bandsaw speed problem

[joseph f merz]

I have an old delta 14" bandsaw . Motor fried -I bought a hbf motor that turns at 3450 rpm .i am certain the old motor was slower but it has no identification plate . I could really use some help figuring what pulley size to put on the motor .I have found formulas but my attempt at understanding what the results are is killing me . presently the driven pully is 8" . Even found a thred someplace with this exact question loaded with formulas and calculations but I am just plane stuck .Can someone help with this .Thankyou

[James Conrad]

What size pulley is on the old motor and will it fit the shaft of the new?

[Jerry Thompson]

The majority of BS motors are 1725-1740 RPM. 3450 is about 2x the RPM and will spin things too fast. I have no idea what pully size would reduce it blade speed or if it would even be practical..

[John TenEyck]

RPM A x Dia A = RPM B x Dia B

Solve for whatever variable you need. Along with that you need to decide what surface speed you want the blade to run at. Let's pick 3000 ft/min, for example. For your 14" BS you would need those wheels to turn at :

3000 / (pi x 14/12) = 819 rpm

So, with your 8" driven pulley, that shaft needs to turn at 1433 rpm. With a 3450 rpm motor, it's pulley would need to be 3.3" diameter.

John

[Myk Rian]

You bought the wrong motor. You'll either have to return it, build up a jack-shaft to reduce the speed, or get a huge pulley for the band saw axle.
Getting a smaller pulley for the motor is the wrong way to go. You have to consider the friction you would lose doing it.

[John TenEyck]

I run a 3450 rpm motor on my 14" Delta. The drive pulley is pretty close to 3.5", and the saw runs just fine. Maybe the friction is a little higher than with a large diameter pulley, but the torque is higher too. If it's wrong, it's been wrong for 20 years, and it's cut a lot of wood over the years including a lot of resawing.

John

[joseph f merz]

thankyou John . I am going to go with that .There is a lot of info out there on this subject .Whew - but how to sort it . Even the speed the blade spins is up to debate .
Motor is mounted today ,I will wire it up tomorrow and get a pully . After I get the pully I will measure for the belt . This is ending up being tool repair week and not building cabinet doors like I planned.
Thankyou again

[glenn bradley]

Pulley calculator: http://www.culvermotor.com/Engineering-Formulas/Pulley-and-RPM-Calculator.html

[John Coloccia]

I would just try the motor as is, to be honest. I often wish my bandsaws turned a bit faster, actually.

[joseph f merz]

Oh I need to purchase a new pully . So there isn't a try as is . Since i am cutting wood I could lean towards more speed so i figure a 3" pully. Found another thred on another forum where someone used the same rpm motor I have increased the speed a bunch and was very impressed with the results.

[Bill White]

I think the important consideration is the SFPM of the blade (surface feet per minute). Most "experts" suggest a speed of about 3000 SFPM for wood cutting.
PS. An expert is a guy with a briefcase, and is more than 6 miles from home.
Bill

[Sam Layton]

Hi Joseph,

Here is another calculator to determine pulley size, blade speed, etc. http://vintagemachinery.org/math/sfpm.aspx

Sam

[Keith Westfall]

An expert is a guy with a briefcase, and is more than 6 miles from home.

I disagree.

If you break the word down as follows: :ex / spert:, you find that "ex" (X) is an unknown quantity, and that "spert" is a drip under pressure.

So an expert is just an unknown drip under pressure...

Hope everyone has a good day!! :D

[joseph f merz]

Ok -wanted to post results . It is a great improvement . Cuts faster but also much easier to track a straight line . Not sure what speed I ended up with .I got a 3 1/2" pully for the motor but it turned out to be an "A" or "B" pulley and my "A" belt sets much deeper .So more like a 3" or 2 1/2" pully . I found a post someplace in my search where someone used a 3hp ,3450 rpm motor and used 2 to one ratio pulleys and also loved the results. Anyhow it worked out well .Thankyou again for all the help . It took some time but it had to be done anyhow and now I have a serious machine .

[Mac McQuinn]

I run a older 1950's 3 wheeled Craftsman which came with a 3450 rpm motor. Fortunately it also came with a older adjustable drive pulley. I adjusted this down to smallest diameter and replaced the driven pulley with largest one I could get into the space available. This dropped my Rpms to a workable level and saw runs very smoothly with a multi-link belt. While farm stores have a good selection of pulleys usually. I picked mine up at Grainger as a close-out.
Mac

[Ronald Blue]

Keep an eye on the belt to pulley relationship. If the pulley is to wide and the belt rides on the bottom of the pulley rather then the sides once you put enough pull on it you will experience slippage. Belts are designed to ride on the sides not the bottom. You may never have an issue depending on how hard you work the saw but the potential is there.

[ian maybury]

There's a huge difference in blade speeds with band saws anyway. Larger 24in industrial models run blade speeds of up around 1,400metres/min, while less heavy duty even 16in models may only run at about half of that. Lighter saws may run even more slowly.

It may be that the long blade on a big saw helps cooling, and that the heavy cast iron wheels and stuff do better at higher RPM - but changing the cutting speed with wood isn't generally that big a deal.

What may matter is that the rate at which wood is being cut away will increase more or less in proportion to the speed of the blade. So that the HP required (at a given feed pressure) will probably increase in proportion to the change in RPM.

Which could mean that a much higher RPM motor of the same size could end up a bit marginal on HP, but against that saws are typically fairly well powered and it's anyway an option to reduce the feed pressure.

The other (theoretical) possibility might be that if a saw is lightly built and/or not well balanced it could possibly start to vibrate a bit. It might be possible to test that by winding it up with a drill or something?

ian