# What causes slitting blade mistracking?



## WobblyHand (Apr 6, 2022)

I was attempting to slit a piece of solid steel stock in half with a slitting saw.  It appears the saw started mistracking and started cutting off at a downward angle.  I was preoccupied with trying to feed the saw and didn't notice the mistrack until too late.  Saw was 0.020" thick.  Material was 1018 5/8" thick.  Was the saw defective?  Is the answer a thicker saw?  What causes the mistracking?  There was plenty of oil.  Sierra American SA-1000 arbor.


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## Cadillac (Apr 6, 2022)

Did the part move maybe?


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## WobblyHand (Apr 6, 2022)

Cadillac said:


> Did the part move maybe?


Don't think so.  Actually, it's still in the 3" toolmakers vise.  I could check if the parallels are still tight.

I thought I had read that this is a problem with thin blades, but didn't think 0.020" was very thin.  I could see this happening with a 0.002" blade if it hit a hard spot?


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## WobblyHand (Apr 6, 2022)

WobblyHand said:


> Don't think so.  Actually, it's still in the 3" toolmakers vise.  I could check if the parallels are still tight.
> 
> I thought I had read that this is a problem with thin blades, but didn't think 0.020" was very thin.  I could see this happening with a 0.002" blade if it hit a hard spot?


edit:  moveable jaw parallel has loosened, can move that parallel along the x-axis.


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## FOMOGO (Apr 6, 2022)

Are your decimal points in the right place re blade thickness?


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## Cadillac (Apr 6, 2022)

Yeah to me something has to move. Part quill not locked down, knee lock slips. If the  saw is cutting on acouple teeth it can vibrate the part loose.


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## Cadillac (Apr 6, 2022)

.002 slitting saw? ICan barely keep a .002 feeler gauge from bending


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## Winegrower (Apr 6, 2022)

I just sawed some brass with a 0.020 slitting saw, after making an arbor for it.    Worked perfectly.   Must have been movement of some kind, or maybe the arbor screw loosened.


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## Lo-Fi (Apr 6, 2022)

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!


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## WobblyHand (Apr 6, 2022)

It was a 0.020" saw.  You can see it in the picture in the first post.  The marking is on the hub.   As for feed rate, it took 20 minutes to go 1", so that is 0.05 ipm, hardly a fast feed.  The quill didn't move.  The z axis didn't move.  I have dro's on both.  The R8 collet was tightened.  The arbor was tight.

I can try to measure the gap between work piece and the parallels.  The movable jaw side parallel can slide side to side.  It wasn't that way when I started, because I always test for that.  So a small amount of jaw lift happened.  I'm not expecting it is much lift.  The last time I tested this vise for jaw lift it was under 0.0005".  But I will check it.


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## WobblyHand (Apr 6, 2022)

Cadillac said:


> .002 slitting saw? ICan barely keep a .002 feeler gauge from bending


0.020" slitting saw, as photo shows in my first post.


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## WobblyHand (Apr 6, 2022)

FOMOGO said:


> Are your decimal points in the right place re blade thickness?


0.020" saw, just like the picture shows.  Was only using 0.002" as an example.  I had a 0.020" Malco slitting saw.  Yes, that is past tense.


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## Firstram (Apr 6, 2022)

WobblyHand said:


> I had a 0.020" Malco slitting saw.  Yes, that is past tense.


You just need to make a much larger arbor


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## MrWhoopee (Apr 6, 2022)

Was it a new slitting saw? Examine the teeth closely. Slightly dull on one side or uneven grind will cause the blade to deflect.  I'm betting the part didn't move, the blade flexed due to unbalanced cutting forces.


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## WobblyHand (Apr 6, 2022)

MrWhoopee said:


> Was it a new slitting saw? Examine the teeth closely. Slightly dull on one side or uneven grind will cause the blade to deflect.  I'm betting the part didn't move, the blade flexed due to unbalanced cutting forces.


Yes it was a new slitting saw.  I will take a look at it.

