What causes slitting blade mistracking?

[WobblyHand]

Just a thought. You might want to quickly confirm that your spindle is square to your table. If that blade goes in at a cant, its going to keep trying to dive into the workpiece.
Of course, I work for the auxiliary back up office of redundancy, so by nature, I have to double check everything, twice.............
Your set up is probably just fine.

It's not perfectly square as evidenced by flycutter results, but it isn't terrible. I think the origin of the blade cant is due to the fact that the screw head hits the counterbore and cants the arbor cap. The screw hole in the arbor is not centered with the spindle axis. It is off.

 

[mmcmdl]

Hard to see how the arbor was made , couple different designs of saw holders out there .

 

[woodchucker]

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!

I totally agree with this, too fast and the metal on the saw will bunch up..yes.. it will flex and that will cause the cut to change direction.
think of it creating a wave washer as the metal is thin it slows down bunching up creating a wave...

 

[WobblyHand]

Wouldnt the blade wobble when being turned by the spindle if the arbor was not square on the bottom? If it was off center, the blade would tell you as it tried to cut as the load changed. That to me could be a screw off center problem. If the bottom of the arbor is not square, I would think the blade would wobble.
Maybe I'm not understanding the problem.

The bottom of the arbor, where the blade would normally touch is square. However, every 120 degrees or so of the screw rotation, the screw head hits the counterbore, causing the arbor cap to cant. Depending on the screw tightness, the blade could be square to the arbor, or it might be canted, depending on the angular relationship of the screw to the arbor and cap.

 

[WobblyHand]

Hard to see how the arbor was made , couple different designs of saw holders out there .

If I was making the arbor I would have drilled it while still in the lathe. If it was really critical, I would have bored it. Just don't understand how it could be this far off, unless it was transferred to a different fixture for drilling and tapping. That's ok, as long as the fixture is on center.

 

[mmcmdl]

Yep , I agree !

 

[WobblyHand]

I totally agree with this, too fast and the metal on the saw will bunch up..yes.. it will flex and that will cause the cut to change direction.
think of it creating a wave washer as the metal is thin it slows down bunching up creating a wave...

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

 

[woodchucker]

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

I don't know. I don't have all the info, nor do I know how it was sounding and looking.
I believe you weren't clearing chips, you were too fast on the feed, and heating up.

coolant/oil/ blowing chips full time? 0.05 means nothing if your rpm are so slow that you are not cutting fast enough.. too high an rpm and you are just generating heat. There is a fine line in there.

 

[WobblyHand]

I don't know. I don't have all the info, nor do I know how it was sounding and looking.
I believe you weren't clearing chips, you were too fast on the feed, and heating up.

coolant/oil/ blowing chips full time? 0.05 means nothing if your rpm are so slow that you are not cutting fast enough.. too high an rpm and you are just generating heat. There is a fine line in there.

Oil all the time. RPM was around 150. RPM control in this range for my lightweight mill is a little lacking. May make some pulleys to help with that, but that is yet another can of worms. Was trying to keep the SFM appropriate for steel, didn't want to burn the blade.

Slitting on my mill is an exercise in patience. 1HP DC motor just isn't powerful enough to keep that blade speed constant enough under load at that RPM. Everyone says to bury the blade. If I do that then it bogs down, catches, speeds up, gets back to normal, and repeats unless I do 0.01"/min. Just can't go that slow manually. Not sure I can get the PF to go that slow either.

 

[WobblyHand]

I sent an email to McMaster about the arbor. Will see what they can do for me. Told them about the screw hole being off center causing cap interference and blade cant. Offered to send photos. I am asking for a new replacement arbor. I did inform them about losing the blade, but didn't directly ask for a replacement.