Blade speeds using smaller cold saws on stainless

reddog278 · Sep 24, 2018

Hi All - quick question
I'm shopping around for a 9" or 10" manual cold saw for furniture prototyping and fab.
With a cold saw, i want to have my cake (stubbornly stay in the 9-10" range) and eat it too (sub-42 rpm cuts on 2" sq, 16g stainless tubing) But, unfortunately, I haven't come across any low-speed 225 or 250s that spin slower than 42 rpm ... the closest i come seem to be the 2-speed 300s and 350s.
Any specific recommendations for benchtop-type cold saws that dip into the 20-30 rpm range? Are 250 users simply getting away with 42 rpm (e.g., the Haberle S225) + special blade geometry to cut smaller-size s.s. sq tubing?
Thanks in advance!

HuFlungDung · Sep 24, 2018

You could run it through a VFD. I did just that with my Scotchman Bewo. You need to use an inverter that is rated at least as much as the motor hp or it will nuisance trip all the time. Cold saws work hard for the brief interval that they are in operation.

16 gauge is narrow to cut and it might be difficult to get a fine enough pitch blade. The real issue is controlling the downfeed because of the drastic change in pressure required between breaking through and cutting past the halfway mark. if any saw had a screw controlled power down feed, that would be a plus.

danil · Sep 24, 2018

HFD is spot on.... I'd only add that some motors are built to be run with a variable input-- I have an Allen Bradley controller on my cold-saw with a dial Rheostat on the side of the control box to adjust my speed right down to about 10 rpm(I'm going to verify this lower end) and up to about 88 rpm. I am a big fan of the Scotchman cold-saws and I use them for cutting stainless most of the time. They'll be happy to shed some light on what blade configuration to use for your application.

DDoug · Sep 24, 2018

If it's square tube, might prove usefull to make a set of
"Vee" jaws to hold the tube on the "diamond" shape.

for a more constant cutting.

guest · Sep 24, 2018

Its not necessary to run that slow, especially on tubing. I run 54 rpm with a 350mm 220T blade on 16 ga 304 tubing, 150-200 cuts before I resharpen the blade. I could get more out of it if I wanted to, but I would be re-toothing more often. The blade isn't in the cut very long, it doesn't get much of a chance to heat up.

Same rpm on steel and 303 solids, but I drop down to a 180T blade.

+1 on clamping on the diagonal for square thin-wall, it's a lot less likely to grab the material when it breaks through.

Arc-On · Sep 24, 2018

I have a Startrite 315M, and it has a 2 speed gearbox. I don't know the exact RPMs (haven't put the tach on it), but the "turtle" speed seems to be very adequate for all the stainless I've cut on it. Best I can find on the interwebs, it has 30 RPM on "turtle" and 60 RPM on "rabbit". I'm very happy with the saw. I cut a lot of 16ga tubing on it. Blade selection is very important. You want the correct number of teeth, and the correct grind on the teeth.

Scotchman sells a saw with a built in variable speed. If I was looking to replace the Startrite, I'd be looking at a Scotchman.

I wouldn't buy anything from Baleigh, they are utter shit. I had one at my last job, I can't describe how terrible that saw was.

DMF_TomB · Sep 24, 2018

what does saw manufacturer recommend ??
.
carbide blades run faster although they dont like cutting vibrating sheet metal. .
.
abrasive saw dont care much if cutting vibrating sheet metal thats why they are popular in China where thin tubing SS hand rails and window bars are done at over 1000% the rate done in USA
.
and Chinese abrasive saws run on 240 volts and got at least 5 hp, often see saw on ground (on sidewalk) with 5 foot handle guy can lean on to cut thicker stuff too. Abrasive wheels tend to be cheaper per cut. too often USA guy picks a less noisy saw cause of noise levels. ear plugs are cheap

HuFlungDung · Sep 24, 2018

guest said:
Its not necessary to run that slow, especially on tubing. I run 54 rpm with a 350mm 220T blade on 16 ga 304 tubing, 150-200 cuts before I resharpen the blade. I could get more out of it if I wanted to, but I would be re-toothing more often. The blade isn't in the cut very long, it doesn't get much of a chance to heat up.