Toolmakers vise.  I did find the piece wasn't seated on the parallels correctly.  The right side of the vise had a 0.0015" gap.  The left side had 0.


But the smoking gun is the arbor itself.  It is new.  Sierra American SA-1000.  I noticed the screw was kind of strange when tightening.  It seems it is slightly eccentric.  The cap screw hits the arbor cap every turn.  And guess what, that cocks the arbor cap and I see more light on one side vs the other.  Of course that can cock the saw.  (Which could cause mistracking...)  Unfortunately, that is hard to take a picture of.  Once the screw is turned enough, and the eccentric part is no longer interfering, it is flat again, and no gaps on either side to let light through.

The original cap screw has worn some of the blue on one side, because it is hitting the arbor cap.  I will try to replace the screw first.  Of course, I don't have the right length...  As a test, I can cut off a 2" partially threaded SHCS.  If that doesn't solve the problem, it is a manufacturing defect in the saw arbor.  Hope it is the screw...


Think I will chuck up the screw and indicate the head.


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## Firstram (Apr 6, 2022)

If your going to chuck it up, just skim the head so it's concentric.


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## MrWhoopee (Apr 6, 2022)

Looking again at the picture of the blade, it was obviously flexing around the arbor cap until it fractured. Chuck up the arbor by the shank and check the runout of the face that contacts the blade.


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## WobblyHand (Apr 6, 2022)

Firstram said:


> If your going to chuck it up, just skim the head so it's concentric.


I did put it in a collet.  The TIR of the head is 0.013".  Pulling out a random 5/16"-18 2" long SHCS and doing the same thing shows a TIR of 0.002".  I don't want to turn the original screw head or alter it in any way, in case I have to return the arbor.  I will turn down the 2" screw to 1-1/4" and try it.  If it works, then all is good, except I am down a saw blade.

If it's the arbor that is the problem, I'm going to contact McMaster and tell them that the arbor they sold me was defective and they owe me both a new arbor and a new saw blade.

If it is just the screw, I may still contact McMaster.  I mean, one does expect to receive compliant product.  An arbor that doesn't run true isn't compliant.  If it really was the screw, it still cost me a blade.  I'd expect some recompense, but I am not sure what that would be.


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## WobblyHand (Apr 6, 2022)

MrWhoopee said:


> Looking again at the picture of the blade, it was obviously flexing around the arbor cap until it fractured. Chuck up the arbor by the shank and check the runout of the face that contacts the blade.


You are keeping me busy   That is a good idea.  Having found the SHCS with a 0.013" TIR makes me want to measure the TIR of the face.


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## MrWhoopee (Apr 6, 2022)

Nevermind.


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## WobblyHand (Apr 6, 2022)

The TIR of the arbor face that the blade rests against is just under 0.0005".  I can measure it more closely, but have to dig out my better DTI.  As far as I can tell, the arbor face is in spec.


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## MrWhoopee (Apr 6, 2022)

WobblyHand said:


> The TIR of the arbor face that the blade rests against is just under 0.0005".  I can measure it more closely, but have to dig out my better DTI.  As far as I can tell, the arbor face is in spec.


No need, that face is fine. Something was causing that blade to flex up and down. Of course, the blade deflecting to one side would cause similar flexing as it entered and exited the kerf.


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## RJSakowski (Apr 6, 2022)

A thought: Saw blades for wood which have a fairly large diameter to thickness ratio will heat on the rim due to friction and the blade will warp into a potato chip.  For a slitting saw with a high diameter to thickness ratio, the same can happen.  For wood saw blades, the common cure is adding radial slits to the blade.  For slitting saws, I would recommend decreasing the rpm and feed rate and use of a coolant/ lubricant to keep the blade cool.


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## benmychree (Apr 6, 2022)

That is not a slitting saw, it is a screw slotting saw; a slitting saw would have much coarser teeth with much more room for chips.


