On 11/21/2020 12:00 PM, John H via groups.io wrote:
> Dear Group!
>
> I have been cutting and TIG / MIG welding ferritic steel tube steel
> successfully for several years, and I am now ready and very eager to
> finally strike an arc on stainless steel.
>
> The tube steel material I can envision working with is from 1/2" X 1/2"
> through 2" X 2" stainless tube steel with wall thickness from about
> 0.043" through around 0.13".
>
> Can I please get advice on the blade teeth / inch, saw blade speed and
> down force. My band saw only has a spring to sort of control down force,
> so I will be lowering the blade onto the material by hand and by feel only.
>
> I have an Harbor Freight 4" X 6" bandsaw that has served me very well on
> ferritic steel, and I want to be sure that I have a good idea for safely
> cutting stainless tube steel so I don't go ruining my blade before I
> blink an eye. And even worse - not know why it happened.
>
> Please help me by providing me with your advice on this subject.
>
> Thank you very much!
>
> John Hayden
>

? An 18 TPI bimetal is a good place to start . It'll be slow at the
start and finish , but you won't be stripping teeth when it's in the
thin . Which alloy are you working with ? 304 has been known to work
harden if you sneeze at it - likes slow blade speeds and a fairly heavy
cut . 303 and 316 not so much . I haven't worked with 400 series , but I
think they are all hardenable .
--
Snag

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 H

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On?Saturday, November 21, 2020,?Terry Coombs?<snagone@...>?wrote:

On 11/21/2020 12:00 PM, John H via wrote:
> Dear Group!
>
> I have been cutting and TIG / MIG welding ferritic steel tube steel
> successfully for several years, and I am now ready and very eager to
> finally strike an arc on stainless steel.
>
> The tube steel material I can envision working with is from 1/2" X 1/2"
> through 2" X 2" stainless tube steel with wall thickness from about
> 0.043" through around 0.13".
>
> Can I please get advice on the blade teeth / inch, saw blade speed and
> down force. My band saw only has a spring to sort of control down force,
> so I will be lowering the blade onto the material by hand and by feel only.
>
> I have an Harbor Freight 4" X 6" bandsaw that has served me very well on
> ferritic steel, and I want to be sure that I have a good idea for safely
> cutting stainless tube steel so I don't go ruining my blade before I
> blink an eye. And even worse - not know why it happened.
>
> Please help me by providing me with your advice on this subject.
>
> Thank you very much!
>
> John Hayden
>

? An 18 TPI bimetal is a good place to start . It'll be slow at the
start and finish , but you won't be stripping teeth when it's in the
thin . Which alloy are you working with ? 304 has been known to work
harden if you sneeze at it - likes slow blade speeds and a fairly heavy
cut . 303 and 316 not so much . I haven't worked with 400 series , but I
think they are all hardenable .
--
Snag

I agree with the previous comment… 24 tpi would be a good choice for thin walled tubing. Another trick is to hold the tube on its diagonal in the vise. That way, the same thickness is being presented to the blade through the whole cut. I’ve had good luck with that.

Another technique that I've used on a thin piece of metal tubing that could chip off a tooth or two is to put in a sacrificial piece of something like plywood, aluminum, hardwood, etc., behind the piece and cut both at the same time.? That way there is much less chance of catching a tooth.??

The waste material is most stable when pulled back against the fixed jaw while being cut.?

To sandwich the tube means the waste on the movable jaw side would be unsupported until it got near the middle of the cut. That would vibrate badly.?

If you've only got thin waste material, multiple layers between the tube and fixed jaw will work as well as a single thick piece - jv

??

On Wed, 25 Nov 2020, 6:54 am John H via , <johnjhayden=[email protected]> wrote:

Thanks Bruce!

I wonder what benefit I’d see if I made a tube?sandwich by placing sacrificial material of about the same height and thickness before and after the stainless tube? Would that arrangement serve to prevent tooth breakage? That seems logical...

John

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On?Tuesday, November 24, 2020,?BRUCE ROGERS?<brogers9941@...>?wrote:

Another technique that I've used on a thin piece of metal tubing that could chip off a tooth or two is to put in a sacrificial piece of something like plywood, aluminum, hardwood, etc., behind the piece and cut both at the same time.? That way there is much less chance of catching a tooth.??