# Slitting saw - how to choose



## martik777 (Sep 8, 2019)

I need a saw that will cut thru 4140 occasionally .190" thick but usually .040" thick.

I've been using 40mm x 1mm x 72t but the teeth dull quickly.

Would a thinner blade wear less? How about less teeth? I don't need a fine finish. I've used angle grinder cutoff wheels but they tend to not cut straight as they are too thin and flexible.

Here's some I am looking at:









						US $3.15 28% OFF|Useful 80mm Outer Diameter Thickness 1.2mm HSS 72T Slitting Saw Cutting Edge Tool Y1K9 For Home And Production Saw Tool-in Saw Blades from Tools on Aliexpress.com | Alibaba Group
					

Smarter Shopping, Better Living!  Aliexpress.com




					tinyurl.com
				












						US $4.18 25% OFF|30T Circular Metal Slitting Saw Blade Cutter 105mm x 20mm|Saw Blades|   - AliExpress
					

Smarter Shopping, Better Living!  Aliexpress.com




					tinyurl.com


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## 38super (Sep 8, 2019)

Slower rpm, light feed and lots of lube.  Thin saws will wrinkle during a heavy feed, the flex will cause a crack.  Watch out if your table has stick slip.


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## Hawkeye (Sep 8, 2019)

I would be running that size of blade at around 180 - 200 RPM in 4140. Much faster eats teeth quite quickly.


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## martik777 (Sep 9, 2019)

Thanks, I've been running them way too fast


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## Janderso (Sep 9, 2019)

Ah,
Are those to be used on a horizontal mill?
Angle grinder?
No key slot.


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## Mitch Alsup (Sep 9, 2019)

martik777 said:


> I need a saw that will cut thru 4140 occasionally .190" thick but usually .040" thick.
> 
> I've been using 40mm x 1mm x 72t but the teeth dull quickly.



I have same saw. 
I run mine at 70 RPMs with a <slow> drip lube system on to the top of the blade.


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## martik777 (Sep 9, 2019)

Vertical mill, for splitting a router collet


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## Weldo (Feb 3, 2020)

I hope I'm not stepping on any toes here but this thread is relevant to my needs so I'd like to post an on topic question.

I'm working on a small project that requires a slit cut into the end of an aluminum round of 0.750 diameter.  The slot will be across the face (like a nock on an arrow) to a depth of 0.875" and width of 0.114".

So I've read that one should choose a saw blade that has as small a diameter as possible that still allows the depth of cut.  Now what about tooth count?  Usually we like a larger tooth with a bigger gullet for cutting aluminum, right?  Or maybe smaller teeth are better because the feeds should be pretty slow for slotting/slitting?

I've never slotted before and this will be attempted on an Atlas lathe with the milling attachment.  I have more questions regarding the actual process but I figure I'd start with choosing equipment!


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## Hawkeye (Feb 3, 2020)

To get that depth of cut, you will need a saw around 3 1/5" - 4" in diameter. What is the lowest RPM of your machine? Good thing it's aluminum. I'd keep it way below 2000 RPM, with lots of kerosene or WD40. Aluminum can heat up in a slot and expand to grab the blade. I'd tend to go with the courser tooth. You'll never use a blade that big on steel.


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## Weldo (Feb 4, 2020)

The lathe I'm gonna try this on has back gears so it can go pretty slow.  I never had a manual for it but from searching around on the net I think the slowest it goes is probably around 28rpm.  That seems maybe too slow?

Also, hypothetically speaking, if you had to make this cut in steel, what could you use?


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## mikey (Feb 4, 2020)

I'm trying to visualize how you're going to use at least a 3" saw to cut the end of a shaft held in a milling attachment sitting on the cross slide of a lathe. Do you even have room to do it?

Have you considered using an end mill?


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## Weldo (Feb 4, 2020)

I'm not even sure either!  I should mock it up and see...

I guess I could use an endmill?  It would have to be less than 1/8" and I'd have to take really light cuts but I would have total control over the slot width.


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## mikey (Feb 4, 2020)

Most importantly, it would be doable. You could use a 1/8" end mill to cut out the bulk from the center, then use an indicator to raise and lower the milling attachment to bring the slot to width. You would need to do each step in stages. I mean, cut the center out until you reach final depth, then set up to cut one side and cut to depth is steps, then repeat for the other side.


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## Weldo (Feb 4, 2020)

Ok, so I mocked up and it looks like I do have room for up to a 4" saw blade.  I will have to start above the saw and feed downwards.

In the following pic I have mocked up a 4" saw blade and a piece similar to what I need to cut.  The piece is projected out form the face of the collet block 1" and my slot will be to depth of 0.875" so there's a wee bit of safety room.




This picture demonstrates how I would need to feed, vertically downwards.  I'm guessing I'd want the lathe turning in reverse to make this cut?  My lathe does not have reverse but I may be able to feed downward from the backside of the spindle.  I actually didn't check that...