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## WobblyHand (Apr 6, 2022)

MrWhoopee said:


> No need, that face is fine. Something was causing that blade to flex up and down. Of course, the blade deflecting to one side would cause similar flexing as it entered and exited the kerf.


I turned down a 2" screw to 1.25".  The head on this screw has a 0.002" TIR.  The problem is pretty obvious now.  If I start the screw in the arbor, the screw head hits the edge of the counterbore in the arbor cap.  The counterbore in the cap is not concentric with the screw head.   So either the threads aren't coaxial with the bore, or the cap is off.  The concentricity error is over 0.030". 

This side of the cap screw is hitting the top of the arbor.


Now rotate the arbor 180 degrees about the spindle axis.  See the gap?


This screw head is 0.005" wider than the stock one.  I could turn down the screw head diameter by about 0.010-0.015" as a test.

Don't know, but this arbor is looking more and more like it is the source of the problem.  Cockeyed screw camming the arbor cap.   Might be saveable, but in my humble opinion, that's not good workmanship, and worse quality control.  Not an import.


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## WobblyHand (Apr 6, 2022)

benmychree said:


> That is not a slitting saw, it is a screw slotting saw; a slitting saw would have much coarser teeth with much more room for chips.


You are probably right.  

However, McMaster seems to call them *High-Speed Steel Slitting Saws *independent on the number of teeth.









						McMaster-Carr
					

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.




					www.mcmaster.com


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## mmcmdl (Apr 6, 2022)

WobblyHand said:


> I was attempting to slit a piece of solid steel stock in half with a slitting saw. It appears the saw started mistracking and started cutting off at a downward angle. I was preoccupied with trying to feed the saw and didn't notice the mistrack until too late. Saw was 0.020" thick. Material was 1018 5/8" thick. Was the saw defective? Is the answer a thicker saw? What causes the mistracking? There was plenty of oil. Sierra American SA-1000 arbor.


You're gonna need a bigger arbor for that blade Wobbly !   Never seen one do that . How were you cutting it ?


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## WobblyHand (Apr 7, 2022)

mmcmdl said:


> You're gonna need a bigger arbor for that blade Wobbly !   Never seen one do that . How were you cutting it ?


I don't understand.  You're the second person to mention this.  What do you mean?  Or is this just a joke?  As a joke I get it, yeah the hole in the saw is bigger, so I need a bigger arbor.

I was cutting from the back of the piece going from right to left.  Teeth facing to the left where contacting the work piece.  Saw turning CW when looking down from the mill head.  Saw arbor had clearance from both the vise and the work piece.

Honestly think the arbor cap counterbore is not concentric with the screw hole in the arbor.  I will check if the screw threads are concentric with the arbor shaft.  The original screw head hits the arbor cap every turn.  So it cocks the cap every turn for an angular sector of say 60 degrees.  Outside of that region, the arbor cap is flat with the arbor.  There's clearly something wrong with the arbor, everything should be concentric with the spindle axis.  The screw shouldn't bind every turn against the cap.  Without the cap the screw goes in without binding.


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## Firstram (Apr 7, 2022)

Yes, the bigger arbor is a joke.


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## WobblyHand (Apr 7, 2022)

Firstram said:


> Yes, the bigger arbor is a joke.


Good.  Thought maybe I was missing something!


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## RJSakowski (Apr 7, 2022)

WobblyHand said:


> I was cutting from the back of the piece going from right to left.  Teeth facing to the left where contacting the work piece.  Saw turning CW when looking down from the mill head.  Saw arbor had clearance from both the vise and the work piece.


From your description, it appears that you are using conventional cutting rather than climb cutting.  Conventional cutting requires moire power and generates more heat than climb cutting.


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## mmcmdl (Apr 7, 2022)

WobblyHand said:


> As a joke I get it, yeah the hole in the saw is bigger, so I need a bigger arbor.


Yes , that WAS a joke . How were you cutting it though was a serious question . The material could have pinched the cutter and thus it broke .


