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Say it ain't so Joe, say it aint so.

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DavidA:
I'm sat here contemplating buying a metal cutting band saw from Machine Mart tomorrow to take advantage of their no VAT offer.  It will save me about £50.

Then I got around to thinking 'Why not just put a metal cutting blade on my small bench top wood cutting band saw?'  And of course I thought that the blade speed would be too fast.

So I did the maths; and the answer is something of a surprise.

The wheel on the motor (blade driving wheel) is about 6" diameter. The motor, according to the plate turns at 1450 rpm.

From this I get 6*Pi = 18.744 inch circumference.

At 1450 rpm this gives me 18.744 * 1450 = 27178.8 inch per minute.

and 27178.8/12 gives 2264.9 feet per minute.

That's a lot considering that a metal cutting band saw runs at around 80 fpm for mild steel.

Can someone tell me where I've got my calculations screwed up ?

Dave.

Edit.  The drive wheel connects direct to the motor shaft; no reduction pulleys.

John Rudd:
Motor RPM multiplied by the Motor pulley diameter divided by the Driven pulley diameter times the Bandsaw wheel diameter times pi (3.1416) divided by 12 = S.F.P.M.

Motor RPM X Motor pulley diameter / Driven pulley diameter X Bandsaw wheel diameter x 3.1416 / 12 = S.F.P.M.

So from the above I get:
Motor speed= 1425 ( nominal speed for a 4 pole motor)
Driver /driven = 1 because its direct drive
Bandsaw wheel dia = 6"
Plug in the numbers turn the handle....
(6* 3.142)/12*1425= 2238 f/min



Hmmm....too fast enough....needs gearing down...

Joe.... :)

sparky961:

--- Quote from: DavidA on November 12, 2016, 04:37:11 PM ---I'm sat here contemplating buying a metal cutting band saw from Machine Mart tomorrow to take advantage of their no VAT offer.  It will save me about £50.

--- End quote ---

For what it's worth, whatever way you decide to go with to introduce a metal cutting band saw into your shop, you will absolutely love it.

I think the horizontal bandsaw is #1 the most important tool in a metal shop.  Vertical bandsaw is ok but not near as versatile.  And of course most of the small 4x6's and such can be used as a vertical in a pinch.

I've found at least a few of these in the used market.  Good restoration project if you're on a tight budget.

DavidA:
..Hmmm....too fast enough....needs gearing down...


About 28:1

Maybe there is an interesting project in there somewhere. With pictures; naturally.

Anyway, thanks chaps for confirming my suspicions.

Oh God, it's decision time.

Can I really justify spending the money or should I concentrate on converting my existing saw.

I hate these moments.  Need a strong coffee.

Who's that looking over my shoulder. The guy with the horns and the pointy tail ?

Dave

AdeV:
We have a saying in our office....

"Get it spent!"

 :lol:

2000+ fpm sounds way too fast, even for a wood saw. Are you sure the motor isn't internally geared?

Edit to add: Here's a way to check... paint a white mark on the outside of the blade (Tippex would do), a nice broad one. Switch saw on. As the white mark passes (and even at a slow speed it'll be whizzing by) start a stopwatch. Count 10 (or some convenient number) of rotations. Or, count until 1 minute has passed. In the latter case, multiply the number you get by the length of the blade in feet to give your your real FPS. The maths for the former case is currently beyond my ken, it involves division and I don't do division after midnight, in case the ghoulies come out and get me...

Edit #2: According to this website, 3000FPS is normal for wood  :bugeye:

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