The main downside to this set up is that it moves the cross slide a bit off of the dovetail.  I still have about 3 turns of the handle before it disengages the cross slide nut.




To make this situation better I could try a 3.5" saw or even a 3".  The spacer rings on my arbor (3/4") are 1.125" so I'd lose half of that from the diameter of the saw, plus my depth of cut (0.875").  So I should be at 1.4375", right?  Then a 3" saw would be juuust big enough?


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## Weldo (Feb 4, 2020)

I just checked and feeding from behind the spindle is impossible.  So that leads to my next question.  

Does it matter how you feed a slitting saw?  If I can't do it as pictured above I'm gonna have to add reverse to my machine.  Which is something I've wanted to do for a while anyway.


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## mikey (Feb 4, 2020)

The way you've mocked it up would work with a slitting saw. The diameter of the saw you get must account for the depth of cut and the OD of the saw arbor/holder. You have to have enough blade exposed to get your depth of cut plus a little clearance. They sell saws with the width of cut you need but you'll have to search for the right saw diameter. 

Keep in mind that saws have different hole diameters. The reason this matters is because the slitting saw arbor you use must fit that saw hole fairly precisely. The most common holes are 1/2", 5/8" and 1". 3/4" is not a common arbor size, although the multi-step ones will work or you can make your own. The bigger the hole in the saw, the bigger the arbor will be and therefore, the bigger your saw OD must be in order to have enough blade area for your depth of cut. Typically, a the arbor for a 1" saw hole will require an arbor with about a 1.5" OD. Add in your 0.875" depth of cut and you're looking at a 3.5" - 4" saw diameter.

You may not be able to find a blade of the right diameter, arbor hole and thickness you need. It is possible to stack two thinner saws on the same arbor to get the width of cut you need. 

Also, the rule of thumb for the number of teeth required is to have at least 3 teeth engaged in the cut at all times. For aluminum, you want a coarser saw to enable chip clearance when possible. This is not a hard and fast rule. If you have more teeth, just feed slower; the saw will still cut fine.


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## Weldo (Feb 4, 2020)

Thanks for the advice!  I have a 3/4" and a 1" arbor so hopefully I can find something that works for me!

Do you think it would work Ok to feed downward like in the second picture above?  It seems likely to grab or chatter as the teeth engage the end of the stock.

Also should I be attempting to set the full depth of cut and just feed slowly or make multiple passes while incrementally increasing the depth of cut?


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## mikey (Feb 4, 2020)

Weldo said:


> Do you think it would work Ok to feed downward like in the second picture above?  It seems likely to grab or chatter as the teeth engage the end of the stock.



I sure hope so because there isn't any other way to feed into the stock with your set up. I would try it and see. It's going to be fun trying to feed smoothly while also lubricating the cut. Slitting saws need a lot of lube to reduce friction and help chips flow out of the cut so your can feed hand over hand to provide a smooth feed, while also lubing the cut with your third hand!



Weldo said:


> Also should I be attempting to set the full depth of cut and just feed slowly or make multiple passes while incrementally increasing the depth of cut?



Slitting saws are intended to take full depth cuts so set your full 0.875" depth of cut and use your feed to control the cut. You want to feed fast enough to feel a slight positive resistance to the feed and then maintain that feed. This keeps the saw cutting continuously but without forcing the cut. Works good this way. I've been doing it for a very long time using manual feed and have yet to see it fail. Steel, stainless, aluminum, brass and one time, wood. The technique is the same, the saw is the same.


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## Weldo (Feb 4, 2020)

Awesome, thank you!  

One last thing, what about these fancy "side milling" saws...




Do they offer any significant advantage over a simpler blade like the one below?


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## mikey (Feb 4, 2020)

Yeah, those big saws can take off a lot of material at a time but you need a lot of power and rigidity. Your set up is nowhere near rigid enough for that kind of saw. I would stay with the slitting/slotting saws if I were you.


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## Weldo (Feb 4, 2020)

I see.  Thanks again!  Hopefully I can report back soon with tales of victory!


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## Driveslayer45 (Feb 5, 2020)

So, wanting a slitting saw i built a 3/4 arbor shaft for a collet and put this blade from harbor freight on it.  it really didn't have and issue with 1/2" aluminum, and i even cut a slot, for fun, in 1" cold rolled. https://www.harborfreight.com/3-38-in-18t-toe-kick-circular-saw-blade-62401.html
Rpm was about 140. i am not sure about DOC in the steel, but i was cutting through the 1/2 aluminum at a slow feed rate


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## Weldo (Feb 6, 2020)

That's a cool idea.  It may not have optimal geometry for metal cutting but as long as your set up is rigid and you feed slowly I guess it can't go too wrong.

