Author Topic: I screwed up using a slitting saw..  (Read 4189 times)

Offline ieezitin

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I screwed up using a slitting saw..
« on: August 11, 2013, 11:05:37 AM »
Lads

In the shot below is a set up on the milling machine of me trying to Slit-saw a taper pin expansion rod i am making. The saw thickness is .007 thou x 1 1/8th od, i ran the mill at 150 rpms the part is made out of 304 stainless.

In this shot you see the work in front of the slitting saw, i centered the saw blade to the pin center and i plunged cut in (moving the part away into the blade) .075 thou. that worked fine, i bathed it in Kroil and slowly fed the part onto the blade.

I then needed to slit the other side of it so i just raised the quill and moved the table 180deg, lowered the quill to center height and started to slit this side. 

The device you see poking into the end of the collet block is a stop for the pin up in the hole, my thought was the blade may want to throw the pin out. That will become clearer on the next photos.







Here is a shot of the first side i successfully cut.






Well!!!!!!!!! here is what happened when i did the other-side, i got to about .050 in the cut and the thing turned to Shite, the blade snapped and at the same time gouged the piece which is now ruined.





Here is the shot of the part with the pin included, i installed a sacrifice pin into the arbor for the machining process in slitting, the wall thickness on the taper tube end is around .032 thou






I figured that what i am trying to explain may be a little hard to do in words so i can show you my drawings for you all to get a better perspective.


Linear drawing showing taper reamer and drill, this is to scale.





Detailed drawing.








And a shot of the pin installed before being turned down.



 






What i shall do now is re-make another one and this time just index the pin, as i know it worked in that location.

if anyone has any experience in using very thin slitting saws i would appreciate the advice, i have never slitted anything this thin.

Happy days      Anthony.
If you cant fix it, get another hobby.

Offline vtsteam

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Re: I screwed up using a slitting saw..
« Reply #1 on: August 11, 2013, 11:48:18 AM »
Take everything I say with a grain of salt from a low experience source, who has made a few deep slitting saw cuts on occasion. But who has experience with larger saws. Apologies in advance for treading where angels fear to.

Plunging with a slittling saw like that seems to me difficult, but I can see why you did that because the saw arbor is too wide to allow slitting as a set of traverses from the end of the piece. I make it out that you were running 44 SFPM (if I didn't screw up calculating) which seems slow for 304. I don't know what the sacrificial piece is made of, and also tpi of slitting saw compared to wall thickness. Seems like sacrificial piece, if necessary should be easy cutting but not something that will grab (like brass -- if relief angle is great) or make grabby swarf.

Hope that helps, or at least doesn't interfere!
I love it when a Plan B comes together.

Offline ieezitin

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Re: I screwed up using a slitting saw..
« Reply #2 on: August 11, 2013, 01:27:22 PM »
V___

thanks for the input.

the sacrificial piece is steel its a shop purchased taper pin. i need to find out what the tooth count was on the saw to give people more information on trying to solve this pesky problem.

again thank you..

Anthony.
If you cant fix it, get another hobby.

Offline vtsteam

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Re: I screwed up using a slitting saw..
« Reply #3 on: August 11, 2013, 02:45:56 PM »
ieezitin, I was thinking about it a little more today while I was working. If you look up my quick change tool holder thread you'll see some pretty deep cuts with a slitting saw, but not stainless and not the thinness of your blade -- so same grain of salt......

But I used a commercial water based coolant and kept a pretty constant spray from a spritzer bottle going while taking small cuts. If that thin blade of yours heats up it probably will warp. And if it does, I think it will jam in the cut.

I don't know about Kroil -- never seen the stuff -- but I think it's an oil based rust buster, not necessarily a coolant, though I'm sure it lubricates. Water based coolants would do a better job I think of actually keeping everything cool.

So, I'm thinking speed and feed should be checked based on your material, blade diameter and tooth count, and then use a real coolant.

And if possible try not to plunge cut. Can you traverse in from the end of the piece towards the other end?
I love it when a Plan B comes together.

Offline ieezitin

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Re: I screwed up using a slitting saw..
« Reply #4 on: August 11, 2013, 03:15:16 PM »
V----------

here is a little more info... i was wrong on the OD of the cutter its 1.740 and it has 17 teeth per inch.

Kroil is a rust / nut- loose type product but it is thin and between the fingers it gets very slippery, i use it on Ali all the time and works fine. i would have used Tap-Majic if i had some but i did not. Neither do i have any water coolant to be honest i do not usually use any coolant on my machining just a little WD40 and fine turbine oil for drills and reamers, maybe that would have worked. 

I too have been thinking about it more and i believe the coolant had a major roll in the destruction of the cutter. 

I plunged cut because the blade is so thin i just was having a hard time in my mind asking the blade to cope with feeding it inn the piece.

we all live and learn............................  Anthony.
If you cant fix it, get another hobby.

Offline AdeV

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Re: I screwed up using a slitting saw..
« Reply #5 on: August 11, 2013, 03:30:55 PM »
Could you use a Dremel-type slitting disk? They are very thin, and you could really ramp the RPMs up to keep it rigid. Plus if it does sh­atter, all you have to do is load a new disk & carry on...
« Last Edit: August 12, 2013, 09:51:12 AM by AdeV »
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Or: Zhengzhou, China. An even longer way from anywhere...
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Offline ieezitin

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Re: I screwed up using a slitting saw..
« Reply #6 on: August 11, 2013, 03:42:50 PM »
Adev......

your suggestion is a superb one, and one i am going to try i have this ball'sed up piece to practice on.