Same rpm on steel and 303 solids, but I drop down to a 180T blade.

+1 on clamping on the diagonal for square thin-wall, it's a lot less likely to grab the material when it breaks through.

That doesn't seem like decent cut life to me. I think you are running it too fast. The heat of cutting is instantaneously generated, the blade might not get warm, but the tips of the teeth still burn off.

DMF_TomB · Sep 24, 2018

some 304 SS can be 10x harder to cut than other 304. basically if work hardened or rolled cold too much it can much harder and is much harder to cut.

guest · Sep 24, 2018

HuFlungDung said:
That doesn't seem like decent cut life to me. I think you are running it too fast. The heat of cutting is instantaneously generated, the blade might not get warm, but the tips of the teeth still burn off.

I used to believe that too, based on the SFM. But 12 years on- I no longer think so. Regrinding the blade is putting more heat into it than cutting with it.

I change the blade when it starts slowing me down- it will make many more cuts than I am asking of it. Looking at the teeth under the loop, no discoloration, no rounding of the corners, and most importantly- no raising a big burr on the material. Flood coolant, the heat of the cut is being taken out in the chip.

150 parts out of a $20 resharp, that's ~0.15 a part- not significant to the overall cost of the parts. 1-1/2 hours of cutting time is 5x that cost. I can slow down, but what I gain in tool life I will give up twice over on time.

reddog278 · Sep 24, 2018

HuFlungDung said:
You could run it through a VFD. I did just that with my Scotchman Bewo. You need to use an inverter that is rated at least as much as the motor hp or it will nuisance trip all the time. Cold saws work hard for the brief interval that they are in operation.

16 gauge is narrow to cut and it might be difficult to get a fine enough pitch blade. The real issue is controlling the downfeed because of the drastic change in pressure required between breaking through and cutting past the halfway mark. if any saw had a screw controlled power down feed, that would be a plus.

Thanks, HFD (Danil, too, below). I'm looking now at your earlier posts recommending VFD, and I see there's a lot of good information I can learn there this week.

BTW, and quite candidly, I'm pretty slow on the uptake when it comes to motors and electric.
I see specs such as "60 Hz Cycle: 1 -phase 1 -speed motor 110 V, 1.2 kW (1.5 HP), or 3-phase 2-speed motor 220 V or 460 V, 0.9/1.35 kW (1.2/1.6 HP)" and I wonder...
- will I need to avoid the 1-phase motor?
- I prototype out of my garage; will the 220 outlet there be enough (just rewiring the power cable from my Miller 200 to fit a 220 dryer outlet was a long lesson for me)?

I'll keep reading up to catch up, but thanks for the nudge in the right direction!

adama · Sep 24, 2018

Why not a bandsaw? Blades are so cheap and will last so much longer + you only need a 1/2hp for cutting this kinda material. The 45 degree is still a good idea. I also find i can run more like a steel band speed on thin stainless, its kinda a similar effect to high speed tool paths in milling. The heat is not generated instantly, its the time the material slides on the tooth and the build up of that energy, once the blade is properly broken in the teeth are fractionally rounded and can dissipate the heat of a 1/16" of material really well.

That said, thin stainless is about the hardest stuff i cut on the bandsaw blade wise, the thin stainless tubes are often noticeably harder than thicker flats too.

reddog278 · Sep 24, 2018

adama said:
Why not a bandsaw? Blades are so cheap and will last so much longer + you only need a 1/2hp for cutting this kinda material.

Good question. I used to have an Ellis in my old shop - worked OK on SS tubing, though on miter cuts, it wasn't as straight and clean as a cold saw. Lots of opinions on this, I'm sure.

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