Re: Need Advice for Cutting Stainless Steel Tube
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Hi John In general (i.e. when cutting solid stainless): Most stainless is softer than mild steel in normal?condition, but can work-harden?to the point where even a bimetal blade won't?touch it.? You have to avoid that as much as possible with your set-up.. Work-hardening happens when you rub a susceptible material, like stainless or titanium, with something hard (like the HSS tip of a bimetal tooth), How long you rub and how hot it gets determines how much it workhardens. The act of cutting stainless always work-hardens it a bit.? In lathe work you use slow speed and high feed to get under the work-hardened?skin, but that's not possible on a bandsaw. In bandsawing solid material, even under optimum conditions, you have many teeth, all skimming off less than a 1/10th of a thou" each? (it really is v.v. thin). So the teeth are always cutting in the work-hardened?zone, and speed should be only 60% of mild steel.? On a 4x6 always?use 'slow' speed. If you have a choice of blade TPI,
on stainless
use 4-6 Teeth-in-Cut rather than the normal optimum of 9 TiC - less teeth means more weight on each tooth and thicker chips so you're cutting in slightly softer material,?
TiC =?blade TPI * length of cut (in inches).? Set the bow weight in range 8-9 lb, no heavier?or you'll?damage the blade.
Its also prone to stalling in the cut at 10 lb or above (with possible motor?damage).
but you do want the weight on the teeth. ? Never let the teeth just rub, lower them into the cut as quickly as possible. Coolant keeps the heat down so it workhardens less, flood coolant is best but even a spray bottle of water is better than nothing.? You're not protecting the edge of the tooth (HSS teeth have more than enough hot-hardness), it's the metal you're cutting that you want to keep cool. To minimise the deflection of the blade from the higher bow weight, keep the top guide as close the work?as possible.? BUT: Be v. careful when you're cutting tube, as it is very easy to go below 3 TiC and?you'll rip the teeth out of the band!?? An 18TPI blade has teeth?spacing of 1/18",? i.e. 0.055", so when you're cutting 0.043" thick tube wall the whole thickness of the material will fit between one tooth and the next, and you take anything up to 100x the correct chip thickness - people often rip the teeth out of the blade when cutting tube and sheet metal.? Even at 0.130" there are less than 3 teeth-in-cut.? A 24TPI straight pitch bi-metal blade is better for the cutting you want to do.? With just 0.042" between teeth-tips, you get 1 tooth-in-cut on 0.043 and just over 3 TiC when cutting 0.130".?? If you're?going?to cut a lot of tube then hydraulic downfeed is well worth the effort and expense (see recent thread on how to DIY). You can back up the tube with a bit of thicker scrap steel to slow down the cutting, but you'll soon get sick of that. If you control the downfeed rate by hand you WILL lose?teeth off the band (esp. if you're using a coarse TPI blade).? But blade TPI doesn't matter at all if you have hydraulic downfeed, what you save in not buying the high-TPI blades, you can put toward the downfeed control conversion and use a normal 10-14 Bimetal blade to cut the tube. All of your cutting, for the life of the machine, will be better with hydraulic downfeed control. Hope this helps - jv On Sun, Nov 22, 2020 at 11:14 AM John H via <johnjhayden=[email protected]> wrote: Thank you! And I should have stated that I¡¯ll be working with 304 stainless. |
John Vreede