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## WobblyHand (Apr 7, 2022)

If I indicate on a screw turned into the arbor, basically bottomed in the thread, and measure the TIR I find the screw has 0.036" TIR.  Which is consistent with the screw head hitting the arbor cap.  If you recall, I had 0 gap on one side and roughly over 0.03" on the other side.


If I traverse the slide towards the chuck the needle doesn't change.  Likewise if I rotate the chuck 90 degrees and traverse the slide towards the chuck.  So the screw may be relatively straight, but offset from the arbor centerline.  I will turn down the head of a screw.  If that doesn't fix it, I am going to return this.  This arbor isn't made correctly.


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## mmcmdl (Apr 7, 2022)

You're saying that the thread in the arbor is out .035 TIR ?


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## WobblyHand (Apr 7, 2022)

mmcmdl said:


> Yes , that WAS a joke . How were you cutting it though was a serious question . The material could have pinched the cutter and thus it broke .


I think later on I may have had a problem with pinching.  This saw broke after only about 1" of cut.  My conclusion is the arbor is machined wrong which can cause blade canting.


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## WobblyHand (Apr 7, 2022)

mmcmdl said:


> You're saying that the thread in the arbor is out .035 TIR ?


That is what it looks like to me!  Correction, the TIR is 0.036" for the thread of the arbor.


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## mmcmdl (Apr 7, 2022)

WobblyHand said:


> That is what it looks like to me!


Strange , hard to believe they could make it that far off .  You could open it up and go with a bigger thread , but I think I would just send it back and try again . .017 is a mile off true position , still can't imagine how they machined it so far off . I'm guessing here , but maybe it was turned soft , hardened and then ground with the grinding not worried about the thread TIR .


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## Eyerelief (Apr 7, 2022)

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.


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## WobblyHand (Apr 7, 2022)

mmcmdl said:


> Strange , hard to believe they could make it that far off .  You could open it up and go with a bigger thread , but I think I would just send it back and try again . .017 is a mile off true position , still can't imagine how they machined it so far off . I'm guessing here , but maybe it was turned soft , hardened and then ground with the grinding not worried about the thread TIR .


I'm kind of astonished.  For $56, or whatever I paid for this allegedly premium product, it doesn't seem so premium.  I'd expect the hole to be on center, or at least close!  I am going to return this arbor.  It is clearly defectively made.  And it cost me a saw blade.


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## Eyerelief (Apr 7, 2022)

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.


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## WobblyHand (Apr 7, 2022)

Eyerelief said:


> 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.


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## mmcmdl (Apr 7, 2022)

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


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## woodchucker (Apr 7, 2022)

Lo-Fi said:


> 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...


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## WobblyHand (Apr 7, 2022)

Eyerelief said:


> 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.


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## WobblyHand (Apr 7, 2022)

mmcmdl said:


> 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.


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## mmcmdl (Apr 7, 2022)

Yep , I agree !


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## WobblyHand (Apr 7, 2022)

woodchucker said:


> 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?


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## woodchucker (Apr 7, 2022)

WobblyHand said:


> 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.


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## WobblyHand (Apr 7, 2022)

woodchucker said:


> 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.


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## WobblyHand (Apr 7, 2022)

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.


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## WobblyHand (Apr 7, 2022)

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.


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## wachuko (Apr 7, 2022)

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

Still in their packages…


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## homebrewed (Apr 7, 2022)

Lo-Fi said:


> 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.


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## mikey (Apr 7, 2022)

WobblyHand said:


> 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.


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## WobblyHand (Apr 7, 2022)

wachuko said:


> 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.


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## WobblyHand (Apr 7, 2022)

mikey said:


> 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.


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## mikey (Apr 7, 2022)

WobblyHand said:


> 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.


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## jmkasunich (Apr 7, 2022)

WobblyHand said:


> 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....


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## WobblyHand (Apr 7, 2022)

mikey said:


> 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.


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## mikey (Apr 7, 2022)

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


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## jmkasunich (Apr 7, 2022)

WobblyHand said:


> 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?
> 
> ...


