Slitting saw sanity check, please?

[Huub Buis]

Slitting saws
1 mm == 40 thou
I normally use 1.2 mm (3/64") slitting saws for steel and aluminum

 

[woodchucker]

I popped one of mine too. I was running it too fast, and heating it up.
Like wobblyhand set, make sure it is tracking. I think I was feeding too fast for what it was as well as running it too fast and caused it to bend and go off its course.

Slow rpm, these burn up easily .. use lubricant or coolant. super slow feed... keep a tooth brush there to clean the chips out from being brought back into the cut. Jamming the chips back is a sure fire way to pack the blade , cause heat, deflection, and off course.

 

[Flynth]

I popped one of mine too. I was running it too fast, and heating it up.
Like wobblyhand set, make sure it is tracking. I think I was feeding too fast for what it was as well as running it too fast and caused it to bend and go off its course.

Slow rpm, these burn up easily .. use lubricant or coolant. super slow feed... keep a tooth brush there to clean the chips out from being brought back into the cut. Jamming the chips back is a sure fire way to pack the blade , cause heat, deflection, and off course.

I wonder, is this "make sure it's tracking" applicable to repeated cuts in the same groove only?

Either way, it makes me a bit worried if these saws like to wander about. I intend to cut all my grooves pretty shallow, but there are lots and all will be using the auto feed. I wonder how soon will I break one...

I would lower the chip load per tooth, but the recommendation I got already is below the "minimum". So at the same time I don't want it rubbing. I guess we'll find out soon.

 

[Justin.P]

Lots of tracking issues mentioned.
I assume tracking and wandering issues are due to lack of coolant.
The outer portion of the blade heats up and expands more than the inner and the whole blade potato chips.

Good slitting saws are expensive, screw slotting saws are cheap. The slotting saws have tiny gullets, little set and to many teeth for slitting. At least that's how the ones I have are designed. They don't clean out well but are still pressed into service as slitting saws often in hobby shops.

 

[woodchucker]

I wonder, is this "make sure it's tracking" applicable to repeated cuts in the same groove only?

Either way, it makes me a bit worried if these saws like to wander about. I intend to cut all my grooves pretty shallow, but there are lots and all will be using the auto feed. I wonder how soon will I break one...

I would lower the chip load per tooth, but the recommendation I got already is below the "minimum". So at the same time I don't want it rubbing. I guess we'll find out soon.

The best way to cut is a single op. Thin blades need super slow feed to keep the blade straight.

 

[Karl_T]

couple more comments.

first the slitting saw is never perfectly centered, only cuts hard on maybe half the teeth, that's why the chip load calcs don't work. Adjust feed based on how perfect the particular saw is cutting.

Second, an airblast is really needed to completely remove chips as it exits the cut.

 

[Jimsehr]

I find that slitting saws as they cut thru a bushing type part have a tendency to pinch the blade and break the blade. Sone times if your slit is long enough you can put a wedge in slot and stop that.

 

[Flynth]

Lots of tracking issues mentioned.
I assume tracking and wandering issues are due to lack of coolant.
The outer portion of the blade heats up and expands more than the inner and the whole blade potato chips.

Good slitting saws are expensive, screw slotting saws are cheap. The slotting saws have tiny gullets, little set and to many teeth for slitting. At least that's how the ones I have are designed. They don't clean out well but are still pressed into service as slitting saws often in hobby shops.

What kind of coolant is best for them? Water based emulsion or straight oil? Also flood, mist, or simple brushing/spray bottle?

couple more comments.

first the slitting saw is never perfectly centered, only cuts hard on maybe half the teeth, that's why the chip load calcs don't work. Adjust feed based on how perfect the particular saw is cutting.

Second, an airblast is really needed to completely remove chips as it exits the cut.

I could rig this up. I've got a DIY mist setup I can run with just air.

 

[Flynth]

Well... Let's put it this way. It's not even half way through the task and I now have a 98 tooth saw (it started with 100).

I seem to have ideal conditions for this screw slotting saw. I have a short (10in) horizontal arbor with almost no runout (about a thou) supported on both ends. A large horizontal milling machine with all but one axes locked. A jet of air with a little oil mist blasting the saw as it exits the cut (to remove chips from going again into the cut). And oil put with a brush on the part.

I'm making flat laps that are 4in in diameter so a total of maybe 4ft (1.3m) of slots per part.

I upped my rpm to 99 as it was mentioned in this thread and I found elsewhere (75sfpm). And I lowered the feed per tooth to about 1 thou. First cut was feeding by hand trying to replicate the speed of the auto feed set at 300mm/min (11.8in/min). It went great, but it was an edge of a circle so only an inch long.

Second cut was the first powered one (1.5in long) and the saw lost a tooth while sounding perfect :-(

I dropped the feed by a third to 200mm/min (7.8in/min). Also I increased air pressure a little. 9 cuts went perfect including the longest 4in one. At the very last cut (an inch long) the saw lost another tooth...

Now I'm really puzzled. I took a break to think for a while. I have 6x more cuting to do and one spare saw. In theory if it looses 2 teeth per 10 cuts I should be able to finish the parts (the finish is unaffected).

But running it this way hurts my perfectionism. Does anyone have any idea what I might be doing wrong? Or are those screw slotting saws basically a useless piece of junk not even able to cut a shallow slot (like in a screw?).

I read some people run them at 0.0003in feed per tooth (7 microns), but elsewhere I found running too low of a feed is equally bad as running too high... I've already lost 2 teeth so I may as well try those 7 microns next although my chips looks rather small. If a bandsaw with similar sized teeth produces them I would be increasing the feed not decreasing. They're not dust, but quite small.

Alternatively maybe my air blast is not strong enough and occasionally a gullet doesn't get blasted clean and it packs on next cut. I'm already filling my shop with oil mist (I'm wearing a respirator and I have windows and doors open - still it feels pretty bad to breathe). I might try upping the pressure, but this will atomise the oil even more

 

[OTmachine]

Somewhere, I have a custom made slotted shell mill to cut multiple slots / serrations in metal. Came with a horizontal mill that I bought.