Bandsaw cutting speeds

[jwsvandr]

Need to pick some brains. I am converting my POS wood cutting bandsaw to metal cutting. I have built a Rube Goldberg contraption to reduce the speed and it works too well. I wanted to get 100fpm which I believe is the proper cutting speed for mild steel. Please check my math below:

Circumference of bandsaw wheel = (14 inches*pi)/12 = 3.63 ft

100fpm/3.63 = 27.55 RPM

This is way too slow. I then checked my 4X6 bandsaw and it was turning at around 128 rpm with a 7in wheel. That means (according to my math) it is cutting at around 234.54 fpm and that my 14in wheel should be turning at 64 RPM.

Where am I going wrong????

 

[Kermit]

radius squared

radius = 1/2 diameter.



could that be your mistake?

 

[Dan Rowe]

Your math looks good but I think the assumption of 100fpm for steel is the problem. Bahco recomends 150-300fpm for un-alloyed steel. See:
http://www.bahco.com/files/Selection Guides for Bandsaw Blades_cmjmkoklqluaoifancqqipjno.pdf

The Doall site has a blade speed calculator but I could not get it to work. It has a lot of prameters including work thickness to select the correct blade speed. http://www.doallsawing.com/pages.aspx?idpage=5 click on the application info header.

Dan

Edit: to get the Doall calculator to work pick a machine, I simply chose the first one, select the material, then the work shape and thickness. Click inputs ok I got 275fpm for mild steel 1008-1013.

 

[GailInNM]

I agree with Dan.
I use a 14 tooth per inch raker 1/2 x 0.025 blade as my general purpose blade on my 14 inch band saw. My normal cutting speed for most everything is 280 FPM which is 75 RPM. Mostly I am cutting either 12L14 or other free cutting material. I cut small section 1018, under 1/2 thickness at the same speed if I am only cutting a small amount. If I am cutting larger section or a large quantity of 1018 I sometimes slow it down to 150 FPM, which is my next slower speed. I use Castrol stick wax blade lubricant on all cuts of thick section.

These speeds are all with in the Starrett blade recommendations for flex back carbon steel blades and seem to work well.

http://www.starrett.com/download/145_bs_cat_09_54_57_cut_table_and_area.pdf

Gail in NM

 

[Kermit]

for calculating sfm of blades on bandsaws, but applies equally well to any pulley driven motor (ized) system.

http://www.owwm.com/math/sfpm.aspx

Going a little slower than a 'recommended' speed is always OK. It just takes longer is all. Going to fast for a material or blade combo is sure to shorten its life and may cause a blade to snap in use.

Every single rotation,or flex cycle of the blade, embrittles the metal and a continues a process of stress fracturing that results in breakage. Just having them rotating, or 'cutting air', uses up that much of the blades useful lifespan.

To slow is alright, to fast never is.

Kermit

 

[JimM]

I then checked my 4X6 bandsaw and it was turning at around 128 rpm with a 7in wheel. That means (according to my math) it is cutting at around 234.54 fpm

Am I missing something here, just checked the spec for my 4x6 bandsaw and it cuts at 20/30/50 m per min which presumably equates to 65/98/165 ft per min

I know each model of saw is likely to be different but that seems a huge drop to what you guys are quoting.

Cheers

Jim

 

[Brian Rupnow]

A good speed to aim for is 180 foot per minute blade speed for cutting mild steel (1018-1020). That means that your 14" bandsaw wheel should be turning at about 49 to 50 RPM. I converted my old Jet woodcutting bandsaw to that speed and it works great with 10TPI bimetal blades.---Brian

 

[jwsvandr]

Thanks all. I will take all the advise and get it to work. Will let you know how the build goes when it's finished.

 

[Omnimill]

Every single rotation,or flex cycle of the blade, embrittles the metal and a continues a process of stress fracturing that results in breakage. Just having them rotating, or 'cutting air', uses up that much of the blades useful lifespan.

To slow is alright, to fast never is.

Kermit

Now that is worth knowing!

Vic.