It's the machine.  That spindle drivetrain was NOT designed for torque at low speed.  Use the smallest diameter cutter that you can get away with to bring the speed up.  Then feed by hand fast enough that it can actually cut.


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## jmkasunich (Apr 7, 2022)

mikey said:


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


For a 2-3/4" diameter HSS cutter?  That would be 215 to 250 SFPM....


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## WobblyHand (Apr 7, 2022)

jmkasunich said:


> 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.
> 
> ...


Thank you for your thoughtful reply. 
1.  I was trying to cut a little too much.  5/8" deep cut in steel.  That pretty much rules out the smallest saws.  Larger saws mean one needs even lower RPM.
2.  I had the low speed pulley on.  Yes, the torque utterly is awful at this low RPM.  The speed control is poor.  The resolution of the pot is poor.  I am lucky if I can get within 40-60 RPM of target.  So maybe it was 120 rpm for a little while, or 145 for a different time.  The motor/spindle stalls out under the slightest of loads.  It simply has no torque nor adequate speed control in the 80-200 RPM range.  This is the crux of the matter.  Once there is a stall the motor overspeeds and 5-8 seconds later finally slows down.


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## jmkasunich (Apr 7, 2022)

WobblyHand said:


> Thank you for your thoughtful reply.
> 1.  I was trying to cut a little too much.  5/8" deep cut in steel.  That pretty much rules out the smallest saws.  Larger saws mean one needs even lower RPM.
> 2.  I had the low speed pulley on.  Yes, the torque utterly is awful at this low RPM.  The speed control is poor.  The resolution of the pot is poor.  I am lucky if I can get within 40-60 RPM of target.  So maybe it was 120 rpm for a little while, or 145 for a different time.  The motor/spindle stalls out under the slightest of loads.  It simply has no torque nor adequate speed control in the 80-200 RPM range.  This is the crux of the matter.  Once there is a stall the motor overspeeds and 5-8 seconds later finally slows down.


I don't know enough about that class of machine to know whether it just is what it is, or whether something is defective.  PM is supposed to have good customer support - try calling them and describing the behavior.  It's never going to have the torque of a geared spindle, but they advertise it as going down to 50 RPM, it ought to have useful torque at that speed.  Maybe something is broken and can be fixed.


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## WobblyHand (Apr 7, 2022)

jmkasunich said:


> It's the machine.  That spindle drivetrain was NOT designed for torque at low speed.  Use the smallest diameter cutter that you can get away with to bring the speed up.  Then feed by hand fast enough that it can actually cut.


It's pretty clear it is the machine.  I was using a 2.75" saw so I could make a cut of 5/8" deep.  That drops the RPM to the low speed range which is torqueless and gutless.  Once in that "regime" any feed rate is too fast.  Only thing that I can think of that might help is to make a new pulley set, so the motor can run faster, but the spindle is slower than the stock ratio.  That or replace the motor and controller.


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## WobblyHand (Apr 7, 2022)

jmkasunich said:


> I don't know enough about that class of machine to know whether it just is what it is, or whether something is defective.  PM is supposed to have good customer support - try calling them and describing the behavior.  It's never going to have the torque of a geared spindle, but they advertise it as going down to 50 RPM, it ought to have useful torque at that speed.  Maybe something is broken and can be fixed.


I wouldn't be surprised if it is a little of both.  (_The way it is_ AND _the possibility of a defect_.)

Have to laugh at the thought of 50 RPM torque on this mill, bet it is very low.  How could I test it?  Didn't Clough42 make a torque stall tester?

Might as well put this in: RPM = SFM * 12/ (pi * D), so if SFM=90 FPM for steel, and D=2.75", RPM = 125


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## jmkasunich (Apr 7, 2022)

WobblyHand said:


> I wouldn't be surprised if it is a little of both.  (_The way it is_ AND _the possibility of a defect_.)
> 
> Have to laugh at the thought of 50 RPM torque on this mill, bet it is very low.  How could I test it?  Didn't Clough42 make a torque stall tester?