I will see what thickness disks they make i really want this slit thin.


Cheers!!!!!!!!!!!!!!!!!!!!!!!!!!

Anthony.

PS........................  if you noticed i put the piece in a collet block with the intentions of indexing it, i done all that then i moved the mill,,   some days i aint all that bright :wack:
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Offline Anzaniste

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Re: I screwed up using a slitting saw..
« Reply #7 on: September 01, 2013, 03:05:37 AM »
Was the table locked in the x axis?
The work piece will be pushed to the left in the first cutting operation and in the second cut to the right. If not locked on the gibs then the table could move to the extent of the play in the backlash. With such a fragile blade only a small amount of movement could spell disaster.
Scrooby, 1 mile south of Gods own County.

Offline ieezitin

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Re: I screwed up using a slitting saw..
« Reply #8 on: September 01, 2013, 10:15:41 AM »
Anzaniste.

That my friend is a good question...... i don't think i locked it thinking this blade had no ass to move it, well!!!! i thought wrong didn't I.   :wack:

I am procuring some more material to re-try this, i will up date my findings.

Anthony.
If you cant fix it, get another hobby.

Offline trapper

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Re: I screwed up using a slitting saw..
« Reply #9 on: October 07, 2015, 05:27:03 AM »
Wonder how you got on with this,first of all doing it like this the head has to be blob on square think about it the blade will jam,stainless the blade has to be sharp,coolant flood it cant saw cut with any degree of success by putting a drop of oil on,revs for that diameter blade no more than 80revs or you will melt your blade,do all this and if you went an inch deep just feed the table accross by hand slowly-shouldnt be a problem do this sort thing all the time with blades the thickness your using down to .030 thick -that particular job theres nothing wrong with hand feeding across into the job-but I would have set my saw to break thro the wall and hand fed longitudial then backed off turned your block and finished the job its probably lack of coolant thats causing your problems

Offline sparky961

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Re: I screwed up using a slitting saw..
« Reply #10 on: October 07, 2015, 07:05:46 PM »
I find that mistakes are often much more instructive than success.  Sure, they suck, but if everything always goes right you don't know where the edge of the envelope lies.

I'm sitting here staring at your picture, which is probably not enough to go on, but I keep looking at the arcs scratched beneath the slot.  I'm thinking that there are only two ways this could have happened: 1) The pin turned (which you probably would have noticed and mentioned) or 2. when the catastrophic event occurred, the blade bent down and rubbed along the bottom for a while but since there's no postmortem photo of the blade I can only guess if it bent or shattered.

I know it's easy when stuff like this happens to "rip" the %$*@#& part out of the vice, whip it across the room and then sit there and almost cry when you've spent so many hours getting it to that point.  However, two things I've learned (seems I'm on a "twos" kick tonight): 1) Leave it and walk away for a while.  There may, in some cases, be a way to fix it if its still set up.  At the least you can examine what went wrong with a clearer head after a little walk.  2) Make a couple parts to work with in the first place.  Its usually only a few more minutes for each setup to run another part or two extra.  But to start over from scratch each time something goes wrong is very time consuming.  Material is cheap, time isn't - even hobby time, which most people consider "free".... it's still your time and its finite.  Make the most of it.

I tend to favour the theory that the saw grabbed your table and moved it, if it wasn't locked.  In the picture I'd say the right table lock is not locked, but the left one is obscured by the vice handle.  It doesn't take much, and the forces would have been in the correct directions to do so.  The likelihood increases if your machine has a lot of backlash and you were on the "wrong" side of it to start with (been there, done that... got the T-shirt).  If the pin had pulled out of the collet the result would be similar, but that seems less likely than everything else.  If, however, you're really squeezing down on a 5C collet, that likelihood goes back up exponentially.  They don't have much effective range.  It could also explain the pin rotating.

Just think though, anything you weren't quite happy with the first time around you get another crack at.  You've also done the setups and found the tools so it should go much quicker this time.

Yet another thought.... if you have it in a collet block why are you moving the cutter around to the opposite side?  Just flip the block 180 degrees.

Brian (Sparky)

(Edit: Just re-read your post and saw that you did mention indexing the pin instead.  Glad you saw that one already.)

Offline PeterE

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Re: I screwed up using a slitting saw..
« Reply #11 on: October 08, 2015, 05:27:33 AM »
My mind goes as follows; Why have a pin in the "tube" when slitting? It might have been so that some swarf got stuck between the inner wall of the tube and the supporting pin in the second run and it pinched the saw, and consequently broke the blade. Without the pin it may have worked nicely.  :scratch:

/Peter
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Offline mcostello

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Re: I screwed up using a slitting saw..
« Reply #12 on: October 08, 2015, 12:32:39 PM »
I make a commercial part for a customer from 303 SS. The slot is .050 wide and 3/8" deep through a wall of SS tubing. Coolant was not heavy duty enough. I go with a mister using cutting oil, it blows the chips off and is the best lubricant I can think of. I still lost the occasional saw blade, went with a small horizontal mill with an arbor and have not lost a blade since.
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