that is 0.0001" per tooth. With the 80 or so teeth that the cutter actually has you are talking a few millionths of an inch per tooth. I'm willing to bet It was rubbing, not cutting. That creates heat, and the rest follows naturally.

Did you see chips coming out of the cut? Or just shiny dust? They aren't going to be big chips, but they should be chips.

Due to runout a slitting saw isn't going to cut on every tooth. But it does need to CUT, not rub. I'm thinking you want to be feeding at least a couple thou per revolution, maybe as much as 10-20 thou per rev.

Getting back to the spindle speed and torque - I just looked up the manual for that machine. It has two mechanical speeds, with a 2:1 ratio. I assume you were on the low range. But even so, the torque is going to be pretty sad at such a low speed. That machine just isn't made to swing 2.75" diameter cutters. Both speeds are belt drive, so limited torque before the belt slips, even if the motor has good low speed torque.

How deep do you need to slot? Can you use a smaller diameter saw, perhaps something that is 1" or 1-1/2" diameter with a 1/2" arbor hole?
Like this maybe?


Or maybe something like this keyseating cutter? With a 1/2" cutting diameter you can spin it at 500 RPM for 65 SFPM surface speed. You'll have at least 5 times more force at the tip of the teeth because of the smaller diameter. Of course, it might not reach where you need to cut....

 

[WobblyHand]

If you feed by hand so that you feel a slight resistance to the feed then there is no way you're going to stall the motor. Forget power feed, forget the DRO. Feel the machine cut.

I was feeding by hand and would get stalling, overspeeding etc at anything but the sloooooowest hand feed rates. It could be the controller for the mill is defective. The controller board is potted, and there are no adjustments to set. However, I will set it up again and try once more.

Honestly, it has to be something I am doing that seems (perfectly) reasonable to me, but isn't something that you do. Or the capabilities of the machines are totally different. It's me (and what I am doing) or the machine, are there other possibilities?

For one, should I be conventional cutting or climb cutting?

I have significantly less problem with cutting aluminum, as I can run the saw faster. At the higher RPMS there are a lot less motor control issues, the speed tends to be relatively constant even with low to moderate load. The saw behaves ok, sort of like you are describing. This is not the case when slitting steel.

 

[mikey]

Do you recall what your speed was? In mild steel, you would be running somewhere near 300-350 rpm.