The "wimpy torque, then stall, then overspeed for several seconds" behavior is suspicious.  The overspeed indicates that the drive realizes that it has stalled and starts to pour on the coal, but it happens too late.  Makes me think something might be tuned wrong in the drive.  I would start by by calling PM and see what they say in response to that description.


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## WobblyHand (Apr 7, 2022)

jmkasunich said:


> The "wimpy torque, then stall, then overspeed for several seconds" behavior is suspicious.  The overspeed indicates that the drive realizes that it has stalled and starts to pour on the coal, but it happens too late.  Makes me think something might be tuned wrong in the drive.  I would start by by calling PM and see what they say in response to that description.


Yeah, don't have much to lose at this point.  It's like the servo control system is improperly tuned.  Seems like a bad controller.  And there are no knobs to turn on this.  The controller is potted and there are no adjustments.

From watching BlondieHack's experience with this, I'm not all that anxious to go through what she did.  She had bad rheostats (check), bad controllers (maybe), displays that were matched with controllers, and a down mill for quite a while.  It was quite a mess.


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## WobblyHand (Apr 7, 2022)

mikey said:


> 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.


It will stall the motor if you didn't use the slow speed position, ie. change the pulleys.  

I must of had a dyslexic moment, _could have sworn I was in slow speed mode, but I wasn't_. So changed the belt position used a 2" diameter cutter, (1/2" arbor) 0.063" thick blade, and was able to cut the stock.  The mill is still no powerhouse, but I was able to make a 6" long cut through 5/8" thick 1018.  

With the correct belt position, I could indeed feel the machine cutting.  In the wrong belt position, this wasn't possible, since the motor would stall at even a very slow feed rate.


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## WobblyHand (Apr 7, 2022)

Ok.  Post mortem.  Had two main issues, with a possible third.

1) Defective arbor.  Arbor screw drilled parallel to but not concentric with the spindle axis.  0.036" TIR on screw.  Screw head when tightened caused interference with arbor cap which tilted the arbor cap and blade.  Blade then followed path of its own until the blade broke.
2) Operator error. Thought the mill was in low speed mode, but it was in high speed mode.  Mill had insufficient torque to cut with low feed rates.  When operated in low speed mode, using 2" cutter, was able to cut through 5/8" 1018 over roughly a 6" long cut.

3) Lesser issue.  Poor motor speed control especially in low speed mode and low speeds.  Unable to set motor speed to proper speed in low speed setting.  Could not set speed to 171 RPM for steel.  Only could set to 220 RPM or 140 RPM (rough numbers).  Seems there's a hole in the potentiometer range.  Ran at 220 RPM, which under load was roughly 180 RPM.  Poor speed regulation under changing load.


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## benmychree (Apr 7, 2022)

WobblyHand said:


> You are probably right.
> 
> However, McMaster seems to call them *High-Speed Steel Slitting Saws *independent on the number of teeth.
> 
> ...


Regardless of definition, a fine tooth saw is not the best tool for deep cuts, there is not room for a lot of chips, hence the use of coarse tooth saws.


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## WobblyHand (Apr 7, 2022)

benmychree said:


> Regardless of definition, a fine tooth saw is not the best tool for deep cuts, there is not room for a lot of chips, hence the use of coarse tooth saws.


Yes, I learned this the hard way!  Used a 28T saw, remembered to set the pulleys to slow speed mode, and was able to make the cut.


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## Toolmaker51 (Apr 7, 2022)

Unlike a circular saw, set for minimum clear depth, a slitting blade runs best a decent distance _under _the part, with sufficient mist coolant to eject all chips re-entering cut (conventional). Slitting though, is normally reserved for thinner material. Either way, the cut must be rapid enough to engage material, there is possibility of heat distortion.
Storage of the blade can be an issue too. When some of the teeth are not right, they'll wander. Just like a worn bandsaw blade.


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