After looking around the interscreen for a while I'm having trouble finding exactly the right saw for my situation.  When they are correct thickness they are wrong diameter.  

So what the deal with stacking blades to achieve a custom width?  OK or sketchy?


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## mikey (Feb 6, 2020)

Weldo said:


> After looking around the interscreen for a while I'm having trouble finding exactly the right saw for my situation.  When they are correct thickness they are wrong diameter.
> 
> So what the deal with stacking blades to achieve a custom width?  OK or sketchy?



I've been stacking blades for a very long time and haven't had any issues. You want to choose saws with a similar tooth count if you can and stagger the teeth so the points don't bear on each other. Then cut as usual. I have taken some deep cuts in most common shop materials like this. While it is always best to have the right saw, there are times when you just have to stack saws so you can get on with it.


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## Weldo (Feb 6, 2020)

To get the teeth to stagger properly you may have to leave out the key from the arbor?


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## mikey (Feb 6, 2020)

I never use the key anyway.


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## Weldo (Feb 6, 2020)

mikey said:


> I never use the key anyway.



Ok, so the clamping of the nut is plenty to keep the blade from slipping.


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## mikey (Feb 6, 2020)

Well, a good arbor helps, too.


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## darkzero (Feb 6, 2020)

I had no idea you could stack saws. Never even thought about that. I'll have to try that some time. Thanks



Weldo said:


> Ok, so the clamping of the nut is plenty to keep the blade from slipping.



Some of my saws have a key slot my my saw arbor doesn't. I have never had one slip, mine are 1" bores.


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## 38super (Feb 7, 2020)

Do not climb cut.  Lots of lube to clear the swarf.  Smooth even feed.  Run a test piece to get the feed feel, don't rush


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## Weldo (Feb 16, 2020)

I just made my first slitting saw cut last night!  It went pretty well.  The only issue I had was some runout on the circumference of the blade.  I think I attribute this to my collet chuck/lathe spindle not being completely perfect and thus the error was magnified by the somewhat long saw arbor.

It seemed like only about 1/3 of the blade was contacting the material per revolution.  Maybe if I fed a bit more heavily it would’ve been better but I kept the feed pretty light.  I’ll post up some pics later!


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## 38super (Feb 16, 2020)

typical, don't worry.


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## Weldo (Feb 16, 2020)

Here's some pictures of the set up I used.

This is the saw arbor in a shop made collet chuck.  The saw is 2-3/4" OD with a 3/4" hole.  It was the only one I could find in the width I needed, 0.114"






Another shot.  If I do it again I'll place the saw all the way back on the arbor instead of near the end.  Might be a bit more rigid that way.  The way I ended up cutting was from the bottom up.  I was nervous about coming from the top down since that would've been a climb cut.  I cranked the milling attachment as far down toward the bed as it would go then centered up the piece on the blade.  I then fed in the cross slide.  Contact was made with the work piece around 0.650" in.  I then fed in slowly to my final number of 0.875" and from there began feeding upward to complete the cut.






Here's the part I cut.  Finish in the slot is pretty good.  The part was held in a collet block which was fixed into the milling attachment on the lathe.  I needed the slot to be 0.875" deep from the point of the cone but based on the dimensions of the saw blade and arbor I could only go 0.8125" deep.  I then realized that since the part comes to a point the 0.114" wide slot will be taking about 0.067" off the width.  Thus the workpiece just cleared the arbor by about 0.005"!







Here you can see that the slot is not exactly on center.  Honestly I just eye-balled it.  I wasn't sure how to indicate it... D'oh!




I broke down the setup last evening.  For these pics I just mocked it up again, except for the milling attachment part.  What's weird though is that out of curiosity I checked the runout of the arbor on the solid part of the shank, it was around 0.003"!

Then I checked the runout of the collet chuck, it was also around 0.003".  I then took the chuck off and checked the spindle, it was about 0.0005".

I also have an ER40 collet chuck that goes into the MT3 spindle bore with a draw bar.  This one I purchased... from Shars I think.  When it's installed and tightened up it has only about 0.0005" runout on the outer body of the chuck.  I don't use it much though because long workpieces cannot pass through, I usually just use it to hold endmills for milling operations.  Next time I'll probably use it to do the slotting.

So finally, I reinstalled my home made collet chuck and checked the runout again and now it's reading between 0.0005 and 0.001"!

I turned this whole chuck on the spindle so I was expecting it to be pretty good on run out.  Any ideas why it can change when removed and reinstalled?


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## John_Dennis (Feb 23, 2020)

Just remember that mills are very rigid and heavy for a reason.  If you make a mistake while milling using a lathe, it can break your saddle or cross slide.


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## Weldo (Feb 24, 2020)

Right.  

The lathe is definitely not ideal for this.  It seems very likely to chatter whenever I’ve done milling operations due to the lack of mass and rigidity.


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