Slitting saws - is there a beginners guide?

[Mayhem]

Once I get my mill up and running, I will probably look to add a slitting saw to my tooling inventory and I know very little about them (hence the title of this thread).

So - anyone out there willing to write up a beginners guide to slitting saws, their selection and use?

[sasquatch]

Very good practical question Mayhem. I need to read that also.

[Highpower]

[EdK]

+1

[TomG]

The heat sink I just made was a good exercise in the use of slitting saws, too bad I didn't video it. I'll have to think about it for a while and see if I can come up with enough material to merit doing a video on the use of slitting saws. It's not something I would think people would have a hard time with, but I do see a fair number of posts on slitting saw issues.

Tom

[ETC57]

Slitting saw, nope I know nothing about choosing or using a slitting saw.
OK bring on the tutorial

Jerry.

[DaveH]

You don’t need a tutorial to use a slitting saw. So I’ll say how I do it.

1. Use a small diameter 2 – 3”
2. Use one with large teeth ie. a small number of teeth.
3. Use a slow spindle speed
4. Use a slow spindle speed
5. Use a slow spindle speed
6. Keep the first cut small .010” this will act as a guide to the additional cuts.
7. Use a feed rate suited to the slow spindle speed, if you hear it “hunting” ie going Brmmm …………….Brmmm…………..Brmmm – that’s fine – nothing to worry about.
8. After each pass clean the cutter and any swarf (chips) in the slot.
9. Cut in the same direction. Not back and forth.


Think of it as a 3 inch dia end mill – how fast (spindle speed) would you use for your mill.
Slitting saws (HSS) will blunt very quickly (seconds) with excessive heat and then it will break – usually by shattering.

Most breakages occur because the operator is in a rush.

Take it slow and steady with small cuts and all will be fine.

Well that’s my best, anyone wish to add.

DaveH

[TomG]

OK, if I had to make a bullet point list of how to use a slitting saw, here is what it would look like:

1) Cutting speed - Calculate your cutting speed just like any other cutter, 4 X CS/DIA. Slitting saws are so large that they need to run deceivably slow. Example: A 3" diameter saw in mild steel should run at 4X100/3, or 133 rpm.

2) Climb mill, as in NEVER do it. Slitting saws are so large that they will easily climb up on your work when you least expect it, so always conventional mill and don't forget to lock the table AND remove the backlash from the leadscrew. Sometimes you need to get creative with odd shaped parts so the cutter can never climb onto the part. For instance, the last cut on that heat sink I made required a different technique. I conventional milled each fin to full depth except for the last one where I cranked the cutter in so it started cutting near the root of the fin rather than the tip. If I had cut the last, unsupported fin like the first 44, it would have grabbed and scrapped the part.

3) Use lots of cutting oil or coolant. There is so much cutter in contact with the work with a slitting saw that lubrication is critical. Lose it and the cutter will grab and break.

4) Be brave and bury the cutter in the work as soon as possible because the work helps to support the cutter. Sneaking in or taking a little at a time is inviting the cutter to wander (and consequently break or at least screw up the part).

5) Keep the feed rates low. In other words, don't force it. Give the cutter time to remove all those chips.

Probably the most important thing to remember when using a slitting saw is that it is out to screw you and will unless you stay one step ahead. Just think ahead and predict what the cutter will try to do before taking the cut and you'll be fine.

Tom

[DaveH]

Just something to note:
Slitting saws from 1/64" to 1/8" were originally designed to put slots in screw heads.

DaveH

[PixMan]

Good points posted by all, particularly that which DaveH and TomG have highlighted...cutting speed. The most common mistake in using them is overspeed. Perhaps it's because they so resemble wood cutting circular saw blades, one might get lulled into a false sense of "speed looks OK". Check it, matching your saw's material (HSS, HSS-Co or carbide) to the material being cut.

When using simple, plain single-cut slitting saws, that is ones with no side cutting relief, avoid cutting any deeper than the depth of the hook on the teeth. If you bury one of those in most materials, the chips will be the same width as the saw and in a deep cut those teeth will often become one of the chips being ejected from the cut. ;) Curiously, those very shallow cuts (such as slotting screw heads) is one of the few times it's perfectly safe to climb mill.

Deeper cuts need side relief, such as that shown in the photo TomG posted further up this thread. If not side cutting clearance, at least use very coarse pitch saws. The overall feed per tooth at even slow feed rates can add up to a high-torque cut when you engage a great many teeth with a long contact patch. That's a formula to overpower a spindle motor and stop it in midcut. This can happen by way of shearing the saw right through the soft drive key (if there is one) or just stopping the motor because it's low speed puts it at the bottom of it's avaialble torque output.